Zimmermann and Goddard Biology and distribution of Atheresthes stomias and A evermanni 



367 



and infrequent catches of medium-size 

 Kamchatka flounder in the study area 

 made it impossible to compare the 

 catch rates of both species across the 

 shallow end of the depth distribution. 

 Whether this situation was a sampling 

 artifact, year-class artifact, or an ac- 

 curate representation of the Kam- 

 chatka flounder depth distribution, it 

 increased the Kamchatka flounder s ap- 

 parent preference for greater depths. 



Comparison of the water tempera- 

 ture distribution of both species may 

 also have been confounded by the lim- 

 ited catches of small- and medium-size 

 Kamchatka flounder in the study area. 

 For arrowtooth flounder, the more 

 common catches on the Bering Sea shelf 

 of small-size ( warmest bottom tempera- 

 ture) and medium-size (coldest bottom 

 temperature) arrowtooth flounder 

 broadened the temperature range for 

 the species. Thus the few trawl catches 

 of small- and medium-size Kamchatka 

 flounder on the Bering Sea shelf might 

 have nairowed the temperature distri- 

 bution of Kamchatka flounder. 



The peculiar relationship of bottom- 

 water temperature with mean fish size 

 (i.e. medium-size fish at moderate 

 depths but coldest water) may be ex- 

 plained by the unusual bottom-water 

 temperature distribution of the east- 

 ern Bering Sea. The coldest bottom 

 temperatures in the eastern Bering 

 Sea in 1991 were on the mid-shelf area 

 (Goddard and Zimmermann 3 ), as is 

 typically the case (Kinder and Schu- 

 macher, 1981 ). These mid-shelf waters 

 are a cold-water remnant of the previ- 

 ous winter's ice cover (Takenouti and 

 Ohtani, 1974). In contrast to the coastal waters, the 

 mid-shelf waters do not increase in temperature with 

 the spring and summer increase in solar radiation 

 ( Kinder and Schumacher, 1981 ). The depths of the mid- 

 shelf waters are too great to permit wind- or tidal-driven 

 mixing, and a thermocline develops that increases the 

 stability of the water column. No strong currents bring 

 warmer waters from the Gulf of Alaska into this area, 

 and the relatively warm slope waters, which are not as 

 affected by the winter ice cover, are fortified with warm 

 waters from the deep (Schumacher 6 ). 



80 



70 



60 







50 



- 



^ males 

 o females 





10 



12 













Figure 7 



Individual length-at-age data (empty symbols) and von Bertalanffy estimates 

 of mean length at age (filled symbols) for arrowtooth flounder, Atheresthes 

 stomias (A), and Kamchatka flounder, A. evermanni (B). 



h Schumacher, J. D. 1994. Pacific Marine Environmental Labo- 

 ratory, 7600 Sand Point Way NE, Seattle, WA 98115. Personal 



commun. 



The temperature data collected off the Aleutian 

 Islands show a more typical relationship with depth; 

 shallow bottom temperatures were warm and bot- 

 tom temperature decreased, approaching 4°C, as 

 depth increased. Most of the temperature data col- 

 lected, however, came from the eastern Bering Sea 

 shelf and slope. 



Studies have shown that the geographic ranges of 

 Atheresthes species do overlap in the north Pacific 

 Ocean (Shuntov, 1965; Wilimovsky et al., 1967; Allen 

 and Smith, 1988). The extent of the overlap and the 

 southeastern boundary of the Kamchatka flounder 

 distribution, however, had not been clearly defined. 

 Kamchatka flounder has been reported to be the 



