IMPLICATIONS OF HARVESTING STRATEGIES ON POPULATION AND PROFITABILITY IN FISHERIES

The effects of different harvesting strategies on the mean and variation in size of the fish stock and net revenues are investigated. The strategies analyzed are constant catch, constant effort, and constant escapement. A Gordon-Schaefer model affected by cyclical disturbances and stochastic disturbances is applied. Factors explaining the differences between the strategies are the length of the recruitment cycles and the presence of stochasticity. With short recruitment cycles the constant catch strategy somewhat surprisingly produces least variation and highest mean with respect to stock size and net revenue, while constant escapement produces most variation and lowest mean. With longer recruitment cycles or pure stochasticity, constant escapement produces highest average stock size and net revenue as well as lowest variation in the stock size, but not in the net revenue. Constant effort is in most cases ranked between the other two strategies.Resource /Energy Economics and Policy,

Generalization of age-structured bioeconomic models in theory and practice

The harvesting functions and the stock dynamics in age-structured bioeconomic models are generalized in order to incorporate density dependence. Using this generalization anything from completely uniformly distributed fish to extreme schooling can be analyzed. The classical Beverton-Holt model comes out as a special case of the generalized model. Both the theoretical outline as well as practical numerical examples are provided, and the generalization can be applied both for simulation as well as optimization purposes given appropriate software. Non-linear programming is applied to maximize the net present value with the new updating and harvesting functions are used as constraints. One practical result is that pulse fishing seems to become less and less econopmically profitable as we move from uniformly distributed fish to schooling species. The main reason why pulse fishing cease to be optimal in schooling fisheries, is that the economies of scale present in search fisheries gradually disappear when we move from search fisheries to schooling fisheries. This has important implications for how fish stocks ought to be managed in the future

Klimaendringer og havbruk

Vi ser på noen mulige konsekvenser av klimaendringer, og spesielt temperaturøkning som følge av global oppvarming, på havbrukssektoren. Dette blir gjort ved at en først går gjennom litteraturen på området og oppsummerer de resultatene som allerede er funnet. Dernest prøver vi å sannsynliggjøre hva som hender hvis en utvider noen av de modellene som har vært anvendt tidligere. I den sammenhengen ser vi spesielt på effektene av størrelsesavhengig pris på optimal slaktevekt, optimalt slaktetidspunkt og potensiell verdiskapning. Hovedkonklusjonen er at fiskeoppdrett er en av de næringene som overveiende vil oppleve positive effekter av høgere temperatur, og hovedårsaken til dette er at høgere temperatur gir raskere vekst. Denne effekten vil sågar forsterkes når en tar hensyn til at prisen kan avhenge av størrelsen på fisken

OPTIMAL STEADY STATES AND THE EFFECTS OF DISCOUNTING

A simple expression for finding and characterizing the optimal steady state of a general dynamic optimization problem is derived. This expression is easy to interpret and easy to apply for various purposes as, for example, to analytically investigate the effect of the discount rate upon optimal steady state stock levels. It is shown that an increase in the discount rate may result in higher optimal stock levels even in the one-dimensional (single species) case in nonlinear models. An important result is that if demand is inelastic at the optimal steady state, a higher discount rate will unequivocally imply higher standing stock(s). Increasing marginal cost of harvest will further strengthen this result. In the multidimensional case it is demonstrated that an increased discount rate may result in higher optimal stock levels for all stocks included in the model.Research Methods/ Statistical Methods,

Betydningen av fiskeri- og havbruksnæringen i området Lofoten og Barentshavet

Denne rapporten vurderer den samfunnsøkonomiske betydningen av fiskeri- og havbruksnæringen i området Lofoten-Barentshavet under ulike forutsetninger om fremtidige rammebetingelser. Det drøftes også hvilken innvirkning olje- og gassvirksomhet i området kan tenkes å ha på fiskeri- og havbruksnæringen

"More is Less": The Tax Effects of Ignoring Flow Externalities

Using a model of nonlinear decay of the stock pollutant, and starting from the same initial conditions, the paper shows that an optimal tax that corrects for both stock and flow externalities may result in a lower tax, fewer cumulative emissions (less decay) and higher output at the steady state than a corrective tax that ignores the flow externality. The "more is less" result emphasises that setting a corrective tax that ignores the flow externality, or imposing a corrective tax at too low a level where there exists only a stock externality, may affect both transitory and steady state output, tax payments and cumulative emissions. The result has important policy implications for decision makers setting optimal corrective taxes and targeted emission limits whenever stock externalities exist.taxes,stock and flow externalities,nonlinear decay,climate change

Generalization of Age-Structured Models in Theory and Practice

A generalization of the harvesting functions and the stock updating functions in age-structured bioeconomic models is outlined. Using this generalization everything from completely uniformly distributed fish to extreme schooling is taken care of. The classical Beverton-Holt model comes out as a special case of the generalized model. Both the theoretical outline as well as practical numerical examples are provided, and the generalization can be applied both for simulation as well as optimization purposes given appropriate software. Here we apply advanced non-linear programming to maximize the net present value in a bioeconomic setting where the new updating and harvesting functions are used as constraints. This is possible thanks to new software, such as KNITRO, for solving highly nonlinear problems. Applications of this generalized model produce interesting new results. One such practical result is that pulse fishing seems to become less and less economically profitable as we move from uniformly distributed fish to schooling species. The main reason why pulse fishing cease to be optimal in schooling fisheries, is that the economies of scale present in search fisheries gradually disappear when we move from search fisheries to schooling fisheries. This may have important implications for how fish stocks ought to be managed in the future, especially with respect to total allowable catches based on bioeconomic criteria.Keywords: Modeling and Economic Theory, Fisheries Modeling, Fisheries Economic

ON THE DYNAMICS OF COMMERCIAL FISHING AND PARAMETER IDENTIFICATION

This paper has two main objectives. The first is to develop a dynamic model of commercial fisheries different from most existing models that assume optimizing behavior. The industry is assumed to have a well-defined index of performance. Based upon this index, the decision to invest or not is made. We do not, however, assume that the industry or firm is efficient or optimal in its operations. The second is that a new approach of fitting model dynamics to time series data is employed to simultaneously estimate the poorly known initial conditions and parameters of nonlinear fisheries dynamics. The approach is a data assimilation technique known as the variational adjoint method. Estimation of the poorly known initial conditions is one of the attractive features of the variational adjoint method.Resource /Energy Economics and Policy,

Resource Rents in the Norwegian Fisheries

Present resource rents in Norway's fisheries were compared for different fleet structures. Alternative values of TACs were assumed, which is consistent with how most fisheries in Norwegian waters are managed. Total allowable catches (TACs) are set on the basis of advice by fisheries biologists where the economics of the industry plays a minor role. The TAC is then shared between the nations sharing the fish stocks, according to agreed formulas. A model of the fisheries was implemented in GAMS. The basis for the model is fleet categorization used in the annual cost and earnings studies. Rents were maximized using an LP-approach, under various constraints regarding divisions of the total catches between different fleet categories. Currently the resource rent in Norway's fisheries is small and possibly even negative, depending on assumptions made with regard to capital costs and other uncertain factors. The potential rent is quite high and could be up to one half of the landed value, depending on constraints with regard to reallocation of fish catches between different categories of boats, and also on assumptions about capital costs and other uncertain factors. In some fisheries in Norway it is now permitted to trade in fish quotas through trading in fishing vessels. Vessels can be removed from the fishery and stripped of their quotas, which then are transferred to other vessels. As the fleet categories involved have undergone downsizing their profitability has increased and the value of the fish quotas has gone up. Data from the cost and earnings studies were used to estimate the value of fish quotas and to study whether they reflect resource rent in the fishery. Transaction value of these fish quotas in many cases seem to overestimate the resource rent in the fishery, probably due to excess capacity in the existing fleet

Klimaendringer og verdiskaping på Vestlandet

Rapporten er skrevet på oppdrag av Bergensscenarier 2020, som en del av et prosjekt mellom SNF og Bergensscenarier 2020. Prosjektet har sett på muligheter og utfordringer for Vestlandsregionen som følge av klimaendringer. Med bakgrunn i arbeider utført ved SNF i samarbeid med en arbeidsgruppe fra næringslivet og en ekspertgruppe legger vi frem resultater fra to typer effekter som forventes å kunne påvirke potensialet for lønnsom næringsdrift, fysiske endringer i klimaet og endrede politiske rammevilkår. Denne rapporten sammenfatter og dokumenterer arbeidet gjennomført ved SNF. Vi ser først på utfordringer knyttet til klimaendringer og innføring av klimapolitiske virkemidler. Dernest gir vi en kortfattet sammenfatning av arbeidet med de fire utvalgte næringene som utgjør de resterende rapportene knyttet til prosjektet. Til sist konkluderer vi kort arbeidet med prosjektet