Distribution and Diet of Flathead Catfish in Virginia Tributaries of Chesapeake Bay
Flathead Catfish are native to many river systems flowing to the Gulf of Mexico, but now exist in several Chesapeake Bay drainages. The species is known to feed primarily on fishes and has been implicated in native fish declines along the Atlantic Coast. Flathead Catfish have taken a backseat for many Bay-region aquatic scientists to Blue Catfish, as Blue Catfish are more abundant. However, a study published in 2017 indicated the feeding habits of Flathead Catfish may be more alarming as their diets are more fish-based (click here to read the article). While the 2017 study described diets of James River Flathead Catfish, the sampling scheme was focused on estimation of the prevalence of American Shad and river herring (Alewife and Blueback Herring) in diets during their spawning migrations. Thus, it was restricted to areas near the fall line during the spring. A soon to be published article sought to understand Flathead Catfish feeding habits in the James River over larger spatial areas and beyond springtime. Further, the study addressed what is known about the distribution of Flathead Catfish in Virginia tidal rivers.
Corbin Hilling presents a 57 lb. Flathead Catfish from the James River during a spring electrofishing survey
A large-scale catfish diet study by Virginia Tech scientists provided an opportunity to learn more about where Flathead Catfish live in Chesapeake Bay subestuaries in Virginia and what they are eating. The study focused on the tidal portions of the James, Pamunkey, Mattaponi, and Rappahannock rivers, where Flathead Catfish were sampled using electrofishing from 2013 to 2016. The study included 766 Flathead Catfish ranging from 8 to 48 inches, mostly from the James River and collected from April to October. Work by Virginia Department of Game and Inland Fisheries (VDGIF) helped us understand trends in survey catches over time.
We found Flathead Catfish were present in the James, Pamunkey and Mattaponi rivers. The James River population appears to be well-established with fish collected at numerous sites and a wide range of sizes. The species was most commonly collected between the fall line and the mouth of the Appomattox River. Flathead Catfish also exist upstream of the tidal portions of the river from the fall line upstream beyond Lynchburg. In the Pamunkey River, Flathead Catfish were first documented in 2008 by VDGIF staff, are known from fewer sites, and appear to be less dense than in the James River. However, catch rates have increased over time from zero in the early 2000s to collecting one approximately every 3-4 minutes of electrofishing. It seems likely that they are established in the Pamunkey as we observed juveniles and adults. Flathead Catfish were primarily collected in upstream portions of these tidal river systems which may reflect a preference for less saline waters or cover provided by rocks and trees near the fall line. Flathead Catfish are only known in the Mattaponi River from a single specimen at one location near the Rainbow Acres Campground. No Flathead Catfish were encountered in the Rappahannock River, but they exist in the two largest adjacent watersheds and may be able to colonize during high freshwater outflows or via illegal introductions by humans.
Map of sampling locations with Flathead Catfish from Virginia Tech catfish diet electrofishing surveys (black dots).
Consistent with what is known about Flathead Catfish in other systems, most of the diet was fish. We only summarized diets of James River fish, as sample sizes were low in the Pamunkey and Mattaponi rivers. Based on the metrics we examined, the two most important prey species were Gizzard Shad and White Perch. Fish less than 16 inches mostly consumed White Perch, with carp and minnows also being important prey. White Perch were the most important prey species for Flathead Catfish 16–32 inches, with Gizzard Shad becoming more important than observed in Flatheads smaller than 16 inches. Gizzard Shad and White Perch were also important to Flatheads larger than 32 inches, in addition to Blueback Herring. Alewife and American Shad were also present in stomachs of larger Flatheads, but were less common than Blueback Herring. For other species of conservation or recreational importance, two Striped Bass and one American Eel were found in Flathead Catfish stomachs, with no Largemouth Bass or sturgeon encountered. Based on calculations to estimate Flathead Catfish's place in the food chain, we concluded Flathead Catfish are an apex predator in the tidal James River.
White Perch (above) along with Gizzard Shad make up a major part of the Flathead Catfish diet in the James River. Photo Harvard Museum of Comparative Zoology.
As the range of Flathead Catfish has expanded, we need to continue monitoring population expansion in the Pamunkey and Mattaponi rivers. Further, predation on Blueback Herring (as well as American Shad and Alewife) in the James River is concerning due to population declines that led to harvest bans beginning in the 1990s. Despite efforts to improve fish passage at Bosher Dam via a fishway, Flathead Catfish may use the dam as an ambush point. Thus, Flathead Catfish and Bosher Dam may present obstacles for James River shad and herring recovery.
Read the original article here.