Development of habitat prediction models to reduce by-catch of sailfish (Istiophorus platypterus) within the purse-seine fishery in the eastern Pacific Ocean

Sailfish (Istiophorus platypterus) is an important apex predator in neritic and oceanic pelagic ecosystems. The species is also a primary target of important catch-and-release sport fisheries that the support local economies of developing countries. However, commercial purse-seine fisheries that target tuna in the eastern Pacific Ocean (EPO) incidentally catch and discard large numbers of sailfish. Sailfish by-catch data recorded by scientific observers in the Mexican tuna purse-seine fleet in the EPO from 1998 to 2007 was used in generalised additive models (GAMs) to predict environmental and spatial preferences of sailfish. GAM predicted the highest sailfish catches to occur in coastal waters during El Ninõ events during late autumn and winter, with sea surface temperatures >26°C, with negative values of deviation in sea surface height (<-10cm), and low chlorophyll-a (<0.25mgm-3). GAM predicted that the catch probability for sailfish increased 1.8-fold during El Ninõ events in coastal waters and 1.5-fold under La Ninã. However, the spatial distribution of sailfish remained largely unchanged during El Ninõ and La Ninã events. Our models may be an additional fisheries management tool that may be used to support temporary spatial-temporal throughout the fishing season to reduce sailfish by-catch in the EPO.