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Identifying the geographical scale at which natural populations structure themselves is essential for conservation. One way to gauge this structure is by estimating local effective population size (Ne) and the associated measure of effective number of breeders (Nb), as the smaller and more isolated natural populations are, the smaller Ne and Nb they will present. However, as Ne and Nb are greatly influenced by demographic events and by both species’ behavior and biology, assessing the effectiveness of sample design is necessary to ensure the reliability of said estimates. Here, we first test the sample size effect on yearly Nb and generational Ne estimates from a lemon shark Negaprion brevirostris nursery in Bimini (The Bahamas) and subsequently compare these parameters to estimates of the minimal number of breeders based on pedigree reconstruction. We found that yearly estimates of Nb are positively correlated to annual variations in number of breeders estimated via pedigree reconstructions. Moreover, we measured that 30 individuals from a single cohort were sufficient to obtain reliable yearly estimates of Nb in Bimini’s lemon sharks. We then estimated generational Ne in 10 lemon shark nurseries across the Western Atlantic. Almost every nursery sampled represents an independent population on a generational time scale, with Ne rarely higher than 100 individuals. Our study reveals strong local population structure in lemon sharks, and thus their exposure to localized depletion or extirpation, suggesting that studies of coastal shark nursery areas could routinely estimate Ne and Nb to obtain management-relevant information on adult populations. .

Shark populations have declined across the Caribbean region, with negative associations between shark abundance and human population density, open access to fishing, and proximity to large markets (‘market gravity’). This decline is frequently attributed to fishing mortality, which increases in areas closer to humans and outside marine reserves. Although it is difficult to disentangle the effects of fishing mortality from other anthropogenic pressures on sharks, comparing shark abundance and diversity in jurisdictions with near zero fishing mortality versus prevalent shark fishing can demonstrate the role of overfishing. We used baited remote underwater video systems to compare shark abundance and diversity on coral reefs in 2 Caribbean nations with contrasting levels of shark exploitation: Belize (shark fishing) and The Bahamas (shark sanctuary). The abundance of targeted shark species and diversity were significantly higher in The Bahamas than in Belize. Caribbean reef and nurse shark abundance in Belize were best predicted by fishing-related factors (marine reserves, market gravity, their interaction). In The Bahamas, abiotic factors (depth, sea surface temperature) best predicted nurse shark abundance, while depth, market gravity, and its interaction with marine reserves predicted Caribbean reef shark abundance. These results indicate that fishing mortality reduces shark abundance and diversity in Belize, while lower fishing mortality in The Bahamas has greatly reduced but not eliminated human impacts on sharks. Future work should elucidate the indirect effects of humans to develop holistic shark conservation plans. We suggest minimizing shark fishing through multinational management plans to improve shark abundance and diversity, especially on reefs near densely populated areas.

Aim The Caribbean reef shark (Carcharhinus perezi) is one of few extant reef sharks inhabiting the Atlantic Ocean. Its variability in movements across habitat types suggests the possibility of a complex genetic population structure. Here, we use mitochondrial and nuclear DNA to investigate the genetic connectivity of the Caribbean reef shark across contemporary and evolutionary time-scales and relate our findings to the ecology of this understudied species. Location Tropical western Atlantic and Caribbean. Methods Samples were obtained from 216 individuals from six western Atlantic and Caribbean locations. Individuals were genotyped at seven nuclear microsatellite DNA loci and sequenced at two mitochondrial (control region [CR]; NADH dehydrogenase subunit 4 [ND4]) and one nuclear locus (lactate dehydrogenase [LDH]). Analyses to resolve the population genetic structure and evolutionary history of this species were adopted. Results Sequencing of the CR (1,068 bp, n = 216), ND4 (741 bp, n = 213) and LDH (258 bp, n = 165) loci, resolved 11, 8 and 13 unique haplotypes (or alleles), respectively. Overall, Caribbean reef sharks showed low levels of genetic diversity and most marker sets identified strong genetic differences (FST and ΦST) between sharks sampled in Brazil versus all other locations (msat FST > 0.017; CR-ND4 ΦST > 0.013). Mitochondrial DNA showed evidence of increased genetic partitioning among western North Atlantic sampling sites, although widespread haplotype sharing (~85%–92%) and a shallow population history were found. Main Conclusions Findings of genetic differentiation are concordant with previous movement studies showing residency and/or site-fidelity to specific locations by individuals. However, similar to other reef shark studies, we found that the level of genetic connectivity among populations was context dependent—i.e., sharks occupying isolated habitats showed greater genetic differentiation compared with those sharks occupying semi-isolated or continuous reef habitats. Furthermore, low genetic diversity and a shallow mitochondrial population history were found, suggesting historical demographic fluctuations, including population collapse and more recent expansions.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Fishing has had a profound impact on global reef shark populations, and the absence or presence of sharks is strongly correlated with national socio-economic conditions and reef governance. Decades of overexploitation have devastated shark populations, leaving considerable doubt as to their ecological status(1,2). Yet much of what is known about sharks has been inferred from catch records in industrial fisheries, whereas far less information is available about sharks that live in coastal habitats(3). Here we address this knowledge gap using data from more than 15,000 standardized baited remote underwater video stations that were deployed on 371 reefs in 58 nations to estimate the conservation status of reef sharks globally. Our results reveal the profound impact that fishing has had on reef shark populations: we observed no sharks on almost 20% of the surveyed reefs. Reef sharks were almost completely absent from reefs in several nations, and shark depletion was strongly related to socio-economic conditions such as the size and proximity of the nearest market, poor governance and the density of the human population. However, opportunities for the conservation of reef sharks remain: shark sanctuaries, closed areas, catch limits and an absence of gillnets and longlines were associated with a substantially higher relative abundance of reef sharks. These results reveal several policy pathways for the restoration and management of reef shark populations, from direct top-down management of fishing to indirect improvement of governance conditions. Reef shark populations will only have a high chance of recovery by engaging key socio-economic aspects of tropical fisheries.

Great barracuda (Sphyraena barracuda) were implanted with acoustic telemetry transmitters (n =4 2) and monitored within a stationary acoustic receiver array (n = 53 receivers) in The Bahamas to examine residency, seasonal movements, and habitat use. Barracuda were mon- itored for up to 980 days and remained within the array area »33% (median value) of the time. Most tagged barracuda were transient and would often disappear from the array for months at a time, particularly in the summer where they were usually last detected on receivers located in deeper shelf habitats, and then return at other times in the year. Habitat use across the footprint of the array diVered, with most detections occurring in coastal areas and compara- tively fewer in deeper mosaic or shelf habitats. Linear home range estimates revealed that some barracuda moved >12 km within a single day and are capable of migrating >100 km to other islands in the Bahamian Archipelago. Our results provide some of the Wrst telemetry data for this apex marine predatory Wsh and the Wrst reliable information on the residency and localized seasonal movements of adult great barracuda in the coastal waters of the Western

To identify the timing and location of spawning activity for boneWsh (Albula spp.) in the Bahamian archi- pelago, we used an acoustic telemetry array spanning 44 km 2 of shallow tidal creeks, Xats, and adjacent deeper coastal waters near Cape Eleuthera. In two successive years, we surgically implanted transmitters in male and female boneWsh (n = 60) and examined their movement patterns within the array. Eight boneWsh surgically implanted with transmitters as part of an earlier study were also tracked. In 2009, the telemetry information was com- plemented with snorkeling observations, underwater video, and manual tracking of the same acoustically tagged Wsh, as well as Wsh (n = 3) gastrically implanted with continuous transmitters. During a period of 4-7 days spanning the full and new moons, primarily between October and May, boneWsh moved from their typical shallow Xats and aggre- gated at sites in close proximity to the deep water drop-oV of the Exuma Sound. Localized movements of the large schools of boneWsh (often >1,000 Wsh) at these presumptive pre-spawning aggregation sites included brief trips ( 1,000 m depth). Tagged boneWsh detected at these aggregation sites were subsequently detected back in the tidal creeks and coastal Xats shortly after new and full moons and remained at these more typical shallow sites (i.e.

Throughout their circumtropical distribution, bone¢sh (Albula spp.) play a vital role in local economies as a highly prized sport ¢sh. Recent interest in stock enhancement to sustain bone¢sh ¢sheries has led to the recognition that there currently are no data on how to live capture large numbers of adults (potential broodstock), transport them to captive facilities and how to handle them to ensure high survival. The objective of this study was to develop strategies for the capture and relocation of wild bone¢sh to a marine research holding facility to enable basic research and explore the potential for culturing bone¢sh for stock enhancement. Bone¢sh Albula vulpes (Linnaeus,1758) were captured as they entered or left tidal creeks on Eleuthera, The Bahamas using seine nets and then transported by boat or truck to the laboratory. The relocation process evoked secondary stress responses at the metabolic, osmoregulatory and haematological levels as indicated by changes in blood glucose, lactate, haematocrit and ion values, relative to control ¢sh. Physical and behavioural disturbances were also observed in bone¢sh that were unable to acclimate to laboratory conditions. Successful laboratory acclimation and long-term holding of wild bone¢sh was achieved through an adaptive learning process, whereby we identi¢ed a series of strategies and handling techniques to facilitate the acclimation of wild adult bone¢sh to captivity. This knowledge will enable future laboratory research on bone¢sh and is a prerequisite to the culture of this highly prized sport ¢sh, and other sub-tropical and tropical marine species.