FISHERY BULLETIN: VOL. 84, NO. 3 



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Figure 5.— Scatter plot of prey fish length consumed by Atheresthes species from the eastern Bering Sea in summer 



1983. 



and the esophagus and stomach are large with four 

 large pyloric caeca and the intestine is a simple loop. 

 All of these characteristics indicate that Atheresthes 

 species are fish feeders as predicted by using De 

 Groot's (1971) morphological criteria. He stated that 

 large gill rakers with teeth are indispensable to fish 

 feeders, since they prevent the prey, grasped alive, 

 from struggling out of the mouth. The high per- 

 centages of fish in the diet of the two Atheresthes 

 species obtained in this study would be expected on 

 the basis of the similarities in the digestive tracts 

 of the two species. 



The results also indicate that Atheresthes species 

 feed up in the water column. According to Allen 

 (1982), flatfishes with large symmetrical mouths 

 (Atheresthes species) probably use sight to locate 

 prey. They are oriented up in the water column 

 when foraging. The presence of pelagic fish (T. 

 chalcogramma) and euphausiids or nektonic bentho- 

 pelagic crustaceans such as shrimps in the diets of 

 Atheresthes species supports Allen's generalizations 

 concerning correlations between morphology and 

 feeding behavior in flatfishes. 



The trend of the feeding habits of Atheresthes 

 species with regard to predator length is toward 

 piscivory; that is, when the predators are bigger, 

 they take more fish (by weight) as food. Specimens 



from the <200 mm size group were found to ingest 

 the greatest variety of prey items in comparison to 

 other size groups. Specimens >400 mm long preyed 

 mainly on other fishes, primarily on pollock. 

 However, euphausiids were of importance in the diet 

 of all size groups. One 460 mm arrowtooth flounder 

 was found to have 838 Thysanoessa inermis in its 

 stomach. Smith et al. (1978) also noted a change in 

 food habits with increasing length in the arrowtooth 

 flounder. In their study, specimens over 450 mm 

 long preyed exclusively on pollock and other 

 gadoids. Euphausiids were important food of the 

 arrowtooth flounder up to 350 mm long; however, 

 none were found among the stomach contents of 

 specimens larger than 350 mm. 



Based on the results of this study and those of 

 Smith et al. (1978) and Gotshall (1969), it appears 

 that Atheresthes species are opportunistic feeders; 

 they feed on those prey items that are most 

 abundant— pollock and euphausiids in the Gulf of 

 Alaska and eastern Bering Sea and ocean shrimp 

 in northern California. In the eastern Bering Sea, 

 the estimated abundance of age-0 pollock in 1982 

 is between 100 billion and 1,300 billion and, based 

 on the results of the 1983 bottom trawl survey by 

 NWAFC, this 1982 year class is the largest observed 

 since the large 1978 year class (Traynor in press). 



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