Aquaculture-Fisheries Interactions

In this paper, I investigate aquaculture externalities on fisheries, affecting either habitat, wild fish stock genetics, or fishing efficiency under open-access and rent-maximising fisheries. This is done with a Verhulst-Schaefer model of fish population-dynamics and production, coupled with a simple aquaculture production model. Externalities are modelled by letting carrying capacity, the stock’s intrinsic growth rate, or catchability coefficient in the fishery depend on aquaculture production. The different externalities can give totally opposite results on steady-state fishing effort, yield, and stock, even for only negative externalities. With a catchability externality, increased unit cost of fishing effort implies reduced aquaculture production to maximise benefits to society under reasonable assumptions. Resource allocation between the industries is analysed under three different coastal management regimes: 1) aquaculture has a primary right of use; 2) joint management of aquaculture and fishery; 3) fishers have a primary right of use, including the right to sell marine farming rights.Aquaculture, fisheries, externality, interactions, carrying capacity, intrinsic growth rate, catchability coefficient, habitat, genetics., Environmental Economics and Policy, International Relations/Trade, Public Economics, Q22, R52,

Open-Access Fishery Models: Relaxing a Constraint and Removing an Econometric Obstacle

Over the past 30 years, a widely accepted model of "open-access" fisheries has been developed, yet empirical tests of the standard model have been relatively few. One difficulty is that fish stocks, the levels of which affect the rate of catch, are not directly observable. Simplifying assumptions are generally required, such as the assumption that catchability does not change over time. Estimation on the basis of the standard model also raises difficulties in specification, if contemporaneous correlation of the error term with one of the regressors is to be avoided. This paper describes an algorithm that imposes a less restrictive pattern (than constancy) on catchability, yet does so in an econometrically acceptable fashion. It also reports on an application of this algorithm to the Flemish Cap groundfishery over the period from 1971 to 1985.Environmental Economics and Policy, Research Methods/ Statistical Methods, Resource /Energy Economics and Policy, catchability, error term, bias, Flemish Cap,

When a Fish is a Fish: The Economic Impacts of Escaped Farmed Fish

The escape of cultured fish from a marine aquaculture facility is a type of biological invasion that may lead to a variety of potential ecological and economic effects on native fish. This paper develops a general invasive species impact model to capture explicitly both the ecological and economic effects of invasive species, especially escaped farmed fish, on native stocks and harvests. First, the possible effects of escaped farmed fish on the growth and stock size of a native fish are examined. Next, a bioeconomic model to analyze changes in yield, benefit distribution, and overall profitability is constructed. Different harvesting scenarios, such as commercial, recreational, and joint commercial and recreational fishing, are explored. The model is illustrated by a case study of the interaction between native and farmed Atlantic salmon in Norway. The results suggest that both the harvest and profitability of a native fish stock may decline after an invasion, but the total profits from the harvest of both native and farmed stocks may increase or decrease, depending on the strength of the ecological and economic parameters.

A Bioeconomic Analysis of a Wild Atlantic Salmon (Salmo salar) Recreational Fishery

A biomass model of a wild salmon (Salmo salar) river recreational fishery is formulated, and the ways in which economic and biological conditions influence harvesting, stock size, profitability, and the benefit of the anglers are studied. The demand for recreational angling is met by fishing permits supplied by myopic profit-maximizing landowners. Both price-taking and monopolistic supply is studied. These schemes are contrasted with an overall river management regime. Gear regulations in the recreational fishery, but also the commercial fishery, are analysed under the various management scenarios, and the paper concludes with some policy implications. One novel result is that imposing gear restrictions in the recreational fishery may have the exact opposite stock effects of imposing restrictions on the marine harvest.Salmon, recreational fishery, conflicting interests, stock dynamics., Demand and Price Analysis, Environmental Economics and Policy, Research Methods/ Statistical Methods, Q26, Q22, Q21.,

Stock assessment of the gulf menhaden, Brevoortia patronus, fishery

A stock assessment of the gulf menhaden. Brevoortia patronus, fishery was conducted with data on purse-seine landings from 1946 to 1985 and port sampling data from 1964 to 1985. These data were analyzed to determine growth rates, yield-per-recruit, spawner-recruit relationships, and maximum sustainable yield (MSY). Virtual population analysis was used to estimate stock size, year-class size, and fishing mortality rates. During the period studied, an average of 27% of age-l fish and 55% of age-2 and age-3 fish were taken by the fishery, and 54% for age-I and 38% for age-2 and -3 fish were lost annually to natural causes. Annual yield-per-recruit estimates ranged from 6.9 to 19.3 g, with recent mean conditions averaging 12.2 g since 1978. Surplus production models produced estimates of MSY from 620 to 700 kilometric tons. Recruits to age-I ranged from 8.3 to 41.8 billion fish for 1964-82. Although there was substantial scatter about the fitted curves, Ricker·type spawner-recruit relationships were found suitable for use in a population simulation model. Estimates of MSY from population simulation model runs ranged from 705 to 825 kilometric tons with F -multiples of the mean rate of fishing ranging from 1.0 to 1.5. Recent harvests in excess of the historical MSY may not be detrimental to the gulf menhaden stock. However, one should not expect long-term harvesting above the historical MSY because of the short life span of gulf menhaden and possible changes from currently favorable environmental conditions supporting high recruitment.(PDF file contains 24 pages.

The Bioeconomic Implications of A Bycatch Reduction Device as a Stock Conservation Management Measure

The proposed regulation to reduce bycatch and discarding of finfish in the southeastern region is a gear modification that excludes finfish from shrimp trawls. This regulation is analyzed using a simple theoretical model of a multispecies fishery whose bycatch is harvested in a directed fishery consisting of commercial and recreational fishermen. The costless reduction in bycatch fishing mortality imposed on the multispecies fishery does not result in an increased stock size for the bycatch fish species or a substantial increase in its level of harvest. Instead, the fish stock is reallocated from the multispecies fishery to the fishery directed at the bycatch species causing fishing effort to expand in the bycatch species fishery that drives the stock size down to the previously existing equilibrium level. Recreational harvest and effort levels remain unchanged since the model is linear in effort and the commercial fishery is given access to the fishery first.Bycatch, policy analysis, bioeconomic model, Environmental Economics and Policy, Resource /Energy Economics and Policy,

HARVEST FUNCTIONS: THE NORWEGIAN BOTTOM TRAWL COD FISHERIES

A detailed and comprehensive set of catch and effort data for the cod fisheries of 18 Norwegian bottom trawlers have been obtained for the period 1971–85, a period with few binding quota restrictions on vessel operations. Harvest functions have been designed and estimated. The independent variables are hours of trawling per vessel day and biomass of the cod stock (3+). Daily biomass estimates have been calculated by polynomial interpolation of the annual estimates of the International Council for the Exploration of the Sea (ICES). By maximizing the log-likelihood function using numerical methods, parameter estimates and performance indicators of the different models were obtained. The best result was obtained for a harvest model allowing for seasonal changes and with an autocorrelated error term. For this model, the stock-output elasticity is estimated at 0.424, the effort-output elasticity at 1.232, and the technological change at about a 2% annual increase in productivity. The seasonal changes in catchability are significant, with the lowest intra-annual catchability being less than 30% of the annual maximum.Resource /Energy Economics and Policy,