Does Prey Abundance Influence Predator Distribution? Perspectives from the Gulf of Alaska

Euphausiids are a key prey item for commercially important fishes the Gulf of Alaska (GOA).  In these cold water coastal and pelagic ecosystems, euphausiids form an important ecological link between primary production and higher trophic levels due to their abundance in the water column.  We created a time series of euphausiid distribution and abundance in the GOA based on summer acoustic-trawl surveys from 2003, 2005, 2011 and 2013.  We sought to determine whether euphausiid prey abundance has an effect on predator distribution in the GOA.  Abundance data for key fish predators, including walleye pollock, Pacific Ocean perch, arrowtooth flounder, capelin, and eulachon, are available from the summer acoustic-trawl survey as well as a concurrent bottom trawl survey.  Generalized additive models (GAM) were used to model the abundance of these fishes in the GOA as a function of environmental conditions and the abundance of euphausiids.  Preliminary results indicate that there are species-specific effects of euphausiid abundance, bottom temperature, depth, and chlorophyll a concentration on the distribution of key predators in the GOA.  Further analysis of these data will help to elucidate these patterns, and help us gain insight on community structure in the GOA.