Conserving Mussels
Research by University of Maine wildlife biologists will help the
state develop management plans to protect threatened species
Stephen Kneeland, a University of Maine
graduate student in wildlife ecology, caught 843 freshwater fish in
Maine this summer, but he didn't cook or sell a single one.
He anesthetized them.
Once the fish were out cold, he
examined their gills for the presence of mussel larvae. If he found a
white speck resembling a grain of salt, he carefully plucked it off and
saved it. If he found a large number of larvae attached to the gills, he
gave the fish a lethal dose of anesthesia and dissected the gills so the
larvae could be removed later.
All of the fish whose gills were left
intact went into a "recovery bucket." Once the effects of the anesthesia
had worn off, Kneeland released them back into the water.
At the end of the summer, Kneeland
brought all the larvae he collected to a UMaine lab where he developed a
DNA method to identify the mussel species.
There are 10 species of freshwater
mussels in Maine, and two of them are listed as threatened by the
Department of Inland Fisheries and Wildlife. A key to protecting these
two species — the tidewater mucket and yellow lamp-mussel — is knowing
to what species of fish the larvae attach.
Most freshwater mussels depend on
specific fish hosts to carry larvae on their gills or fins for a month
or two. When the larvae have completed their development (actually
undergoing metamorphosis from larvae to juvenile mussels while attached
to the fish host), they drop off and drift to the bottom of the stream
or pond, where they can live for 20 or 30 years or, in the case of some
species, more than 100 years.
Scientists have not discovered which
species of fish serve as hosts for most species of freshwater mussels.
"That's a huge information gap," says
Beth Swartz, a state endangered species wildlife biologist and UMaine
alumna. "We wanted to partner with the university to help us identify
the fish hosts for at least the two species of mussels that are listed
as threatened in Maine so we can make management decisions with some
confidence.
"We need to know how things like
building dams or changing the hydrology of a river or pond might affect
the fish host because, if we don't have the fish host, we don't have the
mussels."
Judith Rhymer, a UMaine associate
professor of wildlife ecology, is leading the freshwater mussel study.
She specializes in a field of research called conservation genetics,
which uses genetic information to answer questions related to the
conservation of endangered species. In the past, she has studied
waterfowl from New Zealand, Hawaii and Madagascar to better understand
differences among species, and how introduced species and subsequent
hybridization threatens native populations.
Unlike species of larger,
thicker-shelled mussels in the Southeast that are harvested for the
lucrative Asian pearl culture market, freshwater mussels in Maine have
no commercial value. They also aren't good to eat. But they serve an
important ecological function. As "filter feeders," they help to keep
their environments clean by filtering out bacteria and other impurities
in the water.
The two threatened species of mussels
live in only three river drainages in Maine — the Penobscot, Kennebec
and St. George. In a recent study, Rhymer and former graduate student
Morgan Kelly compared the genetic makeup of mussels of these species in
different localities in those drainages.
"Maine's rivers and streams are fragmented by hundreds of dams. We
wanted to find out if the dams have fragmented the mussel populations
because they prevent fish hosts from moving freely throughout the
system," Rhymer says. "Our genetic analyses found that, with a few
exceptions, mussel populations were quite different among the three
drainages and even within the same drainage."
That is important to know. If a
population of mussels needs to be moved because survival is threatened,
state wildlife officials want to move them where they are genetically
similar to the indigenous mussels. A goal is to ensure that the
relocated mussels have the right genetic makeup to thrive.
"Our preference is to relocate them in the same water system, as close
to the original location as possible," Swartz says. "But we need to know
what their fish hosts are and what their specific habitats are like to
give them any hope of success."
Several types of mussels, including the
two threatened species, live in water impounded behind dams. If the dams
are removed and the water level drops, the mussels that are left exposed
will die. Dam removal also can affect the abundance of fish hosts and
other critical elements of mussel habitats.
The removal of the 160-year-old Edwards
Dam from the Kennebec River in 1999 was impetus for the current mussel
research. When that dam was opened, the water level behind it dropped 10
feet, leaving hundreds of the threatened species of mussels exposed.
Volunteers scrambled to snatch up and relocate as many of the mussels as
possible. But there was no research on the best way to ensure the
mussels' survival and no follow-up on how they fared.
State wildlife officials wanted to be
better prepared the next time a dam was removed. They expected that to
be in August 2003, when the Fort Halifax Dam on the Sebasticook River at
Winslow was scheduled for removal, but that is still on hold pending the
outcome of a lawsuit.
Meanwhile, the UMaine researchers
continue to gather information to help the state develop a mussel
management plan.
"We knew from Morgan Kelly's study that
the mussels at Unity Pond and Sandy Stream were not genetically
different from those in the Sebasticook impoundment, so those were
chosen as new sites if the Fort Halifax Dam came out," Rhymer says. "But
first we wanted to do some translocation experiments to get our
techniques down."
Last year, graduate student Jennifer Kurth, who is co-advised by Cyndy Loftin, an assistant leader with the
USGS Maine Fish and Wildlife Cooperative Research Unit, took some
nonthreatened mussels from above the dam on the Sebasticook. She
attached PIT (passive integrated transponder) tags to their shells with
dental cement and moved them to Unity Pond and Sandy Stream. She went
back to check on them this summer.
With the assistance of Joe Zydlewski
from the USGS Cooperative Research Unit at UMaine, Kurth was the first
person to use a PIT tagging system in mussel research. She was able to
find about three-quarters of the mussels that she moved last year, and
most of them seemed to be doing well. Scientists using ordinary numbered
tags typically find only about 20 percent of their mussels.
Kurth spent the latter part of this
summer counting mussels and estimating the population size of the two
threatened species above the Fort Halifax Dam on the Sebasticook River.
She also tagged some of the threatened species from the Sebasticook
impoundment and moved them to Unity Pond and Sandy Stream. Next summer,
she'll return to check on them.
"Learning how to do the surveys,
getting baseline population information and experimenting with
relocation techniques is important work," Swartz says. "The point is to
learn as much as we can so that, as resource managers, we can do a
better job of protecting these threatened species."
She expects the threat to mussels to
increase over the next few years as more hydroelectric dams in Maine are
decommissioned. It is often less expensive to remove an inoperative dam
than it is to maintain it.
North America has several hundred
species of freshwater mussels; the greatest diversity is in the
Southeast. About 70 percent of all species are threatened or endangered
for a number of reasons, including dam construction, poor water quality,
habitat alteration and degradation, introduced species and
overharvesting. The yellow lampmussel and tidewater mucket are found
from New Brunswick to Georgia; their numbers are dwindling throughout
that range.
As important as freshwater mussels are
ecologically, Rhymer says, they don't get much respect because they are
invertebrates — they aren't warm and fuzzy — and they live out of sight.
Unlike Maine, many states do not even acknowledge the importance of
invertebrates by protecting them.
"Our research is drawing attention to these species within the state and
giving the endangered species biologists more tools to work with," she
says.
"They need all the ammunition they can
get in terms of understanding and protecting mussels."
by Dick Broom
November-December, 2005
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