EE32

Question 1

why manage populations? (3 examples)

Answer 1

1) stop invasive species leading others to extinction ie Goat–> tortoise extinction
2) help endangered species recover e.g Gold lion tamarin
3) balance economics with exploitation ie wwf suggested Saiga antelope could substitute rhino horns of Chinese medicine market

Question 2

what is recruitment?

Answer 2

the number of new individuals

Question 3

what growth does net recruitment curve and productivity curve have? what equation?

Answer 3

LOGISTIC GROWTH

dN/dt = rN(1-N/K)

Question 4

what does dN/dt=rN(1-N/K) show?

Answer 4

basically population growth rate and shows how much you can harvest per unit time with decreasing the population further

Question 5

Problems with net recruitment curve? (3)

Answer 5

• it is an approximation and real life recruitment curves are often not log model shape
• why does density dependence affect growth when pop is 50% of carrying capacity
• maximum growth at pop size of 50% of K is mathematically convenient but doesn’t correspond to reality (e.g Fin whale stocks where enviro effects e.g salinity affects population size)

Question 6

what do net recruitment curves show?

Answer 6

How many new individuals are added per unit time at each level of the population

How much you can harvest per unit time at each level of the population without decreasing the population further

Question 7

Describe the net recruitment curve at deifferent population size as % of K.
0?
50?
100?

Answer 7

0%- small pop so growth limited

50%-growth rate and pop size are middling so max new individuals added

100%-growth limited as reaching K

Question 8

what is an example of an organism with non-logistic recruitment curve?

Answer 8

North sea herring

recruitment declines at a lower population density than 50% of K

Question 9

what is MSY?

Answer 9

maximum sustainable yield

Question 10

how to you calculate MSY from net recruitment curve? what effects can this have on pop size?

Answer 10

• max offtake possible
• use peak of net recruitment curve (not necessarily 50% of K)
• MSY supreses pop depending on net recruitment curve shape

Question 11

what enables inference of what the population will do wrt recruitment curves?

Answer 11

plotting the harvesting strategy and recruitment curve together

Question 12

what is a harvesting strategy?

Answer 12

an amount that you plan to take depending on the population level

Question 13

what are 2 harvesting strategies/ explain them?

Answer 13

fixed quota system- take percentage of K regardless of pop size

fixed effort-proportional off take (good for mammals)

Question 14

what 2 critical points are there on net recruitment curve with harvesting strategy added horizontally?

Answer 14

points where harvesting strategy crosses net recruitment curve

1= STABLE EQUILIBRIUM where the recruitment curve is lower than the harvesting strategy to the right and higher to the left

2=BREAKPOINT where the recruitment curve is higher than the harvesting strategy to the right, lower to the left

Question 15

if harvest= recruitment?

Answer 15

population size stays the same

Question 16

what is unstable equilibria?

Answer 16

when the harvesting strategy JUST touches the recruitment curve as it means either side slightly from where it is touching will lead to the harvest being above recruitment and population falling

Question 17

Dangers of MSY?

Answer 17

• even if you know MSY exactly the population is only going to an unstable equilibrium and random variation will cause eventual extinction
• if overestimate MSY and have a fixed quota harvesting strategy higher =automatic extinction
• ignores individual variation in the population
• harvesting is predominatly on certain individuals ie older larger bigger male fish
• ignores environment

Question 18

Is fixed quota harvesting below MSY sustainable?

Answer 18

tehoretically should stay at equilibrium but if bad year goes below breakpoint for other reasons –> EXTINCTION

Question 19

what is an example of fixed quota system failing?

Answer 19

Peruvian anchovy fishery

Question 20

what happened in the pruvian anchovy fishery case study?

Answer 20

experts estimated MSY was 10 million tonnes/yr and catch was fixed at this–> stocks plunged–> population crash

why fixed quota? 1)20,000 livelihoods depended on it 2) politcal pressure

Question 21

what are examples of tipping point behaviours?

Answer 21

breakpoints

Question 22

What happens if a system crosses the tipping point?

Answer 22

it goes into a new stable state and then it can be very hard to bring back to the original state e.g peruvian anchovies

Question 23

how do el nino events affect anchovian fisheries?

Answer 23

Every few years the pattern of air circulation of the equatorial Pacific changes in a way that affects oceanic upwelling. This weather condition is known as El Niño. During El Nino, upwelling brings up warm water with few nutrients. A serious economic consequences of El Niño is its devastating effect on the Peruvian anchoveta fisheries. Populations of fish and seabirds vanish and anchovy catches dwindle during El Niño.

Question 24

how widescale was the use of MSY in fisheries? give figures

Answer 24

before 1980 all 39 national agencies responsible for managing marine fisheries used MSY

Question 25

what is the fixed harvesting equation? what does it predict/

Answer 25

H=qeN

H=harvest
q=efficiency
e=effort
N=population (stock size)

straight line with respect to N
Safer

Question 26

although the fixed harvesting strategy at MSY is safer what are some associated problems with this harvesting strategy?

Answer 26

we may not know what the recruitment curve looks like.Also fish aggregate in schools.
finally, when fish quotas are low (when fish populations are low) illegal harvesting may be more common.

fishermen may know where the fish schools are and so harvesting may become more efficient at low populations

Question 27

in what species is recruitment constant?

Answer 27

icelandic cod