Defining sources of variation in diets of northern phocids using stable isotopes and quantitative fatty acid signature analysis.

• Main Author: Tucker, Strahan.
• Other Authors: Ph.D.
• Format: Text
• Language: English
• Published: Dalhousie University 2014
• Subjects: Biology; Ecology; Oceanography; Canada; Cystophora cristata; Northwest Atlantic; Phoca groenlandica
• Online Access: http://hdl.handle.net/10222/54975

What animals consume is perhaps one of the most fundamental questions in ecology. Diet has important consequences with respect to energy intake, overall foraging costs and influences the degree of competitive interactions amongst organisms. Recent collapse of fisheries in the northwest Atlantic has renewed concerns over the role of seal predation in marine food webs. Harp (Phoca groenlandica), hooded (Cystophora cristata ) and grey (Halichoerus grypus) seals share considerable overlap in foraging range. However they also exhibit distinct differences in body size, degree of sexual size dimorphism, diving patterns and foraging behaviour. Very little is actually known about what these seals consume across their foraging ranges, especially given that previous diet estimates are biased by nearshore sampling and unavoidable biases associated with stomach content analysis. The development of alternative biochemical methods to estimate diet has overcome some of these problems. The two main approaches are fatty acid (FA) signature and stable isotope analysis. Both of these tracer approaches can provide inferences about or quantitative estimates of diet that are time-integrated. Estimates are made at the level of the individual thereby increasing our ability to understand and detect differences among demographic groups. The main goal of my research was to examine the diet of seals at varying spatial and temporal scales, and by doing so, increase our understanding of factors influencing the dietary niche breath of large marine predators displaying different foraging tactics. Given broad evidence for their importance in other taxa, I sought to evaluate age, size and sex related effects on diet selection for grey, harp and hooded seals. Second, I evaluated large-scale temporal and geographic variation in seal diets over a decade that saw large changes in prey distribution and abundance. Overall I noted broad inter-and intra-specific variation in diets, diet quality and diet breadth. Key findings demonstrate that seals show marked demographic and individual variation in feeding, thus individuals are achieving similar endpoints by exploiting different energy sources. These results lend further support for the idea of multiple foraging strategies with convergent success and underscore the need to account for such variability in developing predation models. Thesis (Ph.D.)--Dalhousie University (Canada), 2007.