Save our clamcakes!
By Bonnie Phillips / ecoRI News staff
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Although they may look like they aren’t doing anything
special besides existing, these quahogs are part of an innovative effort to
study and boost the population of the iconic, native hard clam in Narragansett
Bay.
Funded through a Partnership for Research Excellence in
Sustainable Seafood (PRESS) grant from the University of Rhode Island supported
by the National Oceanic and Atmospheric Administration, the initiative will
help expand hatchery production, strengthen disease monitoring, and accelerate
quahog restoration in Rhode Island.
“The aim of this work is to address commercial and
recreational harvester concerns about the declining clam population in
Narragansett Bay,” said Robert J. Holmberg, RWU assistant professor of marine
biology and the Center
for Economic and Environmental Development’s (CEED) shellfish aquaculture
and hatchery specialist.
“Thanks to the support from this grant, we’re working with the state to provide data on isolated populations and their ability to reproduce, and also what diseases or pathogens they might face in these specific areas,” said Malcolm Bowen, RWU’s aquaculture extension specialist and manager of the university’s marine aquaculture farm.
Quahog seeding
“Narragansett Bay is pretty unique because of the amount of
wild quahogs we have, as compared to other estuary systems,” Bowen said.
That’s because the Narragansett Bay estuary system has just about the best water quality of such systems on the East Coast, he added.
But wild quahog populations in the bay have been slowly
declining over decades due to a number of factors — not all of which are known
— but which include predation, disease, and reproductive issues.
The RWU project will collect data that will help tease out
what the issues affecting the quahog population might be and how to address
them, while also transplanting, or seeding, hatchery-raised quahogs in the bay.
The researchers are starting with quahogs caught in four
diverse locations in and around Narragansett Bay. During the winter, clams are
collected and divided into two groups: half are brought to CEED’s Luther
H. Blount Shellfish Hatchery to be used as brood stock for seed
production, while the other half are sent to CEED’s Aquatic
Diagnostic Laboratory (ADL) for testing for two major shellfish
diseases: quahog parasite unknown (QPX) and hemocytic neoplasia, a contagious disease in clams.
Both diseases, while not dangerous to humans, can weaken or
kill clams. So researchers are focused on diagnostic testing to determine
whether quahogs can be safely moved between areas while keeping the population
healthy. In late spring, researchers will return to each site to assess
reproductive health after the quahogs’ winter dormancy period.
After spawning at RWU’s hatchery, young quahogs are
transferred to the Rhode
Island Shellfisherman’s Association’s (RISA) floating upweller nursery
system in Warwick. Baby oysters start out about the size of a grain of sand,
and grow by consuming nutrients from the water, filtering it in the process.
Upweller systems accelerate growth by storing the young quahogs in containers
and pumping water through, delivering constant food and oxygen, which increases
growth rates and survival. As they grow, the quahogs are sorted into different
containers by size so that they grow and consume nutrients at similar rates.
The baby quahogs are cared for by CEED’s FerryCliffe
Shellfish Farm team, overseen by Bowen. In the fall, once the quahogs
reach an appropriate size, RWU will collaborate with RISA and the Department of
Environmental Management to transplant the clams into state waters.
RWU plans to produce at least 100,000 young quahogs from each of the four test populations for the restoration efforts and, by selecting genetically diverse quahogs that have been screened for diseases, the clams will have a better chance for long-term breeding success.
A state icon
The northern quahog is a source of Rhode Island pride. With
their familiar shape and brown or gray concentric rings lining the outside of
their shells, they are instantly recognizable to most state residents. They’re
featured in the state’s popular “stuffy” appetizers and seen as the backbone of
the state’s seafood industry and Rhode Island’s blue economy.
“Quahogs are one of Rhode Island’s most valuable commercial
fisheries, generating millions of dollars annually,” RWU’s Holmberg said.
But quahoggers working Narragansett Bay today are catching
fewer quahogs than they were a decade ago. In 2022 quahoggers harvested 397,442
pounds of quahog meat, according to data from NOAA. That’s less than half of what they
caught 10 years ago: in 2012, Ocean State quahoggers harvested more than
900,000 pounds of meat.
It’s worrying enough that state lawmakers have gotten
involved, creating a study commission in 2023 to investigate
possible causes of the population changes.
The work at Roger Williams University “trying to assess
these populations and monitor them is a great start at putting numbers to a lot
of the knowledge that folks who work the bay have every day,” said Bowen,
referring to the quahoggers who have, for years — often generations — worked in
Rhode Island’s waters.
The RWU program will help researchers learn the health and
reproductive factors that affect wild quahogs.
“This will help us select which populations we can pull
breed stock from to have the highest chance of successful recruitment,”
Holmberg said.
“So, we’re looking at wild populations and a hatchery
population. One of the various things we hope to come out of it is to make a
comparison between them,” said Kimberly Soule, RWU hatchery technician. The
researchers will study the clams spawned in hatcheries, “and then we’ll go back
and collect more clams from those same four [wild] populations and go, OK, what
do their reproductive organs look like having been left in the wild, versus us
actually kind of helping them in a hatchery.”
The Aquatic Diagnostic Laboratory at CEED has developed a
diagnostic method that detects hemocytic neoplasia, the contagious cancerous
condition that affects the quahog’s equivalent of blood. While there is no firm
data yet on whether the disease is significantly impacting wild quahogs in
Rhode Island, populations in Massachusetts have been found to be significantly
affected in some areas.
“The shellfish team here at CEED is applying research to
gain data so we can tackle questions about disease in this important species,”
said Koty Sharp, director of CEED and an associate professor in biology, marine
biology, and environmental science at RWU. “We are glad to bring tools from
research to this conversation as everyone works together to find solutions to
this problem.”
Typically, the cancer is diagnosed by examining tissue
samples from a quahog under a microscope, which takes up to six weeks and
always results in the death of the clam. RWU researchers developed a faster,
non-lethal method that uses a test that determines whether the clam has the
specific genes that carry the disease, a process that doesn’t kill the quahog,
takes about two weeks, and is less expensive while also being better at
detecting lower levels of the disease.
Making babies
Quahogs grow slowly and live between 12 and 20 years on average. Adults are usually between 3 and 5 inches long and can be harvested once they reach an inch in length between shell hinges. They burrow into the sediment and tend to stay in one place, feeding through their siphons and preferring salty water; they can’t survive if the water’s salt content is too low. When spawning, each female can produce between 1 million and 5 million eggs; the larvae are born without shells but develop them in about 2 days, and the shells grow along with the quahog, resulting in the familiar growth lines.
At Roger Williams, the quahog parents-to-be, also called
brood stock, are brought into the hatchery from the wild, according to
Holmberg. They enter what’s known as a “conditioning phase,” which involves
gradually acclimating them from the cold ocean temps to warmer water, around 60
degrees Fahrenheit. While the quahogs are warming up, they’re also fed micro
algae grown by the university. The algae ranges in color from neon green to
orange to dull brown, filling glass containers in a greenhouse across the hall
from the hatchery.
“When they eat that food, they put the energy that they get
from it into building their shells, but also developing their gonads,” Holmberg
said.
Over a period of five to six weeks the quahogs are allowed
to eat and grow. When they’re deemed ready to make babies, “We take them out of
their tank, and we put them into a shallower tray with water that we crank up
to around 80 degrees Fahrenheit,” Holmberg said.
The warm water tricks them into thinking that the seasons
have changed and it’s time for them to spawn, he said. In a process called
broadcast spawning, usually in mid-summer in the wild, males release sperm and
females release eggs directly into the water column, where external
fertilization occurs. The fertilized eggs become larvae, drifting in the ocean
for weeks before settling on the seafloor to grow.
Once that happens in the lab, Holmberg said, it’s time to
wait.
And wait.
“It’s like watching the grass grow,” Soule said. “We have
different kinds of music depending on their mood.”
Holmberg said, “We tend to sit around the tray, watching
them for hours at a time with flashlights, looking for the release of gametes.
When we see one release, we pull it out, put it into a separate container so
that it can fill the water in that container. And if the spawn is successful,
we hopefully end up with several females releasing eggs, and usually more males
releasing sperm.”
The number of eggs released by the females is what
determines how many larvae can be produced, Holmberg said, because individual
sperm fertilizes individual eggs.
“It’s a numbers game,” he said. “That’s why they produce
millions to hundreds of millions of eggs. And in the wild, a very small
proportion of those end up developing, but in the hatchery, we try to maximize
the percentage of them that are turned into seed.”
It’s those seeds that will eventually be transplanted into
Ocean State waters and, if all goes to plan, keep the state’s iconic quahog
population thriving.
“It’s part of our identity as a state, and it’s very
important for many Rhode Islanders and folks from other places who see that
resource as unique to us,” said Bowen, who quahogged while growing up in Little
Compton, before heading off to heat up his lunch of pasta with red sauce and
chopped quahogs. “It’s part of our heritage.”