UBC Theses and Dissertations
A bioeconomic model approach to predicting the spatial fishing effort distribution in the global longline tuna fishery Keith, Heather Mackenzie
Tuna (Scombridae) are one of the most commercially valuable kinds of fishes on the world market. Much research has been devoted to the study of the population dynamics of tuna stocks worldwide. In contrast, little is known about fisher behaviour in tuna fishery management. Tuna fisheries operate in all oceans and are characterized by multiple highly migratory species, fleets, and gear types. Predictions of fishing effort allocation among species, choice of fishing location, and gear, are thereby made difficult rendering large limitations on effectively setting quotas and restrictions for species and gears. In addition to these difficulties, tuna fisheries management has been hampered by limited collaboration between governing organizations. To more effectively protect areas where highly migratory species populations are considered most vulnerable, emphasis has recently been placed on spatial management policies such as area closures. A primary component in evaluating such spatial regulations is to understand how fishers choose fishing locations. This study focuses on key economic indicators that could be the drivers in fishers’ decisions and choice of fishing locations in all oceans, for all tuna and tuna-like species in the longline fishery. Factors such as market conditions, the cost of fishing and fish abundance were collected from historical catch, effort, and price data for the aggregated global longline tuna fishery to construct a bioeconomic model that predicts spatial fishing effort distribution from 1950-2001. Total fishing effort was distributed to each spatial cell (5° x 5°) each year based on perceived changes in relative profit. A gravity model, as a component of the bioeconomic model, was used to generate a utility weight for each spatial cell based on the expected profit ratio and historical cumulative fishing effort where a higher weight indicates more profit potential and therefore a higher proportion of effort allocated to that cell. From 1960-1980, when many players were involved in the fishery and market prices as well as technological advancements were providing strong competition among vessels, expected profit in an area emerged as a key driver in location choice. Difficulties were encountered in predicting effort in the earlier years, when the fishery was still developing and in later years, when certain species were overfished and gear was altered to target the more valuable species. A sensitivity analysis was performed to determine how much better fishing effort distribution could be predicted given changes in costs, species catchability, and prices. Variations in spatial fishing costs of bigeye (Thunnus obesus), yellowfin (Thunnus albacares), swordfish (Xiphias gladius) and bluefin tuna (Thunnus thynnus, Thunnus maccoyii) improved the model fit to the observed fishing effort. With the ability to capture how fishing effort has changed historically, the model allows for future management policies to be analyzed in terms of fishing effort response to such regulations.
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