Frequently Asked Questions and Myths
Are blue catfish voracious predators capable of decimating native fish species in the Chesapeake Bay?
Answer: This is a complicated question. The vast majority of the blue catfish population is comprised of small fish (less than 15") and these fish can't be classified as apex predators. They mostly eat vegetation, mollusks, and crustaceans such as amphipods. In fact, they feed so heavily on vegetation they occupy a trophic level similar to common carp (estimated trophic level 2.6-3.3). Blue catfish are considered generalists as they feed on the most prevalent resources in their environment. The problem is that generalists are extremely successful (recent papers in ecology call generalists "winner" species) and are resilient to environmental degradation, which may explain their success in the Chesapeake Bay tributaries following centuries of human activities in the watershed. Generalists are known to thrive in degraded habitats, which is exactly what blue catfish have done.
Bigger blue catfish begin to feed on other fish, but the dominant species they consume is gizzard shad.
Medium sized fish in brackish areas do feed on blue crab and menhaden, which is arguably the biggest concern with blue catfish right now.
Are blue catfish responsible for declines in American shad and river herring?
Answer: This is highly unlikely. Dr. Joe Schmitt's team did extensive sampling during March, April, and May in the James River from Bosher Dam all the way downriver to tidal creeks near Jamestown. This study included some 2,500 catfish and hundreds of "trophy" fish (> 30 lbs). American shad and river herring were found in less than 0.5% of blue catfish stomachs. Predation on American shad and river herring is not common with blue catfish.
Schmitt also looked at the diets of thousands of catfish in the fall, the time during which juvenile shad & herring move downriver toward the lower Bay. While they regularly encountered juvenile American shad and river herring during sampling, few were present in the diet (<1% of catfish stomachs). Furthermore, American shad stocks have shown signs of recovery in the Rappahannock River, which supports the most dense population of blue catfish among Virginia's tidal rivers (Greenlee and Lim 2011).
Flathead catfish, on the other hand, do prey on American shad and river herring, which were found in 16.67% of stomachs. Flathead catfish seem to prefer blueback herring, a species of management concern.
Interestingly, we saw the highest predation of American shad & river herring in the rapids near Richmond, which offer numerous ambush points for blue and flathead catfish. American shad & river herring were found in 10% of blue catfish stomachs and 32% of flathead catfish stomachs in the stretch of river from Bosher Dam to the 14th St. Bridge.
"But blue catfish are eating Atlantic sturgeon..."
Answer: We've seen no evidence of this. Dr. Schmitt sampled stomachs from 17,762 catfish, making his study the largest diet study ever conducted on blue catfish, and one of the largest conducted on any fish species. Schmitt saw zero Atlantic sturgeon in stomachs. A valid concern is that blue catfish may prey on sturgeon roe (eggs) during spawning. Dr. Schmitt's diet study occasionally found fish roe in catfish stomachs and identified roe to species using DNA barcoding. Genetic analyses identified the species of the roe in the stomachs of blue catfish as gizzard shad.
"Trotlining and commercial fishing are ruining the trophy fishery in the James River"
Answer: While over-harvest of large individuals can destroy a trophy fishery, the current decline in production of trophy-sized fish is driven by "density dependent growth", meaning that catfish are so abundant they now compete for resources. This decline in growth was first documented by fisheries biologists in the James River in 2011. In fact, other studies have shown that harvest can reduce competition for resources and increase growth rates. Virginia Department of Game and Inland Fisheries currently enforces a "1 fish over 32 inch" policy (click here for details), and this regulation does apply to commercial fisherman.
"Blue catfish are eating the native bass"
Answer: This is a common concern from bass fisherman related to blue catfish. Neither largemouth or smallmouth bass are native to any of our tidal rivers. In fact, both species are non-native throughout most of Virginia. In the thousands of blue catfish stomachs examined, Schmitt's team saw 2 largemouth bass. Predation on black bass is an extremely rare occurrence, as bass were found in less than 0.0001% of blue catfish stomachs. It seems unlikely that bass would be vulnerable to catfish predation, as there are more abundant species to prey on (e.g. gizzard shad).