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Conserving Mussels

 


Conserving Mussels
Research by University of Maine wildlife biologists will help the state develop management plans to protect threatened species

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Luring a host
Some species of fresh-water mussels go to extraordinary lengths to attract fish hosts for their larvae.
 

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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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