Transcript Management of Introduced Fishes

Management of
Introduced Fishes
Chapter 13
Reasons for Fish
Introductions
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Increase local food supplies
Enhance sport & commercial fishing
Manipulate aquatic systems
Accidents
Increase Local Food Supplies
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Aquaculture
Problems: carps, tilapia
Native fishes already adapted to local conditions
usually are ignored
Nonnative fishes escape into local waterways
Enhance Sport & Commercial
Fishing
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“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
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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
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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
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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
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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
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Biological control of aquatic pests
Mosquitoes, weeds, overabundant or stunted prey
Mosquitofish, grass carp, tiger muskie - problems
Accidental Introductions
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Bait-bucket transfers
Ballast water introductions
Ecology of
Species Introductions
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Competition - niche dimensions, niche
compression, species packing, & island
biogeography
Ecology of
Species Introductions
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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
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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
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Disease carried by U.S. crayfish
eliminated European crayfish from much
of northern Europe
Ecology of
Species Introductions
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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
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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
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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
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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
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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
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Guidelines (pp. 367-368) to insure that the
system and all potential impacts of the
introduction are understood before the
introduction occurs