January 9th 2017, Kongsfjorden, the hunt started once again. On a cruise like this one, most of us biologists are looking for specific critters. As it stands, it has almost become a tradition for the fish group to be on the lookout for polar cod. This endemic Arctic species is the most abundant cryopelagic fish at high latitudes and is believed to play an important role in the Arctic marine food web. In recent years, polar cod have not been doing so well on the west coast of Svalbard, and the increasingly warm Atlantic water seems to have displaced them for reasons that remain to be understood. This displacement might be explained by a change in prey or an increase in competition and predation due to the northward expansion of boreal fish, such as Atlantic cod. Because of this, and as I’ve mentioned it in the past, it has become increasingly difficult to find the little fellows on the west coast of Svalbard, and instead of a catch typically composed of Arctic species, ours are now most often composed of boreal species (whether it be fish or invertebrates). Because it lacks a sill, Kongsfjorden is particularly influenced by Atlantic advection and our trawls there testified this. They did contain some rare polar cod along with the more typically boreal Altantic cod, haddock, and capelin. Part of the goal of the polar cod project that is conducted by PhD student Morgan Bender is to document how these different water masses (Arctic versus Atlantic) affect polar cod reproduction and diet. To do so, we’ve been monitoring seasonally and annually their lengths, weight, body condition index, hepato- and gonado- somatic index, and their diet. To this, we’ve added in 2017 blood samples, histology measurements, and otoliths reading.
For this project, the ideal is to obtain polar cod of different size categories from Atlantic and Arctic fjords using both pelagic and demersal trawls. As previously mentioned however, finding polar cod in Atlantic fjords resembles a hide and seek hunt and can be quite frustrating. We did manage to find what we were looking for but we did not get a large sample size until we deployed the trawls in the north eastern part of Svalbard, in Rijpfjorden (nearly 600 specimen were caught in one trawl).
-Marine Cusa (Research Assistant, UiT)