Distribution and biology of the Skipjack tuna Katsuwonus pelamis (Linnaeus) taken by the longline fishery in the Indian Ocean

Abstract

The skipjack tuna Katsuwonus pelamis remains to be one of the least exploited species of commercially important tunas in the Indian Ocean. At present they are taken mainly by the surface fishery and they form a minor component in the long line catches. The present communication provides information on their distribution, availability, abundance, length composition and spawning of skipjack based on the catch statistics and biological data obtained by the longline operations of Japanese commercial and research vessels. Relative density indices show that they were widely distributed in the western Indian Ocean during the first quarter, in the eastern Indian Ocean and northwest coast of Australia in the second quarter and in the third and fourth quarters they were widely distributed in the tropical waters. Their overall abundance and average density were at its peak in June, although they evinced seasonal variation. The fishes of the size group 58-70 cm dominated the longline catches, especially from the northern sector. In the central and eastern Indian Ocean, the specimens examined were relatively smaller. Available information on the gonad indices reveals that spawning activity is an extended one and it is relatively high in the northern and central Indian Ocean areas during September through April.