Reproductive biology, length-weight relationship and diet of co-occurring butterfly rays, Gymnura poecilura and G. zonura, in Malaysian waters.

Recent IUCN assessments had resulted in uplisting of the status of butterfly rays due to concerns of overfishing but inadequate biological understanding of these rays prevent meaningful conservation and management measures. Therefore, this study was undertaken to address knowledge gaps on the reproductive biology and diet of longtail butterfly ray (Gymnura poecilura) and zonetail butterfly ray (G. zonura) in Malaysian waters. From surveys of landing sites and fish markets from years 2017 to 2022, size (disc width, DW), weight, and maturity were recorded and stomachs were collected from 94 G. poecilura (N = 39 females and 55 males) and 20 G. zonura (N = 10 females and 10 males) specimens. The length-weight relationships were significantly different between sexes for G. poecilura. The size at maturity (DW50) was estimated to be 476.0 mm (females), 385.0 mm (males) for G. poecilura, and 442.0 mm (combined) for G. zonura. The number of embryos ranged from 1 to 6, and the embryo size was between 73.90 to 130.44 mm DW. Dietary analysis of stomach contents revealed that fish prey was dominant in both G. poecilura (94.4%IRI) and G. zonura (100%IRI). Ontogenetic shift was seen in G. poecilura that fed on more variety of prey items, including shrimps, squids, and crabs with increase in body size. Both species co-occur all along coastal Malaysia although G. zonura is rarely encountered from fisheries surveys along the Strait of Malacca. Given similar habitat associations and dietary habits, G. poecilura may be able to outcompete G. zonura across their shared habitat range. The validity of G. japonica and G. micrura records in Malaysia remains questionable and requires future investigation. This article is protected by copyright. All rights reserved.