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

Church-Rosser Systems, Codes with Bounded Synchronization Delay and Local Rees Extensions

What is the common link, if there is any, between Church-Rosser systems, prefix codes with bounded synchronization delay, and local Rees extensions? The first obvious answer is that each of these notions relates to topics of interest for WORDS: Church-Rosser systems are certain rewriting systems over words, codes are given by sets of words which form a basis of a free submonoid in the free monoid of all words (over a given alphabet) and local Rees extensions provide structural insight into regular languages over words. So, it seems to be a legitimate title for an extended abstract presented at the conference WORDS 2017. However, this work is more ambitious, it outlines some less obvious but much more interesting link between these topics. This link is based on a structure theory of finite monoids with varieties of groups and the concept of local divisors playing a prominent role. Parts of this work appeared in a similar form in conference proceedings where proofs and further material can be found.Comment: Extended abstract of an invited talk given at WORDS 201

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

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

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

QuickXsort: Efficient Sorting with n log n - 1.399n +o(n) Comparisons on Average

In this paper we generalize the idea of QuickHeapsort leading to the notion of QuickXsort. Given some external sorting algorithm X, QuickXsort yields an internal sorting algorithm if X satisfies certain natural conditions. With QuickWeakHeapsort and QuickMergesort we present two examples for the QuickXsort-construction. Both are efficient algorithms that incur approximately n log n - 1.26n +o(n) comparisons on the average. A worst case of n log n + O(n) comparisons can be achieved without significantly affecting the average case. Furthermore, we describe an implementation of MergeInsertion for small n. Taking MergeInsertion as a base case for QuickMergesort, we establish a worst-case efficient sorting algorithm calling for n log n - 1.3999n + o(n) comparisons on average. QuickMergesort with constant size base cases shows the best performance on practical inputs: when sorting integers it is slower by only 15% to STL-Introsort