Growth overfishing: the race to fish extends to the dimension of size

The gravity of growth overfishing is increasingly recognized. The size-distribution of fish stocks is often severely truncated, even when the overall biomass is reasonably well managed. In a first part of this article, I show how the “race to fish” extends to the dimension of size: Akin to the classical Bertrand competition in prices, each agent has an incentive to target fish at a smaller size. In fact, for perfect selectivity, competition between two agents is sufficient to dissipate all rents. In a second part of this article, I explore the implications of size-differentiated harvesting for ITQ regulation. I show that quotas specified in terms of numbers are far superior to those specified in terms of weight or value

Threatening thresholds? The effect of disastrous regime shifts on the cooperative and non-cooperative use of environmental goods and services

This paper presents an analytically tractable dynamic game in which players jointly use a resource. The resource replenishes fully but collapses should total use exceed a threshold in any one period. The initial level of use is known to be safe. If it is at all optimal to increase resource use, the consumption frontier is pushed once. Moreover, it is shown that the degree of experimentation is decreasing in the safe value of resource use. Non-cooperative agents can take advantage of this feature and coordinate on a "cautious" equilibrium. If the status quo is sufficiently valuable, the threat of the regime shift induces the first-best. If the status-quo is not sufficiently valuable, experimentation will be inefficiently risky. But given that the threshold has not been crossed, the updated consumption frontier will, ex post, be socially optimal. However, there is also a pareto-inferior, "aggressive" equilibrium in which the resource is depleted immediately. Under some conditions, immediate depletion is a self-fulfilling prophecy, although the social optimum is to sustain the resource indefinitely. Closed-form solutions are provided for a specific example and it is shown that the pareto-superior, "cautious" equilibrium is risk-dominant up to a high probability that the opponents play an aggressive strategy. The result that the threat of a disastrous regime shift allows the agents to coordinate on a pareto-superior equilibrium, because it only pays to search for the location of the threshold once, is robust to extensions that account for more general resource dynamics

Growth Overfishing

Growth overfishing squanders large parts of the potential rents in fisheries. Many of today’s fisheries are characterized by a severely truncated age-distribution, which in addition may have irreversible ecological consequences. Nevertheless, the implications of age-differentiated harvesting for management have received surprisingly little attention in the literature. In the present paper, optimal and non-cooperative exploitation paths for a generic age-distributed resource are derived. We show that, in the case of perfect selectivity, competition between two agents is sufficient to dissipate all rents. Akin to the classical Bertrand competition in prices, each agent has an incentive to target fish at a younger age. That is, the “race to fish” extends to the dimension of age. This observation is crucial also with respect to management: Individual quotas are not able to restore efficiency unless accompanied by gear regulation. Moreover, it turns out that quotas specified in terms of numbers are far superior to those specified in terms of volume or value

Where could catch shares prevent stock collapse?

In a widely received study (Science 321: 1678–1681) Costello and his colleagues found that catch shares give better stock persistence and higher catch for fishermen. The conclusions made by Costello et al were further being supported by Grafton and McIlgrom (Marine Policy 33: 714– 719) where they suggested a framework in order to determine the costs and benefits of separate ITQ management in seven Australian commonwealth fisheries, and what the alternatives should be if the net benefits do not justify ITQs. This raises the question why we do not see catch shares being used more often. We explore at a global scale which countries would have the potential for – and indeed do fulfil the conditions necessary to implement such a management strategy

Optimal age- and gear-specific harvesting policies for North-East Arctic cod

We examine optimal harvest policies in a multi-cohort, multi-gear bioeconomic model of North-East Arctic cod (Gadus morhua) which includes cannibalism and contains broader ecosystem effects. By controlling the selectivity of the different fishing equipment, we can partially target different age cohorts. We show that current gear selectivity implies that the wrong fish are targeted. Optimization shifts the exploitation pattern towards older and heavier fish. This increases the harvested biomass while reducing the number of fish removed from the ocean. The result is a much more robust and abundant cod stock with an age/size distribution closer to the stocks natural state. We optimize the Net Present Value (NPV) generated by the fishery by letting effort and selectivity be the control variables and find that NPV may be more than doubled, even when only gear selectivity or harvest effort is allowed to vary. (141 words

Non-cooperative exploitation of multi-cohort fisheries — the role of gear selectivity in the North-East Arctic cod fishery

North-East Arctic cod is shared by Russia and Norway. Taking its multi-cohort structure into account, how would optimal management look like? How would non-cooperative exploitation limit the obtainable profits? To which extent could the strategic situation explain today’s over- harvesting? Simulation of a detailed bio-economic model reveals that the mesh size should be significantly increased, resulting not only in a doubling of economic gains, but also in a biologi- cally healthier age-structure of the stock. The Nash Equilibrium is close to the current regime. Even when effort is fixed to its optimal level, the non-cooperative choice of gear selectivity leads to a large dissipation of rents