4 research outputs found
Bioecology and movements of bull sharks, Carcharhinus leucas , caught in a long-term longline survey off northeastern Brazil
Bioecology and movements of bull sharks, Carcharhinus leucas , caught in a long-term longline survey off northeastern Brazil
ABSTRACT A robust understanding of habitat usage by coastal shark species, and how it overlaps with human presence in densely-populated regions is needed to inform the development of efficient conservation strategies for these important top predators. An intensive longline survey conducted in nearshore waters off northeastern Brazil from 2004 through 2014 caught a total of 18 bull sharks (Carcharhinus leucas) (male-female ratio = 0.63:1), which can be dangerous to humans. Although most sharks were sexually mature, there was no evidence that this region could be used as a parturition or nursery area. Prey items identified in the guts of the sharks comprised teleosts, mollusks and elasmobranchs. Additionally, one satellite-tagged bull shark covered a great distance (> 3,000 km) in 75 days at liberty, making most use of shallow waters (< 20 m depth) and presumably also entering an estuarine area. Although bull sharks are not an important fishery resource in this region, such a reduced abundance coupled with its affinity for coastal and inshore habitats highlights the potential vulnerability of C. leucas to deleterious anthropic interferences off northeastern Brazil
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Multispecies thermal dynamics of air-exposed ectothermic sharks and its implications for fisheries conservation
Body temperature is a crucial component of thermoregulation, being strongly linked to variables such as energy flow, metabolic rates, activity patterns and resilience. With exception of lamnid sharks, elasmobranchs are classified as ectothermic, depending on ambient temperature for heat modulation. Despite often being removed from the water during fisheries interactions, the known effects of air exposure on sharks are limited to the hypoxia experienced. Comparatively little is known about the potential effects of changing ambient temperatures and solar radiation experienced by sharks during air exposure, and if such scenarios may compromise their thermal dynamics and survival. Here we used infrared thermography (IRT) to measure external body temperature of 10 different shark species (N = 62), ranging in size from 106 to 340 cm total length, experimentally exposed to air. We tested the hypothesis that all individuals would exhibit body surface temperature increases when air-exposed, with temperature uniformly distributed across the body surface regardless of species. Our results did not support this hypothesis. Although ectothermic, sharks exhibited significant species-specific variations in heat distribution and warming along the body surface. Moreover, these thermal patterns were significantly impacted by both environmental factors (water temperature at capture) as well as biological traits (shark size and body region). Multivariate analyses separated the 10-shark species into five groups according to the influences of shark body size, body region and water temperature on variations in the thermal profiles detected. We discuss the potential physiological, ecological and conservation implications of these findings.
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•Sharks exhibited significant species-specific variations in heat distribution and warming along the body surface•Thermal patterns were significantly impacted by both environmental factors as well as biological traits•Changes in shark body surface temperatures ranged from 0.1 to 7 °C, with the most significant changes being found in hammerhead sharks•Both ambient water temperatures and duration of air exposure should be considered to promote conservation efforts
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Thermal Imaging Reveals Changes in Body Surface Temperatures of Blacktip Sharks (Carcharhinus limbatus) during Air Exposure
Fish physiology is significantly affected by temperature variability. During fisheries interactions, fish are often exposed to air and subjected to rapid temperature changes. Fish thermal dynamics during such exposure, and the possible outcomes to their physiology, depend on how heat is distributed across their bodies, the speed at which their body temperatures change, and the size of the individual. Nevertheless, such thermal patterns remain unknown for sharks. This study employed a novel application of thermal imaging to evaluate external body temperature profiles of blacktip sharks (Carcharhinus limbatus) above-water exposure after capture. We found that above-water exposure duration, shark total length, and air temperature on the day of capture significantly influenced body surface temperatures of the analyzed sharks (N=28). Body surface temperature significantly increased with increasing exposure; however, thermal profiles of immature sharks (<140 cm) were significantly warmer than those of mature sharks. Moreover, blacktip surface body temperatures were significantly higher during days when air temperatures were at least 2.5°C warmer than water temperatures. We discuss these results as they relate to the ecology of blacktip sharks and their potential vulnerability to fisheries capture due to such changes in peripheral body temperature