obesus) in the catches of the purse-seine fishery of the eastern Pacific Ocean

Abstract

Overfishing of bigeye tuna in the eastern Pacific Ocean has motivated a search for pratical means of reducing bigeye catch. We develop a classification algorithm for the presence/absence of bigeye in purse-seine sets on floating objects, the dominant mode of purse-seining for bigeye, using the tree-based method random forests to explore the effects of gear characteristics. Although the location of the set was the strongest determinant of the presence of bigeye catch with these data, in some areas, bigyeye were more likely to be caught on floating objects with greater underwater depths and with deeper purse-seine nets. Misclassified sets were found to be concentrated within certain vessels, suggesting that the existence of additional ‘vessel effects ’ on the presence of bigeye which may be amenable to further study. Results indicate that fishermen can avoid catching bigeye in some areas by changing the depth of the material hanging from the floating object and the actual fishing depth of the net, or by moving to other fishing areas. However, we believe that the complex nature of gear and environmental interactions, and the impact of gear restrictions on the catches of tuna species other than bigeye, argu