Longline fishing is the most common elasmobranch capture method in the world, both for commercial fishing, and to a lesser extent for scientific surveys. The capture of an animal on a longline initiates a series of physiological responses designed to promote survivorship in the short term, but if unchecked, can cause reduced individual fitness and/or mortality in the long term. Given widespread declines in shark populations, an improved understanding of the physiological costs of longline capture is needed. The aim of this thesis was to investigate the physiological response of sharks to capture and restraint, to assess novel, non-invasive alternatives to scientific longline surveys, and to generate scientific insight into poorly understood elasmobranch populations in The Bahamas. The results presented herein suggest that some species of shark are able to recover from the physiological stress of capture despite the presence of persistent negative stimuli. Tonic immobility was assessed as a means of generating baseline blood chemistry data, but was found to be inappropriate given that it increases the magnitude of physiological perturbation in the short term. To avoid the stress of capture altogether, Baited Remote Underwater Video Surveys (BRUVS) were considered as a non-invasive alternative to capture based surveys, however, it was concluded that they lack the resolution necessary to answer fine scale demographic questions. For the Caribbean reef shark, longline surveys yielded high resolution data allowing the identification of fine scale spatiotemporal shifts in demographic population structure with minimal cost (mortality). Nevertheless, the ethics of using capture based surveys on sensitive species are questionable when alternative techniques are available. Deep water sharks caught on longline surveys exhibited high mortality rates, however, for these very poorly understood species moribund specimens have great scientific value which in some cases can offset the high ecological costs of the surveys. The results presented in this thesis highlight the on-going need for improved biological and ecological research into the majority of elasmobranch populations, particularly with regards to anthropogenic interactions such as capture. Given the tenuous conservation status of many species, the acquisition of applied, management focused data should remain the priority of elasmobranch scientists.

Habitat use of mesophotic coral reefs by sharks is largely unknown. However, it is well established that mesophotic reefs are the site of spawning aggregations for many species of teleost fish. These aggregations represent seasonal concentrations of potential prey biomass that may influence the habitat use of predatory species such as large sharks. I employed acoustic monitoring to examine the movements of three shark species [lemon shark (Negaprion brevirostris), tiger shark (Galeocerdo cuvier), and Caribbean reef shark (Carcharhinus perezi)] to determine 1) the comparative spatiotemporal patterns of mesophotic reef habitat use by the three shark species and 2) the spatiotemporal relationship between these sharks and grouper spawning aggregations at a fish spawning aggregation (FSA) site (Hind Bank and Grammanik Bank) along the southern reef shelf edge off St. Thomas, United States Virgin Islands (USVI). Tiger and lemon sharks were detected across nearly the entire acoustic array, which spanned ~ 1060 km2. When present, Caribbean reef sharks used a much smaller activity space, composed exclusively of mesophotic reef habitat located within FSA sites. Individuals from all three species were typically detected for stretches of several consecutive days, while periods without detections usually lasted less than one week. Lemon sharks were present at the FSA site more often during the grouper spawning season (Dec-May) than the non-spawning season (Jun-Nov), but showed no preference toward specific areas within the FSA site, which varied by location and grouper species composition. In contrast, there was no relationship between the presence of tiger and Caribbean reef sharks at the FSA site and the grouper spawning season. My results suggest that despite different habitat use 5 patterns and varying degrees of fidelity, this mesophotic reef serves as an important habitat to all three shark species.

Habitat use of mesophotic coral reefs by sharks is largely unknown. However, it is well established that mesophotic reefs are the site of spawning aggregations for many species of teleost fish. These aggregations represent seasonal concentrations of potential prey biomass that may influence the habitat use of predatory species such as large sharks. I employed acoustic monitoring to examine the movements of three shark species lemon shark (Negaprion brevirostris), tiger shark (Galeocerdo cuvier), and Caribbean reef shark (Carcharhinus perezi)] to determine 1) the comparative spatiotemporal patterns of mesophotic reef habitat use by the three shark species and 2) the spatiotemporal relationship between these sharks and grouper spawning aggregations at a fish spawning aggregation (FSA) site (Hind Bank and Grammanik Bank) along the southern reef shelf edge off St. Thomas, United States Virgin Islands (USVI). Tiger and lemon sharks were detected across nearly the entire acoustic array, which spanned ~ 1060 km2. When present, Caribbean reef sharks used a much smaller activity space, composed exclusively of mesophotic reef habitat located within FSA sites. Individuals from all three species were typically detected for stretches of several consecutive days, while periods without detections usually lasted less than one week. Lemon sharks were present at the FSA site more often during the grouper spawning season (Dec-May) than the non-spawning season (Jun-Nov), but showed no preference toward specific areas within the FSA site, which varied by location and grouper species composition. In contrast, there was no relationship between the presence of tiger and Caribbean reef sharks at the FSA site and the grouper spawning season. My results suggest that despite different habitat use patterns and varying degrees of fidelity, this mesophotic reef serves as an important habitat to all three shark species.