Physiological Ecology of Elasmobranchs in the Gulf of Mexico and Northwestern Atlantic
Prohaska, Bianca Karoli (author)
Grubbs, R. Dean (professor directing dissertation)
Eckel, Lisa A. (university representative)
Travis, Joseph, 1953- (committee member)
DuVal, Emily H. (committee member)
Burgess, Scott C (committee member)
Gelsleichter, James J. (committee member)
Florida State University (degree granting institution)
College of Arts and Sciences (degree granting college)
Department of Biological Science (degree granting department)
A thorough understanding of the physiology of elasmobranchs (sharks, skates, and rays) is important from an applied aspect as most species are captured either directly or indirectly in commercial and recreational fisheries, or affected by other anthropogenic stressors such as habitat loss. Since we know very little about this group's physiology, it is unknown how they respond to these stressors, and how they survive stressful events. This is particularly important for endangered and threatened species such as the smalltooth sawfish Pristis pectinata, but also for those species that are data deficient like many of the deep-sea sharks in the Gulf of Mexico. Through this dissertation I aimed to investigate the physiology of a variety of elasmobranchs, and investigate ecological, evolutionary, and applied research questions. Similar to other elasmobranchs, the smalltooth sawfish Pristis pectinata is slow-growing, matures late in life, and produces relatively few young, all factors which have contributed to its sensitivity to dramatic population declines from overfishing and habitat loss. Currently, the physiological stress response of these fish to capture or to other physiological challenges such as habitat loss, climatic changes, or pollution is unknown. We examined basic stress physiology over ontogeny and as a function of capture using different fishing gears. We also examined stress parameters to test whether degraded habitat and water quality from altered habitats may have resulted in chronic stress in juveniles. Results suggested that the stress response to capture by all methods was low, particularly for blood lactate, compared to other elasmobranchs examined to date. Metabolic stress was found to change over ontogeny, with young of the year (YOY) eliciting the highest responses. Glucose, pCO2, bicarbonate, potassium, and hematocrit indicated gillnet capture induced greater stress responses than longline capture. Significantly higher metabolic stress was observed in YOY and juveniles captured in the two nurseries most influenced by anthropogenic activities, the Peace and Caloosahatchee rivers, than in the two relatively pristine nurseries in Everglades National Park. Prior to the Deep-Water Horizon (DwH) oil spill, little research effort was focused on studying the physiology of deep-sea sharks inhabiting the Gulf of Mexico. While the biology of these fishes remains virtually unknown, they are routinely captured in commercial fisheries as bycatch. Also unknown is what potential detrimental effects the DwH oil spill, which occurred at 1,500 m deep, has had and will continue to have on these organisms. The basic physiological post-capture stress response was examined and compared among seven deep-sea shark species including Mustelus sinusmexicanus, Mustelus canis, Squalus cubensis, Squalus clarkae, Centrophorus uyato, Centrophorus granulosus, and Hexanchus griseus and as functions of depth and proximity to the oil spill. Results suggested there may be taxonomic similarity in the stress response, but the responses we observed were more likely driven by habitat as two congeners that inhabit two distinct habitats displayed very different responses, and much closer to the other sharks in their respective habitats. We found a greater relative stress response in shallower inhabiting sharks as well as smaller bodied sharks. With increasing body temperature metabolic rate increases, as does the capture stress response; however, the core temperatures of the larger bodied deeper dwelling species were not altered as drastically as the smaller bodied sharks, indicating that the stress response of these sharks in this study may have been delayed. No increase in the stress response was detected with proximity of capture to the DwH oil spill site. The scalloped hammerhead Sphyrna lewini, and the great hammerhead Sphyrna mokarran are large, coastal to semi-oceanic shark species common to waters of the U.S. east coast and are regularly taken in commercial and recreational fisheries, particularly the bottom longline fishery, in this region. High rates of hooking mortality and low rates of population growth are believed to have caused severe declines in the U.S. Atlantic populations of these species. The objective was to determine the physiological stress induced by bottom longline capture in both S. lewini and S. mokarran, and to assess the post-release survivorship of S. lewini using survivorship pop-off archival satellite tags (PSATLIFE). Nine PSATLIFE tags were deployed and the results suggested 89% survival post release, with hook durations ranging from 6-136 minutes, and release conditions of excellent, good and fair. The one observed mortality experienced a hooking duration of 54 min and was released in fair condition. The physiological stress parameters lactate, pCO2, and pH were found to scale negatively with time since hooking and condition factor in both species. These data will be useful for providing at boat mortality estimates of S. mokarran and the physiological stress response to longline capture in both species to the Atlantic bottom longline fishery.
November 13, 2018.
A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
R. Dean Grubbs, Professor Directing Dissertation; Lisa Eckel, University Representative; Joseph Travis, Committee Member; Emily DuVal, Committee Member; Scott Burgess, Committee Member; James Gelsleichter, Committee Member.
Florida State University