By TODD McLEISH/ecoRI News
contributor
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.
A recent study, led by a former research associate at the National Oceanic and
Atmospheric Administration’s Northeast Fisheries Science Center in Narragansett,
R.I., 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 such as
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.
“During the 1980s and ’90s they were overfished, and it seems that they never really recovered,” Bell said.
“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.
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,” Bell said. “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.”
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 such as 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 noted that winter
flounder aren’t 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 isn’t 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 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.
Rhode Island resident
and author Todd McLeish runs a wildlife blog.