Scientific Journal Article Summary
The Economic Efficiency of a Time–Area Closure to Protect Spawning Bluefin Tuna
Paul R. Armsworth, Barbara A. Block, Josh Eagle, Joan E. Roughgarden
Journal of Applied Ecology (2010) 47:36-46
Marine protected areas, such as time-area closures, are a sanctioned strategy for reducing bycatch and/or protecting vulnerable life history stages, like spawning. In this study, ecological and economic modeling is performed to evaluate the economic efficiency of using a time-area closure to manage bycatch of bluefin tuna on the Gulf of Mexico (GOM) spawning ground by the U.S. pelagic longline fishery. The GOM longline fishery targets yellowfin tuna but catches bluefin tuna incidentally as bycatch. For the purposes of this study, the closure is considered to be effective if it maximizes total annual profit of the GOM longline fishery and the New England handgear fishery combined. The former considers profits from both yellowfin and bluefin tuna catch, while the latter includes bluefin tuna only.
Bluefin tuna are present in the Gulf of Mexico from January to June, and the peak spawning months are April and May. The models in this study incorporate electronic tagging data to estimate when individual bluefin tuna will be present in the GOM and therefore available to the longline fishery. Consequently, the effectiveness of the closure relative to start date and duration could be evaluated.
Because the GOM is accounts for a relatively small percentage of Atlantic-wide mortality, the models compare the closure's effectiveness for two contrasting policy scenarios: 1) "status quo," in which management changes are only enacted within the GOM longline and New England handgear fisheries, and 2) "rebuilding," in which the entire western Atlantic fishery is managed in a coordinated fashion to achieve population recovery.
This study found that a GOM closure is always economically costly in the status quo scenario. Longline profits would decrease due to reduced fishing effort, and handgear profits would not increase enough to offset the decreased longline profits since a closure alone is not enough to rebuild the population and in turn increase availability of bluefin and profitability of the handgear fishery.
In the rebuilding case, however, the New England handgear and GOM longline fishery would experience a 460% increase in revenues, from $2.3 million to $12.8 million per year, even without a closure in the Gulf of Mexico. If a closure were implemented upon rebuilding, profits would increase from $44.4 million to $45.3 million per year (just 2%) for all western Atlantic fisheries combined, and this economic benefit would only be realized after 14-30 years on the rebuilding trajectory. In this scenario, a February 26th-May 17th closure would be economically optimal if the entire GOM were to be closed to longlining. This analysis shows conclusively that the economic benefit of a GOM closure pales in comparison to the economic benefit of rebuilding.
The model underwent extensive sensitivity testing and was proven robust to all of its key assumptions, including but not limited to mixing of the eastern and western Atlantic populations, maturation age, and redistribution of longline effort to times and/or areas outside the closure.
In conclusion, this study tells us that closures in the GOM would be economically costly if there is little scope for rebuilding, but that such closures would offer limited economic benefits if there were a broader commitment to rebuild the western Atlantic bluefin tuna population. Importantly, the study shows that even when a time-area closure is optimal, the overall economic improvement it provides over the best management action without such a closure is much smaller than the more elementary difference between allowing the stock to rebuild and allowing overfishing to continue.