Are Indian mackerel (Rastrelliger kanagurta) populations in the eastern Indian Ocean truly homogeneous? Insights from geometric morphometric analysis

Abstract

The boundaries of Indian mackerel (Rastrelliger kanagurta) populations/stocks in the three Large Marine Ecosystems (LMEs) in the eastern Indian Ocean (Arabian Sea, Bay of Bengal, and Andaman Sea) are not clearly discriminated or delineated, resulting in conflicting population boundaries. Inherent limitations of the methodologies adopted could be the major reason behind this lack clarity in the population boundaries. Geometric morphometric analysis (GMA) using landmarks has been found to be the most appropriate approach under these conditions. Thus, the present study aims to differentiate between the populations of R. kanagurta in the eastern Indian Ocean (Arabian Sea, Bay of Bengal, and Andaman Sea) by employing GMA of body shape. The results indicate significant differences in body shape between the populations of R. kanagurta inhabiting the eastern Indian Ocean. The variations are primarily observed in the relative sizes of body depth, head, dorsal and anal fins, and the position of eyes, mouth, pectoral, anal, and dorsal fins. The Bay of Bengal populations were mainly characterized with a deeper body, large heads, dorsally oriented eyes, posterior pectoral fins and longer anal and second dorsal fin. Andaman populations were characterized with a more streamlined body, anterior pectoral fins, ventral eyes and shorter anal and second dorsal fins. Arabian Sea population possess an intermediate shape between Bay of Bengal and Andaman populations. These observed variations confirm that R. kanagurta constitutes a discrete population in the eastern Indian Ocean. This study provides valuable information on the population structure of R. kanagurta in the Arabian Sea, Bay of Bengal, and Andaman Sea, which can be useful in fisheries management and conservation efforts.