The Return of the Brook Floater

The brook floater, a state endangered freshwater mussel, was recently reintroduced into waters it hasn’t inhabited in more than 100 years, thanks to a partnership between the N.C. Wildlife Resources Commission and Duke Energy.

In July, agency biologists stocked approximately 350 brook floaters (Alasmidonta varicosa) downstream of Lake James in the Catawba River bypass reach near Bridgewater Road in Burke County. The last time a brook floater was documented in this stretch of the river was in 1919, shortly before the impoundment of Lake James, which diminished the flow of water to a trickle and made the habitat unsuitable for most mussel species.

A requirement put in place by the Federal Energy Regulatory Commission in 2015 to increase the minimum water flows in the reach downstream of Lake James dramatically improved the amount and quality of habitat available to freshwater mussels, particularly brook floaters, which need consistently flowing water in order to survive.

In 2018, agency biologists developed a conservation strategy to re-establish a brook floater population in the reach, and augment other existing but small populations in the Catawba and Yadkin River Basins.

To start the augmentation process, biologists had to first identify an area where they could collect adult brook floaters to use as broodstock. In 2018, they collected 15 brook floaters from Wilson Creek in Caldwell County and took them to the agency’s Conservation Aquaculture Center in Marion, where the intricate and arduous process of raising mussels from a larval stage to juveniles began.

Due to their unique life cycle and mode of feeding, freshwater mussels are difficult to propagate. Larval mussels, also called glochidia, must attach themselves to the gills or fins of suitable host fish before they can develop further into juvenile mussels. Eventually, the juvenile mussels drop off the fish and onto the river bottom, where they spend their lives, if the habitat is suitable.

The Conservation Aquaculture Center, which opened in 2008, provides all the necessary elements to replicate this intricate natural process in a controlled, artificial setting. From the water that constantly flows through the tanks to the substrate at the bottom of the tanks to the temperature of the air in the building, everything is set up to mimic, as closely as possible, the reproduction process mussels undergo in the wild. All aspects of mussel culture – from the infestation of fish hosts to “grow-out” of juveniles – is conducted at the hatchery.

Once center staff had grown out enough juveniles to suitable stocking size – about 24 months – they tagged the mussels before they were released, so that biologists can track their survival. Biologists plan to conduct monitoring surveys every spring and will consider the stocking successful if they detect stocked mussels in consecutive surveys and these mussels reproduce naturally.

Over the next five years, biologists hope to augment populations in other areas of the Catawba river upstream of Lake James, the North Fork Catawba River in the Catawba Basin, as well as the Fisher River, Buffalo Creek, and Elk Creek of the Yadkin River Basin. Exact numbers of mussels stocked in each area will depend on propagation success and resources.

Augmenting existing populations or establishing new populations in suitable areas can be a powerful tool for conservation and is a key component of the N.C. Wildlife Action Plan, a comprehensive planning tool developed by the Commission to help conserve and enhance the state’s fish and wildlife species and their habitats. Freshwater mussels are an indicator species of water quality and play an important role in improving water quality by filtering out bacteria, algae and pollutants. Their presence in a streambed may go unnoticed by most people; however, freshwater mussels play an important role in keeping waters clean and aquatic ecosystems healthy.

Today however, many, if not most, mussel species are in trouble, with high extinction or extirpation rates documented, particularly in the last few decades. In North Carolina alone, of the 48 species native to the state, 30 are listed as endangered, threatened or special concern. Even more concerning, several species have either gone extinct or been extirpated from the state.

Threats, such as the creation of dams, which can create unsuitable mussel habitat for hundreds of miles downstream, along with sedimentation, channel modification, pollution, low oxygen conditions, and loss of riparian buffers have resulted in habitat loss and impaired water quality for many freshwater mussels. This notable decline in habitat has diminished overall populations of brook floaters in North Carolina, so much so that they are now listed as state endangered.

“Mussels are important because they help keep our waters clean,” said T.R. Russ, the lead Commission biologist on this project. “Mussels also provide other aquatic animals substrate and habitat to attach to and are an important food source for numerous other critters. “Returning all of the previously known species to this part of the Catawba River will improve the ecological health of the watershed and hopefully provide a stable place for more mussels to persist.”

The stocking effort was funded by Duke Energy’s Catawba Wateree-Habitat Enhancement Program (CWHEP) and State Wildlife Grants. The CWHEP is a cooperative initiative by Duke Energy, the Commission and the South Carolina Department of Natural Resources, to provide funding for habitat creation, enhancement and protection for fish and wildlife adjacent to and in the Catawba- Wateree watershed and associated reservoirs.

Contributed by NCWRC