Database Reference
In-Depth Information
The disease decimates some of the cohorts but the population quickly recovers
due to the hardiness of those in the reproductive age classes. The total adult density
seems to fluctuate around a value of about 1 million, down from a disease-free adult
density of about 1.2 million.
This model replicates the complex interaction between the sneaker male
and adult male population, and demonstrates the trade-off between successfully
managing for adult bluegill while trying to keep the sneaker population to a
minimum. This model allows resource managers to test the effect of creel lim-
its on the population of sneaker males before actually integrating the solutions
in the management plan of a natural population. Could the model be made more
instructive by splitting natural mortality into its components (i.e., winterkill, pre-
dation, disease, and so forth)? Although the precision of the model may increase
due to accuracy of these measurements, would the complexity be increased to the
point that the model is not useful? The reader is encouraged to expand the model in
this way.
11.2.4 Questions and Tasks
1. a) Introduce a size limit on catch and observe its results.
b) Can you find size restrictions (maximum and/or minimum allowable size of
the catch) that stabilize the bluegill population for a given fishing pressure?
2. Assume the disease introduced in earlier discussion only affects juveniles. What
are the effects on the size of the population as a whole, and on the average size
of fish in the population?
BLUEGILL FISHERY MANAGEMENT
FEMALE 030(t)
=
FEMALE 030(t
−
dt)
+
(FRYADULT
−
F GROWTH 1
−
F NAT MORT 1) * dt
INIT FEMALE 030
=
1000000
INFLOWS:
FRYADULT
=
FEMALE FRY
OUTFLOWS:
F GROWTH 1
=
FEMALE 030*GROW1
F NAT MORT 1
=
FEMALE 030*FNATURAL MORT RATE 1
FEMALE FRY(t)
=
FEMALE FRY(t
−
dt)
+
(FEMALE
−
FRYADULT) * dt
INIT FEMALE FRY
=
1000000
INFLOWS:
FEMALE
=
FRY * (1
−
PROPORTIONMALE)
OUTFLOWS:
FRYADULT
=
FEMALE FRY
FRY(t)
=
FRY(t
−
dt)
+
(FRY PRODUCTION
−
FRY MORTALITY
−
