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