Article

Range extension of the endangered great hammerhead shark Sphyrna mokarran in the Northwest Atlantic: Preliminary data and significance for conservation

January 2011
Endangered Species Research 13(2):111-116

DOI:10.3354/esr00332

Authors:

Neil Hammerschlag

Shark Research Foundation

Austin J Gallagher

Beneath the Waves

We provide pilot data from a satellite-tracked great hammerhead shark Sphyrna mokarran in the Atlantic, representing the first such data on this species in the literature. The 250 cm shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic international waters of the Northwest Atlantic. When compared to the primary literature, this migration represented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.

Cornuda gigante

Chapter

Full-text available

Aug 2022

Una revisión de la ecología y biología pesquera de la cornuda gigante (Sphyrna mokarran), con especial énfasis en el Océano Atlántico y mares adyacentes.

Great hammerhead

Chapter

Full-text available

Aug 2022

A review of the ecology and fishery biology of the great hammerhead shark (Sphyrna mokarran), with a special focus on the Atlantic Ocean and adjacent seas.

Identifying Suitable Habitat for Three Highly Migratory Sharks (Great Hammerhead, Tiger, and Bull) and Assessing Their Spatial Vulnerability to Commercial Longline Fishing in the Southwest Atlantic Ocean and Gulf of Mexico

Thesis

Dec 2016

Hannah Calich

Aquatic highly migratory species (HMS) are economically and ecologically important, however, their highly migratory nature makes them difficult to study and thus there are knowledge gaps relating to their movement and habitat use patterns. Highly migratory sharks are likely to interact with commercial longline fishing gear and be caught as target or bycatch, which can threaten their populations. Understanding the environmental factors that influence and drive the movements of highly migratory sharks may help researchers better predict their presence and subsequently identify areas where they are vulnerability to fisheries. Here I evaluated the overlap between habitat suitability and gear restricted zones for three co-occurring apex predatory sharks in the Southwest Atlantic Ocean and Gulf of Mexico (great hammerhead Sphyrna mokarran, tiger Galeocerdo cuvier, and bull sharks Carcharhinus leucas) to identify areas in this region where these species are vulnerable to and protected from commercial longline fishing. This research was accomplished in three integrated steps. First, I reviewed and summarized what is known about the environmental drivers of great hammerhead, tiger, and bull shark habitat use and movement patterns. Second, I used the results of this review to parameterize and subsequently generate habitat suitability models for these three species. Third, I used these models to spatially compare where each species’ highly suitable habitat overlaps with longline gear restricted areas within the Southwest Atlantic Ocean and Gulf of Mexico, to identify regions where these species were both vulnerable to and protected from longline fishing gear. The results of this thesis have implications to the management of these species as well as for the conservation of other highly migratory aquatic species.

Philopatry and Regional Connectivity of the Great Hammerhead Shark, Sphyrna mokarran in the U.S. and Bahamas

Article

Full-text available

Jan 2017

A thorough understanding of movement patterns of a species is critical for designing effective conservation and management initiatives. However, generating such information for large marine vertebrates is challenging, as they typically move over long distances, live in concealing environments, are logistically difficult to capture and, as upper-trophic predators, are naturally low in abundance. Large-bodied, broadly distributed tropical shark typically restricted to coastal and shelf habitats, the great hammerhead shark Sphyrna mokarran epitomizes such challenges. Highly valued for its fins (in target and incidental fisheries), it suffers high bycatch mortality coupled with fecundity conservative life history, and as a result, is vulnerable to over-exploitation and population depletion. Although there are very little species-specific data available, the absence of recent catch records give cause to suspect substantial declines across its range. Here, we used biotelemetry techniques (acoustic and satellite), conventional tagging, laser-photogrammetry, and photo-identification to investigate the level of site fidelity/residency for great hammerheads to coastal areas in the Bahamas and U.S., and the extent of movements and connectivity of great hammerheads between the U.S. and Bahamas. Results revealed large-scale return migrations (3030 km), seasonal residency to local areas (some for 5 months), site fidelity (annual return to Bimini and Jupiter for many individuals) and numerous international movements. These findings enhance the understanding of movement ecology in great hammerhead sharks and have potential to contribute to improved conservation and management.

Physiological stress response, reflex impairment, and survival of five sympatric shark species following experimental capture and release

Article

Jan 2014

In many fisheries, some component of the catch is usually released. Quantifying the effects of capture and release on fish survival is critical for determining which practices are sustainable, particularly for threatened species. Using a standardized fishing technique, we studied sublethal (blood physiology and reflex impairment assessment) and lethal (post-release mortality with satellite tags) outcomes of fishing stress on 5 species of coastal sharks (great hammerhead, bull, blacktip, lemon, and tiger). Species-specific differences were detected in whole blood lactate, partial pressure of carbon dioxide, and pH values, with lactate emerging as the sole parameter to be significantly affected by increasing hooking duration and shark size. Species-specific differences in reflex impairment were also found; however, we did not detect any significant relationships between reflex impairment and hooking duration. Taken together, we ranked each species according to degree of stress response, from most to least disturbed, as follows: hammerhead shark > blacktip shark > bull shark > lemon shark > tiger shark. Satellite tagging data revealed that nearly 100% of all tracked tiger sharks reported for at least 4 wk after release, which was significantly higher than bull (74.1%) and great hammerhead (53.6%) sharks. We discuss which mechanisms may lead to species-specific differences in sensitivity to fishing and suggest that observed variation in responses may be influenced by ecological and evolutionary phenomena. Moreover, our results show that certain species (i.e. hammerhead sharks in this study) are inherently vulnerable to capture stress and mortality resulting from fisheries interactions and should receive additional attention in future conservation strategies.

First insights into the population characteristics and seasonal occurrence of the great hammerhead shark, Sphyrna mokarran (Rüppell, 1837) in the Western Tuamotu archipelago, French Polynesia

Article

Full-text available

Aug 2023

The occurrence and seasonality of the Critically Endangered great hammerhead shark, Sphyrna mokarran, is data deficient in the Central Pacific region. Using photo-identification and laser-photogrammetry, we describe the seasonal population of great hammerhead sharks in the Tiputa pass (Rangiroa atoll) and Tuheiava pass (Tikehau atoll) in the Tuamotu archipelago of French Polynesia. During the austral summer of 2020 and 2021, we recorded a female-biased aggregation of at least 55 individuals (54 females; 1 unknown sex), representing an unprecedented number of S. mokarran in one study. All measured sharks were likely mature with pre-caudal lengths ranging from 147 cm to 297 cm (n = 35). Videos from citizen scientists recorded over a 15-year period enable us to identify 30 additional individuals between 2006 and 2019, with strong evidence of sexual segregation during the year. Our findings revealed seasonal residency (n = 32) of up to 6 days/month and for up to 5 months at the study site during the austral summer. We also demonstrated site fidelity with 32 individuals returning to the same atoll for up to 12 years between the first and last sighting, and with limited evidence of connectivity between the two sites. Our analysis also provides preliminary insight into the environmental factors driving S. mokarran aggregation in the Tiputa pass, suggesting a marked influence of the lunar cycle and of ocellated eagle rays (Aetobatus ocellatus) abundance. This study, conducted in situ with non-invasive methods offers a unique opportunity to study a great hammerhead shark population in a near-pristine ecosystem and provides important life-history elements for the Central Pacific region.

Global tracking of shark movements, behaviour and ecology: A review of the renaissance years of satellite tagging studies

Article

Jan 2023
J EXP MAR BIOL ECOL

Satellite telemetry as a tool in marine ecological research continues to adapt and grow and has become increasingly popular in recent years to study shark species on a global scale. A review of satellite tag application to shark research was published in 2010, provided insight to the advancements in satellite shark tagging, as well as highlighting areas for improvement. In the years since, satellite technology has continued to advance, creating smaller, longer lasting, and more innovative tags, capable of expanding the field. Here we review satellite shark tagging studies to identify early successes and areas for rethinking moving forward. Triple the amount of shark satellite tagging studies have been conducted during the decade from 2010 to 2020 than ever before, tracking double the number of species previously tagged. Satellite telemetry has offered increased capacity to unravel ecological questions including predator and prey interactions, migration patterns, habitat use, in addition to monitoring species for global assessments. However, <17% of the total reviewed studies directly produced results with management or conservation outcomes. Telemetry studies with defined goals and objectives produced the most relevant findings for shark conservation, most often in tandem with secondary metrics such as fishing overlap or management regimes. To leverage the power of telemetry for the benefit of shark species, it remains imperative to continue improvements to tag function and maximize the outputs of tagging efforts including increasing data sharing capacity and standardization across the field, as well as spatial and species coverage. Ultimately, this review offers a status report of shark satellite tagging and the ways in which the field can continue to progress.

SPECIES COMPOSITION, COMMERCIAL LANDINGS, DISTRIBUTION AND SOME ASPECTS OF BIOLOGY OF SHARK (CLASS PISCES) OF PAKISTAN: PELAGIC SHARKS

Article

Full-text available

Jan 2022

Sharks are important part of coastal and offshore pelagic ecosystems and being caught mainly as bycatch of tuna gillnet fishing operations. There are 12 species of pelagic sharks caught in Pakistan which belongs to 5 families and 7 genera. Silky shark (Carcharhinus falciformis) is the most dominating pelagic shark followed by shortfin mako (Isurus oxyrhinchus) and pelagic thresher shark (Alopias pelagicus). Blue shark (Prionace glauca) is the rarest pelagic shark that is seldom caught by tuna gillnet vessels. There is general concern regarding over-exploitation of pelagic sharks globally as well as in Pakistan, as some species including scalloped hammerhead (Sphyrna lewini) are disappearing very fast and it is feared that they may become extinct in near future. Although most pelagic sharks are included in the Appendix-II of CITES which restricts their global trade as well as there is a ban on their catching, landing, marketing and trade has been imposed through national fisheries legislations, however, there is no effective implementation mechanism in place for ensuring these restrictions in Pakistan. Exploitation of pelagic sharks, therefore, continue unabated in Pakistan as well as some other regional countries which may lead to their disappearance from commercial catches or may ends up in regional or global extinction.

Bonnethead (Sphyrna tiburo) use of Gray’s Reef National Marine Sanctuary.

Technical Report

Full-text available

Sep 2019

This study analyzed nearly ten years of acoustic telemetry monitoring at Gray’s Reef National Marine Sanctuary, to understand its role in fish movements along the U.S. Atlantic coast. Designated in 1981, Gray’s Reef lies 19 miles off the coast of Georgia where water depths are ~60-70 feet and the habitat is comprised of a mosaic of ledges, flat live-bottom, and unconsolidated sediments. Biotic communities there are seasonally influenced by warm waters from the south and cooler temperate waters from the north. The unique geographic location and complex habitat provided by Gray’s Reef attracts many transient fish species, however a quantitative understanding of the timing and frequency of their presence is lacking. Here, we identify all transient species that were detected by telemetry receivers at the sanctuary from 2008 to 2017, summarize the timing and seasonality of their visits, and discuss their connectivity to the broader coastal Atlantic ecosystem.

Molecular identification of sharks from the genus Sphyrna (Elasmobranchii: Chondrichthyes) in Maranhão Coast (Brazil)

Article

Full-text available

Mar 2024
Braz J Biol

Sharks of the genus Sphyrna are under intense exploitation globally. In Brazil’s northern coast, this genus represents a high proportion of fisheries landings and comprises four species. However, due to difficulty of specific identification when specimens are landed, most of the records are limited to the genus level. Here we analyzed the effectiveness of ITS2 (Internal Transcribed Spacer 2 of rDNA) fragment length protocol (Abercrombie et al., 2005) for identifying hammerhead shark species, comparing with the analysis of COI (Cytochrome oxidase subunit I) and ITS2 sequences. We evaluated samples of muscle tissue acquired in the main fishing ports of Maranhão: Carutapera, Raposa e Tutóia. Sampling was conducted between March 2017 to March 2018 and complemented with material deposited in collection (2015). COI results indicated the occurrence of endangered species which are prohibited to be landed. These include Sphyrna mokarran (67%), S. lewini (15%), S. tudes (3%), and S. tiburo (15%). For the ITS2 marker, we investigated the optimization of the protocol developed by Abercrombie (2005) for to improve the use in this geographical area througout design of a new primers.

Trophic ecology shapes spatial ecology of two sympatric predators, the great hammerhead shark (Sphyrna mokarran) and bull shark (Carcharhinus leucas)

Article

Full-text available

Nov 2023

Information on how the trophic ecology of predators shapes their movement patterns and space-use is fundamental to understanding ecological processes across organisational levels. Despite this, studies combining spatial and trophic ecology to determine how prey preference and/or resource availability shape space use are lacking in marine predators as these can occur at low density and are often difficult to track over extended periods. Furthermore, many exhibit behavioural variability within species and among closely related, sympatric species adding further complexity. We applied a context-focused, multi-method approach to the understudied great hammerhead shark (Sphyrna mokarran) to test if movement and home ranges relate to prey preference and availability. Movement data from satellite and acoustic telemetry in Queensland, Australia, were combined with stable-isotope analysis, drone surveys, and videos of hunting behaviour. Limited dispersal, and small home ranges in S. mokarran were linked to trophic specialisation on stingray prey. Drone surveys and videos showed predation events on stingrays and demonstrated high, year-round availability of this prey in shallow, inshore habitats, which may allow the majority of S. mokarran to remain resident. This affinity for inshore habitats suggests that critical life-history requirements are performed over local or regional scales, although some larger movements were evident. These results were interpreted in comparison to the well-studied bull shark (Carcharhinus leucas), which showed reliance on pelagic food webs. Carcharhinus leucas had high individual variability in movement, with both large-scale migrations and residency. This could indicate that only some individuals are locally sustained on dynamic, pelagic food webs, while others undergo large-scale excursions over distant habitats. The specialised foraging of S. mokarran indicates they play an apex predator role in shallow, inshore habitats, potentially shaping space-use, and foraging behaviour of batoids. As inshore habitats are disproportionately affected by anthropogenic stressors, S. mokarran’s trophic specialisation and limited demographic connectivity may make the species particularly vulnerable to anthropogenic threats.

Conservación, uso y aprovechamiento sustentable de tiburones mexicanos listados en la CITES

Book

Full-text available

Nov 2022

La presente obra es resultado de la participación de expertos provenientes del sector gubernamental, académico y privado, con un total de 36 autores que compilaron información contenida en investigaciones científicas y material bibliográfico (tesis de posgrado, libros y artículos científicos). Sin duda, el contenido facilitará significativamente la labor de la Autoridad Científica cites de México, pues aporta elementos para analizar y emitir DENP de manera oportuna, además de apoyar a las autoridades Administrativa y de Aplicación de la Ley de México para su efectiva implementación de la cites, cuyo tratado internacional es uno de los más efectivos para la gestión de nuestro patrimonio natural, del cual dependen la subsistencia y modos de vida en el largo plazo de las comunidades pesqueras.

Carcharhinus falciformis (Müller y Henle, 1839) Tiburón sedoso, silky shark

Chapter

Full-text available

Nov 2022

El Tiburón sedoso, Carcharhinus falciformis, tiene una distribución circunglobal, se localiza tanto en el Atlántico Occidental y Pacífico Oriental. En México, C. falciformis se encuentra en el Pacífico Mexicano, incluyendo el Golfo de California, así como en el litoral del Golfo de México y Mar Caribe. Los tiburones sedosos habitan generalmente plataformas continentales e insulares, pendientes e incluso se han registrado ocasionalmente en aguas someras (18 m) hasta profundidades de 550 m. La edad máxima estimada para C. falciformis varía considerablemente para las distintas poblaciones, desde ocho a 11 años hasta más de 30 años. Los parámetros de crecimiento son también altamente variables, con longitudes asintóticas que van de 240 cm a 340 cm de LT (longitud total). El Tiburón sedoso presenta una estrategia de reproducción vivípara placentaria, con un periodo de gestación de 11 a 12 meses y una fecundidad de una a 25 crías con tallas entre 50 y 83 cm (LT). En el 2014 C. falciformis fue enlistada en el Apéndice II de la Convención sobre la Conservación de las Especies Migratorias de Animales Silvestres (CMS) y en 2017 se incluyó en el Apéndice II de la Convención sobre el Comercio Internacional de Especies Amenazadas de Fauna y Flora Silvestres (CITES). En México, la falta de información de captura y esfuerzo pesquero específico ha complicado la evaluación del estado de las poblaciones de tiburones, en donde C. falciformis no es la excepción. Por ello, es necesario hacer registros específicos de las capturas, esfuerzo pesquero, datos biológicos-pesqueros, con el fin de realizar análisis demográficos y proyecciones del efecto de la pesca en el stock e identificar áreas de importancia para su protección.

Vertical space use and thermal range of the great hammerhead (Sphyrna mokarran), (Rüppell, 1837) in the western North Atlantic

Article

Full-text available

Sep 2022
J FISH BIOL

The great hammerhead (Sphyrna mokarran) is a highly mobile, large‐bodied shark primarily found in coastal‐pelagic and semi‐oceanic waters across a circumtropical range. It is a target or by‐catch species in multiple fisheries, and as a result, rapid population declines have occurred in many regions. These declines have contributed to the species being assessed as globally critically endangered on the IUCN Red List. Although conservation and management measures have yielded promising results in some regions, such as the United States, high levels of at‐vessel and post‐release mortality remain a major concern to the species population recovery. This examined the vertical space use and thermal range of pop‐off archival satellite–tagged S. mokarran in the western North Atlantic Ocean, expanding the understanding of the ecological niche of this species and providing insight into by‐catch mitigation strategies for fisheries managers. The results showed that S. mokarran predominantly used shallow depths (75% of records <30 m) and had a narrow temperature range (89% of records between 23 and 28°C). Individual differences in depth use were apparent, and a strong diel cycle was observed, with sharks occupying significantly deeper depths during the daytime. Furthermore, two individuals were confirmed pregnant with one migrating from the Bahamas to South Carolina, U.S.A., providing further evidence of regional connectivity and parturition off the U.S. East Coast. The findings suggest that S. mokarran may be vulnerable to incidental capture in the western North Atlantic commercial longline fisheries due to substantial vertical overlap between the species and the gear. The results can be incorporated into conservation and management efforts to develop and/or refine mitigation measures focused on reducing the by‐catch and associated mortality of this species, which can ultimately aide S. mokarran population recovery in areas with poor conservation status.

Urban sharks: residency patterns of marine top predators in relation to a coastal metropolis

Article

Full-text available

Jun 2022

Understanding and ultimately predicting how marine organisms will respond to urbanization is central for effective wildlife conservation and management in the Anthropocene. Sharks are upper trophic level predators in virtually all marine environments, but if and how their behaviors are influenced by coastal urbanization remains understudied. Here, we examined space use and residency patterns of 14 great hammerheads Sphyrna mokarran , 13 bull sharks Carcharhinus leucas , and 25 nurse sharks Ginglymostoma cirratum in proximity to the coastal metropolis of Miami, Florida, using passive acoustic telemetry. Based on the terrestrial urban carnivore literature, we predicted sharks would exhibit avoidance behaviors of areas close to Miami, with residency patterns in these urban areas increasing during periods of lower human activity, such as during nocturnal hours and weekdays, and that dietary specialists (great hammerhead) would exhibit comparatively lower affinity towards highly urbanized areas relative to dietary generalists (bull and nurse shark). However, we did not find empirical support for these predictions. Space use patterns of tracked sharks were consistent with that of ‘urban adapters’ (species that exhibit partial use of urban areas). Modeling also revealed that an unmeasured spatial variable was driving considerable shark residency in areas exposed to high urbanization. We propose several hypotheses that could explain our findings, including food provisioning from shore-based activities that could be attracting sharks to urban areas. Ultimately, the lack of avoidance of urban areas by sharks documented here, as compared to terrestrial carnivores, should motivate future research in the growing field of urban ecology.

Identification of the southernmost aggregation of scalloped hammerhead sharks ( Sphyrna lewini ) in Australia

Article

Full-text available

Feb 2022

Scalloped hammerheads (Sphyrna lewini) occur in tropical to subtropical waters across all ocean basins and are globally assessed as Critically Endangered by the International Union for the Conservation of Nature. In Australia, scalloped hammerheads range from Sydney, New South Wales (34° S; 151° E), around northern Australia, down to Geographe Bay, Western Australia (33° S; 115° E). However, in Western Australia, the species has rarely been recorded south of Jurien Bay (30° S; 115° E). We report a recurrent aggregation of scalloped hammerheads within the Shoalwater Islands Marine Park (32° S; 115° E), 240 km south of Jurien Bay, observed from drone footage collected during the 2019 and 2020 Austral summers. These new records challenge previous understanding of the distributional range of this Critically Endangered species and prompt questions about the adequacy of current protection measures. Scalloped hammerheads are amongst the most threatened of vertebrates globally and are listed as Critically Endangered by the International Union for the Conservation of Nature. Using aerial drones we report the southernmost aggregation of scalloped hammerheads in Australia, potentially extending the known distribution of the species. These new records challenge previous understanding of the distributional range of the species and prompt questions about the adequacy of current protection measures.

Comprehensive analytical approaches reveal species‐specific search strategies in sympatric apex predatory sharks

Article

Full-text available

Sep 2021
ECOGRAPHY

Animals follow specific movement patterns and search strategies to maximize encounters with essential resources (e.g. prey, favourable habitat) while minimizing exposures to suboptimal conditions (e.g. competitors, predators). While describing spatiotemporal patterns in animal movement from tracking data is common, understanding the associated search strategies employed continues to be a key challenge in ecology. Moreover, studies in marine ecology commonly focus on singular aspects of species' movements, however using multiple analytical approaches can further enable researchers to identify ecological phenomena and resolve fundamental ecological questions relating to movement. Here, we used a set of statistical physics‐based methods to analyze satellite tracking data from three co‐occurring apex predators (tiger, great hammerhead and bull sharks) that predominantly inhabit productive coastal regions of the northwest Atlantic Ocean and Gulf of Mexico. We analyzed data from 96 sharks and calculated a range of metrics, including each species' displacements, turning angles, dispersion, space‐use and community‐wide movement patterns to characterize each species' movements and identify potential search strategies. Our comprehensive approach revealed high interspecific variability in shark movement patterns and search strategies. Tiger sharks displayed near‐random movements consistent with a Brownian strategy commonly associated with movements through resource‐rich habitats. Great hammerheads showed a mixed‐movement strategy including Brownian and resident‐type movements, suggesting adaptation to widespread and localized high resource availability. Bull sharks followed a resident movement strategy with restricted movements indicating localized high resource availability. We hypothesize that the species‐specific search strategies identified here may help foster the co‐existence of these sympatric apex predators. Following this comprehensive approach provided novel insights into spatial ecology and assisted with identifying unique movement and search strategies. Similar future studies of animal movement will help characterize movement patterns and also enable the identification of search strategies to help elucidate the ecological drivers of movement and to understand species' responses to environmental change.

The Drone Revolution of Shark Science: A Review

Article

Full-text available

Jan 2021

Over the past decade, drones have become a popular tool for wildlife management and research. Drones have shown significant value for animals that were often difficult or dangerous to study using traditional survey methods. In the past five years drone technology has become commonplace for shark research with their use above, and more recently, below the water helping to minimise knowledge gaps about these cryptic species. Drones have enhanced our understanding of shark behaviour and are critically important tools, not only due to the importance and conservation of the animals in the ecosystem, but to also help minimise dangerous encounters with humans. To provide some guidance for their future use in relation to sharks, this review provides an overview of how drones are currently used with critical context for shark monitoring. We show how drones have been used to fill knowledge gaps around fundamental shark behaviours or movements, social interactions, and predation across multiple species and scenarios. We further detail the advancement in technology across sensors, automation, and artificial intelligence that are improving our abilities in data collection and analysis and opening opportunities for shark-related beach safety. An investigation of the shark-based research potential for underwater drones (ROV/AUV) is also provided. Finally, this review provides baseline observations that have been pioneered for shark research and recommendations for how drones might be used to enhance our knowledge in the future.

Bioaccumulation of organochlorine compounds in large, threatened elasmobranchs off northern New South Wales, Australia

Article

Jan 2019
MAR POLLUT BULL

Persistent organic pollutants (POPs) include polychlorinated biphenyls (PCBs) dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB), which are resistant to biodegradation and therefore accumulate in the marine environment. In Australia, POPs occur in high concentrations primarily in coastal water near farming regions and urban centres. From contaminated sediments and biota, POPs are transferred and biomagnified in larger marine organisms. We quantified POPs concentrations in 57 individuals from ten species of sharks and rays caught in bather-protection gillnets deployed off northern New South Wales, Australia. Polychlorinated biphenyls, DDTs and HCB were detected in all species. For some individuals, concentrations were at levels known to have deleterious sub-lethal effects. Overall, the POP concentrations analysed in this study were comparable to those in similar species from more polluted regions, and may have negative impacts on longer-term health. Future research is warranted to investigate spatio-temporal patterns of species-specific contaminant loads and their implications.

Overlap between highly suitable habitats and longline gear management areas reveals vulnerable and protected regions for highly migratory sharks

Article

Aug 2018

Highly migratory species (e.g. sharks, tunas, turtles, cetaceans) present unique conservation management challenges due to their wide-ranging movements. Consequently, the extent to which management areas protect habitats for highly migratory species is often unknown. Within the southeast region of the USA’s exclusive economic zone, highly migratory sharks are target and/or bycatch species in pelagic and bottom longline fisheries. Here, we developed maximum entropy habitat suitability models for great hammerhead sharks Sphyrna mokarran, tiger sharks Galeocerdo cuvier, and bull sharks Carcharhinus leucas within the southeast region based on satellite tag (n = 96) and remotely sensed environmental data. Modeled highly suitable habitats were compared to longline gear management areas to determine what proportion of these habitats are protected from, and vulnerable to, longline fisheries. The percentages of highly suitable habitats overlapping with longline management areas varied by species and season (78% warm, 36% cool season for great hammerhead sharks; 48% warm, 79% cool for tiger sharks; and 2% warm, 100% cool for bull sharks). Highly suitable great hammerhead and tiger shark habitats were relatively well protected from pelagic longline fisheries yet vulnerable to bottom longline fisheries. Additionally, both species were vulnerable to pelagic and bottom longline fisheries off southwestern Florida; thus, extending gear restrictions to this area may benefit both species. Bull shark highly suitable habitats were only well protected from longline gear during the cool season. These results demonstrate how habitat suitability modeling can be used to help assess the efficacy of spatial management strategies and inform conservation plans for highly migratory species.

Double tagging clarifies post-release fate of great hammerheads (Sphyrna mokarran)

Article

Full-text available

Dec 2017

Abstract Background Biotelemetry applications have advanced our understanding of many highly migratory species, but present a challenge for species that suffer high capture and/or post-release stress. Failing to accurately characterize post-release fate can obfuscate our understanding of animal movement patterns and complicate the development of effective conservation and management plans. The great hammerhead (Sphyrna mokarran) is a long-lived, highly migratory shark listed by the International Union for the Conservation of Nature as Endangered. Accordingly, we used a combination of tags designed to report horizontal position estimates and verify post-release fate, to examine movements of great hammerheads in the northern Gulf of Mexico. Results Between May and September 2016, three individuals (one male and two females) were equipped with both fin-mounted smart position and temperature transmitting (SPOT) tags and survivorship pop-off archival tags (sPAT) to provide information on post-release fate. Tagged sharks measured 187 (F), 203 (M), and 250 (M) cm total length. All three sharks surfaced daily, yet individuals showed variability in vertical habitat use, with maximum daily depths ranging from 5 to 98 m. A single fin-mounted SPOT tag, attached to the smallest of the three sharks, reported position estimates over an 81-day period and moved a straight-line distance of approximately 400 km; however, the other two fin-mounted SPOT tags failed to generate position estimates. All three sPAT tags indicated post-release survival. Final positions of the sPAT tags from the two largest sharks suggested restricted horizontal movements (

Integrating reflexes with physiological measures to evaluate coastal shark stress response to capture

Article

Nov 2017

In both commercial and recreational fisheries, sharks are captured and released alive to comply with regulations or due to low economic value or voluntary conservation ethic. As a result, understanding the physiological and behavioural responses of sharks to capture stress is important for determining subsequent effects of fisheries interactions on a species-specific basis, as well as for identifying factors that influence mortality. Here, we employed a suite of conventional blood physiology endpoints (glucose, lactate, and haematocrit) integrated with assessments of reflex impairment on blacktip (Carcharhinus limbatus), great hammerhead (Sphyrna mokarran), nurse (Ginglymostoma cirratum) and sand-bar sharks (Carcharhinus plumbeus) captured via experimental drumline gear. We documented a wide range of species-specific differences in all parameters assessed, with nurse sharks consistently having the lowest relative levels of physiological disturbance and reflex impairment; and with great hammerheads exhibiting the highest level of physiological disturbance and reflex impairment, suggesting higher vulnerability to fishing. In general, increases in lactate were positively associated with hook time and correlated with reflex impairment assessment. Moreover, reflex indices showed significant impairment with hook time, with the "jaw" reflex emerging as the most potential predictor of disturbance. Our study results connect previously reported species-specific at-vessel and post-release mortality rates to their physiological disturbance and reflex impairment.

The sharks and rays of the Solomon Islands: a synthesis of their biological diversity, values and conservation status

Article

Full-text available

Oct 2017

Sharks and rays are facing increasing anthropogenic pressure globally, including in the Pacific. However, data on their status and biodiversity are lacking for many Pacific Large Ocean Island States. This study aimed to construct a species checklist for the sharks and rays occurring in the Solomon Islands, review the human interactions with these species, and present a synthesis of their conservation status. Given the paucity of available data, a wide range of data sources were used including fisheries data, citizen science, and ethnobiological studies. Results were validated through a review process involving expert informants. Fifty sharks and rays were identified from the Solomon Islands, of which 20 are assessed as Vulnerable or Endangered on the IUCN Red List, 10 in the Convention on International Trade in Endangered Species, and 11 in the Convention for Migratory Species. The checklist also presents an eastwards range extension for the Endangered dwarf sawfish Pristis clavata. Fishing appears to be the main impact, though impacts from habitat loss and degradation are possible. This study provides a systematic synthesis and review of the biological diversity, uses, and cultural significance of Solomon Islands sharks and rays, and describes a process for assembling species checklists and reviews in data-poor contexts. However, this synthesis is based on limited information and a complete assessment of shark and ray status in the Solomon Islands will require primary fieldwork.

The contemporary economic value of elasmobranchs in The Bahamas: Reaping the rewards of 25years of stewardship and conservation

Article

Full-text available

Mar 2017
BIOL CONSERV

Elasmobranch populations in The Bahamas offer a unique juxtaposition to the widespread decline of many species around the world, largely due to management and conservation initiatives implemented over the last 25 years. Several industries have been built around the diverse and abundant elasmobranch assemblages found in The Bahamas, however a comprehensive assessment of the non-consumptive economic value of this resource has yet to be undertaken. In this study, we identified various sectors that benefit from elasmobranch populations in The Bahamas, which included tourism, film and television and research. We incorporated data from operator and participant surveys, government sources and information available on the Internet to calculate the economic value and location of these various sectors. This study establishes The Bahamas dive industry as the largest in the world, contributing approximately $113.8 million USD annually to the Bahamian economy in direct and value added expenditures. Elasmobranch tourism generated 99% of the total revenue, and the balance generated by film and television and research. The relative economic importance of shark diving was greater in economically disadvantaged out-islands where specific charismatic species are sought. This was also in locations where a large proportion of the revenue generated by those activities does not enter the Bahamian economy. The sustained national stewardship demonstrated by the Bahamian government will ensure that this important economic resource continues to be productive, but also highlights the need for regional Caribbean-wide commitment to the management of highly migratory species that are important to many economically depressed areas of The Bahamas.

Use of marine protected areas and exclusive economic zones in the subtropical western North Atlantic Ocean by large highly mobile sharks

Article

Full-text available

Feb 2016

Study aim and location: Many populations of highly mobile marine fishes, including large sharks, are experiencing declines. The benefits of spatial management zones, such as marine protected areas (MPAs), for such animals are unclear. To help fill this knowledge gap, we examined core habitat use areas (CHUAs) for bull (Carcharhinus leucas), great hammerhead (Sphyrna mokarran) and tiger sharks (Galeocerdo cuvier) in relation to specific MPAs and exclusive economic zones (EEZs) in the western North Atlantic Ocean. Methods: Bull, great hammerhead and tiger sharks (N = 86 total) were satellite tagged and tracked in southern Florida and the northern Bahamas between 2010 and 2013. Filtered and regularized positions from Argos locations of tag transmissions were used to generate CHUAs for these sharks. Overlaps of CHUAs with regional protected areas and exclusive economic management zones were quantified to determine the proportion of each tracked shark’s CHUA under spatial protection from exploitation. Results: A total of 0%, 17.9% and 34.7% of the regional CHUAs for tracked bull, great hammerhead and tiger sharks, respectively, were fully protected from exploitation in the study area. Main conclusions: Expansion of protected areas to include U.S. territorial waters would effectively protect 100% of the CHUAs for all tracked sharks in the study area. This finding is particularly significant for great hammerhead sharks, which are currently overfished, vulnerable to bycatch mortality and are the focus of strident regional conservation efforts. These findings also provide a means to inform decision makers and marine conservation planning efforts as to the types of management actions available and potential efficacy of spatial protections for these marine predators.

A minimally invasive technique to assess several life-history characteristics of the endangered great hammerhead shark Sphyrna mokarran

Article

Feb 2016
J FISH BIOL

A dorsal-fin photo-identification technique paired with a non-invasive parallel laser photogrammetry technique was used to non-invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean±s.d. pre-caudal length: 220⋅82±13⋅66 cm; mean±s.d. cephalofoil width: 71⋅38±7⋅94 cm) were identified using dorsal-fin photo-identification, with a mean±s.d. shark re-sighting frequency of 4⋅05±3⋅06 at-sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser pho- togrammetry and dorsal-fin photo-identification may be a plausible multi-year approach to aid in non-invasively determining the growth rate and inter-annual site fidelity of these animals.

Ocean-wide tracking of pelagic sharks reveals extent of overlap with longline fishing hotspots

Article

Full-text available

Jan 2016

Significance Shark populations are declining worldwide because of overexploitation by fisheries with unknown consequences for ecosystems. Although the harvest of oceanic sharks remains largely unregulated, knowing precisely where they interact with fishing vessels will better aid their conservation. We satellite track six species of shark and two entire longline fishing vessel fleets across the North Atlantic over multiple years. Sharks actively select and aggregate in space-use “hotspots” characterized by thermal fronts and high productivity. However, longline fishing vessels also target these habitats and efficiently track shark movements seasonally, leading to an 80% spatial overlap. Areas of highest overlap between sharks and fishing vessels show persistence between years, suggesting current hotspots are at risk, and arguing for introduction of international catch limits.

SPECIAL ISSUE: SHARK DEFENSE

Article

Aug 2014
OCEAN COAST MANAGE

Integrating the findings from this special issue and suggestions for future conservation efforts – A brief synopsis

Article

Aug 2014

The populations of several elasmobranch species have experienced a marked decline over the past several decades. Such declines may be attributed to the unsustainable harvest of these animals in combination with their K-selected life-history characteristics. To help reduce this mortality typically associated with commercial fisheries and beach nets, scientists have employed the use of electrosensory and chemical stimuli as elasmobranch deterrents. This paper describes the findings from several studies that assess elasmobranch deterrent efficacy, briefly integrates these findings, and provides useful insight for future conservation approaches.

Evolved for Extinction: The Cost and Conservation Implications of Specialization in Hammerhead Sharks

Article

Full-text available

May 2014
BIOSCIENCE

The interactions between the evolutionary history of species and contemporary changes in their environment can result in both positive and negative outcomes for fitness and survival. Sharks are one the oldest groups of all extant vertebrates but, today, are among the most threatened globally, primarily because of destructive fishing practices. Hammerhead sharks (Sphyrnidae) exhibit extremely specialized traits and complex behaviors that have increased their vulnerability to human exploitation, which impedes conservation efforts. By bringing together published data on aspects of hammerhead shark phylogeny, morphology, biology, physiology, and ecology, we argue that the same novel adaptations that have historically contributed to evolutionary success have become maladaptive under current levels and modes of exploitation. Therefore, we suggest that future management be made in light of—rather than in spite of—the unique evolutionary and ecological traits possessed by hammerhead sharks, because similar patterns are threatening other taxa with high extinction risk.

Detecting climate impacts with oceanic fish and fisheries data

Article

Full-text available

Mar 2013

Anthropogenic climate change is affecting the environment of all oceans, modifying ocean circulation, temperature, chemistry and productivity. While evidence for changes in physical signals is often distinct, impacts on fishes inhabiting oceanic systems are not easily identified, and therefore, quantification of responses is less common. Correctly attributing changes associated with a changing climate from other drivers is important for the implementation of effective harvest and management strategies and for addressing associated socio-economic impacts, particularly for countries highly dependent on oceanic resources. Data supporting investigation of responses of oceanic species to climate impacts include fisheries catch, fisheries-independent surveys, and conventional and electronic tagging data. However, there are a number of challenges associated with detecting climatic responses with these data, including (i) data collection costs (ii) small sample sizes (iii) limited time series relative to temporal scales at which environmental variability occurs, (iv) changing fisher and fisheries behavior due to non-climate drivers and (v) changes in population dynamics due to natural climate variability and non-climate drivers. We highlight potential biases and suggest strategies that should be considered when using oceanic fish and fisheries data in the evaluation of climate change impacts. Consideration of these factors is important when assessing variability in exploited species and designing management responses to climate or fisheries threats.

A Comparison of Spatial and Movement Patterns between Sympatric Predators: Bull Sharks (Carcharhinus leucas) and Atlantic Tarpon (Megalops atlanticus)

Article

Full-text available

Sep 2012
PLOS ONE

Predators can impact ecosystems through trophic cascades such that differential patterns in habitat use can lead to spatiotemporal variation in top down forcing on community dynamics. Thus, improved understanding of predator movements is important for evaluating the potential ecosystem effects of their declines. We satellite-tagged an apex predator (bull sharks, Carcharhinus leucas) and a sympatric mesopredator (Atlantic tarpon, Megalops atlanticus) in southern Florida waters to describe their habitat use, abundance and movement patterns. We asked four questions: (1) How do the seasonal abundance patterns of bull sharks and tarpon compare? (2) How do the movement patterns of bull sharks and tarpon compare, and what proportion of time do their respective primary ranges overlap? (3) Do tarpon movement patterns (e.g., straight versus convoluted paths) and/or their rates of movement (ROM) differ in areas of low versus high bull shark abundance? and (4) Can any general conclusions be reached concerning whether tarpon may mitigate risk of predation by sharks when they are in areas of high bull shark abundance? Despite similarities in diet, bull sharks and tarpon showed little overlap in habitat use. Bull shark abundance was high year-round, but peaked in winter; while tarpon abundance and fishery catches were highest in late spring. However, presence of the largest sharks (>230 cm) coincided with peak tarpon abundance. When moving over deep open waters (areas of high shark abundance and high food availability) tarpon maintained relatively high ROM in directed lines until reaching shallow structurally-complex areas. At such locations, tarpon exhibited slow tortuous movements over relatively long time periods indicative of foraging. Tarpon periodically concentrated up rivers, where tracked bull sharks were absent. We propose that tarpon trade-off energetic costs of both food assimilation and osmoregulation to reduce predation risk by bull sharks.

Resource use of Sphyrna mokarran and S. lewini (Chondrichthyes) neonates and juveniles in the western Arabian Gulf: a stable isotope analysis

Article

Full-text available

Jun 2024

The great hammerhead shark Sphyrna mokarran and the scalloped hammerhead shark S. lewini are marine top predators with global distributions. However, limited information is available on the trophic ecology of hammerhead sharks in the Indian Ocean. In this study, we measured stable nitrogen and carbon isotopes in the muscle tissues of neonates and juveniles of S. mokarran and S. lewini from the waters of the western Arabian Gulf. In general, values of δ ¹⁵ N were lower in S. mokarran (10.8-18.7‰) than in S. lewini (12.2-18.7‰), indicating a reliance on food sources with low nitrogen values. Isotopic niche similarities were observed between female and male S. mokarran . We further observed considerable ontogenetic changes in the δ ¹⁵ N values of both S. mokarran and S. lewini neonates (a reduction from 19 to 12‰), reflecting the maternal effect. The effects of total length and sex on the nitrogen and stable isotope values were nonsignificant in S. mokarran juveniles. The western Arabian Gulf likely serves as a key feeding ground for both the neonates and the juveniles of S. mokarran . By contrast, S. lewini appears to have a low level of reliance on this region.

Oceans

Chapter

Jan 2017

Antony Joseph

Habitat Use Patterns of Coastal Shark Species in Relation to Boat Activity along an Urban Marine Gradient

Thesis

May 2020

The effects of boat activity on various aspects of fish biology and ecology have been widely studied in the past few decades. However, these studies primarily focused on teleost fish species and not elasmobranchs. The goal of this study was to determine if there was a negative relationship between boat activity and the habitat use of three coastal shark species (bull (Carcharhinus leucas), nurse (Ginglymostoma cirratum), and great hammerhead (Sphyrna mokarran)) in Biscayne Bay, Florida - an area subject to intense boat activity (both commercial and recreational). According to past studies on marine mammals and teleost fish species, we expected sharks to present patterns of avoidance (reduced residency and activity space) during times and in areas of intense boat activity. Using aerial surveys and underwater recording stations, patterns of boat activity were quantified both spatially and temporally, while shark activity space and residency were determined using acoustic telemetry. Our results indicated that boat activity was more intense both on the weekends/holidays and closer to Miami Proper. However, there was no relationship between boat activity patterns and the activity space or residency of each species. These results may be explained by each species' hearing ability and how their detectable frequency range does not overlap with that produced by boat engines. Additionally, it is possible that the shark species in this area have habituated to the human activity and associated sound as demonstrated by a population of bottlenose dolphins (Tursiops truncates) in the same area. This study lays a foundation that future research can use to explore the relationship between boat activity and other vulnerable species as well as expand our current understanding of the relationship between sharks and urbanization.

Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia

Article

Full-text available

Oct 2019
J FISH BIOL

Great hammerhead sharks Sphyrna mokarran are the largest member of Sphyrnidae, yet the roles of these large sharks in the food webs of coastal ecosystems are still poorly understood. Here we obtained samples of muscle, liver and vertebrae from large S. mokarran (234–383 cm total length; LT) caught as by‐catch off eastern Australia and used stable‐isotope analyses of δ¹⁵N, δ¹³C and δ³⁴S to infer their resource use and any associated ontogenetic patterns. The results indicated large S. mokarran are apex predators primarily relying on other sharks and rays for their diet, with a preference for benthic resources such as Australian cownose rays Rhinoperon neglecta during the austral summer. Teleosts, cephalopods and crustaceans were not significant components of S. mokarran diets, though some conspecifics appeared to rely on more diverse resources over the austral summer. Ontogenetic shifts in resource use were detected but trajectories of the increases in trophic level varied among individuals. Most S. mokarran had non‐linear trajectories in ontogenetic resource‐use shifts implying size was not the main explanatory factor. Stable isotope values of δ¹³C and δ³⁴S in muscle suggest S. mokarran span coastal, pelagic and benthic food webs in eastern Australia.

The biology and conservation status of the large hammerhead shark complex: the great, scalloped, and smooth hammerheads

Article

Full-text available

Dec 2018
REV FISH BIOL FISHER

Hammerhead sharks are among the most intriguing yet imperiled groups of large sharks globally. Until recently, our understanding of their biology, movements, diet, and life histories was challenged by a lack of studies. In recent years there has been a surge of published studies on this group of sharks, incorporating new information on age and growth, behavior, and the threats they face. Here we summarize and compare what is known on the biology and conservation of the three largest species of hammerhead sharks: the great hammerhead (Sphyrna mokarran), the scalloped hammerhead (Sphyrna lewini), and the smooth hammerhead (Sphyrna zygaena). We chose these species since they are the most well-studied of the hammerheads, and also because they are commonly captured in target and non-target fisheries worldwide. Thus, we also discuss population trends and the vulnerabilities of each species, and make recommendations for future studies on these fascinating and complex elasmobranch fishes.

The utilization of prey-simulating electrodes to analyze the predatory behavior of the great hammerhead shark (Sphyrna mokarran)

Article

Apr 2018

Craig P. O'Connell

A new observation of a great hammerhead shark (Sphyrna mokarran) natural predation on a southern stingray (Hypanus americana) is described in combination with two novel field experiments that investigate both: (1) the sensory cues that elicit S. mokarran foraging responses, as well as (2) the unique prey handling techniques that make this hammerhead such a specialized predator. This study is the first to demonstrate the importance of electro-sensory cues at close ranges for prey detection in S. mokarran. In addition, both the observed natural predation and field experiments provided visual evidence of the repeated prey manipulation technique, termed ‘lateral headshake repositioning’, that may maximize prey handling and foraging success. Further research using more accurate chemo-sensory cues (e.g. those from southern stingrays – Hypanus americana) or varying decoy manipulations (e.g. a buried decoy with active electrodes) is warranted to enhance our understanding of the sensory allocation and prey handling behavioral patterns in relation to the foraging success of this endangered predator.

Satellite Remote Sensing in Support of Fisheries Management in Global Oceans

Chapter

May 2016

The world’s oceans are dynamic: environmental conditions and ecosystems in marine environments fluctuate spatially and temporally on multiple scales. Spatially, the ocean varies with water depth, ocean currents, and oceanic fronts. This abiotic and biotic variability makes managing resources in the dynamic ocean environment extremely difficult, and as a result, fisheries management often serves as one of the textbook examples of an unstructured or ‘wicked’ environmental problem. This chapter provides an overview of the role satellite remote sensing can play in ocean and fisheries management. Currently, there are very few applications available that enable managers to use satellite earth observations in a scientifically robust but straightforward manner. The chapter recommends collaboration between researchers, scientists, data analysts and conservation practitioners to develop accessible tools, all the while ensuring such approaches are scientifically robust and defensible and are directly meeting the needs of the management community. Continued support and resources for satellite earth observations, distribution, integration, and management-relevant science are needed to maximize the return on this investment in support of sustainable fisheries.

Shallow water tidal flat use and associated specialized foraging behavior of the great hammerhead shark ( Sphyrna mokarran )

Article

Full-text available

Apr 2016

Evidence suggests the great hammerhead shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of shark due to its cryptic nature and wideranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great hammerhead shark utilizes an inshore shallow water flats environment (<1.5 m in depth), five of which involve prey capture. These observations permitted identification of two novel behaviors that may allow great hammerheads to inhabit these shallow habitats: a (1) prey-capture technique termed ‘grasp-turning’ that involves burst swimming at tight turning angles while grasping prey and (2) a post-predation recovery period whereby the shark maintains head-first orientation into the current that may facilitate respiration and prey consumption. These behavioral observations provide insights into the natural history of this species.

Incorporating movement in the modelling of shark and ray population dynamics: approaches and management implications

Article

Full-text available

Mar 2016
REV FISH BIOL FISHER

The explicit incorporation of movement in the modelling of population dynamics can allow improved management of highly mobile species. Large-scale movements are increasingly being reported for sharks and rays. Hence, in this review we summarise the current understanding of long-scale movement patterns of sharks and rays and then present the different methods used in fisheries science for modelling population movement with an emphasis on sharks and rays. The use of movement data for informing population modelling and deriving management advice remains rare for sharks and rays. In the few cases where population movement was modelled explicitly, movement information has been solely derived from conventional tagging. Though shark and ray movement has been increasingly studied through a range of approaches these different sources of information have not been used in population models. Integrating these multiple sources of movement information could advance our understanding of shark and ray dynamics. This, in turn, would allow the use of more adequate models for assessing stocks and advising management and conservation effort.

The Value of Taxon-focused Science: 30 Years of Elasmobranchs in Biological Research and Outreach

Article

Dec 2014
COPEIA

Due to an intense level of interest from the media, the public, conservation NGOs, and policymakers, the scientific study of charismatic megafauna is perceived by some researchers as associated with glory-seeking or other less-than-noble behavior. However, the study of elasmobranchs has led to important discoveries in the fields of physiology, evolution, neurobiology, behavior, and ecology that would not have been possible with other study systems. These animals are ecologically and economically important, and many species are of great conservation concern. Additionally, public interest in these animals can be leveraged for science and conservation education and outreach efforts, and they can be used as “flagship species” for conservation and management policy. In this paper, we discuss the value of taxon-focused scientific research using examples from the work of American Elasmobranch Society scientists. We argue for the importance of taxon-based societies, such as the American Elasmobranch Society (AES), and the societies it meets jointly with, including the American Society of Ichthyologists and Herpetologists, the Society for the Study of Reptiles and Amphibians, and the Herpetologists' League. Together these four societies make up the Joint Meeting of Ichthyologists and Herpetologists (JMIH). While this paper will focus on AES, the general principles apply broadly to all members of JMIH as well as other taxon-based societies, and speak to their importance amongst a backdrop of broadly discipline-based research societies.

Effects of barium-ferrite permanent magnets on great hammerhead shark Sphyrna mokarran behavior and implications for future conservation technologies

Article

Full-text available

Jan 2014

The great hammerhead shark Sphyrna mokarran is an endangered species that is exposed to several sources of anthropogenic mortality, including beach nets. Although not a major contributor to S. mokarran mortality, beach nets are utilized in several locations to minimize the potential harmful interaction between sharks and beachgoers. To address this mortality, permanent magnets have been employed to determine if these materials can deter sharks away from netted areas. The present study examined the effects of barium-ferrite (BaFe12O19) permanent magnets on S. mokarran behavior under several environmental and biological conditions. In the bait experiment, feeding frequency significantly decreased and avoidance frequency significantly increased with the magnet treatment, with exposure quantity yielding an increase in feeding frequency, although this effect was not statistically significant. For the barrier experiment, entrance frequency significantly decreased and avoidance and pass-around frequencies significantly increased with the magnet treatment, with heterospecific density also being a significant pre - dictor of entrance frequency. The findings demonstrate how permanent magnets can modify S. mokarran behavior and how this behavior is modified based on situational context. Since several other sphyrnid species are caught in beach nets more frequently than S. mokarran (e.g. scalloped hammerheads S. lewini), the present results may serve as a model for these other sphyrnid species and illustrate the potential conservation implications of future magnetic deterrent barrier technologies.

MARINE ECOLOGY PROGRESS SERIES

Article

Jan 2014

Don't bite the hand that feeds: Assessing ecological impacts of provisioning ecotourism on an apex marine predator

Article

Full-text available

Jun 2012
FUNCT ECOL

1. There has been considerable debate over the past decade with respect to wildlife provisioning, especially resultant behavioural changes that may impact the ecological function of an apex predator. The controversy is exemplified by the shark diving industry, where major criticisms based on inference, anecdote and opinion stem from concerns of potential behaviourally mediated ecosystem effects because of ecotourism provisioning (aka‘chumming’ or feeding). 2. There is a general lack of empirical evidence to refute or support associated claims. The few studies that have investigated the behavioural impacts of shark provisioning ecotourism have generated conflicting conclusions, where the confidence in such results may suffer from a narrow spatial and temporal focus given the highly mobile nature of these predators. There is need for studies that examine the potential behavioural consequences of provisioning over ecologically relevant spatial and temporal scales. 3. To advance this debate, we conducted the first satellite telemetry study and movement analysis to explicitly examine the long-range migrations and habitat utilization of tiger sharks (Galeocerdo cuvier) originating in the Bahamas and Florida, two areas that differ significantly with regards to the presence/absence of provisioning ecotourism. 4. Satellite telemetry data rejected the behaviourally mediated effects of provisioning ecotourism at large spatial and temporal scales. In contrast, to the restricted activity space and movement that were hypothesized, geolocation data evidenced previously unknown long-distance migrations and habitat use for both tiger shark populations closely associated with areas of high biological productivity in the Gulf Stream and subtropical western Atlantic Ocean. We speculate that these areas are likely critically important for G. cuvier feeding forays and parturition. 5. We concluded that, in the light of potential conservation and public awareness benefits of ecotourism provisioning, this practice should not be dismissed out of hand by managers. Given the pressing need for improved understanding of the functional ecology of apex predators relative to human disturbance, empirical studies of different species sensitivities to disturbance should be used to guide best-practice ecotourism policies that maximize conservation goals.

Cyanobacterial Neurotoxin β-N-Methylamino-L-alanine (BMAA) in Shark Fins

Article

Full-text available

Feb 2012
MAR DRUGS

Sharks are among the most threatened groups of marine species. Populations are declining globally to support the growing demand for shark fin soup. Sharks are known to bioaccumulate toxins that may pose health risks to consumers of shark products. The feeding habits of sharks are varied, including fish, mammals, crustaceans and plankton. The cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) has been detected in species of free-living marine cyanobacteria and may bioaccumulate in the marine food web. In this study, we sampled fin clips from seven different species of sharks in South Florida to survey the occurrence of BMAA using HPLC-FD and Triple Quadrupole LC/MS/MS methods. BMAA was detected in the fins of all species examined with concentrations ranging from 144 to 1836 ng/mg wet weight. Since BMAA has been linked to neurodegenerative diseases, these results may have important relevance to human health. We suggest that consumption of shark fins may increase the risk for human exposure to the cyanobacterial neurotoxin BMAA.

Biology of the dolphinfish (Coryphaena hippurus) in the western central Atlantic: A review

Article

Full-text available

Dec 1999

Hazel Oxenford

The dolphinfish, Coryphaena hippurus, is a circum-tropical oceanic epipelagic species which is of significant importance to both commercial and sport fisheries in the western central Atlantic. Despite this, little attention has been paid to conducting biological stock assessments and developing management strategies for this species, and it remains unmanaged across most of the region. This paper summarizes aspects of the biology of dolphinfish that are relevant to assessment and management from studies of this species in the southeastern United States, Gulf of Mexico and the Caribbean. Throughout their range in the western central Atlantic, dolphinfish are seasonally abundant and presumed to be highly migratory. They exhibit high growth rates, early maturity, batch spawning over an extended season, a short life span and a varied diet. Marked differences in some biological characteristics and in the frequency of IDH-2 alleles between dolphinfish from the southeastern USA and the Caribbean suggest a relatively complex stock structure for this species, which needs further investigation to improve the information base for development of management strategies for dolphinfish across this region.

UPDATED CATCHES OF ATLANTIC SHARKS

Article

Full-text available

This document presents updated commercial and recreational landings and discard estimates of Atlantic sharks up to 2004, with special emphasis on sharks of the Large Coastal complex. Species-specific information on the geographical distribution of both commercial and recreational catches is presented along with the different gear types used in the commercial fisheries. Length-frequency information and average weights of the catches in three separate recreational surveys and in the directed shark bottom-longline observer program are also included.

Age and growth of the great hammerhead shark, Sphyrna mokarran, in the north-western Atlantic Ocean and Gulf of Mexico

Article

Full-text available

Sep 2010

The great hammerhead shark, Sphyrna mokarran, is a cosmopolitan species that is caught in a variety of fisheries throughout much of its range. The apparent decline of great hammerhead shark populations has reinforced the need for accurate biological data to enhance fishery management plans. To this end, age and growth estimates for the great hammerhead were determined from sharks (n = 216) ranging in size from 54- to 315-cm fork length (FL), captured in the Gulf of Mexico and north-western Atlantic Ocean. Growth curves were fitted using multiple models and evaluated using Akaike’s information criterion. The von Bertalanffy growth model was the best fitting model, with resulting growth parameters of L∞ = 264.2-cm FL, k = 0.16 year–1, t0 = –1.99 year for males, and L∞ = 307.8-cm FL, k = 0.11 year–1, t0 = –2.86 year for females. Annual band pair deposition was confirmed through marginal-increment analysis and a concurrent bomb radiocarbon validation study. Great hammerheads have one of the oldest reported ages for any elasmobranch (44 years) but grow at relatively similar rates (on the basis of von Bertalanffy k value) to other large hammerhead species from this region. The present study is the first to provide vertebral ages for great hammerheads.

Biology of three hammerhead sharks (Eusphyra blochii, Sphyrna mokarran and S. lewini) from Northern Australia

Article

Full-text available

Apr 1989

The hammerhead sharks Eusphyra blochii, Sphyrna mokarran and S. lewini form part of the incidental catch of a commercial gill-net fishery off northern Australia. Of the specimens sampled between June 1980 and December 1986, 46% of S. mokarran, 41% of E. blochii and 31% of S. lewini were females. Few adult female S. lewini were caught and it is suggested that these occur offshore of the study area. In northern Australia, the usual size at maturity of male E. blochii, S. lewini and S. mokarran is 108, 150 and 225 cm total length (TL), ,and of females is 120, 200 and 210 cm TL, respectively. S. mokarran and E. blochii gave birth in January and February/March, respectively, after a gestation period of 10-11 months. S. Iewini appears to have a more extended seasonal cycle: the young are born between October and January after 9-10 months gestation. Size at birth is about 45-50 cm TL in E. blochii and S. lewini, and 65 cm TL in S. mokarran. Mean litter size is 12 in E. blochii, 15 in S. mokarran and 17 in S. lewini. Individual E. blochii females breed every year, whereas S. mokarran females probably breed every other year. Fish are an important component of the diet of all three species as, to a lesser extent, are cephalopods for S. lewini and crustaceans for S. mokarran and E. blochii.

Tracking the fin trade: Genetic stock identification in western Atlantic scalloped hammerhead sharks Sphyrna lewini

Article

Full-text available

Dec 2009

Location or stock-specific landing data are necessary to improve management of shark stocks, especially those imperiled by overexploitation as a result of the international shark fin trade. In the current absence of catch monitoring directly at extraction sites, genetic stock identification of fins collected from major market supply chain endpoints offers an overlooked but potentially useful approach for tracing the fins back to their geographical, or stock of, origin. To demonstrate the feasibility of this approach, we used mitochondrial control region (mtCR) sequences to trace the broad geographical origin of 62 Hong Kong market-derived Sphyrna lewini fins. Of these fins 21% were derived from the western Atlantic, where this species is listed as 'Endangered' by the International Union for the Conservation of Nature (IUCN). We also show that S. lewini mtCR sequences are geographically segregated in the western Atlantic (overall ΦST = 0.74, n = 177 sharks), indicating that breeding females either remain close to, or home back to, their natal region for parturition. Mixed stock analysis simulations showed that it is possible to estimate the relative contributions of these mitochondrial stocks to fin mixtures in globally sourced trade hubs. These findings underscore the feasibility of using genetic stock identification to source market-derived shark fins to obtain essential and otherwise unavailable data on exploitation levels, and thus to productively inform stock assessment and management of S. lewini and potentially also of other fished shark species.

Migration of an upper trophic level predator, the salmon shark Lamna ditropis, between distant ecoregions

Article

Full-text available

Dec 2008

Knowledge of how animals move through heterogeneous environments is essential to understanding the ecological functions they fulfill in each habitat and their responses to environmen- tal change. Upper trophic level organisms exert structural influences through the food web, so infor- mation on their range, migration and foraging strategy is necessary to understanding ecosystem function. Recent technological advances have enabled researchers to follow individual animals over seasonal and multi-year timescales, revealing long-distance migrations in a variety of taxa. We used satellite telemetry to monitor female salmon sharks Lamna ditropis and remote sensing to character- ize their environment. Salmon sharks ranged throughout the entire eastern North Pacific Ocean dur- ing a seasonal migration cycle. During long-distance migrations, quantitative movement analyses of speed, path straightness and first passage time (FPT) revealed area-restricted search (ARS) behaviors in northern and southern regions, with transiting behaviors at mid-latitudes. Individuals migrating to a highly productive southern region displayed more ARS behaviors than those moving to a low pro- ductivity region. The combination of multi-year time-series of animal behavior with synoptic environ- mental data reveals factors influencing migration and indicates that different life history functions are fulfilled in each habitat.

An Evaluation of the Relationship Between Small Cetacean Tag Design and Attachment Durations: A Bioengineering Approach

Article

Full-text available

Jan 2001

M. Bradley Hanson

Harbour seal spatial distribution estimated from Argos satellite telemetry: overcoming positioning errors Jakob Tougaard1,*, Jonas Teilmann1, Svend Tougaard2

Article

Full-text available

Dec 2008

A limiting factor of satellite telemetry in the context of habitat ase by marine mammals is the low accuracy of the received positions. A novel statistical analysis to overcome the low accuracy was developed in the context of processing data on harbour seals phoca vitulina for the atlas of Danish mammals. Ten harbour seals were caught in the Danish Wadden Sea and tracked with satelite transmitters. The statistical analysis reversed the problem of positioning: Instead of attempting to correctly assign each individual position to a single grid cell, our approach considers the combined probability that at least one position originated in each grid cell. Thus, all satellite-derived positions, including positions of poor precision, can contribute to the evaluation. The method is an alternative to other methods describing spatial use, such as kernel home range, and constitutes a viable approach for inclusion of satellite-derived positional data into spatial modeling of animal distribution and habitat use.

Satellite tagging and cardiac physiology reveal niche expansion in salmon sharks

Article

Full-text available

Jan 2005

Shark bycatch and depredation in the US Atlantic pelagic longline fishery

Article

Full-text available

Nov 2008

The non-target bycatch of sharks in pelagic longline (PLL) fisheries represents a potential source of compromise to shark populations world-wide. Moreover, shark bycatch and depredation (damage inflicted on gear, bait, and catch) compli-cates management of sharks and other species, and can undermine the operations and financial interests of the pelagic longline industry. Thus, deducing means to reduce shark interactions is in the best interest of multiple stakeholder groups. Prior to doing so, however, the extent, cause and effect of these interactions must be better understood. In this review we address or conduct the following in relation to the U.S. Atlantic, Gulf of Mexico and Caribbean PLL fishery: (1) U.S. management governing shark inter-actions in the Atlantic; (2) the primary species encountered and historical shark catch data associ-ated with PLL fishing in the Atlantic; (3) a historical comparison of area-specific shark species catch records between the two primary sources of shark catch data in this fishery; (4) the conditions and dynamics that dictate shark interactions in this fishery, and potential means to reduce these interac-tions, and; (5) a synthesis of the estimated impacts of this fishery on shark populations relative to other fisheries in the Atlantic. As has been found in other PLL fisheries, the blue shark (Prionace glauca) is clearly the shark species most commonly encountered in this fishery in the Atlantic, and receives the majority of attention in this review. U.S. management areas with high relative shark species diversities had a greater divergence in historical shark species percent-compositions between data sources (Pelagic Observer Program versus mandatory pelagic Log-book databases); this complicates the ability to conclude which species are most impacted by PLL fishing in those areas. The current fishing effort by the U.S. PLL fleet is small compared to that of PLL fishing targeting sharks in the Atlantic by non-U.S. fleets, and therefore poses a comparatively lower threat to the stability of Atlantic shark populations. However, incidental shark encounters are inevitable in U.S. Atlantic PLL fishing operations. Thus, it is in the best interest of all stakeholders in the Atlantic to better understand the extent and conditions governing these interactions, and to explore methods to reduce both their occurrence and those aspects leading to higher rates of incidental shark mortality.

Direct and indirect fishery effects on small coastal elasmobranchs in the northern Gulf of Mexico

Article

Full-text available

Oct 2005
ECOL LETT

Globally, bycatch in tropical/subtropical shrimp trawl and longline fisheries is threatening many marine species. Here we examine the joint effects of increased mortality caused by shrimp trawling bycatch, and reduced predation caused by losses of large sharks because of longline fishing. Research surveys in the Gulf of Mexico (1972–2002) demonstrated precipitous declines in shallow water coastal elasmobranchs where shrimping effort was highest (bonnethead 96%, Bancroft's numbfish (lesser electric ray) 98%, smooth butterfly ray > 99%) and consistent increases in deeper water elasmobranchs (Atlantic angel shark, smooth dogfish). These increases are the first empirical support for predation release caused by the loss of large sharks, which have been theorized to structure tropical/subtropical marine ecosystems. Bycatch of elasmobranchs in shrimp trawls is a critical conservation concern which is not solved by present mitigation measures; similar loss of elasmobranchs is expected to be occurring in tropical/subtropical regions worldwide where ever intensive shrimp trawling occurs.

Global-scale genetic identification of hammerhead sharks: Application to assessment of the international fin trade and law enforcement

Article

Full-text available

Jan 2005

The future status of sharks is an issue of widespread conservation concern due to declines in many species in the face of high levels of exploitation to satisfy market demands for products, especially fins. Substantial declines in the large-bodied hammerhead sharks, Sphyrna lewini, S. mokarran and S. zygaena, even in regions where some management occurs, indicate that informed conservation measures are warranted for these circumglobally distributed species. Despite the importance of assessing shark catch and trade on a species-specific basis to detect potential overexploitation of individual species, achieving this goal for hammerheads has proven elusive due to difficulties in identification of their products. Here, we present the development and application of a diagnostic, streamlined, five-primer multiplex polymerase chain reaction assay utilizing species-specific primers based on nuclear ribosomal ITS2 for the three hammerhead species throughout their global distribution. Application of this assay to investigations of the fin market confirmed the presence of hammerhead fins in the international trade. A study of the world’s largest fin market in Hong Kong revealed a high concordance between specific Chinese-name trade categories and fins from these three species (“Bai Chun” with S. lewini, “Gui Chun” with S. zygaena and “Gu Pian” with S.␣mokarran), and clear species preferences. This concordance information allows the use of market records for monitoring species-specific trends in trade and exploitation rates. The assay is also proving useful for identification of shark body parts in U.S. fisheries law-enforcement activities. Screening of morphologically identified “ S. lewini” from globally distributed areas using this assay with subsequent whole ITS2 sequencing suggests a cryptic species closely related to S. lewini occurs off the SE USA coast.

Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean

Article

Full-text available

Mar 2007
SCIENCE

Impacts of chronic overfishing are evident in population depletions worldwide, yet indirect ecosystem effects induced by predator removal from oceanic food webs remain unpredictable. As abundances of all 11 great sharks that consume other elasmobranchs (rays, skates, and small sharks) fell over the past 35 years, 12 of 14 of these prey species increased in coastal northwest Atlantic ecosystems. Effects of this community restructuring have cascaded downward from the cownose ray, whose enhanced predation on its bay scallop prey was sufficient to terminate a century-long scallop fishery. Analogous top-down effects may be a predictable consequence of eliminating entire functional groups of predators.

Collapse and Conservation of Shark Populations in the Northwest Atlantic

Article

Full-text available

Feb 2003
SCIENCE

Overexploitation threatens the future of many large vertebrates. In the ocean, tunas and sea turtles are current conservation concerns because of this intense pressure. The status of most shark species, in contrast, remains uncertain. Using the largest data set in the Northwest Atlantic, we show rapid large declines in large coastal and oceanic shark populations. Scalloped hammerhead, white, and thresher sharks are each estimated to have declined by over 75% in the past 15 years. Closed-area models highlight priority areas for shark conservation, and the need to consider effort reallocation and site selection if marine reserves are to benefit multiple threatened species.

Global estimates of shark catches using trade records from commercial markets

Article

Full-text available

Nov 2006
ECOL LETT

Despite growing concerns about overexploitation of sharks, lack of accurate, species-specific harvest data often hampers quantitative stock assessment. In such cases, trade studies can provide insights into exploitation unavailable from traditional monitoring. We applied Bayesian statistical methods to trade data in combination with genetic identification to estimate by species, the annual number of globally traded shark fins, the most commercially valuable product from a group of species often unrecorded in harvest statistics. Our results provide the first fishery-independent estimate of the scale of shark catches worldwide and indicate that shark biomass in the fin trade is three to four times higher than shark catch figures reported in the only global data base. Comparison of our estimates to approximated stock assessment reference points for one of the most commonly traded species, blue shark, suggests that current trade volumes in numbers of sharks are close to or possibly exceeding the maximum sustainable yield levels.

Loss of Large Predatory Sharks from the Mediterranean Sea

Article

Full-text available

Jul 2008
CONSERV BIOL

Evidence for severe declines in large predatory fishes is increasing around the world. Because of its long history of intense fishing, the Mediterranean Sea offers a unique perspective on fish population declines over historical timescales. We used a diverse set of records dating back to the early 19th and mid 20th century to reconstruct long-term population trends of large predatory sharks in the northwestern Mediterranean Sea. We compiled 9 time series of abundance indices from commercial and recreational fishery landings, scientific surveys, and sighting records. Generalized linear models were used to extract instantaneous rates of change from each data set, and a meta-analysis was conducted to compare population trends. Only 5 of the 20 species we considered had sufficient records for analysis. Hammerhead (Sphyrna spp.), blue (Prionace glauca), mackerel (Isurus oxyrinchus and Lamna nasus), and thresher sharks (Alopias vulpinus) declined between 96 and 99.99% relative to their former abundance. According to World Conservation Union (IUCN) criteria, these species would be considered critically endangered. So far, the lack of quantitative population assessments has impeded shark conservation in the Mediterranean Sea. Our study fills this critical information gap, suggesting that current levels of exploitation put large sharks at risk of extinction in the Mediterranean Sea. Possible ecosystem effects of these losses involve a disruption of top-down control and a release of midlevel consumers.

Collins Field Guide to Sharks of the World

Book

Jan 2005

The marine fishes of Nova Scotia

Article

Notes on the Dolphin (Coryphaena hippurus) in North Carolina Waters

Article

Mar 1951

Howard A. Schuck

A preliminary investigation of the stock structure of the dolphin, Coryphaena hippurus, in the Western central Atlantic

Article

Jan 1986
FISH B-NOAA

Community structure of fishes attracted to shallow water fish aggregation devices off South Carolina, U.S.A

Article

Dec 1990

Rodney A. Rountree

Synopsis Twenty-two fish aggregation devices were deployed in 14 m of water off South Carolina. Species composition and abundance were determined by diver visual census on eight occasions from May through November, 1985. A total of 21 families and 36 species of fishes was observed at 121 stations. Pelagic fishes dominated the fauna with a 99.3% relative abundance, and Decapterus punctatus accounted for 97.6% of the individuals. Caranx crysos, Diplectrum formosum, Decapterus punctatus, Centropristis striata and Monacanthus hispidus were the most frequent species. Total fish abundance, number of species and abundance of four of the six most common species were significantly affected by season. Hurricane activity may have caused a significant drop in pelagic fish abundance at the FADs in July. No significant correlations among species abundances were found after removal of season and FAD type effects. Spatial zonation and seasonal occurrence patterns suggest some competition among pelagic fishes. Several factors that regulate FAD faunal abundance and composition are hypothesized, including: juvenile fish availability, availability of shelter, availability of adequate food resources, interspecific and intraspecific competition, severe sea conditions, and sporadic intrusions of large predatory fishes. It is hypothesized that the abundances of benthic and pelagic FAD fishes are correlated and that there is a direct or indirect energetic link between shallow water pelagic and benthic fish assemblages near FADs.

A review of shark satellite studies

Article

Feb 2011
J EXP MAR BIOL ECOL

The Habitat, Movements, and Management of Dolphin, Coryphaena hippurus, in the Western North Atlantic, Caribbean, and Gulf of Mexico

Article

Edward Farrell

Dolphin, Coryphaena hippurus, is a highly migratory cosmopolitan pelagic fish that is found seasonally in the Caribbean, Gulf of Mexico, and along the Atlantic coast of the United States. Dolphin are considered as one unit stock throughout the study area. This study used release-recapture data from a long-term tagging project to investigate baseline environmental preferences, habitat suitability based on dynamic ecogeographical variables, spatio-temporal movement through marine cadastral zones, and related policy implications. The data was collected from hundreds of recreational fishermen that tagged dolphin and also recaptured dolphin. A combination of in situ observations from recreational taggers and remotely sampled physical and biological variables (depth, bathymetric slope, distance to shore, distance to continental shelf, sea surface temperature, and sea surface chlorophyll-a) were used to establish an updated and novel baseline of environmental characteristics. A presence-only spatially explicit multivariate modeling approach was used to reveal the bio-physical seasonal preferences of dolphin that define the ecological niche. The results of the models show strong spatial sensitivity to sea surface temperature and surface chlorophyll-a concentration. The tagrecapture analysis showed that dolphin are capable of crossing multiple national and international marine jurisdictional zones throughout their lives. These movements bring the current management insufficiencies to light. Recommendations based on this multifaceted analysis focus on horizontal domestic and international fisheries integration.

Measurement error causes scale-dependent threshold erosion of biological signals in animal movement data

Article

Mar 2007

Recent advances in telemetry technology have created a wealth of tracking data available for many animal species moving over spatial scales from tens of meters to tens of thousands of kilometers. Increasingly, such data sets are being used for quantitative movement analyses aimed at extracting fundamental biological signals such as optimal searching behavior and scale-dependent foraging decisions. We show here that the location error inherent in various tracking technologies reduces the ability to detect patterns of behavior within movements. Our analyses endeavored to set out a series of initial ground rules for ecologists to help ensure that sampling noise is not misinterpreted as a real biological signal. We simulated animal movement tracks using specialized random walks known as Lévy flights at three spatial scales of investigation: 100-km, 10-km, and 1-km maximum daily step lengths. The locations generated in the simulations were then blurred using known error distributions associated with commonly applied tracking methods: the Global Positioning System (GPS), Argos polar-orbiting satellites, and light-level geolocation. Deviations from the idealized Lévy flight pattern were assessed for each track after incrementing levels of location error were applied at each spatial scale, with additional assessments of the effect of error on scale-dependent movement patterns measured using fractal mean dimension and first-passage time (FPT) analyses. The accuracy of parameter estimation (Lévy mu, fractal mean D, and variance in FPT) declined precipitously at threshold errors relative to each spatial scale. At 100-km maximum daily step lengths, error standard deviations of > or = 10 km seriously eroded the biological patterns evident in the simulated tracks, with analogous thresholds at the 10-km and 1-km scales (error SD > or = 1.3 km and 0.07 km, respectively). Temporal subsampling of the simulated tracks maintained some elements of the biological signals depending on error level and spatial scale. Failure to account for large errors relative to the scale of movement can produce substantial biases in the interpretation of movement patterns. This study provides researchers with a framework for understanding the limitations of their data and identifies how temporal subsampling can help to reduce the influence of spatial error on their conclusions.

The directed shark gillnet fishery: right whale season (eds) SFD Contribution PCB-02/13. Southeast Fisheries Science Center Biology of the dolphinfish (Coryphaena hippurus) in the western central Atlantic: a review

Jan 1999
277-301

National Marine Fisheries Service (2002) The directed shark gillnet fishery: right whale season 2002. In: Carlson J, Baremore I (eds) SFD Contribution PCB-02/13. Southeast Fisheries Science Center, Panama City, FL Oxenford HA (1999) Biology of the dolphinfish (Coryphaena hippurus) in the western central Atlantic: a review. Sci Mar 63:277–301

first annual report to The Pew Charitable Trusts: a comprehensive study of the ecological impacts of the worldwide pelagic longline industry

Jan 2001

L B Crowder
R A Myers

Crowder LB, Myers RA (2001) 2001 first annual report to The Pew Charitable Trusts: a comprehensive study of the ecological impacts of the worldwide pelagic longline industry. Available at http://moray.ml.duke.edu/faculty/crowder/ research/crowder_and_myers_Mar_2002.pdf

Heupel MR and others (2010) Sphyrna mokarran. IUCN Red List

J Denham
J Stevens
C A Simpfendorfer

Denham J, Stevens J, Simpfendorfer CA, Heupel MR and others (2010) Sphyrna mokarran. IUCN Red List. Available at www.iucnredlist.org

Species-specific distribution and habitat characteristics of shark nurseries in Gulf of Mexico waters off peninsular Florida and Texas

Jan 2007
193-223

R E Hueter
J P Tyminski

Hueter RE, Tyminski JP (2007) Species-specific distribution and habitat characteristics of shark nurseries in Gulf of Mexico waters off peninsular Florida and Texas. Am Fish Soc Symp 50:193-223

The directed shark gillnet fishery: right whale season

Jan 2002

Range extension of the endangered great hammerhead shark Sphyrna mokarran in the Northwest Atlantic: Preliminary data and significance for conservation

Abstract

No full-text available

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