MEPS 355:247-256 (2008)  -  DOI: https://doi.org/10.3354/meps07335

ABSTRACT: Based on the analysis of otolith microstructure, polar cod larvae and pelagic juveniles (20 to 55 mm standard length) sampled in September in the Laptev Sea (Siberian Arctic Ocean) hatched under sea-ice cover from mid-March to early July in 2003, and from early January to early July in 2005. During the polar night in January and February 2005, frequent winter polynyas (mesoscale areas of open water amidst ice cover) likely provided the first-feeding larvae with the minimum light necessary to detect and capture plankton prey. The absence of survivors from January to mid-March 2003 coincided with a low occurrence of polynyas. On average, polar cod 59 to 171 d old were 4 mm longer at a given age in 2005 than in 2003, a difference arising early in larval life and reflecting faster growth and more frequent winter–spring polynyas in 2005. Earlier hatching and faster growth resulted in young-of-the-year polar cod on average 8.6 mm longer in September 2005 (34.8 mm) than in September 2003 (26.2 mm). Assuming that a larger pre-winter size provides protection against predation, the increasing frequency of winter-spring polynyas on the immense Siberian shelves could improve early survival and population size in polar cod.

KEY WORDS: Polar cod · Boreogadus saida · Hatching season · Growth · Survival · Polynyas · Laptev Sea · Arctic Ocean · Climate