YANG and LIVINGSTON: FOOD HABITS AND DIET OF TWO CONGENERIC SPECIES 



(U 

 Q- 



Pollock 

 Other fish 



Predator length: 



• 400 mm 

 n= 15 

 x= 147.2 



1 



> I i | I | ' I 



T 



Predator length 

 301-400 mm 

 n = 15 

 x = 117.58 



I 'T ' I ' I ' I i | ' | 



Predator length: 

 201-300 

 n = 10 

 x = 72.31 



I l I ' I l I I I i I i I ' I 



Predator length: 

 < 200 mm 

 n = 47 

 x = 43.03 



c"* 



I "i " l i I I I ' I I I ' I I 1 1 I i I 



120 160 200 240 280 



Prey (fish) length (mm) 



Figure 4.— Frequency distribution of standard lengths of prey fish 

 found in the stomachs of Atheresthes species from the eastern 

 Bering Sea in summer 1983. 



pollock (100-200 mm) for the two larger size groups. 

 The fish prey length was plotted against the 

 predator length (Fig. 5). Fish prey size appears to 

 increase linearly with increasing predator size. 



Diet Overlap 



Values for Schoener's (1970) index of dietary over- 

 lap were obtained from a comparison (by weight) 

 between the diets of Kamchatka and arrowtooth 

 flounder of the same size groups (Table 2). All the 

 values obtained were >0.60, an indicator of high 

 dietary overlap (Langton 1982). The <200 mm size 

 group had an overlap value of 0.72 and the 201-300 



mm size group had an overlap value 0.82. Within 

 each of these two size groups, fairly similar propor- 

 tions by weight of walleye pollock, euphausiids, and 

 shrimps were consumed. The 301-400 mm size group 

 had the lowest overlap value of 0.67. This is probably 

 because Kamchatka flounder ate less walleye pollock 

 by weight (56%) than did the arrowtooth flounder 

 (77%). Most of the remainder of the diet for Kam- 

 chatka flounder in this size group was composed of 

 different fish groups, such as zoarcids, stichaeids, 

 and pleuronectids, which were almost totally absent 

 from the arrowtooth' s diet at this size. The largest 

 size group of flounders (>400 mm) had the highest 

 overlap value of 0.90. This size group ate very 

 similar proportions by weight of walleye pollock and 

 euphausiids. 



DISCUSSION 



From this study, it appears that both Kamchatka 

 flounder and arrowtooth flounder are largely fish 

 feeders. Walleye pollock was the most frequently 

 observed prey and contributed the largest percent- 

 age by weight to the diets, followed by euphausiids 

 and shrimps (Table 2, Fig. 3). Gotshall (1969) found 

 that ocean shrimp, Pandalus jordani, was the most 

 common food item of arrowtooth flounder (because 

 the stomachs were collected on commercial shrimp 

 grounds), followed by fishes and euphausiids. Pacific 

 sanddabs, Citharichthys sordidus, were the most 

 numerous prey fish found in his study. Kabata and 

 Forrester (1974) examined 753 arrowtooth flounder 

 collected off the west coast of Vancouver Island. 

 Their study showed that euphausiids, followed by 

 fish were the predominant foods taken by arrow- 

 tooth flounder. The most commonly found species 

 of fish were eulachon, Thaleichthys pacificus, and 

 Pacific herring, Clupea pallasii. Smith et al. (1978) 

 found that fish constituted 41.09% and euphausiids 

 37.22% by volume of the food of 236 arrowtooth 

 flounder collected from the northeast Gulf of Alaska. 

 Walleye pollock were most commonly consumed fish 

 prey. Moiseev (1953) found that Kamchatka flounder 

 fed almost exclusively on pollock and only occa- 

 sionally on herring and other fishes. 



The type of prey eaten by a fish is strongly corre- 

 lated with the morphology of the alimentary tract 

 of the fish (De Groot 1971; Ebeling and Cailliet 1974; 

 Allen 1982). Structure of the digestive tract of 

 arrowtooth flounder and Kamchatka flounder are 

 very similar. Both have a very large terminal mouth 

 that is nearly symmetrical with a wide gape; teeth 

 are arrow-shaped and well developed on both sides 

 of the jaws; gill rakers are long and strongly dentate; 



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