Transcript Great Lakes
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 Sedimentation Warming Dams Industrial/domestic pollution Nutrient runoff Wetlands destruction Exotic Species Problems Sea lamprey predation Alewife, rainbow smelt - competition for zooplankton, predation on eggs, larvae Great Lakes System Exotic Species Problems Oligotrophy - Response to Stress Pelagic organisms dominate Prey species increase Top predators decrease Food webs simplify Reproduction may cease Production declines 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 nonnative rainbow smelt 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 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) 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 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? 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 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 Round goby in all lakes - compete with small, benthic fishes, but preyed on by smallmouth bass, walleye