Management of Introduced Fishes Chapter 13

Reasons for Fish Introductions Increase local food supplies Enhance sport & commercial fishing Manipulate aquatic systems Accidents

Increase Local Food Supplies Aquaculture Problems: carps, tilapia Native fishes already adapted to local conditions usually are ignored Nonnative fishes escape into local waterways

Enhance Sport & Commercial Fishing “Introduced fish are superior to native forms” Major approach to “solving” management problems in North America in late-1800s Local fishes often considered unsuitable prey for the “sophisticated” angler

Enhance Sport & Commercial Fishing Led to worldwide distribution of common carp, rainbow and brown trouts, largemouth bass Introductions now may be “admission of defeat in managing native species to meet existing needs” Great Lakes problems (e.g., alewife)

Enhance Sport & Commercial Fishing Alewife invades in 1880s, overabundant by 1960s Chinook salmon stocked to control alewife $4.5 billion sport fishery, plus alewife control!!! Chinook start reproducing, too few alewife, now what to do?

Enhance Sport & Commercial Fishing Introducing commercial species generally unsuccessful unless species is also a sport fish (lake trout) Conflicts arise between user groups when demand becomes high

Enhance Sport & Commercial Fishing Introducing prey species like shads, golden shiner, smelt Accelerate growth rates of adult predators May compete directly with young predators for food, slowing their growth rate

Manipulate Aquatic Systems Biological control of aquatic pests Mosquitoes, weeds, overabundant or stunted prey Mosquitofish, grass carp, tiger muskie - problems

Accidental Introductions Bait-bucket transfers Ballast water introductions

Ecology of Species Introductions Competition - niche dimensions, niche compression, species packing, & island biogeography

Ecology of Species Introductions If niches are all filled and cannot be further compressed, introduction will fail unless introduced species is superior competitor Brown trout vs. brook trout

Ecology of Species Introductions Disease introductions - accompany introduced species, and may have severe impact on native species Whirling disease carried by exotic trout from Europe have destroyed rainbow, cutthroat trout populations in Rocky Mountain rivers

Ecology of Species Introductions Disease carried by U.S. crayfish eliminated European crayfish from much of northern Europe

Ecology of Species Introductions Predator-prey interactions - introduction of predator can have dramatic, unexpected consequences on prey community Introduction of Nile perch to Lake Victoria virtually eliminated 300 species of cichlids and 40 species of non-cichlids

Ecology of Species Introductions Indirect effects - trophic cascade and habitat modification Introductions can cause complex, often unpredictable effects on organisms throughout food web (e.g., opossum shrimp introduction led to increased bald eagle mortality)

Ecology of Species Introductions Opossum shrimp intended for kokanee salmon and cutthroat trout in Flathead Lake, MT Competed with salmon for zooplankton --- fewer salmon --- fewer post-spawn salmon for bears & eagles --- eagles scavenging road-kills --- cars kill eagles

Ecology of Species Introductions Hybridization - introduced species crossbreed with closely related native species Elimination of native cutthroat trout by rainbow trout in Great Basin of western U.S.

Alternatives to Introductions Use of native species Better water management Habitat protection Use of sterile fishes - triploid, single-sex introductions into highly disturbed or artificial habitats

Evaluating Potential Introductions Guidelines (pp ) to insure that the system and all potential impacts of the introduction are understood before the introduction occurs