24 Butterfly Rays

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Butterﬂy Rays: Family Gymnuridae

Chapter · January 2016

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The user has requested enhancement of the downloaded file. 24 BUTTERFLY R AYS Family Gymnuridae Yokota, L., White, W.T. & Carvalho, M. R. de

Butterfly rays are distinguished from other batoids by a distinct lozenge-shaped disc (at least 1.5 times broader than long), and short, slender whip-like tail. They are medium-sized to large rays (adults less than 1 m disc width to at least 2.6 m). The snout is short and obtuse, without a rostral cartilage, and the head is not raised above the strongly depressed, flat disc. Sexual dimorphism is evident in some species, with adult males presenting a more angular disc, and acute and longer snouts. Eyes are dorsolateral and small, followed by rather large spiracles that may have a small tentacle on the inner posterior margin. Mouth is relatively wide, arched and without papillae on floor. Jaws are very slender, bearing numerous, uniform small teeth in bands. Tail is slender and short, usually cross-banded; dorsal and ventral skin folds may be present. A small dorsal fin at tail base and serrated caudal stings are variously present. Skin is usually entirely smooth. Colour patterns are variable and may be associated to substrate. Butterfly ray species are similar to each other morphologically and exhibit intraspecific variation; taxonomic uncertainties involving their identification are common. Identification relies on a combination of characters, such as presence/absence of spiracular tentacles, dorsal fin and caudal sting(s), and relative size of the tail, as well as the number of black bands on tail. Ten named species are recognized in a single genus, Gymnura (Aetoplatea is a synonym); the group is being revised and new species will be described soon. Marine, coastal and demersal, usually occurring on soft bottoms. Viviparous (lipid histotrophy), produces 1–16 pups; some tropical species may reproduce throughout the year. Primarily eats fishes, but they also consume invertebrates. Caught mainly as bycatch in various tropical fisheries, generally of low commercial value, with the flesh used as fishmeal in some areas.

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SPINY BUTTERFLY RAY 24.1

Gymnura altavela (Linnaeus, 1758)

IDENTIFICATION. Very large butterfly ray with a small tentacle on inner posterior margin of spiracle, short tail (post-cloacal length 18–23% DW) with 3–5 black bands (usually not well demarcated), one or more caudal stings, and dorsal fin absent or tiny and vestigial. Disc much broader than long (1.8–2.2 times). Snout short, preoral length 8–10% DW. No sexual dimorphism in disc shape. Eyes very small (orbital length 11–24% interorbital width). Spiracle with concave inner margin but with a subtle convex undulation anterior to tentacle; spiracular tentacles slender, length 1–2.1% DW. Mouth arched, lower jaw with concave symphysis due to mid-lateral projections (sometimes forming hard protuberances). Skin usually entirely smooth, but large individuals may have a few denticles on upper surface. HABITAT AND BIOLOGY. Atlantic Ocean and Mediter- Caudal stings strong and well developed. Tail usually long- ranean Sea; discontinuous off Africa and Americas. Benthic, est in embryos and small juveniles (post-cloacal length in shallow coastal waters over sand and mud generally to 24–30% DW). depths of 150 m; distribution probably habitat dependent. 1–8 pups produced annually after a 4–9 month gestation. COLOUR. Dorsal surface light to dark brown, greyish or Feeds on fishes (which sometimes includes other rays), blackish; variously marked with small dark dots or crustaceans and molluscs. irregular dark or pale spots or blotches, often in a marbled pattern (sometimes vermiculate); distinct white blotch SIMILAR SPECIES. Resembles the Backwater (24.7) and rarely present near one or both spiracles. Ventral surface Australian (24.2) Butterfly Rays; former has a smaller white to brownish. Tail banding not well demarcated, often spiracular tentacle (0.1–0.6% DW), and latter is a much diffuse. smaller species with 1–7 bands on tail, usually a larger dorsal fin (when present), and usually without caudal stings. SIZE. Attains at least 260 cm DW, maximum recorded Population off tropical Africa thought to be a similar weight 290 kg. Males mature at 78–130 cm DW, females at undescribed species (currently under investigation). Gymnura 102–108 cm DW; birth size 38–44 cm DW. hirundo (Lowe) is probably a junior synonym.

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AUSTRALIAN BUTTERFLY RAY 24.2

Gymnura australis (Ramsay & Ogilby, 1886)

IDENTIFICATION. Small butterfly ray possessing a small tentacle on the inner posterior margin of spiracle, short tail (post-cloacal length 16–29% DW) with 1–7 blackish bands, small dorsal fin on tail base present or absent, and caudal stings mostly absent. Disc much broader than long (1.8–2.0 times). Snout short, preoral length 8–10% DW. Sexual dimorphism in disc shape not evident. Eyes small (orbital length 16–30% interorbital width). Spiracular tentacle slender (eastern form) to more rounded and thickened (northern form). Mouth arched, lower jaw with concave symphysis due to mid-lateral projections (sometimes forming hard protuberances). Skin entirely smooth. Often with a single, poorly developed caudal sting. continental shelf in relatively open sandy, muddy and silty COLOUR. Dorsal surface greenish, greyish or light to dark environments, including estuaries and intertidal zones, to a brown; often with a peppering of black spots varying in depth of at least 250 m. Produces litters of 1–6 pups. density and intensity, over a delicate mosaic pattern; an Primarily a specialist feeder on bony fishes; frequently irregular blotch often present near each pectoral-fin ingests very large fishes for its size. insertion; some specimens with a few large, irregular whitish blotches. Ventral surface whitish to copper, SIMILAR SPECIES. Two distinct variants of this species sometimes with margins darkened. Individuals from exist: an eastern Australian form with a shorter tail (post- eastern Australia sometimes with extremity of tail uniformly cloacal length 16–25% DW) with 1–3 bands, and sometimes black due to merging of bands posteriorly. with a dorsal fin; and a northern Australian form, having a longer tail (post-cloacal length 22–29% DW) with 4–7 SIZE. Attains at least 94 cm DW and 7.4 kg. Males mature at bands, and always with a dorsal fin. Most similar to the 35–42 cm DW, females 44–46 cm DW; born at 22–25 cm Spiny Butterfly Ray (24.1), which is a significantly larger DW. species with 3–5 black tail bands that are usually not clearly HABITAT AND BIOLOGY. Northern and eastern demarcated, dorsal fin absent (or tiny and vestigial), and Australia, and New Guinea. Benthic, coastal to offshore on always with caudal stings.

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MAZATLAN BUTTERFLY RAY 24.3

Gymnura crebripunctata (Peters, 1869)

IDENTIFICATION. Small butterfly ray lacking a tentacle on inner posterior margin of spiracle, very short tail (post- cloacal length 16–22% DW) without caudal stings or dorsal fin, bands on tail diffuse and faint. Disc much broader than long (1.6–1.9 times). Snout short, preoral length 8–14% DW. Sexual dimorphism evident, juveniles and females with a rounded disc and obtuse snout; adult males with a more angular disc and longer, more acute snout. Eyes very small (orbital length 12–24% interorbital width). Spiracle with strongly concave inner margins. Mouth arched, lower contour usually convex. Skin entirely smooth. COLOUR. Dorsal surface often fully covered with irregular circular spots flanked by smaller black spots, sandy and muddy substrates of coasts and estuaries to at sometimes resembling leopard spots; may be uniformly least 30 m depth. No life history information available, but pale to dark brown, vermiculate, or with a few pale or dark diet appears to consist primarily of teleost fishes. May utilize spots, and pale stripes on disc edges. Ventral surface inshore habitats for breeding and nursery functions. whitish to copper. SIMILAR SPECIES. Californian Butterfly Ray (24.5) has a SIZE. Attains at least 81 cm DW; males mature at ~30 cm tail with a slightly diphycercal tip with caudal stings; DW; size at maturity of females and at birth unknown. Smooth Butterfly Ray (24.6) has a weaker dorsal fold on tail HABITAT AND BIOLOGY. Eastern Pacific; southern and more pronounced tail banding. Gymnura afuerae California (USA) to northern Peru. Benthic, inshore, on (Hildebrand) is a junior synonym.

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JAPANESE BUTTERFLY RAY 24.4

Gymnura japonica (Temminck & Schlegel, 1850)

IDENTIFICATION. Large butterfly ray lacking a tentacle on inner posterior margin of spiracle, short tail (post- cloacal length 20–28% DW) with 5–9 black bands, lacking a small dorsal fin at tail base, and caudal stings always present. Disc much broader than long (1.8–2.2 times). Snout short, preoral length 2.0–3.3 in post-cloacal length. Sexual dimorphism in disc shape less evident than in some other Gymnura species, but adult males tend to have a relatively longer snout than females. Eyes very small (orbital length 9–24% interorbital width). Spiracle with curved and concave inner margins. Mouth arched, lower jaw with concave symphysis due to mid-lateral projections (sometimes forming hard protuberances). Skin entirely smooth. Caudal sting usually poorly developed. Tail length SIZE. Attains at least 145 cm DW. Males mature at 40–50 45–60% of snout–cloaca length. Embryos and small cm DW; born at ~18 cm DW. juveniles usually have longer tails than adults (post-cloacal HABITAT AND BIOLOGY. North-West Pacific; Japan to length 27–34% DW). southern China. Benthic inshore on sandy and muddy bottoms. Produces litters of 2–8 pups. Diet poorly documented, COLOUR. Dorsal surface uniform brown, black or grey, possibly based on bony fishes as for other members of family. sometimes with some irregular dark spots; a large white spot occasionally present behind (or lateral to) each or just SIMILAR SPECIES. Most similar to the Zonetail Butterfly one spiracle. Ventral surface whitish to brownish or copper, Ray (24.10), which has a longer tail (post-cloacal length often with darker disc margins. Tail bands sometimes 52–80% of snout–vent length, 6–10 black bands) often with diffuse with tail becoming black (mainly in large a small dorsal fin on its base, and preoral length 2.8–4.5 specimens); occasionally a single dark spot present between times post-cloacal length. Gymnura bimaculata (Norman) is each black band. a junior synonym.

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CALIFORNIAN BUTTERFLY RAY 24.5

Gymnura marmorata (Cooper, 1864)

IDENTIFICATION. Medium-size butterfly ray lacking a tentacle on inner posterior margin of spiracle, very short tail (post-cloacal length 14–23% DW) without bands, one or more serrated caudal stings present on tail, but dorsal fin absent. Disc much broader than long (1.6–1.9 times). Snout short, preoral length 9–15% DW. Sexual dimorphism evident, juveniles and females with rounded disc and obtuse snout; adult males with a more angular disc and longer, more acute snout. Eyes very small (orbital length 10–27% interorbital width). Spiracle with concave inner margin. Mouth arched, lower-jaw symphysis straight to slightly concave. Skin entirely smooth. Caudal stings thinner and proportionally smaller in juveniles, eventually covered by a fleshy layer. Tail somewhat diphycercal at tip. Benthic, inshore in sandy bays, beaches, silty or muddy channels, and estuaries, to a depth of 94 m. Pregnant COLOUR. Dorsal surface light to dark brown, greyish or females move inshore in aggregations to pup; newborns use blackish; occasionally marked with a few discrete and shallow waters as nursery grounds. Produces litters of 4–16 irregular, pale or dark spots (sometimes vermiculate). pups, mainly in May to September, although the births can Ventral surface white to brownish with brown-grey shading occur throughout the year. Diet consists almost exclusively along outer disc margins, more prominent posteriorly. of teleost fishes. SIZE. Attains at least 125 cm DW (possibly to 150 cm DW). SIMILAR SPECIES. Most similar to the Mazatlan Butterfly Males mature at 41 cm DW, females 62 cm DW; born Ray (24.3), which has a tail without a diphycercal tip and between 21–26 cm DW. lacking caudal stings. HABITAT AND BIOLOGY. Eastern Pacific; southern California (USA) to Mexico, including Gulf of California.

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SMOOTH BUTTERFLY RAY 24.6

Gymnura micrura (Bloch & Schneider, 1801)

IDENTIFICATION. Medium-size butterfly ray lacking a tentacle on inner posterior margin of spiracle, short tail (post-cloacal length 16–28% DW) with 3–5 black bands, usually lacking a small dorsal fin at tail base, and no caudal stings. Disc much broader than long (1.5–2.0 times). Snout short, preoral length 8–16% DW. Sexual dimorphism evident, juveniles and females with rounded disc and obtuse snout; adult males with more angular disc and a longer, more acute snout. Eyes very small (orbital length 13–26% interorbital width). Spiracle with concave inner margin. Mouth arched, lower contour usually convex. Skin entirely smooth. Some males with a small dorsal fin at tail base, its size variably developed. HABITAT AND BIOLOGY. Western Atlantic; (northern COLOUR. Dorsal surface light to dark brown or greyish; USA to Brazil) and possibly Eastern Atlantic (Senegal to sometimes with vermiculate patterns or speckled with Angola). Benthic, coastal and primarily on sandy and muddy lighter and darker shades or faint dark round patches; some bottoms, to depths of at least 40 m. Produces litters (1–8 specimens with light stripes on disc edges. Ventral surface pups) continuously throughout year in tropical regions. Diet whitish to dusky, darkening toward edges, yellowish in some large individuals; tail normally prominently banded, consists mainly of bony fishes with evidence of feeding bands less distinct in some very large adults. specialization; may ingest proportionally very large fishes. SIZE. In North-West Atlantic, to ~110 cm DW; males SIMILAR SPECIES. Most similar to the Mazatlan Butterfly mature at ~35 cm DW, females ~55 cm DW, birth size 15–26 Ray (24.3), which has a higher dorsal fold on tail and less cm DW. Smaller in South-West Atlantic, <80 cm DW; males obvious tail banding. The eastern Atlantic population is mature at ~27 cm DW, females ~40 cm DW, birth size 14–18 under investigation and may be a separate undescribed cm DW. species.

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BACKWATER BUTTERFLY RAY 24.7

Gymnura natalensis (Gilchrist & Thompson, 1911)

IDENTIFICATION. Very large butterfly ray with a rudimentary tentacle on inner posterior margin of spiracle, very short tail (post-cloacal length 18–24% DW) with 3–5 black bands (usually poorly demarcated), one or more caudal stings, and lacking a dorsal fin. Disc much broader than long (1.8–2.2 times). Snout short, preoral length 8–10% DW. No sexual dimorphism in disc shape. Eyes very small (orbital length 11–21% interorbital width). Spiracle inner margin concave with a subtle convex undulation before tentacle; spiracular tentacle length 0.1–0.7% DW. Mouth arched, lower jaw with concave symphysis due to mid-lateral projections (sometimes forming hard protuberances). Skin usually entirely smooth, but large individuals with some denticles on upper surface. Caudal stings strong and well HABITAT AND BIOLOGY. Southern Africa: Namibia to developed. Tail relatively longer in embryos and small southern Mozambique. Coastal, benthic on sandy beaches, juveniles (post-cloacal length 25–29% DW). estuaries, lagoons, and offshore banks, to a depth of 75 m. Produces litters of 2–9 pups after a 1 year gestation; reaches COLOUR. Dorsal surface brown or greyish; disc sometimes maturity at about 2 years of age in males, 6 years in females. with small dark dots or irregular pale spots or blotches, often in a marbled pattern. Ventral surface white to Diet consists of fishes, crabs, polychaete worms, and squids. brownish. Tail banding not well demarcated, often diffuse SIMILAR SPECIES. Very similar to the Spiny Butterfly (mainly in large individuals). Ray (24.1), which has longer spiracular tentacles (1–2.1% SIZE. Attains ~250 cm DW (~120 kg). Males mature at DW). These forms are possibly synonyms, but the Backwater ~95 cm DW, females at ~145 cm DW; birth size 38–47 cm Butterfly Ray is maintained as valid pending results of DW. research in progress.

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LONGTAIL BUTTERFLY RAY 24.8

Gymnura poecilura (Shaw, 1804)

IDENTIFICATION. Medium-size butterfly ray lacking a tentacle on inner posterior margin of spiracle, very long tail (post-cloacal length up to 54% DW) with 8–14 black bands, lacking a small dorsal fin at tail base, and caudal stings variously absent or present. Disc much broader than long (1.7–2.1 times). Snout short, preoral length 3.2–6.7 times post-cloacal length. Sexual dimorphism in disc shape not evident. Eyes very small (orbital length 11–21% interorbital width). Spiracle with straight to concave inner margins. Mouth arched, lower-jaw contour may be entirely convex or with a slightly concave symphysis. Skin entirely smooth. Caudal sting seems to emerge during development, so it tends to be absent in juveniles and present in adults (when present, it is small and slender). Characterized by a long tail, HABITAT AND BIOLOGY. Indo-West Pacific; Red Sea to but tail size variable (post-cloacal length 31–54% DW); Shanghai, China (including Indonesia and Malaysia). largest individuals tend to have relatively longer tails. Benthic inshore, primarily on sandy and muddy substrates to a depth of at least 30 m. Produces litters of 1–7 pups; off COLOUR. Dorsal surface uniform light to dark brown; India, found to breed throughout the year. Diet consists sometimes with black dots or with weak round whitish spots. mainly of bony fishes. Ventral surface whitish to brownish. Tail banded; dark spot frequently between each black band, sometimes surrounded SIMILAR SPECIES. Resembles the Zonetail Butterfly Ray by 4 smaller black dots (more common in adults); tail banding (24.10), which has a shorter tail (post-cloacal length 23–36% diffuse, less well defined in very large individuals. DW, 6–10 black tail bands) and a small dorsal fin at tail base is frequently present. Gymnura crooki is probably a junior SIZE. Attains at least 104 cm DW, maximum estimated synonym of this species. weight 8.3 kg. Males mature at ~35 cm DW, females at ~41 cm DW; birth size 22–26 cm DW.

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TENTACLE BUTTERFLY RAY 24.9

Gymnura tentaculata (Müller & Henle, 1841)

IDENTIFICATION. Small butterfly ray possessing a small tentacle on inner posterior margin of spiracle, long tail (post-cloacal length 23–33% DW) and lacking a banding pattern, small dorsal fin at tail base always present, and caudal stings variously absent or present. Disc much broader than long (1.7–2.0 times). Snout short, preoral length 7–10% DW. Sexual dimorphism in disc shape subtle. Eyes medium- sized, relatively larger than congeners (orbital length 25–38% interorbital width). Spiracle spiracular tentacle usually rounded and thick. Mouth arched, lower symphysis slightly concave. Skin entirely smooth. Caudal sting poorly developed when present. Dorsal fin located at tail base, well developed. HABITAT AND BIOLOGY. Indo-West Pacific; Red Sea to COLOUR. Dorsal surface uniform light to dark brown, Bay of Bengal. Benthic inshore to a depth of at least 74 m. frequently covered with numerous small whitish spots or Little known of its habitat and biology. Diet probably based dots. Ventral surface whitish to brownish. Tail banding on teleosts, like other butterfly rays. absent. SIMILAR SPECIES. Most similar to the Australian SIZE. Attains at least 76 cm DW. Males mature at ~40 cm Butterfly Ray (24.2), which has a distinctive tail banding DW; size at maturity of females and size at birth unknown. pattern (otherwise absent).

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ZONETAIL BUTTERFLY RAY 24.10

Gymnura zonura (Bleeker, 1852)

IDENTIFICATION. Medium-size butterfly ray lacking a tentacle on inner posterior margin of spiracle, long tail (post-cloacal length 23–36% DW) with 6–10 black bands, small dorsal fin at tail base often present (but may be absent), and caudal stings mostly present. Disc much broader than long (1.8–2.1 times). Snout short, preoral length 2.8–4.5 times post-cloacal length. Sexual dimorphism in disc shape less evident than in many other species of family. Eyes small (orbital length 15–30% interorbital width). Spiracle with curved and concave inner margin. Mouth arched, lower symphysis slightly concave. Skin entirely smooth. Caudal sting usually poorly developed, with a relatively large base; tail usually with a groove when sting missing. Tail length 52–80% of snout–cloaca length. over soft substrates to a depth of at least 37 m. Produces litters of 2–4 pups. Diet consists primarily of bony fishes and COLOUR. Dorsal surface uniform brown or with numerous small round whitish spots. Ventral surface whitish to crustaceans. brownish. Tail banded, pale sections often with single dark SIMILAR SPECIES. The Japanese Butterfly Ray (24.4) has spot between each black band. a shorter tail (post-cloacal length 45–60% of snout–cloaca SIZE. Attains at least 108 cm DW, maximum weight length, 5–9 black bands), lacks a dorsal fin, and the preoral exceeding 7.3 kg. Males mature at ~48 cm DW, females by 78 length is 2.0–3.3 times post-cloacal length. The Longtail cm DW; born 20–21 cm DW. Butterfly Ray (24.8) has a longer tail (post-cloacal length HABITAT AND BIOLOGY. Indo-West Pacific; Bay of 31–54% DW, 8–14 black bands) and always lacks a dorsal Bengal (India) to Philippines and Taiwan. Benthic, inshore fin.

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