Non-native fish: The controversy, impacts and management

Non-indigenous fish are widespread across the globe. There is evidence that the rate of introductions is increasing. But how these fish impact the receiving ecosystem is unclear. Impacts of non-native fish are a controversial issue. Much evidence of their impacts is anecdotal and precise effects are difficult to pinpoint. When coupled with other impacts to the system (e.g., anthropogenic influences), determining the changes brought on solely by new species is further confounded.

There are many possible impacts that non-native fish can have. These can range from moderation of native fish behavior, restructuring of food webs, and alteration of community composition and habitat, to name a few. But there is evidence that most introductions have little if any impact on the receiving ecosystem. However, there is ample evidence that certain species have had widespread effects on their new environment. This presents a challenge for managers on how to best apply limited resources to mediating those invasive fish which present a problem. There are assessments which can determine the risk of invasiveness, and these assessments are useful for setting regulations restricting the possession and trade of these higher risk species. But what to do about those fish already established and potentially causing undesired changes?

Limited management resources require that any efforts to control non-native populations be efficient and hopefully effective. Efforts in the past have included such activities as manual removal, restoration, or stocking of desired species. These are resource-heavy activities that show mixed results.  However, one interesting approach to managing (not eradicating) non-native species can actually turn a problem into a resource. In the 1960s, blue tilapia were introduced into several water bodies in south-central Florida and quickly became a dominant fish in many communities. This dominance, in some cases, led to a displacement in other fishes such as largemouth bass and native centrarchids The state Game and Fish Commission applied a great deal of effort in removing these invasive fish with little success. However, blue tilapia are highly edible and efficient to catch using cast nets. The Game and Fish Commission changed tactics and began a permitting program to encourage the development of a commercial blue tilapia industry. The program took off (Se Hale et al. 1995) millions of pounds of blue tilapia were removed from lakes via commercial cast netting. While this has not eradicated the species, it has allowed for native game fish populations to recover in some areas. This is one example among many. There is also an active cast netting industry in Florida for brown hoplo, another non-native fish which has become abundant in some areas of Florida.

The use of a problem as a resource may not be applicable for all troublesome non-native species, but I appreciate the novel approach and creative application these programs represent. There are other applications beyond the realm of just non-native fish, such as using invasive plants as a form of biofuel. The point is, in many cases we are stuck with a problem in the form of a non-native species and there just aren’t the resources available to launch big eradication programs. Why not take advantage of the situation, turn it into a resource, while at the same time helping to manage non-native populations?

HALE, M.M., J.E CRUMPTON, AND R.J. SSCHULER JR.  1995.  From sportfishing bust to commercial fishing boom: a history of the Blue Tilapia in Florida.  Amer. Fish. Soc. Symp. 15:425-430.