Insights into shark ecology and physiology with stable isotope analysis.

摘要

Elasmobranchs include approximately 900 described species of sharks, skates, and rays, which can be found throughout marine ecosystems and some freshwater habitats. These species share unique physiological and morphological traits, but have varying ecological roles as meso- and apex predators in estuarine and pelagic environments. However, many elasmobranch species are difficult to study using traditional methods, so relatively little is known about their diet and movement patterns. Stable isotope analysis, a biogeochemical tool, is often used to study the ecology of mammals, birds, and teleosts. However, the preparation methods necessary to apply this technique to elasmobranch ecology and the biological parameters needed to interpret the results are not established.;To apply stable isotope analysis to elasmobranch ecology, new preparation methods and biological parameters are necessary. I examined the effects of various methods to collect, preserve, and prepare elasmobranch tissues for stable isotope analysis. Then, I conducted a feeding experiment for approximately 1200 days with leopard sharks (Triakis semifasciata) and established trophic enrichment factors (the isotopic difference between consumer tissues and their diet) and tissue turnover rates (which controls the temporal resolution of nutrient assimilation). My results are the first robust trophic enrichment factors and turnover rates established for elasmobranch plasma, red blood cells, and muscle.;Individual dietary preferences within a population can also be identified and quantified with stable isotope analysis. Shark vertebral centra grow by accretion and therefore provide lifetime records for individuals. I analyzed the carbon and nitrogen isotope composition of annual vertebral growth bands from white sharks caught in the northeast Pacific Ocean. A comparison between young and adult growth bands indicate ontogenetic differences, but there are different patterns among individuals. In addition, the northeast Pacific population has a relatively high degree of individuality and a bimodal distribution of specialists and generalists.;This work will improve the application and accuracy of stable isotope techniques when applied to elasmobranch ecology. With these established methods and biological parameters, the trophic structure and food web dynamics of elasmobranchs can be better understood and characterized. Stable isotope analysis provides a potentially powerful tool to better understand elasmobranch ecology that will inform management, conservation, and paleontological research.