Length frequency, length-weight relationship and catch per unit of effort (CPUE) of Longtail tuna (Thunnus tonggol) and Yellowfin tuna (Thunnus albacares) caught by purse seine in Oman Sea

Length frequency, length-weight relationship and catch per unit of effort (CPUE) for longtail tuna and yellowfin tuna in purse seine fishing were studied in Oman Sea between July and August 2015. Length range and mean of longtail tuna were obtained 56-98 and 74.13±0.41 cm, respectively. Length range and mean of yellowfin tuna were obtained 51-128 and 74.62±0.46 cm, respectively. The length-weight relationship of longtail tuna and yellowfin tuna were calculated as W = 0.0174L2.9142 and W = 0.0655L2.7934, respectively. Totally, 802 tonnes of longtail tuna and yellowfin tuna were caught including 220 tonnes (27.43%) longtail tuna and 582 tonnes (72.57%) yellowfin tuna. Mean of CPUE (± S.E) was obtained 21.98±1.61 tonnes/setting for longtail tuna and 32.65±2.63 tonnes/setting for yellowfin tuna. Minimum and maximum CPUE of longtail tuna were calculated 7 tonnes/setting and 35 tonnes/setting, respectively. Minimum and maximum CPUE of yellowfin tuna were calculated 5 tonnes/setting and 150 tonnes/setting, respectively. Results indicated that about 31% of caught longtail tuna and 39% of caught yellowfin tuna were immature and had no opportunity to spawn.  Continuation of this exploitation process can lead to recruitment overfishing of these two species.