Fishery meltdown

 

Alaska commercial fisheries look to be  global-warming losers, according to a new study by a group of U.S. scientists, but the study is missing one vital component:

 

Salmon.

Pound-for-pound salmon remain among the most valued fish in the 49th state, and Pacific Northwest scientists last year concluded salmon are now more abundant than at any time in recorded history, in part due to a warmer ocean.

“High overall salmon abundances primarily reflect high numbers of natural-origin and hatchery salmon in northern regions where habitat is less degraded and warming ocean conditions have been generally favorable for pink, chum, and sockeye salmon,” as the American Fisheries Society summarized the work of researchers Greg Ruggerone and James Irvine.

What is good for one fish, however, is not necessarily good for all fish, a team of scientists led by Christopher Free of Rutgers University reported in a paper published in Science earlier this month.

The study focuses on marine – not anadromous – species.

Free said all salmon were left out. Alaska and Russia are the big natural producers of those fish. Russia had so many pink salmon returning to its streams and rivers last year that the fish overwhelmed processing capacity.

Russia salmon fishermen, like those in Alaska, appear to have benefited heavily from a warmer North Pacific ocean. Alaska salmon harvests hit rock bottom in the 1960s and early 1970s when the Pacific was dominated by a cold regime.

Alaska harvests for more than a decade averaged about 40 million and fell to a mere 22 million in 1974. The 10-year average harvest is now up around 175 million.

Winners and losers

The paper by Free and researchers from the University of California, the University of Washington and the National Oceanic and Atmospheric Administration recognizes the up-and-down realities of climate shifts.

The news might cover only the doom and gloom, but the study notes there are winners as well as losers.

“Some populations responded significantly positively,” the study says, “and others responded significantly negatively to warming….

“Losses from populations responding negatively to warming outweighed gains from those responding positively because negatively responding populations constituted a larger biomass. The greatest losses in productivity occurred in the Sea of Japan, North Sea, Iberian Coastal, Kuroshio Current, and Celtic-BiscayShelf ecoregions, whereas the greatest gains occurred in the Labrador Newfoundland, Baltic Sea, Indian Ocean, and Northeast U.S.Shelf ecoregions.”

Alaska gains and losses were small enough that it failed to make either the biggest-loser list or the biggest-winner list.

The authors said they could find no evidence to, at this time, support the conventional wisdom that as the planet warms there has been a steady, northward movement of ecoregions driving greater productivity in the subArctic and Arctic.

“Studies that project fisheries productivity under future emissions scenarios often predict increases in productivity at the poles and decreases at the equator,” they wrote. “We see no evidence for this prediction over the observed time period, suggesting that contemporary range shifts have yet to drive productivity to the poles or that this prediction is driven by populations not evaluated in this work.”

The authors admit conclusions as to the fate of global fishery stocks are difficult because of the complexity of marine ecosystems and the inherent problems in studying them.

Activity takes place largely out of sight beneath the ocean’s surface in  ecosystems where little things are eaten by big things until some of the surviving little things grow big enough to eat the young of some of the big things.

Complicated predator-prey interactions makes it difficult to predict future productivity based solely on temperatures changes.

“Declines in East Asian fisheries productivity are consistent with single-species studies documenting negative climate impacts in the region,” they write, “though community-scale studies suggest that declining predator productivity may be balanced by corresponding increases in prey productivity.”

Not to mention that there is more to the picture than just temperature.

“Other factors such as changing primary production, dissolved oxygen, pH, and habitat availability may also be influential,” the study says. In many cases, those factors remain little investigated and undefined on a global scale.

Management importance

Where fisheries have been well-managed, the authors added, fish populations seemed more resistant to climate shifts whereas the opposite was true in areas where management was lax.

“We also found that exploitation history and temperature change interacted to determine the vulnerability of populations to warming,” they wrote. “Populations that had experienced intense and prolonged overfishing were more likely to be negatively influenced by warming, especially when they had also experienced rapid warming.”

Alaska fish managers usually get good grades for conservation management.

The study has what might be considered a significant margin of error.

Thought it estimated “that the combined multiple sustained yield (MSY) from the 235 populations (studied) decreased by 4.1 percent  (1.4 million metric tons) from 35.2 million metric tons in 1930 to 1939 to 33.8 million metric tons in 2001 to 2010….the 95 percent confidence interval for this trend ranged from a 9.0 percent decline to a 0.3 increase….”

The weighting of the range toward a decline does, however, make a negative outcome far more likely than a positive outcome, but the losses are so far relatively small.