Shark and related species catch in tuna fisheries of the tropical western and central Pacific Ocean

The tropical waters of the western and central Pacific Ocean currently support the largest industrial tuna fishery in the world with an annual catch approaching one million metric tonnes. The two main gear types, longline and purse seine, currently account for over ninety percent of the target tuna catch in this area.

A variety of elasmobranch species is taken as by-catch in these two fisheries, with at least 16 species of sharks and rays regularly encountered in longline sets and at least 10 species of sharks and rays encountered in purse seine sets, according to recent observer-collected data. The most prevalent species found in longline sets are blue shark (Prionace glauca), silky shark (Carcharhinus falciformis), pelagic stingray (Dasyatis violacea), and the oceanic whitetip (C. longimanus). The most prevalent species found in purse seine sets are silky shark (Carcharhinus falciformis) and the oceanic whitetip (C. longimanus).

Some indication of the exploitation of shark in these tuna fisheries is available from observer data, but the observer coverage is presently too low to be able to apply any robust stock assessment procedures. Shark catch reporting via logsheets suffers from the inevitable problems of non-reporting and species mis-identification, and therefore this form of data collection is not a viable option at this stage. Estimates of nominal catch rates, distribution, survival rates and size composition of the shark species taken in these fisheries have been summarised from observer data and are presented. Observer and anecdotal data provide some indication of market preferences and the economics of shark products. There has yet to be consideration of shark management in tropical tuna fisheries of the western and central Pacific Ocean, as economic factors have primarily dictated the management of the tuna fishery to this point in time. The information and procedures that are likely to be used in any future management planning process are described, and some suggestions that may be considered in any future review of shark by-catch management are also offered.