Study Finds Non-native James River Flathead Catfish Are Fast Growers
Virginia Tech scientists present an impressive Flathead Catfish from the James River during an electrofishing survey.
Although Blue Catfish receive a lot of attention in the Chesapeake Bay region, Flathead Catfish also present a potential threat to native species. A study on the diets of the two species reported that Flathead Catfish may have a greater per capita impact on native fishes (Schmitt et al. 2017), as Flathead Catfish diets become more fish-based after they reach about 12 inches (Baumann and Kwak 2011). Flathead Catfish are reported to have entered the James River in the mid-1960s when a pond at Hog Island Wildlife Management Area was flooded (Jenkins and Burkhead 1994). Flathead Catfish are both above and below the fall line in the James River, but densities in the tidal James River are considerably lower than Blue Catfish. However, given their feeding habits (click here for summary), we wanted to learn more about the population's growth and survival rates to add to the knowledge base on this non-native population. Based on fish collections from 1997 to 2015, we examined the growth and survival of James River Flathead Catfish below the fall line near Richmond.
Map of tidal James River depicting electrofishing survey locations and whether Flathead Catfish were collected in a given survey run (Absent/Present, denoted by color of points). Virginia Department of Game and Inland Fisheries, unpublished data.
We wanted to answer two questions related to Flathead Catfish growth in the James River (in terms of length): has growth changed over time and how does it compare to other systems? The results of the study supported differences in growth among years, but there were no obvious patterns as growth rates did not seem to be on an increasing or decreasing trend. Our study also supports that James River Flathead Catfish grow fast compared to other systems. We compared growth in length to a published standard called the "relative growth index". The relative growth index is based on growth information from across Flathead Catfish's range and helps us understand if a population of interest grows more slowly or quickly than the average for the species. Fish in this study were often in or above the 95th percentile for length. When comparing growth of James River Flatheads to native and non-native river populations, non-native populations typically grow faster. When considering only non-native populations, tidal James Flatheds still grow faster than most populations examined (see below).
Average growth trajectories of seven native and eleven non-native Flathead Catfish populations from rivers across the United States in relation to the tidal James River, Virginia. Adapted from Hilling et al. (in press).
Anglers often discuss catches in terms of weight and weight information is also useful in many fisheries science models. We produced a model of weight at age that predicts the average Flathead Catfish reaches 10 lbs in about 5 years, 20 lbs. in about 7.5 years, and 30 lbs in about 10.5 years. Based on the growth curve below, James River Flathead Catfish reach citation weight (25 lbs., VA Angler Recognition Program) at 9 years on average. Weight at a given age can be quite variable, as individual fish experience different growth rates. Consequently, not all fish will ultimately reach trophy size, regardless of their lifespan.
Growth in terms of weight from individual tidal James River Flathead Catfish (points) and predicted weight at ages based on a statistical model (red curve). Red vertical lines show ages at which fish are expected to reach 10, 20 and 30 lbs. Adapted from Hilling et al. (in press).
Finally, we estimated an average rate of annual survival over time based on the age composition of the population. We estimated annual survival as 61%, suggesting that 39% of James River Flathead Catfish die each year from natural and fishing-related causes. Our survival rate estimates are lower than many other Flathead Catfish populations. Other studies on non-native populations had higher estimates of survival, however, our estimates were comparable with a population in Georgia that has undergone a removal program. The maximum age of fish in the samples was 15 years, whereas other studies have reported Flathead Catfish can reach or exceed 30 years (Massie et al. 2018).
This work provides crucial population parameters and information for development of population models to help improve understanding of James River Flathead Catfish. This study supports that James River Flathead Catfish grow quickly which is great news for anglers hoping to land a monster catfish. However, based on our estimated growth curve, James River Flathead Catfish reach sizes conducive to fish consumption in two years (based on assumption of fish becoming more important at 12 inches). Using information on growth and survival, we can develop population assessments, estimate consumption rates and simulate various management strategies to help fishery managers understand tradeoffs and likely outcomes of various fishing regulations.
To read the original work, click here.
Baumann JR, Kwak TJ. 2011. Trophic relations of introduced Flathead Catfish in an Atlantic river. Transactions of the American Fisheries Society 140:1120–1134.
Hilling CD, AJ Bunch, JA Emmel, JD Schmitt, DJ Orth. In press. Growth and mortality of invasive flathead catfish in the tidal James River, Virginia. Journal of Fish and Wildlife Management.
Jenkins RE, Burkhead NM. 1994. Freshwater fishes of Virginia. Bethesda, Maryland: American Fisheries Society.
Massie DL, Smith GD, Bonvechio TF, Bunch AJ, Lucchesi DO, Wagner T. 2018. Spatial variability and macroscale driver of growth for native and introduced Flathead Catfish populations. Transactions of the American Fisheries Society 147:554–565.
Schmitt JD, Hallerman EM, Bunch A, Moran Z, Emmel JA, Orth DJ. 2017. Predation and prey selectivity by nonnative catfish on migrating alosines in an Atlantic slope estuary. Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science 9:108–125.