1048 



Fishery Bulletin 97(4), 1999 



Study area 



Alaska 



S5N 



Western 



Central 



Eastern 



■*»^ie-*" 



M 



Figure 1 



The subareas of the Aleutian Islands trawl survey area. 



the samples arrived at the laboratory, they were 

 transferred to 70*^ ethanol before the contents were 

 analyzed. 



Stomach content analysis 



In the laboratory, stomach contents were first blot- 

 ted with a paper towel and the wet weight recorded 

 to the nearest one-tenth of a gram. After obtaining 

 the total weight of the contents, these were placed 

 in a petri dish and examined under a dissecting mi- 

 croscope. Each prey item was classified to the lowest 

 practical taxonomic level. The numbers of noncom- 

 mercially important prey were not counted; instead 

 the percent total volume of these prey items in stom- 

 achs was visually estimated. Prey weights and num- 

 bers of commercially important crabs and fish were 

 recorded. If walleye pollock otoliths were found, 

 otolith lengths were measured and the pollock's stan- 

 dard length (SL) was derived through an otolith 

 length-fish length regression table (from REFM's 

 Ageing Task ). Other fish otoliths were not treated as 

 walleye pollock otoliths either because they were not 

 found as frequently as walleye pollock or were diffi- 



cult to identify to the species level. Standard lengths 

 of prey fish, carapace widths (CW) of Tanner crabs 

 (Chionoecetes spp.), and Korean horse-hair crabs 

 (Erimacrus isenbeckii) were also recorded. 



Data analysis 



Atka mackerel as prey and predator The general 

 diet of each species was analyzed to determine the 

 overall percent total weight that each prey item rep- 

 resented in the stomach and to identify predators of 

 Atka mackerel. Marine fishes that were mainly fish 

 eaters were then selected for an analysis of popula- 

 tion consumption of Atka mackerel. Stomach content 

 analysis of Atka mackerel were performed to under- 

 stand the role of Atka mackerel as a predator in the 

 Aleutian Islands area. 



Population level consumption of Atka mackerel by 

 marine fish Following their identification as preda- 

 tors, the consumption of Atka mackerel by four ma- 

 rine fish species. Pacific cod, Pacific halibut, 

 arrowtooth flounder, and Kamchatka flounder, was 

 estimated. The amount of Atka mackerel consumed 



