17.2. Model Descripti on
377
izing the cod popul ations took place during much of the first half of the
twentieth century (see Wilson et al. 1998), whereas enhancement programs
in Norway existed into the 1970s (Solemdale al. 1984). Although no demonstrable increase in the fish po pulations could be attributed directly to these
enh ancement efforts, their success was vehemently defended by some and
equally condemned by others in both the fishing and scientific communities. Ultimately, the lack of direct, empirical evidence of the be nefits of restocking the ocean (in contrast to stocking lakes) led to the abando nment
of most marine fishery enhancement programs. Nevertheless, the successful
mass rearing of juvenile Atlantic cod by a group in Norway in the early
1980s rekindled the enhancement deb ate and resulted in renewed efforts to
evaluate the efficacy of marine fish stock enh ancement programs (0iestad
et al. 1985).
Subsequent to the Norwegian success at mass rearing Atlantic cod , there
have been a number of symposia dedicated to fish population enhancement (see the following symposia proceedings, Solemdal et al. 1984;
Danielssen et al. 1994; Schramm and Piper 1995; Cowx 1998; Coleman et al.
1998; Howell et al. 1999). This has resulted in the produ ction of a series of
pap ers reconsidering factors that influence the survival and successful recapture of hatchery-reared fish once released into the sea . These papers
offer a thorough discussion of the current und erstand ing and status of enhancement efforts in different ecosystems and for different species. Interestingly, however, in most of the papers there is a focus on either the biological aspects of enhancement, or the costs of the enhance ment operations
relative to the recapture and conseq ue nt economic return from the augmented popul ation. A consideration of both the interactions between the
life history of hatchery-released fish and the limits of an ecosystem's fish
productivity together with an evaluation of the eco nomic consequences of
the fish's survival and rep rodu ction in the wild has not bee n do ne. The following model develops that logic, using STELLA, to rep resent the hatche ry
rearing of fish, the life history of the released fish, and the eco nomics of
fishing on an enhanced population relative to the overall carrying capacity
of the system.
17 .2. Model Description
The model consists of three sectors, or submodels, whose outputs are utilized by the other sectors to form the overall model (Figures 17.1 and 17.2).
Figure 17.1 contains a Hatchery sector and a Life History sector, and Figure
17.2 shows the Financial Flow sector. Although this is a generalized mod el,
it utilizes leng th/weight and fecundity data for Atlantic cod, Gadus morhua,
and incorporates other published biological and eco nomic data for this
species as input values where appro priate. The simulations therefore result
in patterns that could approac h reality for this species, but these inputs can
377
izing the cod popul ations took place during much of the first half of the
twentieth century (see Wilson et al. 1998), whereas enhancement programs
in Norway existed into the 1970s (Solemdale al. 1984). Although no demonstrable increase in the fish po pulations could be attributed directly to these
enh ancement efforts, their success was vehemently defended by some and
equally condemned by others in both the fishing and scientific communities. Ultimately, the lack of direct, empirical evidence of the be nefits of restocking the ocean (in contrast to stocking lakes) led to the abando nment
of most marine fishery enhancement programs. Nevertheless, the successful
mass rearing of juvenile Atlantic cod by a group in Norway in the early
1980s rekindled the enhancement deb ate and resulted in renewed efforts to
evaluate the efficacy of marine fish stock enh ancement programs (0iestad
et al. 1985).
Subsequent to the Norwegian success at mass rearing Atlantic cod , there
have been a number of symposia dedicated to fish population enhancement (see the following symposia proceedings, Solemdal et al. 1984;
Danielssen et al. 1994; Schramm and Piper 1995; Cowx 1998; Coleman et al.
1998; Howell et al. 1999). This has resulted in the produ ction of a series of
pap ers reconsidering factors that influence the survival and successful recapture of hatchery-reared fish once released into the sea . These papers
offer a thorough discussion of the current und erstand ing and status of enhancement efforts in different ecosystems and for different species. Interestingly, however, in most of the papers there is a focus on either the biological aspects of enhancement, or the costs of the enhance ment operations
relative to the recapture and conseq ue nt economic return from the augmented popul ation. A consideration of both the interactions between the
life history of hatchery-released fish and the limits of an ecosystem's fish
productivity together with an evaluation of the eco nomic consequences of
the fish's survival and rep rodu ction in the wild has not bee n do ne. The following model develops that logic, using STELLA, to rep resent the hatche ry
rearing of fish, the life history of the released fish, and the eco nomics of
fishing on an enhanced population relative to the overall carrying capacity
of the system.
17 .2. Model Description
The model consists of three sectors, or submodels, whose outputs are utilized by the other sectors to form the overall model (Figures 17.1 and 17.2).
Figure 17.1 contains a Hatchery sector and a Life History sector, and Figure
17.2 shows the Financial Flow sector. Although this is a generalized mod el,
it utilizes leng th/weight and fecundity data for Atlantic cod, Gadus morhua,
and incorporates other published biological and eco nomic data for this
species as input values where appro priate. The simulations therefore result
in patterns that could approac h reality for this species, but these inputs can