Non-native fish species threatens to crowd out native stocks

Non-native fish species threatens to crowd out native stocks

New Bern, NC – INTRO - The discovery of a non-native species in the White Oak River raises concerns about fish native to the region being crowded out. George Olsen has more.

A sampling trip in April on the White Oak River yielded two flathead catfish, a species native to the Mississippi River basin but not to North Carolina. It's not the first time the flathead has shown up in North Carolina bodies of water.

"It's been well established in the Tar River, Neuse River, the Cape Fear River northeast, Sutton Lake. There's also records from the Catawba River as well as the Yadkin PeeDee River as well."

Bob Barwick, a District Fisheries Biologist with the N-C Wildlife Resources Commission. The flathead catfish is becoming common to the area but the more it's introduced to local waters, the harder it becomes for native species.

"It's a species that relies primarily on other fish as a large part of its diet, and that's where the concern lies, the concern with finding a new flat head catfish population in a river is that the fish, as it becomes established, may feed on other native species and may also feed on important sport fish species as well, and if that is the case there may be a decline in the quality of fishing that occurs in an area where flathead catfish are well established."

The flathead is certainly an attractive species for sport fishermen in size if not in appearance. Barwick says they can attain weights of between 40-and-60 pounds and sometimes larger. A photo of Barwick on the North Carolina Wildlife Resources Commission website shows him holding a 32-pound flathead pulled from the Tar River. But they reach that size by eating voraciously, to the detriment of native species.

"The main concern with what's going on with our white catfish population is that we're concerned in rivers that have well established flathead catfish that they are consuming the white catfish directly."

And that's been the case in the Tar River. Barwick says the flathead was introduced in the late 1990s and that typically it takes about 10 years for the flathead to fully establish itself. It's been right on schedule, to the detriment of the native white catfish species.

"We have seen that population continue to build since they were introduced and in fact now we've seen in just the past few years to go from relatively unabundant compared to other types of catfish like white catfish for example to now the flathead catfish is the dominant type of catfish in the Tar River."

The North Carolina Wildlife Resources webpage says a 2006 survey in the Tar River showed that flatheads accounted for 14 percent of the catfish population in the River. By 2008, that percentage had quadrupled, to 56 percent. Barwick says it was just a few years ago the white catfish was numerically the dominant catfish in the river now he says their numbers seem to be very low. The native catfish population is not the only population threatened by the introduction of the flathead.

"But as an example in the Lumber River flathead catfish populations became very abundant and concurrent with that building population we saw very sharp declines in redbreast sunfish populations there as well. Redbreast sunfish are still present there but they aren't nearly as abundant as prior to flathead catfish being established."

Barwick says the typical introduction of a non-native species is by fishermen moving a species from one body of water to another in hopes of establishing a new sportfish population. With this introduction of the flathead catfish to the White Oak River, the Wildlife Resources Commission is reminding fishermen that introducing non-natives can have harmful ecological consequences. It's also a move that once made can't be undone whatever the effect.

"There is no real safe or practical way to eradicate a non-native once it is introduced into a coastal river, for example. Once it's introduced it's in the river for good."

Bob Barwick is a District Fisheries Biologist based in Greenville with the N-C Wildlife Resources Commission. I'm George Olsen.