Minimizing the Impacts of Predatory Fish Stocking with Habitat Enhancement

Largemouth Bass (Micropterus salmoides) photographed at Gavins Point National Fish Hatchery in Yankton, SD. (Credit: Sam Stukel / USFWS)

While the term “fish stocking” may conjure up images of conservation measures deployed by fishery managers to stock endangered native fish, it can also refer to stocking predatory fish, including non-native species, for the sake of anglers. Even in cases where native predators are stocked, fishery managers must balance efforts in order to protect prey populations.

Why Stock Non-Native Fish?

With so many stories about non-native species overtaking ecosystems—unintentionally released as baitfish, hitching a ride on boat exteriors, or released in ballast waters—it may seem odd that non-native fish would ever be intentionally introduced into a water body.

However, predatory fish like bass are popular with anglers, and since fisheries rely on the funds from licenses and permits to keep the fishery healthy and sponsor conservation efforts, many managers find themselves stocking these non-native fish in addition to native threatened or endangered fish.

Impacts of Stocking Predatory Fish

While predatory fish stocking keeps anglers happy and provides consistent income to the fishery each year, these actions are not free of consequences to the ecosystem. According to a 2006 study, the stocking of predatory fish (native and non-native) can trigger a trophic cascade, leading to changes in the relative populations of predator and prey.

A 2001 study also notes that declines in prey populations can impact primary production and nutrient cycling as prey species that typically consume smaller organisms are eaten by stocked predators.

Finally, a 2021 and 2004 study found that hatchery-reared stocked fish often display behaviors unlike those of their native-born counterparts. In particular, foraging behavior may differ in feeding location as hatcheries feed on the surface of the water. This conditions predator fish to go to the surface for food, impacting the distribution of prey species as previously safe waters are now frequented by predators hunting for food.

Can Habitat Enhancement Mitigate Damages of Non-Native Predatory Fish Stocking?

Knowing that stocking predatory fish can negatively impact the ecosystem, it’s important for fishery managers to take steps to mitigate the possible harms if they choose to stock them.

A 2024 study theorizes that early habitat enhancement prior to stocking could help protect prey fish by giving them more complex structures to hide in. However, the study found that in the case of largemouth bass, habitat enhancement alone was not sufficient to mitigate the rapid consequences of fish stocking.

Instead, if managers are going to continue stocking predator fish, conducting research on where, when, and how best to release them must be a top priority. Additionally, studies on water quality and prey populations following the stocking event must be thorough and frequent in order to monitor the trophic cascade.

The results of such studies should go on to inform any future stocking and, hopefully, minimize harm to the ecosystem caused by stocked predatory fish.

Conclusion

Ultimately, the stocking of predatory fish must be handled with care, as these fish can trigger top-down issues in the food chain that could threaten the fishery.