Fish Ecology During the Polar Night

Abstract

This chapter summarizes the winter ecology of the ten most abundant fish species captured in bottom and midwater trawls during Polar Night surveys conducted in January 2016, 2017, and 2018 in the Svalbard region. It reviews the distribution and feeding habits of these species during the Polar Night as well as their spawning ecology. Most species feed to a certain extent in the dark of night, but their stomach fullness is generally lower and the proportion of empty stomachs consistently higher during winter than the rest of the year. A combination of low irradiance and seasonal factors, such as reduced energy intake during spawning and change in prey availability during winter, likely explains the higher proportion of empty stomachs during the Polar Night. In contrast to Arctic (i.e. polar cod and arctic cod) and arcto-boreal (i.e. Greenland halibut and daubed shanny) fishes that reproduce during winter to benefit from the Arctic spring bloom just after yolk resorption, most boreal species reproduce from spring to autumn which, in the Arctic, results in a mismatch between the apparition of first-feeding planktonic lar-vae and the production of zooplankton prey. This review thus supports the hypothesis that the ability to reproduce during the Polar Night, rather than the ability to feed, might be the key adaptive trait of Arctic fishes and the main factor limiting boreal fishes to colonize the high Arctic.