Population management

Question 1

What type of survivorship curve do fish have?

Answer 1

A type III curve. 99% of mortality in the first year.

Question 2

How do we calculate the mortality rate, Z?

Answer 2

Z = F + M
F = fishing mortality
M = natural mortality
(In fisheries)

Question 3

What is mortality like in a Type 1 fishery?

Answer 3

In a Type 1 fishery, natural mortality occurs at a time of year separate from the period of Harvest
Fishing seasons tend to be very short
Mortality is additive

Question 4

What is mortality like in a Type 2 fishery?

Answer 4

In a Type 2 fishery (more common), natural and fishing mortality occur simultaneously.
The higher the fishing mortality, the steeper the decline in fishing populations

Question 5

How do we estimate natural mortality with no data?

Answer 5

Borrowing data from closely related species
Predictive models

Question 6

How do we estimate natural mortality with data?

Answer 6

Catch curve analysis for non-harvested life stages
Regress Z vs. F or effort (f)
Predation models
Tagging studies

Question 7

Processes are considered compensatory when?

Answer 7

if they result in slowed pop. growth at high densities and fast pop. growth at low densities

Question 8

Give an example of a compensatory process.

Answer 8

Egg superimposition in salmon. Occurs in high densities, likely in streams. Salmon will destroy nests as they enter the stream, causing lower birth rates.

Question 9

Processes are depensatory when?

Answer 9

Processes are depensatory if they result in fast pop. growth at high densities and slow pop. growth at low densities

Question 10

Give an example of a depensatory process.

Answer 10

A real example of this is the Northern cod population off the coast of Newfoundland. The fishery was mismanaged and the population crashed
However, the population never rebounded, which is likely owing to the grey seals preying on the cod.