RALEIGH — Fisheries biologists with the N.C. Wildlife Resources Commission are again asking for anglers’ assistance after reports of gill lice on rainbow trout in three western North Carolina trout streams were confirmed last week.
And they aren’t the only problem.
Aquatic nuisance species — either plants or animals — are organisms that cause ecological and/or economic harm when moved outside their historical range. In the mountain region, whirling disease and gill lice are aquatic nuisance species most troubling to biologists right now because of their impacts on trout populations.
However, in other parts of the state, one of the most troublesome aquatic nuisance species isn’t an animal or a parasite but a non-native aquatic plant, hydrilla, which forms dense mats and can take over a good fishing spot, consume oxygen and cause fish kills.
Hydrilla is having major impacts on Columbus County’s Lake Waccamaw. It’s also a nuisance in the Eno River in Durham County and various reservoirs throughout the state. It tends to spread quickly, outcompeting native vegetation and interfering with boating, swimming, fishing and other water-related activities.
Biologists ask anglers to be diligent when cleaning their equipment and offer these recommendations:
• Remove any visible mud, plants, fish or animals before transporting equipment.
• Eliminate water from equipment before transporting.
• Clean and dry anything that comes into contact with water.
In addition, biologists stress the importance of not moving fish from one body of water to another. Not only is it illegal, but it is also one of the primary ways these nuisance species spread.
“Illegal stockings can have unforeseen and irreversible consequences,” said Doug Besler, the Commission’s fisheries supervisor for the Mountain Region. “We now have four confirmed cases of gill lice established in wild trout populations within the last year. (This) shows how rapidly nuisance species can spread.”
The new reports of gill lice came on the heels of the recent confirmation of whirling disease in rainbow trout collected from the Watauga River.
“While whirling disease can be fatal for infected individuals, gill lice may not directly lead to substantial mortalities in trout populations,” Besler said.
“However, their presence is a stressor that is cumulative over time. Each new stressor, whether it’s drought, or high water temperatures, or even another aquatic nuisance species, is additive in terms of stress placed on each infected trout and those stresses can add up to declines in abundance if enough individuals are affected.”
Gill lice—tiny, white crustaceans also known as copepods—attach to a fish’s gill, which can damage gills and inhibit the fish’s ability to breathe.
While most fish are able to tolerate a moderate infestation of gill lice, some fish, particularly those that are suffering from other stressors like drought or high water temperatures, can succumb to a gill lice infestation. Impacts to local trout populations can be devastating.
The gill lice reported last week on rainbow trout in the West Fork Pigeon River, Boone Fork Creek and Watauga River is a different species of gill lice than the one found on brook trout in 2014.
That one, Salmincola edwardsii, is found only on brook trout, while this latest species, Salmincola californiensis, is known to infect not only rainbow trout but also kokanee salmon.The only population of kokanee salmon found in North Carolina is in Nantahala Lake in Clay and Macon counties.
The confirmation of this new species of gill lice is particularly concerning to fisheries biologists because it highlights the ongoing and increasing threat that aquatic nuisance species pose to native aquatic wildlife, and how quickly and easily they can spread.
Throughout the Great Lakes Region and in the Mississippi River Basin, quagga mussels and zebra mussels are wreaking havoc on waterways, causing issues with boaters, swimmers and others who enjoy water-related recreation. These species have not been found in North Carolina waters — yet.
Biologists continue to work with anglers and boaters to keep these species from being introduced in North Carolina and causing similar problems.
Although the vast majority of aquatic nuisance species are non-natives, a few, such as white perch and river herring, are species native to the Atlantic Coast that have become nuisance species after they were introduced into North Carolina reservoirs where they weren’t historically found and began outcompeting, or even preying on, native fish.
Lake James is an example of a reservoir where white perch and river herring have been introduced. In their native coastal rivers, river herring are an important food fish for other fish species and white perch are popular game fish for anglers. However, in Lake James, they have preyed on walleye eggs and have effectively eliminated walleye reproduction. As a result, the Commission has implemented a walleye fingerling stocking program in Lake James to maintain this popular fishery.
“Anyone, whether you’re an angler or a boater or just someone who enjoys using our waters, can help prevent the spread of aquatic nuisance species,” Besler said.
“Once established, they can be nearly impossible to eradicate and can diminish fishing opportunities for decades to come.”