Defining Essential Fish Habitat for Atka Mackerel Pleurogrammus monopterygius with Respect to Feeding within and Adjacent to Aleutian Islands Trawl Exclusion Zones

Distribution patterns of Atka mackerel (Pleurogrammus monopterygius) were examined, both seasonally and spatially, to identify essential fish habitat with respect to feeding and to add to the existing knowledge of diet composition.  This study focused on two local aggregations in the Aleutian Islands, Alaska; Seguam Pass and near Amchitka Island.  At each locale, we examined mean stomach fullness (i.e., feeding intensity) and diet composition of randomly selected fish, relative to trawl exclusion zones (TEZ). Trawl exclusion zones extend out 10 to 20 nm from Steller sea lion (Eumetopias jubatus) rookeries and haulouts; no trawling is allowed inside these habitats. During four of the six time periods examined, mean stomach fullness was higher inside the TEZ than outside the TEZ.  At Seguam Pass, fish were distributed into northern and southern aggregations and diet composition varied by age, seasonally and relative to TEZs.  Feeding intensity appeared to be greatest in the northern portion of Seguam Pass, inside the TEZ, near a productive frontal region that is characterized by a transition zone of well-mixed (upwelling) and stratified water. At Seguam Pass, piscivory occurred almost entirely inside the TEZ in June.  Near Amchitka Island, feeding intensity was significantly higher inside the TEZ, which coincided with an increase in egg cannibalism in October.  Based on these observations, we suggest that the areas of increased feeding activity in conjunction with diet composition at Seguam Pass and Amchitka Island may represent essential fish habitat for feeding of Atka mackerel.