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Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management.
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Global spatial risk assessment of sharks
under the footprint of fisheries
Effective ocean management and the conservation of highly migratory species depend on resolving the overlap between
animal movements and distributions, and fishing effort. However, this information is lacking at a global scale. Here we
show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets,
that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use
hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines
(up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort. We conclude that
pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions
(the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots
of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool
for near-real-time, dynamic management.
Industrialized fishing is a major source of mortality for large marine
animals (marine megafauna)
. Humans have hunted megafauna in
the open ocean for at least 42,000 years7, but international fishing fleets
that target large, epipelagic fishes did not spread into the high seas until
the 1950s8. Prior to this, the high seas constituted a spatial refuge that
was largely free from exploitation, as fishing pressure was concentrated
on continental shelves
. Pelagic sharks are among the widest-ranging
vertebrates, with some species exhibiting annual migrations on
the ocean-basin scale9, long term trans-ocean movements10 and/or
fine-scale site fidelity to preferred shelf and open ocean areas5,9,11.
These behaviours could cause extensive spatial overlap with different
fisheries that exploit regions ranging from coastal areas to the deep
ocean. On average, large pelagic sharks account for 52% of all of the
identified shark catch worldwide, from both shark-targeting fisheries
and as bycatch
. Regional declines in abundance of pelagic sharks have
previously been reported
, but it is unclear whether exposure to high
levels of fishing effort extends across ocean-wide population ranges and
overlaps areas of the high seas in which sharks are most abundant5,13.
The conservation of pelagic sharks—the management of which on
the high seas is currently limited
—would benefit greatly from a
clearer understanding of the spatial relationships between the habitats
of sharks and active fishing zones. However, obtaining unbiased esti-
mates of the distributions of sharks and fishing effort is complicated by
the fact that most data on pelagic sharks come from catch records and
other fishery-dependent sources4,15,16.
Here we provide a global estimate of the extent of overlap in the use
of space between sharks and industrial fisheries. This estimate is based
on analysis of the movements of pelagic sharks tagged with satellite
transmitters in the Atlantic, Indian and Pacific Oceans, together with
the movements of fishing vessels that are monitored globally by the
automatic identification system (AIS), which was developed as a vessel
safety and anti-collision system (Methods). Our study focuses on 23
species of large pelagic sharks that occupy oceanic and/or neritic hab-
itats, which span a broad distribution from cold–temperate to tropical
waters (Supplementary Table1). All of these species face some level
of fishing pressure from coastal, shelf and/or high-seas fisheries: the
International Union for the Conservation of Nature (IUCN) Red List
assesses almost two-thirds of these species as being endangered (26%)
or vulnerable (39%), and a further quarter as near-threatened (26%)
(Supplementary Table2). Although regional-fisheries management
organizations are tasked with the management of sharks in the high
seas, little or no management is in place for most species3,5,1218.
Movement patterns of sharks and fishing vessels
The 11 shark species (or taxa groups) that accounted for 96% of the
1,804 satellite tags that were deployed are among the largest of shark
species: blue sharks (Prionace glauca); shortfin mako sharks (Isurus
oxyrinchus); tiger sharks (Galeocerdo cuvier); salmon sharks (Lamna
ditropis); whale sharks (Rhincodon typus); white sharks (Carcharodon
carcharias); oceanic whitetip sharks (Carcharhinus longimanus); por-
beagle sharks (Lamna nasus); silky sharks (Carcharhinus falciformis);
bull sharks (Carcharhinus leucas); and hammerhead sharks (Sphyrna
spp.) (Supplementary Tables35). Movement patterns indicated that
multiple species aggregated within the same major oceanographic
features (Fig.1), such as the Gulf Stream (blue sharks, shortfin mako
sharks, tiger sharks, white sharks and porbeagle sharks), the California
Current (blue sharks, shortfin mako sharks, white sharks and salmon
sharks) and the East Australian Current (blue sharks, shortfin mako
sharks, tiger sharks, white sharks and porbeagle sharks), (Extended
Data Fig.1; see ‘Supplementary results and discussion, section2.1’
intheSupplementary Information). The global relative density map
(Fig.2a) reveals distribution patterns of pelagic sharks and the locations
of space-use hotspots (defined here as areas with75th percentile of
weighted daily location density) (Methods). Major space-use hotspots
of tracked pelagic sharks in the Atlantic Ocean were in the Gulf Stream
and its western approaches, the Caribbean Sea, the Gulf of Mexico
and around oceanic islands such as the Azores (Fig.2a, Supplementary
Table6). In the Indian Ocean, space-use hotspots were evident in the
Agulhas Current, Mozambique Channel, the South Australian Basin
and northwest Australia, and in the Pacific Ocean, space-use hotspots
were in the California Current, Galapagos Islands and around New
Zealand. Although, as expected, tagging sites occurred in some space-
use hotspots (as tagging rates are inherently higher in hotspots), we also
identified space-use hotspots in which no tagging sites occurred in the
North Atlantic Ocean (outer Gulf Stream, Charlie Gibbs Fracture Zone,
western European shelf edge and the Bay of Biscay), the Indian Ocean
(southern Madagascar, the Crozet and Amsterdam Islands, and the
South Australian Basin) and the Pacific Ocean (Alaska Current, outer
California Current, the white shark ‘café’ area, halfway between Baja
California and Hawaii11, North Equatorial Current, Clipperton Island
A list of authors and their affiliations appears in the online version of the paper.
22 AUGUST 2019 | VOL 572 | NATURE | 461
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... Global studies have emphasized the problems inherent in assessing the status of sharks, providing detailed descriptions of the difficulties on every level [1][2][3][4]13,26]. For a shark fishery to be sustainable, it must be possible to determine not only what the shark fishing mortality is, but also the mortality that will produce maximum sustainable yield (MSY), yet in the case of sharks those reference points are often not known or are extremely uncertain [4,5,20,41,80]. Most shark hunting nations still do not keep species-specific catch records [1,2,6,26,81], and recorded catches are known to be inaccurate. Catch data from artisanal fisheries are generally ignored, but in many regions, they are significant [82]. ...
... Blue sharks dominate the bycatch of longline fisheries [15] and they are considered to be at high risk due to their distribution, which overlaps heavily fished regions [80]. Further, as oxygen minimum zones (OMZs) expand due to global warming, blue sharks may be shifting their distribution patterns into surface waters to avoid deeper, oxygen depleted waters [139]. ...
... For pelagic species of sharks, large MPAs and no-take zones that include the High Seas are required for effective protection because most are highly migratory. There is a particularly urgent need for conservation and management measures at high-seas and coastal hotspots of shark space [80,187]. Designation of such MPAs should take the high degree of spatial overlap between sharks and industrial fishing vessels into consideration, especially in those areas that attract fish, because of their favourable productivity and temperature profiles [187,188]. ...
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The expanding shark fin market has resulted in intensive global shark fishing and with 90% of teleost fish stocks over-exploited, sharks have become the most lucrative target. As predators, they have high ecological value, are sensitive to fishing pressure, and are in decline, but the secretive nature of the fin trade and difficulties obtaining relevant data, obscure their true status. In consumer countries, shark fin is a luxury item and rich consumers pay high prices with little interest in sustainability or legal trade. Thus, market demand will continue to fuel the shark hunt and those accessible to fishing fleets are increasingly endangered. Current legal protections are not working, as exemplified by the case of the shortfin mako shark, and claims that sharks can be sustainably fished under these circumstances are shown to be misguided. In the interests of averting a catastrophic collapse across the planet’s aquatic ecosystems, sharks and their habitats must be given effective protection. We recommend that all sharks, chimaeras, manta rays, devil rays, and rhino rays be protected from international trade through an immediate CITES Appendix I listing. However, a binding international agreement for the protection of biodiversity in general is what is needed.
... Large obligate swimming fish (or ram ventilators), such as many large pelagic species, routinely encounter capture from recreational sports fishers (catch-and-release angling), as bycatch in global longline fisheries (e.g. protected elasmobranchs), or as part of management or research programmes [1,2]. In the field study of large free-ranging fishes, capture and release is required to attach animal-borne bio-loggers, which can directly measure swimming speed [3][4][5][6][7]. ...
... For most sharks, β ranges between a few negative thousandths [23] and a few positive hundredths [24]. 2 Formally, parasite drag is the drag at zero lift and it mainly comprises of the friction between the body and the water; induced drag is the cost of generating hydrodynamic lift. 3 The first term in this equation is the potential energy of the swimmer; it has a negative sign because depth is the greatest at the nadir. ...
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Marine organisms normally swim at elevated speeds relative to cruising speeds only during strenuous activity, such as predation or escape. We measured swimming speeds of 29 ram ventilating sharks from 10 species and of three Atlantic bluefin tunas immediately after exhaustive exercise (fighting a capture by hook-and-line) and unexpectedly found all individuals exhibited a uniform mechanical response, with swimming speed initially two times higher than the cruising speeds reached approximately 6 h later. We hypothesized that elevated swimming behaviour is a means to increase energetic demand and drive the removal of lactate accumulated during capture via oxidation. To explore this hypothesis, we estimated the mechanical work that must have been spent by an animal to elevate its swim speed and then showed that the amount of lactate that could have been oxidized to fuel it comprises a significant portion of the amount of lactate normally observed in fishes after exhaustive exercise. An estimate for the full energetic cost of the catch-and-release event ensued.
... 24,25 In contrast, over the past several years researchers have increasingly relied on public, high-resolution Automatic Identification Systems (AISs) data, originally designed as a real-time collision avoidance tool, to describe and evaluate the behaviors and attributes of fishing vessels across global oceans. 19,26,27 Although AIS is recognized as an imperfect data source given regional differences in usage and satellite coverage, 23,28 the technology has been successfully used to identify patterns of transshipment behavior 29,30 and port usage; 31 detect illegal, unreported, and unregulated (IUU) fishing activity; 32,33 and monitor marine protected area effectiveness. 34,35 As the fishing capacity intensifies and ecological impacts accelerate, 36 harnessing increased observational power to improve understanding of how fishers allocate their effort in time and space is of critical importance. ...
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Ensuring the long-term sustainability of tuna, billfish, and other transboundary fisheries resources begins with data on the status of stocks, as well as information concerning who catches what fish, when, where, and how. Despite recent improvements in fisheries monitoring and surveillance, such dynamics remain poorly understood across the high seas. Here we delineate and describe pelagic longline activity in the Pacific Ocean using a framework that integrates descriptive vessel information and tracking data with species-specific catch reports. When parsed by distinct vessel behaviors and attributes, disaggregated fisheries data highlight the existence of multi-national, multi-specific (i.e., targeting multiple species) fishing fleets, many of which target waters that span more than one management area. Our findings emphasize the need for increased coordination across regional and sub-regional governance bodies and suggest that effective and equitable management of the sector may require efforts to move beyond single-species, single-area controls and operational distinctions based primarily on vessel flag and/or gear type alone.
... Given the significance of these risks, conservation and management efforts can be improved by incorporating a multifaceted approach [3]. However, these efforts are complicated for highly mobile species, especially those which spend considerable time moving between areas of jurisdiction or in 'high-seas' fishing zones [4]. Understanding regional movements can help to identify areas of high use and thereby inform conservation efforts [5] and improve marine spatial planning for essential habitats [6,7]. ...
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Understanding space use and movement behavior can benefit conservation and management of species by identifying areas of high importance. However, this can be challenging for highly mobile species, especially those which use a wide range of habitats across ontogeny. The Bahamas is hypothesized to be an important area for tiger sharks, but the utility of the area for this species within the broader western North Atlantic is not fully understood. Therefore, we assessed (1) whether the area near Bimini serves as an important pupping location for tiger sharks, (2) their level of residency and site fidelity to the area, and (3) regional dispersal across ontogeny. Frequent captures of young of- year tiger sharks, as well as ultrasonography showing near-term and recently postpartum females supports the hypothesis that pupping occurs in the area. However, small juveniles had low overall recapture rates and sparse acoustic detections near Bimini, indicating they do not reside in the area for long or may suffer high natural mortality. Large juvenile and sexually mature tiger sharks had higher overall local residency, which increased during cooler water winter months. The probability of dispersal from Bimini increased for larger individuals. Repeated, long-term site fidelity was displayed by some mature females, with several returning to Bimini across multiple years. Satellite tracking showed that tiger sharks extensively used areas outside of The Bahamas, including traveling more than 12,000 km. Together, these results show that Bimini is an important area for tiger sharks, serving as a pupping ground, rather than a nursery ground, a finding which could be incorporated into future conservation and management efforts.
... They can record at very fine temporal scales (subsecond) and can be set to register oceanographic parameters such as water temperature or light levels. This information can be used to determine environmental preferences, assess behavioral patterns such as diel changes and seasonal migrations, or infer behavioral states such as foraging (Chapman et al. 2015;Queiroz et al. 2017Queiroz et al. , 2019. ...
Methods for Fish Biology, 2nd edition Chapter 16: Behavior Julianna P. Kadar, Catarina Vila Pouca, Robert Perryman, Joni Pini-Fitzsimmons, Sherrie Chambers, Connor Gervais, and Culum Brown doi: Kadar, J. P., C. V. Pouca, R. Perryman, J. Pini-Fitzsimmons, S. Chambers, C. Gervais, and C. Brown. 2022. Pages 593–642 in S. Midway, C. Hasler, and P. Chakrabarty, editors. Methods for fish biology, 2nd edition. American Fisheries Society, Bethesda, Maryland. Humans interact with fish in a wide variety of contexts. Fish are rapidly becoming the go-to model for medical research because of the conservative nature of vertebrate physiology. We catch and grow fish in captivity for human consumption and frequently rear fish for release into the wild either to supplement wild populations to enhance fisheries or as a conservation measure. In all cases, understanding fish behavior is vital whether you are interested in stock management, conservation biology, or animal welfare (Brown 2015). Gone are the days when fish were viewed as mindless automata. We now know that fish behavior is highly flexible, providing the plasticity to allow individuals to adjust to prevailing conditions or contexts (Bshary and Brown 2014). Their level of cognitive and behavioral sophistication is on par with the rest of the vertebrates (Bshary and Schäffer 2002; Vila Pouca and Brown 2018a; 2018b). Unsurprisingly, a change in behavior is often the first sign that something has shifted in the environment; thus, behavioral studies are at the forefront of environmental and ecotoxicological research (Brown 2012; Oulton et al. 2014). The massive diversity of fishes (currently more than 32,000 described species), and the range of niches they occupy, means that generalization is nearly impossible. Thankfully, the approaches for studying fish behavior are also many and varied and rapidly developing with changes in technology. Here we provide a brief overview of some of the emerging methods for studying fish behavior. We will not be reviewing fish behavior in general since this is the topic of multiple books (e.g., Magnhagen et al. 2008; Brown et al. 2011), nor will we be providing a general overview of how to study animal behavior. Such details can readily be found in any of the many excellent texts on animal behavior or behavioral ecology (Davies 1991; Dugatkin and Earley 2004; Alcock 2005; Goodenough et al. 2009). Many people study fish behavior under captive conditions where it is possible to control the environment and observe behaviors that can be attributed to specific cognitive processes. In most instances, it is simply a matter of refining the standard methods to suit the aquatic environment and the species of interest. The main difficulties of studying fish behavior arise when trying to observe them in their natural environment. The underwater world is not a place with which most people are comfortable or familiar. Humans can stay only so long in the watery world of fishes, so many of the methods we describe here attempt to overcome these problems by studying fish behavior remotely.
... Yet, SSF have been systematically overshadowed by the large-scale fisheries sector and largely understudied 11 . Most of the available information on the status of elasmobranch species and fishing impact is obtained from the large-scale fishery sector [12][13][14][15] . Much less is known about elasmobranchs and their interactions with SSF in coastal areas, which represent data-poor systems 5,10 . ...
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Elasmobranchs are heavily impacted by fishing. Catch statistics are grossly underestimated due to missing data from various fishery sectors such as smallscale fisheries. Marine Protected Areas are proposed as a tool to protect elasmobranchs and counter their ongoing depletion. We assess elasmobranchs caught in 1,256 fishing operations with fixed nets carried out in partially protected areas within Marine Protected Areas and unprotected areas beyond Marine Protected Areas borders at 11 locations in 6 Mediterranean countries. Twenty-four elasmobranch species were recorded, more than onethird belonging to the IUCN threatened categories (Vulnerable, Endangered, or Critically Endangered). Catches per unit of effort of threatened and data deficient species were higher (with more immature individuals being caught) in partially protected areas than in unprotected areas. Our study suggests that despite partially protected areas having the potential to deliver ecological benefits for threatened elasmobranchs, poor small-scale fisheries management inside Marine Protected Areas could hinder them from achieving this important conservation objective.
... Shark populations are particularly vulnerable to overfishing on account of slow growth rates, late age at sexual maturity and relatively low fecundity, which makes them more prone to extinction risk than most other marine fishes (Dulvy et al., 2014). Large declines in global abundance of oceanic pelagic sharks driven by overfishing have occurred over the past half century (Pacoureau et al., 2021) as a result of substantial overlap of preferred shark habitats co-occurring with industrialised fisheries, within which fishing-induced mortality is higher where spatial overlap is greater (Queiroz et al., 2019(Queiroz et al., , 2021. ...
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Groups of basking sharks engaged in circling behaviour are rarely observed and their function remains enigmatic in the absence of detailed observations. Here, underwater and aerial video recordings of multiple circling groups of basking sharks during late summer (August and September, 2016–2021) in the eastern north Atlantic Ocean showed groups numbering between 6 and 23 non‐feeding individuals of both sexes. Sharks swam slowly in a rotating ‘torus’ (diameter range: 17–39 m) with individuals layered vertically from the surface to a maximum depth of 16 m. Within a torus, sharks engaged in close‐following, echelon, close flank‐approach or parallel swimming behaviours. Measured shark total body lengths were 5.4 – 9.5 m (mean LT, 7.3 m ± 0.9 S.D.; median 7.2 m, n = 27), overlapping known lengths of sexually mature males and females. Males possessed large claspers with abrasions that were also seen on female pectoral fins. Female body coloration was paler than that of males, similar to colour changes seen during courtship and mating in other shark species. Individuals associated with most other members rapidly (within minutes) indicating toroidal behaviours facilitate multiple interactions. Sharks interacted through fin‐fin and fin‐body contacts, rolling to expose ventral surfaces to following sharks, and breaching behaviour. Toruses formed in late summer when feeding aggregations in zooplankton‐rich thermal fronts switched to non‐feeding following and circling behaviours. Collectively, our observations explain a courtship function for toruses. This study highlights northeast Atlantic coastal waters as critical habitat supporting courtship reproductive behaviour of endangered basking sharks, the first such habitat identified for this species globally. This article is protected by copyright. All rights reserved.
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It can be difficult to determine whether a prohibition to exploitation ensures effective conservation or recovery for species that remain exposed to fishing effort and other sources of mortality throughout their range. Here we used simulation modeling of four life history scenarios (different productivity and population size) to contextualize potential population response to multiple levels of mortality, using white sharks (Carcharodon carcharias) in South Africa as a case study. The species has been protected since 1991, yet substantial uncertainty about population dynamics persists and recent declines at two aggregation sites have renewed conservation concern. All scenarios indicated that annual removals in the 10s of individuals would substantially limit the potential for and magnitude of any abundance increase following prohibition. Because average known removals from the KwaZulu-Natal Sharks Board's Bather Protection Program have typically remained higher than these thresholds, they likely eliminated much of the conservation benefit derived from prohibition. The only life history scenario to achieve appreciable increase when simulated removals were similar to published averages assumed maturation occurred at a much younger age than currently understood. Our results demonstrate why general application of life history-based simulations can provide a useful mechanism to evaluate the biological plausibility of life history information and abundance trends, and to explore the scope for population response to recovery actions. For South Africa, our results suggest that even known levels of white shark removals, which likely underestimate total removals within their range, may be sufficient to drive abundance decline and new mitigation measures may be required to ensure population recovery.
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Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra-and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmo-branchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements.
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The importance and difficulty of large-scale quantitative analysis of fishing vessel footprints and fishing intensities with high resolution have received more and more attention and recognition in fishery research. In this study, a framework for identifying and analyzing fishing footprints and activities based on AIS data is proposed. The first step is the AIS data pre-processing. Through the screening and cleaning of AIS data, noise data such as non-fishing vessel trajectories are removed to retain only fishing vessel trajectories. The second step is the behavior detection of fishing vessels. Based on the proposed speed identification method, the trajectory of a fishing vessel is divided into three states: Fishing, stationary, and sailing. The third step is the calculation of fishing vessel activities. An adjacent point mean method is proposed to calculate the fishing time of each fishing point. In addition, two simple and efficient quantitative indicators, namely unit cell activity frequency (UCAF) and unit cell fishing time (UCFT), are proposed to quantify the activities of fishing vessels. The last step is the spatial and temporal analysis of fishing activities. The global Moran's index and Getis-Ord Gi* index are used to quantitatively describe the global spatio-temporal distribution and local spatio-temporal hotspots of fishing activities. Based on >130 million AIS data from 2015 to 2016, the footprints of fishing vessels in the waters of China's exclusive economic zone (EEZ) were analyzed and the 0.01° × 0.01° high-resolution fishing vessel activity distribution maps and fishing time distribution maps were generated. It is found that the footprints of fishing vessels in China's EEZ waters have a positive spatial correlation, and the areas with high fishing intensities are clustered in the coastal waters of Shandong Province, Zhejiang Province, Fujian Province and Guangdong Province. The research results can be used for fishing area identification, fishery policy making, and sustainable fisheries development.
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Amoroso et al. demonstrate the power of our data by estimating the high-resolution trawling footprint on seafloor habitat. Yet we argue that a coarser grid is required to understand full ecosystem impacts. Vessel tracking data allow us to estimate the footprint of human activities across a variety of scales, and the proper scale depends on the specific impact being investigated.
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Postwar growth of industrial fisheries catch to its peak in 1996 was driven by increasing fleet capacity and geographical expansion. An investigation of the latter, using spatially allocated reconstructed catch data to quantify “mean distance to fishing grounds,” found global trends to be dominated by the expansion histories of a small number of distant-water fishing countries. While most countries fished largely in local waters, Taiwan, South Korea, Spain, and China rapidly increased their mean distance to fishing grounds by 2000 to 4000 km between 1950 and 2014. Others, including Japan and the former USSR, expanded in the postwar decades but then retrenched from the mid-1970s, as access to other countries’ waters became increasingly restricted with the advent of exclusive economic zones formalized in the 1982 United Nations Convention on the Law of the Sea. Since 1950, heavily subsidized fleets have increased the total fished area from 60% to more than 90% of the world’s oceans, doubling the average distance traveled from home ports but catching only one-third of the historical amount per kilometer traveled. Catch per unit area has declined by 22% since the mid-1990s, as fleets approach the limits of geographical expansion. Allowing these trends to continue threatens the bioeconomic sustainability of fisheries globally.
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Full-subsets information theoretic approaches are becoming an increasingly popular tool for exploring predictive power and variable importance where a wide range of candidate predictors are being considered. Here, we describe a simple function in the statistical programming language R that can be used to construct, fit, and compare a complete model set of possible ecological or environmental predictors, given a re- sponse variable of interest and a starting generalized additive (mixed) model fit. Main advantages include not requiring a complete model to be fit as the starting point for candidate model set construction (meaning that a greater number of predictors can potentially be explored than might be available through functions such as dredge); model sets that include interactions between factors and continuous nonlinear pre- dictors; and automatic removal of models with correlated predictors (based on a user defined criterion for exclusion). The function takes continuous predictors, which are fitted using smoothers via either gam, gamm (mgcv) or gamm4, as well as factor vari- ables which are included on their own or as two- level interaction terms within the gam smooth (via use of the “by” argument), or with themselves. The function allows any model to be constructed and used as a null model, and takes a range of arguments that allow control over the model set being constructed, including specifying cyclic and linear continuous predictors, specification of the smoothing algorithm used, and the maximum complexity allowed for smooth terms. The use of the function is dem- onstrated via case studies that highlight how appropriate model sets can be easily constructed and the broader utility of the approach for exploratory ecology.
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Incidental catch of nontarget species (bycatch) is a major barrier to ecological and economic sustainability in marine capture fisheries. Key to mitigating bycatch is an understanding of the habitat requirements of target and nontarget species and the influence of heterogeneity and variability in the dynamic marine environment. While patterns of overlap among marine capture fisheries and habitats of a taxonomically diverse range of marine vertebrates have been reported, a mechanistic understanding of the real-time physical drivers of bycatch events is lacking. Moving from describing patterns toward understanding processes, we apply a Lagrangian analysis to a high-resolution ocean model output to elucidate the fundamental mechanisms that drive fisheries interactions. We find that the likelihood of marine megafauna bycatch is intensified in attracting Lagrangian coherent structures associated with submesoscale and mesoscale filaments, fronts, and eddies. These results highlight how the real-time tracking of dynamic structures in the oceans can support fisheries sustainability and advance ecosystem-based management.
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While the ecological impacts of fishing the waters beyond national jurisdiction (the “high seas”) have been widely studied, the economic rationale is more difficult to ascertain because of scarce data on the costs and revenues of the fleets that fish there. Newly compiled satellite data and machine learning now allow us to track individual fishing vessels on the high seas in near real time. These technological advances help us quantify high-seas fishing effort, costs, and benefits, and assess whether, where, and when high-seas fishing makes economic sense. We characterize the global high-seas fishing fleet and report the economic benefits of fishing the high seas globally, nationally, and at the scale of individual fleets. Our results suggest that fishing at the current scale is enabled by large government subsidies, without which as much as 54% of the present high-seas fishing grounds would be unprofitable at current fishing rates. The patterns of fishing profitability vary widely between countries, types of fishing, and distance to port. Deep-sea bottom trawling often produces net economic benefits only thanks to subsidies, and much fishing by the world’s largest fishing fleets would largely be unprofitable without subsidies and low labor costs. These results support recent calls for subsidy and fishery management reforms on the high seas.
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Abstract Whale sharks (Rinchodon typus) are found in shallow coastal and deep waters of tropical and warm temperate seas. Population genetic studies indicate high connectivity among populations, and an Indo-Pacific meta-population has been suggested with potential migrations among some ocean basins. Here, we present the satellite track of a trans-Pacific migration of a female whale shark, which we tagged at Coiba Island (Panama), and which travelled over 20,000 km from the Tropical Eastern Pacific (Panama) to the western Indo-Pacific (Mariana Trench) in 841 d, primarily via the North Equatorial Current. This finding illustrates the migratory pathway between two ocean basins and potential passageway to reach the Philippine Sea into the South China Sea.
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Designated large-scale marine protected areas (LSMPAs, 100,000 or more square kilometers) constitute over two-thirds of the approximately 6.6% of the ocean and approximately 14.5% of the exclusive economic zones within marine protected areas. Although LSMPAs have received support among scientists and conservation bodies for wilderness protection, regional ecological connectivity, and improving resilience to climate change, there are also concerns. We identified 10 common criticisms of LSMPAs along three themes: (1) placement, governance, and management; (2) political expediency; and (3) social-ecological value and cost. Through critical evaluation of scientific evidence, we discuss the value, achievements, challenges, and potential of LSMPAs in these arenas. We conclude that although some criticisms are valid and need addressing, none pertain exclusively to LSMPAs, and many involve challenges ubiquitous in management. We argue that LSMPAs are an important component of a diversified management portfolio that tempers potential losses, hedges against uncertainty, and enhances the probability of achieving sustainably managed oceans.
There have been efforts around the globe to track individuals of many marine species and assess their movements and distribution, with the putative goal of supporting their conservation and management. Determining whether, and how, tracking data have been successfully applied to address real-world conservation issues is, however, difficult. Here, we compile a broad range of case studies from diverse marine taxa to show how tracking data have helped inform conservation policy and management, including reductions in fisheries bycatch and vessel strikes, and the design and administration of marine protected areas and important habitats. Using these examples, we highlight pathways through which the past and future investment in collecting animal tracking data might be better used to achieve tangible conservation benefits.
Kroodsma et al. (Reports, 23 February 2018, p. 904) mapped the global footprint of fisheries. Their estimates of footprint and resulting contrasts between the scale of fishing and agriculture are an artifact of the spatial scale of analysis. Reanalyses of their global (all vessels) and regional (trawling) data at higher resolution reduced footprint estimates by factors of >10 and >5, respectively.
Understanding the distribution of fishing activity is fundamental to quantifying its impact on the seabed. Vessel monitoring system (VMS) data provides a means to understand the footprint (extent and intensity) of fishing activity. Automatic Identification System (AIS) data could offer a higher resolution alternative to VMS data, but differences in coverage and interpretation need to be better understood. VMS and AIS data were compared for individual scallop fishing vessels. There were substantial gaps in the AIS data coverage; AIS data only captured 26% of the time spent fishing compared to VMS data. The amount of missing data varied substantially between vessels (45-99% of each individuals' AIS data were missing). A cubic Hermite spline interpolation of VMS data provided the greatest similarity between VMS and AIS data. But the scale at which the data were analysed (size of the grid cells) had the greatest influence on estimates of fishing footprints. The present gaps in coverage of AIS may make it inappropriate for absolute estimates of fishing activity. VMS already provides a means of collecting more complete fishing position data, shielded from public view. Hence, there is an incentive to increase the VMS poll frequency to calculate more accurate fishing footprints. © International Council for the Exploration of the Sea 2017. All rights reserved.