In collaboration with scientists at the National Marine Fisheries Service, we have examined changes in long-term populations of fish in the Gulf of Alaska by analyzing data from small-mesh trawl catches (more than 9500 trawls) between 1953 and 1997 (note all data are smoothed by taking 3-year running averages). We found a complete transition in the species composition of trawl catches during the late 1970's and early 1980's following a major change in atmospheric circulation patterns (as indicated by the North Pacific Pressure Index; NPPI) and water tempertures in the Gulf of Alaska. The so-called "climate regime shift" occurred as water temperatures went from being colder than average to warmer than average. About 50% of variability in shrimp catches can be explained by water temperature alone. A decline in abundance of other marine organisms, particularly many forage fish species, has been linked to declines in abundance of seabirds and marine mammals such as the Steller's sea lion.

Small Mesh Trawl Catches in the Gulf of Alaska between 1953 and 1997.