Harvesting Natural Populations

Question 1

What increases ‘stock’?

Answer 1

Growth of organism

recruitment of organism

Question 2

What decreases stock?

Answer 2

Natural mortality

Harvest

Question 3

Maximum yield equation

Answer 3

S2=S1+R+G-NM-H

S= Stock
R= mass of new recruits (recruitment)
G=growth of mass of fish remaining alive
H= mass harvested
NM=mass lost to natural mortality

Question 4

Balance resource equation

Answer 4

R+G=NM+H

Question 5

Assumption of maximum yield

Answer 5

Harvest losses and natural mortality are compensatory

it is best to have harvest occur just before period of maximum natural mortality

Question 6

Logistic growth equation

Answer 6

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

Question 7

for optimal yield, assume the populations follow….

Answer 7

a logistic growth pattern

Question 8

For maximum yield at what point can one harvest

Answer 8

inflection point, have the greatest input of individuals per unit time.

Question 9

Logistic model, harvesting equation

Answer 9

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

K= asymptotic density in absence of fishing
q=catchability (constant given current technology)
X=fishing effort (thus qX=fishing mortality rate)

Question 10

What is ‘qXN’ in the equation dN/dt=rN((K-N)/K)-qXN?

Answer 10

it is what human take. They act as the predators in this system

q= catchability 
X= fishing effort 

qX=fishing mortality rate

Question 11

What information can we gain from the graph of the maximum sustainable yield?

Answer 11

the number of individuals can be taken before over-harvesting occurs.

Indicates the number of recruitments annually. That number indicates a safe number that can be taken.

Question 12

sustained yield defined

Answer 12

long term harvest that does not lead to extinction or unacceptable decline in a population.

Question 13

Where on the maximum sustainable yield graph is absolute recruitment rate at its highest?

Answer 13

The middle

Where incline meets the annual recruitment parabola.

Question 14

Assumptions of a logistic model (5)

Answer 14

1. No time lag
2. Age structure has no effect on population growth
3. catchability remains constant all densities
4. enviornmental conditions do not change
5. our estimate of the removable stock is accurate

Question 15

Consequences of variable form from density dependence?

Answer 15

GRAPH!

Question 16

Assumptions of Dynamic pool models (4)

Answer 16

1. natural mortaliy constant
2. natural mortality same for all age classes
3. growth rate age- specific but independent of N
4. fishing mortality (human effort) independent of density and constant for all age classes

Question 17

Beverton and Holt model assumes: (3)

Answer 17

1. Growth rate of individual fish independent of density
2. Constant recruitment (independent of density and year)
3. Natural mortality rate independent of density and constant

Question 18

Nt=Re-^(F+M)t

Answer 18

Nt= number of recruits alive a time t after entering fishery
R= # recruits at start
F= fish mortality
M= natural mortality 

Beverton holt ,dynamic pool model