At the present time, climate change is an undeniable fact, with global ocean warming and Polar ice melting among the most notable consequences. In this context, the increased temperature in the Barents Sea has caused favorable conditions for many species of zooplankton (e.g., krill), as well as for its predators, such as Atlantic cod, or several species of baleen whales, namely rorquals (whales with longitudinal grooves), to expand further north. Consequently, this led to changes in the entire food chain in these areas.
Due to these new expansions, a group of researchers intended to analyze the presence of blue whales, fin whales, minke whales and Atlantic cod, and the relationship with their prey, in order to understand their abundance and distribution in the Norwegian Arctic (around the north of Svalbard), as well as physical factors such as depth. That is, are these species moving north because there is abundance of prey in these regions? For this purpose, they carried out oceanographic surveys during the months of August and September, in 4 consecutive years from 2014 to 2017, which included whale observation, acoustic data and biological collections of their prey (populations of zooplankton and fish) at different depths. Samples were separated between depths upper than or lower than 200 meters, since the rorquals feed essentially at depths above 200 meters.
For large species of rorquals, such as the blue and fin whales, there is no relationship between their distribution and the distribution of their prey. It seems like large rorquals (blue and fin whales) have difficulties detecting their prey. On the other hand, minke whales can detect their prey at distances farther than 10 km, with their distribution being related to that of their preferred prey at depths less than 200 meters, and also related to that of Atlantic cod for depths deeper than 200 meters. The presence of Atlantic cod at depths deeper than 200 meters makes prey such as zooplankton and small fishes move up in the water column. As a consequence, they become more easily available for minke whales to feed on. Therefore, this whale species ends up benefitting by the presence of the Atlantic cod.
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Source: Solvang, H. K. et al. Distribution of rorquals and Atlantic cod in relation to their prey in the Norwegian high Arctic. Polar Biology, 1-22 (2021). DOI: 10.1007/s00300-021-02835-2
Author: Rui Santos
