NOAA Fisheries researchers say temperature shifts in the southeast Bering Sea and Gulf of Alaska are increasing the risk of prey mismatch and starvation for Pacific cod larvae.
The study, led by NOAA Fisheries scientist Ben Laurel of the Alaska Fisheries Science Center, notes that the first feeding of the young Pacific cod is a life-or death situation. Cod larvae are nourished by a yolk sac after they hatch, but once the nourishment in that sac is depleted, they must find food within days to avoid starvation, so there must be prey available at that time for first feeding.
“Warming (waters) can increase the metabolic demands of fish and shift the timing of their food production,” Laurel said. “So, you have temperature unraveling the system, moving food around.”
When mismatched prey timing and increased metabolic demand line up, he said, “it can be pretty disastrous. The better we can understand and predict these effects, the more effectively we can manage them now and in the future.”
Laurel has been studying the early life stages of cold-water commercial fish species for over 20 years, with a particular focus on how cod respond to rapidly changing environmental conditions.
While researchers have always seen relationships between temperature and marine populations, they don’t always know how temperature drives change. Stakeholders want to know why there are no fish in a given year, so it is important to understand why things are happening.
The research team found that in the Bering Sea timing of prey
production has historically been more variable, but mismatch effects continue
to be buffered by cooler temperatures.
“Spring plankton production in the Bering Sea is tied to the timing and extent of sea ice cover, which fluctuates widely from year to year,” Laurel explained. “But cooler temperatures in the Bering Sea buffer food demands of fish larvae so that they are not as sensitive to timing.”
In the Gulf of Alaska, the timing of prey production historically has been less variable, but warmer temperatures mean larvae are more sensitive to variability. There, the larvae use yolk sac reserves faster and have less time to find food when the yolk sac reserves run out.
Climate warming means both metabolic demands and shifts in timing
of prey production,” he said. “In the Gulf of Alaska, young cod are facing
double jeopardy.”