NOAA Fisheries scientists say they have developed a new modeling approach to evaluate the changing productivity of fish populations as ocean temperatures continue to warm.
This new approach was used to evaluate productivity for Alaska Pollock and Pacific cod in the Gulf of Alaska. They found that for Alaska Pollock and especially Pacific cod, sea surface temperatures in the Gulf are already less conducive to successful fish development, growth and survival than in recent decades. Fish productivity is determined by estimating how many fish survive from the egg and larvae stages annually to become adults.
According to Mike Litzow, director of the Kodiak laboratory of the Alaska Fisheries Science Center, a critical step in climate change adaptation is the ability to effectively evaluate the likely impacts on individual fisheries.
“We have to make inferences about how fish populations are likely to fare in ecosystem states that have never been observed before on short time scales- this decade and the next,” Litzow said.
In evaluating these two important commercial fish stocks, which are caught in huge annual harvests, researchers considered three pieces of information. First, the results from climate models that show that recent extreme temperatures in the Gulf were only possible with global emissions from fossil fuel consumption and other human activities.
Second they considered observations that both Pacific cod and Alaska Pollock stocks produce very few young fish during periods of extreme temperature anomalies. The third consideration was results from climate models that show that these extreme events are expected to be much more common in the current climate than in recent decades.
Scientists looked at how fish responded to a range of temperatures that could be expected under historical conditions, when human influences on the Gulf climate were not so strong. They then compared those historical responses to the level of productivity that can be expected from these fish stocks in the current climate, with strong human influences on Gulf temperatures.
The results show how expectations for fisheries productivity can be adjusted to take the current effects of climate change into effect, they said.
Both Pacific cod and Alaska Pollock at different stages of development are more or less susceptible to warmer water temperatures. Using this approach, scientists are projecting a decline during this decade, of between 38% and 88% in median Pacific cod and Alaska Pollock recruitment, based on the number of larval fish to reach maturity.
Such a decline suggests a reduced likelihood of recovery for Pacific cod and increased likelihood of population declines for Alaska Pollock as well. These projections suggest that maintaining sustainable fisheries for these populations are increasingly unlikely in the contemporary Gulf, they said.
Michael Malick, co-author of the study, who is at the Northwest Fisheries Science Center, said such projections must be viewed with caution because other factors affect fish stock recruitment beyond just ocean temperatures.
“Fish populations,” he said, “may also be able to adapt, move to new locations, or acclimate to warming temperatures.”