Bimini Biological Field Station Foundation

Age information is often non‐existent for most shark populations due to a lack of measurable physiological and morphological traits that can be used to estimate age. Recently, epigenetic clocks have been found to accurately estimate age for mammals, birds, and fish. However, since these clocks rely, among other things, on the availability of reference genomes, their application is hampered in non‐traditional model organisms lacking such molecular resources. The technique known as Methyl‐Sensitive Amplified Polymorphism (MSAP) has emerged as a valid alternative for studying DNA methylation biomarkers when reference genome information is missing, and large numbers of samples need to be processed. Accordingly, the MSAP technique was used in the present study to characterize global DNA methylation patterns in lemon sharks from three different age groups (juveniles, subadults, and adults). The obtained results reveal that, while MSAP analyses lack enough resolution as a standalone approach to infer age in these organisms, the global DNA methylation patterns observed using this technique displayed significant differences between age groups. Overall, these results confer that DNA methylation does change with age in sharks like what has been seen for other vertebrates and that MSAP could be useful as part of an epigenetics pipeline to infer the broad range of ages found in large samples sizes.

Understanding dispersal in large marine fauna is necessary for conservation, but movement patterns often vary widely by sex and life stage. In sharks, genetic studies have shown evidence of widespread male-biased dispersal, though tagging and tracking studies on the same populations show both sexes using site fidelity, including philopatry, and moving similar distances. We used a suite of microsatellite loci and DNA samples from 362 previously-tagged tiger sharks (Galeocerdo cuvier) in the northwestern Atlantic, including a large number of residential juveniles, to evaluate reproductive dispersal in light of demographic and published tracking data. We found that lumping size classes together resulted in genetic panmixia across sites, but systematic removal of large individuals showed significant population-level differentiation and three separate population clusters among juveniles less than 260 cm total length. Tests for relatedness found that 8.9% of our sample set was composed of first-order related pairs (N = 16), including several full siblings from different litters, a sign of multi-cycle genetic monogamy which carries implications for effective population size. By mapping genetic assignments of juveniles, we identified a signature of fine-scale genetic structure suggesting broad biparental site fidelity to reproductive habitat in the northeast Gulf of Mexico, which is concordant with both genetic and tracking data. Taken together, these findings demonstrate how lumping individuals from different life stages in genetic studies may obscure fine-scale genetic structure, confounding future conservation efforts.

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.

Abstract Shark predation risk impacts many facets of dolphin life, including habitat use and foraging strategies. Because direct predation is rarely observed, researchers instead examine dolphins in situ for past injuries that can be attributed to sharks. We analyzed existing photo‐ID catalogs of common bottlenose (Tursiops truncatus) and Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas. A minimum of 29% of individual T. truncatus had evidence of a past, nonlethal shark bite, while for S. frontalis this was only 15%. For both species, shark‐induced injuries were predominantly on the dorsal side. Regression analyses indicated that T. truncatus were more likely to have shark bite scars than S. frontalis and the likelihood of documenting a shark bite scar increased with a higher percentage of the body photographed. T. truncatus were less likely to have scars in the dorsal region, but sampling differences could have influenced these results. While the shark species responsible for scars was not determined, T. truncatus and S. frontalis overlap spatially and temporally with tiger (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas) off Bimini. This study builds on the understanding of dolphin/shark interactions from longitudinal studies of dolphins in this region, providing insight into factors influencing predation risk.

Dynamic body acceleration (DBA), measured through animal-attached tags, has emerged as a powerful method for estimating field metabolic rates of free-ranging individuals. Following respirometry to calibrate oxygen consumption rate (ṀO2) with DBA under controlled conditions, predictive models can be applied to DBA data collected from free-ranging individuals. However, laboratory calibrations are generally performed on a relatively narrow size range of animals, which may introduce biases if predictive models are applied to differently sized individuals in the field. Here, we tested the mass dependence of the ṀO2-DBA relationship to develop an experimental framework for the estimation of field metabolic rates when organisms differ in size. We performed respirometry experiments with individuals spanning one order of magnitude in body mass (1.74-17.15 kg) and used a two-stage modelling process to assess the intraspecific scale dependence of the ṀO2-DBA relationship and incorporate such dependencies into the coefficients of ṀO2predictive models. The final predictive model showed scale dependence; the slope of the ṀO2-DBA relationship was strongly allometric (M1.55), whereas the intercept term scaled closer to isometry (M1.08). Using bootstrapping and simulations, we evaluated the performance of this coefficient-corrected model against commonly used methods of accounting for mass effects on the ṀO2-DBA relationship and found the lowest error and bias in the coefficient-corrected approach. The strong scale dependence of the ṀO2-DBA relationship indicates that caution must be exercised when models developed using one size class are applied to individuals of different sizes.

Limited data pertaining to life history and population connectivity of the data-deficient southern stingray (Hypanus americanus) are available. To determine potential vulnerabilities of their populations, this study aimed to analyse their movement patterns and genetic variability. A population of southern stingrays encompassing nine sites around Cape Eleuthera, the Bahamas, has been monitored using mark-recapture, spanning a 2.5 year period. Out of 200 individual stingrays, more than a third were encountered again. The home range of the females appears to be restricted, which supports the notion of high site residency. As resident populations of stingrays could suffer from a lack of population connectivity and be predestined for genetic isolation and local extirpation, this study further investigated the genetic connectivity of four sample sites in the central and western Bahamas. A haplotype analysis from the mitochondrial D-loop region showed that no distinct population structure strictly correlated with the sample site. These findings were complemented by five microsatellite loci that revealed high degrees in genotypic variability and little population differentiation. The results suggest gene flow mediated by both males and females.

Accurately estimating contacts between animals can be critical in ecological studies such as examining social structure, predator–prey interactions or transmission of information and disease. While biotelemetry has been used successfully for such studies in terrestrial systems, it is still under development in the aquatic environment. Acoustic telemetry represents an attractive tool to investigate spatio-temporal behaviour of marine fish and has recently been suggested for monitoring underwater animal interactions. To evaluate the effectiveness of acoustic telemetry in recording interindividual contacts, we compared co-occurrence matrices deduced from three types of acoustic receivers varying in detection range in a benthic shark species. Our results demonstrate that (i) associations produced by acoustic receivers with a large detection range (i.e. Vemco VR2W) were significantly different from those produced by receivers with smaller ranges (i.e. Sonotronics miniSUR receivers and proximity loggers) and (ii) the position of individuals within their network, or centrality, also differed. These findings suggest that acoustic receivers with a large detection range may not be the best option to represent true social networks in the case of a benthic marine animal. While acoustic receivers are increasingly used by marine ecologists, we recommend users first evaluate the influence of detection range to depict accurate individual interactions before using these receivers for social or predator–prey studies. We also advocate for combining multiple receiver types depending on the ecological question being asked and the development of multi-sensor tags or testing of new automated proximity loggers, such as the Encounternet system, to improve the precision and accuracy of social and predator–prey interaction studies.