FISH POPULATION DYNAMICS
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Transcript of FISH POPULATION DYNAMICS
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FISH POPULATION DYNAMICS
Fish Population Dynamics includes temporal (seasonal or year-to-year) variation in:
•population numbers
•age structure
•biomass
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FISH POPULATION DYNAMICS
Information on Fish Population Dynamics is used to:
•Determine the current status of a fishery
•Develop fisheries management plans
•Evaluate management success and failure
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FISH POPULATION DYNAMICS
2 Major Subcategories• Population Assessment
• Modeling Population Trends (dynamics of a population under different management scenarios)
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Key Demographic Processes that Cause Populations to
Change over Time
Births
Immigrants
Deaths
Emigrants
Population Change = B + I – D – E
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Factors that Cause a Population to Change can be the result of either
• Density-Dependent (D-D)
• Density-Independent (D-I)
Processes
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Density-Dependent Processes• Demographic rates (b,d,i,e) are related to population
density.
• Forces: Food availability, availability of spawning habitats, predation, cannibalism, disease, parasites, exploitative vs. interference competition
• Example: With increasing fish density, there is a reduction in the amount of food per fish. This results in reduced fish growth and condition. With reduced condition, there is an increase in fish mortality rates and a reduction in fish reproductive rates. This causes the rate of population increase to decrease with increasing population density.
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Density Dependent Mortality and Recruitment (simple linear)
Density Dependence
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Population Size
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e Mortality Rate
Recruitment Rate
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Density Independent Processes
• Demographic rates are variable from year-to-year but not in relation to density.
• Forces: water temperature, flow extremes, water chemistry variability, demographic stochasticity
• Example: year-to-year variation in the severity of spring time flows causes scour of stream bottoms. This results in high mortality rates of trout eggs and larvae, and mortality rates are independent of the number of eggs present to start with.
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Density Independent Mortality and Recruitment
Density Independence
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D-D and D-I Interaction
Non-Linear D-D
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Relative Importance of D-D and D-I
In General:
• Ponds, Lakes, Oceans are dominated by D-D processes with D-I processes important but secondary.
• Rivers and Streams are dominated by D-I processes with D-D processes important but secondary.
• Most populations regulated in part by both D-D and D-I processes.
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Fish Population Modeling
Births
Immigrants
Deaths
Emigrants
Population Change = B + I – D – E
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EXPONENTIAL MODEL OF POPULATION GROWTH
Nt+1 = Nt x (1+R)
Nt = N0 x (1+R)t
Where R = b – d
= “Finite Rate of Population Increase”
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EXPONENTIAL MODEL
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R=0.15
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Logistic Model of Population Growth
Nt+1 = Nt + Nt x R x (1- Nt / K)
Where:
K = Carrying Capacity
Maximum population size that can be supported in a particular environment.
Encompasses many potential limiting factors: food, space, shelter, mates
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LOGISTIC MODEL OF POPULATION GROWTH
Nt = K; N
Nt < K; N
Nt > K; N
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LOGISTIC MODEL OF POPULATION GROWTH
LOGISTIC
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Characteristic Dynamics of Fish Populations
• Equilibrium Concept – Populations tend to stay at or near a certain level
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Complementary vs Supplementary Habitats
Complementary Habitat: necessary for the completion of an individual’s life cycle and maintenance of the population
Supplementary Habitat: unnecessary but results in increased population productivity (density and/or biomass)
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Complementary vs Supplementary Habitats: Steelhead Example
Small StreamOcean
Reproduce
Refuge
Forage
Forage
Small Streams COMPLEMENT Ocean
Ocean SUPPLEMENTS Small Streams
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Scale of Spatial Links is Determined by Movement Rates
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Movement Rate (m / 45 days)
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lati
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uen
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Mottled Sculpin
Max Distance = 225 m
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Movement Rate (m/d)
Cu
mu
lati
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Brook Trout
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Scale of Spatial Links
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Brook Trout
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Good for reproduction• groundwater• stable temp• stable flow• bed-moving flows rare
Good for eating
•high light
•high productivity
•lots of small fishes
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Headwaters Larger Tributaries
Mainstem
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7-D
ay A
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axim
um T
empe
ratu
re (
C) Shavers 1999
Shavers 2000Shavers 2001Rocky Run 2001
Despite higher summer temperatures in the mainstem
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Cumulative Daily Growth
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Cu
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ve d
aily
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wth
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Mainstem
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Ambient Temperature (C)
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mbi
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Brook Trout
Brown Trout
Brook trout survive summer by finding coldwater “pockets” in the mainstem