DENSITY DISTRIBUTION OF JUVENILE ARCTIC COD, 

 BOREOGADUS SAIDA, IN THE EASTERN CHUKCHI SEA 



IN THE FALL OF 1970 



Jay C. Quasti 

 ABSTRACT 



The Arctic cod, Boreogadus saida, is a key element in the ecosystem of the Arctic Ocean. 

 Juveniles, principally young-of-the-year, were taken by Isaacs-Kidd mid-water trawl at night 

 during September and October 1970 in the eastern Chukchi Sea. Their average concentration was 

 about 28/1,000 m^ and their average biomass about 0.7 metric ton/km^ of ocean surface. In 20 

 stations (representing about 30 x 10^ km^, or 8,714 square nautical miles), the number of 

 juvenile cod {N) per standard haul (about 8,223 m^ of water filtered per haul) increased with 

 depth in meters {D) at about the same rate [logio (A^ + 1) = 0.0669Z)]. Yet the depth at which 

 equivalent concentrations occurred varied over a range of 38 m between stations. The zone of 

 increased concentration with depth, called a density structure, appears to be the nighttime relict 

 of a graded negatively phototactic response to sunlight by the juvenile cod during preceding daylight. 

 Apparently the structure was vertically displaced after dark by wand-induced upwelling and down- 

 welling. The juvenile cod may have originated in the northwestern Bering Sea, off Arctic 

 Siberia, or within the Chukchi Sea, and probably had recycled in the Chukchi Sea prior to 

 capture. 



This study of biomass and distribution of juvenile 

 Arctic cod, Boreogadus saida (Lepechin), in the 

 Chukchi Sea is an outgrowth of the Western 

 Beaufort Sea Ecological Cruise of 1970 (WEBSEC- 

 70) sponsored by the U.S. Coast Guard. My 

 original objective was to explore the fishes of the 

 marine ecosystem in the Arctic Ocean east of 

 Point Barrow, Alaska, and if possible to quantify 

 the occurrence of important forms. Because of an 

 early southward shift of the arctic ice pack, the 

 study was moved to the eastern Chukchi Sea. 

 The sampling schedule — date, location, depth of 

 water, and number and types of hauls — is given 

 in Table 1 and Figure 1. The species offish and 

 where they occurred are summaried in 

 Quast (1972). 



Juvenile Arctic cod and Pacific sand lance, 

 Ammodytes hexapterus Pallas, were virtually the 

 only fish species trawled in the surface and mid- 

 depths at night. The cod occurred at every station; 

 also they were more numerous and had a larger 

 biomass than the sand lance — a subjective 

 estimate suggests a minimum 10 fold difference in 

 both respects. Although sand lance were chiefly 

 taken at the surface, the number of Arctic cod 



'Auke Bay Fisheries Laboratory, National Marine Fisheries 

 Service, NOAA, Auke Bay, AK 99821. 



usually increased with depth. Because of the 

 apparent importance of the Arctic cod in the off- 

 bottom marine ecosystem of the eastern Chukchi 

 Sea during WEBSEC-70, 1 further analyzed their 

 data to estimate their numbers and biomass 

 over the study area. 



General life history, distribution, and literature 

 on Arctic cod are summarized by Andriyashev 

 (1954:195-198). The species is circumpolar and 

 occurs to or nearly to the North Pole. Off Alaska, 

 it occurs along the Arctic coast, in the Chukchi 

 Sea, and in the Bering Strait; it also has been 

 recorded in the winter from Norton Sound and the 

 Gulf of Anadyr. Although most authors term the 

 species "pelagic," "demersal" is probably better 

 because adults appear to be associated with a 

 shallowwater substrate, whether it be ocean 

 bottom over the continental shelf or the under- 

 surface of ice. Maximum size is about 320 mm 

 total length (TL). Association with low tempera- 

 tures is an important characteristic: Rass ( 1968: 

 136) gives the thermal environment of eggs as 

 0° to 2°C, of larvae as 2° to 5°C, and of fry as 

 5° to 7°C and probably higher. During WEBSEC- 

 70, specimens of 0-age fish occurred at -1.5° 

 to 3.5°C. According to Andriyashev (1954), Arctic 

 cod mature when about 4 yr old and 190 mm TL; 

 they spawn near coasts, principally in January 



Manuscript accepted February 1974. 

 FISHERY BULLETIN: VOL. 72, NO. 4, 1974. 



1094 



