Great Lakes Fisheries Chapter 23

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

Overfishing

Habitat Loss/Degradation Problems Spawning stream degradation Spawning stream degradation Sedimentation Sedimentation Warming Warming Dams Dams Industrial/domestic pollution Industrial/domestic pollution Nutrient runoff Nutrient runoff Wetlands destruction Wetlands destruction

Exotic Species Problems Sea lamprey - predation Sea lamprey - predation Alewife, rainbow smelt - competition for zooplankton, predation on eggs, larvae Alewife, rainbow smelt - competition for zooplankton, predation on eggs, larvae

Great Lakes System

Exotic Species Problems

Oligotrophy - Response to Stress Pelagic organisms dominate Pelagic organisms dominate Prey species increase Prey species increase Top predators decrease Top predators decrease Food webs simplify Food webs simplify Reproduction may cease Reproduction may cease Production declines Production declines

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

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

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

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

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

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

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

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

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…

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

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