Winter flounder is one of the most
popular fish among recreational anglers and commercial fishermen, due in part
to their thick fillets and great taste. Once abundant in Rhode Island waters,
their numbers have declined significantly in recent decades, and new research
suggests that the warming climate will likely make it impossible to rebuild
their stocks to targeted levels.
The study, led by a former research
associate at the NOAA Northeast Fisheries Science Center in Narragansett,
concluded that even if fishing were to be curtailed entirely, winter flounder
populations are unlikely to rebound.
According to Rich Bell, who now
works as a fisheries scientist for The Nature Conservancy, winter flounder is a
cold-water, coastal species that spawns in estuaries like
Narragansett Bay and
Buzzards Bay during the fall and winter when most other flounders migrate south
or offshore. Their eggs and larvae develop in the estuaries during the coldest months
of the year.
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| Winter flounder (Jerry Prezioso/NOAA) |
“During the 1980s and 90s they were
overfished, and it seems that they never really recovered,” said Bell. “We
believe that they come into the bays to spawn in winter where they have a
thermal refuge from predation. When it’s cold, there are no predators around,
giving them time to grow big enough before it warms up and the predators
arrive.”
The concern is that as the climate
has warmed and spring arrives earlier and earlier, the predators are now
arriving before the larvae have a chance to grow big enough to escape. Common
predators on larval winter flounder include sea robins, summer flounder,
sculpins and crangon shrimp.
By combining winter flounder
population models with climate models, Bell and his NOAA colleagues projected
future population numbers as the climate continues to heat up. They factored in
three fishing scenarios into their models: no fishing, moderate fishing
representing a small fishery or incidental catch, and fishing at the expected
long-term sustainable level assuming the stock was rebuilt to historic levels.
“We found that as temperature
increases, it’s going to be more challenging for the population to recover. And
more importantly, even if there is no fishing and the temperature goes up as
expected, they may be unable to reach the targeted recovery level,” said Bell.
A large part of the problem is that
winter flounder produce fewer young in warm waters. The species is now rarely
caught in southern estuaries like Chesapeake Bay, and numbers are way down in
Delaware Bay and Long Island Sound.
“There might be so few in Long
Island that there are subtle signs of inbreeding occurring,” he said.
Bell notes that winter flounder are
not headed toward extinction. Populations are healthy in colder water regions
like the Gulf of Maine, Georges Bank and the Canadian Maritimes. But the
continuing declines in southern New England raise challenging questions for
their management.
“It becomes a larger issue of what
do we as a society want to do,” Bell said. “Do we want to stop fishing them
entirely? Do we want to fish them all now before they’re gone?”
While Bell wasn’t willing to weigh
in on those questions, he said the phenomenon of cold-water fish species
experiencing a decrease in productivity and an increase in mortality is not
exclusive to winter flounder. Other researchers are documenting similar results
in other species as ocean temperatures rise.
Whether the target levels for
rebuilding winter flounder stocks are even plausible is another question. Bell
said that those targets are based in part on data collected in the 1960s and
70s before significant warming had occurred and when the species was
reproducing at high levels.
“Rebuilding plans developed assuming
constant rates for demographic variables such as growth, reproduction and
mortality may not be realistic for stocks like winter flounder,” he said.
The research was published in September in the Canadian Journal of Fisheries and Aquatic
Sciences.
This article first appeared on EcoRI.org on December 7, 2018.
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