Large Sharks Research Articles

Integrative Taxonomy Reveals Molicola uncinatus and Gymnorhynchus gigas (Cestoda: Trypanorhyncha) Coinfection in the Atlantic Pomfret Brama brama From the Mediterranean Sea, With Notes on the Phylogenetic Position of G. gigas Within the Family Gymnorhynchidae.

The cestode family Gymnorhynchidae Dollfus, 1935 (Trypanorhyncha) comprises three genera and six valid species that are typically intestinal parasites of large pelagic sharks. Members of Gymnorhynchidae show a wide geographic distribution and represent a global sanitary concern because as larvae they infect the edible flesh of several commercially important fishes with some species having allergenic potential. Larval Gymnorhynchidae collected from the muscles of the Atlantic pomfret Brama brama from various localities in the Mediterranean Sea were identified and characterized by combining traditional morphology, scanning electronic microscopy, and molecular analyses using newly generated nuclear 18S and 28S rRNA sequences. Overall, 98 larvae were collected from 20 (100%) Atlantic pomfrets (intensity of infection: 4.9; range: 1–12). High-quality sequences were obtained for 54 larvae. Of these, 11 and 43 larvae were identified as Molicola uncinatus and Gymnorhynchus gigas, respectively. The phylogenetic analysis showed the existence of three main clades within Gymnorhynchidae. The first included species of G. gigas and M. uncinatus from the Mediterranean and Atlantic; the second and third major clades included an unidentified species of Molicola from the Indian Ocean and specimens of Gymnorhynchus isuri from the Mediterranean and Atlantic, respectively. Finally, Chimaerarhynchus rougetae was the basal and most diverging taxon. The phylogenetic analysis suggested that G. gigas is more closely related to the members of Molicola. We demonstrated the coinfection of M. uncinatus and G. gigas from all localities studied and extended the intermediate hosts and geographical range of M. uncinatus by including the Atlantic pomfret and the Tyrrhenian and Ionian Seas, respectively. The present results supported the previous proposal that G. gigas and Molicola species should be included in the same genus. Our study demonstrated the usefulness of the integrative taxonomy for the unequivocal recognition of larval trypanorhynch species, resolving the current difficulties in the taxonomy, and elucidating the poorly known ecological and biological aspects of members of Gymnorhynchidae.

Thirty-five years of tiger shark Galeocerdo cuvier relative abundance near Bimini, The Bahamas, and the Southeastern United States with a comparison across jurisdictional bounds.

Abundances of large sharks are reported to have declined worldwide, and in response various levels of fisheries management and conservation efforts have been established. For example, marine-protected areas have been suggested as a means to protect large expanses of ocean from fishing and other industrial activities (e.g., habitat destruction), and in 2011 The Commonwealth of The Bahamas established The Bahamas Shark Sanctuary. Nonetheless, assessing the effectiveness of conservation efforts is challenging because consistent long-term data sets of shark abundances are often lacking, especially throughout the Caribbean and The Bahamas. In this study, the authors investigated the catch rates and demographics of tiger sharks Galeocerdo cuvier caught in a fishery-independent survey near Bimini, The Bahamas, from 1984 to 2019 to assess relative abundance trends following the banning of longline fishing in 1993 and the subsequent establishment of the shark sanctuary. To contextualize the relative abundance trends near Bimini, the authors compared this to the relative abundance of tiger sharks in a fishery-dependent survey from the Southeastern USA (SE USA), conducted from 1994 to 2019. The data of this study suggest that local abundance of tiger sharks has been stable near Bimini since the 1980s, including after the ban of longline fishing and the implementation of the shark sanctuary. In comparison, the abundance near the SE USA has slowly increased in the past decade, following potential declines in the decade preceding the USA Shark Management Plan. The results of this study provide some optimism that current conservation efforts in The Bahamas have been effective to maintain local tiger shark abundance within the protected area. In addition, current fisheries management in the SE USA is allowing this species to recover within those waters.

Hammer it out: shifts in habitat are associated with changes in fin and body shape in the scalloped hammerhead (Sphyrna lewini)

Abstract Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.

Predator-prey landscapes of large sharks and game fishes in the Florida Keys.

Interspecific interactions can play an essential role in shaping wildlife populations and communities. To date, assessments of interspecific interactions, and more specifically predator-prey dynamics, in aquatic systems over broad spatial and temporal scales (i.e., hundreds of kilometers and multiple years) are rare due to constraints on our abilities to measure effectively at those scales. We applied new methods to identify space-use overlap and potential predation risk to Atlantic tarpon (Megalops atlanticus) and permit (Trachinotus falcatus) from two known predators, great hammerhead (Sphyrna mokarran) and bull (Carcharhinus leucas) sharks, over a 3-year period using acoustic telemetry in the coastal region of the Florida Keys (USA). By examining spatiotemporal overlap, as well as the timing and order of arrival at specific locations compared to random chance, we show that potential predation risk from great hammerhead and bull sharks to Atlantic tarpon and permit are heterogeneous across the Florida Keys. Additionally, we find that predator encounter rates with these game fishes are elevated at specific locations and times, including a prespawning aggregation site in the case of Atlantic tarpon. Further, using machine learning algorithms, we identify environmental variability in overlap between predators and their potential prey, including location, habitat, time of year, lunar cycle, depth, and water temperature. These predator-prey landscapes provide insights into fundamental ecosystem function and biological conservation, especially in the context of emerging fishery-related depredation issues in coastal marine ecosystems.

Fear at the top: killer whale predation drives white shark absence at South Africa’s largest aggregation site

Risk-induced fear effects exerted by top predators are pervasive in terrestrial and marine systems, with lasting impacts on ecosystem structure and function. The loss of top predators can disrupt ecosystems and trigger trophic cascades, but the introduction of novel apex predators into ecosystems is not well understood. We documented the emigration of white sharks Carcharodon carcharias in response to the presence of a pair of killer whales, Orcinus orca, at a large white shark aggregation site in South Africa. Between February and June in 2017, five white shark carcasses washed up on beaches in Gansbaai, Western Cape Province, four of which had their livers removed. Sightings per unit effort (sea days) and telemetry data demonstrated that white sharks emigrated from Gansbaai following these predation events, and in response to further sightings of this pair and other killer whale pods in the vicinity. Tagging data demonstrated the immediate departure of white sharks from Gansbaai, and some sharks were subsequently moving east. Contrary to expected and well-documented patterns of white shark occurrence at this site, their sightings dropped throughout the following 2.5 years; change-point analysis on both datasets confirmed these departures coincided with killer whale presence and shark carcasses washing out. These findings suggest that white sharks respond rapidly to risk from a novel predator, and that their absence triggered the emergence of another predator, the bronze whaler Carcharhinus brachyurus. Predator–prey interactions between white sharks, other coastal sharks, and killer whales are increasing in South Africa and are expected to have pronounced impacts on the ecosystem.

Microbiome structure in large pelagic sharks with distinct feeding ecologies

BackgroundSharks play essential roles in ocean food webs and human culture, but also face population declines worldwide due to human activity. The relationship between sharks and the microbes on and in the shark body is unclear, despite research on other animals showing the microbiome as intertwined with host physiology, immunity, and ecology. Research on shark-microbe interactions faces the significant challenge of sampling the largest and most elusive shark species. We leveraged a unique sampling infrastructure to compare the microbiomes of two apex predators, the white (Carcharodon carcharias) and tiger shark (Galeocerdo cuvier), to those of the filter-feeding whale shark (Rhincodon typus), allowing us to explore the effects of feeding mode on intestinal microbiome diversity and metabolic function, and environmental exposure on the diversity of microbes external to the body (on the skin, gill).ResultsThe fecal microbiomes of white and whale sharks were highly similar in taxonomic and gene category composition despite differences in host feeding mode and diet. Fecal microbiomes from these species were also taxon-poor compared to those of many other vertebrates and were more similar to those of predatory teleost fishes and toothed whales than to those of filter-feeding baleen whales. In contrast, microbiomes of external body niches were taxon-rich and significantly influenced by diversity in the water column microbiome.ConclusionsThese results suggest complex roles for host identity, diet, and environmental exposure in structuring the shark microbiome and identify a small, but conserved, number of intestinal microbial taxa as potential contributors to shark physiology.

Functional Roles and Ecological Importance of Small Cetaceans in Aquatic Ecosystems

Small cetaceans (dolphins, porpoises, and small toothed whales) occur from the poles to the tropics, and from freshwater habitats to the open ocean. Most ecological research has focused on the influence of abiotic factors on the abundance, distribution, and behavior of these species. The ecological impacts of small cetaceans on communities and ecosystems remain poorly quantified. Their movement patterns, often high local and regional abundances across a range of ecosystems, and high metabolic rates suggest that small cetaceans could have large effects on ecosystem structure, dynamics, and function through a variety of mechanisms. These include top-down (e.g., direct predation and risk effects) and bottom-up effects (e.g., translocation of nutrients within and across ecosystems), but also behavior-mediated processes where these predators can facilitate access to resources to other predators or modify the physical properties of habitat (e.g., bioturbation). Most small cetaceans can be consumed by other marine predators, particularly killer whales (Orcinus orca) and large sharks. Although consumption rates of small cetaceans can be high, there is a paucity of information on their effects on population sizes or behaviors of their prey. Mass-balance ecosystem models suggest that small cetaceans may impact the populations of short-lived prey species (particularly fish and cephalopods), but other factors (e.g., eutrophication and fisheries) also affect ecosystem functioning and population trends. Delphinids can also mediate the translocation and recycling of limiting nutrients between spatially distinct ecosystems on a diel basis. Despite intriguing possibilities, large gaps remain in our understanding of the roles and importance of small cetaceans in aquatic ecosystems, both marine and freshwater.

Evaluating the effects of a SharkSafe Barrier™ shoreline deployment on bull shark (Carcharhinus leucas) behaviour

Abstract Beach nets and drumlines are lethal devices that are used to minimize the interaction between potentially dangerous sharks and beachgoers. Mortality to these large shark species as a result of these lethal measures has led to the development of non‐invasive technologies that may minimize the risks of rare encounters with beachgoers while simultaneously protecting vulnerable sharks and other marine species. One such technology is the SharkSafe Barrier™, which uses visual and magnetic stimuli to non‐invasively deter sharks from a designated area. Previous experiments using this technology were performed on a small scale (e.g. 13 m × 13 m), with an attempt made to extrapolate the results to a larger scale application without actual large‐scale deployments and experimentation. The present study examined whether a large‐scale SharkSafe Barrier™ shoreline deployment could successfully exclude the bull shark (Carcharhinus leucas) from acoustic and olfactory cues and evaluated whether the technology could serve as a less invasive replacement to current culling practices. Generalized linear mixed‐model analyses based on 59 trials illustrate that C. leucas swimming behaviour (i.e. avoidances, entrances, and pass arounds) significantly differed between the control (i.e. unmanipulated area) and the experimental (i.e. SharkSafe Barrier™) regions. Unlike previous small‐scale experiments, 10 of 16 sharks repeatedly penetrated the barrier and swam in an accelerated manner once within the experimental barrier region. The present findings raise concerns that the size of the previous experimental areas may have been insufficient to provide a realistic representation of barrier efficacy for large‐scale deployments. With continued shark‐culling measures in various locations, a non‐invasive and eco‐friendly alternative is needed, but substantial modifications to the current Sharksafe barrier design or an entirely new eco‐friendly approach are needed as the barrier in its present state does not reliably deter large and potentially dangerous sharks from a large‐scale area.

Filling in knowledge gaps: Length–weight relations of 46 uncommon sharks and rays (Elasmobranchii) in the Mediterranean Sea

Large sharks and rays are generally understudied in the Mediterranean Sea, thus leading to a knowledge gap of basic biological characteristics that are important in fisheries management and ecosystem modeling. Out of the 76 sharks and rays inhabiting the Mediterranean Sea, the length–weight relations (LWR) are available for 28 (37%) of them, usually for common small-sized species that are not protected and may be marketed. The aim of the presently reported study was to fill in the knowledge gap through the estimation of LWR of rare and uncommon sharks and rays in the Mediterranean Sea using the information from single records or few individuals. The analysis was based on a Bayesian hierarchical method for estimating length–weight relations in fishes that has been recently proposed for data-deficient species or museum collections and uses the prior knowledge and existing LWR studies to derive species-specific LWR parameters by body form. The use of this method was applied to single records of rare and uncommon species and here we report the LWR of 46 uncommon sharks and ray species, 14 of which are first reported LWR at a global scale and 21 are the first reported LWR for the Mediterranean Sea; the remaining 11 species are first time records for the western or eastern Mediterranean regions. Museum collections and sporadic catch records of rare emblematic species may provide useful biological information with the use of appropriate Bayesian methods.

Filling in knowledge gaps: Length–weight relations of 46 uncommon sharks and rays (Elasmobranchii) in the Mediterranean Sea

Large sharks and rays are generally understudied in the Mediterranean Sea, thus leading to a knowledge gap of basic biological characteristics that are important in fisheries management and ecosystem modeling. Out of the 76 sharks and rays inhabiting the Mediterranean Sea, the length–weight relations (LWR) are available for 28 (37%) of them, usually for common small-sized species that are not protected and may be marketed. The aim of the presently reported study was to fill in the knowledge gap through the estimation of LWR of rare and uncommon sharks and rays in the Mediterranean Sea using the information from single records or few individuals. The analysis was based on a Bayesian hierarchical method for estimating length–weight relations in fishes that has been recently proposed for data-deficient species or museum collections and uses the prior knowledge and existing LWR studies to derive species-specific LWR parameters by body form. The use of this method was applied to single records of rare and uncommon species and here we report the LWR of 46 uncommon sharks and ray species, 14 of which are first reported LWR at a global scale and 21 are the first reported LWR for the Mediterranean Sea; the remaining 11 species are first time records for the western or eastern Mediterranean regions. Museum collections and sporadic catch records of rare emblematic species may provide useful biological information with the use of appropriate Bayesian methods.

Site fidelity, spatial use, and behavior of dwarf sperm whales in Hawaiian waters: using small‐boat surveys, photo‐identification, and unmanned aerial systems to study a difficult‐to‐study species

AbstractDwarf sperm whales (Kogia sima) have been studied rarely at sea. We used photo‐identification, boat‐ and drone‐based behavioral observations, and citizen science photo contributions to examine site fidelity, spatial use, and behavior in Hawaiʻi. Sighting rates were highest in island slope (500–1,000 m) waters. Over 40% of photo‐identified individuals were linked by association in the same social network. More than half of the very distinctive individuals were seen more than once, and 28.5% were seen in multiple years, with one individual seen 14 times over a 15‐year span. Resighted individuals and those in the main cluster of the social network were found in significantly shallower water than individuals that were not resighted or that were in isolated clusters. Distances between resighting locations suggest small home ranges. This suggests an insular slope‐dwelling population that overlaps with an offshore population. Evidence of unsuccessful predatory attempts by large sharks was recorded on four individuals, and linear wounds consistent with interactions with line fisheries were documented on three individuals. Surface and subsurface behavior recorded by drone revealed vigilance behavior likely to minimize predation risk. Lessons learned from this study can be applied elsewhere to increase knowledge of this poorly known and difficult‐to‐study species.

Nurse sharks, space rockets and cargo ships: Metals and oxidative stress in a benthic, resident and large-sized mesopredator, Ginglymostoma cirratum

It is widely recognized that apex predators, such as large sharks with highly migratory behavior, are particularly vulnerable to pollution, mainly due to biomagnification processes. However, in highly impacted areas, mesopredator sharks with resident behavior can be as vulnerable as apex sharks. In this context, this study evaluated cadmium (Cd), mercury (Hg), lead (Pb), and rubidium (Rb) concentrations, as well as the potentially protective effects of selenium (Se) and the behavior of two non-enzymatic biomarkers, metallothionein (MT) and reduced glutathione (GSH), employing the Atlantic nurse shark Ginglymostoma cirratum as a study model and compared the results with other resident benthic sharks, as well as highly mobile apex sharks. Muscle tissue samples from 28 nurse sharks opportunistically sampled from the Brazilian Amazon Coast were analyzed. Lower metal concentrations were observed for Pb, Rb and Se in the rainy season, while statistically significant correlations between metals were observed only between Hg and Cd and Pb and Se. Molar ratio calculations indicate potential protective Se effects against Pb, but not against Cd and Hg. No associations between MT and the determined metals were observed, indicating a lack of detoxification processes via the MT detoxification route. The same was noted for GSH, indicating no induction of this primary cellular antioxidant defense. Our results indicate that benthic/mesopredator sharks with resident behavior are, in fact, as impacted as highly mobile apex predators, with the traditional detoxification pathways seemingly inefficient for the investigated species. Moreover, considering the studied population and other literature data, pollution should be listed as a threat to the species in future risk assessments.

A closer look at the bycatch of medium‐sized and large sharks in the northern Catalan coast (north‐western Mediterranean Sea): Evidence of an ongoing decline?

Abstract Historically, the Mediterranean Sea supported a rich shark fauna. Presently, however, populations of most shark species have significantly declined, largely due to intense fishing pressure. Interviews with crew members of bottom trawlers, drifting longliners and bottom longliners operating off the Costa Brava (Catalonia, NE Spain) were conducted between October 2016 and July 2017 in order to gather information on the current bycatch rate of several shark species. Interviews covered 41.2% of the fleet and respondents were asked for the bycatch of selected shark species—Alopias vulpinus, Cetorhinus maximus, Galeorhinus galeus, Hexanchus griseus, Isurus oxyrinchus, Mustelus spp., Prionace glauca, and Squalus acanthias—in two distinct time periods. Bottom trawlers captured the highest diversity of species (eight) followed by bottom longliners (seven), and drifting longliners (three). Most respondents (89.7%) declared having captured at least one shark from 2006 to 2016 but only 56.4% declared having captured at least one shark from 2016 to 2017. From 2016 to 2017, the whole fleet captured 89 specimens of H. griseus (95% confidence interval (CI) = 145, 34), 14 of G. galeus (95% CI = 30, 0), 3 of A. vulpinus (95% CI = 8, 0), 3 of I. oxyrinchus (95% CI = 8, 0), 3 of C. maximus (95% CI = 6, 0), and no Mustelus spp. The total bycatch of P. glauca and S. acanthias was uncertain due to extremely loose confidence intervals. A significant decline was perceived by fishermen in the bycatch of C. maximus and S. acanthias, whereas the bycatch of H. griseus was considered to have remained stable. This study suggests a dramatic reduction in the abundance of most of the medium‐sized and large sharks of the Costa Brava and the likely disappearance of Mustelus spp. from the area. Only H. griseus, S. acanthias, and P. glauca are still being bycaught frequently.

Recreationist perceptions of lethal and non-lethal management of sharks in two of South Africa’s marine areas

Despite growing public pressure to use non-lethal strategies for managing predators (e.g., sharks) in marine ecosystems, the response of many governments remains largely lethal. This article examined recreationist support and understanding of approaches for managing sharks in two of South Africa’s marine areas. Questionnaires completed by 575 ocean recreationists at beaches near Cape Town and Durban showed they strongly disagreed with lethal management of sharks. The non-lethal Shark Spotters program was the most strongly supported strategy, followed by heat sensor cameras to detect sharks. Other non-lethal strategies (exclusion nets, personal repellent devices, deterrent cables, camouflage wetsuits) were supported by fewer than 50% of respondents, but were still more strongly supported than specific lethal strategies (shark hunts, drumlines, shark nets). Shark Spotters was more strongly supported near Cape Town, whereas the lethal strategies and a few of the other non-lethal approaches (personal electric repellent devices, electric deterrent cables, exclusion nets) were more strongly supported near Durban. Few respondents understood that shark nets and drumlines are designed to catch and kill large sharks. Understanding the function of shark nets correlated negatively with support for their use and positively with support for temporary exclusion nets. Implications of these results were discussed within the framework of a global transition from lethal to non-lethal management.

Large sharks exhibit varying behavioral responses to major hurricanes

Under global climate change, storm events are predicted to increase in strength and frequency. Although aquatic animals can be affected by acute natural disturbances, information on the immediate consequences of these weather systems on the behavioral ecology of highly mobile aquatic predators remains limited. Here we examine the spatial distributions, activity spaces, and ecological change-points of four large shark species (mean: 193 cm fork length ± 70 SD) via passive acoustic telemetry in two different locations in the subtropical Atlantic (Little Bahama Bank, Bahamas, and Biscayne Bay, Florida, USA) in relation to two separate major hurricane events (category 4 and 5). We tested whether sharks would evacuate shallow coastal habitats (and thus exit the acoustic arrays) during the hurricanes and exhibit comparable size of activity spaces pre- and post-storms, as has been previously found for smaller (50–150 cm fork length) sharks elsewhere. Located on the northwest edge of the Little Bahama Bank, Bahamas, an acoustic array consisting of 32 acoustic telemetry receivers tracking tiger sharks Galeocerdo cuvier sustained a direct hit from Hurricane Matthew in 2016. Daily detections of tagged tiger sharks within the array were consistent before and during the hurricane. Immediately following the storm, daily tiger shark detections approximately doubled. Size and extent of tiger shark activity space within the array were consistent pre- and post-storm. Located off Miami, within Biscayne Bay, an array of 32 acoustic receivers tracking bull Carcharhinus leucas, nurse Ginglymostoma cirratum, and great hammerhead sharks Sphyrna mokarran was exposed to tropical-storm-force winds from Hurricane Irma in 2017. As the eye of the storm passed 140 km to the west, most sharks previously present in the array were no longer detected, while two nurse sharks remained at receivers near Miami. Numbers of tagged bull sharks declined following Hurricane Irma, whereas other species did not. Ecological change point analyses indicated that seasonal changes - rather than storm conditions - cannot be ruled out as the primary driver of post-storm shark behavior. Unlike smaller shark species which have previously been found to evacuate shallow water habitats during storms, we found variable responses of large sharks to storm events.

Uso de BRUVS para describir el ensamble de peces y su estacionalidad en dos caletas marinas poco profundas dentro de áreas protegidas de la Patagonia, Argentina

Baited Remote Underwater Video Stations (BRUVS) complemented with fishing methods were used to describe the fish assemblage and its seasonal pattern in two marine inlets from Patagonia. The combined results for BRUVS and fishing sessions identified 13 fish species. Our results agree with the biogeographic schemes proposed for the southern Southwest Atlantic. The fish species belonging to the Argentine Biogeographic Province presented a seasonal pattern with a peak of maximum abundance (Notorynchus cepedianus and Galeorhinus galeus) or were recorded during warm months only (Mustelus schmitti, Myliobatis goodei, and M. ridens), coinciding with the general latitudinal pattern expected for fish species richness. The use of BRUVS in this study allowed for the assessment of different fish species and wide range of sizes, from large sharks (N. cepedianus) to small cryptic species (Patagonotothem sp.). However, three of 13 species were only recorded by fishing methods, like it was the case for M. ridens. The record of M. ridens is the first in Patagonian waters, extending its distribution for c. 180 km south of the previously known southern limit. This study contributes to filling large data gaps along the Southwest Atlantic regarding the description and understanding of the temporal dynamics of fish assemblages in particular environments within protected areas.

High resolution biologging of breaching by the world\u2019s second largest shark species

Basking sharks, the world’s second largest fish, are endangered globally following two centuries of large-scale exploitation for their oily livers. In the northeast Atlantic, they seasonally gather in key sites, including the western Scottish Isles, where they feed on plankton, but their breeding grounds are currently completely unknown. Using high-resolution three-axis accelerometry and depth logging, we present the first direct records of breaching by basking sharks over 41 days. We show that basking sharks breach both during the night and day, starting at approximately 20 m depth and can breach multiple times in short succession. We also present early evidence of potential lateralisation in basking sharks. Given the energetic nature of breaching, it should have an important biological function, but this remains unclear.

A Hooghly head‐scratcher

A Hooghly head‐scratcher

Spatial patterns of shark-inflicted injuries on coastal bottlenose dolphins in the Mesoamerican Reef System

ABSTRACT Understanding predator–prey relationships is critical in ecology, but relatively challenging when investigating elusive marine megafauna. In this study, we document the presence of shark-inflicted injuries on coastal bottlenose dolphins (Tursiops truncatus) in the Mesoamerican Reef System using photo-identification methods. We analyzed data from a total of 533 photo-identified bottlenose dolphins in Mexico (Ascención Bay, Espíritu Santo Bay, and Chetumal Bay), Belize (Turneffe Atoll, Drowned Cayes, Barrier Reef, and Placencia), and Honduras (Utila). We identified 16 individuals with shark-inflicted injury scars consistent with attacks by large sharks of the Family Carcharhinidae. Additionally, two bottlenose dolphins were encountered with round-shaped crater wounds, likely inflicted by a cookiecutter shark (Isistius spp.). The prevalence of shark-inflicted wounds in bottlenose dolphins varied markedly between sites, with the highest prevalence in Placencia and Ascención Bay (Mexico), and lowest in Turneffe Atoll and Drowned Cayes (Belize). Further research is required to evaluate how predation risk shapes the ecology of bottlenose dolphins in the Mesoamerican Reef region.

A comparison of alternative systems to catch and kill for mitigating unprovoked shark bite on bathers or surfers at ocean beaches

Responses to unprovoked shark bite involve public policies and management approaches that contend with the needs of public safety and the responsibility to protect threatened species. In Australia (Queensland and New South Wales) and South Africa, methods that aim to capture and kill large sharks adjacent to popular beaches are a long-standing approach aimed at reducing the risk of shark bite. This paper reviews non-lethal alternatives to catch and kill methods, and suggests optimal conditions for non-lethal systems that will assist policy makers and beach authorities in choosing public safety responses that can be applied at the ocean beach scale. Deployment needs to be strategic with sufficient knowledge of their likely effectiveness under local conditions. At this stage we believe there is no single approach universally applicable to ocean beaches where unprovoked shark bite occurs, although well considered and locally appropriate mitigation measures can reduce risk.