When a tropical fish called a
crevalle jack turned up this summer in the Narragansett Bay trawl survey that
the University of Rhode Island conducts every week, it was the first time the
species was detected in the more than 50 years that the survey has taken place.
The Rhode Island Department of Environmental Management’s seine survey of fish
in Rhode Island waters also captured a crevalle jack this year for the first
time.
While it’s unusual that both
organizations would capture a fish they had never recorded in the Bay before,
it’s not unusual that fish from the Tropics are finding their way to
Narragansett Bay. In fact, fish from Florida, the Bahamas and the Caribbean
have been known to turn up in local waters in late summer every year for
decades. But lately they’ve been showing up earlier in the season and in larger
numbers, which is raising questions among those who pay attention to such
things.
Crevalle jack captured in Florida (Photo by Clare Sunquist) |
“There’s been a lot of speculation
about how they get here,” said Jeremy Collie, the URI oceanography professor
who manages the weekly trawl survey. “Most of them aren’t particularly good
swimmers, so they probably didn’t swim here. They don’t say ‘It’s August, so
let’s go on vacation to New England.’ They’re not capable of long migrations.”
Instead, fish eggs and larvae and
occasionally adult fish are believed to arrive in late summer on eddies of warm
water that break from the Gulf Stream. Collie said they “probably hitch a ride”
on sargassum weed or other bits of seaweed that the currents carry toward
Narragansett Bay.
Most of these tropical species,
including spotfin butterflyfish, damselfish, short bigeye, burrfish and several
varieties of grouper, don’t survive long in the region. When the water begins
to get cold in November, almost all perish.
“There’s no transport system to
carry them back south, which is the reason they can’t get back where they came
from,” Collie said.
While climate change and the warming
of the oceans has been responsible for many unusual marine observations in
recent years, that does not appear to be the case with the annual arrival of
tropical fish in local waters.
“Warming doesn’t really have an
effect on it,” said Mark Hall, the owner of Biomes Marine Biology Center in
North Kingstown, which has been exhibiting locally-caught tropical fish since
it opened in 1989. “It’s just the way
the Gulf Stream meanders and carries these fish our way.”
Ocean warming does appear to be
affecting the timing of the arrival of the fish, however.
“Twenty years ago I wouldn’t bother
trying to find tropicals until mid-August, but now we’re seeing them in July,”
Hall said.
The good news is that none of these
tropical species appear to be harming or out-competing the native marine life
in Narragansett Bay.
“They arrive in July or August and
are dead by November, so they’re just not here long enough to have an impact,”
said Hall. “I can’t think of a single animal that’s having a negative effect.”
Collie agrees. “These strays are
small and appear here in small numbers,” he said. “The threat would come from
wholesale movements of new species that can stay here for long periods.
Tropicals aren’t a threat.”
For those interested in seeing some
of the tropical species that are making their way to Rhode Island, visit Biomes
in North Kingstown or Save the Bay’s Exploration Center and Aquarium at Easton’s
Beach in Newport. Save the Bay just opened a new exhibit this month featuring
tropical fish species collected locally by its staff, volunteers and partner
organizations, including Norman Bird Sanctuary and DEM. The exhibit, called The
Bay of the Future, features a wide variety of what manager Adam Kovarsky calls
Gulf Stream orphans.
“We want to spark people’s thought
processes about the things that can happen from climate change,” Kovarsky said.
“While tropical strays have been showing up here forever and ever, there’s
evidence that now they’re showing up in larger numbers and arriving earlier and
surviving later. It’s not a problem now, but eventually they may stay year
round, and that could stress our local species.”
The Save the Bay exhibit, the largest
display of warm-water species it has ever featured, includes striped burrfish,
pinfish, short bigeyes, scamp groupers, spotfin butterflyfish and many others
in a tank 12 feet long and 7 feet high.
This article first appeared on EcoRI.org on August 17, 2016.
This article first appeared on EcoRI.org on August 17, 2016.
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