Survival of Arctic cod larvae (Boreogadus saida) in relation to sea ice and temperature in the Northeast Water Polynya (Greenland Sea)

We tested the hypothesis that the survival of Arctic cod larvae (Boreogadus saida) is limited at sea ice cover > 50% and sea surface temperature (SST) < 0 degrees C. In 1993 in the Northeast Water Polynya, a spring cohort (14 May - 15 June) was hatched under heavy ice cover (58%-91%) and cold SST (-1.7 to -1.0 degrees C) and a summer cohort (21 June - 21 July) under low ice cover (4%-31%) and above-zero SST (1.5 to 3.9 degrees C). Consistent with the hypothesis, the spring cohort had almost completely vanished by age 10 days (first feeding stage), while the summer cohort survived well and dominated the population by the end of our sampling in early August. By then, the few surviving spring larvae were on average 5.7 mm longer than summer larvae (18.6 vs. 12.9 mm). A retrospective analysis of ice cover in the polynya (1979 to 2003) indicated that first-feeding larvae of the spring cohort encountered good survival conditions (sea ice < 50% and SST > 0 degrees C) in only 12% of the years compared with 80% for the summer cohort. The survival advantage provided by a larger size at the onset of Arctic winter could explain the evolutionary persistence of a spring cohort despite the low probability of initial survival.