EE Lecture 32: Population Management Flashcards
name some species that have been helped through popn management
the golden lio tamarin
saiga antelope in russia
using the logistic growth model, when is there max growth
when K =50%
in what species is recruitment constant
icelandic cod
in what species does recruitment appear to decline at lower density than others
N Sea Herring
NE Arctic cod
due to weak regulation
what is MSY
the max sustianable yield (peak of net recruitment “n shape” curve, suppresses the popn level differently, depending on the curve
what do net recruitment curves show
how many new individuals are added per unit time at each level of pop
how much you can harvest per unit time at each level of the pop without further decreasing the pop
how can you infer whether a popn will grow or shrink
by plotting the harvesting strategy and the recruitment curve together
at a given popn level N, if the harvesting strategy line is lower than the recruitment curve, what happens to popn
popn grows
at what given popn level does popn grow
if the harvesting strategy line is lower than the recruitment curve
at a given popn level N, if the harvesting strategy line is higher than the recruitment curve
pop shrinks
at what popn level does popn shrink
if the harvesting line is above the recruitment curve
what happens to pop level N if recruitment curve and harvesting curve are equal
the popn stays the same
what is a stable eqbm
the recruitment curve is lower than the harvesting strategy to the right, highter to the left
what is the break point
the recruitment curve is higher than the harvesting strategy to the right, lower to the lefft
what are the dangers of a fixed quota harvesting strategy @ MSY if you know MSY exactly
the popn is only going to an unstable eqbm
eventual extinction, because of random variation
what are the dangers of a fixed quota harvesting strategy if you overestimate MSY
extinction occurs automatically without random factors
what is unstable eqbm
recruitment is lower both sides (@ peak)
what eqbm is it when ercruitment is lower to the left
break point
what eqbm is it when recruitment is lower both sides
unstable eqbm
what eqbm is it when recruitment is highter to the left
stable eqbm
which type of recruitment is safer
stable recruitment because even if the population is lower than predictions, recruitment is still higher
give an example of where fixed quota systems have been dangerous if you dont extract the whole MSY from the system
Peruvian anchovy fishery
used to be biggest in world - said MSY was 10mill tonnes/yr, catch fixed @10mill - stocks plunged - until industry collapsed`
`what is a harvesting strategy
an amount that you plan to take, depending on the popn level - a plot of planned offtake vs pop size
what is a fixed quota system
fixed offtake, regardless of pop size
what is a fixed effort system
proportional offtake (% of existing pop per year)
which system takes a proportional amount off pop per year
fixed effort system
which system takes % off pop regardless of pop size
fixed quota system
what is eqtn for fixed effort harvesting strategy @ MSY
H = q * e * N H - harvest q - efficiency e - effort N - pop/stock size
what does eqtn for fixed effort harvesting strategy do
predicts a straight line wrt N
when is illegal harvesting more common
when quotas are low - when popns sare low
what are breakpoints examples of
tipping point behaviour - if the system crosses the tipping point, it goes to a new stable state and then it can be very hard to bring it back to the original state
how long did the recovery of Peruvian anchovies tak
20yrs
collapse of the whole exploiting industry
what are dangers of MSY
ignores variation in pop
harvesting is predominantly on certiain individuals eg. bigger/larger
it ignores enviro
