Are there fewer large Blue Catfish in Virginia’s tidal rivers?
Fish size is an important aspect of any fishery, whether recreational or commercial. Recreational fishers want to catch bragging size trophies or fish big enough to justify cleaning them. Commercial fishers may also target fish to match consumer demand. Many anglers believe large Blue Catfish in Virginia’s tidal rivers have become less common over time, but there are no routine records of size of Blue Catfish caught by anglers. To determine if this was the case, my colleagues and I examined sizes over time from electrofishing surveys and the Virginia Angler Recognition Program. Primarily, we wanted to know are there fewer large Blue Catfish in Virginia than in the past?
Corbin holds a Blue Catfish from a tidal tributary of the James River while volunteering during a Virginia Department of Game and Inland Fisheries electrofishing survey in August 2016.
A simple way to examine sizes of a whole fish population is to look at the proportion of fish in various size classes, specifically Quality = 20+, Preferred = 30+, Memorable = 35+, and Trophy = 45+ inches (see paper by Gabelhouse from 1984 for details). There is a minimum size (12 inches for Blue Catfish) that serves as the smallest fish considered, as fish smaller are often not sampled effectively. A count of fish 12 inches and larger is compared to counts of fish from the four other size classes These size classes were developed in relation to the world record size.
Length frequency histogram of Blue Catfish collected during electrofishing surveys in the James, Mattaponi, Pamunkey and Rapphannock rivers from 2002 to 2016 using 1 inch bins. A majority of fish collected are smaller than 20 inches. Data collected by Virginia Department of Game and Inland Fisheries.
We found that proportions of fish at least 30 inches had declined in all four river systems examined (James, Mattaponi, Pamunkey and Rappahannock), but declines in the James and Rappahannock were weak and not statistically significant. The proportion of large fish in those systems likely mostly declined prior to our study period, as Blue Catfish were introduced at least ten years earlier. Over the period (2002–2016), no fish 45 inches or larger were collected in the Rappahannock River. Of the fish considered in this analysis (larger than 12 inches), more than 90% were smaller than 24 inches in the Rappahannock. In addition, fish 45 inches or larger made up less than 0.3% of fish at least 12 inches in the James, Mattaponi and Pamunkey rivers.
The annual number of trophy Blue Catfish reported by anglers declined over time. However, examination of maximum size by year showed increasing trends in all rivers except the Rappahannock from 1990–2015. However, maximum sizes appear to be leveling off since around 2005. The reduction in reported trophy catches is likely due to a couple factors. Our results show that the proportion of large fish is declining across most river systems. Other work has shown that growth rates are declining in these populations over time likely due to competition within populations (see the paper by Greenlee and Lim from 2011 for details). Another possible explanation is that anglers are reporting fewer citation catches over time. The Virginia Angler Recognition Program is good program in that it recognizes anglers catching big fish. The downside is that processing the awards has associated costs and a $5 fee must accompany award applications. Part of the decline in citations could be related to decreased participation by those catching trophy catfish. Also, discussions with fishing guides have indicated they are fishing the Potomac River with greater frequency and angling effort in Virginia may have changed. Consequently, the decline in trophy fish awards is likely due to both reductions in trophy fish abundance and changes in angler behavior.
Maximum annual reported Blue Catfish (Ictalurus furcatus) weight by river system from the Virginia Angler Recognition Program from 1990–2015. Data collected by Virginia Department of Game and Inland Fisheries.
Understanding sizes of Virginia’s Blue Catfish is important because of fishing opportunities and predatory behavior. Fewer big Blue Catfish could mean greater dissatisfaction among anglers and fewer angler trips. Many anglers have already begun fishing the Potomac River with greater frequency. However, harvest for the commercial market does not depend on big Blue Catfish. Size is also important as diets of Blue Catfish shift with size. Large Blue Catfish are more likely to consume fish (most commonly Gizzard Shad and White Perch), whereas smaller Blue Catfish primarily eat vegetation and invertebrates (see papers by Schmitt and co-authors from 2017 & 2018 for details). Our study indicated the proportion of large Blue Catfish in Virginia has declined significantly in the Mattaponi and Pamunkey rivers with weak declines in the James and Rappahannock rivers. Fewer large fish likely means reduced predation on at-risk fishes, such as American Eel, American Shad and river herring, but fewer opportunities for trophy fishing. In response, trophy anglers may begin exploring other Blue Catfish fisheries, including the Potomac River, Buggs Island Reservoir, and Lake Gaston, with greater frequency.
Number of trophy Blue Catfish reported (Citations Reported) to the Virginia Angler Recognition Program annually and contribution to total by river system. A large majority of citations are reported from the James River system. Data collected by Virginia Department of Game and Inland Fisheries.
To read the original work click here.
Gabelhouse, D.W. 1984. A length-categorization system to assess fish stocks. North American Journal of Fisheries Management 4:273-285.
Greenlee RS, Lim CN (2011) Searching for equilibrium: population parameters and variable recruitment in introduced blue catfish populations in four Virginia tidal river systems. In: Michaletz PH, Travinichek VH (eds) Conservation, ecology and management of catfish: the second international symposium, pp 349–367. American Fisheries Society, Symposium 77, Bethesda, Maryland, USA.
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.
Schmitt JD, Peoples BK, Castello L and Orth DJ (2018) Feeding ecology of a generalist consumer: A case study of invasive blue catfish Ictalurus furcatus in the Chesapeake Bay. Environmental Biology of Fishes.