Study of alternative models of artificial floating objects for tuna fishery (experimental purse-seine campaign in the Indian Ocean)

The target species of Spanish tuna purse-seiners are Tropical tuna: yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis), the secondary species being bigeye (Thunnus obesus). The fleet operates in the inter-tropical waters of the three oceans. Catches are obtained through two types of fishing: associated with artificial floating objects and over free schools. Catches obtained with both types of sets are composed of the same species. However, specific composition is different, since sets over floating objects deliver more important bigeye catches than over free schools; sizes are also different, as are catch volume and the type and number of species that constitute the accompanying fauna.

Since the beginning of large-scale fishing over artificial floating objects, the type of objects used has not varied substantially (not so their detection systems and the type of locator carried by the objects). Although fishing over floating objects has increased purse-seiner efficiency and, subsequently, the catches (fundamentally of skipjack), the large-scale use of objects has produced effects on the fishery that were not habitual before their introduction. Such effects are catches of numerous accessory species (especially in certain time-space strata), including sharks, turtles and other fish species - none of them usable species in this kind of purse-seine fisheries.

In 2005, a Pilot Fishery Action was undertaken in the Indian Ocean, which was presented to the Spanish Fisheries Administration by the shipowners' company ALBACORA, S.A., financed by the aforementioned Administration, and followed up by the Spanish Oceanographic Institute (IEO). One of its main objectives was to further improvements to this mode of fishing where impact on stocks of sensitive species and the ecosystem was concerned. To this end, experiments have involved various prototypes of artificial floating objects and their behaviour, with a view to finding a typology that would result in fewer accessory catches (with particular emphasis on excluding entangled sea turtles), without reducing catches of target species. The design for this Pilot Action was presented at the Indian Ocean Tuna Commission's first session of the working party on bycatch, held in Phuket (Thailand), in 2005.