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# Harvesting and Control - PowerPoint PPT Presentation

Photo: J.-D. Lebreton. Harvesting and Control. Harvest :. Number removed is the parameter of interest. How many deer can be taken from management unit?. Control:. Number remaining is the parameter of interest. Maintaining herd size of wild horses. Concept of Sustainable Harvest.

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Presentation Transcript

Harvesting and Control

Number removed is the parameter

of interest

How many deer can be taken

from management unit?

Control:

Number remaining is the parameter

of interest

Maintaining herd size of wild horses

Consider the logistic model

dN/dt = RN*(K - N)/K

Nt+1 = Nt + RNt(1-Nt)/K

size to population size

What’s going on?

The maximum per

capita growth rate

occurs when ….

“The largest harvest rate that can be

imposed without causing population

to decline”

For the logistic model:

MSY occurs at 1/2 K.

The value is RK/4

dN/dt = rN(1-N/K) – L

L=loss from harvest

Fixed-Quota Harvest Model:

L = some constant

Fixed-Effort Harvest Model:

dN/dt = rN(1-N/K)-(E*C*N)

where E = effort, C = catchability, E*C*N = L

What’s happening here

Q

N2

N1

Note: trend of pop declining to extinction is

indistinguishable from pop decline to ½ K

Proportion

removed

MSY

A yield

curve with

varying effort

is useful—

On board

• Environmental variability

• Estimation of carrying capacity

• Estimating population parameters

• More complex relationships

• age/stage structure

• Motivation:

• Many harvest strategies select specific

• age/stage class

• Implications of life history strategy

• Experimental work frequently done

• on invertebrates

on Harvest

Harvest of youngest

age class:

1. Reduced total popn size

2. Altered popn structure

Before harvest

After

• Total yield inc to 90%

• harvest rate

• -yield/ind increased

• (compensation)

Total yield

Ind. yield

4. Increase in life expectancy

Importance of

regulation

Two main goals:

• Limit populations of desired species

• (usually exotic species)

N

Control

Consider the logistic model once again…

How could control work?

Issues and Biological Considerations

Considerations?...

Two goals:

limitation of populations

Mechanism:

prevent reproduction

Population-level implications?

Technological

Ethical

Biological

• Both harvest and control draw heavily

• on population ecology of target species

• Harvest and control primarily differ in

• objective not in scientific principles

• Ethical/societal issues of major importance

• (this is as much about policy as it is