Changes in length-base demographic parameters of Yellowfin tuna (Thunnus albacares Bonnaterre, 1788) during two periods of time in the northern waters of the Oman Sea

This research looked at the basic information aboutThunnus albacaresfound in the northern part of Oman's Sea, and give useful information on how correctly manage of this resource. During the years of this study)1992and 2022(, over 6000fish were measured and the average length (range) of Yellowfin tuna fish in 1992and 2022was 93±26 (21-157) cm and77±18 (24-175) cm, respectively.The average weight (range) of this species was 9127±1251 (3500-55000) grams in 1992 and 10639±1450 (1100-85000) grams in 2022. The relationship between fork length and total body weight for the year 1992, W=0.014×L2.51(R2=0.83, N=750) and the year 2022, W=0.019×L2.46(R2=0.89, N=703) was obtained.Vonbertalanffy equation for this species in the northern waters of the Oman Sea (Iran)was calculated in 1992 and 2022 respectively as: Lt= 182 (1-exp (-0.39 (t +0.25)) and Lt= 177(1-exp (-0.55 (t +0.18))). The ratio of spawning potential based on length (LBSPR) in 1992 and 2022 were 0.22 (0.20-0.25) and 0.10 (0.09-0.12), respectively. Based on ratio of Pmega< 0.1, Lmean/ Lopt<1andLmean/LF=M<1show considered undesirable. Decrease of the average length, LBSPR index and increase of fishing and total mortality can be a reason for overfishing. The present study showed that the Yellowfin tuna stock has reached 'overfished' status. The findings of this study can assist management and sustainable harvestof this species stocks.