This project will assess spatial and ontogenetic variability in the trophic status of Pacific halibut (Hippoglossus stenolepis) using natural stable isotope abundance of carbon and nitrogen which is hypothesized to vary over the distribution of the species in the N.E. Pacific. Natural stable isotope abundance is a useful research tool for fish ecology because of the predictable relationships of isotope signatures among food web constituents and isotopic gradients existing in the study area. Increase in trophic level is hypothesized to explain the large decrease in growth exhibited by halibut since the 1976-1977 regime shift that also affected many species in the region. Ontogenetic shifts in isotope signature are expected to indicate a shift to feeding offshore as adults. This will provide a linkage to the regime shift because changes in zooplankton abundance have been noted offshore near the continental shelf break. Showing a relationship to this carbon source through isotope matching will provide the first line of evidence for a mechanism for explaining changing halibut growth patterns. There will be a synergy between this project and other fish ecology projects (also involving the P.I.'s) using natural stable isotope abundance in the N.E. Pacific region.



Expected results or products: The analysis data are prepared and submitted to the International Pacific Halibut Commission.

Timeline: The work began in 1999 and continues indefinitely.
Project budget: On an ad-hoc basis; currently $30,000
Funding source: International Pacific Halibut Commissioner