Fish in LakesFish in Lakes
Lake Food ChainLake Food Chain
Generally represent the end of the food Generally represent the end of the food chain in most lakeschain in most lakes
Only a small fraction of the energy fixed in Only a small fraction of the energy fixed in the system makes it to this levelthe system makes it to this level
Lake Food ChainLake Food Chain
Important group because of effects they Important group because of effects they can have on all other levels of living things can have on all other levels of living things in lakesin lakes
Feeding CategoriesFeeding Categories
PiscivoresPiscivores - feed - feed on fishon fish
Basses, pikes, Basses, pikes, walleyewalleye
Feeding CategoriesFeeding Categories
PlanktivoresPlanktivores - feed - feed on phytoplankton, on phytoplankton, zooplanktonzooplankton
Visual particulate Visual particulate feeders or strainersfeeders or strainers
Young of many Young of many species, clupeids species, clupeids like alewifelike alewife
Feeding CategoriesFeeding Categories
BenthivoresBenthivores - pick - pick materials off bottommaterials off bottom
Macroinvertebrates, Macroinvertebrates, algae, plants, detritusalgae, plants, detritus
Suckers Suckers
Feeding CategoriesFeeding Categories
OmnivoresOmnivores - feed - feed on everythingon everything
Carp, gizzard shad Carp, gizzard shad (planktivore (planktivore tendencies) tendencies)
Trophic ControlTrophic Control
Each trophic group Each trophic group is important, but is important, but piscivores & piscivores & omnivores have omnivores have more overall more overall control on the control on the entire systementire system
Trophic ControlTrophic Control
Strong populations Strong populations of of piscivorespiscivores can can keep other fish keep other fish types in check and types in check and keep system keep system “balanced”“balanced”
Top-down controlTop-down control
Out of Control!Out of Control!
In absence of In absence of predators, other predators, other fish types can fish types can dominate, affect dominate, affect other lake other lake componentscomponents
Planktivores - shadPlanktivores - shad Benthivores - Benthivores -
stunted bluegillstunted bluegill
The Carp CascadeThe Carp Cascade
Feeding activities of Feeding activities of carp can modify littoral carp can modify littoral substrate and muddy substrate and muddy the waterthe water
Macrophytes cannot Macrophytes cannot growgrow
Muddy water - reduced Muddy water - reduced transparency, reduced transparency, reduced phytoplankton, reduced phytoplankton, reduced zooplankton, etc.zooplankton, etc.
The Bottom LineThe Bottom Line
Presence or absence of a single species Presence or absence of a single species may have significant impact on the may have significant impact on the functioning of the entire lakefunctioning of the entire lake
Fish ProductivityFish Productivity
Varies greatly Varies greatly among different among different fishesfishes
Fishes feeding Fishes feeding nearer the base of nearer the base of the food chain the food chain (herbivores) are (herbivores) are more productive more productive than predatory formsthan predatory forms
Fish ProductivityFish Productivity
The younger the fish The younger the fish population (mean population (mean age), the more age), the more productive it isproductive it is
Young fish, greater Young fish, greater % of food intake to % of food intake to growthgrowth
Older fish, greater % Older fish, greater % of food intake to of food intake to maintenancemaintenance
Fish ProductivityFish Productivity
In temperate zone In temperate zone lakes, production of lakes, production of fish limited mostly to fish limited mostly to spring, summer, spring, summer, autumnautumn
Considerably lower Considerably lower than in tropical lakesthan in tropical lakes
Fish ProductivityFish Productivity
Tropics: 100s of Tropics: 100s of g/mg/m22/year/year
Temperate lakes: 1-Temperate lakes: 1-20 g/m20 g/m22/year/year
Temperate streams: Temperate streams: ~50 g/m~50 g/m22/year/year