Bioaccumulated trace element toxicity in commercially harvested bronze whaler sharks (Carcharhinus brachyurus) of South Africa.

Shark meat consumption may pose a significant risk to human health as high levels of toxic pollutants bioaccumulate in muscular tissue. Commercial harvest of Carcharhinus brachyurus meat in South Africa is estimated at 100-300 filleted tons per annum. Muscle tissue samples from 41 sharks were collected from the southern and eastern coastlines of South Africa in 2022 and analysed for 10 trace elements and 8 polychlorinated biphenyl congeners. All trace elements were found to be lower than the regulatory maximum limits for human consumption in most samples irrespective of shark length, sex, and sampling region. However, the estimated daily intake for Mercury and Arsenic exceeded the oral reference dose set by international agencies. The meat from this shark may be consumed due to its low toxic potential for human health, however long-term exposure to C. brachyurus meat should be avoided as it could pose detrimental health risks to consumers.

A Mozambican marine protected area provides important habitat for vulnerable pelagic sharks.

Pelagic sharks play key roles in marine ecosystems, but are increasingly threatened by human extraction, habitat degradation and mismanagement. We investigated the use of protected and unprotected coastal habitats by bull (Carcharhinus leucas) and oceanic blacktip (Carcharhinus limbatus) sharks in southern Mozambique. Five INNOVASEA VR2W-69 kHz acoustic receivers were positioned in the Bazaruto Archipelago National Park (BANP) as well as one to the south of the park's boundaries. Seven receivers were also deployed 250 km south in the Inhambane estuary and on reef sites off Praia de Tofo. Twelve bull, and six oceanic blacktip sharks, were fitted with INNOVASEA V16 acoustic tags, which generated 933 detections of bull and 12,381 detections of oceanic blacktip sharks over a period of 1391 days. A generalised additive model was used to estimate the effects of seven spatiotemporal and environmental parameters on the frequency of each species' detections. In general, calculated residency indices were highest around the locations monitored in the BANP and one unprotected location off Tofo. Both species were more abundant across the monitored sites, during the summer when water temperatures were ~ 27 °C, when the moon was < 50% illuminated, and when the tide was rising. Detections coincided with each species' reproductive season indicating that both species may be reproductively active in the BANP region. Oceanic blacktip sharks were largely resident and so fisheries management may significantly benefit their population(s) around certain reef habitats in the BANP. The low residency and seasonal detections of bull sharks indicates that they may be transient and so effective conservation may require coordination between regional fisheries managers.

The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling.

Although shark teeth are abundant in the fossil record, their bodies are rarely preserved. Thus, our understanding of the anatomy of the extinct Otodus megalodon remains rudimentary. We used an exceptionally well-preserved fossil to create the first three-dimensional model of the body of this giant shark and used it to infer its movement and feeding ecology. We estimate that an adult O. megalodon could cruise at faster absolute speeds than any shark species today and fully consume prey the size of modern apex predators. A dietary preference for large prey potentially enabled O. megalodon to minimize competition and provided a constant source of energy to fuel prolonged migrations without further feeding. Together, our results suggest that O. megalodon played an important ecological role as a transoceanic superpredator. Hence, its extinction likely had large impacts on global nutrient transfer and trophic food webs.

Are you really what you eat? Stomach content analysis and stable isotope ratios do not uniformly estimate dietary niche characteristics in three marine predators.

Calculation of dietary niche characteristics using stable isotopes has become a popular approach to understand the functional role of taxa across food webs. An underlying assumption of this approach is that stable isotopes accurately reflect the dietary breadth of a species over a temporal duration defined by tissue-specific isotopic turnover rates. In theory, dietary niche estimates derived from fast turnover rate tissues (e.g., blood plasma and liver) may augment stomach content-derived estimates more agreeably than slower turnover rate tissues (e.g., muscle or fin). We tested this hypothesis by comparing commonly used dietary niche estimates derived from stomach contents (nicheSCA: Levins', Shannon-Wiener's, and Smith's), with those estimated using stable isotopes [nicheSIA: standard ellipse area (SEA), convex hull total area (TA), theta (θ), and ellipse eccentricity (E)] of liver and muscle tissue. Model species were three large-bodied sharks: white (Carcharodon carcharias), dusky (Carcharhinus obscurus), and scalloped hammerhead (Sphyrna lewini). Within-technique comparisons for nicheSCA and nicheSIA metrics (i.e., SEA vs. TA) were often correlated; however, we did not observe any statistically significant correlations between nicheSCA and liver/muscle tissue nicheSIA (i.e., Levins' vs. SEA). We conclude that nicheSCA and nicheSIA do not provide comparable estimates of dietary niche, at least for the three predator species examined. This fundamental discrepancy highlights technique-specific limitations to estimating organismal dietary niche and identifies a need for the use of clearly defined niche metrics, i.e., the standardized use and reporting of the term isotopic niche as proposed by Newsome et al. (Front Ecol Environ 5:429-436, 2007). Finally, further investigation into the factors underpinning nicheSIA is required to better contextualize this popular ecological metric when compared to nicheSCA.