Indian Ocean albacore stock structure studies by morphometric and DNA sequence methods
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Both morphometric and DNA sequence analyses were applied in this study for throwing light on the stock structure of the albacore (Thunnus alalunga) resource in the Indian Ocean. A total of 144 albacore individuals, sampled from vessels fishing in 6 different localities of the Indian Ocean, were used for morphometric comparison. Two fisheries research surveys were carried out in 1990-1991 by the R/V Haikung, which belongs to the Taiwan Fisheries Research Institute, for collecting albacore specimens. Seven well-preserved muscle tissue specimens, removed from 7 albacores caught from 3 different localities of the Indian Ocean, were used for DNA sequence comparison. The results show that: 1) the first 2 eigen values absorb about 99% of the total within-character variability, it is thus advisable to use the first 2 canonical variables for comparison of morphometric samples; 2) the resultant mutual relationships drawn from morphometric analysis agree surprisingly well with those from the DNA sequence comparison: 3) albacore samples from the Indian Ocean can be categorised into 2 major groups -- those collected from the area west of 90 degree E and those from the area east of that longitude; and, 4) within-group heterogeneity is much less than between-group heterogeneity, no matter which method is applied. Based on the results so far obtained, the authors believe that it is possible to have 2 albacore stocks delimited by the 90 degree E longitude in the Indian Ocean.