Doctor of Philosophy (PhD)
Oceanography & Coastal Sciences
The enactment of wide-ranging conservation laws in the United States enabled the recovery of many marine mammal species. However, as many species have surpassed predicted recovery goals, there is an increasing number of marine mammal-human interactions. For example, in the northeast US, the recovery of gray seals (Halichoerus grypus atlantica), coupled with declines in commercially important fishery species, has prompted discussions of revised management, and potentially lethal control measures. Much of this concern stems from seal-fisheries interactions, which necessitates an understanding of seal diets and foraging ecology. However, existing research is out of date and reliant primarily on analysis of hard prey remains from feces. Alternative methodologies, such as stable isotope and DNA metabarcoding analyses, have the potential to overcome the limitations associated with hard prey remain analysis.
The goal of this dissertation is to use these techniques to gain an improved understanding of the foraging ecology of gray seals around Cape Cod, Massachusetts. Using a suite of tissues, I determined that adult gray seals seasonally shift their foraging behaviors between the breeding and molting periods. However, individual seals are generally consistent relative to each other in their foraging habitats, though not necessarily the prey resources they use, such that adults can be considered individual specialists in a population of generalists. Analysis of seal pup prenatal fur allowed me to analyze female gray seals during pregnancy and revealed consistent behavior in population level trophic niches over four breeding seasons, though variation in individual adult female foraging behaviors was correlated with variation in pup body condition. An investigation of diet using the three methods (hard prey remains, stable isotope, and DNA metabarcoding analyses) in tandem revealed largely concordant diet estimates during the summer and fall months, with seals at this time relying primarily upon sand lance (Ammodytes spp.) and other fish and invertebrate prey species with little to no commercial importance to Massachusetts fisheries. Overall, my dissertation research provides an improved understanding of the trophic role of gray seals inhabiting the northeast US coastal marine ecosystem and can be used for more effective management and mitigation of seal-human interactions.
Hernandez, Keith Michael, "Insights to Gray Seal (Halichoerus grypus) Foraging Ecology from Stable Isotope and DNA Metabarcoding Analyses" (2020). LSU Doctoral Dissertations. 5317.
Available for download on Monday, June 26, 2023