BIO220 Lecture 16 Flashcards Preview

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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

Cons of fixed escapement

- expensive & complicated
- not useful for non-migratory fish