My family is not the least bit outdoorsy. My mom came out to the field with me once before she died, but refused to step foot out of the car once I parked at the edge of the trail. At times my father has shown interest in my research. However, once I tell him I’m not trying to find new ways to grow larger, more tasty fish, he quickly loses interests. “What good is your research if the fish don’t get large enough to eat?” is a question that I hear all too often.
Little does he know, wrapped up in his disappointment is some interesting science that has lately been receiving a lot of attention. In addition to my dad (who doesn’t really fish, by the way), a common complaint among anglers is that fish aren’t getting as big as they used to. To add gas to the fire, technology makes it easy to find historic images of people proudly displaying their catch of 2+ foot long brook trout, surely caught with little more than a stick and line.
It’s 2017. Managers should be able to get the fish are large as we want them, right? Unfortunately, it’s not that easy. Yes, things like climate change, habitat loss, and invasive species have caused declines in the maximum growth of many fish species. But, we can restore and protect habitats to help minimize some of those impacts. What we can’t do is reverse time, and the reason we can’t get large fish today has a lot to do with harvest regulations (or the lack thereof) hundreds of years ago.
For most fish species, state and federal biologist have done a lot of math in order to determine the minimum harvestable size. This number is ultimately a compromise. You want the minimum size to be small enough that anglers have a good chance of being able to keep a fish, but you also want it large enough that the population remains robust and juveniles are not harvested before they can reproduce.
So, you go fishing. You check minimum harvestable size, and when you catch a big fish you put in your cooler. When you catch a small fish, you return it to the water so it can grow larger, reproduce, and be ready for you next year. The logic seems sound, right?
Not entirely. When you only harvest the biggest fish, you’re not only removing the oldest fish. You’re also removing the fish that are genetically programmed to grow faster and larger. Put another way, by keeping the big fish, you’re harvesting both the grandparents and the “tall kids” from the population. After many generations of anglers keeping only the big fish, the genes responsible for rapid growth are simply gone from the population. At that point, no amount of habitat restoration or food supplementation is going to end in larger fish. The population has lost the genetic capability of producing big fish.
This idea isn’t new to fisheries science, but has more prominence in marine ecosystems where biologists first recognized the need to protect both the smallest and the largest fish from harvest. Many marine fish species are regulated with slot limits, where only fish of a certain mid-range size are allowed to be harvested. Slot limits help protect both young juveniles, large pre-spawn females, but also the young fish with the “tall kid” genes.
Slot limits can help preserve some of the genetic integrity of a population. However, scientists have lately realized that traditional harvesting regulations are probably doing more than just removing genes. For example, it’s been shown that angling selectively targets largemouth bass with bold personalities, that populations exposed to heavy angling have altered rates of gene expression (recall: gene expression can be important for many things, including allowing fish to survive stressful situations like high stream temperatures), and that reproduction declines with increases angling pressure. Consequently, biologists are now predicting that angling is indirectly reducing overall population health and future evolutionary potential.
So, should you stop fishing? Absolutely not. But, it does highlight the need to rethink management goals and harvest regulations. We can’t just think about fish size, but need to start considering the more subtle effects that angling has on genetics, reproduction, and behavior.