Intraguild processes drive space-use patterns in a large-bodied marine predator community

Interspecific interactions, including predator-prey, intraguild predation (IGP) and competition, may drive distribution and habitat use of predator communities. However, elucidating the relative importance of these interactions in shaping predator distributions is challenging, especially in marine communities comprising highly mobile species. We used individual-based models (IBMs) to predict the habitat distributions of apex predators, intraguild (IG) prey and prey. We then used passive acoustic telemetry to test these predictions in a subtropical marine predator community consisting of eight elasmobranch (i.e. shark and ray) species in Bimini, The Bahamas. IBMs predicted that prey and IG prey will preferentially select habitats based on safety over resources (food), with stronger selection for safe habitat by smaller prey. Elasmobranch space-use patterns matched these predictions. Species with predator-prey and asymmetrical IGP (between apex and small mesopredators) interactions showed the clearest spatial separation, followed by asymmetrical IGP among apex and large mesopredators. Competitors showed greater spatial overlap although with finer-scale differences in microhabitat use. Our study suggests space-use patterns in elasmobranchs are at least partially driven by interspecific interactions, with stronger spatial separation occurring where interactions include predator-prey relationships or IGP.

Longest recorded migration of a silky shark (Carcharhinus falciformis) reveals extensive use of international waters of the Tropical Eastern Pacific

Despite being a heavily fished species, little is known about the movements of silky sharks (Carcharhinus falciformis). In this study, we report the longest (in duration and distance traveled) and most spatially extensive recorded migration for a silky shark. This shark, tagged with a fin-mount satellite transmitter at the Galapagos Islands, traveled >27,666 km over 546 days, making two westerly migrations into international waters as far as 4755 km from the tagging location. These extensive movements in an area with high international fishing effort highlights the importance of understanding silky shark migrations to inform management practices.

Collecting baleen whale blow samples by drone: A minimally intrusive tool for conservation genetics

In coastal British Columbia, Canada, marine megafauna such as humpback whales (Megaptera novaeangliae) and fin whales (Balaenoptera physalus velifera) have been subject to a history of exploitation and near extirpation. While their populations have been in recovery, significant threats are posed to these vulnerable species by proposed natural resource ventures in this region, in addition to the compounding effects of anthropogenic climate change. Genetic tools play a vital role in informing conservation efforts, but the associated collection of tissue biopsy samples can be challenging for the investigators and disruptive to the ongoing behaviour of the targeted whales. Here, we evaluate a minimally intrusive approach based on collecting exhaled breath condensate, or respiratory 'blow' samples, from baleen whales using an unoccupied aerial system (UAS), within Gitga'at First Nation territory for conservation genetics. Minimal behavioural responses to the sampling technique were observed, with no response detected 87% of the time (of 112 UAS deployments). DNA from whale blow (n = 88 samples) was extracted, and DNA profiles consisting of 10 nuclear microsatellite loci, sex identification and mitochondrial (mt) DNA haplotypes were constructed. An average of 7.5 microsatellite loci per individual were successfully genotyped. The success rates for mtDNA and sex assignment were 80% and 89% respectively. Thus, this minimally intrusive sampling method can be used to describe genetic diversity and generate genetic profiles for individual identification. The results of this research demonstrate the potential of UAS-collected whale blow for conservation genetics from a remote location.

Genetic identification of three CITES-listed sharks using a paper-based Lab-on-a-Chip (LOC)

Threatened shark species are caught in large numbers by artisanal and commercial fisheries and traded globally. Monitoring both which shark species are caught and sold in fisheries, and the export of CITES-restricted products, are essential in reducing illegal fishing. Current methods for species identification rely on visual examination by experts or DNA barcoding techniques requiring specialist laboratory facilities and trained personnel. The need for specialist equipment and/or input from experts means many markets are currently not monitored. We have developed a paper-based Lab-on-a-Chip (LOC) to facilitate identification of three threatened and CITES-listed sharks, bigeye thresher (Alopias superciliosus), pelagic thresher (A. pelagicus) and shortfin mako shark (Isurus oxyrinchus) at market source. DNA was successfully extracted from shark meat and fin samples and combined with DNA amplification and visualisation using Loop Mediated Isothermal Amplification (LAMP) on the LOC. This resulted in the successful identification of the target species of sharks in under an hour, with a working positive and negative control. The LOC provided a simple "yes" or "no" result via a colour change from pink to yellow when one of the target species was present. The LOC serves as proof-of-concept (PoC) for field-based species identification as it does not require specialist facilities. It can be used by non-scientifically trained personnel, especially in areas where there are suspected high frequencies of mislabelling or for the identification of dried shark fins in seizures.

Adaptation of sea turtles to climate warming: Will phenological responses be sufficient to counteract changes in reproductive output?

Sea turtles are vulnerable to climate change since their reproductive output is influenced by incubating temperatures, with warmer temperatures causing lower hatching success and increased feminization of embryos. Their ability to cope with projected increases in ambient temperatures will depend on their capacity to adapt to shifts in climatic regimes. Here, we assessed the extent to which phenological shifts could mitigate impacts from increases in ambient temperatures (from 1.5 to 3°C in air temperatures and from 1.4 to 2.3°C in sea surface temperatures by 2100 at our sites) on four species of sea turtles, under a "middle of the road" scenario (SSP2-4.5). Sand temperatures at sea turtle nesting sites are projected to increase from 0.58 to 4.17°C by 2100 and expected shifts in nesting of 26-43 days earlier will not be sufficient to maintain current incubation temperatures at 7 (29%) of our sites, hatching success rates at 10 (42%) of our sites, with current trends in hatchling sex ratio being able to be maintained at half of the sites. We also calculated the phenological shifts that would be required (both backward for an earlier shift in nesting and forward for a later shift) to keep up with present-day incubation temperatures, hatching success rates, and sex ratios. The required shifts backward in nesting for incubation temperatures ranged from -20 to -191 days, whereas the required shifts forward ranged from +54 to +180 days. However, for half of the sites, no matter the shift the median incubation temperature will always be warmer than the 75th percentile of current ranges. Given that phenological shifts will not be able to ameliorate predicted changes in temperature, hatching success and sex ratio at most sites, turtles may need to use other adaptive responses and/or there is the need to enhance sea turtle resilience to climate warming.

Comparing acoustic and satellite telemetry: an analysis quantifying the space use of Chelonia mydas in Bimini, Bahamas

Passive acoustic and Argos satellite telemetry are common methods for tracking marine species and are often used similarly to quantify space use. However, data-driven comparisons of these methods and their associated ecological inferences are limited. To address this, we compared temporal durations, spatial resolutions, financial costs and estimates of occurrence and range distributions for each tracking approach using nine juvenile green turtles (Chelonia mydas) in Bimini, Bahamas. Tracking durations were similar, although acoustic tracking provided higher spatiotemporal resolution than satellite tracking. Occurrence distributions (95%) estimated from satellite telemetry were 12 times larger than those from acoustic telemetry, while satellite range distributions (95%) were 89 times larger. While individuals generally remained within the extent of the acoustic receiver array, gaps in coverage were identified. These gaps, combined with the lower accuracy of satellite telemetry, were likely drivers for the larger satellite distributions. Costs differed between telemetry methods, with acoustic telemetry being less expensive at larger sample sizes with a previously established array. Our results suggest that acoustic and satellite telemetry may not provide similar inferences of individual space use. As such, we provide recommendations to identify telemetry methods appropriate for specific study objectives and provide discussion on the biases of each.

Elemental analysis of vertebrae discerns diadromous movements of threatened non-marine elasmobranchs

River sharks (Glyphis spp.) and some sawfishes (Pristidae) inhabit riverine environments, although their long-term habitat use patterns are poorly known. We investigated the diadromous movements of the northern river shark (Glyphis garricki), speartooth shark (Glyphis glyphis), narrow sawfish (Anoxypristis cuspidata), and largetooth sawfish (Pristis pristis) using in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on vertebrae to recover elemental ratios over each individual's lifetime. We also measured elemental ratios for the bull shark (Carcharhinus leucas) and a range of inshore and offshore stenohaline marine species to assist in interpretation of results. Barium (Ba) was found to be an effective indicator of freshwater use, whereas lithium (Li) and strontium (Sr) were effective indicators of marine water use. The relationships between Ba and Li and Ba and Sr were negatively correlated, whereas the relationship between Li and Sr was positively correlated. Both river shark species had elemental signatures indicative of prolonged use of upper-estuarine environments, whereas adults appear to mainly use lower-estuarine environments rather than marine environments. Decreases in Li:Ba and Sr:Ba at the end of the prenatal growth zone of P. pristis samples indicated that parturition likely occurs in fresh water. There was limited evidence of prolonged riverine habitat use for A. cuspidata. The results of this study support elemental-environment relationships observed in teleost otoliths and indicate that in situ LA-ICP-MS elemental characterization is applicable to a wide range of elasmobranch species as a discriminator for use and movement across salinity gradients. A greater understanding of processes that lead to element incorporation in vertebrae, and relative concentrations in vertebrae with respect to the ambient environment, will improve the applicability of elemental analysis to understand movements across the life history of elasmobranchs into the future.

Comparative population genomics of manta rays has global implications for management

Understanding population connectivity and genetic diversity is of fundamental importance to conservation. However, in globally threatened marine megafauna, challenges remain due to their elusive nature and wide-ranging distributions. As overexploitation continues to threaten biodiversity across the globe, such knowledge gaps compromise both the suitability and effectiveness of management actions. Here, we use a comparative framework to investigate genetic differentiation and diversity of manta rays, one of the most iconic yet vulnerable groups of elasmobranchs on the planet. Despite their recent divergence, we show how oceanic manta rays (Mobula birostris) display significantly higher heterozygosity than reef manta rays (Mobula alfredi) and that M. birostris populations display higher connectivity worldwide. Through inferring modes of colonization, we reveal how both contemporary and historical forces have likely influenced these patterns, with important implications for population management. Our findings highlight the potential for fisheries to disrupt population dynamics at both local and global scales and therefore have direct relevance for international conservation of marine species.

First records of the Pacific sleeper shark Somniosus cf. pacificus in the western tropical Pacific

Technological advances have enabled the expansion of ocean exploration to include the deep ocean, providing new species observations. Here, the authors present two new observations, captured by deep-sea cameras, of the sleeper shark Somniosus cf. pacificus from the Solomon Islands and Palau. This presents the first observation of S. cf. pacificus in the western Pacific tropics and extends its range about 2000 nautical miles south. The observations presented here provide much-needed information on the range of this species which can help guide future management and conservation actions.

Public perception of an important urban estuary: Values, attitudes, and policy support in the Biscayne Bay-Miami Social Ecological System

Understanding public perceptions, values, and preferences can be fundamental to effective conservation governance, management, and outreach. This is particularly true in socially and ecologically complex marine and coastal spaces, where many relevant questions remain. The social-ecological system of Biscayne Bay and Miami-Dade are on the frontier of problems that will soon engulf many coastal-urban systems. Despite the economic, ecological, and cultural importance of Biscayne Bay, research into the social components of this social-ecological system is distinctly lacking. In order to effectively address urgent coastal management issues, practitioners and policy-makers need a clear understanding of public perceptions, values, and priorities. In this paper I present the results of a large online survey (n = 1146) exploring public attitudes toward Biscayne Bay as a case study of management and opportunity in a complex coastal social-ecological system. Results describe a public that interacts with and utilizes Biscayne Bay in a variety of ways, from leisure and recreation, to subsistence. This public believes the Bay to be moderately healthy, though somewhat in decline, and has experienced a range of local environmental threats, about which they feel considerable concern. These interactions and concerns are in turn reflected in overwhelming endorsement of value statements regarding the ecological, material, cultural and economic importance of the ecosystem to the city, as well as high levels of support for policy actions to protect and restore that ecosystem. Together these findings indicate that additional policy steps to preserve and restore Biscayne Bay would enjoy support from the local public and demonstrate the power of public perceptions research to identify gaps and opportunities for management and outreach.

Observations of fin injury closure in Great Hammerheads and implications for the use of fin-mounted geolocators

OBJECTIVE

Sharks face a high risk of injuries throughout all life stages and are therefore expected to show a good wound closure capacity.

METHODS

Here, the wound closure of one major injury and one minor injury to the first dorsal fins of two free-ranging, mature female Great Hammerheads Sphyrna mokarran is described macroscopically.

RESULT

The sharks showed complete wound closure of single, clean-cut lacerations measuring 24.2 and 11.6 cm in length after an estimated 323 and 138 days. These estimates were based on the observed closure rate and visual confirmation of a complete wound closure upon multiple resightings of the same individuals. Additionally, the posterior lateral displacement of fin-mounted geolocators within the fin and outside of the fin without causing external damage was documented in three additional Great Hammerheads.

CONCLUSION

These observations supplement findings about wound closure capabilities in elasmobranchs. The documented geolocator displacement furthers the discussion about the safe use of these geolocators to track shark movements but also has implications for future tagging studies.

Elucidating the role of competition in driving spatial and trophic niche patterns in sympatric juvenile sharks

The coexistence of ecologically and morphologically similar species is often facilitated by the partitioning of ecological niches. While subordinate species can reduce competition with dominant competitors through spatial and/or trophic segregation, empirical support from wild settings, particularly those involving large-bodied taxa in marine ecosystems, are rare. Shark nursery areas provide an opportunity to investigate the mechanisms of coexistence. We used experimental and field studies of sympatric juvenile sharks (blacktip reef shark, Carcharhinus melanopterus; sicklefin lemon shark, Negaprion acutidens) to investigate how competitive ability influenced realized niches at St. Joseph Atoll, Seychelles. Captive trials revealed that sicklefin lemon sharks were dominant over blacktip reef sharks, consistently taking food rewards. In the field, blacktip reef sharks were captured over a broader area than sicklefin lemon sharks, but daily space use of actively tracked sharks showed a high degree of overlap across microhabitats. While stomach contents analysis revealed that blacktip reef shark diets included a broader range of prey items, stable isotope analysis demonstrated significantly higher mean δ¹³C values for sicklefin lemon sharks, suggesting diverging dietary preferences. Overall, our results matched theoretical predictions of subordinate competitors using a greater range of habitats and displaying broader feeding niches than competitively dominant species. While separating the realized and fundamental niche of marine predators is complicated, we provide evidence that resource partitioning is at least partially driven by interspecific competition.

Conserving threatened species during rapid environmental change: using biological responses to inform management strategies of giant clams

Giant clams are threatened by overexploitation for human consumption, their valuable shells and the aquarium trade. Consequently, these iconic coral reef megafauna are extinct in some former areas of their range and are included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and Convention on International Trade in Endangered Species of Wild Fauna and Flora. Now, giant clams are also threatened by rapid environmental change from both a suite of local and regional scale stressors and global change, including climate change, global warming, marine heatwaves and ocean acidification. The interplay between local- to regional-scale and global-scale drivers is likely to cause an array of lethal and sub-lethal effects on giant clams, potentially limiting their depth distribution on coral reefs and decreasing suitable habitat area within natural ranges of species. Global change stressors, pervasive both in unprotected and protected areas, threaten to diminish conservation efforts to date. International efforts urgently need to reduce carbon dioxide emissions to avoid lethal and sub-lethal effects of global change on giant clams. Meanwhile, knowledge of giant clam physiological and ecological responses to local-regional and global stressors could play a critical role in conservation strategies of these threatened species through rapid environmental change. Further work on how biological responses translate into habitat requirements as global change progresses, selective breeding for resilience, the capacity for rapid adaptive responses of the giant clam holobiont and valuing tourism potential, including recognizing giant clams as a flagship species for coral reefs, may help improve the prospects of these charismatic megafauna over the coming decades.

Fin whales of the Great Bear Rainforest: Balaenoptera physalus velifera in a Canadian Pacific fjord system

Fin whales (Balaenoptera physalus) are widely considered an offshore and oceanic species, but certain populations also use coastal areas and semi-enclosed seas. Based upon fifteen years of study, we report that Canadian Pacific fin whales (B. p. velifera) have returned to the Kitimat Fjord System (KFS) in the Great Bear Rainforest, and have established a seasonally resident population in its intracoastal waters. This is the only fjord system along this coast or elsewhere in which fin whales are known to occur regularly with strong site fidelity. The KFS was also the only Canadian Pacific fjord system in which fin whales were commonly found and killed during commercial whaling, pointing to its long-term importance. Traditional knowledge, whaling records, and citizen science databases suggest that fin whales were extirpated from this area prior to their return in 2005-2006. Visual surveys and mark-recapture analysis documented their repopulation of the area, with 100-120 whales using the fjord system in recent years, as well as the establishment of a seasonally resident population with annual return rates higher than 70%. Line transect surveys identified the central and outer channels of the KFS as the primary fin whale habitat, with the greatest densities occurring in Squally Channel and Caamaño Sound. Fin whales were observed in the KFS in most months of the year. Vessel- and shore-based surveys (27,311 km and 6,572 hours of effort, respectively) indicated regular fin whale presence (2,542 detections), including mother-calf pairs, from June to October and peak abundance in late August-early September. Seasonal patterns were variable year-to-year, and several lines of evidence indicated that fin whales arrived and departed from the KFS repeatedly throughout the summer and fall. Additionally, we report on the population's social network and morphometrics. These findings offer insights into the dynamics of population recovery in an area where several marine shipping projects are proposed. The fin whales of the Great Bear Rainforest represent a rare exception to general patterns in this species' natural history, and we highlight the importance of their conservation.

A hitchhiker guide to manta rays: Patterns of association between Mobula alfredi, M. birostris, their symbionts, and other fishes in the Maldives

Despite being among the largest and most charismatic species in the marine environment, considerable gaps remain in our understanding of the behavioural ecology of manta rays (Mobula alfredi, M. birostris). Manta rays are often sighted in association with an array of smaller hitchhiker fish species, which utilise their hosts as a sanctuary for shelter, protection, and the sustenance they provide. Species interactions, rather than the species at the individual level, determine the ecological processes that drive community dynamics, support biodiversity and ecosystem health. Thus, understanding the associations within marine communities is critical to implementing effective conservation and management. However, the underlying patterns between manta rays, their symbionts, and other hitchhiker species remain elusive. Here, we explore the spatial and temporal variation in hitchhiker presence with M. alfredi and M. birostris throughout the Maldives and investigate the factors which may influence association using generalised linear mixed effects models (GLMM). For the first time, associations between M. alfredi and M. birostris with hitchhiker species other than those belonging to the family Echeneidae are described. A variation in the species of hitchhiker associated with M. alfredi and M. birostris was identified, with sharksucker remora (Echeneis naucrates) and giant remora (Remora remora) being the most common, respectively. Spatiotemporal variation in the presence of manta rays was identified as a driver for the occurrence of ephemeral hitchhiker associations. Near-term pregnant female M. alfredi, and M. alfredi at cleaning stations, had the highest likelihood of an association with adult E. naucrates. Juvenile E. naucrates were more likely to be associated with juvenile M. alfredi, and a seasonal trend in E. naucrates host association was identified. Remora were most likely to be present with female M. birostris, and a mean number of 1.5 ± 0.5 R. remora were observed per M. birostris. It is hoped these initial findings will serve as the basis for future work into the complex relationships between manta rays and their hitchhikers.

Environmental drivers of reef manta ray (Mobula alfredi) visitation patterns to key aggregation habitats in the Maldives

A detailed understanding of the dynamics of small-scale (10s km) habitat use by the reef manta ray (Mobula alfredi) in the Maldives Archipelago is required to develop an effective national conservation management plan for this wide-ranging species. Here, a combination of photo-ID sightings data and acoustic telemetry were used to investigate both long-term M. alfredi visitation trends and small-scale movement patterns to key habitats on the eastern side of Baa Atoll (Hanifaru Bay feeding area, Dhigu Thila multifunctional site, and Nelivaru Thila cleaning station). All tagged and most of the sighted M. alfredi exhibited high affinity to the eastern side of Baa Atoll, where 99% of detections occurred, and 69% of individuals were re-sighted in multiple years. Sightings data suggests that visitation patterns may be associated with differences in habitat use by sex and maturity status. Boosted regression trees indicated that tag detection probability at Hanifaru Bay increased with increased westerly wind speed (>5ms-1) during the day, close to a new and full moon just after high tide, and when the tidal range was low. Interaction effects between predictors suggest that wind-driven oceanographic processes, such as Langmuir Circulation, maybe working to increase zooplankton concentration at this location. Tag detection probability increased at Dhigu Thila under similar conditions. At Nelivaru Thila, it increased at lower wind speeds (<5ms-1), close to a full moon, three hours after high tide. These results suggest that M. alfredi may utilise cleaning stations during the day when environmental conditions are not suitable for feeding. There was a high level of connectivity between these three locations, which suggests they form part of a network of key habitats that provide essential services to M. alfredi locally. Future conservation efforts should focus on identifying all areas of key habitat use for this species within the Maldives; applying strict protective measures to these sites and any connecting migration corridors which link them.

Social survival: Humpback whales (Megaptera novaeangliae) use social structure to partition ecological niches within proposed critical habitat

Animal culture and social bonds are relevant to wildlife conservation because they influence patterns of geography, behavior, and strategies of survival. Numerous examples of socially-driven habitat partitioning and ecological-niche specialization can be found among vertebrates, including toothed whales. But such social-ecological dynamics, described here as ‘social niche partitioning’, are not known among baleen whales, whose societies—particularly on foraging grounds—are largely perceived as unstructured and incidental to matters of habitat use and conservation. However, through 16 years of behavioral observations and photo-identifications of humpback whales (Megaptera novaeangliae) feeding within a fjord system in the Canadian Pacific (primarily within Gitga’at First Nation waters), we have documented long-term pair bonds (up to 12 years) as well as a complex societal structure, which corresponds closely to persistent patterns in feeding strategy, long-term site fidelity (extended occupancy and annual rate of return up to 75%), specific geographic preferences within the fjord system, and other forms of habitat use. Randomization tests of network congruency and clustering algorithms were used to test for overlap in patterns of social structure and habitat use, which confirmed the occurrence of social niche partitioning on the feeding grounds of this baleen whale species. In addition, we document the extensive practice of group bubble net feeding in Pacific Canada. This coordinated feeding behavior was found to strongly mediate the social structure and habitat use within this humpback whale society. Additionally, during our 2004–2019 study, we observed a shift in social network structure in 2010–2012, which corresponded with environmental and demographic shifts including a sudden decline in the population’s calving rate. Our findings indicate that the social lives of humpback whales, and perhaps baleen whales generally, are more complex than previously supposed and should be a primary consideration in the assessment of potential impacts to important habitat.

Overfishing and habitat loss drive range contraction of iconic marine fishes to near extinction

Extinctions on land are often inferred from sparse sightings over time, but this technique is ill-suited for wide-ranging species. We develop a space-for-time approach to track the spatial contraction and drivers of decline of sawfishes. These iconic and endangered shark-like rays were once found in warm, coastal waters of 90 nations and are now presumed extinct in more than half (n = 46). Using dynamic geography theory, we predict that sawfishes are gone from at least nine additional nations. Overfishing and habitat loss have reduced spatial occupancy, leading to local extinctions in 55 of the 90 nations, which equates to 58.7% of their historical distribution. Retention bans and habitat protections are urgently necessary to secure a future for sawfishes and similar species.

Revision of the sixgill sawsharks, genus Pliotrema (Chondrichthyes, Pristiophoriformes), with descriptions of two new species and a redescription of P. warreni Regan

Recent sampling efforts in Madagascar and Zanzibar, as well as examinations of six-gilled sawsharks in several museum collections provided evidence for a complex of species within Pliotrema warreni Regan. The present manuscript contains a redescription of P. warreni involving the syntypes and additional material, as well as formal descriptions of two new species of Pliotrema Regan. All specimens of both new species were found in the western Indian Ocean. Individuals of the first new species, hereafter referred to as P. kajae sp. nov., were identified originating from Madagascar and the Mascarene Ridge. Specimens of the second new species, hereafter referred to as P. annae sp. nov., were only found off Zanzibar. Pliotrema kajae sp. nov. appears to inhabit upper insular slopes and submarine ridges at depths of 214–320 m, P. annae sp. nov. so far is only known from shallow waters (20–35 m). Both new species differ from P. warreni in a number of characteristics including the known distribution range and fresh coloration. Taxonomical differences include barbels that are situated approximately half way from rostral tip to mouth, with prebarbel length equidistant from barbel origin to symphysis of the upper jaw in P. kajae sp. nov. and P. annae sp. nov. (vs. about two thirds way from rostral tip to mouth, with prebarbel length about twice the distance from barbel origin to symphysis of upper jaw in P. warreni) and rostra that are clearly and slightly constricted between barbel origin and nostrils, respectively (vs. rostrum not constricted). Pliotrema kajae sp. nov. differs from P. annae sp. nov. in a longer snout, more numerous large lateral rostral teeth and upper jaw tooth rows, jaw teeth with (vs. without) sharp basal folds, and coloration, particularly pale to light brown (vs. medium to dark brown) dorsal coloration with (vs. without) two indistinct yellowish stripes. A revised diagnosis of Pliotrema and a key to the species are provided.

Local drivers of declining shark fisheries in India

This study evaluates local-scale drivers of shark harvests in India, one of the world's largest shark fishing nations. Focusing on key harbours in the states of Gujarat and Maharashtra, which together contribute 54% of India's shark harvest, this study uses a semi-structured survey to examine the practices of shark fishers and traders, their knowledge of shark trade and policy, and perceptions of shark declines. Findings indicate that a domestic market for shark meat is presently the main local driver for harvests rather than the global trade in shark fins. Sharks are mostly non-target catch, landed whole, contributing to the protein needs of coastal communities. Consumer demand is the greatest for small-bodied and juvenile sharks. Perceived steep declines in shark numbers and sizes have had economic impacts on fishers and traders. The unregulated domestic market for shark meat is a key challenge requiring nuanced local approaches that diverge from global shark conservation priorities.

Stable isotope analyses reveal unique trophic role of reef manta rays (Mobula alfredi) at a remote coral reef

Stable isotope analyses provide the means to examine the trophic role of animals in complex food webs. Here, we used stable isotope analyses to characterize the feeding ecology of reef manta rays (Mobula alfredi) at a remote coral reef in the Western Indian Ocean. Muscle samples of M. alfredi were collected from D'Arros Island and St. Joseph Atoll, Republic of Seychelles, in November 2016 and 2017. Prior to analysis, lipid and urea extraction procedures were tested on freeze-dried muscle tissue in order to standardize sample treatment protocols for M. alfredi. The lipid extraction procedure was effective at removing both lipids and urea from samples and should be used in future studies of the trophic ecology of this species. The isotopic signatures of nitrogen (δ¹⁵N) and carbon (δ¹³C) for M. alfredi differed by year, but did not vary by sex or life stage, suggesting that all individuals occupy the same trophic niche at this coral reef. Furthermore, the isotopic signatures for M. alfredi differed to those for co-occurring planktivorous fish species also sampled at D'Arros Island and St. Joseph Atoll, suggesting that the ecological niche of M. alfredi is unique. Pelagic zooplankton were the main contributor (45%) to the diet of M. alfredi, combined with emergent zooplankton (38%) and mesopelagic prey items (17%). Given the extent of movement that would be required to undertake this foraging strategy, individual M. alfredi are implicated as important vectors of nutrient supply around and to the coral reefs surrounding D'Arros Island and St. Joseph Atoll, particularly where substantial site fidelity is displayed by these large elasmobranchs.

Summer at the beach: spatio-temporal patterns of white shark occurrence along the inshore areas of False Bay, South Africa

BACKGROUND

Understanding white shark (Carcharodon carcharias) habitat use in coastal areas adjacent to large cities, is an important step when formulating potential solutions to the conservation conflict that exists between humans and large predatory sharks. In this study, we present the findings of a 2.5-year study of white shark occurrence and movement patterns adjacent to the City of Cape Town in False Bay, South Africa, with a focus on spring and summer months. Fifty-one white sharks were monitored annually at three offshore and twelve inshore sites by VR2 acoustic receivers, over 975 days from 1 May 2005 to 31 December 2007.

RESULTS

Occurrence patterns at inshore sites during spring and summer were analysed using a generalized additive mixed model (GAMM) with a spatial term (longitude, latitude), time of day and year included as explanatory variables for site use. We found that sharks occurred more frequently at inshore sites along the northern and northwestern shores, compared to the rest of the bay, and they transitioned most frequently between four adjacent beach sites that encompass the most popular recreational water use areas in Cape Town. There was significant diel variation, with higher shark occurrence around midday, and a peak in shark occurrence in 2005, when human-shark interactions also peaked. However, we found no effect of shark size on occurrence patterns at inshore sites.

CONCLUSIONS

White sharks showed the highest levels of occurrence at specific inshore sites between Muizenberg and Strandfontein beach, and thus inclusion of these sites within False Bay's marine protected area (MPA) network or recognition as Ecological or Biological Significant Areas (EBSAs) should be a future consideration. These insights into white shark habitat use at inshore sites in False Bay are important for successfully applying the principles of marine spatial planning (MSP) and for making science-based policy decisions. Furthermore, this information can be used to reduce potential shark-human conflict by incorporating it into future shark safety education campaigns.

Biogeophysical and physiological processes drive movement patterns in a marine predator

BACKGROUND

Blue sharks (Prionace glauca) are among the most abundant and widely distributed of oceanic elasmobranchs. Millions are taken annually in pelagic longline fisheries and comprise the highest component of auctioned fin weight in the international shark fin trade. Though studies of blue sharks outnumber those of other large pelagic sharks, the species' complicated and sexually segregated life history still confound current understanding of Atlantic movement patterns. Lack of detailed information regarding movement and vertical behavior continues to limit management efforts that require such data for stock assessment and sustainable catch modeling. Therefore, this study aims to describe behavioral and ecological patterns distinct to aggregating and migrating blue sharks, and compare the findings to existing Atlantic movement models.

RESULTS

Data collected from 23 blue sharks instrumented with pop-up satellite archival tags were used in statistical predictive regression models to investigate habitat use during a localized aggregation in the northwest Atlantic, while undergoing seasonal migrations, and with respect to environmental variables. Deployment durations ranged from 4 to 273 days, with sharks inhabiting both productive coastal waters and the open ocean, and exhibiting long-distance seasonal movements exceeding 3700 km. While aggregating on the continental shelf of the northwest Atlantic, blue sharks displayed consistent depth use independent of sex and life stage, and exhibited varied response to environmental (temperature and chlorophyll a) factors. As sharks dispersed from the aggregation site, depth use was influenced by bathymetry, latitude, demography, and presence in the Gulf Stream. Mature females were not observed at the New England tagging site, however, two mature females with recent mating wounds were captured and tagged opportunistically in The Bahamas, one of which migrated to the Mid-Atlantic Ridge.

CONCLUSIONS

Vertical behaviors displayed by blue sharks varied greatly among locales; depth use off the continental shelf was significantly greater, and individuals exhibited a greater frequency of deep-diving behavior, compared to periods of aggregation on the continental shelf. Sexual segregation was evident, suggesting mature and immature males, and immature females may be subjected to high levels of anthropogenic exploitation in this region during periods of aggregation. Analysis of the spatio-temporal tracks revealed that nine individuals traveled beyond the United States EEZ, including a mature female captured in The Bahamas that migrated to the Mid-Atlantic Ridge. These results reflect and augment existing Atlantic migration models, and highlight the complex, synergistic nature of factors affecting blue shark ecology and the need for a cooperative management approach in the North Atlantic.