SCIENTIFIC COMMITTEE FOURTH REGULAR SESSION 11-22 August 2008 Port Moresby, Papua New Guinea ACOUSTIC IMAGING, VISUAL OBSERVATIONS, AND OTHER INFORMATION USED FOR CLASSIFICATION OF TUNA AGGREGATIONS ASSOCIATED WITH FLOATING OBJECTS IN THE PACIFIC OCEAN WCPFC-SC4-2008/FT-IP-2

Purse seiners operating in the Pacific Ocean catch large quantities, in various proportions, of skipjack, yellowfin, and bigeye tunas associated with floating objects, in particular fish-aggregating devices (FADs). There is concern about the high fishing mortality rates on small bigeye and yellowfin tunas associated with floating objects from purse-seine fisheries, and the negative impact on sustainable yields from those populations. Most captains of large-scale industrial purse-seine vessels operating in the Pacific Ocean have 10 or more years experience fishing for tunas in association with FADs. Through the use of echo-sounders and sonars on the bridges of these vessels, along with a priori knowledge of the acoustic signatures, depth distributions, and behavior, by geographical region and oceanographic conditions, of the various species, along with visual observations of the mixed-species aggregations, captains should have a fairly good idea of the quantities and sizes of each species before they set their nets. Each set provides an opportunity to verify their estimates, and thus develop their expertise in determining the species and size compositions of the fish in the aggregations before they set their nets. This paper describes the anatomical and behavioral differences in these three tuna species, their acoustic images, and other relevant information used for estimation of their presence, quantity, and sizes when associated with floating objects in the Pacific Ocean.