Spatial variation in age and growth of the kingfish (Scomberomorus commerson) in the coastal waters of the Sultanate of Oman

Age and growth parameters were determined for the kingfish (Scomberomorus commerson) at six locations in the Sultanate of Oman. During 2 years of sampling, 1244 kingfish were collected, from which 962 sagittal otoliths were sectioned and read. The fishery is characterized by a prevalence of 0+, 1+ and 2+ year classes, which made up approximately 90% of the total fish collected. Maximum fork lengths, weights and ages for all sexes combined were 166 cm, 40.4 kg and 20 years, respectively. Sex specific differences were evident in length, weight and growth. Growth parameters show that female S. commerson (L∞ = 140.44, K = 0.309, t0 = −1.501) grew at a slower rate but reached a greater asymptotic length than male fish (L∞ = 118.80, K = 0.595, t0 = −0.730). There were significant differences in growth between regions with Ash-Sharqiyah recording the greatest asymptotic length (L∞ = 172.82) and Al-Wusta the lowest (L∞ = 122.596). Fish from Al-Wusta also grew at a much greater rate (K = 0.796) than those from the other five regions. A comparison of VBGF values using length frequency data and age at length data at one region, Muscat, revealed differences in all three growth parameters. Catch curves reveal large differences in total mortality (Z) between geographic regions, with the highest recorded at Al-Batinah (1.321 year−1) compared with 0.405 year−1 at Muscat. Large discrepancies in age structure, growth parameters and annual mortality between regions suggest overexploitation of this species may have already occurred in places like Al-Batinah and Dhofar. However we recommend that mortality estimates (Z, M and F) be used with caution until catch curve data for different fishing gear is made available.