by Joe Schmitt, Ph.D. and Fisheries Biologist
Our knowledge of other fish suggests that it is logical to release the giants for the future of the species.
Highly variable growth rates
Most anglers enjoy catching big fish, and blue catfish are one of the largest freshwater fish you target in North America. Regularly exceeding 100 pounds, only sturgeon, alligator gar, flathead catfish, and paddlefish fight in the same weight class. While blue catfish can grow quite large, research has demonstrated that less than 1% of individuals will ever grow to trophy sizes. In many systems, it can take 15-20 years for them to reach 30 inches or so. Unlike many other gamefish, growth rates for blue catfish are variable and unpredictable. Research has shown that a 20-year-old fish can weigh 5 pounds, or it can weigh 120 pounds.
These patterns have been observed in populations across the U.S., and they raise many questions. Are genetics controlling growth rates? Are some fish simply “programmed” to reach trophy sizes? Could growth be controlled by other factors like diet?
My own research shows that blue catfish have incredibly broad diets and suggests that some individuals may feed exclusively on vegetation while other individuals may feed exclusively on gizzard shad. Could these feeding behaviors explain observed differences in growth rates?
It seems intuitive that a fish slurping down gizzard shad would grow faster than one feeding on salad. To date, all of these questions remained unanswered. In fact, very little research has focused on blue catfish compared to more popular species like bass, walleye, and trout. Only one thing is for certain; large blue catfish are a rare anomaly.
Ecological benefits of large fish
The popularity of trophy catfishing has increased steadily since the early 2000s, and most trophy anglers now adhere to catch and practices made popular in the bass fishing arena. While the factors controlling blue catfish growth are not fully understood, our knowledge of other fish suggests that releasing large individuals is the logical choice.
First, if genetics control growth rates, selective removal of large fish could mean poorer growth for subsequent generations. Releasing large fish would allow them to continue to contribute their genetics to the population through subsequent reproductive events.
Second, numerous studies of other species have shown that large females produce more eggs, larger eggs, and superior offspring when compared to smaller females.
Third, the offspring from large females may be more resilient to unfavorable conditions, as bigger fish typically spawn earlier and for longer periods. If a weather anomaly like a 30-year flood happens, larger catfish will have a better chance at reproductive success since it may be able to avoid unfavorable circumstances.
While large female fish are evolutionarily important for most fish species, both genders are important for blue catfish. Male blue catfish often grow larger than females, and they actively defend their spawning nests. Studies of other nest-guarding species (like largemouth bass) show that progeny from large males have improved survival and fitness.
This protective instinct is most certainly the case for large blue catfish, as any small fish that tries to raid the nest of an angry 70-pound male catfish will get obliterated. Ultimately, our knowledge of other fish species insists that large individuals of both genders are ecologically important to blue catfish populations.
Mandatory release of large catfish is the most logical approach for conserving these rare animals, and many states now enforce limits on larger fish (for example, Oklahoma only allows one fish over 30 inches to be harvested per day).
Blue catfish are very durable animals; therefore, catch and release should be effective since post-release mortality is usually less than 5%, even when caught with more stressful gears like juglines, trotlines, and limblines.
While conserving large fish is important, a recent study also suggests that excessive harvest of small individuals can damage the growth potential of a population. This means that commercial harvest of small individuals could damage the trophy potential of a system, but so could excessive recreational harvest. While casual harvest of a few eater-size cats by the average rod and reel angler is unlikely to be an issue, I have seen extensive use of juglines and trotlines by recreational fisherman in reservoirs in Oklahoma. Some of these guys might be harvesting their limit on a daily or weekly basis, which could add up to a substantial drain on the resource.
Interestingly, most of these heavily-fished systems were what we called “meat factories” that routinely produced 5-to 15-pound fish, but rarely produced fish over 40 pounds. It’s quite possible that the constant harvest of catfish lowered the density and individual longevity just enough to essentially eliminate trophy fish from the population.
Think about it—trophy blue catfish are already a rare anomaly and generally exhibit faster growth than other individuals. What are the odds of one of these rare beasts surviving to 20 years old when it has to constantly swim through a maze of 6/0 circle hooks baited with tasty shad chunks? Every year, the probability of survival gets lower, and after 20 years, the probability may well be near zero if fishing pressure is high enough.
Health Concerns
Catch and release seems especially important for blue catfish, as these rare fish often take decades to reach trophy sizes. Additionally, eating large catfish of any species is foolish from a human health standpoint, because many of these fish will have contaminant burdens (methyl-mercury, PCBs, DDT, and PBDEs) that exceed the EPA’s recommended thresholds.
While some rivers and reservoirs may be better than others, pretty much all inland waters have issues with persistent lipophilic contaminants, all of which are magnified as they move up the food chain, through a process called “biomagnification”.
This means that older, predatory fish are most likely to be “hot” or contain high contaminant loads. Many of these contaminants are dangerous neurotoxins, and pose a serious health risk for pregnant women, children, and the elderly. Research has shown that eating large blue, channel, and flathead catfish is a sure-fire way to ingest these contaminants.
In tidal rivers in Virginia, blue catfish begin to carry excessive contaminant loads once they reach approximately 22 inches, meaning the health-conscious consumer should probably stick to eating fish in the 1- to 3-pound range. These consumption advisories will vary from location to location, but it is probably not wise to eat catfish over 20 pounds from any location.
Conclusion
Trophy blue catfish are a blast to catch, and deserve our admiration and respect. These fish are rare and often take decades to reach trophy size, and may be ecologically important to the future of the species. Releasing these giants allows them to contribute to future generations of blue cats, and may provide future angling opportunities through subsequent recapture.
