Acoustical estimation of fish distribution and abundance in two Spitsbergen fjords

Over recent decades, the Arctic region has been subjected to rapid climate change stemming from global warming. The advance of Atlantic waters to high latitudes is notable. The increased abundance of fish, such as cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), has been reported near the western coast of Spitsbergen and entering fjords together with Atlantic waters. This study used multifrequency acoustics to measure fish distribution and abundance in 2013–2014 in two Arctic fjords, the colder Hornsund, which is typically of Arctic character, and the warmer Kongsfjorden, which is more of Atlantic character. The study revealed a bimodal fish size distribution with larger fish in the deep parts of fjords, and smaller fish distributed in more shallow waters. An evident increase in the abundance of large fish, most probably Atlantic cod, was observed in Hornsund and especially in Kongsfjorden in 2014 in comparison to 2013. The intense inflow of Atlantic water on the shelf in 2014 is suggested as the explanation for this phenomenon.