1052 



Fishery Bulletin 97(4), 1999 



from the western Aleutian and southeastern Bering 

 Sea areas. Because the diet of arrowtooth flounder 

 and Kamchatka flounder are very similar (Yang and 

 Livingston, 1986), the daily ration values (Table 1) 

 and the values of the mean percent of the Atka mack- 

 erel consumed by arrowtooth flounder (Table 3) were 

 used for the calculation of the consumption of Atka 

 mackerel by Kamchatka flounder. The total biomass 

 of Atka mackerel consumed by the main marine 

 fishes in the Aleutian Islands areas was 48,534 t 

 (Table 5). 



The number of Atka mackerel consumed by ma- 

 rine fishes was also estimated from the biomass con- 

 sumed (Table 5) and the prey length recorded from 

 stomach content analysis. The total number of Atka 

 mackerel consumed by marine fishes in the Aleutian 

 Islands area was about 284 million (Table 6), 84% of 

 which were consumed by Pacific cod. The size and 

 age composition of Atka mackerel consumed by 

 groundfishes is listed in Table 7. Age-2 fish repre- 

 sented about 40'7f of the total numbers of Atka mack- 

 erel consumed by groundfishes, including predators 

 of all sizes from different areas. Age-1 and age-3 fish 

 accounted for 30% and 22% of the total numbers con- 

 sumed, respectively. Age-0 Atka mackerel (4%f I were 

 consumed only by Pacific cod >60 cm FL in the cen- 

 tral Aleutian area. Some age-4 and age-6 Atka mack- 

 erel were also found in marine fish stomachs, but 



they accounted for only about 4% of the total num- 

 ber consumed compared with about 25% of the Atka 

 mackerel that were age 3. In terms of biomass, the age 

 2-1- Atka mackerel consumed by marine fishes (41,071 1) 

 represented about 3.2% of the estimated Atka mack- 

 erel population biomass (age 2-i-) (Lowe and Fritz^). 



Discussion 



Atka mackerel as prey of marine fishes 



In addition to groundfish, such as Pacific halibut, 

 Pacific cod, arrowtooth flounder, and Kamchatka 

 flounder that feed on Atka mackerel, other marine 

 fishes also consume Atka mackerel. Several authors 

 have reported that pelagic salmonids prey on Atka 

 mackerel. Davis^ found that coho salmon (Oncor- 

 hynchus kisiitch) ate Atka mackerel in the North 

 Pacific Ocean. Volkov et al. (1995) found that Atka 

 mackerel represented 30%: and 13% of the food com- 

 position of coho salmon in the Sea of Okhotsk and 

 the western Kamchatka areas, respectively, (jrorbimova 

 ( 1970) stated that 25-30 mm long larvae of Atka mack- 

 erel were found frequently in the stomachs of salmon 

 caught in the open sea. In this study, no larval Atka 

 mackerel were found in the stomachs of marine 

 fishes, only juveniles or adults. 



