FOOD HABITS AND DIET OVERLAP OF TWO CONGENERIC SPECIES, 

 ATHERESTHES STOMIAS and ATHERESTHES EVERMANNI, IN 



THE EASTERN BERING SEA 



M. S. Yang 1 and P. A. Livingston 2 



ABSTRACT 



Stomachs of 196 arrowtooth flounder, Atheresthes stomias, and 152 Kamchatka flounder, A. evermanni, 

 collected from the same area of the eastern Bering Sea in summer 1983 were examined. Each species 

 was divided into four fork-length groups: less than 201 mm, 201-300 mm, 301-400 mm, and greater than 

 400 mm. The principle diet of both species was comprised of walleye pollock, Theragra chalcogramma, 

 shrimp (mostly Crangonidae), and euphausiids. Pollock was the most important prey item for both species 

 in all four size groups, ranging from 56 to 86% and 66 to 88% of the total stomach content weight of 

 Kamchatka flounder and arrowtooth flounder, respectively. Schoener's indices of diet overlap were 

 calculated between the two species for each size group. The high value of the indices (ranging from 0.67 

 to 0.90) indicate that these two congeneric species basically consume the same resources. 



The genus Atheresthes of the family Pleuronectidae 

 has two species: Kamchatka flounder, A. evermanni 

 (Jordan and Starks), and arrowtooth flounder (Nor- 

 man, 1934), A. stomias (Jordan and Gilbert). Ather- 

 esthes evermanni is distributed from northern Japan 

 (Hokkaido) through the Sea of Okhotsk to the 

 western Bering Sea north to Anadyr Gulf (Willimov- 

 sky et al. 1967). Atheresthes stomias is distributed 

 from Central California to the eastern Bering Sea. 

 In the Bering Sea, it meets about on a line with Saint 

 Matthew Island, overlaps with, and is replaced by 

 A. evermanni (Hart 1973). 



Because the morphological differences between A. 

 evermanni and A. stomias are subtle, they have been 

 recorded as one species, A. stomias, in the eastern 

 Bering Sea resource assessment surveys of the 

 Northwest and Alaska Fisheries Center (NWAFC) 

 (Smith and Bakkala 1982). Food habits of A. stomias 

 have been studied by some researchers (Gotshall 

 1969; Kabata and Forrester 1974; Smith et al. 1978), 

 but none of those studies covered the food habits 

 of A. evermanni. Shuntov (1970) studied the feeding 

 intensity of the two Atheresthes species, but he did 

 not compare the diets of these species. 



Using electrophoretic examination, Ranck et al. 

 (1986) have confirmed that these two types of Ather- 

 esthes are separate species. The purpose of this study 

 is to analyze stomach samples of these two con- 



1 Fisheries Research Institute, University of Washington, WH-10, 

 Seattle, WA 98195. 



2 Northwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, 7600 Sand Point Way N.E., Seattle, WA 

 98115. 



Manuscript accepted December 1985. 

 FISHERY BULLETIN: VOL. 82, NO. 3, 1986. 



generic species collected in the area of their distri- 

 butional overlap in the eastern Bering Sea and 

 compare the diets of both fish species to calculate 

 the degree of diet similarity to determine whether 

 the two species can be considered trophically 

 equivalent. 



COLLECTION AND PROCESSING OF 

 SAMPLES 



Specimens were collected from 6 July to 16 July 

 1983 in the eastern Bering Sea aboard the Alaska, 

 a research vessel participating in the annual sum- 

 mer resource assessment survey conducted by the 

 Resource Assessment and Conservation Engineer- 

 ing (RACE) division of the NWAFC in Seattle, WA. 

 Stomachs of arrowtooth flounder and Kamchatka 

 flounder were taken at standard resource assess- 

 ment stations where half-hour tows were made 

 using an 83-112 Eastern bottom trawl net with an 

 estimated 2.3 m vertical and 16.4 m horizontal 

 mouth opening. 



The samples were collected in an area around and 

 to the northwest of the Pribilof Islands at bottom 

 depths ranging from 71 to 137 m (Fig. 1, Table 1). 

 A random subsample of individuals of both arrow- 

 tooth flounder and Kamchatka flounder was ob- 

 tained at each station with a total collection of 348 

 stomachs from 19 stations. 



Individual fish were first checked for signs of re- 

 gurgitation, i.e., food items in mouth or gill plates 

 or flaccid stomach, and were discarded if any such 

 signs were noted. Stomachs from the remaining fish 



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