Great Lakes Fisheries Chapter 23

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Great Lakes FisheriesChapter 23
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Overfishing Problems

• Sport and commercial fishing concerns
• Oligotrophic lakes - low productivity - low
  standing crop biomass of top carnivores

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Overfishing
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Habitat Loss/Degradation Problems

• Spawning stream degradation
• Sedimentation
• Warming
• Dams
• Industrial/domestic pollution
• Nutrient runoff
• Wetlands destruction

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Exotic Species Problems

• Sea lamprey - predation
• Alewife, rainbow smelt - competition for
  zooplankton, predation on eggs, larvae

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Great Lakes System
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Exotic Species Problems
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Oligotrophy - Response to Stress

• Pelagic organisms dominate
• Prey species increase
• Top predators decrease
• Food webs simplify
• Reproduction may cease
• Production declines

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Lake Superior Changes

• Lake trout and lake whitefish overfished
• Sea lamprey made things worse
• Lake sturgeon and ciscoes overfished
• Lake herring declined from overfishing,
  competition with non-native rainbow smelt

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Lake Superior Changes

• Commercial fishing restrictions banned gill
  nets, quotas established, sportfishing-only zones
• Sea lamprey controls TFM, electric weirs
• Stocking of lake trout, salmon
• Smelt declined, whitefish rebounded, herring
  returned to dominance

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Lake Michigan Changes

• Overfishing greatly reduced lake trout, lake
  whitefish, lake sturgeon, bigger ciscoes
• Sea lamprey killed off the lake trout, further
  reduced lake whitefish
• Alewife and smelt caused collapse of lake herring
  (competition and predation)

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Lake Michigan Changes

• Alewife exploded with elimination of lake trout
• Chinook and coho stocked to control alewife, once
  lamprey were controlled
• Lake trout stocked, but little natural
  reproduction
• Whitefish and bloater recovered after lamprey and
  alewife declined

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Lake Michigan Changes

• Non-native salmon fishery worth 200 million
  annually
• Commercial fishery for alewife (pet food)
  competes with salmon for prey - value?
• Natural reproduction of chinook now established -
  interfere with lake trout recovery?

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Lake Erie Changes

• Shallower and warmer than other Great Lakes
• Same problems from overharvest, introduced
  species, plus pollution
• Blue pike eliminated
• Warmwater commercial species doing well (channel
  catfish, carp, shad), and walleye are increasing

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Alewife Management

• Non-native species - pelagic feeder competes with
  planktivores, eats eggs of pelagic species
• Out of control with lake trout collapse
• Littered beaches, clogged water intakes

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Alewife Management

• Stocking of non-native salmon to control them (30
  million annually)
• Alewife decline in Lake Huron so great, not
  enough to support salmon
• Same might happen in Lake Michigan

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Sea Lamprey Management

• 50 years of controls
• TFM - 8 million per year to protect
  multi-billion dollar sport and commercial
  fisheries
• Estimates of up to 90 control
• But

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Sea Lamprey Management

• Average lamprey now twice as large as in 1970s
• Ammocoete larvae may live off river mouths where
  treatment is not possible
• TFM may lose potency, or lamprey may develop
  resistance to it
• Controls using sterilized males, ammocoete
  pheromones

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Continuing Invasions

• Ruffe in St. Louis harbor of Lake Superior -
  competing with yellow perch
• Round goby in all lakes - compete with small,
  benthic fishes, but preyed on by smallmouth bass,
  walleye