Stable carbon and nitrogen signatures have proved useful in reconstructing migratory pathways and food webs in marine fishes. Otoliths are particularly amenable to suitable for such analyses because they contain a dated record of environmental and physiological conditions experienced by a fish throughout its life. However, the full potential of stable isotope analysis has yet to be realized due to the small quantity of organic material present in otoliths. Hence, the investigators will develop a new technique, based on moving wire isotope ratio mass spectrometry, for compound-specific analyses of d13C and d15N ratios in small (2-5 nmol) amounts of purified amino acids from otoliths in marine fishes. Once developed, the technique will be suitable for any application that requires measurement of C and N isotopes in organic material where sample quantity is limited. These data will be transformative when coupled with migratory information recorded in the inorganic isotope and trace element chemistry of otolith aragonite because researchers will be able to determine not only where an individual fish was living, but also what it was eating, throughout its life.
The broader impacts include support for the PhD research of one student and incorporation of the research into courses taught by the investigator. The research will also benefit society by providing critical information for the development of ecosystem management strategies for marine-capture fisheries. The use of amino acids that fractionate trophically more than bulk C and N will undoubtedly improve resolution of diet studies based on C and N isotopes. This will, in turn, allow fisheries scientists to better understand the links between climate and fisheries production, and to explore these relationships during past regime shifts on the west coast of the U.S., and trophic cascades in the western Atlantic Ocean
