Some biological aspects of Thunnus albacares and Katsuwonus pelamis in Oman Sea (Sistan-o-Balochestan Province)

Some biological aspects of yellowfin and skipjack tuna according to catch data of traditional gillnet fisheries were studied in the north of Oman Sea during 1997-99. Based on Gonadosomatic Index (GSI) results, the spawning period or yellowfin begins in spring and reaches to the peak level in May-June. For skipjack tuna, in addition to the above mentioned spawning period, the other observed period was found in autumn-winter with a peak in January-February. The first length or maturity (LM50%) of yellowfin and skipjack tuna females were estimated 76 and 61 cm, respectively. Observation of stomach contents showed that squid was the major components of diet for yellowfin and fish for skipjack tuna. A comparison between mean length of different years and landing sites using two-way analysis of variance indicated a significant differences, The length-weight equations showed an algometric growth in tuna and isometric growth in skipjack