LDWF Working To Better Understand State’s Mussel Populations
story by Ashley Counce, LDWF Public Information
It’s a steamy summer morning on the Pearl River. LDWF fisheries staff has loaded their gear and begin making their way up the river, slowing the boat down as the sun peaks over the tree line.
They head toward the banks on the downstream end of one of the many sand bars along the way. There is no fish sampling gear onboard. Instead, the crew is equipped with some less predictable items - dive boots, snorkels, even scuba gear. A survey of the local mussel population is about to commence.
Louisiana waters are home to 66 species of mussels, including the pearlshell, which is found only in the state of Louisiana. The freshwater mussels that inhabit Louisiana’s lakes, rivers and bayous are possibly one of the most overlooked natural resources the state possesses. Though once a commodity for their shells, mussels are not considered an important commercial natural resource in Louisiana. However, all have an inherent ecological value in the waters in which they live.
Unfortunately, freshwater mussels are on the decline numerically as well as in diversity as a result of human activity, namely loss of seepage (shallow groundwater discharge) by agricultural and urban compaction of soil, sedimentation from erosion, channeling of natural streams by dredging, gravel mining (producing extensive channel erosion) and contamination of waterways from urban and industrial runoff and dumping. Freshwater mussels that once cobbled the stream bottoms in Louisiana are now among the most endangered animals in fresh waters.
Historically, Native Americans used freshwater mussels for both food and eating utensils (shell). Shells were later used to make pearl buttons until the advent of the plastics industry. By the early 1900s, this multi-million dollar business was in full swing along the Mississippi River. Because there were no controls on the industry, mussels were over harvested and numbers of many species dwindled.
Freshwater mussels have a unique life cycle. To understand a mussel’s life cycle, think of a butterfly. A butterfly hatches into a caterpillar or larva that must undergo metamorphosis. The larval form of a mussel is parasitic and called a glochidia. The glochidia undergo their metamorphosis while attached to the gills or fins of a fish including catfish, bluegill and freshwater drum. The fact that mussels require specific species of fish to reproduce means that mussels are also good indicators of the health of their host fish populations. Like the monarch butterfly whose caterpillar only lives on milkweed plants, certain mussels can only undergo metamorphosis on certain species of fish. Metamorphosed glochidia are called transformers. Once these transformers have completed their metamorphosis, they break free from the fish and settle to the bottom of the river or lake, and there they begin to grow. In a few months the transformers will go from microscopic to being large enough to see.
Prior to 2011, the only sampling efforts conducted by the department specific to mussels were special projects and partnerships with universities and federal agencies. It wasn’t until August 2011, when a paper mill in Bogalusa released an unauthorized amount of paper-making byproduct into the Pearl River, killing an estimated 500,000 fish and freshwater mussels that LDWF began paying closer attention to the species.
Since then, the department has made a concerted effort to monitor freshwater mussel communities. This marked a paradigm shift from a species centric assessment to an ecosystem approach in managing and monitoring Louisiana’s rivers and streams. A new sampling protocol was developed to include freshwater mussels. Timed qualitative searches are performed at each established sample site. A 90-minute sample is conducted at each site where biologists will work along the littoral zones (less than 1 meter in depth) locating mussels using their hands, retrieving both living mussels and shell. All collected mussels are identified by species. Additional samples are sometimes conducted in water greater than 1 meter in depth in areas adjacent to the littoral zone. Biologists utilize SCUBA equipment to collect these samples.
Mussels play an important role in the aquatic ecosystem. The presence of diverse and reproducing populations of mussels indicate a healthy aquatic system which means good fishing, good water quality for waterfowl and other wildlife species, as well as insurance that our water is not impaired. Conversely, when mussel populations are at risk, it indicates problems for other fish and wildlife species, and people too.
“Mussel assemblages can be one of the first things affected by disturbances in the watershed,” explained LDWF freshwater fisheries biologist Gary Vitrano. “It’s important to have a baseline of those mussels populations, because they’re our indicators of a freshwater system’s health.”
The future of freshwater mussels has become entirely dependent upon the further actions of man. Our best defense against total loss of this resource is knowledge.
“At the end of the day, as fisheries biologists, it is important to have an intimate relationship with all the aquatic organisms in the waterbodies we manage,” said Vitrano.
Vidrine, Malcom F.; Quillman-Vidrine, Gail J.; Vidrine, Malcolm F. II; Vidrine, Daniel J.; and Vidrine, Caroline E., “Freshwater Mussels (Bivalvia: Unionidae) in the Cajun Prairie Ecosystem in Southwestern Louisiana” (2004). Proceedings of the North American Prairie Conferences
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