Great Lakes FisheriesGreat Lakes FisheriesChapter 23Chapter 23

Overfishing ProblemsOverfishing Problems

Sport and Sport and commercial fishing commercial fishing concernsconcerns

Oligotrophic lakes Oligotrophic lakes - low productivity - - low productivity - low standing crop low standing crop biomass of top biomass of top carnivorescarnivores

OverfishingOverfishing

Habitat Habitat Loss/Degradation Loss/Degradation

ProblemsProblems Spawning stream Spawning stream

degradationdegradation SedimentationSedimentation WarmingWarming DamsDams

Industrial/domestic Industrial/domestic pollutionpollution

Nutrient runoffNutrient runoff Wetlands Wetlands

destructiondestruction

Exotic Species ProblemsExotic Species Problems

Sea lamprey - Sea lamprey - predationpredation

Alewife, rainbow Alewife, rainbow smelt - competition smelt - competition for zooplankton, for zooplankton, predation on eggs, predation on eggs, larvaelarvae

Great Lakes SystemGreat Lakes System

Exotic Species ProblemsExotic Species Problems

Oligotrophy - Response Oligotrophy - Response to Stressto Stress

Pelagic organisms Pelagic organisms dominatedominate

Prey species Prey species increaseincrease

Top predators Top predators decreasedecrease

Food webs simplifyFood webs simplify Reproduction may Reproduction may

ceasecease Production declinesProduction declines

Lake Superior ChangesLake Superior Changes Lake trout and lake Lake trout and lake

whitefish overfishedwhitefish overfished Sea lamprey made Sea lamprey made

things worsethings worse Lake sturgeon and Lake sturgeon and

ciscoes overfishedciscoes overfished Lake herring declined Lake herring declined

from overfishing, from overfishing, competition with non-competition with non-native rainbow smeltnative rainbow smelt

Lake Superior ChangesLake Superior Changes Commercial fishing Commercial fishing

restrictions: banned gill restrictions: banned gill nets, quotas established, nets, quotas established, sportfishing-only zonessportfishing-only zones

Sea lamprey controls: Sea lamprey controls: TFM, electric weirsTFM, electric weirs

Stocking of lake trout, Stocking of lake trout, salmonsalmon

Smelt declined, Smelt declined, whitefish rebounded, whitefish rebounded, herring returned to herring returned to dominancedominance

Lake Michigan ChangesLake Michigan Changes Overfishing greatly Overfishing greatly

reduced lake trout, reduced lake trout, lake whitefish, lake lake whitefish, lake sturgeon, bigger sturgeon, bigger ciscoesciscoes

Sea lamprey killed off Sea lamprey killed off the lake trout, further the lake trout, further reduced lake whitefishreduced lake whitefish

Alewife and smelt Alewife and smelt caused collapse of lake caused collapse of lake herring (competition herring (competition and predation)and predation)

Lake Michigan ChangesLake Michigan Changes Alewife exploded with Alewife exploded with

elimination of lake troutelimination of lake trout Chinook and coho Chinook and coho

stocked to control stocked to control alewife, once lamprey alewife, once lamprey were controlledwere controlled

Lake trout stocked, but Lake trout stocked, but little natural little natural reproductionreproduction

Whitefish and bloater Whitefish and bloater recovered after lamprey recovered after lamprey and alewife declinedand alewife declined

Lake Michigan ChangesLake Michigan Changes Non-native salmon Non-native salmon

fishery worth $200 fishery worth $200 million annuallymillion annually

Commercial fishery Commercial fishery for alewife (pet food) for alewife (pet food) competes with salmon competes with salmon for prey - value?for prey - value?

Natural reproduction Natural reproduction of chinook now of chinook now established - interfere established - interfere with lake trout with lake trout recovery?recovery?

Lake Erie ChangesLake Erie Changes Shallower and warmer Shallower and warmer

than other Great Lakesthan other Great Lakes Same problems from Same problems from

overharvest, introduced overharvest, introduced species, plus pollutionspecies, plus pollution

Blue pike eliminatedBlue pike eliminated Warmwater commercial Warmwater commercial

species doing well species doing well (channel catfish, carp, (channel catfish, carp, shad), and walleye are shad), and walleye are increasingincreasing

Alewife ManagementAlewife Management

Non-native species - pelagic feeder competes Non-native species - pelagic feeder competes with planktivores, eats eggs of pelagic specieswith planktivores, eats eggs of pelagic species

Out of control with lake trout collapseOut of control with lake trout collapse Littered beaches, clogged water intakesLittered beaches, clogged water intakes

Alewife ManagementAlewife Management

Stocking of non-native salmon to control them Stocking of non-native salmon to control them (30 million annually)(30 million annually)

Alewife decline in Lake Huron so great, not Alewife decline in Lake Huron so great, not enough to support salmonenough to support salmon

Same might happen in Lake MichiganSame might happen in Lake Michigan

Sea Lamprey Sea Lamprey ManagementManagement

50 years of controls50 years of controls TFM - $8 million per year to protect multi-billion TFM - $8 million per year to protect multi-billion

dollar sport and commercial fisheriesdollar sport and commercial fisheries Estimates of up to 90% controlEstimates of up to 90% control But…But…

Sea Lamprey Sea Lamprey ManagementManagement

Average lamprey now twice as large as in 1970sAverage lamprey now twice as large as in 1970s Ammocoete larvae may live off river mouths where Ammocoete larvae may live off river mouths where

treatment is not possibletreatment is not possible TFM may lose potency, or lamprey may develop TFM may lose potency, or lamprey may develop

resistance to itresistance to it Controls using sterilized males, ammocoete pheromonesControls using sterilized males, ammocoete pheromones

Continuing InvasionsContinuing Invasions RuffeRuffe in St. Louis in St. Louis

harbor of Lake harbor of Lake Superior - Superior - competing with competing with yellow perchyellow perch

Round gobyRound goby in all in all lakes - compete lakes - compete with small, benthic with small, benthic fishes, but preyed fishes, but preyed on by smallmouth on by smallmouth bass, walleyebass, walleye