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

Abstract

Recent IUCN assessments had resulted in up listing of the status of butterfly rays due to concerns of overfishing, but inadequate biological understanding of these rays prevents meaningful conservation and management measures. Therefore, this study was undertaken to address knowledge gaps in the reproductive biology and diet of longtail butterfly ray (Gymnura poecilura) and zone tail butterfly ray (Gymnura 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% Index of Relative Importance (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 an 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.

Size at sexual maturity, seasonal variation by maturity stages, and fecundity of the spotted round ray (Urobatis maculatus) and the thorny stingray (Urotrygon rogersi) from the northern tropical eastern Pacific

“…In contrast, the DW 50 of the females of U. rogersi was larger than that of males, which coincides with reports from Mejía‐Falla et al (2012). This pattern in many species of elasmobranchs may be in part explained by the need for females to attain a larger size to support pups (Cortés, 2000, 2004; Leung et al, 2023). However, this pattern was not evidenced in U. maculatus , probably due to the small size of this species (Pollom et al, 2020), which has also been suggested for some species of rays like the zipper sand skate Psammobatis extenta (Garman 1913) and the Venezuela round stingray Urotrygon venezuelae Schultz 1949 (Acevedo et al, 2015; Braccini & Chiaramonte, 2002).…”