1056 



Fishery Bulletin 97(4), 1999 



Atka mackerel as prey of marine mammals 



Many marine mammals feed on Atka mackerel. 

 Merrick (1995) found that Atka mackerel was the 

 most common prey identified in Steller sea lion scats 

 from the Aleutian Islands from 1990 to 1993. Nemoto 

 (1957) found that Atka mackerel was the preferred 

 food of humpback whales (Megapfera novaeangliae) 

 in the waters west of the Attn Islands and the wa- 

 ters south of Amchitka Island. Kasamatsu and 

 Tanaka (1992) stated that in the southwestern 

 Hokkaido region, Pleurogfammus azonus, a conge- 

 ner distributed mainly in the northern part of the 

 Sea of Japan, represented SO-lOO'^ of the diet of 

 minke whale (Balaenoptera acutorostrata). Kenyon 

 (1965) fovmd that 85% (by volume) of the food of har- 

 bor seals iPhoca vitiilina) in the Amchitka Islands area 

 was Atka mackerel. Atka mackerel have also been found 

 in the stomachs of sperm whales iPhyseter macroceph- 

 alus) (Kawakami, 1980), killer whales iOrciniis orca) 

 (Nishiwaki and Handa, 1958), fin whales (Balaenoplera 

 physalus) (Nemoto, 1957), Ball's porpoise (Phocoenoides 

 dalli) (Crawford, 1981; Perez and McAlister, 1993), 

 minke whale (Perez and McAlister, 1993), harbor seal 

 (Perez, 1990), northern fur seals (Callorinus ursinus) 

 (Perez, 1990), and sea otters iEnhydra lutris) (Kenyon, 

 1969). Consumption of Atka mackerel at the popula- 

 tion level by marine mammals was not estimated in 

 this study because of insufficient data on their bio- 

 mass, daily ration, and diet of marine mammals. 



Atka mackerel as prey of seabirds 



Seabirds are important predators in the Aleutian 

 Islands marine ecosystem. Some seabirds feed on fish 

 larvae or young juveniles, and some feed on zoop- 

 lankton. Ogi (1980) analyzed the prey of 320 thick- 

 billed murres iUria lomvia) that drowned in Pacific 

 salmon gill nets in the oceanic waters ranging from 

 the Kuril Islands to a region east and south of the 

 Aleutian Islands (160'W) and found that juvenile 

 Atka mackerel and several species of lantern fish 

 (Myctophidae) were important prey (17% of the to- 

 tal weight). Wehle (1983) found that Atka mackerel 

 represented 42.3%, by occurrence, of the food of 

 horned puffin iFratercula corniculata), and it oc- 

 curred in 6.3% of the stomachs of tufted puffin (F. 

 cirrhata) at Buldir Island. Hatch and Sanger ( 1992) 

 found only two Atka mackerel ( 138 and 139 mm ) con- 

 sumed by the tufted puffin, but Byrd et al.'^ found 



•I Byrd, G. V.. J. C. Williams, and R. Walder. 1992. Status and 

 biology of the tufted puffin in the Aleutian Islands, Alaska, 

 after a ban on salmon driftnets. U.S. Fish and Wildlife Ser\'ice. 

 Alaska Maritime National Wildlife Refuge. Aleutian Islands Unit, 

 PSC 486, Box .5251. FPO AP 96506-5251, Adak. Alaska. 



that Atka mackerel were important food of tufted 

 puffin in 1990 at Buldir Island and Aiktak Island. 

 Consumption of Atka mackerel at the population 

 level by seabirds (like marine mammals) was not 

 estimated in this study because of the lack of quan- 

 titative data on the biomass, daily ration, and diet of 

 many seabirds in this area. 



Summary 



This study assessed the importance of Atka mack- 

 erel in the Aleutian Islands marine ecosystem. As a 

 predator (mainly adults in this study), Atka mack- 

 erel were basically zooplanktivores. Calanoid copep- 

 ods, euphausiids, planktonic tunicates, amphipods, 

 and other crustaceans were principal food items. Atka 

 mackerel also consumed some benthic fishes (cottids 

 and young-of-the-year walleye pollock) and mesope- 

 lagic fishes (myctophids and bathylagids) and can- 

 nibalized its own eggs. As prey, about 48,500 t of Atka 

 mackerel (mainly age 2+) were consumed by marine 

 fishes. Table 7 indicates that about 26% of the consumed 

 Atka mackerel were age-3 and older. Because of insuf- 

 ficient data, consumption of Atka mackerel at the popu- 

 lation level by marine mammals and seabirds could 

 not be estimated. Human beings also consumed a large 

 amount of Atka mackerel. The total commercial catch 

 of Atka mackerel was 26,740 t in 1991 (about 2.2% of 

 the exploitable biomass [age 3-i-] in that year). 



This study provides information about predator- 

 prey relationships between Atka mackerel and their 

 predators (marine fishes, marine mammals, and sea- 

 birds), and between Atka mackerel and their prey 

 (zooplankton and other invertebrates) in the Aleu- 

 tian Islands marine ecosystem. More information 

 about the early life history (eggs, larvae, and juve- 

 niles) of Atka mackerel is needed to improve our 

 understanding of their trophic role in the marine 

 ecosystem. 



Acknowledgments 



I would like to thank Troy Buckley, Patricia Livingston, 

 Susanne McDermott, and Thomas Wilderbuer for 

 their reviews of this manuscript and many sugges- 

 tions. Robin Harrison and Mike Martin (RACE) pro- 

 vided the survey biomass estimates and their help is 

 appreciated. Thanks is also given to Doug Smith 

 (REFM) for assisting with the computer programs 

 and to Debbie Blood and Morgan Busby (RACE) for 

 helping identify some juvenile fish, larvae, and eggs. 

 I also want to thank three anonymous reviewers for 

 their comments and suggestions. 



