June 22, 2024 — Scientists placed specially designed moorings, equipped with sonar, on the seafloor to acoustically monitor pollock abundance and movements between U.S. and Russian waters. They found that a substantial amount of pollock travel between the two exclusive economic zones (EEZs) seasonally.
The study was conducted from summer 2019 to summer 2020. During this time, pollock moved southeast over the maritime boundary in winter as the sea ice formed. They were largely absent in late spring when ocean temperatures were near freezing and the sea ice was still present. They subsequently migrated northwest in late spring and early summer as waters warmed. The extent of the movement between EEZs) appears to be partially driven by water temperature.
When the moorings were deployed in summer 2019 the area was unusually warm. Following the winter migration into U.S. waters, conditions were cooler in summer 2020. Over the year of observations, 2.3 times more pollock moved into the U.S. EEZ in fall and winter then exited during the subsequent spring and summer. Scientists believe the cooler conditions in 2020 led to fewer pollock moving into Russian waters than had the previous year.
“There are some important implications for pollock management,” said Robert Levine, physical scientist and lead author on a new paper published in the ICES Journal of Marine Science. “Our research suggests that in years when water temperatures are warmer than average, the proportion of fish moving across the boundary will be greater.”
Scientists suspect that continued warming in the eastern Bering Sea will increase the proportion of the pollock stock found in Russian waters. Currently, pollock support the top U.S. commercial fishery, which harvests more than 1 million metric tons annually.