Longtail Butterfly Ray

The Longtail Butterfly Ray (Gymnura poecilura), belonging to the family Gymnuridae, is an elasmobranch species indigenous to the Indo-Pacific region, ranging from the 🌊 Red Sea to southern 🇯🇵 Japan and western 🇮🇩 Indonesia. This ray species can reach a maximum wingspan of 92 cm (36 in). Its distinguishing morphological features include a lozenge-shaped pectoral fin disc, approximately twice as wide as it is long, displaying a dorsal coloration of brown to gray with numerous small, light spots. Notably, the spiracles located posterior to the eyes exhibit smooth rims. A key identifying trait of this species is its tail, which mirrors the snout-to-vent distance in length, is unadorned by fins, and is adorned with nine to twelve alternating black and white bands.

The Longtail Butterfly Ray is benthic, inhabiting sandy or muddy environments within coastal waters at depths shallower than 30 meters (98 feet). Its diet primarily consists of bony fishes, molluscs, and crustaceans. The species is viviparous, with embryos initially reliant on yolk and later nourished by histotroph, or "uterine milk," from the mother. Breeding lacks a seasonal pattern, with females producing litters of up to seven offspring. Despite its economic value for meat, the Longtail Butterfly Ray is frequently harvested by both artisanal and commercial fisheries.

Detailed anatomical features of the Longtail Butterfly Ray include a lozenge-shaped pectoral fin disc with gently sinuous leading margins, convex trailing margins, and mildly angular outer corners. The snout is characterized as short and broad, with a slight protruding tip. Medium-sized eyes are followed by larger, smooth-rimmed spiracles. The nostrils are positioned in proximity to the mouth, connected by a short, broad skin membrane with a smooth margin. The considerable oral cavity forms a transverse curve and houses over 50 rows of teeth in each jaw, the number of which increases with age; the teeth are small, narrow, and pointed. Positioned on the ventral side of the disc are five pairs of short gill slits, and the pelvic fins are notably small and rounded.

The species' elongated tail lacks dorsal or caudal fins, containing instead low ridges along the dorsal and ventral surfaces. It shares the same length as the snout-vent distance, differentiating this species from others within the family. Occasionally, a small stinging spine may be present near the tail's base. The dermal layer is smooth, devoid of dermal denticles. Its coloration ranges from brown to greenish-brown to gray with numerous small pale spots and occasional dark dots on the tail, which bears nine to twelve alternating black and white bands. The underside presents a white pigmentation with darker edges on the fins.

Ecologically, the Longtail Butterfly Ray is the most geographically distributed member of its family within the Indo-Pacific, present from the 🌊 Red Sea and 🇸🇴 Somalia to regions westward across 🇮🇳 India and 🇱🇰 Sri Lanka, extending to 🇨🇳 China, southern 🇯🇵 Japan, the 🇵🇭 Philippines, and the western 🇮🇩 Indonesian islands such as Borneo, Sumatra (🇮🇩 Indonesia), and Java. It has been occasionally documented in 🇵🇫 French Polynesia. Preferring coastal waters with sandy or muddy seabeds at depths of 10–30 meters (33–98 feet), its populations do not demonstrate seasonal migratory behaviors.

The diet of the Longtail Butterfly Ray predominantly comprises bony fishes, notably those within the genus Leiognathus, as well as molluscs and crustaceans. Observations indicate a lack of shoaling behavior. Documented parasitic associations include the nematode Hysterothylacium poecilurai and the tapeworm Acanthobothrium micracantha. Reproductive strategies align with other butterfly rays, being viviparous with yolk and later histotroph serving as nourishment for developing young. Females possess two functional ovaries and uteri, engaging in reproductive activities year-round, peaking from April to October. While the gestation period remains undetermined, it is plausible that females produce multiple litters annually. Litter sizes reach at least seven offspring, with no significant correlation to female size. Neonates measure between 20–26 cm (7.9–10.2 in) across, resembling diminutive stingless adults, exhibiting potential coloration variations among siblings. Sexual maturity is reached at approximately 45 cm (18 in) and 41 cm (16 in) across for males and females, respectively.

Economically, the Longtail Butterfly Ray is extensively harvested for its meat, appearing as bycatch in artisanal and commercial fisheries across regions including 🇮🇳 India, 🇹🇭 Thailand, and 🇮🇩 Indonesia. Capture methods include bottom trawls, bottom-set gillnets, trammel nets, and other fishing apparatus. Despite limited data on population dynamics and catch rates, the species is considered vulnerable to overexploitation, attributed to its low reproductive rate and the tendency of pregnant females to abort young upon capture. Given the prevalent fishing intensity across its range, the International Union for Conservation of Nature (IUCN) has classified this species as Vulnerable.