ESTIMATION OF OPTIMUM FISHING MORTALITY AND MINIMUM LEGAL SIZE OF SKIPJACK TUNA IN THE NORTHEASTERN WATERS OF INDONESIA (ESTIMASI OPTIMUM MORTALITAS PENANGKAPAN DAN UKURAN MINIMUM IKAN YANG DAPAT DITANGKAP UNTUK CAKALANG DI PERAIRAN UTARA KAWASAN TIMUR INDONESIA) RIDWAN SALA MARINE SCIENCE DEPARTMENT, FPPK, UNIPA, MANOKWARI. EMAIL: ridwansala@gmail.com Abstract Study on estimation of optimum fishing mortality and minimum legal size of skipjack taken from the northeastern waters of Indonesia was done by using yield per recruitment analysis. The analysis adopted biological parameters of skipjack taken from various sources. The results of the study reveals that optimum yield per recruits would be attained when the fishing mortality is about fishing mortality of the fishery in 1998 and minimum legal size is about 40 cm (assumed M equals to 0.82) or about 36 cm (assumed M equals to 1.2). Key words: skipjack tuna, fishing mortality, minimum legal size, yield per recruitment, Northeastern Indonesia. 1. INTRODUCTION Based on observations during survey at commercial fish landings in Bitung, Sorong, Penambuan, Manokwari and Biak in 2002 and 2003, it was found that there were skipjack with size less than one kilogram caught by pole- and-line and purse seine fisheries fishing in the northeastern waters of Indonesia (NEWI) (Sala, 2007). This indicates that the fisheries caught skipjack which are in juvenile stage. From conservation point of view, catching juvenile fish will lead to reduction of chance of fish to reproduce. This it would not warrant a sustainable development of fishery. Regulation on minimum legal size (MLS) of fish has limited the MLS by regulating minimum mesh size This article should be cited as: Sala, R. 2008. Estimation of Optimum Fishing Mortality and Minimum Legal Size of Skipjack Tuna in the Northern Waters of Indonesia. Jurnal Perikanan dan Kelautan 4(2): 119-126