Feeding success and survivorship of Arctic cod larvae,Boreogadus saida,in the Northeast Water polynya (Greenland Sea)*

We tested the hypothesis that enhanced feeding success and survivorship of Arctic cod larvae in the Northeast Water polynya (Greenland Sea) are associated with high densities of their zooplankton prey in areas of low sea ice concentration. From late May to early August 1993, first-feeding yolk-sac larvae (6.5–8.5 mm long) were collected primarily along the coast and over shallow banks in the polynya, whereas post yolk-sac larvae (8.5–14 mm) were more uniformly dispersed over the sampling area. Arctic cod larvae < 14 mm fed almost exclusively on copepod nauplii (74% of total prey number) and copepod eggs (16%). Feeding success was defined as the residuals of the regression of the number of prey ingested against larval length. Nauplii density varied from 9600 to 731300 nauplii m^-2(equivalent to 0.16 to 12.2 nauplii 1^-1) but, contrary to our hypothesis, seldom limited the feeding success of Arctic cod larvae. Water temperature was the best predictor of feeding success in larvae of all sizes. First-feeding success and survivorship were low for larvae hatched before mid-July, and improved thereafter as surface temperatures increased in the open waters of the polynya. There was no relationship between feeding success and irradiance or wind. Assuming a fixed spawning season, it is concluded that a larger fraction of the newly hatched larvae would experience adequate temperatures in years when the polynya opens early. Based on this conclusion, we propose that the timing of the opening of polynyas is a critical determinant of year- class strength in Arctic cod, a key species in the Arctic food web.