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Shining a light on fish at night: an overview of fish and fisheries in the dark of night, and in deep and polar seas
Abstract
In aquatic environments, what one observes during the day can differ substantially by night. The species composition and associated ecological processes that occur during the day are often different than night. In polar seas and at great depths, " night " can span, months, years, and beyond. Teleosts and elasmobranchs have evolved unique sensory and behavioral modalities for living in darkness. As a consequence, fishers have adopted unique strategies for exploiting fish at night or in dark systems. We propose that neglecting the night has led to an incomplete understanding of aquatic organismal ecology, population/community dynamics, and ecosystem function with consequences for fisheries conservation management. To address this knowledge gap and stimulate the exchange of new data and ideas on behaviors, patterns, and processes relating to fish and fisheries in darkness, Fish at Night: an International Symposium was held in Miami, Florida (USA), from 18 to 20 November, 2015. Here, we synthesize the findings from the symposium, providing an overview on the state-of-knowledge of fish studies in the dark, identifying critical information gaps, and charting a course for future research. We focus our commentary and synthesis on six areas: (1) nocturnal fish behavior and ecology; (2) fishing, fisheries, and enforcement; (3) deep and polar seas; (4) diel fish distribution and abundance comparisons; (5) methods for studying fish in darkness; (6) human threats to fish at night; and (7) larval fish at night. Taken together, we attempt to " shine a light " on fish at night, generating a greater interest and understanding of fishes and fisheries during darkness.
... This allows the synchronization of key life history events such as maturation, migration and reproduction with their long-term average optimum timing (Foster, Ebling, & Claypool, 1988;Gwinner, 1989;Robart, McGuire, & Watts, 2018;Walton, Weil, & Nelson, 2011). Additionally, photoperiodic transitions between darkness and light provide daily signals for entraining circadian rhythms (Hammerschlag et al., 2017;Metcalfe, Fraser, & Burns, 1998). However, variation in other environmental factors such as temperature, tide or rainfall that reliably predict fitness outcomes can provide additional nonphotoperiodic signals that allow the timing of behaviours to be fine-tuned within a particular year, season or even day (McNamara et al., 2011;Visser & Both, 2005). ...
... The apparent reluctance of the lake-tagged trout to move through transitional habitat around the full moon reflects previous observations of trout moving smaller distances during the full than the new moon (Slavik, Horky, Randak, Balvin, & Bíly, 2012;Slavik, Horky, Maciak, Horka, & Langrova, 2018). Analogous patterns of reduced activity or presence within exposed habitats during the full moon have been recorded in terrestrial rodents (Daly, Behrends, Wilson, & Jacobs, 1992;Kotler et al., 1991;Lockard & Owings, 1974), catadromous eels (Poole, Reynolds, & Moriarty, 1990;Sandlund et al., 2017), marine fishes (Hammerschlag et al., 2017), bats (Morrison, 1978), armadillos (Pratas-Santiago, Gonçalves, Nogueira, & Spironello, 2017), ungulates (Palmer, Fieberg, Swanson, Kosmala, & Packer, 2017) and zooplankton (Last et al., 2016). Such 'lunar phobia' is regarded as an evolved response that reduces exposure to visually oriented predators. ...
... Nocturnal activity patterns (Cozzi, Broekhuis, McNutt, Turnbull, & Macdonald, 2012), detection range and hunting efficiency Metcalfe, Valdimarsson, & Fraser, 1997;Robinson & Tash, 1979) of visually oriented predators tend to decline significantly as lunar illumination levels decrease. Although moving during the new moon is likely to reduce migrant visibility and predation rates, it is also possible that nocturnal spawning during the new moon provides a fitness advantage by reducing egg predation by other fish (Hammerschlag et al., 2017;Smejkal et al., 2018). We detected a significant interaction between RiverHeight and MoonPhase, whereby the reduction in movement probabilities at higher values of MoonPhase (fuller moons) was more pronounced when water levels were lower. ...
Animals often exhibit extensive flexibility in movement behaviours on a range of temporal and spatial scales in response to cues that reliably predict fitness outcomes. The annual timing of movements between distinct habitats can be crucial, particularly in seasonal environments with narrow ecological windows of opportunity. In polygamous species, sexual selection may further shape sex-specific phenology and movement behaviours. Here, we characterized seasonal, daily and diel movement patterns in adult brown trout, Salmo trutta, between a lake feeding habitat and two spawning streams in northwestern Ireland, using passive integrated transponder (PIT) telemetry. Antennae positioned at the inflow and outflow of the lake were used to monitor movements of 197 lake-tagged adults between lake and stream habitats. Across 2 years in both streams, movements were overwhelmingly nocturnal and exhibited distinct seasonality, with a peak in daily detections close to the winter solstice. In both streams, seasonal movement activity of males began and peaked before that of females (protandry). Daily detection probabilities for both sexes increased as the moon waned (decreasing lunar illumination) and as river depth increased, the latter being associated with reduced water clarity. These findings are consistent with fish favouring movement between fluvial and lacustrine habitats when light (both solar and lunar) or hydrological conditions decrease their exposure to visually oriented predators. The observed protandry also suggests a role for intrasexual male competition, whereby earlier male arrival could increase mating opportunities.
... Estuarine fish are highly mobile, with daily habitat use varying across a fish's life cycle, across diel periods, tidal cycles, and season (Rountree and Able 2007). The influence of time of day on large and adult fish activity remains poorly understood, with high variability detected at various sites highlighting the need to better understand these cyclic ecological processes (Hammerschlag et al. 2017;Ley and Halliday 2007). Examining nocturnal behaviour among fishes has logistical and technological challenges; however, for conservation and fishery management to achieve optimal results, fish behaviour, across all time periods, species, and life history stages should be well documented (Hammerschlag et al. 2017). ...
... The influence of time of day on large and adult fish activity remains poorly understood, with high variability detected at various sites highlighting the need to better understand these cyclic ecological processes (Hammerschlag et al. 2017;Ley and Halliday 2007). Examining nocturnal behaviour among fishes has logistical and technological challenges; however, for conservation and fishery management to achieve optimal results, fish behaviour, across all time periods, species, and life history stages should be well documented (Hammerschlag et al. 2017). Understanding how factors, such as diel variability (i.e. over the circadian cycle of 24 h), influence adult fish movement patterns is key to determine how fish use estuaries (Niella et al. 2022). ...
Estuaries present a unique interface between ocean and freshwater systems and support key fish habitats. While the role of estuaries for juvenile fish has been studied extensively, the daily movement patterns of large fish and the exchange of fishes between estuary and ocean are less understood, particularly in developed estuaries. This study examines the quantity of fish biomass transiting through an important commercial fishing estuary in New South Wales, Australia, over 4 months, at four sites, and across diel periods. We used an imaging sonar across diurnal and nocturnal sampling events to reveal the size of fish, their movement patterns, and the biomass flux occurring throughout the estuary. Across ~ 60 h of footage, > 66,200 fish were counted and measured. Fish activity was the greatest at night, with 77% of fish biomass flux (kg h−1) occurring during nocturnal sampling. The total observed fish biomass over the 60 h amounted to ~ 15,500 kg, with the highest activity recorded at the estuary mouth at night (736 ± 463 kg h−1). Overall, mean fish length was the greatest at night (25.2 ± 2.0 cm); however, fish observed during the day at the estuary mouth had the highest mean length (27.8 ± 6.9 cm). Extrapolated across the width of the estuary, total fish movement ranged to a maximum of 47 Tons h−1 in the lower estuary (Stockton) and a minimum of 0.4 Tons h−1 in the upper estuary (Throsby Creek Lower). These results demonstrate the importance of estuaries, despite their level of development, in supporting the daily movement patterns of fish biomass between habitats, estuary, and ocean.
... With more than 35,000 species (WWF, 2021), fishes represent the largest and most diverse group of vertebrates (Ravi & Venkatesh, 2008). Most species rely on visual cues for some combination of prey localization and capture, avoidance of predators, mate finding and reproductive activities, recognition of conspecifics, habitat selection, navigation and utilizing refugia (Hammerschlag et al., 2017). ...
... The relative paucity of research available on this topic has likely partially stemmed from the difficulty in observing fish communities at night in darkness (i.e. to obtain control conditions) without creating artefacts (Hammerschlag et al., 2017). Direct sampling has obviously contributed important information, though it is important to acknowledge that alternative capture techniques can lead to bias in the size and age of fishes sampled. ...
Nearly all organisms rely on natural fluctuations of light as cues for synchronizing physiological processes and behavioural actions associated with foraging, growth, sleep and rest, reproduction, and migration. Consequently, although artificial lighting sources have provided a plethora of benefits for humans, they can lead to disruptions for wild organisms. With one quarter of the human population living within 100 km of coastlines, there is great potential for artificial light at night (ALAN) to influence the physiology, behaviour and fitness of fishes. Through a review of the literature (n = 584 publications focused on the effects of ALAN on individual organisms or ecosystems), we illustrate that most papers have concentrated on terrestrial species (59%) compared with aquatic species (20%) or a mixed approach (21%). Fishes have been underrepresented in comparison with many other taxa such as birds, insects and mammals, representing the focus of less than 8% of taxa-specific publications. While the number of publications per year focusing on fishes has generally been increasing since the mid-2000s, there has been a downturn in publication rate in the last few years. To understand where research related to ALAN in fishes has been focused, we partitioned studies into categories and found that publications have mostly concerned behaviour (41.0%), abundance and community structure (24.4%), and physiology (22.8%), while the longer-term effects on fitness (6.9%) are lacking. We synthesize the research completed in fishes and outline future priorities that will help ascertain the short- and long-term consequences of this relatively novel stressor for fish health and persistence.
... Ecologists have long known that key aspects of community structure, animal behavior, and food webs in terrestrial, freshwater, and marine ecosystems can change over a diel cycle Communicated by Matthew D. Taylor (Park et al. 1931;MacGinitie 1935;Ricketts et al. 1985). Despite this, researchers still have a bias for collecting data during the day and most ecological studies have been conducted during daylight hours (Mattila et al. 1999;Kopp et al. 2007;Hammerschlag et al. 2017). Over a diel cycle, many seagrassassociated organisms are known to vary in their habitat occupancy patterns (selected studies in Table 1). ...
... For example, Heck and Orth (1980) reported a 25-fold increase in Palaeomonetes vulgaris during a July sampling in the Chesapeake Bay. These results suggest that such daily migrations in and out of seagrass beds over a diel period may be common across a wide range of taxa, and these patterns may be missed by sampling only during daylight hours (Mattila et al. 1999;Sogard and Able 1994;Unsworth et al. 2007;Hammerschlag et al. 2017). ...
Seagrasses are productive habitats that support diverse communities of economically and ecologically important fishes and macroinvertebrates. However, most seagrass faunal assessments are conducted only during daylight hours. Here, we documented diel patterns in seagrass-associated fish and macroinvertebrate community structure in seagrass near Seahorse Key, Florida (USA). Artificial light is prevalent in many coastal areas and may influence day/night assemblages; therefore, we added lights to the natural environment to get a better understanding of its effect on community composition. Seagrass inhabitants were quantified using 25-m seine transects during different diel periods (day or night) and in areas where light was manipulated to mimic light pollution (artificial + natural light or natural light). Results suggest that the magnitude of diel effects exceeded that of light addition. While total abundance was similar between day and night, communities did change, with Lagodon rhomboides (Pinfish) dominating day samples and Farfantepenaeus duorarum (pink shrimp) most abundant at night. Other fishes such as Orthopristis chrysoptera (Pigfish) and Strongylura notata (Needlefish) had higher catches during the day, while invertebrates such as Callinectes sapidus (blue crab) and Palaeomonetes spp. (grass shrimp) were more prominent at night. In addition to the differences in abundance and community structure, we also identified diel differences in sizes for some species. No clear patterns were observed with the short-term addition of artificial light. This research highlights the role of diel variability in seagrass communities and suggests that diel movement of organisms may represent an important conduit for the transfer of energy to adjacent habitats.
... In general, the responses of fishes to artificial light are difficult to predict since underwater light perception is dependent on the lighttransmittance qualities of the water and the visual pigments as well as the ecology, adaptation, and life stage of the species, among other factors (Nightingale et al., 2006). Several studies, such as that by Marchesan et al. (2005), have tested the effects of various light sources and their impact on species or ecosystems (for overviews and example see Perkin et al. (2011), Franke et al. (2013, Schroer and Hölker (2016) and Hammerschlag et al. (2017)). One study that examined both constant and intermittent lighting (simulating car headlights) on a coastal fish species could not demonstrate any differences in behavior or cortisol levels, but the exposure to artificial light resulted in elevated blood glucose levels, which was interpreted as a stress indicator (Szekeres et al., 2017). ...
... One study that examined both constant and intermittent lighting (simulating car headlights) on a coastal fish species could not demonstrate any differences in behavior or cortisol levels, but the exposure to artificial light resulted in elevated blood glucose levels, which was interpreted as a stress indicator (Szekeres et al., 2017). Nevertheless, for most fishes, the impacts of light on their biology or ecology are little known and thus do not give a comprehensive understanding of how such implications translate to populations or ecosystems (Hammerschlag et al., 2017). ...
There are several environmental and ecological effects of shipping. However, these are rarely assessed in total in the scientific literature. Thus, the aim of this study was to summarize the different impacts of water-based transport on aquatic and nearshore ecosystems and to identify knowledge gaps and areas for future research. The review identified several environmental and ecological consequences within the main impact categories of water discharges, physical impacts, and air emissions. However, although quantitative data on these consequences are generally scarce the shipping contribution to acidification by SOx- and NOx-emissions has been quantified to some extent. There are several knowledge gaps regarding the ecological consequences of, for example, the increasing amount of chemicals transported on water, the spread of non-indigenous species coupled with climate change, and physical impacts such as shipping noise and artificial light. The whole plethora of environmental consequences, as well as potential synergistic effects, should be seriously considered in transport planning.
... The demanding on-board environment leaves samplers vulnerable to fatigue or conflicting priorities, obscuring their judgements of representativeness and encouraging convenience sampling if all fish do not have an equal chance of being sampled (Cotter and Pilling, 2007). For example, diurnal variations in sampling effort may bias catch size and composition (Casey and Myers, 1998), an issue addressed more in recreational fisheries (Diogo and Pereira, 2016;Hammerschlag et al., 2017) but is relatively under-researched in commercial fisheries. There is also a constant risk of intentional manipulation for economic or regulatory incentives (Figus and Criddle, 2019), such as samplers avoiding certain hauls or ignoring juvenile fish. ...
Fisheries catch sampling is often done using non-probabilistic methods to tackle the operationally challenging sampling environment, but where the sampler must judge whether the sample is representative, there is a risk of intentional or unintentional biases being introduced. In this study, I investigate potential biases in sampling by fishers in the Norwegian Reference Fleet. Biases in haul selection were identified by modelling the effect of available covariates on sampling probability using mandatory catch logbooks as a census dataset. The model detected small biases in haul selection, favouring larger catches which are more representative of typical catch sizes in the fishery, and larger variations in sampling probability during daylight, which is partly driven by the availability of the sampler because of shift patterns. Biases in sub-sampling of fish was investigated by comparing length frequency distributions with monitoring, control, and surveillance inspections, revealing marginally larger proportions of undersized fish in Norwegian Reference Fleet sampling. In conclusion, there is no evidence of either convenience sampling or intentional manipulation of sampling. Rather, deviations from random sampling were small and isolated to individual vessels, suggesting that targeted feedback would be effective for improving future sampling.
... Likewise, except in specific studies that include the nyctimeral dynamics or species that are not active during daylight, censuses should be carried out at times when the sun is high (between 12 and 2 pm) (Harmelin-Vivien et al., 1985). To study fish stocking at night or in dark conditions, such as in polar areas during winter or in deep waters, other techniques must be used like traditional fishing gears, plankton trawls, light traps, sonar systems, or airborne lidar (Hammerschlag et al., 2017). Finally, as has been mentioned, the variations in the turbidity of the water, and therefore in the visibility, can introduce alterations in the counts that are unrelated to the real variations of the population. ...
... As such, by only studying one half of the diel cycle, nocturnal species, and the key roles and niches they facilitate in ecosystem patterns and processes go unaccounted for, with day-only sampling events presenting an incomplete ecological story. This diurnal sampling bias is further exacerbated in marine ecosystems, with logistical and technological constraints limiting the capacity to observe marine communities at night (Dornburg et al., 2017;Hammerschlag et al., 2017). ...
Diel partitioning of animals within ecological communities is widely acknowledged, yet rarely quantified. Investigation of most ecological patterns and processes involves convenient daylight sampling, with little consideration of the contributions of nocturnal taxa, particularly in marine environments. Here we assess diel partitioning of reef faunal assemblages at a continental scale utilizing paired day and night visual census across 54 shallow tropical and temperate reefs around Australia. Day–night differences were most pronounced in the tropics, with fishes and invertebrates displaying distinct and opposing diel occupancy on coral reefs. Tropical reefs in daytime were occupied primarily by fishes not observed at night (64% of all species sighted across day and night, and 71% of all individuals). By night, substantial emergence of invertebrates not otherwise detected during sunlit hours occurred (56% of all species, and 45% of individuals). Nocturnal emergence of tropical invertebrates corresponded with significant declines in the richness and biomass of predatory and herbivorous diurnal fishes. In contrast, relatively small diel changes in fishes active on temperate reefs corresponded to limited nocturnal emergence of temperate invertebrates. This reduced partitioning may, at least in part, be a result of strong top‐down pressures from fishes on invertebrate communities, either by predation or competitive interference. For shallow reefs, the diel cycle triggers distinct emergence and retreat of faunal assemblages and associated trophic patterns and processes, which otherwise go unnoticed during hours of regular scientific monitoring. Improved understanding of reef ecology, and management of reef ecosystems, requires greater consideration of nocturnal interactions. Without explicit sampling of nocturnal patterns and processes, we may be missing up to half of the story when assessing ecological interactions.
... For example, much hunting and trapping for bushmeat, poaching, and fishing activity ( both legal and illegal ) occurs at night ( Waluda et al. 2004, Holmern et al. 2006 . Often, this is because the target organisms are most active at night, as is the case for krill, squid, many marine fish ( Taki et al. 2005, Hammerschlag et al. 2017 , and the majority of terrestrial mammals . At night, they can also be less able to see and so are less able to evade hunting techniques such as trawling nets ( e.g., Walsh 1991, Rakowitz et al. 2012 ) -except where these depend on herding behavior and, therefore, on nets being visible ( Ryer et al. 2010 ) . ...
How the relative impacts of anthropogenic pressures on the natural environment vary between different taxonomic groups, habitats, and geographic regions is increasingly well established. By contrast, the times of day at which those pressures are most forcefully exerted or have greatest influence are not well understood. The impact on the nighttime environment bears particular scrutiny, given that for practical reasons (e.g., researchers themselves belong to a diurnal species), most studies on the impacts of anthropogenic pressures are conducted during the daytime on organisms that are predominantly day active or in ways that do not differentiate between daytime and nighttime. In the present article, we synthesize the current state of knowledge of impacts of anthropogenic pressures on the nighttime environment, highlighting key findings and examples. The evidence available suggests that the nighttime environment is under intense stress across increasing areas of the world, especially from nighttime pollution, climate change, and overexploitation of resources.
... The increased exploitation of hydrological resources has resulted in an increase in eutrophication, habitat loss, and other disturbances (Collier et al., 2015), leading to habitat degradation and biodiversity loss (Vörösmarty et al., 2010), particularly in densely populated urban ecosystems. The impacts of urbanization on river systems are mainly habitat alteration and fragmentation, water quality modification (i.e., increased loading of nutrients, sediment, and pollutants), and biological invasion (Seilheimer et al., 2007;Simpson et al., 2016;Hammerschlag et al., 2017). ...
With the population increasing, fish communities, as important components in the river system, were inescapably impacted by human activities. To investigate these impacts, we characterized the fish community's composition by environmental DNA metabarcoding in the urban and suburban sites along Xiang River in central China. The results showed that 32 species were identified, and most species were from Cypriniform. The analysis indicated no significant differences in fish communities among the three urban areas. However, significant differences were observed between the bank solidified and non-solidified areas, which indicated that the channelization significantly influenced the biodiversity and abundances. An alien species, Clarias gariepinus, was discovered in all examined sites, and it was negatively associated with ten native species. Furthermore, human populations and acidification were also negatively related to diversity. Our findings clearly showed that the consequences of anthropogenic activities shaped ichthyofauna and caused biodiversity loss in the urban river.
... Light has been shown to be one of the major triggers for this migration (Neilson and Perry 1990;Mehner 2012) and some studies have found that diurnal migration cycles interact with tidal cycles (Wilcockson and Zhang 2008). However, most research is done during daytime, potentially leading to a wrong estimate about the utilisation and importance of different habitats (Hammerschlag et al. 2017). ...
Review on the current knowledge of the impact of artificial light on marine and coastal habitats with special focus on the Waddensea and intertidal areas.
... Though interest in moon-related effects on coral reefs has grown steadily over recent years (Figure 1a), far more attention is given to the moon's role in shaping tides and currents than its effects on nocturnal brightness (Figure 1b). In part, this reflects a general lack of research emphasis on nocturnal processes (but see [12][13][14][15][16][17]). Of the more than 28 000 published A B Figure 1. ...
The lunar cycle drives variation in nocturnal brightness. For the epipelagic larvae of coral reef organisms, nocturnal illumination may have widespread and underappreciated consequences. At sea, the onset of darkness coincides with an influx of mesopelagic organisms to shallow water (i.e. 'diel vertical migrants') that include predators (e.g. lanternfishes) and prey (zooplankton) of zooplanktivorous coral reef larvae. Moonlight generally suppresses this influx, but lunar periodicity in the timing and intensity of nocturnal brightness may affect vertically migrating predators and prey differently. A major turnover of species occurs at sunset on the reef, with diurnal species seeking shelter and nocturnal species emerging to hunt. The hunting ability of nocturnal reef-based predators is aided by the light of the moon. Consequently, variation in nocturnal illumination is likely to shape the timing of reproduction, larval development, and settlement for many coral reef organisms. This synthesis underscores the potential importance of trophic linkages between coral reefs and adjacent pelagic ecosystems, facilitated by the diel migrations of mesopelagic organisms and the ontogenetic migrations of coral reef larvae. Research is needed to better understand the effects of lunar cycles on life-history strategies, and the potentially disruptive effects of light pollution, turbidity, and climate-driven changes to nocturnal cloud cover. These underappreciated threats may alter patterns of nocturnal illumination that have shaped the evolutionary history of many coral reef organisms, with consequences for larval survival and population replenishment that could rival or exceed other effects arising from climate change.
... The TMS and ROV were redeployed and the third and fourth sides of the platform surveyed. Surveys were conducted during the daylight hours only with recordings commencing one and a half hours after dawn and finishing 1 h before dusk to avoid the crepuscular behavior that fish are known to exhibit (Myers et al., 2016;Hammerschlag et al., 2017). ...
Decommissioning of offshore oil and gas structures is either occurring, or imminent in most regions of the world. Most jurisdictions require that offshore structures be removed for onshore disposal. However, there is growing interest in understanding the ecological and socio-economic benefits of leaving structures in the water. Descriptions of how fish utilize the vertical structure created by wellhead platform jackets (platforms) will provide insights into possible outcomes of decommissioning alternatives, such as full removal, leave in situ, or translocation to a designated reefing site. We surveyed fish assemblages associated with seven platforms and five reference sites located ∼150 km offshore in the central Gulf of Thailand. The platforms spanned the entire water column (∼75 m) and were a mix of three and four legged structures. We used a Remotely Operated Vehicle (ROV) fitted with an underwater stereo video system to quantify the abundance, size, biomass, and economic value of fish associated with the platforms. We recorded 43 species of fish on the platforms and five reference sites with most fishes on platforms categorized as coral-reef or coral-reef-associated species. We observed a strong vertical zonation in the fish assemblage on the platforms. The Regal demoiselle (Neopomacentrus cyanomos) was numerically dominant (75% of all fish observed). We measured 3,933 kg of fish on the platforms with Caranx sexfasciatus accounting for 76.12% of that. We conservatively estimate each platform had a scaled mean biomass of ∼2,927 kg and the fished species had scaled mean economic value of 175,500 Thai Baht per platform. We estimated that the biomass of fish associated with the seven platforms was at least four times higher per unit area than some of the world’s most productive coral reefs.
... Pope et al., 2017;Veiga et al., 2010), complicating the quantification of nocturnal recreational fishing effort. Nocturnal fishing can comprise a substantial portion of fishing activity (reviewed in Cooke et al., 2017) and nocturnal effort may be very different to that measured from diurnal fishing (Diogo and Pereira, 2016;Hammerschlag et al., 2017). Therefore, relying solely on data derived from surveys that provide incomplete coverage of the temporal scope of the fishery will lead to biased or imprecise estimates of recreational catch and effort (Steffe et al., 2008;Taylor et al., 2018). ...
The collection of fine-scale recreational fishing data can assist in assessing the potential impacts on target species and sensitive biota. We employed a thermographic camera, laser rangefinder, compass and custom-designed mobile application to estimate fine-scale recreational fishing effort for blue-swimmer crabs (Portunus armatus) within Peel-Harvey Estuary, a Ramsar-listed wetland. Geo-referenced locations for shore-based recreational fishers were recorded for sixty 18-h fishing days in a 12-month period. Annual fishing effort was estimated to be 100,815 (SE 12,521) fisher hours, 16.3 % greater than estimates that excluded nocturnal fishing from the analysis. Generalized linear models were applied to determine significant factors describing the variability in fishing activity and for planning future cost-effective surveys. The main effects of time of day and wind condition, and the interaction of season with day type and season with region, were significant at the α = 0.05 level. These data suggest that fishers respond to the abundance of legal-sized crabs within the estuary, with peak fishing activity concentrated on discrete areas and times of the year. The methods used in this study can be applied to quantify nocturnal recreational fishing effort, optimize cost-effective recreational fishing surveys, and determine where recreational fishing activity overlaps areas of sensitive biota.
... Powerboat retrievals that occurred at night (1-4% of retrievals at each ramp) were excluded from subsequent expansion because the traditional access point survey was restricted to the daytime and many species of teleost have crepuscular or nocturnal activity patterns (Hammerschlag et al., 2017), which could result in different catch rates and proportions of boats fishing between day and night. The number of powerboat retrievals between nautical dawn and nautical dusk (hereon in referred to as "daytime") was calculated for each day type stratum in each season. ...
Obtaining accurate estimates of catch can be challenging for small-scale recreational fisheries. Using inner Shark Bay as a case-study, we investigated whether a state-wide phone-diary (PD) survey could provide robust estimates of boat-based fishing effort and catch (kept and total) of pink snapper (Chrysophrys auratus) and grass emperor (Lethrinus laticaudis). Estimates were compared with those from concurrent surveys for two spatial scales corresponding to the fishery and the three pink snapper stocks within the fishery. A supplementary access point (SAP) survey incorporated remote camera data and interviews with fishers at boat ramps. An aerial survey was used to adjust the SAP estimates, accounting for catches from boat fishers launching from remote beaches (SAP_Aerial). The SAP survey provided the most precise estimates but underestimated catches for one of the stocks. Estimated fishing effort from the SAP_Aerial survey was comparable to the PD survey (3% lower) for inner Shark Bay, as was the estimated kept catch of pink snapper (7% lower) and these estimates were considered robust (Relative Standard Error < 40% and sample size ≥ 30). In contrast, estimates of the total catch of pink snapper and the catch (kept and total) of grass emperor from the PD survey were consistently lower. While the on-site surveys generally provided robust estimates of catch for each stock, most PD estimates were not robust at this scale. The SAP_Aerial survey is considered to be the most appropriate for ongoing monitoring because it provides robust estimates for the spatial scales examined. However, estimates of catch from periodic PD surveys for the entire fishery could be adjusted using the on-site data to provide the stock-specific information required for ongoing assessments of sustainability. Our study demonstrates that corroborative studies assist in monitoring recreational fisheries.
... Waluda et al. [40] used satellite-derived nighttime lights to show that fish catch was positively correlated with estimated fishing extent. Indeed, light intensity at night affects fish activity levels and aggregation [41,42]. Because monthly fish catch data at the study sites are not available, we used nighttime light intensity to approximate the temporal changes in fishery activity levels. ...
Two large fish assemblages were recorded in the overwintering fishing grounds of the East China Sea in February and March 2017. In this study, available time series of satellite-derived sea surface temperature, wind, chlorophyll a, and reanalysis data were used to explore the relationships between the observed large fish aggregations and environmental factors. The bottom waters of the fishing grounds were abnormally warm in winter 2017, and then experienced significant cooling due to the eastward movement of the Yellow Sea Cold Current, which was driven by the increased northwesterly wind from January to mid-March 2017. Fishing areas in the affected region, including No. 1891, which was abnormally warm, and No. 1592, which had a strong thermal front and high chlorophyll a concentration, might have provided suitable environments for the warm-temperature fish, resulting in the observed large fish assemblages. The abnormal temperature changes between winter and early spring 2017 may have been associated with changes in local ocean circulation.
... This may reflect a cognitive bias that shapes our conceptual frameworks and the data that we choose to collect [29]. Half of the lives of larval fishes-and important events shaping their growth and survival-occur at night [30][31][32][33]. Over the typical lifespan of a larval fish (1-10 weeks [34][35][36]), the night-time ocean environment may be far more variable than the day-time environment. ...
Growth and survival of larval fishes is highly variable and unpredictable. Our limited understanding of this variation constrains our ability to forecast population dynamics and effectively manage fisheries. Here we show that daily growth rates of a coral reef fish (the sixbar wrasse, Thalassoma hardwicke ) are strongly lunar-periodic and predicted by the timing of nocturnal brightness: growth was maximized when the first half of the night was dark and the second half of the night was bright. Cloud cover that obscured moonlight facilitated a ‘natural experiment’, and confirmed the effect of moonlight on growth. We suggest that lunar-periodic growth may be attributable to light-mediated suppression of diel vertical migrations of predators and prey. Accounting for such effects will improve our capacity to predict the future dynamics of marine populations, especially in response to climate-driven changes in nocturnal cloud cover and intensification of artificial light, which could lead to population declines by reducing larval survival and growth.
... As baited cameras typically use lower intensity and less-sustained illumination, compared to ROV and submersible surveys, the BRUVS method is less likely to disturb deep-sea fauna (Jamieson, 2016). Because of the systemic bias of artificial light introduced to a dark environment during deep-sea deployments, it is important that lighting intensity remains consistent among video surveys, in order to produce comparative relative estimates of biodiversity and community composition among locations (Hammerschlag et al., 2017). ...
There is a growing need for marine biodiversity baseline and monitoring data to assess ocean ecosystem health, especially in the deep sea, where data are notoriously sparse. Baited cameras are a biological observing method especially useful in the deep ocean to estimate relative abundances of scavenging fishes and invertebrates. The National Geographic Society Exploration Technology Lab developed an autonomous benthic lander platform with a baited camera system to conduct stationary video surveys of deep-sea megafauna. The first-generation landers were capable of sampling to full ocean depth, however, the form factor, power requirements, and cost of the system limited deployment opportunities. Therefore, a miniaturized version (76 cm × 76 cm × 36 cm, 18 kg in air) was developed to provide a cost-effective method to observe ocean life to 6000 m depth. Here, we detail this next-generation deep-sea camera system, including the structural design, scientific payload, and the procedures for deployment. We provide an overview of NGS deep-sea camera system deployments over the past decade with a focus on the performance improvements of the next-generation system, which began field operations in 2017 and have performed 264 deployments. We present example imagery and discuss the strengths and limitations of the instrument in the context of existing complementary survey methods, and for use in down-stream data products. The key operational advantages of this new instrument are spatial flexibility and cost-efficiency. The instrument can be hand-deployed by a single operator from a small craft concurrent with other shipboard operations. The main limitation of the system is battery power, which allows for 6 h of continuous recording, and takes up to 8 h to recharge between deployments. Like many baited-camera methods, this instrument is specialized to measure the relative abundance of mobile megafauna that are attracted to bait, which results in a stochastic snapshot of the species at the deployment location and time. The small size and ease of deployment of this next-generation camera system allows for increased sample replication on expeditions, and presents a path forward to advance cost-effective biological observing and sustained monitoring in the deep ocean.
... Impacts on marine fish in the Arctic may be greater in the winter than the summer, due to the nearly constant use of vessel lights in extended hours of darkness (if vessels are present at that time of year). In the Arctic, many fish have unique sensory and behavioural adaptations for living in darkness (Hammerschlag et al. 2017) which could increase impacts of artificial light. ...
Vessels involved in commercial marine shipping in Canada engage in the movement of goods or people by sea on the Arctic, Atlantic, and Pacific oceans. To explore the ways that the activities associated with commercial shipping can impact the marine environment, a suite of activity-based Pathways of Effects (PoE) conceptual models were developed. PoE conceptual models describe the pathways (linkages) between human activities, associated stressors, and their effects on endpoints, based on current knowledge. A visual representation of each PoE model is supported by text describing each pathway linkage based on scientific literature or expert opinion. Indigenous and local knowledge were not used in the current work. PoE models are useful tools for the scoping phase of a variety of environmental assessment, such as ecological risk assessment, environmental impact assessment, and cumulative effect assessments as they clearly outline activities and stressors and clarify connections between human activities and potential effects on ecological endpoints, and provide a science-based foundation for decision-making. The objective of these models and their supporting evidence is to provide a systematic review of the effects of shipping-associated activities on marine ecosystems. PoE models have been developed for five activities associated with commercial marine shipping in Canada: 1) anchoring and mooring, 2) vessel at rest, 3) grounding and sinking, 4) movement underway, and 5) discharge (divided into two PoE models: ‘debris’ and ‘other’). The PoEs were developed to be broad enough to be adapted for application in a range of environments and locations and detail the potential stressors and effects that could be considered in an assessment. The activity-based PoE models contain fourteen stressors (e.g., substrate disturbance, vessel strikes) and are related to three effects (change in fitness, mortality, and change in habitat) on ten generic endpoints (e.g., marine mammals, physical habitat). The models only include activities related to the commercial movement of goods and people by vessels, not included in this document are other vessel activities such as fishing, seismic surveying, dredging, port operations (e.g., when at-berth and while berthing). Non-commercial vessels (e.g., recreational vessels) are also not specifically included in these models. Though endpoints have been identified for illustrative purposes here, ultimately the assessor is responsible for comprehensively scoping the specific endpoints (e.g., valued components) and stressors to be considered in any assessment. PoE models do not include any evaluation of the relative or absolute impact from these activities on specific endpoints; this would occur in a subsequent assessment step, such as risk assessment.
... This is the first attempt to evaluate the daily dynamic of community change at Rapa Nui. Future studies could include the seasonal variability of the benthic community structure, fish size distribution around the island, the effects of moon phases on the activity patterns of benthic and pelagic communities and potential changes in the ability of predators to detect prey (Hammerschlag et al., 2017). This study provides important scientific information for the management planning and implementation of the recently created Rapa ...
• 1. On shallow reefs, day‐night activity patterns between fishes and invertebrates are presumed to reflect trade‐offs between feeding and predation; however, quantitative data on daily community dynamics are scarce. Moreover, night surveys may contribute important information for biodiversity inventories or baselines that normally are not considered.
• 2. This study used standardized day–night visual surveys of fishes and mobile invertebrates on the same transect lines in Rapa Nui (Easter Island) and investigated how diel patterns vary between taxonomic and trophic groups.
• 3. Distinct differences between taxonomic groups were observed, with fishes being more abundant during the day (>twice), whilst invertebrate abundance and richness showed an opposite trend with higher numbers at night (>three times).
• 4. Analysis of trophic groups showed that herbivorous and planktivorous fishes were more abundant during the day. Carnivorous fishes did not show any trends. Top predators (Apex) were observed only at very low abundances. However, a replacement amongst carnivorous fish species between day and night was found, where labridae fishes were practically absent during nights.
• 5. Most of the mobile invertebrates remained concealed during the day, probably due to the influence of predation risk (labrid fishes). The results emphasize the need for consideration of nocturnally active invertebrates in biodiversity inventories or baselines of reefs, which focus heavily only on diurnal surveys.
• 6. Day–night reef surveys should be included in marine protected area planning and monitoring as this provides a better understanding of shallow benthic communities and helps inform proper management decisions.
... Animals engage in a range of behaviors related to foraging, mating, migrations, or resting. To date, especially the night time behavior of marine animals, such as fish, remains largely elusive, mostly due to methodological restrictions (Hammerschlag et al., 2017). Mesopelagic fish and other diel vertical migrants are usually expected to feed near the surface at night. ...
Nocturnal migration of mesopelagic fish into surface waters is well-documented. Yet, although there is increasing evidence of individual-based deviations from average population migrations and of the importance of small-scale individual behavior for predator-prey interactions and energetic cycling, little is known about what mesopelagic animals do when in upper waters. Using high-resolution data from an upward-facing, moored, split-beam echosounder we analyzed the night-time individual vertical swimming behavior of pearlsides (Maurolicus muelleri) over one winter. The population behavior is characterized by migration to the surface after sunset, “midnight-sinking” and another migration to the surface in the morning, followed by return to the daytime habitat. Focusing on individuals unveiled diverse behavioral patterns during different phases of the migration. After ascending to upper layers at dusk, M. muelleri leaves the surface waters, not by sinking, but by actively swimming in a step-wise pattern characterized by relocations alternated by pauses. Following the descent, vertical swimming is sustained at lower levels. Around midnight, the vertical swimming direction changes from predominantly downward to upward. Several hours before dawn, the fish start ascending toward the surface in a step-wise pattern. During population ascent in the afternoon and descent in the morning, some individuals at the fringes of schools migrate without intermittent pauses. This study documents the feasibility of using submerged, stationary echosounders in unveiling the individual behavior of mesopelagic fish.
... It will also be necessary to perform group trials to see how schooling behaviour affects rates of passage. This could be particularly interesting as Atlantic salmon are known to complete their journey downstream as smolts in kin groups [46]. ...
Hydrokinetic turbines are an industry with growing interest. With many varying designs being put forward it is important to assess in depth the effects such technologies are likely to have on the local environment. In this study, the response of two downstream migrating juvenile salmonid species (brown trout and Atlantic salmon) to a three-bladed vertical axis hydrokinetic turbine was assessed in an experimental setup. A large, flow-controlled tank was used for 15 minute individual trials, in which 80 individuals were tested (40 of each species). Four water velocity settings (0 m/s-0.4 m/s) were assessed during the study with 10 replicates for each treatment. No direct collisions were observed. Behavioural responses to the turbine were analysed in terms of pass events and active avoidance. It was found that trout were less likely to pass the turbine than salmon. In the case of both species fish preferentially passed around the turbine rather than passing through the turbine structure. This could have implications for turbine placement.
... Eye size (Es = Ed/Hd) is the maximum eye diameter divided by the head depth, which is the length from the dorsal to the ventral edge of the head, as measured through the middle of the eye. This trait was previously described by Villéger et al. (2010) and is of interest here given the dramatic change in light levels with increasing depth in marine ecosystems (Hammerschlag et al., 2017). ...
Understanding patterns and processes governing biodiversity along broad‐scale environmental gradients, such as depth or latitude, requires an assessment of not just taxonomic richness, but also morphological and functional traits of organisms. Studies of traits can help to identify major selective forces acting on morphology. Currently, little is known regarding patterns of variation in the traits of fishes at broad spatial scales.
The aims of this study were (a) to identify a suite of key traits in marine fishes that would allow assessment of morphological variability across broad‐scale depth (50–1200 m) and latitudinal (29.15–50.91°S) gradients, and (b) to characterize patterns in these traits across depth and latitude for 144 species of ray‐finned fishes in New Zealand waters.
Here, we describe three new morphological traits, namely fin‐base‐to‐perimeter ratio, jaw‐length‐to‐mouth‐width ratio, and pectoral‐fin‐base‐to‐body‐depth ratio. Four other morphological traits essential for locomotion and food acquisition that are commonly measured in fishes were also included in the study. Spatial ecological distributions of individual fish species were characterized in response to a standardized replicated sampling design, and morphological measurements were obtained for each species from preserved museum specimens.
With increasing depth, fishes, on average, became larger and more elongate, with higher fin‐base‐to‐perimeter ratio and larger jaw‐length‐to‐mouth‐width ratio, all of which translates into a more eel‐like anguilliform morphology. Variation in mean trait values along the depth gradient was stronger at lower latitudes for fin‐base‐to‐perimeter ratio, elongation and total body length. Average eye size peaked at intermediate depths (500–700 m) and increased with increasing latitude at 700 m.
These findings suggest that, in increasingly extreme environments, fish morphology shifts towards a body shape that favours an energy‐efficient undulatory swimming style and an increase in jaw‐length vs. mouth width for opportunistic feeding. Furthermore, increases in eye size with both depth and latitude indicate that changes in both the average ambient light conditions as well as seasonal variations in day‐length can act to select ecomorphological adaptations in fishes.
... The development of successful conservation, fisheries management and restoration strategies for aquatic ecosystems depends on a sound scientific understanding of the relationships between the characteristics of the ecosystem and the distribution of fish diversity patterns. These include knowledge about fish-habitat associations, habitat sharing and partitioning, the use of essential habitats during different life phases as well as the importance of habitat connectivity (Lowry and Suthers, 1998;Able, 2005;Bortröm et al., 2011;Pittman et al., 2011;Childs et al., 2015;Hammerschlag et al., 2017). The type of habitat, for example, has proven to be a good predictor of the local fish assemblage, although the more mobile species, in particular, will depend on a variety of habitats and depth zones over the course of their life histories (Heyns-Veale et al., 2016;McLean et al., 2016;Wellington et al., 2018). ...
The success of marine management initiatives and our capability for dealing with environmental change largely depend on our understanding regarding the distribution of species and their habitat preferences. In the present study, we deployed baited remote underwater video systems (BRUVs) in a portion of Brazilian central coast (i.e., Todos os Santos Bay) to describe fish species-habitat associations along an estuary-bay-continental shelf gradient. Significant variation in the fish assemblage was found among three ecosystems, four depth classes, and eight different types of habitat, confirming that the structure and composition of fish assemblages is mediated by a set of habitat characteristics forming an ecological mosaic. The highest species richness and relative abundance were found in the mangroves and reefs. The data demonstrated that some species, such as Lutjanus jocu, Lutjanus synagris, Carangoides bartholomaei, Eucinostomus argenteus and Eucinostomus melanopterus had clear ontogenetic shifts among habitats and across ecosystems. Some species (Sphoeroides greeley, L. synagris, and Eucinostomus gula) were widespread along the ecosystem-level gradient and were observed in a number of different habitats, reflecting more generalist habitat associations. By contrast, a large number of species (54; e.g., Ptereleotris randali, Decapterus macarellus and Mugil curema) were recorded in a single habitat type, indicating they were habitat specialists. Despite this apparent habitat-related pattern, the size-mediated relationships found in many species indicate cross-migration along the ecosystem gradient. Our findings have implications for the conservation and monitoring of fish assemblages highlighting the role of the connectivity of marine habitats as a conservation priority toward to an ecosystem-based management strategy.
Keywords: Fish assemblage, Baited remote underwater video, Size-structured assemblage, Marine multi-habitats, Coastal conservation
... These effort data could be combined with catch rate information, enabling the estimation of total catch estimates that include daytime, crepuscular and nocturnal fishing activity. As many species of teleosts and crustaceans have crepuscular or nocturnal activity patterns (Helfman, 1986;Fox and Bellwood, 2011;Hammerschlag et al., 2017), the collection of catch rate information would ideally also extend to crepuscular and nocturnal periods, albeit at a lower sampling intensity if required. The use of thermographic cameras has broader applications for the design of other fisheries and wildlife surveys. ...
Although recreational fishing at night is a popular activity, crepuscular and nocturnal fishing effort and catches are often unaccounted for in fisheries assessments. Here, we present a method for estimating 24-h shore-based recreational fishing effort involving the analysis of data from dual-lens thermographic cameras. Cameras were installed at three sites along the foreshore in Peel-Harvey Estuary, a Ramsar Wetland in Western Australia. Stratified random sampling was used to select days for image analysis between March 2015 and February 2016 and examination of images enabled fishing effort to be calculated for the 12-month period. Crepuscular recreational fishing effort at the three sites ranged between 4.5% and 11.3% and nocturnal recreational fishing effort ranged between 6.1% and 26.9% of total recreational fishing effort. Crepuscular and nocturnal recreational fishing were more prevalent between November and March and occurred on both weekdays and weekend days. The majority of recreational fishers identified from the day-time images (96.5%) were targeting blue swimmer crabs (Portunus armatus) using scoop nets. Multiple lines of evidence suggest that most crepuscular and nocturnal activity involved the same method of fishing. The results demonstrate that restricting onsite recreational fishing surveys to daylight hours can lead to large underestimates of total fishing effort and total recreational catches within a fishery. Our method can easily be applied to other fisheries to justify the inclusion of night-time onsite sampling and to design cost-effective sampling strategies.
... Traditional evaluations of effects from invasive species, such as M. spicatum and other habitat-forming species, have often failed to account for diel variability in associated environmental metrics as well as faunal presence. While we know from various marine, estuarine, and freshwater ecosystems that nighttime can be very important for many organisms (reviewed in Hammerschlag et al. 2017), this work suggests that failing to account for this variability may lead to erroneous conclusions. Here, community structure in M. spicatum was dependent on diel hypoxic patterns that are triggered by the lack of water movement impeded by hydrological modification and suggests that restoration of natural flow patterns may not only deter M. spicatum colonization and proliferation (Martin & Valentine 2012) but also prevent hypoxia that develops in these habitats, which may also impact adjacent areas. ...
Gulf of Mexico estuaries contain an abundance of habitat-forming submerged vegetation that provide various ecosystem services. However, these estuaries now harbor numerous invasive macrophytes, such as Eurasian milfoil Myriophyllum spicatum. Previously, we showed that milfoil gained a foothold in the Mobile-Tensaw Delta, Alabama, USA, in protected waters north of a manmade causeway that significantly reduces wave action. Here, we collected associated organisms using a suction sampler and compared the composition and abundances of fauna residing in M. spicatum and wild celery Vallisneria americana, the most abundant native macrophyte, during day and night. North of the causeway, where water flow is limited, a 5-fold reduction in the abundance of organisms was documented in M. spicatum at night, while abundance in V. americana varied little. We found that this nocturnal decrease was accompanied by changes in community structure in M. spicatum north of the causeway, driven by reductions in invertebrates such as Gammarus amphipods, Neritina snails, and Callinectes sapidus crustaceans. In contrast, communities in V. americana, although distinct from M. spicatum, exhibited little spatial or temporal difference. Subsequent analyses indicated that reduced dissolved oxygen in M. spicatum north of the causeway at night drives assemblage patterns. These results suggest that hydrological alterations exacerbate M. spicatum's negative effects through the creation of hypoxic zones and that daily migrations into these habitats may be necessary for organisms to garner the benefits of this vegetation. Finally, this work highlights that our understanding of the concomitant impacts of altered hydrology and invasive macrophytes is incomplete without considering diel variability.
... Currently, assessments of nocturnal coral reef fish populations is not a priority within the NOAA PIFSC; however, one principal benefit from the addition of night time surveys would be a more holistic examination of habitat use by coral reef fishes, including those that may be of management concern. Comparative examples include the migration of snappers from coral reef refuges to seagrass foraging areas, shifts in nocturnal reef fish assemblages and functional groups versus their daytime counterparts, and increased nighttime movements of some predator species in Hawaiian Marine Life Conservation Districts (Harvey et al. 2012a;Filous et al. 2017;Hammerschlag et al. 2017). ...
Research, monitoring and management of Hawaiian coral reef fishes remains heavily reliant on data collected using underwater visual censuses by SCUBA divers. However, diver-based visual sampling is subject to limitations, including: 1.) Biases caused by different responses of fishes to divers at fished versus remote locations. For example increased wariness of target fishes at heavily fished locations could lead to substantial undercounts. Equally, the attraction of large bodied roving predatory species, such as sharks and jacks, to divers at remote locations has likely led to inflated predator biomass estimates; and 2.) Domains limited to ‘shallow’ depths that can be readily surveyed by divers on open-circuit SCUBA – i.e. ~30m or less. As many ‘depth generalist’ coral reef fish species are distributed across a broad range of depths, and in some cases more abundant in deeper ‘mesophotic’ waters > 30 m, underwater visual censuses do not assess large portions of coral reef fish populations, and potentially overlook important conservation or management information (e.g. mesophotic depths may act as refuges from fishing). Conversely, ‘depth specialist’ species may be constrained to shallow or deeper depth strata, affecting overall community structure and limiting refuge potential.
Baited Remote Underwater Stereo-Video systems (stereo-BRUVs, herein denoted as ‘BRUVS’) represent one widely-used, alternative approach to bridge these knowledge gaps. However, this method has not been adopted as a standard tool surveying and monitoring reef fish and large-bodied roving predators in the Hawaiian Archipelago. While BRUVS may be capable of generating valuable information in data-deficient areas, concerns over additional biases relating to use of baited video surveys (e.g. attraction of predators, herbivore avoidance) have yet to be addressed in Hawaii. There is a need to increase the use of remote survey methods for surveying and monitoring reef fish and large-bodied roving predators and to critically assess the strengths, advantages, weaknesses, limitations and biases of BRUVS in comparison with other underwater visual census approaches. The interpretation of data collected from different methods, which have disparate biases and depth limitations, may result in very dissimilar estimates of coral reef fish populations leading to conflicting management actions.
This thesis combines several novel methodological and ecosystem-based comparisons for the Hawaiian Archipelago. Chapter 2 compares and contrasts the functional group composition of coral reef fish communities and a subset of predatory target species over a range of soak time intervals (i.e. 0 – 20, 0 – 40, and 0 – 60 minute sampling intervals) for both BRUVS and its unbaited analogue (RUVS). I also investigate the time of first arrival (‘TOFA’) and the time to maximum abundance (‘MaxNT’). I conclude that while shorter RUVS or BRUVS soak times of 20 minutes are sufficient to capture overall assemblage group structure and to survey resident or “fast reacting” species, longer BRUVS soak times (i.e. 60 minutes) improve herbivore assessments, and are better at capturing predatory sessile macropiscivores (eels belonging to Muraenidae and Ophichthidae) and generalist macropiscivores (large-bodied, roving sharks, jacks, and snapper), particularly targeted jack species that are considered depleted around human population centers.
In Chapter 3, I use BRUVS to compare and contrast reef fish communities between shallow water and mesophotic depths in the Main Hawaiian Islands (MHI), with continued emphases on
fishery-targeted species, and expanded to include Hawaiian endemics and linkages between assemblage counts and environmental features. A combination of multivariate PERMANOVA, pair-wise permutational ANOVA, and Canonical Analysis of Principal Components (CAP) analyses showed that while significant community shifts were detected when transitioning from shallow water to mesophotic depths, relative abundance and species richness were highest in < 30 m habitats. Two functional groups (mobile invertivores, generalist macropiscivores) were notable exceptions, having higher abundance and richness values in mesophotic depths. Multivariate regression trees (MRT) and distance-based linear modeling (DistLM) indicated that depth, habitat complexity, unconsolidated sediment (sand), and macroalgae act as structural reef fish assemblage drivers, with indicator species assigned to specific environmental node breaks. There was also evidence of depth-based shifts in the composition and abundance of endemic species, and mesophotic refugia for target species belonging to several functional groups (using length-based kernel density estimates). Finally, I discovered a mesophotic ground fish interface in Halimeda beds that are utilized by juvenile Pristipomoides filamentosis.
Chapter 4 focuses exclusively on reef-associated generalist macropiscivores (roving predators) from shallow to mesophotic depths, and includes BRUVS assessments from both the (populated) MHI and the (unpopulated) NWHI. Through a combination of tests (Bootstrapping, PERMANOVA, Hierarchical Clustering, SIMPER, non-parametric quantile regression splines), I found clear shifts in roving predator community composition, and differences in relative abundance between regions and depth zones. For example, I observed that there was up to an order of magnitude more jacks and five times more sharks sampled in the NWHI compared to the MHI. In addition, differences in target species length-distributions between depth zones and regions were examined using non-parametric Kolmogorov-Smirnov tests, which provided evidence for;
1.) Depth-based predator refuges around populated areas in the MHI – e.g. that target fishes tended to be larger in deeper waters. This assertion was complemented by stark differences between shallow and mesophotic predator abundances in the MHI (e.g. Caranx ignobilis solely encountered in mesophotic zones); and
2.) The prevalence of smaller Carcharhinus galapagensis and Caranx ignobilis in < 30 m depths in the NWHI suggests possible body size and depth segregation, or potential avoidance of intra- or inter-specific predation pressures in deeper waters.
In Chapter 5, I investigate the scope for diver-based underwater visual censuses to properly assess the abundance of large-bodied, roving predators across the Hawaiian Archipelago. Specifically, there are recurring, long-standing concerns that (i) divers are typically limited to only a narrow part of the depth range used by these species; and (ii) acquired behavioral differences of roving predatory species – such as avoidance of divers at fished locations – seriously and substantially bias estimates of relative abundance between populated and remote locations. Here, I compared roving predator abundance estimates gathered by shallow water point-count and towed-diver surveys in < 30 m against data collected using RUVS and BRUVS across the Hawaiian Archipelago, including comparisons among datasets collected in shallow depths exclusively, as well as with data from RUV-BRUV spanning 0 – 100 m. The ‘boot’ and ‘boot.ci’ functions were used from the boot package in R, Version 3.3.0, with 10,000 iterations to produce adjusted 95% confidence intervals (type = “bca”) for each diver census and video assessment method used. Although RUVS and BRUVS data showed significantly higher roving predator densities in the remote NWHI, they also generated substantially lower NWHI:MHI ratios than were generated from diver data – i.e. significantly decreased scales of difference. Comparative example include (but are not limited to) the snapper Aprion virescens (SPC NWHI:MHI ratio was 62:1, towed-diver 24:1, RUVS 5:1, BRUVS 3:1), reef sharks (SPC 142:1, towed-diver 76:1, RUVS 20:1, BRUVS 11:1), and jacks (e.g. trevallies: SPC 5:1, towed-diver 17:1, RUVS 2:1, BRUVS 2:1). Clearly, these results corroborate concerns about the limitations of data that can be readily collected by divers for those groups of fishes, and emphasizes the need to further evaluate diver-based predator estimates in order to foster effective management policies for predatory species.
In conclusion, I demonstrate that BRUVS are an appropriate alternative and/or complement to diver-based visual censuses that provide a means to gain a more holistic representation of reef fish communities and higher-level predator groups. As a relatively new approach to US coral reef fish assessment strategies, the use of BRUVS could be further expanded to include comparatively understudied mesophotic coral reefs and other associated habitats in the Hawaiian Archipelago, along with other poorly studied deep-water regions in the US Pacific Territories (Pacific Remote Islands, American Samoa, Guam and the Commonwealth of the Northern Marianas). Lastly, the extension of BRUVS surveys to other areas hosting large, sustained roving predator populations would allow for a more nuanced assessment of the plausibility of ‘inverted biomass pyramids’ as part of future monitoring procedures and management approaches.
... Sampling multispecies fish assemblages effectively and repeatedly is challenging as different species occupy a range of depths and habitats Zintzen et al., 2012Zintzen et al., , 2017, may be active diurnally or nocturnally (Hammerschlag et al., 2017) and have different mobility (migratory to sedentary) and home ranges (square metres to scales encompassing oceans) (Kramer and Chapman, 1999). In recent years, technological advancements have enabled the development and adaptation of efficient, cost-effective video-based methods for sampling fish communities and marine ecosystems (Harvey and Mladenov, 2001;Mallet and Pelletier, 2014). ...
Rapid changes in video technology have allowed for the development of sophisticated, efficient methods for surveying fish communities, including systems that use single or stereo video cameras, which are baited or unbaited and used remotely, by divers or on Remote Operated Vehicles. Video methods are non-extractive and their deployment can be standardised. As a result of the spatial and temporal repeatability of video techniques they are often used to monitor the biodiversity, assemblage composition and size structure of marine fishes. Because of the biases and sampling efficiencies of different configurations, consideration is required as to which is the most appropriate design for the objectives of a particular study. Baited remote underwater stereo-video systems (stereo-BRUVs), which record across the seascape, and downward-facing single camera baited underwater video systems (downward-BUVs) were deployed in temperate reef habitats on the west coast of Australia to compare the numbers of species and individuals, the assemblage composition, and the relative abundances and size distributions of focal species recorded by both techniques. Stereo-BRUVs sampled a different assemblage composition of fishes than downward-BUVs, observing significantly more species (84 vs 63) and individuals (7321 vs 4490). In general, stereo-BRUVs sampled a greater range of trophic groups than downward BUVs, including species not directly attracted to the bait (e.g. herbivores). Some carnivores that were recorded on the stereo-BRUVs were rarely, or never observed by downward-BUVs. This is attributed to the increased numbers of fish and species recorded in the broader field of view of the stereo-BRUVs. The power to detect a 20, 50 or 100% change (at α = 0.05) in numbers of species and individuals was comparable between methods, but typically greater for stereo-BRUVs for some of the focal species. Length distributions of focal species differed significantly between methods in most cases, with stereo-BRUVs providing accurate and precise measurements, while downward-BUVs often over-estimated lengths. We conclude that forward-facing stereo-BRUVs were superior to downward-facing single camera BUVs in virtually all aspects tested.
The intensity of light received by the waters changes according to the phase of the moon, which affects the behavior of fish that have positive or negative phototaxis properties towards light. This directly affects the volume of fishermen's catches. A lack of deep understanding of the influence of the moon phase often makes fishermen unable to maximize their catches. The purpose of this study was to analyze the effect of the moon phase on purse seine catches and the composition of purse seine catches based on the moon phase in Amahai Waters. This research was conducted in February-March 2024 in Amahai Waters, Seram Island. The method used in this study was the survey method by conducting direct observations in the field. The results of the analysis showed that the moon phase did not have a significant effect on purse seine catches where the significance value was 0.529> 0.05. The purse seine catch was 25,570 ton with the composition of the catch in the New Moon phase, namely layang fish (Decapterus sp) 62%, selar fish (Selar sp) 38%. The composition of the catch in the First Quarter moon phase is layang fish (Decapterus sp) 63%, selar fish (Selar sp) 37%. The composition of the catch in the Full Moon moon phase is layang fish (Decapterus sp) 57%, selar fish (Selar sp) 30%, and skipjack tuna (Katsuwonus pelamis).
Labeo catla (catla) is the second most commercially important and widely cultured Indian major carp (IMC). It is indigenous to the Indo-Gangetic riverine system of India and the rivers of Bangladesh, Nepal, Myanmar, and Pakistan. Despite the availability of substantial genomic resources in this important species, detailed information on the genome-scale population structure using SNP markers is yet to be reported. In the present study, the identification of genome-wide single nucleotide polymorphisms (SNPs) and population genomics of catla was undertaken by re-sequencing six catla populations of riverine origin from distinct geographical regions. DNA isolated from 100 samples was used to perform genotyping-by-sequencing (GBS). A published catla genome with 95% genome coverage was used as the reference for mapping reads using BWA software. From a total of 472 million paired-end (150 × 2 bp) raw reads generated in this study, we identified 10,485 high-quality polymorphic SNPs using the STACKS pipeline. Expected heterozygosity (He) across the populations ranged from 0.162 to 0.20, whereas observed heterozygosity (Ho) ranged between 0.053 and 0.06. The nucleotide diversity (π) was the lowest (0.168) in the Ganga population. The within-population variation was found to be higher (95.32%) than the among-population (4.68%) variation. However, genetic differentiation was observed to be low to moderate, with Fst values ranging from 0.020 to 0.084, and the highest between Brahmani and Krishna populations. Bayesian and multivariate techniques were used to further evaluate the population structure and supposed ancestry in the studied populations using the structure and discriminant analysis of principal components (DAPC), respectively. Both analyses revealed the existence of two separate genomic clusters. The maximum number of private alleles was observed in the Ganga population. The findings of this study will contribute to a deeper understanding of the population structure and genetic diversity of wild populations of catla for future research in fish population genomics.
Bar racks at water intakes of hydropower plants serve mainly to protect the turbines from floating debris. Additionally, they can be utilized to protect downstream migrating fish in order to prevent a potentially harmful turbine passage. The Bar Rack FishProtector consists of a common bar rack equipped with electrodes mounted on the upstream side of the bars. The application of a low voltage current at the electrodes creates an electric field in the water which is actively avoided by fish. Thus, a hybrid barrier consisting of a mechanical barrier and a behavioral barrier is formed. An unscaled model of a Bar Rack FishProtector (bar spacing sb = 50 mm, bar thickness tb = 20 mm) was used in field experiments to investigate the retention rate in an experimental setup with only one possible migration route (downstream, rack passage) and an average flow velocity of 0.43 m/s. Ethohydraulic experiments were performed with three indicator species barbel (Barbus barbus), bream (Abramis brama) and roach (Rutilus rutilus) and additionally perch (Perca fluviatilis) in selected trials. The twelve trials included four reference trials without electric field present (Nday = 2, Nnight = 2) and eight trials with electric field (Nday = 6, Nnight = 2). The results show that the experimental retention rate could be increased significantly by the application of an electrical field during the night and during the day with an even more pronounced effect during the night. The differences between the functionality of the system during the day and at night as well as other influencing parameters are discussed. No significant influence of the applied voltage on the electrodes or significant influence of fish size could be identified.
Many fishes encounter periods of prolonged darkness within their lifetime, yet the consequences for the visual system are poorly understood. We used an amphibious fish (Kryptolebias marmoratus) that occupies dark terrestrial environments during seasonal droughts to test whether exposure to prolonged darkness diminishes visual performance owing to reduced optic tectum (OT) size and/or neurogenesis. We performed a 3-week acclimation with a 2 × 2 factorial design, in which fish were either acclimated to a 12 h:12 h or 0 h:24 h light:dark photoperiod in water or in air. We found that water-exposed fish had poorer visual acuity when acclimated to the dark, while air-acclimated fish had poorer visual acuity regardless of photoperiod. The ability of K. marmoratus to capture aerial prey from water followed a similar trend, suggesting that good vision is important for hunting effectively. Changes in visual acuity did not result from changes in OT size, but air-acclimated fish had 37% fewer proliferating cells in the OT than water-acclimated fish. As K. marmoratus are unable to eat on land, reducing cell proliferation in the OT may serve as a mechanism to reduce maintenance costs associated with the visual system. Overall, we suggest that prolonged darkness and air exposure can impair vision in K. marmoratus, and that changes in visual performance may be mediated, in part, by OT neurogenesis. More broadly, we show that plastic changes to the visual system of fishes can have potential consequences for organismal performance and fitness. K E Y W O R D S brain, eyeless fish, neurogenesis, optic tectum, optokinetic response, PCNA
The fine-scale movement of Mustelus mustelus in relation to environmental conditions was investigated at various temporal scales with acoustic telemetry and temperature–depth transmitters inside a coastal marine protected area in South Africa. Twenty-four sharks were equipped with acoustic tags and logged by an array of 28 acoustic receivers from November 2006 to November 2008. Generalised additive and generalised additive mixed models (GAMMs) were used to explain patterns of movement in terms of the environmental conditions related to temperature, the rate of change of temperature, tidal flow, diel cycle and moon phase. The most important environmental parameters affecting movement and direction of movement were related to absolute temperature and changes in temperature at the position of the shark. The movement of M. mustelus was not affected by tide and only minimally affected by the diel cycle, suggesting behavioural thermoregulation as the ultimate cause of the movements. M. mustelus preferred temperatures from 18 to 22°C, as determined by GAMMs for environmental conditions experienced in summer. The combination of the thermal environment, rich feeding grounds and protective effect of the Langebaan Marine Protected Area may explain the high abundance and regular occurrence of M. mustelus within this marine protected area.
Sharks are an interesting group of vertebrates, as many species swim continuously to “ram” oxygen-rich seawater over their gills (ram ventilators), whereas other species “pump” seawater over their gills by manipulating buccal cavity volume while remaining motionless (buccal pumpers). This difference in respiratory physiology raises the question: What are the implications of these differences in lifestyle for circadian rhythms? We investigated the diel activity patterns of 5 species of sharks, including 3 ram ventilating species: the school shark (Galeorhinus galeus), the spotted estuary smooth-hound (Mustelus lenticulatus), and the spiny dogfish (Squalus acanthias); and 2 buccal pumping species: the Port Jackson (Heterodontus portusjacksoni) and draughtsboard (Cephaloscyllium isabellum) sharks. We measured the amount, duration, and distance traveled while swimming over multiple days under a 12:12 light:dark light regime for all species and used modified light regimes for species with a clear diel rhythm in activity. We identified a surprising diversity of activity rhythms. The school shark and smooth-hound swam continuously; however, whereas the school shark swam at the same speed and covered the same distance during the day and night, the smooth-hound swam slower at night and traversed a shorter distance. A similar pattern was observed in the spiny dogfish, although this shark swam less overall. Both the Port Jackson and draughtsboard sharks showed a marked nocturnal preference for swimming. This pattern was muted and disrupted during constant light and constant dark regimes, although circadian organization of this pattern was maintained under certain conditions. The consequences of these patterns for other biological processes, such as sleep, remain unclear. Nonetheless, these 5 species demonstrate remarkable diversity within the activity rhythms of sharks.
Monitoring programs that aim to measure the diversity, abundance and biomass of fishes depend on accurate and reliable biological data to guide the development of robust management plans. It is important to implement an appropriate sampling technique that provides a comprehensive assessment, while reducing associated biases in the data collection process. We compared the sampling abilities of four different underwater stereo-video techniques; baited remote underwater stereo-video systems (BRUV), diver operated stereo-video (DOV), and two relatively new methodologies; slow towed stereo-video (STV) and remotely operated vehicle (ROV) fitted with a stereo-video. Comparisons were conducted in a temperate reef system along a single limestone ridge within Geographe Bay, Western Australia. More fish species and individuals were sampled by BRUVs, while transect based methods (DOV, STV, and ROV) were comparable. Combining BRUVs with a transect method resulted in a ~10% increase in observed diversity. BRUVs had a higher statistical power to detect change in comparison to the transect methods. This was due to the higher variability observed in transect methods that may sample greater habitat heterogeneity within a sample unit compared to BRUVs. Although differences did exist, data collected with the ROV was generally comparable to the other transect methods. We believe further research into ROV use is warranted as they provide a safer alternative to diver-based techniques and have the ability to extend into deeper-waters. We recommend that for fish diversity and abundance assessments a sampling strategy that combines BRUVs and a transect method should be adopted.
Shark depredation, where a shark partially or completely consumes an animal caught by fishing gear before it can be retrieved to the fishing vessel, occurs in commercial and recreational fisheries worldwide, causing a range of negative biological and economic impacts. Despite this, it remains relatively understudied compared to other fisheries issues. This is the first review of the literature relating to shark depredation, which also includes an overview of the potential mechanisms underlying its occurrence and options for mitigation. Furthermore, this review highlights key research gaps that remain to be investigated, thereby providing impetus for future research. In total, 61 studies have been published between 1955 and 2018, which include information on shark depredation. These studies recorded quantitative rates of depredation between 0.9 and 26% in commercial and recreational fisheries and during research fishing, identified 27 shark species from seven families that were responsible for depredation and discussed potential factors influencing its occurrence. Information from research into bycatch mitigation and the testing of shark deterrent approaches and technologies is also presented, in the context of applying these approaches to the reduction of shark depredation. This review presents an holistic overview of shark depredation in fisheries globally and, in doing so, provides a central resource for fisheries researchers and managers focusing on this topic to stimulate further collaborative research on this important fisheries issue.
The blacktip shark (Carcharhinus limbatus) is a common coastal species in tropical and subtropical waters around the world. To examine the fine-scale movement ecology of this species in a Caribbean nursery, 17 neonate blacktip sharks were acoustically tagged in May, 2012 and tracked for one year in Coral Bay, St John, USVI. By quantifying linear movement and shifts in position from a fixed Inner harbor location, we identified a diel movement pattern where blacktip sharks spend daylight hours within core habitat of Inner Coral Harbor and move each night to the central and outer portions of the Bay, a linear shift of 174–934 m. When compared to standard home range calculations applied to the overall movement data, these nightly positions were outside of the 95% activity space and, therefore, undetected using traditional space utilization methods, despite their predictable daily occurrence. Cluster analysis and nonmetric multidimensional scaling indicated distinct movement periods and locations: daytime (sun up) within Inner Coral Harbor; nighttime (sun down) in the center of the Bay; and brief periods approximately six hours after sunset at the mouth of the Bay. This diel shift in habitat use is likely associated with nocturnal foraging because it coincides with similar shifts in potential prey species. Habitat and resource management that incorporates the blacktip shark movements described herein is critical to the protection of these vulnerable life stages. The findings of this paper advance the understanding of blacktip shark behavior and acoustic telemetry experimental design.
Knowledge of the diel spatial ecology of wild animals is of great interest to ecologists and relevant to resource management and conservation. Sharks are generally considered to be more active during nocturnal periods than during the day; however, few studies have empirically evaluated diel variation in shark habitat use and how anthropogenic disturbances may influence these patterns. In the western central Atlantic Ocean, tiger sharks (Galeocerdo cuvier) are highly abundant in the shallow waters of the Little Bahama Bank, Bahamas. Within the northwest edge of the Bank, there is an area nicknamed “Tiger Beach,” where tiger sharks are provisioned year-round at spatially discrete ecotourism dive sites spanning ~ 1.5 km². In this study, we used an array of acoustic receivers encircling an area of 102.4 km² to evaluate for potential differences in diel spatial habitat use patterns for 42 tagged tiger sharks at Tiger Beach and the surrounding area. Using tracking data from 24 June 2014 to 13 May 2015, we evaluated spatial and diel patterns of shark activity space, centers of activity, residency and the daily proportion of sharks detected within the array. Sharks were detected during both day and night with no significant diel differences in habitat use metrics across the array, although spatial differences in residency existed. Four sharks accounted for 53.8% of residency data throughout the tracking period, with the majority of sharks primarily entering and exiting the array, except during summer months when the most of the tagged tiger sharks were absent from the array. We also found limited empirical support for hypothesized effects of provisioning tourism on tiger shark habitat use. However, additional research at finer, individual scales, may be needed to better resolve the potential influence of provisioning on tiger sharks at Tiger Beach.
In marine communities, resource partitioning can be as important as abiotic environmental preferences in determining habitat use patterns. Elasmobranchs are generally assumed to be crepuscular or nocturnal, but diel temporal habitat partitioning is poorly studied in this group. We attempted to identify habitat preferences and find evidence of resource partitioning among the elasmobranch community in Back and Core Sounds, North Carolina, using a multi-gear, fishery-independent survey with a temporal focus on the diurnal-nocturnal transition. Gillnet, longline, drumline, and rod-and-reel sampling captured a total of 160 elasmobranchs, representing 12 species within the estuary, and differences between the seven most abundant species were assessed in terms of temporal, environmental, and spatial habitat factors. The elasmobranch community was broadly divided into cool and warm temperature assemblages. Most species showed evidence of generalist habitat preferences, but spatial overlap between species was generally low. Blacknose sharks [Carcharhinus acronotus (Poey, 1860)] appeared to be nocturnal, and aggregations of smooth dogfish [Mustelus canis (Mitchill, 1815)] and spiny dogfish (Squalus acanthias Linnaeus, 1758) were found during mid-afternoon hours. Blacknose sharks and blacktip sharks [Carcharhinus limbatus (Müller and Henle, 1839)] showed evidence of spatial resource partitioning based on distance from the nearest inlet. Temperature appears to be a strong influence on the presence of elasmobranch species within Back and Core Sounds, but behavioral interspecific avoidance may be a greater influence on fine-scale habitat use by elasmobranchs in this estuarine system.
It is commonly assumed that elasmobranchs (sharks, skates, and rays) are most active during dark periods (dawn, dusk, night). However, this assertion has not been critically evaluated. It is also unclear whether dark periods are primarily utilized for the performance of important life-history events, such as mating. If this were the case, low-light periods would be of significance to elasmobranch conservation as some anthropogenic activities (night fishing, lighting) could disproportionately impact fitness of species that are more active in the dark. Here, we review and summarize previous studies on elasmobranch behavior during nocturnal and crepuscular periods focusing on patterns of movement, habitat use, foraging, and reproduction. A review of 166 studies provided mixed results for widely-assumed increased elasmobranch activity when dark. Frequency of foraging and horizontal movement (distance travelled, activity space) were reported as greater only during crepuscular periods in the majority (>50%) of reviewed studies (28 of 43 and 78 of 125 studies, respectively), a pattern not evident during night. No pervasive patterns emerged for increased habitat use or reproductive behaviors during dark. We did not find any particular habitat type consistently supporting increased activity during dark, nor did we find evidence that higher trophic level elasmobranchs were more active when dark. Thus, generalizations about increased elasmobranch activity during dark periods are currently not supported. While research on the behavior of elasmobranchs during dark periods has been increasing, many knowledge gaps remain and we present a set of research priorities to assist in the development of future investigations.
Light pollution is a prevalent, but often overlooked, ecological concern in a variety of ecosystems. Marine environments are subjected to artifcial lighting from coastal development, in addition to ofshore sources, such as fshing vessels, oil platforms and cruise ships. Fish species that rely on nearshore habitats are most signifcantly impacted by coastal light pollution, as they are often limited to nearshore habitats due to predation risk in deeper ofshore waters, particularly as juveniles. Juvenile bonefsh [Albula vulpes (Linnaeus, 1758)] inhabit the nearshore environment, and are therefore exposed to coastal lighting and other watershed development impacts. Here, we assessed juvenile bonefsh behavior and physiology in the presence of two common light sources: constant street lighting (high pressure sodium) and intermittent car headlights (H4 halogen). Te behavioral responses were compared with a night and day control, whereas physiology was compared only with a night control. Each behavioral trial had two time periods: light and recovery (2 hrs each). Physiology (blood glucose and whole body cortisol) was assessed after an overnight 8-hr exposure. Te results suggest that there is no effect of light pollution on the swimming behavior or whole body cortisol of juvenile bonefsh, but that both forms of light pollution resulted in elevated blood glucose concentrations (a simple stress indicator) relative to controls, with constant light glucose levels being signifcantly higher. Further research is needed to understand the ecological consequences of light pollution on bonefsh and other coastal marine fsh using additional endpoints, assessing fsh over longer time periods, and ideally combining data from the laboratory and the feld. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Flying fishes (family Exocoetidae) are important components of epipelagic ecosystems and are targeted by fishing fleets in the Caribbean Sea and elsewhere. However, owing to their anti-predator behavior and habitats, their ecology, abundance, and distributions are only partially known. From September 20 to October 6, 2011, we conducted a series of surveys over a large area (approximately 75,000 km2) of the northern Gulf of Mexico (87°W–90.5°W, 28°N–30°N). The surveys used an airborne lidar and vessel-based sampling, supported by near real time satellite observations of oceanic conditions. The aerial survey was conducted from a fixed wing aircraft that flew repeated surveys day and night, enabling data collection that was both broad-scale and synoptic. Vessel-based sampling included quantitative visual observations, trawl sampling, and qualitative dip-netting for species identifications. The combined surveys identified large aggregations of epipelagic organisms dominated by flying fishes. Large numbers of jellyfish (Aurelia sp.) and low numbers of numerous other species were also observed. The putative flying fish aggregations had an average length scale of 6.1 km and an average population estimated at 10,000 individuals. While always near the surface, flying fish aggregations were slightly deeper at night than during the day and found most often off the continental shelf in warm water with low chlorophyll concentrations. At least three species were present: Hirundichthys rondeletii (Valenciennes, 1847), Cheilopogon melanurus (Valenciennes, 1847), and Prognichthys occidentalis Parin, 1999. This combination of aerial and surface surveys afforded repeated synoptic, ground-truthed data collection over a large area and indicates that this method could be useful for surveying such mobile epipelagic fishes.
Over the past two decades, the United States' recreational fshery for North Atlantic swordfsh, Xiphias gladius Linnaeus, 1758, has grown along the coasts of the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Successful management and high recruitment during an historical period of low biomass contributed to rebuilding the North Atlantic swordfsh stock, leading to sustainable harvest opportunities. Over time, fsheries have shifted fshing gears and techniques to increase access to swordfsh, a crepuscular fsh that occupies deep waters during the day and ascends to shallower depths at night. Particularly among recreational anglers, a decline in drift (surface) fshing and popularization of the deep-drop technique shifted much of the fshing activity from night to day. Private angler and for-hire (charter) self-reported data on swordfsh landings (retained catch) from 2003 to 2014 illustrated this shift in recreational fshing, including trip, technique, and catch characteristics. Te majority of the landings occurred o? southeast Florida (88%), where 70% of the swordfsh were caught on private trips. Te shift in technique was observed in reports from 2008 to 2014, which revealed a nearly synchronous 40% increase in deep-drop fshing and decrease in drift fshing, shifting the peak hookup (bite) times from 21:00-23:00 to 10:00-13:00 hrs. Te average size of drift-and deep-drop caught swordfsh increased; however, deep-drop caught swordfsh were, on average, larger than those caught while drift fshing. Tese summaries re?ect a modern characterization of this fshery and potential areas of improvement to this data collection. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Fish chorusing is a major component of the marine acoustic environment, and much of this chorusing activity happens at night. These nocturnal sounds are commonly associated with reproductive behavior. For many co-occurring taxa, increases in vocal activity may intensify acoustic competition within a constrained signaling environment; for nocturnal species, there is a limited time window for these critical behaviors, and competition to be heard by conspecifics likely increases. Using passive acoustic recording units deployed in the nearshore waters off Georgia and eastern Florida, we evaluated the nocturnal acoustic habits of fishes and examined how the sounds from nocturnal fish chorusing contribute to the overall soundscape. We examined long-term spectrograms for spatial and temporal patterns of fish calling. Black drum [Pogonias cromis (Linnaeus, 1766)] and toadfish (Opsanus sp.) dominated the nocturnal acoustic scene, but calls of other identified [e.g., red drum, Sciaenops ocellatus (Linnaeus, 1766); silver perch, Bairdiella chrysoura (Lacépède, 1802)] and unidentified calling species also occur. We examined the acoustic indices of entropy, acoustic diversity, and acoustic complexity to compare nocturnal and diurnal fish calling activity across the region. When sustained fish chorusing activity increases, entropy and acoustic diversity decrease, but acoustic complexity increases. With the acoustic differences in composition of nocturnally- and diurnally-active species groups, there is a different nocturnal soundscape than during the day. Passive acoustic surveys represent an exciting approach to understand the nocturnal reproductive activity of coastal fishes.
Structurally complex estuarine habitats, such as seagrass beds, salt marshes, and oyster reefs, are used by fsh for foraging, avoiding predators, and spawning. Here, we used passive acoustics to characterize spatiotemporal patterns in the soundscape of an estuarine reserve that contained a mosaic of habitat types, and focused on relating characteristics of the soundscape [e.g., low-frequency (150-1500 Hz) sound pressure levels (SPLs), amount of fsh chorusing] to patterns in the seascape (percent cover of estuarine habitats surrounding the recording sites). Over a 3-mo period, 2-min duration underwater sound recordings were made every 20 min at eight sites within Middle Marsh in Back Sound, North Carolina, USA. While habitat composition was not related to spatial patterns in low-frequency SPLs, there was a positive and statistically signifcant relationship between the percent recordings with fsh chorusing, and percent cover of seagrass for silver perch [Bairdiella chrysoura (Lacépède, 1802)], spotted seatrout [Cynoscion nebulosus (Cuvier, 1830)], and other fsh, irrespective of spatial scale (10 vs 25 m). Moreover, silver perch and spotted seatrout, soniferous species that share similar spawning locations, exhibited temporal partitioning in the soundscape with seatrout calls occurring just before sunset and peaking several hours after sunset, and declining sharply as perch chorusing increased after sunset with a peak at midnight. Overall, local habitat composition and the soundscape at these sites were not highly correlated; where major sound producing fsh species are transient, other seascape characteristics, such as proximity to channels, likely have a larger influence on the resulting soundscape. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
The Mesoamerican Reef (MAR) system has major ecological and economic importance, yet faces threats to ecosystem health and is understudied. Current methods for monitoring marine life in the northern MAR system of the state of Quintana Roo, Mexico, are inadequate for assessing the nocturnal biology and ecology of fishes, including quantification of abundance and diversity. In the present study, a marine passive acoustic monitoring (MPAM) approach was initiated at a site within the MAR system to characterize localized temporal patterns in fish acoustic behavior. Tis is the first study to collect data on fish sound production at night in this region. Pulsed fish sounds were a major contributor to the nighttime soundscape and were persistent and low frequency (50-1000 Hz), with a wide range of pulse rates. Fish sounds were more frequent, more persistent, and more diverse at night than during the day. Nocturnally-active fish are a more important part of the local ecosystem than had previously been recognized. Implementation of MPAM in this area has great potential as a long-term fish monitoring technique. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Elopomorph fshes are distinguished in part by a shared leptocephalus larval form. Tese glassclear, ribbon-like larvae are remarkably similar across the elopomorpha, yet they mature to radically different forms as adults. Along the timecourse of development, they transition through a variety of spectrally distinct habitats, occupying very different temporal niches as adults-some diurnal predators in high-light environments, others crepuscular, and others nocturnal. We found that in concert with these changes, the retinas of a variety of elopomorph fsh change in similarly dramatic ways over the course of development. While the mature bonefsh [Albula vulpes (Linnaeus, 1758)] retina is specialized for visual tasks in a high-light environment, the Atlantic tarpon (Megalops atlanticus Valenciennes, 1847) and ladyfsh (Elops saurus Linnaeus, 1766) exhibit multiple specializations for function at night or otherwise in very dim light conditions. Tese include stacked rod photoreceptors that are gathered into massive bundles, retinomotor movement of photoreceptor outer segments, and a highly refective tapetum. In the adult form, the speckled worm eel (Myrophis punctatus Lütken, 1852) maintains a retina with nearly all rods. Te dramatic divergence among taxa over the course of development produces species with distinctly specialized visual capabilities. Moreover, the ability to change over the course of development may underlie the capacity for resilience in the face of anthropogenic insults, including light pollution in increasingly developed coastal zones. On the other hand, if light history can drive retinal change, exposure to artifcial light at night may be detrimental to the survival of individuals that move between light-polluted and naturally dark locations. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Bycatch in pelagic longline fisheries is of substantial international concern, and the mitigation of bycatch in the Gulf of Mexico has been considered as an option to help restore lost biomass following the 2010 Deepwater Horizonoil spill. The most effective bycatch mitigation measures operate upon a differential response between target and bycatch species, ideally maintaining target catch while minimizing bycatch. We investigated whether bycatch vs target catch rates varied between day and night sets for the United States pelagic longline fishery in the Gulf of Mexico by comparing the influence of diel time period and moon illumination on catch rates of 18 commonly caught species/species groups. A generalized linear model approach was used to account for operational and environmental covariates, including: year, season, water temperature, hook type, bait, and maximum hook depth. Time of day or moon phase was found to significantly alter catch rates for 88% of the taxa examined. Six taxa—swordfish (Xiphias gladius Linnaeus, 1758); tiger shark (Galeocerdo cuvier Péron and Lesueur, 1822); silky shark (Carcharhinus falciformis Müller and Henle, 1839); oilfish (Ruvettus pretiosus Cocco, 1833); bigeye thresher shark (Alopias superciliosus Lowe, 1841); and escolar (Lepidocybium flavobrunneum Smith, 1843)—exhibited higher catch rates at night, while eight taxa—skipjack tuna (Katsuwonus pelamis Linnaeus, 1758); wahoo (Acanthocybium solandri Cuvier, 1832); white marlin [Kajikia albida (Poey, 1860]; dolphinfish (Coryphaena sp.); yellowfin tuna (Thunnus albacares Bonnaterre, 1788); rays (Pteroplatytrygon violaceaBonaparte, 1832, Mobulidae sp.); lancetfish (Alepisaurus sp.), and blue marlin (Makaira nigricans Lacépède, 1802)—had higher daytime catch rates. These results reveal that shifts in effort between daytime and nighttime fishing (which are highly correlated with shifts between yellowfin tuna and swordfish targeting strategies) could have substantial, species-specific effects on bycatch rates. Whether driven by fishery conditions, market influences, or management measures, such temporal shifts in the timing of pelagic longline sets may have important implications for species-specific conservation goals and warrant further consideration.
Recreational fshing is a popular activity around the globe, generating billions of dollars in economic beneft based on fsheries in marine and inland waters. In most developed countries, recreational fsheries are managed to achieve diverse objectives and ensure that such fsheries are sustainable. While many anglers fsh during daylight hours, some target fsh species during the night. Indeed, sensory physiology of some species makes them vulnerable to capture at night, while being more difcult to capture during the day. However, night creates a number of challenges for recreational fsheries assessment and management. In some jurisdictions, fshing is prohibited at night (through both effort and harvest controls) or there are specifc restrictions placed on night fsheries (e.g., no use of artifcial lights). Here, we summarize the science and management of recreational fsheries at night covering both inland and marine realms. In doing so, we also provide a review of different angling regulations specifc to night fsheries across the globe, as well as the basis for those regulations. We discuss the extent to which there is both need and opportunity to actively manage anglers who are targeting fsh at night and how this differs from fsheries that occur during lighted periods. We provide two case studies, one for white sturgeon (Acipenser transmontanus Richardson, 1836) and one for walleye [Sander vitreus (Mitchill, 1818)], for which nighttime closures have been used as a fsheries management tool to control effort and harvest (illegal harvest in the case of the sturgeon case study). Based on the synthesis, we conclude that natural resource management agencies should decide if and how they need to manage recreational fsheries at night, recognizing the practical challenges (e.g., compliance monitoring, stock assessment) with doing so in the dark. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Many fish species migrate to form fsh spawning aggregations. Te temporal and spatial predictability of these migrations and spawning aggregation locations makes species vulnerable to overfshing, as the majority of an adult population within a large region may be harvested quickly with minimal effort. Historically, the Nassau grouper, Epinephelus striatus (Bloch, 1792), was an important fshery species throughout its range, but due to spawning aggregation overfshing, it is now rare in many reef ecosystems. In Te Bahamas, stocks continue to decline despite the implementation of spawning aggregation protections. While more Nassau grouper spawning aggregations have been reported in Te Bahamas than any other country, very few have been validated, and the dynamics of spawning migrations to and from these sites is poorly understood. Here, we used acoustic telemetry to describe, for the frst time, Nassau grouper migrations along Andros Island, Te Bahamas, which is bordered by one of the longest barrier reefs in the world. We report the likely extirpation of a historically important spawning aggregation and suggest Nassau grouper are migrating to a previously undocumented spawning location. Fish migrated in groups during the January 2015 full moon along the barrier reef shelf edge traveling roundtrip distances of 71.5-260.3 km [-x = 164.5 (SD 65.7) km, n = 9]. Tese results are critical to assess the efcacy of current management strategies in Te Bahamas. Tus far, all known spaning aggregations have been reported to the scientifc community by fshers. Data from our study, however, suggest the presence of a potential spawning aggregation informed by passive telemetry and warrants further investigation. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Understanding the promotion and regulation of circadian rhythms in marine fishes is important for studies spanning conservation, evolutionary biology, and physiology. Given numerous challenges inherent to quantifying behavioral activity across the full spectrum of marine environments and fish biodiversity, case studies offer a tractable means of gaining insights or forecasting broad patterns of diel activity. As these studies continue to accumulate, assessing whether, and to what extent, the cumulatively collected data are biased in terms of geography, habitat, or taxa represents a fundamentally important step in the development of a broad overview of circadian rhythms in marine fish. As such investigations require a phylogenetic framework, general trends in the phylogenetic sampling of marine fishes should be simultaneously assessed for biases in the sampling of taxa and trait data. Here, we compile diel activity data for more than 800 marine species from more than five decades of scientific studies to assess general patterns of bias. We found significant geographic biases that largely reflect a preference toward sampling warm tropical waters. Additionally, taxonomic biases likewise reflect a tendency toward conspicuous reef associated clades. Placing these data into a phylogenetic framework that includes all known marine fishes revealed significant under-dispersion of behavioral data and taxon sampling across the whole tree, with a few subclades exhibiting significant over-dispersion. In total, our study illuminates substantial gaps in our understanding of diel activity patterns and highlights significant sampling biases that have the potential to mislead evolutionary or ecological analyses.
In marine communities, resource partitioning can be as important as abiotic environmental preferences in determining habitat use patterns. Elasmobranchs are generally assumed to be crepuscular or nocturnal, but diel temporal habitat partitioning is poorly studied in this group. We attempted to identify habitat preferences and find evidence of resource partitioning among the elasmobranch community in Back and Core Sounds, North Carolina, using a multi-gear, fishery-independent survey with a temporal focus on the diurnal-nocturnal transition. Gillnet, longline, drumline, and rod-and-reel sampling captured a total of 160 elasmobranchs, representing 12 species within the estuary, and differences between the seven most abundant species were assessed in terms of temporal, environmental, and spatial habitat factors. The elasmobranch community was broadly divided into cool and warm temperature assemblages. Most species showed evidence of generalist habitat preferences, but spatial overlap between species was generally low. Blacknose sharks [Carcharhinus acronotus (Poey, 1860)] appeared to be nocturnal, and aggregations of smooth dogfish [Mustelus canis (Mitchill, 1815)] and spiny dogfish (Squalus acanthias Linnaeus, 1758) were found during mid-afternoon hours. Blacknose sharks and blacktip sharks [Carcharhinus limbatus (Müller and Henle, 1839)] showed evidence of spatial resource partitioning based on distance from the nearest inlet. Temperature appears to be a strong influence on the presence of elasmobranch species within Back and Core Sounds, but behavioral interspecific avoidance may be a greater influence on fine-scale habitat use by elasmobranchs in this estuarine system.
The increasing popularity of catch-and-release angling indicates a need to identify best practices that minimize sublethal injuries, impairments, and mortality. One factor impacting the viability of catch and release is the risk of hooking injury, which can impact survival in released fishes. In particular, deep hooking is known to increase post-release mortality in numerous species. As such, best practices include the use of equipment and promotion of angler behaviors that reduce incidences of deep hooking. In some areas, angling at night is restricted because of concerns that deep hooking is elevated relative to angling during the day. However, there has been little empirical research investigating whether deep hooking is influenced by the time of day (light levels). In the present study, we captured bluegill (Lepomis macrochirus Rafinesque, 1810) and pumpkinseed (Lepomis gibbosus Linnaeus, 1758) using active angling (cast and retrieve) and passive angling (with a bobber) throughout the 24-hr period, and recorded hook depth and hook location for each fish. We found that passive angling methods resulted in deeper hooking than active angling methods for both bluegill and pumpkinseed across all time periods. Although few pumpkinseed were caught at night, we found that the pumpkinseed caught were hooked more deeply and in more damaging hooking locations at night relative to the day. Hooking injury was independent of diel period for the more frequently landed species, bluegill. These findings emphasize the species-specific nature of catch-and-release outcomes, and suggest that further research is warranted to adequately quantify the impacts of recreational fishing at night.
Tropical Atlantic reef fishes in the family Haemulidae (grunts) remain quiescent on reefs during the day and migrate to seagrass beds or sand flats at night. Hypothesized advantages of such nocturnal migrations are increased food availability and/or decreased predation risk. Here, we tested predictions of an alternative hypothesis that nocturnal migrations of French grunt, Haemulon flavolineatum (Desmarest, 1823), reduce exposure to blood-feeding gnathiid isopods. The departure of grunts from the reef coincides with increasing gnathiid activity. In field experiments, subadult fish placed in cages and deployed on the reef at night harbored significantly more gnathiids than those placed in the seagrass habitat. However, this was not the case during the day when gnathiid activity in all habitats is low. In another experiment, the timing of return to the reef was determined to coincide with the postdawn decrease in gnathiid activity. Estimates of cumulative gnathiid exposure at two sites revealed that grunts remaining in reef habitat at night would experience an average of 3 and 44 times more gnathiids than if they spent the night in the seagrass bed, and could reach more than 300 gnathiids on a single fish. In a final field experiment, even recently-settled (<2 cm) juvenile grunts were infested by gnathiids, supporting previous laboratory experiments showing that a single third-stage gnathiid will infest and kill grunts of this size. Combined, these findings suggest that nocturnal feeding migrations of French grunts and ecologically similar fishes result in reduced exposure to blood-feeding gnathiid isopods. Many animals undergo daily or seasonal migrations between habitats (Rubenstein and Hobson 2004, Møller and Szép 2011, Poulin et al. 2012). Given the costs of travel, evolutionary ecologists seek to understand the net benefits of migration, while community and population ecologists are interested in the ecological consequences of
The diel, lunar, and seasonal timing of spawning in Atlantic goliath grouper Epinephelus itajara (Lichtenstein, 1822) in the United States is highly specific, occurring at night during new moon phases of August, September, and October. We derive these patterns from four lines of evidence apparent on spawning sites during the known spawning season: (1) from the transitory appearance of fish aggregations; (2) from simultaneous recordings of goliath grouper nighttime calls and nighttime vertical ascents that were far more frequent during the new moon phase than on the full moon; (3) from collections of goliath grouper eggs (genetically verified) at night downstream from known spawning sites; and (4) from significantly higher frequencies of both hydrated oocytes (indicating imminent spawning) and postovulatory follicles (indicating recent spawning) in ovarian biopsies taken from goliath grouper captured on spawning sites during new moon phases relative to full moon phases. We suggest that dark-night spawning is an adaptation minimizing egg predation by several species of scad [Decapterus punctatus (Cuvier, 1829), Decapterus tabl Berry, 1968, and Decapterus macarellus (Cuvier, 1833)] and herring [Sardinella aurita Valenciennes, 1847 and Etrumeus teres (DeKay, 1842)] that are abundant on goliath grouper spawning sites. The seasonal spawning of goliath grouper, late summer–early fall, coincides with habitat conditions considered ideal for settlement of early juveniles in mangrove nurseries.
Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs.
Artificial light at night (ALAN) is gaining recognition as having an important anthropogenic impact on the environment, yet
the behavioural and physiological impacts of this stressor are largely unknown. This dearth of information is particularly
true for freshwater ecosystems, which are already heavily impacted by anthropogenic pressures. Atlantic salmon (Salmo salar L.) is a species of conservation and economic importance whose ecology and behaviour is well studied, making it an ideal
model species. Recent investigations have demonstrated that salmon show disrupted behaviour in response to artificial light;
however, it is not yet clear which physiological processes are behind the observed behavioural modifications. Here, two novel
non-invasive sampling methods were used to examine the cortisol stress response of dispersing salmon fry under different artificial
lighting intensities. Fish egg and embryos were reared under differing ALAN intensities and individual measures of stress
were subsequently taken from dispersing fry using static sampling, whereas population-level measures were achieved using deployed
passive samplers. Dispersing fry exposed to experimental confinement showed elevated cortisol levels, indicating the capacity
to mount a stress response at this early stage in ontogenesis. However, only one of the two methods for sampling cortisol
used in this study indicated that ALAN may act as a stressor to dispersing salmon fry. As such, a cortisol-mediated response
to light was not strongly supported. Furthermore, the efficacy of the two non-invasive methodologies used in this study is,
subject to further validation, indicative of them proving useful in future ecological studies.
Theory and some empirical evidence suggest that groups of animals orient better than isolated individuals. We present the first test of this hypothesis for pelagic marine larvae, at the stage of settlement, when orientation is critical to find a habitat. We compare the in situ behaviour of individuals and groups of 10-12 Chromis atripectoralis (reef fish of the family Pomacentridae), off Lizard Island, Great Barrier Reef. Larvae are observed by divers or with a drifting image recording device. With both methods, groups orient cardinally while isolated individuals do not display significant orientation. Groups also swim on a 15% straighter course (i.e. are better at keeping a bearing) and 7% faster than individuals. A body of observations collected in this study suggest that enhanced group orientation emerges from simple group dynamics rather than from the presence of more skilful leaders.
To get a complete picture of how fish assemblages are affected by recreational fishing
it may be necessary to combine daytime and nocturnal sampling. Most of the scientific literature
on recreational fishing, however, neglects the nocturnal component. Discrepancies between
daytime and night-time catches in a shore angling fishery in the mid-Atlantic were investigated in
this study. Significant diel patterns in catch composition, fish sizes, and catch rates were detected.
Catch diversity was lower at night, although the species profile overlapped by 35.9%. Different
fish sizes were targeted by the fishery when night and day periods were compared. Larger specimens
of some commercially important species, e.g. Pseudocaranx dentex, were also caught at
night. Findings highlight the importance of evaluating differences between day and night catches
before defining a sampling design of a recreational fishing survey. If significance differences in
diel patterns exist, the incorporation of a nocturnal component is necessary to avoid misrepresentation
of the diversity and quantification of catch composition.
Background: Biologging technology has enhanced our understanding of the ecology of marine animals and has
been central to identifying how oceanographic conditions drive patterns in their distribution and behavior. Among
these environmental influences, there is increasing recognition of the impact of dissolved oxygen on the distribution of marine animals. Understanding of the impact of oxygen on vertical and horizontal movements would be advanced by contemporaneous in situ measurements of dissolved oxygen from animal-borne sensors instead of relying on environmental data that may not have appropriate spatial or temporal resolution. Here, we demonstrate the capabilities of dissolved oxygen pop-up satellite archival tags (DO-PATs) by presenting the results from calibration experiments and trial deployments of two prototype tags on bluntnose sixgill sharks (Hexanchus griseus).
Results: The DO-PATs provided fast, accurate, and stable measurements in calibration trials and demonstrated high correlation with vertical profiles obtained via traditional ship-borne oceanographic instruments. Deployments on bluntnose sixgill sharks recorded oxygen saturations as low as 9.4 % and effectively captured the oceanography of the region when compared with World Ocean Atlas 2013 values.
Conclusions: This is the first study to use an animal-borne device to autonomously measure and record in situ dissolved oxygen saturation from non-air-breathing marine animals. The DO-PATs maintained consistency over time and yielded measurements equivalent to industry standards for environmental sampling. Acquiring contemporaneous in situ measurements of dissolved oxygen saturation alongside temperature and depth data will greatly improve our ability to investigate the spatial ecology of marine animals and make informed predictions of the impacts of global climate change. The information returned from DO-PATs is relevant not only to the study of the ecology of marine animals but will also become a useful new tool for investigating the physical structure of the oceans.
Background
Understanding movement patterns of species requires that the spatial and temporal scales of experimental designs are appropriate to the proposed ecological questions. Previous research on large-scale movements of the exploited reef fish Lethrinus miniatus suggested that adult individuals may use coral reef slope habitat during the day, shifting to adjacent deeper sandy habitat at night. However, investigation of movement at a fine spatial and temporal scale is required to verify this diel activity pattern. Using a closely positioned acoustic telemetry system, movements of 11 L. miniatus were monitored among habitats from the reef crest, to reef slope and deeper adjacent sandy habitat over 3 months. Fine-scale movement patterns among these habitats were compared among four different 3 h periods of the day: dawn, day, dusk and night.
Results
Initial observations demonstrated significantly larger horizontal core areas and vertical areas of extent during crepuscular and night periods compared to during the day. Vertical space use (core area and extent) was consistently larger during dawn, dusk and night compared to during the day. Area of activity space extent within the water column and proportional overlap among areas used during different periods of the day varied among weeks, and displayed a pattern consistent with full moon periods.
Conclusions
Although previous evidence suggested that L. miniatus adults may shift to deeper habitats adjacent to the reef slope at night, greater space use across the shallow crest to deeper sand habitat was observed during dawn, dusk and night periods. Increased luminosity during dawn, dusk and night periods may cause L. miniatus to utilise a larger search area for foraging. While further research is required to confirm foraging during the hours of twilight and darkness, this fine-scale approach identified patterns in nocturnal activity for an important reef teleost. Knowledge of these temporal and spatial differences in L. miniatus behaviour and movement are important to understanding how this species coexists within ecological niches.
The current understanding of Arctic ecosystems is deeply rooted in the classical view of a bottom-up controlled system with strong physical forcing and seasonality in primary-production regimes. Consequently, the Arctic polar night is commonly disregarded as a time of year when biological activities are reduced to a minimum due to a reduced food supply. Here, based upon a multidisciplinary ecosystem-scale study from the polar night at 79°N, we present an entirely different view. Instead of an ecosystem that has entered a resting state, we document a system with high activity levels and biological interactions across most trophic levels. In some habitats, biological diversity and presence of juvenile stages were elevated in winter months compared to the more productive and sunlit periods. Ultimately, our results suggest a different perspective regarding ecosystem function that will be of importance for future environmental management and decision making, especially at a time when Arctic regions are experiencing accelerated environmental change [1
• Comiso J.C.
• Parkinson C.L.
• Gersten R.
• Stock L.
Accelerated decline in the Arctic Sea ice cover.Geophys. Res. Lett. 2008; 35: L01703
• Crossref
• Scopus (1106)
• Google Scholar
].
Several recent lines of evidence indicate that the polar night is key to understanding Arctic marine ecosystems. First, the polar night is not a period void of biological activity even though primary production is close to zero, but is rather characterized by a number of processes and interactions yet to be fully understood, including unanticipated high levels of feeding and reproduction in a wide range of taxa and habitats. Second, as more knowledge emerges, it is evident that a coupled physical and biological perspective of the ecosystem will redefine seasonality beyond the “calendar perspective”. Third, it appears that many organisms may exhibit endogenous rhythms that trigger fitness-maximizing activities in the absence of light-based cues. Indeed a common adaptation appears to be the ability to utilize the dark season for reproduction. This and other processes are most likely adaptations to current environmental conditions and community and trophic structures of the ecosystem, and may have implications for how Arctic ecosystems can change under continued climatic warming.
Quantifying the ecological importance of individual habitats to highly mobile animals is challenging because patterns of habitat reliance for these taxa are complex and difficult to observe. We investigated the importance of lagoons to the manta ray, Manta alfredi, a wide-ranging and vulnerable species in a less-disturbed atoll ecosystem. Lagoons are highly sensitive to anthropogenic disturbance and are known to be ecologically important to a wide variety of mobile species. We used a novel combination of research tools to examine the reliance of M. alfredi on lagoon habitats. Stable isotope analysis was used to assay the recent energetic importance of lagoons to M. alfredi; high-resolution tracking data provided information about how M. alfredi utilised lagoonal habitats over long and short time periods; acoustic cameras logged patterns of animal entrances and departures from lagoons; and photo identification/laser photogrammetry provided some insight into why they may be using this habitat. M. alfredi showed strong evidence of energetic dependence on lagoon resources during the course of the study and spent long periods of residence within lagoons or frequently transited into them from elsewhere. While within lagoons, they demonstrated affinities for particular structural features within this habitat and showed evidence of temporal patterning in habitat utilization. This work sheds light on how and why M. alfredi uses lagoons and raises questions about how this use may be altered in disturbed settings. More generally, these observations contribute to our knowledge of how to assess the ecological importance of particular habitats situated within the broader home range of mobile consumers.
The distribution and interactions of aquatic organisms across space and time structure our marine, freshwater, and estuarine ecosystems. Over the past decade, technological advances in telemetry have transformed our ability to observe aquatic animal behavior and movement. These advances are now providing unprecedented ecological insights by connecting animal movements with measures of their physiology and environment. These developments are revolutionizing the scope and scale of questions that can be asked about the causes and consequences of movement and are redefining how we view and manage individuals, populations, and entire ecosystems. The next advance in aquatic telemetry will be the development of a global collaborative effort to facilitate infrastructure and data sharing and management over scales not previously possible.
Copyright © 2015, American Association for the Advancement of Science.
We do not expect non air-breathing aquatic animals to exhibit positive buoyancy. Sharks, for example, rely on oil-filled livers instead of gas-filled swim bladders to increase their buoyancy , but are nonetheless ubiquitously regarded as either negatively or neutrally buoyant. Deep-sea sharks have particularly large, oil-filled livers, and are believed to be neutrally buoyant in their natural habitat, but this has never been confirmed. To empirically determine the buoyancy status of two species of deep-sea sharks (bluntnose sixgill sharks, Hexan-chus griseus, and a prickly shark, Echinorhinus cookei) in their natural habitat, we used ac-celerometer-magnetometer data loggers to measure their swimming performance. Both species of deep-sea sharks showed similar diel vertical migrations: they swam at depths of 200–300 m at night and deeper than 500 m during the day. Ambient water temperature was around 15°C at 200–300 m but below 7°C at depths greater than 500 m. During vertical movements, all deep-sea sharks showed higher swimming efforts during descent than ascent to maintain a given swimming speed, and were able to glide uphill for extended periods (several minutes), indicating that these deep-sea sharks are in fact positively buoyant in their natural habitats. This positive buoyancy may adaptive for stealthy hunting (i.e. upward gliding to surprise prey from underneath) or may facilitate evening upward migrations when muscle temperatures are coolest, and swimming most sluggish, after spending the day in deep, cold water. Positive buoyancy could potentially be widespread in fish conducting daily vertical migration in deep-sea habitats.
The light regime is an ecologically important factor in pelagic habitats, influencing a range of biological processes. However, the availability and importance of light to these processes in high Arctic zooplankton communities during periods of 'complete' darkness (polar night) are poorly studied. Here we characterized the ambient light regime throughout the diel cycle during the high Arctic polar night, and ask whether visual systems of Arctic zooplankton can detect the low levels of irradiance available at this time. To this end, light measurements with a purpose-built irradiance sensor and coupled all-sky digital photographs were used to characterize diel skylight irradiance patterns over 24 hours at 79°N in January 2014 and 2015. Subsequent skylight spectral irradiance and in-water optical property measurements were used to model the underwater light field as a function of depth, which was then weighted by the electrophysiologically determined visual spectral sensitivity of a dominant high Arctic zooplankter, Thysanoessa inermis. Irradiance in air ranged between 1–1.5 x 10-5
μmol photons m-2 s-1 (400–700 nm) in clear weather conditions at noon and with the moon below the horizon, hence values reflect only solar illumination. Radiative transfer modelling generated underwater light fields with peak transmission at blue-green wavelengths, with a 465 nm transmission maximum in shallow water shifting to 485 nm with depth. To the eye of a zooplankter, light from the surface to 75 m exhibits a maximum at 485 nm, with longer wavelengths (>600 nm) being of little visual significance. Our data are the first quantitative characterisation, including absolute intensities, spectral composition and photoperiod of biologically relevant solar ambient light in the high Arctic during the polar night, and indicate that some species of Arctic zooplankton are able to detect and utilize ambient light down to 20–30m depth during the Arctic polar night.
Marine benthic communities face multiple anthropogenic pressures that compromise the future of some of the most biodiverse and functionally important ecosystems in the world. Yet one of the pressures these ecosystems face, night-time lighting, remains unstudied. Light is an important cue in guiding the settlement of invertebrate larvae, and altering natural regimes of nocturnal illumination could modify patterns of recruitment among sessile epifauna. We present the first evidence of night-time lighting changing the composition of temperate epifaunal marine invertebrate communities. Illuminating settlement surfaces with white light-emitting diode lighting at night, to levels experienced by these communities locally, both inhibited and encouraged the colonization of 39% of the taxa analysed, including three sessile and two mobile species. Our results indicate that ecological light pollution from coastal development, shipping and offshore infrastructure could be changing the composition of marine epifaunal communities.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
Daily, lunar and seasonal cycles of natural light have been key forms of environmental variation across the Earth’s surface since the first emergence of life. They have driven the development of biological phenomena from the molecule to the ecosystem, including metabolic and physiological pathways, the behaviour of individuals, geographical patterns of adaptation and species richness, and ecosystem cycles (e.g. [1–4]). Indeed, biological systems are arguably organized foremost by light [5–7].
The natural patterns of light have over the last 100 years come to be greatly disrupted through the introduction of artificial light into the night-time environment: artificial light at night (ALAN). This derives from a diversity of sources, including street lighting, advertising lighting, architectural lighting, security lighting, domestic lighting and vehicle lighting. ALAN disrupts natural patterns of light both via direct effects of illumination from these sources as well as via skyglow (the scattering by atmospheric molecules or aerosols in the atmosphere of ALAN that is emitted or reflected upwards; [8–10]).
Polar organisms must cope with an environment that periodically lacks the strongest time-giver, or zeitgeber, of circadian organization-robust, cyclical oscillations between light and darkness. We review the factors influencing the persistence of circadian rhythms in polar vertebrates when the light-dark cycle is absent, the likely mechanisms of entrainment that allow some polar vertebrates to remain synchronized with geophysical time, and the adaptive function of maintaining circadian rhythms in such environments.
©2015 Int. Union Physiol. Sci./Am. Physiol. Soc.
Flying fshes (family Exocoetidae) are important components of epipelagic ecosystems and are targeted by fshing feets in the Caribbean Sea and elsewhere. However, owing to their anti-predator behavior and habitats, their ecology, abundance, and distributions are only partially known. From September 20 to October 6, 2011, we conducted a series of surveys over a large area (approximately 75,000 km2) of the northern Gulf of Mexico (87°W-90.5°W, 28°N-30°N). Te surveys used an airborne lidar and vessel-based sampling, supported by near real time satellite observations of oceanic conditions. Te aerial survey was conducted from a fxed wing aircraft that few repeated surveys day and night, enabling data collection that was both broad-scale and synoptic. Vessel-based sampling included quantitative visual observations, trawl sampling, and qualitative dip-netting for species identifcations. Te combined surveys identifed large aggregations of epipelagic organisms dominated by flying fshes. Large numbers of jellyfsh (Aurelia sp.) and low numbers of numerous other species were also observed. Te putative flying fsh aggregations had an average length scale of 6.1 km and an average population estimated at 10,000 individuals. While always near the surface, flying fsh aggregations were slightly deeper at night than during the day and found most often off the continental shelf in warm water with low chlorophyll concentrations. At least three species were present: Hirundichthys rondeletii (Valenciennes, 1847), Cheilopogon melanurus (Valenciennes, 1847), and Prognichthys occidentalis Parin, 1999. Tis combination of aerial and surface surveys aforded repeated synoptic, ground-truthed data collection over a large area and indicates that this method could be useful for surveying such mobile epipelagic fshes. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Swordfish (Xiphias gladius Linnaeus, 1758) are increasingly sought after by recreational anglers globally. The Florida Straits in particular is an important breeding and nursery area for North Atlantic swordfish, as well as the historical fishing grounds for both recreational and commercial swordfish fisheries. The traditional nighttime recreational fishery for swordfish in southeastern Florida is categorized into two periods. The first period started in 1977 and consists of the first tournaments in the area to specifically target swordfsh. Despite high initial catches, low catch numbers resulted in the conclusion of the swordfsh tournament fishery in 1983. The second period of the fishery started in 2000 and continues to the present (2015). Data were collected from a total of 118 swordfish tournaments (17 historical, 101 modern). For comparison, data were also gathered from 66 billfish tournaments that occurred during the modern period. The tournaments studied occurred on the southeast coast of Florida from Stuart to Key West. Although participation correlated to the number of catches, catch per hour (CPH) remains on a slow decrease over time. The entry fees for modern period swordfish tournaments range from 1000, while those for the more exclusive billfish tournaments were tenfold higher. The average weight of landed swordfish remained roughly the same throughout the two time periods, despite the oscillation of catch numbers, which may be due to the minimum length restrictions implemented in the modern period tournaments. Analysis of the nighttime tournament fishery, especially across two distinct time periods, provides new insight into the swordfish stock. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Although turnover of reef-fsh assemblages based on time of day has been generally well documented, much less is known regarding diel dynamics of demersal fsh communities along the continental shelf of the US Gulf of Mexico. We analyzed trawl data collected as part of the Gulf of Mexico Southeast Area Monitoring and Assessment Program (SEAMAP) to document diel changes in fsh abundance and assess the relative importance of space and time of day in structuring demersal fsh assemblages. Trawling operations were conducted day and night in neritic waters from southern Florida to eastern Alabama (West Florida Shelf). Ichthyofaunal assemblages difered by region and depth, but also by time of day (day, night, crepuscular) within region and depth categories. Both fsh abundance and diversity were generally highest at night. Some day/night differences in abundance for particular species can be attributed to specifc behaviors, such as nighttime foraging in open areas coupled with cryptic habits (e.g., burrowing, shelter-seeking). Prominent examples of such behavior-associated abundance patterns include cusk-eels (Ophidiidae), which are burrowers, and grunts (Haemulidae), which are closely associated with structural habitats during daytime. We document these strong diel trends in the SEAMAP trawl data and interpret them based on current understanding of the behavior of fsh species and families and in relation to the development of ecosystem models for management purposes. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Te Atlantic tarpon (Megalops atlanticus Valenciennes, 1847) is a visually-guided marine predator that may be active at any time in the 24-hr light-dark cycle despite dramatic changes in light intensity over the course of the day. To test the hypothesis that retinal sensitivity changes with time of day in M. atlanticus, possibly under the influence of a circadian clock, populations of fsh (three populations of 6 fsh per lighting treatment for two treatments = 36 fsh total) were exposed to different lighting treatments and sensitivity of the retina was measured periodically by electroretinography (ERG). Te intensity of light required to elicit a half-maximal ERG response was signifcantly greater during the day than the night in fsh held in 12L:12D light-dark cycles (LD). To determine whether this cycle of retinal sensitivity is driven by an internal timekeeping mechanism, ERG was performed at 4-hr intervals over the course of 24 hrs in constant darkness (DD). Sensitivity was signifcantly higher during subjective night than during subjective day, though the rhythm in DD was damped relative to the cycle in LD. Tese results show that retinal sensitivity is much higher at night than during the day in a light-dark cycle, and that this cycle of retinal sensitivity is driven at least in part by an internal biological clock. Such endogenous timekeeping mechanisms enhance survivability by allowing organisms to anticipate change in their external environments. Rhythms of retinal sensitivity are likely important for survival by supporting prey capture, predator avoidance, and reproduction, but they may be disrupted by abnormally-timed exposure to light, including artifcial light at night. © 2017 Rosenstiel School of Marine & Atmospheric Science of the University of Miami.
Wildlife tourism has been shown to cause behavioural changes to numerous species. Yet, there is still little understanding if behavioural changes have consequences for health and fitness. The current study combined accelerometry and respirometry to show that provisioning whitetip reef sharks (Trianadon obesus) for tourism increases their daily energy expenditure by elevating activity levels during periods when they normally rest. Field metabolic rate increased by 6.37% on provisioning days compared to non-provisioning days. Since metabolism is a key parameter influencing most biological and ecological processes, this represents some of the clearest evidence to date that ecotourism can impact critical biological functions in wild animals.
Life in the World's Oceans: Diversity, Abundance and Distribution is a true landmark publication. Comprising the synthesis and analysis of the results of the Census of Marine Life this most important book brings together the work of around 2000 scientists from 80 nations around the globe. The book is broadly divided into four sections, covering oceans past, oceans present, oceans future and a final section covering the utilisation of the data which has been gathered, and the coordination and communication of the results. Edited by Professor Alasdair Mcintyre, Marine Life is a book which should find a place on the shelves of all marine scientists, ecologists, conservation biologists, oceanographers, fisheries scientists and environmental biologists. All universities and research establishments where biological, earth and fisheries science are studied and taught should have copies of this essential book on their shelves. A true landmark publication. One of the most important marine science books ever published. Contributions from many world leading researchers. Synthesis of a huge amount of important data. Represents the culmination of 10 years' research by 2000 scientists from 80 countries.
The distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day–night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine-scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary.
Studies carried out on a wide variety of Arctic species during the polar night reveal continued feeding, growth and reproduction, changing our view of this period from one of biological stasis to a time of continued high activity levels.
Larval coral-reef fishes have good orientation abilities. Through-water orientation of
larvae in some species is location-dependent at meso-scales <10s of km, whereas other species
have location-independent orientation at meso-scales. In situ observation of the damselfish
Chromis atripectoralis showed that settlement-stage larvae swam in a southerly direction (mean =
175 ± 11°) at 100 to 1000 m from shore, both east and west of Lizard Island, northern Great Barrier
Reef (NGBR), in 10 datasets from 1998 to 2008. Wind direction did not directly influence throughwater
swimming direction at NGBR. During 2014, in situ diver observation tested if orientation of
C. atripectoralis differed regionally in the central Great Barrier Reef (CGBR), 620 km south of
NGBR, and in the New Caledonia reef lagoon (NCRL), 1950 km east of CGBR. In all 3 regions,
>90% of larvae swam directionally with similar precision and speeds, and with significant amongindividual
orientation. Yet through-water orientation was easterly at CGBR (72 ± 30°) and NCRL
(87 ± 20°), and significantly different from NGBR. Over-bottom orientation (i.e. the result of current
and larval swimming), measured by GPS at start and end of observing each larva, was weak
east-southeasterly at NGBR (116 ± 40°, p = 0.045), not significantly directional at CGBR, and
strongly westerly at NCRL (246 ± 28°, p = 0.0006), indicating that dispersal of C. atripectoralis is
both current- and behaviour-dependent. This is the first report of location-dependent larval fish
orientation at a regional scale. This might be an evolutionary response to regional hydrodynamic
conditions to limit downstream dispersal.
Unlike the mammalian retina, the teleost fish retina undergoes persistent neurogenesis from intrinsic stem cells. In marine teleosts, most cone photoreceptor genesis occurs early in the embryonic and larval stages, and rods are added primarily during and after metamorphosis. This study demonstrates a developmental paradigm in elopomorph fishes in which retinas are rod-dominated in larvae, but undergo periods of later cone genesis. Retinal characteristics were compared at different developmental stages among three ecologically distinct elopomorph fishes—ladyfish (Elops saurus), bonefish (Albula vulpes), and speckled worm eel (Myrophis punctatus). The objectives were to improve our understanding of (1) the developmental strategy in the elopomorph retina, (2) the functional architecture of the retina as it relates to ecology, and (3) how the light environment influences photoreceptor genesis. Photoreceptor morphologies, distributions, and spectral absorption were studied at larval, juvenile, and adult stages. Premetamorphic retinas in all three species are rod-dominated, but the retinas of these species undergo dramatic change over the course of development, resulting in juvenile and adult retinal characteristics that correlate closely with ecology. Adult E. saurus has high rod densities, grouped photoreceptors, a reflective tapetum, and longer-wavelength photopigments, supporting vision in turbid, low-light conditions. Adult A. vulpes has high cone densities, low rod densities, and shorter-wavelength photopig- ments, supporting diurnal vision in shallow, clear water. M. punctatus loses cones during metamorphosis, develops new cones after settlement, and maintains high rod but low cone densities, supporting primarily nocturnal vision. M. punctatus secondary cone genesis occurs rapidly throughout the retina, suggesting a novel mechanism of vertebrate photoreceptor genesis. Finally, in postsettlement M. punctatus, the continuous presence or absence of visible light modulates rod distribution but does not affect secondary cone genesis, suggesting some degree of developmental plasticity influenced by the light environment.
The simple diel cycle of rising and setting of the sun imposes on the behaviour and activity of fishes a dramatic, overriding set of predictable constraints. As a direct result, many kinds of behaviour and the species that engage in them follow characteristic convergent patterns that transcend geographic and taxonomic boundaries. These patterns can be recognised in such fundamental activities as the times when fishes feed, breed, aggregate and rest, in the transitions between activities, in the kinds of things that fishes eat, and in the ways in which fishes feed and avoid being eaten. The objectives of this chapter are to review the available information concerning the influences of day, night and twilight on various classes of fish behaviour; to delimit general diel activity patterns that characterise fishes in different habitat types; and to explore the environmental, ecological, physiological and developmental factors that interact with the cycle of daylight and darkness in determining diel patterns of fish behaviour. Throughout the chapter, day and daytime refer to daylight hours; night and nighttime refer to periods of darkness; crepuscular refers to twilight periods of dusk and dawn (sunset and sunrise); and diel refers to the 24-hour cycle.
The activity of most fishes is synchronised with the daily cycle of light and darkness (Helfmann, 1986) but in the sea many are exposed to the additional stimulus of the tides. In comparison with the light-dark cycle, the tidal cycle varies considerably in form, amplitude and frequency. The diel light cycle has a solar-day period of 24 hours and its form and amplitude are modulated relatively slowly by the seasonal cycle to a degree that is dependent on latitude. In contrast, the tidal cycle is based on the lunar-day period of 24.8 hours and can vary in duration by several hours between one high tide and the next. Its amplitude is modulated on a fortnightly (spring/neap) basis and its form is greatly dependent upon local coastal geography (Barnwell, 1976; Pugh, 1987; Fig. 1). This variety in tidal pattern, and the rapid and major effects that tides can have on the suitability of shallow water habitats, means that marine fishes exhibit a wide range of behaviour patterns synchronised with the tidal cycle. Simultaneous responses to changes in light intensity may further modify these tidally-synchronised activities leading to complex patterns of behaviour whose exact nature depends on the relative phase of the diel and tidal cycles.
Identifying the drivers that explain the distribution of tropical coastal fishes remains a central goal in biogeography. However, a lack of comparisons with standardized data still prevents more robust generalizations. Here, we assess if general assembly rules apply in two intertidal mangrove fish assemblages from different biogeographical regions (Tropical Eastern Pacific and Western Atlantic). Using multivariate analyses on field data collected for about 1 year at each location, we examined if different community attributes (species richness, taxonomic, and trophic composition, density, and catch mass) varied temporally (according to tidal-diel rhythms) and spatially (salinity gradients and between biogeographical regions). Similar total fish species richness (ca. 50 species) mirrored the regional species richness of coastal fishes in these regions. Pufferfishes (Tetraodontidae) and catfishes (Ariidae) dominated (in catch mass) fish assemblages in both regions. Closely related species within these families responded in similar ways to tidal-diel changes suggesting the existence of a phylogenetic signal in temporal niche use. The strength of the influence of tidal-diel forces determining fish habitat use were likely related to differences in mangrove topography. The biogeography of the adjacent freshwater fish fauna could explain differences in taxonomic and trophic composition between regions. Our results highlight the role that tidal-diel dynamics play in influencing the structure of fish assemblages in macrotidal areas, and suggest that considering the regional biogeographical history and the local seascape configurations could help to explain differences in mangrove fish assemblage structure across regions.
Artificial reef placements are becoming an important part of fisheries management strategies worldwide due to the loss of natural reefs, and in the Western Gulf of Mexico due to the scarcity of hard structures and vertical relief near shore, which are essential habitat for reef fish. Current visual survey techniques can be crippled by low visibility and unpredictable currents in the Gulf of Mexico, but hydroacoustics can provide a solution to these problems. This study focuses on using ground-truthed side scan sonar technology to determine fish community biomass. Through fish abundance surveys and in situ fish sampling, we developed a fish survey protocol using side scan sonar to quantify fish assemblages over artificial reefs. The effectiveness of this technology for management purposes was also demonstrated by comparing it with visual census methods.