Early Life Ecology of Skipjack Tuna, Katsuwonus pelamis, Based on Survey Cruises off Palau and Micronesia, 1992-1996

Abstract

In order to clarify the ecological habit of the skipjack tuna, Katsuwonus pelamis, at the juvenile stage, we implemented a research program from 1992 to 1996. For the main activity of the program, we conducted survey cruises to determine the distribution of juvenile skipjack tuna in the offshore areas of Palau and Micronesia, in the tropical western Pacific, during October to December. We developed a new sampling gear, a high-speed midwater trawl net with a large mouth that enables to collect large numbers of juvenile tunas. We analyzed the relationship between the horizontal and vertical distribution of the juveniles and oceanographic conditions, feeding habit of the juveniles based on stomach content analysis, and growth process of juveniles by otolith increment analysis. The results of our analyses indicated that juvenile skipjack tuna was widely distributed in the offshore area from the North Equatorial Current to the North Equatorial Counter Current, around the Palau and Micronesian Islands. We concluded that these areas were important for juvenile skipjack tuna as a nursery ground.