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17. An Age-structured Model of Fish Population Enhancement
realistic is that a fishery cooperative or public agency would back the
hatchery, and therefore have a broader financial base to service the debt in
the years prior to the commencement of a fishery based on enhancement.
The example simulated is a worst-case scenario , since no attempt to pay
down the debt prior to the initiation of the fishery is considered, but the increase in the fish population is adequate to offset a large initial and growing debt under most circumstances . The important thing to notice, under
whatever financing scheme is utilized, is that there is a significant period
during which the investment is at risk, and it is therefore quite likely that a
governmental body would and should undertake any long-term enhancement experiments in the public domain of the sea.
17.9. Questions and Tasks
1. What effect does the frequency, duration and magnitude of the enhancement effort have on the net profits? That is, what enhancement
strategy is the most cost-effective? Alter the inputs for the number of fish
raised, the years enhancing and also the pulse function in the fish raised
flow to explore what effects this has on net profits. What strategy would
you adopt if you had one hatchery and multiple spawning populations
to re-establish?
2. Alter input values for parameters such as emigration and catch rate to
see what effect they have on the structure of the population of mature
fish.
3. Carrying capacity is one of the most enigmatic aspects of the model.
What happens if the carrying capacity for juvenile age 2 is set to O? This
can be done by altering the mortality function for this stock of fish. Does
the population collapse? What happens if the mortality rate for adult fish
is altered so that there is a constant rate of natural mortality?
4. Once a hatchery in built and paid for, the ongoing operating costs reflect the cost of producing juvenile fish for release . This can be an expensive process and increases the longer the fish are held in the hatchery. It has also been shown that survival of hatchery-reared fish upon
release in the wild increases with size. What effect does the cost per
fish have on the financial success of the enhancement program? Would
it be cost-effective to raise fish to a larger size, and therefore reduce
mortality?
5. Atlantic cod is an extremely fecund animal. Find fecundity and
age/weight data for other species and substitute them into the model.
How does the prospect of enhancement look for these species in comparison with cod?
17. An Age-structured Model of Fish Population Enhancement
realistic is that a fishery cooperative or public agency would back the
hatchery, and therefore have a broader financial base to service the debt in
the years prior to the commencement of a fishery based on enhancement.
The example simulated is a worst-case scenario , since no attempt to pay
down the debt prior to the initiation of the fishery is considered, but the increase in the fish population is adequate to offset a large initial and growing debt under most circumstances . The important thing to notice, under
whatever financing scheme is utilized, is that there is a significant period
during which the investment is at risk, and it is therefore quite likely that a
governmental body would and should undertake any long-term enhancement experiments in the public domain of the sea.
17.9. Questions and Tasks
1. What effect does the frequency, duration and magnitude of the enhancement effort have on the net profits? That is, what enhancement
strategy is the most cost-effective? Alter the inputs for the number of fish
raised, the years enhancing and also the pulse function in the fish raised
flow to explore what effects this has on net profits. What strategy would
you adopt if you had one hatchery and multiple spawning populations
to re-establish?
2. Alter input values for parameters such as emigration and catch rate to
see what effect they have on the structure of the population of mature
fish.
3. Carrying capacity is one of the most enigmatic aspects of the model.
What happens if the carrying capacity for juvenile age 2 is set to O? This
can be done by altering the mortality function for this stock of fish. Does
the population collapse? What happens if the mortality rate for adult fish
is altered so that there is a constant rate of natural mortality?
4. Once a hatchery in built and paid for, the ongoing operating costs reflect the cost of producing juvenile fish for release . This can be an expensive process and increases the longer the fish are held in the hatchery. It has also been shown that survival of hatchery-reared fish upon
release in the wild increases with size. What effect does the cost per
fish have on the financial success of the enhancement program? Would
it be cost-effective to raise fish to a larger size, and therefore reduce
mortality?
5. Atlantic cod is an extremely fecund animal. Find fecundity and
age/weight data for other species and substitute them into the model.
How does the prospect of enhancement look for these species in comparison with cod?