San Diego State University
Department of Biology
Fish Ecology Lab
Trophic ecology of the common thresher (Alopias vulpinus) and shortfin mako (Isurus oxyrinchus) from the Northeast Pacific (funded by NOAA Fisheries Service)
Sean Suk's thesis project --
The common thresher, Alopias vulpinus, and the shortfin mako, Isurus oxyrinchus, are top predators in marine pelagic food webs. What is currently known about the diet of these two large sharks comes primarily from anecdotal observations of their stomach contents. Stomach contents provide a snapshot view of an individualís most recent diet providing high resolution, but large year-round standardized sampling is necessary to capture temporal differences, and the large volume of unidentifiable digested matter confounds interpretations.
Stable isotopes are naturally occurring forms of an element that differ only in their number of neutrons. Stable isotope analysis can be used to infer the feeding ecology of organisms because the isotopic signature of an organism is derived from its diet and environment. Thus, stable isotopes can be used to complement and validate stomach content-based diet studies.
In this study, Sean investigated the
trophic ecology of the common thresher and shortfin mako from the Northeast Pacific by using stable isotope analysis of
δ13C and δ15N from white muscle, liver, and vertebral
centra. He compared the trophic position between the two sharks
where they co-occurred, and investigated both intraspecific and interspecific
ontogenetic differences in their isotopic signatures, including suspected
shifts in diet. By utilizing multiple
tissues with different rates of isotopic turnover, Sean also investigated localized and
cumulative feeding patterns of these species.
This page was last modified on May 10, 2012.
SDSU Fish Ecology Lab
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