Flashcards in BIO220 Lecture 16 Deck (36):

1

## General harvesting stragety

### harvest out the recruitment and leave the stock alone

2

## recruitment

### new additions to the population

3

## stock

### current population

4

## logistic equation of population growth

###
dN/dt = rN[(K-N)/K]

= Change in abundance / change in time

= rate of population growth

r = intrinsic rate of population growth of the species

K = carrying capacity

N = number of individuals in population

5

## What is the logistic equation of population growth saying?

### As number of individuals in population nears the carrying capacity of that population (N = K), rate of population growth is slow (logistic growth)

6

## What happens when N -> 0 (logistic population growth equation)

###
dN/dt = rN

= exponential growth

7

## ____ growth rate can limit population size

### density-dependent

8

## example of density-dependent population

###
Tern (type of seagull) on islands is limited by nesting space

- Bird island

- Ram island

- Penikese island

9

## logistic curves can be used to predict...

###
harvesting & its consequences

- what would give us the best yield without harvesting the stock?

10

## Ideal harvesting strategy would be to harvest ____ individuals per year. This ensures ____

###
K/2;

Max growth rate

11

## calculation: overall rate of population increase

### per capita rate of increase x population size = overall rate of population increase

12

## How do we know that we should harvest K/2 individuals per year?

###
inflection point on "overall rate of population increase"

= max rate of population increase is at K/2

13

## Recruitment axis = ___ axis

### harvest amount

14

## A "best case scenario" for harvesting does not account for...

###
- random chance

- weather

- seasonal year-to-year fluctuations

- predation

15

## MEY

###
max economic yield

= max profit (benefit - cost)

16

## MEY is good for business // species populations?

### business & fishermen

17

## MSY

###
max sustained yield

= point of max population growth

= K/2

18

## MSY is good for business // species populations?

### species population

19

## The fisheries tend to fish to the ___ point. Why?

###
break even point

- incentive to catch more fish until benefit doesn't > cost

- fish as long as there is positive profit

20

## Cons of the break even point

###
- not max profit

- populations have low growth rates

- high effort

- more harvest short-term, but screwed long-term

21

## why do fisheries harvest to the break even point, not MSY or MEY?

### constant financial pressure to harvest more

22

## Effect of new technologies on fishing curve

###
- decrease slope of cost curve

- no effect on population dynamics curve

23

## what can be found on the fishing curve?

###
1. population dynamics ("n" parabola)

2. cost of harvesting ("/" slope)

24

## 3 methods to improve the overfishing situtation

###
1. fixed quota (set at MSY)

2. fixed effort (time, size of net...)

3. fixed escapement (allow some fish to escape fishery before fishing begins)

25

## Problems with fixed quota harvesting strategy

###
In a bad year, population won't grow as fast. Next year, stock will be harvested. Eventually deplete population.

- Do not account for the random factors influencing population growth

26

## requirements for using fixed effort harvesting strategy

### define "effort" strictly

27

## Problem with fixed effort harvesting strategy

###
- political pressure to change "effort" leads to rachet effect

- Good years: increased pressure to harvest more

- Bad years: political & economic pressure will always increase harvest, never decrease

28

## Rachet effect

### Political pressure to harvest more when there is a good year, but no pressure to harvest less when there are bad/normal years in the future

29

## What is the ideal harvesting curve?

###
Set so that break-even point (B=C) is @ MSY

- fisheries will harvest to MSY

30

## What does the fishing curve look like when there is over-harvesting?

### When cost curve is very steep

31

## What does the fishing curve look like when there is under-harvesting?

### Cost curve is very flat

32

## What further complicates fixed effort harvesting strategy?

###
multiple fish caught in the same net

- different fishing curves for different fish, so cost curve of 1 fish can't be applied to the other without some kind of consequence

33

## What is the best solution to overfishing (currently)?

### Fixed escapement

34

## fixed escapement works best with...

### salmon & migratory fisheries

35

## Benefit of fixed escapement

### ensures that a fraction of the population escapes into the wild to spawn every generation

36