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Blacktip shark Carcharhinus limbatus presence at fishing piers in South Carolina: association and environmental drivers
... Globally vulnerable bull (Carcharhinus leucas) and oceanic blacktip (Carcharhinus limbatus) sharks are large, apex marine predators that are regularly caught by coastal fisheries and have been implicated in near-shore shark attacks [12][13][14] . Acoustic studies have identified that spatiotemporal and environmental variables such as the season, time of day, water temperature (reported preference ~ 25 °C), tidal flow, and lunar cycle, influence their abundance and use of coastal habitats 1,10,14,15 , (including MPAs) where they feed, socialise, and reproduce 8,11,16,17 . ...
... By swimming with the tides, the sharks may reduce some of the bioenergetic costs associated with movement 28,31 . In southern Mozambique bull and oceanic blacktip sharks principally forage on large teleost species (e.g., Caranx spp.) which are known to congregate around inshore reef systems 14,18,24 . The detections that we recorded may indicate that both sharks forage on inshore reefs during rising tides 14,18,24 . ...
... In southern Mozambique bull and oceanic blacktip sharks principally forage on large teleost species (e.g., Caranx spp.) which are known to congregate around inshore reef systems 14,18,24 . The detections that we recorded may indicate that both sharks forage on inshore reefs during rising tides 14,18,24 . ...
Pelagic sharks play key roles in marine ecosystems, but are increasingly threatened by human extraction, habitat degradation and mismanagement. We investigated the use of protected and unprotected coastal habitats by bull (Carcharhinus leucas) and oceanic blacktip (Carcharhinus limbatus) sharks in southern Mozambique. Five INNOVASEA VR2W-69 kHz acoustic receivers were positioned in the Bazaruto Archipelago National Park (BANP) as well as one to the south of the park’s boundaries. Seven receivers were also deployed 250 km south in the Inhambane estuary and on reef sites off Praia de Tofo. Twelve bull, and six oceanic blacktip sharks, were fitted with INNOVASEA V16 acoustic tags, which generated 933 detections of bull and 12,381 detections of oceanic blacktip sharks over a period of 1391 days. A generalised additive model was used to estimate the effects of seven spatiotemporal and environmental parameters on the frequency of each species’ detections. In general, calculated residency indices were highest around the locations monitored in the BANP and one unprotected location off Tofo. Both species were more abundant across the monitored sites, during the summer when water temperatures were ~ 27 °C, when the moon was < 50% illuminated, and when the tide was rising. Detections coincided with each species’ reproductive season indicating that both species may be reproductively active in the BANP region. Oceanic blacktip sharks were largely resident and so fisheries management may significantly benefit their population(s) around certain reef habitats in the BANP. The low residency and seasonal detections of bull sharks indicates that they may be transient and so effective conservation may require coordination between regional fisheries managers.
... However, there is a paucity of research into the impacts on mid-water and benthic species, such as teleost fishes and elasmobranchs, despite a considerable portion of discards sinking below the surface. Likewise, a range of species have been documented foraging on recreational fishing discards, including invertebrates, teleost fishes, marine mammals (Donaldson et al. 2010;Christiansen et al. 2016;Voohris 2016), elasmobranchs (Newsome et al. 2004;Pini-Fitzsimmons et al. 2018;Martin et al. 2019), sea birds, and even terrestrial predators, such as dingoes (Behrendorff et al. 2016;Déaux et al. 2018), but few studies have assessed the potential impacts on these animals. The few existing studies suggest that species alter their behaviour and space use to access these resources. ...
... Indeed, elasmobranchs have been shown to form specific individual preferences with provisioning sites. For example, Martin et al. (2019) found a surprising level of individual variation in terms of association with piers where fishing waste is discarded by blacktip sharks (Carcharhinus limbatus). Without tagging individuals from non-provisioning sites in the present study, it is difficult to account for such individualistic differences in behaviour or whether the creek is used by other individuals that do not use the provisioning site. ...
Context It is common for recreational anglers to discard waste produced from filleting catches back into the water, which results in a highly spatio-temporally predictable food subsidy for wildlife to scavenge. However, the behavioural responses of these scavengers has received little attention. Aims We aimed to assess the visitation of a common mesopredatory scavenger in relation to temporal patterns in waste discarding at a boat ramp in south-eastern Australia. Methods Using passive acoustic telemetry, the movements of 13 adult female smooth stingrays (Bathytoshia brevicaudata) were tracked, and patterns in their acoustic detections and duration of time spent in different sections within the study area were compared. Key results Use of the study area was strongly focused around the boat ramp, and peaked during periods of increased provisioning activity (i.e. afternoons and weekends). Environmental variables had limited influence on visitation, suggesting that the use of the area was not likely to be linked to natural behaviours. Conclusions The observed patterns indicated that the movements of smooth stingrays were linked to waste-discard practices by recreational anglers. Implications This study has implications for the management of discard practices for recreational fishing.
... Our findings suggest a preference for pelagic prey for the one-year juveniles, and inshore δ 13 C values or related to maternal reserves in the neonates. The movement of main prey can potentially drive C. limbatus further from the coast, which would cause a decrease in δ 13 C signatures (Martin et al. 2019). This behavior has been confirmed with telemetry studies in juvenile blacktip sharks (Heupel and Simpfendorfer 2005;Martin et al. 2019). ...
... The movement of main prey can potentially drive C. limbatus further from the coast, which would cause a decrease in δ 13 C signatures (Martin et al. 2019). This behavior has been confirmed with telemetry studies in juvenile blacktip sharks (Heupel and Simpfendorfer 2005;Martin et al. 2019). Moreover, a predator that exhibits trophic flexibility may have a large prey base and feed opportunistically, taking advantage of less numerically available prey items to supplement their diet (Bolnick et al. 2003;Bearhop et al. 2004). ...
The blacktip shark (Carcharhinus limbatus) is a placental shark that uses coastal nursery areas in the Galapagos Marine Reserve, where juveniles live during their early life stages. To better understand the feeding behavior of early juvenile blacktip sharks, we conducted stable isotope analysis on 57 samples from three coastal nurseries around the archipelago. We evaluated the intraspecific variation in trophic shifts of four size classes (<60, 60–69, 70–79 and ≥ 80 cm TL) based on δ¹³C and δ¹⁵N signatures. No significant differences in δ¹³C and δ¹⁵N values were observed among nursery areas (P = 0.127 and P = 0.736, respectively) nor between sexes (P = 0.881 and P = 0.993, respectively). However, there were significant differences among size classes, with δ¹³C and δ¹⁵N values showing a negative relationship with size (R = −0.54, P = 0.001 and R = −0.60, P = 0.001, respectively). Neonates (TL < 60 cm) exhibited a larger trophic niche, whereas larger individuals (TL ≥ 80 cm) exhibited a reduction in trophic niche as a result of different use of resources. Clustered δ¹⁵N signatures for the two largest size classes showed similar feeding patterns and same trophic level, while δ¹³C signatures in all size classes showed the use of several primary carbon sources. Our results showed trophic variations among early life stages, as a result of maternal reminiscence in neonates and foraging variation in larger size classes across coastal nursery areas. This is baseline information on the feeding behavior of early juvenile blacktip sharks in the Tropical Eastern Pacific.
... Similarly, these structures promote attachment of epibiota, like copepods, bivalves, and bryozoans which provide opportunistic food for small fishes (Moreau et al., 2008). Docks, pilings, and jetties are also well known to attract and aggregate predators, like large teleosts and sharks (Martin et al., 2019;Wilson et al., 2019). By concentrating predators, such structures may pose a significant threat to populations of vulnerable species. ...
... flatback sea turtles (Natator depressus) in Australia was seven times higher adjacent to jetties compared to unmodified sections of coast because the jetties provided daytime refuges for predators that hunted along the nearshore at night (Wilson et al., 2019). Docks, jetties, and piers also indirectly affect aquatic systems by providing an unnatural platform from which recreational fishers can reliably encounter species aggregating to the structures (Barwick et al., 2004;Martin et al., 2019). This may present an "ecological trap" for species that would otherwise not be as spatially aggregated close to shore. ...
In reflecting on the human domination of our planet in the Anthropocene, some have argued that concrete is among the most destructive materials created by humans. Here we explore this idea, specifically in the context of what we consider “the concrete conquest of aquatic ecosystems.” The ubiquitous use of concrete in transportation and building infrastructure has contributed to alterations in freshwater and coastal marine systems. Yet, in some cases, there are no appropriate alternative building materials such that concrete itself is confounded by its application. For example, as the foundation for most dams, concrete fragments rivers and channelizes streams, often creating unnatural systems, yet dams are necessary for hydropower generation and flood control with few alternative materials for construction. In riparian and coastal environments, concrete harbours and inland canal systems are often used to address erosion or reclaim areas for human development. Even when removed (e.g., dam removal, naturalization of shorelines), concrete dust is a major aquatic pollutant. Instances do exist, however, where concrete has been used to benefit aquatic ecosystems – such as the installation of fish passage facilities at barriers or the development of fish-friendly culverts – though even then, there is a movement towards nature-like fishways that avoid the use of harmful materials like concrete. There are also opportunities to achieve conservation gains in the development of seawalls that include more natural and complex features to benefit biota and allow for essential biogeochemical processes to occur in aquatic environments. There have been several innovations in recent years that increase the permeability of concrete, however these have limited application in an aquatic context (e.g., not relevant to dam construction or erosion control but may be relevant in stormwater management systems). We provide a brief overview of the history of concrete, discuss some of the direct and indirect effects of concrete on aquatic ecosystems, and encourage planners, engineers, developers, and regulators to work collaboratively to explore alternatives to concrete which benefit aquatic ecosystems and the services they offer. The status quo of concrete being the default construction material is failing aquatic ecosystems, so we recommend that efforts are made to explore alternative materials and if concrete must be used, to increase structural complexity to benefit biodiversity.
... It is a widely accepted practice for recreational anglers to discard carcasses and offal into the water when processing fish for consumption. These discards are often concentrated at shore-based fish cleaning facilities, and a myriad of species forage on these resources (Déaux et al., 2018;Donaldson et al., 2010;Finn et al., 2008;Martin et al., 2019;Newsome et al., 2004;Pini-Fitzsimmons et al., 2018;Voohris, 2016). While the effects of commercial fishing discards have been factored into assessments on the wider impacts of fishing, discards from recreational fishing are not currently included in estimates of global fishery discards (Kelleher, 2005;Zeller et al., 2018) due to a dearth of comparable recreational fishing data and monitoring programs for many countries and target species (e.g., Radford et al., 2018). ...
Recreational fishing waste, produced from processing catches at shore-based fish cleaning facilities and discarded into adjacent waters, is foraged by various aquatic species. However, the potential alterations to the diet of consumers of these resources are poorly studied. Smooth stingrays (Bathytoshia brevicaudata) are a large demersal mesopredatory ray species and common scavenger of recreational fishing discards around southern Australia. Due to their attraction to fish cleaning sites, they are also common targets of unregulated 'stingray feeding' tourism where they are fed commercially produced baits (e.g., pilchards). This study provides a preliminary assessment of the diet of smooth stingrays provisioned recreational fishing discards and baits at two sites in southern NSW, Australia (Discard Site: recreational fishing discards only; Provisioning Site: recreational fishing discards and commercial baits) using stable isotope analysis of carbon (δ13 C) and nitrogen (δ15 N) and Bayesian stable isotope mixing models. Our results indicated that at both sites invertebrates, considered a main part of the natural diet of smooth stingrays, made a limited contribution to the diets of provisioned stingrays, while a benthic teleost fish that is a common recreational catch was the dominant contributor. As the assessed teleost is potentially a natural prey item for smooth stingrays, it remains unclear whether the contribution came from recreational fishing discards or natural foraging. However, due to smooth stingrays' typically opportunistic foraging strategy, we expected a greater mixture of resources from low to high trophic level prey than was observed. These results suggest either that smooth stingrays have a lower reliance on invertebrates as a result of utilising provisioned resources or higher reliance on teleost fishes than previously thought. Commercial bait products fed to stingrays at the Provisioning Site were not a major contributor to the diets of smooth stingrays, suggesting this activity has a low impact on their nutrition.
... Fitzpatrick et al., 2011;Heinrich et al., 2021;Mitchell et al., 2020). Sharks can also associate a splash in the water with feeding (Martin et al., 2019), so could have mistakenly identified the splash of a person jumping into the water with food being thrown from a boat. Moreover, the presence of other sharks can increase competition and aggression (e.g. ...
Shark bites are of high public concern globally. Information on shark occurrence and behaviour, and of the effects of human behaviours, can help understand the drivers of shark‐human interactions. In Australia, a number of shark bite clusters occurred over the last decade. One of these took place in Cid Harbour the Whitsundays, Queensland, a region for which little was known about the shark community. Here, we describe and evaluate the research in response to that shark bite cluster.
Fishing methods, acoustic and satellite tracking, and baited remote underwater video cameras (BRUVs) were used to identify the shark species using Cid Harbour, estimate relative abundance, and describe habitat use and residency. Side‐scan sonar and BRUVs were also used to assess prey availability. Recreational users were surveyed to understand human behaviour and their awareness and perceptions of ‘Shark Smart’ behaviours. This allowed shark occurrence and behaviour to be interpreted in the context of human behaviours in the Harbour.
Eleven shark species were identified. Relative abundance was not unusually high, and residency in Cid Harbour was typically low. For example, 79% of acoustically tagged sharks visited the harbour on <10% days at liberty. Shark prey was available year‐round. Notably, anchored boats regularly conduct activities that can attract sharks (dumping food scraps, provisioning and cleaning fish).
Alone, the methods used in this study had variable success, but combined they provided a large amount of complementary information. Including a social science component in the research response to the shark bite incidents allowed for a more holistic understanding of the Cid Harbour bite incidents.
This study did not identify anything unusual about the shark community that could have contributed to the Cid Harbour shark bite cluster. However, the three incidents involved people bitten almost instantly after entering the water, which is unusual and suggests that feeding/attracting sharks to boats could have been a contributor and also that any species capable of biting humans could have been responsible.
The eradication of activities that attract sharks to areas where people enter the water may reduce shark bite risk.
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In 2009, the Fundy Ocean Research Centre for Energy (FORCE) developed a 1.6 x
1.0 km Crown Lease Area (CLA) to test Marine Hydrokinetic devices (MHKs) in Minas
Passage (MP), a strait that connects the Bay of Fundy to Minas Basin (MB), Nova
Scotia. Minas Basin is an important summer feeding aggregation site for numerous
fishes including Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) stocks from
Canada and the US. In this study, acoustic tagging technology was used to describe
sturgeon presence in the CLA, as well as an adjacent site proposed for MHKs deployment.
During 2018 and 2019, 33.9% (n = 19/56 Atlantic sturgeon tagged) and
29.9% (n = 23/77 Atlantic sturgeon tagged) respectively, of sturgeon acoustically
tagged in MB during 2014–2019
were detected in these two FORCE sites. Binomial
General Linear Models (GLMs) were fit to determine if environmental parameters
influenced the presence, or depth of Atlantic sturgeon in the FORCE sites. The only
significant predictor of Atlantic sturgeon depth and presence at the FORCE sites was
tide type. Atlantic sturgeon was found to have a higher likelihood of being detected
during ebb tide (12%) as opposed to flood tide (3%). Apparent decline in the presence
of sturgeon during flood tide was probably due to poor signal reception caused
by turbulence from higher current speeds. Tagged sturgeon travelled through the
FORCE sites pelagically at similar depths (27.5 ± 14.57 m) to those proposed for
seabed mounted MHKs (~30 m), travelling deeper during flood tide than ebb, suggesting
they may be at risk of spatial overlap with MHKs. While this study indicated
that the duration Atlantic sturgeon utilized the FORCE sites throughout the summer
appeared to be low, sturgeon from both endangered and threatened stocks migrated
through this region during their yearly entry and exit to MB and were present for approximately 12% of the days assessed in this study.
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.
Southeast Florida witnesses an enormous seasonal influx of upper trophic level marine predators each year as massive aggregations of migrating blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream current to the Palm Beach County shoreline drive tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate relative abundance. Over a four year period from 2011-2014, an aerial survey was flown approximately biweekly along the length of Palm Beach County. A high definition video camera and digital still camera mounted out of the airplane window provided a continuous record of the belt transect which extended 200 m seaward from the shoreline between Boca Raton Inlet and Jupiter Inlet. The number of sharks within the survey transect was directly counted from the video. Shark abundance peaked in the winter (January-March) with a maximum in 2011 of 12,128 individuals counted within the 75.6 km-2 belt transect. This resulted in a maximum density of 803.2 sharks km-2. By the late spring (April-May), shark abundance had sharply declined to 1.1% of its peak, where it remained until spiking again in January of the following year. Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25°C. Shark abundance was also correlated with day of the year but not with barometric pressure. Although shark abundance was not correlated with photoperiod, the departure of the sharks from southeast Florida occurred around the vernal equinox. The shark migration along the United States eastern seaboard corresponds spatially and temporally with the spawning aggregations of various baitfish species. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.
The Northwestern Hawaiian Islands (NWHI) host a variety of large vertebrate animals including seabirds, green sea turtles (Chelonia mydas), Hawaiian monk seals (Monanchus schauislandi), and large teleost fish such as trevally (Family Carangidae) and several species of sharks. The air-breathing vertebrates have been the subjects of relatively continuous and well-funded research programs over the past several decades, and many aspects of their biology in the NWHI have been documented fairly well. However, studies directed at understanding the biology and ecology of large teleost fishes and sharks in the NWHI have lagged substantially behind research conducted on birds, turtles and seals. In the summer of 2000, an array of autonomous acoustic receivers was deployed at French Frigate Shoals (FFS) in the NWHI as part of a project investigating the movement patterns of tiger sharks (Galeocerdo cuvier) within the atoll, particularly in relation to the high seasonal abundance of potential prey (birds, turtles, seals). Shortly after the establishment of the initial array of monitors in 2000, additional monitors were deployed in an effort to monitor the movements of Galapagos sharks (Carcharhinus galapagensis) at FFS, particularly at locations where monk seal pups had been preyed upon by these sharks. The scope of the monitoring study was further expanded to Midway Atoll during summer of 2001 to monitor movements of Galapagos sharks near seal haul-out beaches and to examine survivorship and behavior of giant trevally (Caranx ignobilis) captured and released in a commercial sport fishing operation conducted within the Midway National Wildlife Refuge. For each study, experimental animals were captured and surgically fitted with long-life, individually-coded acoustic transmitters. During nearly 4 years of acoustic monitoring at FFS and 2 years of monitoring at Midway, a total of over 45,000 detections of sharks and fish with transmitters were recorded on acoustic monitors. These data enable an assessment of long-term movement patterns of these large predators within the NWHI. Each species investigated demonstrated somewhat repeated and predictable behavioral patterns that provide a basis for improved understanding of determinants of behavior and for enhanced management of these animals and prey (birds, seals, turtles) with which they may interact.
Description Fit linear and generalized linear mixed-effects models. The models and their components are represented using S4 classes and methods. The core computational algorithms are implemented using the 'Eigen' C++ library for numerical linear algebra and 'RcppEigen' ``glue''.
Intense shading under large piers is known to negatively affect benthic fishes. However, effects on pelagic fishes are poorly known. We employed the equivalent of acoustic video, dual frequency identification sonar (DIDSON), under a kayak to evaluate the response of pelagic fishes at a large (351 x 255 m) urban pier (Pier 40) in Hudson River. A repeated measures design (322 occupations) sampled 3 transects each across both the northern and southern open water-pier edge-under pier continuum during the day and night from June 2009 to September 2010. Over 22 000 individual fish, ranging from small schooling forage species (e. g. Anchoa mitchilli, Menidia menidia) to large predators (Morone saxatilis, Pomatomus saltatrix) were detected with DIDSON and verified with conventional sampling nets. Small (<250 mm) schooling pelagic fishes avoided areas under the pier where light is dramatically reduced during both day and night (when municipal lights illuminate the water away from the pier). Less abundant large (>250 mm) predatory fish responded somewhat differently from small schooling fish in that large predatory fish were slightly more abundant under the pier than in open water, but only from the edge extending to 5 m under the pier where there was still some light. Beyond that, abundance declined sharply. Together, these observations indicate that areas under large piers are suboptimal habitats for many of the abundant pelagic fishes, a pattern similar to that for benthic fishes.
Historically, acoustic telemetry studies tracking movement of aquatic organisms have lacked rigorous, long-term evaluations of detection range. The purpose of the present study was to identify potential sources of variability in long-term acoustic telemetry data, focusing specifically on environmental variability. The study was conducted for 15 mo in Gray's Reef National Marine Sanctuary, Georgia, USA, using 2 submersible Vemco VR2W hydrophone receivers and 2 stationary range test transmitters (controls). Tag detections (+/- 1 SE) decreased from 54.2 +/- 2.5 to 11.4 +/- 0.5 detections d(-1) as transmission distance increased from 100 to 300 m. Detections varied seasonally (likely due to stratification), with the direction of flood and ebb tidal currents (12.4 h cycle), and with tidal current speed (6.2 h cycle). Tides explained up to 92% of the short-term variability in hourly detection data. Detections also increased or decreased during episodic weather events depending on the season and type of event. These results suggest that stationary control tags are useful for characterizing variability in sound transmission in open water marine acoustic telemetry studies.
Behavioral and physiological responses to hypoxia were examined in three sympatric species of sharks: bonnethead shark Sphyrna tiburo, blacknose shark, Carcharhinus acronotus, and Florida smoothhound shark, Mustelus norrisi, using closed system respirometry. Sharks were exposed to normoxic and three levels of hypoxic conditions. Under normoxic conditions (5.5–6.4 mg l^−1), shark routine swimming speed averaged 25.5 and 31.0 cm s^−1 for obligate ram-ventilating S. tiburo and C. acronotus respectively, and 25.0 cm s^−1 for buccal-ventilating M. norrisi. Routine oxygen consumption averaged about 234.6 mg O_2 kg^−1 h^−1 for S. tiburo, 437.2 mg O_2 kg^−1 h^−1 for C. acronotus, and 161.4 mg O_2 kg^−1 h^−1 for M. norrisi. For ram-ventilating sharks, mouth gape averaged ∼1.0 cm whereas M. norrisi gillbeats averaged 56.0 beats min^−1. Swimming speeds, mouth gape, and oxygen consumption rate of S. tiburo and C. acronotus increased to a maximum of 37–39 cm s^−1, 2.5–3.0 cm and 496 and 599 mg O_2 kg^−1 h^−1 under hypoxic conditions (2.5–3.4 mg l^−1), respectively. M. norrisi decreased swimming speeds to 16 cm s^−1 and oxygen consumption rate remained similar. Results support the hypothesis that obligate ram-ventilating sharks respond to hypoxia by increasing swimming speed and mouth gape while buccal-ventilating smoothhound sharks reduce activity.
Sharks are found in association with main Hawaiian Island ocean fish farms more frequently and at higher densities than is typical for coastal Hawaiian waters. Sharks attracted to fish farms could potentially threaten human water users, interact negatively with other fisheries, and seasonal migrations could be disrupted if individuals become entrained around farms throughout the year. We hypothesised that smaller coastal species would reside near farms, whereas more wide-ranging species would associate with farms only for short periods. We utilised passive acoustic telemetry to monitor the movements and behaviour of sandbar (Carcharhinus plumbeus) and tiger (Galeocerdo cuvier) sharks adjacent to two open ocean fish farms in Hawaii. Approximately half the tagged sandbar sharks showed site fidelity to the farms, with some individuals being detected repeatedly for 2.5 years. Sandbar sharks moved seasonally to the west coast of Oahu, suggesting that fish farms are not disrupting natural seasonal cycles in this species. Tiger sharks tagged near the cages were more transient, and showed much shorter residence times although some individuals returned sporadically to the cages over the 3-year period. Ocean fish cages appear to aggregate sandbar sharks, but are only ‘visited’ by tiger sharks. Although threats to public safety are probably minimal, the ecological effects of aggregating top-predators are still unknown.
Acoustic telemetry systems are an increasingly common way to examine the movement and behaviour of marine organisms. However, there has been little published on the methodological and analytical work associated with this technology. We tested transmitters of differing power outputs simultaneously in several trials, some lasting ~50 days, to examine the effects of power output and environmental factors (water movement, temperature, lunar cycle and time of day). There were considerable and volatile changes in detections throughout all trials. Increased water movement and temperature significantly reduced detection rates, whereas daytime and full-moon periods had significantly higher detection rates. All nine transmitters (from seven transmitter types tested) showed a sigmoidal trend between detection frequency and distance. Higher-powered transmitters had a prolonged detection distance with near-maximal detections, whereas lower-powered transmitters showed an almost immediate decline. Variation of detection frequency, transmitter type and the modelled relationship between distance and detection frequency were incorporated into a positioning trial which resulted in markedly improved position estimates over previous techniques.
Residence time, site fidelity and movements for red snapper Lutjanus campechanus (Lutjanidae) were estimated from long-term telemetry monitoring (December 2005 to June 2010) at 6 sites (1 natural and 5 artificial reefs) in the northeastern Gulf of Mexico. Each site consisted of an array of 5 receivers, with 1 at the center reef site and 4 receivers placed 1100 m north, south, east and west of center (2 km radius detection area). Throughout the study, a stationary control transmitter was located 400 m south of the center receiver at each site to estimate changes in detection rates from environmental factors. These receiver arrays enabled fishery independent estimations of fishing mortality, natural mortality and emigration. Event analysis was used to estimate site fidelity and residence, based on right-censoring fishing and natural mortality. Median residence time was 542 d, ranging from 1 to 1099 d, with 72% of fish staying at least 1 yr at the site. Some fish (n = 12) showed seasonal and directed movements to other sites (up to 8 km away) and returned to original sites up to 7 mo later. Diel movements away from the structure tended to occur at night. Site fidelity and residence times of red snapper in the present study were greater than in any previous study and show the importance of artificial reefs for this species.
Movement patterns and habitat use of juvenile lemon sharks Negaprion brevirostris were monitored at Atol das Rocas, Brazil, an atypical nursery area for this species, characterized by extreme tides and a lack of seagrass flats and mangroves. Twenty-three sharks carrying transmitters were monitored using an array of bottom-fixed automated receivers during 3 trips over a total of 60 d. Transmitters were recorded on receivers over 13 000 times, and the majority of sharks were detected more than 100 times. Newborn sharks (60 to 80 cm total length, TL) showed restricted but repeated movements between small tide pools on reef flats at low tide and a small, shallow, nearby tidal creek at high tide. Larger sharks (up to 106 cm TL) sampled 6 and 20 mo after the study in March 2000 frequented the tidal creek and several other locations at high tide and a variety of larger pools at low tide, and in general exhibited more extensive movements within the atoll than did newborn sharks. Sharks approaching 2 yr of age were generally observed in specific pools or shallow water locations within the atoll during high and low tides, but also expanded their movements to include more of the atoll. Throughout the study, young lemon sharks appeared to concentrate movements within shal- low-water low-tide refuges and separate high tidal areas. Movement patterns of sharks in Atol das Rocas differ from those at other well-studied lemon shark nursery locations, where individuals con- tinuously occupy shallow flats and mangrove habitats. Nevertheless, lemon sharks in general restrict their movements to shallow-water habitats regardless of the specific nursery area occupied. This behavior is most likely related to predator avoidance. This study provides an example of the inter- action between the physical environment and the biology of animals—in this case, the influence of the physical characteristics of a nursery area and the behavioral ecology of young lemon sharks.
Acute disturbance events like tropical storms can have significant effects on coastal habitats and animals that utilise them. We examined environmental parameters as cues for flight behaviour based on movement data from 5 species of elasmobranch (Carcharhinus limbatus, C. tilstoni, C. melanopterus, C. sorrah and C. amboinensis) during 3 tropical storm events in 2 coastal bays on 2 continents (Cleveland Bay, Australia, and Terra Ceia Bay, USA). Individuals were monitored using passive acoustic telemetry before, during and after the storms. Short-term effects on movement and distribution were investigated in relation to environmental parameters (barometric pressure, wind speed and wave height) along with longer-term changes in size and location of activity spaces of individuals due to extreme weather events. Short-term flight behaviour was observed in 4 species, with C. melanopterus the only species showing no reaction to storm events. Change of activity space size and location varied within the 2 study sites, with significant changes in activity spaces only occurring in Terra Ceia Bay. Examination of environmental parameters as cues for flight behaviour showed that species had varying tolerances to environmental conditions during storm events. Flight behaviour was observed in juvenile individuals that had not experienced such conditions before, which may suggest that this behavioural response is innate.
White sharks (Carcharodon carcharias) are threatened apex predators and identification of their critical habitats and how these are used are essential to ensuring improved local and ultimately global white shark protection. In this study we investigated habitat use by white sharks in False Bay, South Africa, using acoustic telemetry. 56 sharks (39 female, 17 male), ranging in size from 1.7-5 m TL, were tagged with acoustic transmitters and monitored on an array of 30 receivers for 975 days. To investigate the effects of season, sex and size on habitat use we used a generalized linear mixed effects model. Tagged sharks were detected in the Bay in all months and across all years, but their use of the Bay varied significantly with the season and the sex of the shark. In autumn and winter males and females aggregated around the Cape fur seal colony at Seal Island, where they fed predominantly on young of the year seals. In spring and summer there was marked sexual segregation, with females frequenting the Inshore areas and males seldom being detected. The shift from the Island in autumn and winter to the Inshore region in spring and summer by females mirrors the seasonal peak in abundance of juvenile seals and of migratory teleost and elasmobranch species respectively. This study provides the first evidence of sexual segregation at a fine spatial scale and demonstrates that sexual segregation in white sharks is not restricted to adults, but is apparent for juveniles and sub-adults too. Overall, the results confirm False Bay as a critical area for white shark conservation as both sexes, across a range of sizes, frequent the Bay on an annual basis. The finding that female sharks aggregate in the Inshore regions when recreational use peaks highlights the need for ongoing shark-human conflict mitigation strategies.
The blacktip shark is a cosmopolitan species found throughout tropical and subtropical waters, It is common along the southeast coast of the United States, where it migrates northward to Georgia and the Carolinas in summer and southward to Florida in winter. The blacktip shark feeds on small bony fishes, primarily menhaden, and small elasmobranchs. Males mature between 1,425 and 1,450 mm TL, and all males over 1450 mm TL are mature. Females mature at about 1,560 mm TL. The reproductive cycle lasts 2 years and includes biennial ovulation with a 1-year gestation period. Mating and ovulation occur in Bulls Bay, South Carolina, from mid-May to early June. Parturition occurs the following year from early May to early June in the shallow coastal waters of the Carolinas. The blacktip shark is a viviparous, placental species. Implantation usually occurs during the 10th and 11th weeks of gestation when the embryos measure 178-194 mm TL. The young are born at about 550-600 mm TL during May and early June in the shallow water, coastal nurseries of Georgia and the Carolinas. The neonate stage lasts about a month. The young remain in the shallow water nurseries until fall.
The fish communities occupying a natural reef site and an artificial reef site near the mouth of Botany Bay, a marine-dominated estuary in southeastern Australia, were assessed by a diver transect method bimonthly over a two-year period. Temporal and spatial differences in community structure were analyzed. One hundred and two fish species from 50 families were observed, 93 at the natural reef site and 59 at the artificial reef site, with 49 being common to both. Twenty-five of these species were of some economic importance. The natural reef site, as well as having a higher number of species, had higher total abundance, species heterogeneity and species richness. The artificial reef site attracted slightly larger abundances of fishes of economic importance.
Silky sharks, Carcharhinus falciformis (Müller and Henle, 1839), are the primary elasmobranch bycatch species in tuna purse seine fisheries throughout the world's major oceans. Juveniles of this species commonly associate with drifting fish aggregating devices (Fads) deployed to enhance tuna catches in these fisheries. Here we present results from the first investigation into the behavior of juvenile silky sharks associated with drifting Fads in the western indian ocean. A total of 10 silky sharks were tagged with coded acoustic transmitters around drifting Fads equipped with acoustic receivers. Following release, all sharks undertook an excursion away from the Fad with which they were associated. Two individuals were subsequently never detected, while the initial absence period of the eight detected sharks ranged between 0.1 and 3.5 d. After returning, total association times averaged 5.19 d (sd = 3.15 d) and related horizontal movement rates ranged from 8 to 50 km d-1. Short excursions away from the Fad were undertaken by some individuals, all of which lasted a few hours and were made at night. During periods of association, silky sharks typically occupied the upper 35 m of the water column for the majority of the observation period. These results provide new insights into our understanding of associative behaviors. Further studies are needed to improve assessment of the impacts of Fads on the ecology of this species, a major concern considering the large number of Fads deployed.
We conducted a two-year gillnet survey of the relative abundance, species diversity, and reproductive condition of sharks from southeastern North Carolina coastal waters. Sixteen shark species were recorded of which Rhizoprionodon terraenovae (Richardson, 1836) was the most common, representing >80% of the total catch in both years. Large coastal species such as Carcharhinus limbatus (Müller and Henle, 1839) and Carcharhinus plumbeus (Nardo, 1827) were caught infrequently, representing 1% of the total catch. Juvenile, or sub-adult size classes in the total catch were dominated by Carcharhinus brevipinna (Müller and Henle, 1839), Carcharhinus obscurus (LeSueur, 1818), C. plumbeus, and Carcharias taurus Rafinesque, 1810. Sub-adult, or adult size classes in the total catch were dominated by Sphyrna tiburo (Linnaeus, 1758), C. limbatus, Carcharhinus isodon (Müller and Henle, 1839), and Carcharhinus acronotus (Poey, 1860). The smallest mature specimen of R. terraenovae, C. limbatus (female) and C. isodon were smaller than previously documented minimum sizes at maturity. Based on the association of gravid females present in catches with neonates, or small juveniles of the same species, southeastern North Carolina was identified as a primary and/or secondary nursery ground for R. terraenovae , C. brevipinna, C. acronotus and C. obscurus during the months of investigation. Our data also suggest that C. limbatus and Sphyrna lewini (Griffith and Smith, 1834) use southeastern North Carolina as a nursery ground, although more infrequently. Similarly, C. plumbeus uses southeastern North Carolina as an over-wintering ground and neonates are reported infrequently. Almost 100% mature female R. terraenovae and S. tiburo were gravid; most were caught from AugustOctober. Embryos of S. tiburo, based on growth rate extrapolation, were at documented parturition size by September.
Associative behaviour is defined as the spatial relationship between an animal (or a group) of a given species and another animal of another species, which is based on a decision by at least one of the two individuals to maintain contact with the other associate, but not for the purpose of feeding on the other. This definition is expanded to include objects and topographic structures (seamount, island, etc) that are not the exclusive habitat of the associated animal.Associations between fish and objects, mammals, topographic structures and other species of fish are reviewed, and the different hypotheses for these associations analysed. Finally, a generalisation of the meeting point hypothesis, fitting all types of association, is proposed. This hypothesis, initially applied to the association between tuna and floating objects, proposes that fish make use of animate or inanimate targets to increase the encounter rate between isolated individuals or small schools and other schools in order to constitute bigger schools that are more efficient to the survival of the species.It is strongly recommended to move from the scientific description of the association to specific experimental studies aimed at identifying ethological processes. This would provide a better understanding of the dynamics of associative behaviour of pelagic species, which in turn would permit better stock assessment and fishery management.
Herbivory and other ecosystem processes are widely accepted as important factors in maintaining coral reef resilience. While
the spatial scales over which these processes occur have been evaluated, the spatial ecology of individual taxa responsible
for shaping these processes is almost entirely unknown. This study combined acoustic telemetry and ecological assessments
to evaluate the movement patterns and feeding range of a functionally important coral reef fish, Chlorurus microrhinos (f. Labridae). The diurnal home range and feeding areas of C. microrhinos, on Orpheus Island, Great Barrier Reef, were quantified using active acoustic telemetry. The average diurnal home range of
C. microrhinos was 7,830m2±940 (SE). Core areas of activity (50% kernel utilization distributions) were relatively small, encompassing approximately
22% of an individual’s home range (1,690m2±220). Core areas exhibited greater topographic complexity. C. microrhinos may select these areas because of decreased predation risk. Feeding intensities were not homogenous throughout the home range.
Core areas were found to have a greater number of feeding scars and are thus exposed to increased bioerosion and algal removal
by C. microrhinos. While important in shaping key ecosystem processes, the ecosystem impact of individual C. microrhinos in Pioneer Bay appears to be restricted to small areas within a narrow band along the reef crest.
KeywordsHome range–Ecosystem function–Coral reefs–Spatial resilience–Herbivory–Telemetry
Externally and internally implanted sonic transmitters were used to track the movements of eight tiger sharks (Galeocerdo cuvier) ranging between 200 and 417 cm total length (TL), captured by hook-and-line on the south coast of Oahu, Hawaii, between
1993 and 1997. Attachment of the transmitters was facilitated by the fact that captured sharks exhibited tonic immobility
when restrained and inverted at the side of the tagging vessel. Three common themes emerged from the horizontal movements
of the tracked sharks: (1) offshore movements away from the island, (2) extended periods of directed, “straight-line” swimming,
(3) orientation to the Penguin Banks – a shallow bank located ≃35 km from the release point. In shallow water (<300 m) the
sharks swam predominantly close to the bottom, in open water (>300 m) they swam within the mixed layer at depths of ∼80 m.
One shark dove briefly to 335 m. The average estimated swimming speed of sharks traversing open water was 0.29 body length
(BL) s−1. Two sharks were recaptured after termination of the tracks; one of these sharks was recaptured twice, with a total time
at liberty of 377 d. The data suggest that Hawaiian tiger sharks move within large home ranges and that they can efficiently
navigate between distant parts of their range, even when this requires crossing open ocean waters.
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.
Length at age and growth rates for 54 blacktip, Carcharhinus limbatus, and 15 spinner, C. brevipinna, sharks from the northwestern Gulf of Mexico were estimated from bands formed seasonally in vertebral centra. For C. limbatus, males mature at 130 cm total length (TL) or 4-5 yr, females at 150-155 cm TL or 7-8 yr. With sexes combined, von Bertalanffy curve parameter estimates were: L oo=176 cm TL, K = 0.274, t o=-1.20 yr. The oldest specimen, a 171 cm TL female, was 9.3 yr of age. For C. brevipinna, males mature at 170 cm TL or 6-7 yr of age, females at 180 cm TL or 7-8 yr of age. The oldest specimen, a 208 cm TL female, was 11.3 yr of age. With sexes combined, von Bertalanffy curve parameter estimates were: L oo=214 cm TL, K = 0.212, t o=-1.94 yr. Growth rates for both species are in excess of 20 cm/yr for the first 2 yr, about 10 cm/yr through adolescence, and 5 cm/yr or less for adults.
Behavioral activities of a colony of 10 bonnethead sharks, Sphyrna t. tiburo, held under semi-natural conditions, were examined over a period of six months. All sharks had attained, or were approaching, sexual maturity. Objectives of the study were to describe species-typical motor patterns and postures, to analyze the diurnality of patrolling activity and to characterize pattern(s) of organization underlying social interactions noted within the colony. Eighteen postures and patterns of movement were described, almost half of them having apparent social relevance. In specific instances, functional significance of a pattern was cautiously given. Patrolling activity appeared to have a diurnal rhythm, with a peak occurring in the late afternoon; smaller individuals were more erratic in their patrolling. Finally, a clear but subtle social organization, based on a straight-line, size-dependent, dominance hierarchy was found. Though position within the hierarchy was not determined by sex, data indicated that all individuals tended to shy away from larger males. Sexual differences in the performance of certain patterns of movement were also established.
The overexploitation of sharks has become a global environmental issue in need of a comprehensive and multifaceted management response. Tracking studies are beginning to elucidate how shark movements shape the internal dynamics and structure of populations, which determine the most appropriate scale of these management efforts. Tracked sharks frequently either remain in a restricted geographic area for an extended period of time (residency) or return to a previously resided-in area after making long-distance movements (site fidelity). Genetic studies have shown that some individuals of certain species preferentially return to their exact birthplaces (natal philopatry) or birth regions (regional philopatry) for either parturition or mating, even though they make long-distance movements that would allow them to breed elsewhere. More than 80 peer-reviewed articles, constituting the majority of published shark tracking and population genetic studies, provide evidence of at least one of these behaviors in a combined 31 shark species from six of the eight extant orders. Residency, site fidelity, and philopatry can alone or in combination structure many coastal shark populations on finer geographic scales than expected based on their potential for dispersal. This information should therefore be used to scale and inform assessment, management, and conservation activities intended to restore depleted shark populations. Expected final online publication date for the Annual Review of Marine Science Volume 7 is January 03, 2015. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
An observer program of the shark drift gillnet fishery off the Atlantic coast of Florida and Georgia was begun in 1993 to define the fishery and estimate bycatch including bottlenose dolphin, Tursiops truncatus, and sea turtles. Boats in the fishery were 12.2-19.8 m long. Nets used were 275-1,800 m long and 3.2-4.1 m deep. Stretched-mesh sizes used were 12.7-29.9 cm. Fishing trips were usually <18 h and occurred within 30 n.mi. of port. Fishing with an observer aboard occurred between Savannah, Ga., and Jacksonville, Fla., and off Cape Canaveral, Fla. Nets were set at least 3 n.mi. offshore. Numbers of boats in the fishery increased from 5 in 1993 to 11 in 1995, but total trips decreased from 185 in 1994 to 149 in 1995. During 1993-95, 48 observer trips were completed and 52 net sets were observed. No marine mammals were caught and two loggerhead turtles, Caretta caretta, were caught and released alive. A total of 9,270 animals (12 shark, 21 teleast, 4 ray, and 1 sea turtle species) were captured. Blacknose, Carcharhinus acronotus; Atlantic sharpnose, Rhizoprionodon terraenovae; and blacktip shark, C. limbatus), were the dominant sharks caught. King mackerel, Scomberomorus cavalla; little tunny, Euthynnus alleteratus; and cownose ray, Rhinoptera bonasus, were the dominant bycatch species. About 8.4% of the total catch was bycatch. Of the totals, 9.4% of the sharks and 37.3% of the bycatch were discarded.
Archival tags were used to study the movement and depth behaviour of school sharks, Galeorhinus galeus, in southern australia. Thirty fish were tagged in late 1997, and to date there have been nine recaptures (30% recapture rate). Periods at liberty varied from 8 days to 18 months. The sharks spent about 80% of their time on the continental shelf, and appeared to swim close to the bottom during the day. At night they often ascended for periods of up to several hours, except at times around the full moon. When in deep water, the sharks typically descended at dawn to depths of up to 600 m, before ascending at dusk. It was not possible to use the light data from the tags to estimate position when the sharks were in deep water, because they were often at depths beyond the sensitivity of the tag. In shallower water, longitude was estimated from the light data but latitude was estimated from the maximum daily depth, assuming the fish were on the bottom. The timing of the dives in deepwater appeared sufficiently regular to offer the prospect of using it to estimate longitude. We propose future research using archival tags on this species should address questions about female reproductive migrations, pelagic behaviour and vertical movements.
Previous research suggests that nursery areas provide an abundant food source
as well as protection from predation for young sharks, and that these benefits
are the reasons they use these areas. This study examined the abundance of
prey species within a known nursery area, Terra Ceia Bay, Florida, and
compared those data with the amount of time blacktip sharks spent within
various geographic zones within the nursery. The most abundant prey species
within the study site were pinfish, Lagodon rhomboides,
pigfish, Orthopristis chrysoptera, spotfin mojarra,
Eucinostomus argenteus, and silver perch,
Bairdiella chrysoura. Prey species were found to be most
abundant in the mid to southern portion of the nursery area, whereas sharks
spent the majority of their time within the northern portion of the study
site. There was no correlation between the amount of time sharks (as a whole
and by individual) spent within a geographic zone and the abundance of prey
species within that area. These results suggest that prey abundance is not the
main factor directing the movement patterns and habitat choice of juvenile
Carcharhinus limbatus within Terra Ceia Bay. Predator
avoidance may be more important in the use of the nursery grounds by these
young animals than prey abundance.
It is argued that P-values and the tests based upon them give unsatisfactory results, especially in large samples. It is shown that, in regression, when there are many candidate independent variables, standard variable selection procedures can give very misleading results. Also, by selecting a single model, they ignore model uncertainty and so underestimate the uncertainty about quantities of interest. The Bayesian approach to hypothesis testing, model selection, and accounting for model uncertainty is presented. Implementing this is straightforward through the use of the simple and accurate BIC approximation, and it can be done using the output from standard software. Specific results are presented for most of the types of model commonly used in sociology. It is shown that this approach overcomes the difficulties with P-values and standard model selection procedures based on them. It also allows easy comparison of nonnested models, and permits the quantification of the evidence for a null hypothesis of interest, such as a convergence theory or a hypothesis about societal norms.
Age and growth of the blacktip shark, Carcharhinus /imbatus, was investigated in the Tampa Bay area of Florida during May 1985 February 1987. Two hundred and eighteen sharks were captured, and vertebrae were examined from 86 females (52.4-183.0 cm TL.I and 54 males (59.8 160.5 cm TL). Minimum and maximum number of translucent winter rings was 0 and 11. Marginal increment analysis on juvenile blacktips with one to three translucent vertebral rings suggested an annual ring deposition during December-January. Length-frequency and length-month analyses sug gested three age.classes for blacktips
A primary concern associated with reservoir shoreline residential development is reduction of littoral habitat complexity and diversity. One potential approach to compensate for this is the deployment of artificial-habitat modules under existing piers, but the benefit of this practice has not been demonstrated. To evaluate the effect of pier habitat modifications on fish populations in two Piedmont Carolina reservoirs, we studied 77 piers located on forty-seven, 100-m transects that were modified using plastic “fish hab” modules augmented with brush (brushed habs), hab modules alone (habs), or left unaltered for reference purposes. We sampled fish from all piers and transects during April, July, and October 2001 using a boat-mounted electrofisher. With few exceptions, catch rates were higher at brushed-hab piers and piers with habs than at reference piers during all seasons. Similarly, during spring and summer, fish abundance was generally higher on transects containing natural woody debris, brushed habs, and habs than on reference-developed transects; however, during fall, there were exceptions. Therefore, fish abundance associated with shorelines in these reservoirs appears to be related to the structural complexity of available habitat rather than structure composition. One year after installation, 92% of pier owners responding to a mail survey expressed satisfaction with pier modifications. Supplementing piers with habitat structures is recommended to enhance littoral habitat complexity for fishes in residentially developed reservoirs.
Stomach contents and vertebrae from neonate and juvenile blacktip sharks Carcharhinus limbatus (n= 334) were examined to describe their diet, feeding patterns and growth within the Timbalier–Terrebone Bay complex, LA, U.S.A. In the study area, both neonate and juvenile C. limbatus feed primarily on gulf menhaden Brevoortia patronus. However, based on the index of relative importance (IRI), gulf menhaden constituted a larger portion of the diet of neonates (84·05 %IRI) than for juveniles (47·91 %IRI). An increase in the index of relative fullness between the afternoon and dusk time intervals and a large decrease in the percentage of empty stomachs between the night and early morning time intervals suggested that these fish exhibited a diel feeding pattern with crepuscular periods being the times of highest feeding activity. A higher percentage of empty stomachs (neonates 68% and juveniles 39%) and a significantly lower growth rate (age 0+ year C. limbatus, 0·62 mm day−1; age 1+ year fish, 0·89 mm day−1) could indicate that neonate C. limbatus are less efficient predators than older conspecifics.
Sharks were collected from the estuarine and nearshore waters of South Carolina in an effort to delineate nursery grounds for coastal sharks within state waters. From March 1998 through December 2003, 4,098 sharks, representing 12 species, were collected using gill-net and hand-deployed longline fishing gears provided by the Cooperative Atlantic States Shark Pupping and Nursery Survey. To supplement these data, records of 6,648 shark captures, representing 16 species, from a long-term longline survey in South Carolina coastal waters were incorporated into the analyses. The results of this study indicate that the estuarine and nearshore waters of South Carolina represent an important primary nursery area for finetooth sharks Carcharhinus isodon, blacktip sharks C. limbatus, sandbar sharks C. plumbeus, Atlantic sharpnose sharks Rhizoprionodon terraenovae, and scalloped hammerheads Sphyrna lewini.
Global declines of shark populations are of concern because of their largely assumed role as moderators of ecosystem function. Without long-term data on movement patterns for many species, it is impossible to infer relative extinction risk, which varies as a function of range, dispersal and habitat specificity and use. The past 50 yr of research on coastal sharks has revealed common movement patterns among species. In the horizontal plane, measured home range size generally increases with body size. We demonstrate meta-analytically the effects of increasing body size and monitoring time on home range size. Changes in the extent of horizontal movement might arise from ontogeny, predator avoidance or environmental tolerances. In the vertical plane, movement patterns include oscillatory vertical displacement, surface swimming, diel vertical migration and swimming at depth. These vertical movements are often attributed to foraging or navigation, but have been quantified less than horizontal patterns. Habitat specificity is often correlated with environmental conditions such as depth, salinity, substratum, and in some cases, prey availability. Site fidelity is common in species that use nursery areas. However, fidelity to mating, pupping, feeding and natal sites has only been observed in a few species. To date, few studies have examined habitat partitioning, although some general patterns have emerged: habitats appear to be subdivided by benthos type, prey availability and depth. The conservation of coastal sharks can be facilitated in some cases by the use of marine protected areas, especially for coastal resident species using specific nursery, reproduction or feeding areas. Partial protected-area closures might be effective during aggregation or migration periods to protect older size classes, but these must be applied with other management strategies such as reduced fishing and size or bag limits to protect individuals throughout different life history phases. More long-term research on habitat use, migration patterns and habitat partitioning is essential for developing successful management initiatives for coastal shark populations.
The importance of interactions between sharks and cetaceans has been a subject of much conjecture, but few studies have addressed these interactions. Sharks (order Selachii) have been hypothesized to be important predators on dolphins and porpoises (suborder Odontoceti). Unfortunately, there are often few data to back up claims that certain shark species are major threats to cetaceans. To help identify potential shark predators in speci®c locations, available data on interactions with odontocetes for all shark species that may include cetaceans in their diet are reviewed. Shark species are categorized into groups based on predatory interactions with dolphins and porpoises (regular predators, occasional predators, potential predators, ectoparasites and insuf®cient data). Several shark species that have been overlooked in the cetacean literature are identi®ed as potentially important predators while others that have been suspected to be important predators are probably at most occasional predators. How shark predation can in¯uence dolphin populations, habitat use, group size and behaviour is discussed. How risk of shark predation can vary with habitat attributes in both nearshore and pelagic waters is also discussed. Predator±prey interactions have been the focus of most studies of shark±dolphin interaction, but competitive interactions may also occur. The ®rst analysis of shark±dolphin dietary overlap is presented, which shows it to be signi®cant between common dolphins and several species of sharks, including species that prey upon these dolphins.
A small population of juvenile (<1 year old) blacktip sharks Carcharhinus limbatus responded to the approach of a tropical storm by moving to deeper water. Examination of meterological variables suggested that the movement of the blacktip sharks was triggered by a drop in barometric pressure associated with the approach of the storm. This response was consistent for all the fish being studied, and all blacktip sharks returned to the shallow nursery area after the storm's passage, suggesting that this was an innate behaviour.
Occurrences of 18 scalloped hammerhead sharks tagged with coded ultrasonic transmitters were recorded at seamount El Bajo Espiritu Santo in the Gulf of California over a 10-day period by automated, data-logging monitors. These sharks remained grouped at the seamount during the day and moved separately into the surrounding pelagic environment at night. The temporal pattern of shark occurrences was related to the light-dark cycle: individuals departed prior to dusk and returned near dawn next morning. However, arrivals and departures of more than one shark within short daytime periods indicated group movements to and from the seamount. Sharks returned repeatedly to the tagging site and not to another site centred less than 240 m from the former site.
Aggregation patterns of a population of juvenile blacktip sharks (Carcharhinus limbatus) within a summer nursery area were examined over a period of 3years using an array of acoustic monitors. Individually coded
acoustic tags were surgically implanted into 33–40 neonate sharks each year from 2000 to 2002 and their presence monitored
continuously by the acoustic array. Data from the acoustic monitors was processed to estimate the center of activity location
of each tagged shark every 30min. Nearest neighbor analysis of shark locations revealed that sharks aggregated within the
nursery in all years of the study. Sharks were aggregated most commonly during the early and late summer months (June, October
and November) and became less common through the middle of the study period each year (July–September). Temporal periodicity
within the data revealed a strong diel pattern with sharks aggregating during the day and dispersing at night, except in June
when aggregations often persisted through the night. Aggregations were generally restricted to the mid and northern sections
of the study site. Reasons for aggregations may include predator avoidance or improved feeding efficiency.
Effects of environmental factors on frequency and success rate of 2,546 natural predatory attacks by white sharks, Carcharodon carcharias, on Cape fur seals, Arctocephalus pusillus pusillus, were studied over an 8-year period at Seal Island, South Africa. Attacks occurred primarily during winter months (June–August). Attack frequency increased significantly during northerly winds, during high tides, and within 400m of the island, but predatory success rate decreased with proximity to the island. Attacks occurred over a depth range of 5–31m, with significantly more occurring at depths of 26–30m. Attack frequency and success rate increased significantly at low light levels. These results are compared with published effects of environmental factors on white shark predation frequency at the Farallon Islands, California, and discussed in terms of the Predation Cycle. Suggestions for future work at this site are offered.
I studied diet and feeding habits in juvenile scalloped hammerhead sharks in Kne'ohe Bay, Hawai'i, from August 1995 to May 1998. The most common prey items were a single species of alpheid shrimp and two species of goby. Benthic surveys indicated that the shrimp and gobies are the most abundant benthic megafauna in Kne'ohe Bay. Sharks had small amounts of food in their stomachs (median = 0.22% of body weight), and sharks with open umbilical scars were more likely to have an empty stomach than sharks with healed umbilical scars. There was a significant diel change in the amount of food in the stomach. Analysis of stage of digestion data and the frequency of occurrence of empty stomachs also indicated that sharks fed more at night than during the day. A number of other factors that might influence diet and feeding were also investigated, including the effect of area, sex, year, season, and proximity to the patch reefs. Season and year had significant effects on the amount of food in sharks' stomachs, but sex and proximity to the patch reef did not.
This study describes the diet of the sandbar shark, Carcharhinus plumbeus, highlighting differences in diet within various regions of the Virginia (USA) nursery area, as well as ontogenetic changes
in diet. Stomach samples were obtained in 2001 and 2002 from 232 sharks caught by gillnets or longlines. Historical data from
the Virginia Institute of Marine Science (VIMS) Shark Ecology Program were also analyzed. Ontogenetic changes in diet were
evident, with crustacean prey decreasing in frequency with increasing shark size, and elasmobranch prey importance increasing
with increasing shark size. Whereas previous research in Chincoteague Bay, VA showed the blue crab, Callinectes sapidus, was the dominant crustacean in sandbar shark diet, the mantis shrimp, Squilla empusa, dominated the crustacean portion of the diet in this study. Differences in diet of sharks were observed among locations
within the study area. Small juveniles (≤80cm precaudal length) in the lower Chesapeake Bay ate more fishes, whereas Eastern
Shore juveniles ate more crustaceans. Crustacean prey items varied among locations along the Eastern Shore, with more portunid
crabs consumed in waters near Wachapreague and more mantis shrimp consumed near Sand Shoal Inlet. Our study showed that Carcharhinus plumbeus is a generalist predator and is thus unlikely to strongly impact the population of any particular prey species, and in turn
is not likely to be strongly affected by fluctuations in abundance of a single prey species.