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Marine Ecology and Stock Assessment Program

Stable Isotopic Variability Along Spiny Dogfish Spines: Implications For Retrospective Ecological Studies

Spiny dogfish are an abundant and commercially important species of fish off both the Atlantic and Pacific coasts of North America. They are opportunistic feeders and have a varied diet that can include many fish species, especially small forage fish such as herring, capelin, and sand lance, as well as crustaceans, worms, euphausiids, gelatinous zooplankton, and cephalopods. The purpose of our present study is to investigate the utility of the second dorsal spine in providing multiyear information on the feeding habits of dogfish using stable isotope (C and N) analysis.

The outer dentine and enamel layers of a spine from three dogfish (caught off the coast of British Columbia) were analyzed to obtain their stable nitrogen and carbon isotope composition (δ15N and δ13C, respectively). Each sample had annuli from multiple years, allowing possible seasonal migrations to be averaged over samples.

The δ15N ranged from a low of 11.6 to a high of 14.9 over the three spines and δ13C ranged from -11.5 to -18.4. The variable isotopic signatures along the spine indicate that the method may be used to assess ecological changes.

Stable isotope measurements of the dogfish spines could be a valuable means of determining long-term changes in habitat usage and feeding ecology.

By Alex Andrews

Growth and Survival of Sockeye Salmon from Karluk Lake and River in Relation to Climatic and Oceanic Regimes and Indices, 19222000

ABL staff examined whether the relationship between climate and salmon production was linked through the effect of climate on growth of sockeye salmon (O. nerka) at sea. Smolt length and juvenile, immature, and maturing growth rates were estimated from increments on scales of adult sockeye salmon that returned to the Karluk River and Lake system on Kodiak Island, Alaska, over 77 years, 19242000.

Survival was higher during the warm climate regimes and lower during the cool regime. Growth was not correlated with survival, as estimated from the residuals of the Ricker stock-recruitment model.

Juvenile growth was correlated with an atmospheric forcing index and immature growth was correlated with the amount of coastal precipitation, but the magnitude of winter and spring coastal downwelling in the Gulf of Alaska and the Pacific Northwest atmospheric patterns that influence the directional bifurcation of the Pacific Current were not related to the growth of Karluk sockeye salmon. However, indices of sea surface temperature, coastal precipitation, and atmospheric circulation in the eastern North Pacific were correlated with the survival of Karluk sockeye salmon.

Winter and spring precipitation and atmospheric circulation are possible processes linking survival to climate variation in Karluk sockeye salmon.

By Ellen Martinson

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