QUASI: DISTRIBUTION OF ARCTIC COD 



area. Both should produce transient cells of 

 upwelling and downwelling, but the wind-caused 

 cells should have broader distribution. 



Currents apparently flow predominantly north- 

 ward in the southern Chukchi Sea and accelerate 

 around headlands (Fleming and Heggarty, 1966: 

 744). Therefore, at an early stage in analysis, 

 it appeared that the density structure of juvenile 

 cod encountered during WEBSEC-70 may have 

 been a result of bird predation off the Cape 

 Lisburne-Point Hope headland or in Kotzebue 

 Sound with subsequent vertical displacement of 

 the density structure in an eddy north of Cape 

 Lisburne. However, this hypothesis was rejected 

 because, as mentioned previously, birds were not 

 abundant during WEBSEC-70; most of them had 

 probably left the region at least a month pre- 

 viously. Moreover, oceanic mixing should quickly 

 dissipate a density structure that formed near the 

 cape. The apparent occurrence of the structure 

 over the entire sampling area indicated that it 

 1) was quite permanent, 2) was probably main- 

 tained by the juvenile cod, and 3) was not in very 

 large measure induced by currents around Cape 

 Lisburne. These requirements were satisfied by 

 the hypothesis of negative phototaxis and wind- 

 induced upwelling. 



Horizontal Density Distribution 

 of Juvenile Cod 



Regardless of possible origins of the density 

 structure or reasons for its vertical displacement, 

 it was necessary to take the vertical elevation 

 of the density structure (Table 7) into considera- 

 tion when estimating the concentration and bio- 

 mass of juvenile cod at each station. This correc- 

 tion was accomplished by regarding the density 

 structure as a unit that extended downward 47 

 m (the depth equivalent on the density structure 

 of the highest number of cod sampled) in un- 

 disturbed water. The structure would be trun- 

 cated in its upper part by the ocean surface 

 when raised, or truncated in its lower part when 

 it intersected the ocean bottom because of lower- 

 ing of the structure or shallowness of the sea. 

 Thus, for a structure that appeared to be raised 

 10 m in the water column, the number of cod 

 remaining in the structure was taken as the 

 number that occurred between 10 and 47 m in an 

 entire structure. If a structure appeared to be 

 truncated by the ocean bottom for 17 m, the 

 number of cod remaining in the structure was 

 taken as the number between and 30 m in an 

 entire structure. Estimation of the density of 



Table 7. — Reconstruction of numbers of juvenile cod beneath a standard swath at the IKMT stations, eastern 



Chukchi Sea. 



'Negative values indicate apex above the surface. 



^Stations at which hypothetical depth of bottom of density structure is deeper than the bottom. The number of juvenile 

 cod represented by the overlap is subtracted from the total. 



3|n some instances the number of juvenile cod estimated for a density structure that was truncated at the surface was 

 slightly higher than the theoretical number in an entire density structure. This discrepancy seems to be due to rounding 

 errors in the Integrations about the point where the parabolic equation approaches and forms a small angle with the 

 X-axis. Since very few juvenile cod were present in the apex of the density structure, the error is small and probably unimportant. 



1101 



