Economics of harvesting age-structured fish populations

Tahvonen, Olli

doi:10.1016/j.jeem.2009.02.001

Cited by 106 publications

(69 citation statements)

References 42 publications

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“…On the contrary, evolution here promoted faster growth, yet still could exact an economic cost. These results underscore the importance of management taking into account the detailed age and size structure of the stock (30)(31)(32).…”

Section: Discussionmentioning

confidence: 72%

Economic repercussions of fisheries-induced evolution

Eikeset

Richter

Dunlop

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Fish stocks experiencing high fishing mortality show a tendency to mature earlier and at a smaller size, which may have a genetic component and therefore long-lasting economic and biological effects. To date, the economic effects of such ecoevolutionary dynamics have not been empirically investigated. Using 70 y of data, we develop a bioeconomic model for Northeast Arctic cod to compare the economic yield in a model in which life-history traits can vary only through phenotypic plasticity with a model in which, in addition, genetic changes can occur. We find that evolutionary changes toward faster growth and earlier maturation occur consistently even if a stock is optimally managed. However, if a stock is managed optimally, the evolutionary changes actually increase economic yield because faster growth and earlier maturation raise the stock's productivity. The optimal fishing mortality is almost identical for the evolutionary and nonevolutionary model and substantially lower than what it has been historically. Therefore, the costs of ignoring evolution under optimal management regimes are negligible. However, if fishing mortality is as high as it has been historically, evolutionary changes may result in economic losses, but only if the fishery is selecting for medium-sized individuals. Because evolution facilitates growth, the fish are younger and still immature when they are susceptible to getting caught, which outweighs the increase in productivity due to fish spawning at an earlier age.Atlantic cod | genetic adaptations | harvest control rule | marine governance | adaptive management L ife-history theory, experiments, and field-based studies strongly suggest that fishing is capable of inducing genetic adaptations, especially when it removes individuals with characteristics such as large body size (1-5). Even if fishing is not size-selective, high fishing mortality may be sufficient to induce genetic change (6, 7). It is difficult to predict how genetic changes at the individual level affect population-level properties. Genetic adaptations may, in principle, be beneficial for the state of a stock, by enabling individuals to invest more into reproduction and growth (1, 8). As a consequence, the stock may become more productive, allowing exploited populations to withstand higher fishing mortalities than they could in the absence of such adaptation, possibly permitting higher yields. However, although an individual's increased reproductive investment leads to larger gonads, this happens at the expense of slower postmaturation growth. Maturing earlier may also reduce fecundity, because individuals are smaller when they reproduce (9). Moreover, adapting to fishing may bear a cost of maladaptation, resulting in increased natural mortality (10, 11). Therefore, fisheries-induced evolution (FIE) may reduce yield (2, 4, 12, 13) and may even imply a "Darwinian debt" (14) to be paid back by future generations, at least if genetic changes are difficult to reverse (1,15,16). Clearly, FIE has the potential for causing positiv...

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Section: Discussionmentioning

confidence: 72%

Economic repercussions of fisheries-induced evolution

Eikeset

Richter

Dunlop

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…This result is in line with Skonhoft et al (2012, result 4) Is periodic fishing (one fallow cycle) the optimal harvesting rule? Tahvonen (2009) shows in a similar context that there is also a stationary solution to maximise problem (1). Let F ss be the stationary solution such that F t = F t+1 = F ss associated with µ t = 0.…”

Section: The Simplest Fishery With Two Age Classesmentioning

confidence: 92%

“…This means that is not technically possible to catch adults without catching juveniles. Moreover, like Tahvonen (2009), assume that there is "growth overfishing", that is pr 1 = 0. The optimal policy is the solution to the problem…”

Section: The Simplest Fishery With Two Age Classesmentioning

confidence: 99%

“…Since the Beverton-Holt multi-cohort models used to assess the stock are not globally concave, the stationary solution described may be a local rather than a global optimum (Tahvonen, 2009). Because of this, standard global maximisation algorithms are used to determine the trajectory that drives the NSH fishery for the initial conditions to the global optimal solution of (10).…”

Section: A Numerical Illustrationmentioning

confidence: 99%

“…Tahvonen (2009), proves that in a 2-age structured fisheries model with endogenous recruitment and harvesting costs, optimal harvesting consists of pulse fishing under specific conditions such as nonselective gear. Steinshamn (2011) extends Beverton-Holt models by incorporating density dependence growth.…”

Section: Introductionmentioning

confidence: 97%

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Selectivity, Pulse Fishing and Endogenous Lifespan in Beverton-Holt Models

Rocha

Gutiérrez

Antelo

2012

Environ Resource Econ

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Optimal management in a multi-cohort Beverton-Holt model with any number of age classes and imperfect selectivity is equivalent to finding the optimal fish lifespan by chosen fallow cycles. Optimal policy differs in two main ways from the optimal lifespan rule with perfect selectivity. First, weight gain is valued in terms of the whole population structure. Second, the cost of waiting is the interest rate adjusted for the increase in the pulse length. This point is especially relevant for assessing the role of selectivity. Imperfect selectivity reduces the optimal lifespan and the optimal pulse length. We illustrate our theoretical findings with a numerical example. Results obtained using global numerical methods select the optimal pulse length predicted by the optimal lifespan rule.JEL classification: O1, AMS 91B76, 92D25.

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Economic effects of global warming under stock growth uncertainty: the European sardine fishery

2013

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Global warming of the oceans is expected to alter the environmental conditions that determine the growth of a fishery resource. Most climate change studies are based on models and scenarios that focus on economic growth, or they concentrate on simulating the potential losses or cost to fisheries due to climate change. However, analysis that addresses model optimization problems to better understand of the complex dynamics of climate change and marine ecosystems is still lacking. In this paper a simple algorithm to compute transitional dynamics in order to quantify the effect of climate change on the European sardine fishery is presented. The model results indicate that global warming will not necessarily lead to a monotonic decrease in the expected biomass levels. Our results show that if the resource is exploited optimally then in the short run, increases in the surface temperature of the fishery ground are compatible with higher expected biomass and economic profit.

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Economics of harvesting age-structured fish populations

Cited by 106 publications

References 42 publications

Economic repercussions of fisheries-induced evolution

Economic repercussions of fisheries-induced evolution

Selectivity, Pulse Fishing and Endogenous Lifespan in Beverton-Holt Models

Economic effects of global warming under stock growth uncertainty: the European sardine fishery

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