Elemental analysis of otoliths and eye lenses in the assessment of Steller sea lion diets

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Title: Elemental analysis of otoliths and eye lenses in the assessment of Steller sea lion diets
Author: Ferenbaugh, Joy
Abstract: Steller sea lions (Eumetopias jubatus ) have historically ranged along the North Pacific Rim from the coast of California to Japan , but the population has dramatically declined since the 1960s . Research has indicated that nutritional stress is likely to be the main cause of the decline . Scat analysis is the preferred technique for dietary analysis of Steller sea lions , and fish otoliths and eye lenses are routinely recovered from pinniped scat . Fisheries scientists use elemental analysis of otoliths and eye lenses to provide information on fish biology , but marine mammalogists have not incorporated this technique to study prey fish or foraging behavior . In this dissertation , I examined the use of elemental analysis of prey fish otoliths and eye lenses in dietary studies for Steller sea lions . I first examined the use of otoliths as indicators of total body burdens of metal contaminants in the fish . Then , I assessed the effects of Steller sea lion digestion on the microchemistry of otoliths . Third , I examined the microchemistry of fish eye lenses , the effects of digestion on eye lenses , and their potential use in dietary analysis . Concentrations of some metals , such as zinc and barium , in undigested otoliths are significantly correlated with concentrations found in homogenized tissues , but several factors affect this relationship , such as fish species , sampling site on the otolith , and the specific metal being analyzed . The degradation of an otolith in the sea lion digestive tract is also likely to affect correlations between otolith and tissue metal concentrations . Steller sea lion digestion has significant effects on otolith microchemistry . These effects do not prohibit the use of digested otoliths in species determination for dietary analysis , but they may preclude using otoliths recovered from sea lion scat for fish stock separation , determination of foraging locations , and fish life history analyses . Eye lenses appear to be resistant to sea lion digestion , and they form sequential growth layers that can be used to age fish . The fibrous structure of the layers may inhibit symmetrical distributions across the lens for some elements , but the distinct elemental distributions across the lens may be useful in distinguishing fish species , discriminating between fish stocks , and tracking fish movements and spatial locations .
URI: http : / /hdl .handle .net /2346 /14280
Date: 2007-05

Citation

Elemental analysis of otoliths and eye lenses in the assessment of Steller sea lion diets. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /14280 .

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