Stock structure delineation of Kawakawa Euthynnus affinis (Cantor, 1849) from Malaysian Borneo using multivariate morphometric analysis

Euthynnus affinis, also known as Kawakawa, is a species of fish that is very significant to the fishing industry, particularly in the Indo-Pacific area. Regrettably, its stock structure and regional species’ management are poorly understood. This research aimed to employ a morphometric approach and determine if different stocks exist among 188 specimens of E. affinis obtained from three different areas: the Celebes Sea, the South China Sea, and the Sulu Sea, all surrounding Malaysian Borneo. Multivariate studies, including PCA (Principal Component Analysis) and DFA (Discriminant Function Analysis), were utilized to differentiate eight E. affinis populations based on 12 morphometric parameters. The findings divulged that E. affinis populations of Malaysian Borneo (Sabah and Sarawak) were relatively homogenous, as indicated by the DFA and the principal component’s scatterplot. Moreover, hierarchical cluster analysis focused on the Mahalanobis distances demonstrated that eight populations of E. affinis were grouped into three separate groups. The first group comprises Kota Kinabalu (Sabah), Mukah, Bintawa, and Pulau Bruit (Sarawak) populations. Euthynnus affinis from Lahad Datu and Kudat (Sabah) were clustered in the second group, while the third group consisted of Tawau and Sandakan (Sabah) populations. This study’s findings will give important preliminary data on E. affinis for effectively managing and protecting Malaysian Borneo’s regional waterways.