Until recently, Pacific cod were rarely encountered in the northern Bering Sea. Fishery surveys in the 1970s reported “trace amounts” of cod there. A 2010 Alaska Fisheries Science Center survey estimated that the entire northern population amounted to about 3% of the large southeastern Bering Sea stock that supported a valuable commercial fishery.
Then in 2017, the summer survey recorded dramatically higher abundances in the north: a 900-fold increase since 2010. In the same year, southeastern Bering Sea abundances were down 37% from 2016. Strikingly, the increase in the north nearly matched the decrease in the southeastern Bering Sea.
A 2018 survey revealed an even more remarkable shift: there were more cod in the northern than southeastern Bering Sea.