Wade L. Griffin

Cycles in Agricultural Production: The Case of Aquaculture

The problem of determining optimal harvest and restocking time and levels is considered. A continuous time deterministic control problem is used to study the case where production occurs in a controlled environment. A stochastic control problem is then used to determine rules for the cultivation of P. stylirostris which occurs in a stochastic environment. The deterministic analog of the problem is also solved. The two solutions are used to develop a measure for the value of a controlled environment and for the value of information about the stochastic environment.

Optimum Effort and Rent Distribution in the Gulf of Mexico Shrimp Fishery

Traditional methods used to estimate fishing effort that maximizes rent to an open access resource have almost universally assumed all costs are directly proportional to effort. When crews receive a fixed share of gross returns, labor costs are proportional to catch; hence, rent accrues to crews as well as vessel owners under limited entry. A model that allowed costs to be proportional to effort and catch was applied to the Gulf of Mexico shrimp fishery. This study indicates that traditional analysis would result in management schemes that overtax vessels and ignore rent accruing to crews.

Size and bag limits in recreational fisheries: theoretical and empirical analysis.

Size and bag limits are among the most common forms of regulations for recreational fisheries. In this paper, we theoretically study and compare the short- and long-term impacts of these policies on individual anglers and fish stocks. Particular attention is paid to the issue of release mortality, which can have important consequences for policy effectiveness. Theoretically, we show the conditions under which these policies will be successful in achieving biological objectives. Implications for recreation demand analysis are discussed. We also study these policies using a simulation model of various policy combinations for the Gulf of Mexico red snapper fishery.

A general bioeconomic simulation model for annual-crop marine fisheries

Abstract A generalized bioeconomic simulation model of annual-crop marine fisheries is described and its use in marine fisheries management is demonstrated. The biological submodel represents the recruitment of new organisms into the fishery, the movement of organisms from one fishing area to another and from one depth to another, the growth of organisms and the mortality of organisms resulting both from natural causes and from fishing. The economic submodel represents the fishing effort exerted on each resource species, the monetary costs of fishing, the value of the harvest and the rent (or excess profits) to the fishery. Basic dynamics of the model results from changes in the number of organisms in the fishery over time, which can be summarized as a set of difference equations of the general form ΔN / Δt = R + I − E − M − F where ΔN / Δt is the net change in number of organisms in the fishery over time, R is recruitment, I is immigration, E is emigration, M is natural mortality and F is fishing mortality. R is a driving variable, whereas I, E, M and F are functions of the state of the system at any given point in time. The model can be run in a deterministic or stochastic mode. Values for parameters affecting rates of recruitment, movement, growth, natural mortality and fishing mortality can be selected from uniform, triangular or normal distributions. Use of the model within a fisheries-management framework is demonstrated by evaluating several management alternatives for the pink shrimp ( Penaeus duorarum ) fishery on the Tortugas grounds in the Gulf of Mexico. Steps involved in use of the model, including parameterization, validation, sensitivity analysis and stochastic simulations of management policies, are explained.

A Bioeconomic Analysis of the Texas Shrimp Fishery and Its Optimal Management

Overfishing in the Texas shrimp fishing industry by time period and fishing area is investigated. An optimal harvesting pattern is determined using a multiperiod mathematical programming model where prices, fishing effort, catch, and resource dynamics are treated endogenously. These results are then compared with actual effort. The comparison indicates substantial excess effort in spring and early summer, especially in the bays and shallow offshore areas. The peak fishing season also occurs later in the fall in optimal harvest pattern than in practice. The results indicate both producers and consumers gain from reduced fishing effort because of improved size composition of the harvest.

The Value of the Gulf of Mexico Recreational Red Snapper Fishery

This study estimates the value of recreational red snapper fishing in the Gulf of Mexico. Additionally, the study shows how to decompose the estimated red snapper recreation demand function into changes: (i) due to recreationists who were not taking recreational red snapper fishing trips but were induced to take a trip in response to changes in catch rates and (ii) due to recreationists already taking trips and responding to changes in catch rates. The decomposition allows us to also decompose the estimated elasticities and consumer surplus. The results indicate that an improvement in expected fishing quality will increase consumer surplus and that most of the increase is contributed by recreationists who initially do not take recreational red snapper fishing trips, but later take a positive number of trips. This finding has important policy implications for managing the red snapper fishery in the Gulf of Mexico.

Integrated Cattle Feeding Hedging Strategies, 1972-1976

Most major crop and livestock prices became considerably more variable after 1972, resulting in increased producer price risk. Uncertainty in cattle feeding was compounded in that both input (feeder cattle and feed) and product (fed cattle) prices became quite variable after 1972. This uncertainty, accompanied by considerable losses in cattle feeding during the 1973-1975 period, has made hedging a more desirable option [1, 9]. Several studies have examined a short hedge on live cattle at the beginning of the feeding period as a means of reducing risk and increasing returns to cattle feeders. Selective hedging strategies generally reduced the variance of returns per head as well as improved returns during periods when cash feeding was unprofitable [2, 5]. Routine hedging of every pen clearly reduced profits during periods when cattle prices were rising while providing some protection during cash-feeding loss periods [6]. Feeding live cattle on a cash basis was more profitable than routine hedging prior to 1973 [6].

A Bioeconomic Model of the Gulf of Mexico Shrimp Fishery

Abstract A bioeconomic model of the brown shrimp (Penaeus aztecus) fishery in Galveston Bay, Texas and adjacent offshore waters accurately predicts the general trends in the seasonality of shrimp harvest and the distribution of the harvest in relation to size of shrimp and water depth.

A Bioeconomic Assessment of Gulf of Mexico Red Snapper Management Policies

Abstract The stocks of red snapper Lutjanus campechanus in the Gulf of Mexico have experienced a serious decline owing to (1) the overharvesting of adults by the commercial and recreational fisheries and (2) the incidental harvesting and discarding of juveniles by the shrimp fishery. In an effort to rebuild these stocks, since 1984 a series of policies has been implemented by the National Marine Fisheries Service and the Gulf of Mexico Fishery Management Council. To date, however, the results of these policies have not been completely addressed. This study comprehensively assesses their biological and economic consequences using integrated biological and economic models of the red snapper and shrimp fisheries. The analysis indicates that a combined-policy approach (implementing a joint policy for the red snapper and shrimp fisheries) is preferable to an individual-policy approach.

Dynamic Modeling of the Eastern Gulf of Mexico Shrimp Fishery

The impact of alternative management schemes on the shrimp fishery of the eastern Gulf of Mexico is analyzed and compared to a baseline using simulation techniques. The fisherys biological and economic functions are modeled including intraseasonal shrimp growth rates, differences in demand for shrimp by size, and a heterogenous fishing fleet. Using consumer and producer surplus techniques, new fishing regulations appear socially optimal compared to the baseline. A rent-maximization scheme increases social surplus to its highest level. However, applying such a scheme to one part of the total Gulf of Mexico shrimp fishery is not recommended.