Management of Introduced Fishes

1. Management of Introduced Fishes Chapter 13

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

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

4. 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

5. 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)

6. 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?

7. 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

8. 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

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

10. Accidental Introductions • Bait-bucket transfers • Ballast water introductions

11. Ecology ofSpecies Introductions • Competition - niche dimensions, niche compression, species packing, & island biogeography

12. Ecology ofSpecies 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

13. Ecology ofSpecies 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

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

15. Ecology ofSpecies 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

16. Ecology ofSpecies 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)

17. Ecology ofSpecies 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

18. Ecology ofSpecies 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.

19. 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

20. Evaluating Potential Introductions • Guidelines (pp. 367-368) to insure that the system and all potential impacts of the introduction are understood before the introduction occurs