February 21, 2020 — The following was released by NOAA Fisheries:
The 2013 to 2016 marine heatwave—known as “The Blob”—is the largest warm anomaly ever recorded in the North Pacific. In the Gulf of Alaska, scientists have connected low numbers of Pacific cod larvae, juveniles, and adults to loss of spawning habitat. This occured during and immediately following the heatwave. Compounding the ecological loss is the significant economic impact on the second most valuable commercial fishery in Alaska. The fishery experienced large reductions in their annual catch limits in 2018 (a 58 percent cut) and a fishery closure in 2020.
“We combined results of laboratory studies, stock assessment model output and survey data to help us better understand what happens to Pacific cod in warm and cold years,” said Benjamin Laurel, NOAA Fisheries biologist and lead researcher for this new study. “We found that the recent three-year heatwave and return to similar conditions in 2019 potentially had the greatest effect on spawning habitat for the years we had available data (1994 to 2019).”
Water temperature is an important component of fish habitat. Temperature influences every stage of a fish’s life. During the first year of life, fish eggs are particularly sensitive to changes in environmental conditions.
Laurel and colleague Lauren Rogers determined that Pacific cod eggs have a narrow optimal range for hatching success, only 3-6º C. This is much narrower than other related species like walleye pollock and Atlantic cod.
“Early life stage distribution and survival may set biogeographic boundaries and limit productive capacity for fish stocks,” added Rogers. “Pacific cod are unique among cod species; they only spawn once in a season and have eggs that adhere to the seafloor. Pacific cod females can actually place their eggs in habitats with temperatures that optimize hatch success. However, during these warm years, it may have been more challenging to find suitable habitat because the warmer water temperatures extended into the ocean depths.”