Dasyatis microps ( Annandale, 1908 )

Pierce, Simon J., White, William T. & Marshall, Andrea D., 2008, New record of the smalleye stingray, Dasyatis microps (Myliobatiformes: Dasyatidae), from the western Indian Ocean, Zootaxa 1734, pp. 65-68 : 65-67

Dasyatis microps ( Annandale, 1908)

Trygon microps Annandale, 1908: 393 ; Annandale, 1909: 26. Dasybatus microps: Garman, 1913: 381 .

Dasyatis (Amphotistius) microps: Fowler, 1941: 431 ; Misra, 1947: 36. Dasyatis (Himantura) microps: Misra, 1952: 124 .

Dasyatis microps was first described by Annandale (1908) from a single, large specimen caught in the Bay of Bengal off Chittagong in Bangladesh. A further four large specimens were reported by Annandale (1909) off the Orissa coast in eastern India. Additional observations on this species in Indian waters were provided by Nair and Soundararajan (1976), which also extended its known range to the southern part of the east coast of India. Furthermore, Ishihara et al. (1998) recorded D. microps from the Ganges River Estuary. Dasyatis microps has also been recorded from the north Malé Atoll, Maldives ( Adam, 1998), Gulf of Thailand ( Last & Compagno, 1999), Malaysia ( Mohsin & Ambak, 1996), Indonesia ( White et al. 2006; White & Dharmadi, 2007) and the Arafura Sea off northern Australia ( Last & Compagno, 1999). Although Fowler (1941) recorded D. microps from the Philippines and adjacent areas, Compagno et al. (2005) did not report this species as occurring in the Philippines.

Dasyatis microps is an extremely large dasyatid species, attaining widths of up to 222 cm ( Garman, 1913). Nair and Soundararajan (1976) examined a pregnant female of 206 cm DW which contained a single, late-term male embryo of 33 cm DW. Mohsin and Ambak (1998) noted that most individuals of D. microps caught were 31–55 cm DW, and thus it is likely that the size at birth is around 31–33 cm DW. Dasyatis microps is a very distinctive dasyatid with the following combination of characters: disc very broad (width more than 1.4 times disc length); outer angles more than 90°; snout rounded, with tip projecting slightly; spiracles large; mouth large, with 5 papillae; disc with numerous stellate-based, enlarged denticles, mostly around snout; tail almost as long as disc, basal portion broad and flat, distal portion slender and round, tapering rapidly beyond sting; ventral cutaneous fold on tail thick and low, originating below spine base; base of tail with enlarged denticles; dorsal surface whitish brown, eyes dark; ventral surface pale ( Garman, 1913; Nair & Soundararajan, 1976).

Several sightings of D. microps were made over reefs within 15 km of Tofo Beach, Mozambique (23°51’S, 35°32’E) between September 2004 and November 2007. Tofo Beach lies ca. 425 km north of the South African coastal border and 820 km east of the southern tip of Madagascar. Specimens were observed at depths between 15 m and 25 m in water temperature of ca. 23–28°C. All sightings were of free-swimming individuals that were generally accompanied by cobia ( Rachycentron canadum L.) and in one case a Jenkins’ whipray Himantura jenkinsii (Annandale) .

Photographs were taken of a free-swimming female D. microps (ca. 200 cm DW) at a depth of 25 m over a subtropical reef (23°50’S, 35°33’E) approximately 1.5 km east of Tofo Beach, on October 22nd 2007 ( Figure 1 a). Another female D. microps (ca. 150 cm DW) was photographed at the same location on 7th March 2007 ( Figure 1 b,c). The dorsal surface of the discs in these individuals were medium-brown in colour, with a longitudinal row of large whitish spots on either side of the disc at about two thirds distance from dorsal midline to pectoral-fin apex, additional large whitish spots lateral of eyes and on either side of mid-disc, and several rows of small whitish spots on either side of tail base ( Figure 1 a,c). The presence of whitish spots on the dorsal surface was not mentioned by Annandale (1908) or Garman (1913), but was noted by Nair and Soundararajan (1976) for both adults and an embryo and are also evident in the illustration provided for this species by White et al. (2006). The tail is similar in colour to the dorsal disc basally and becomes much darker towards the spine and is almost blackish distally ( Figure 1 c). The ventral surface is almost uniformly white, with very light dusky margins along the anterior and posterior margins of the disc ( Figure 1 b). The basal part of the ventral tail is much paler than the dorsally, but darker than the ventral surface of the disc, and is almost blackish distally.

Another specimen of D. microps was caught offshore by spear-fishers and landed at Tofo Beach on 15th August 2006 ( Figure 1 d). This individual had a reddish-brown dorsal surface with similar white spots to the free-swimming individuals observed. Although this species has been recorded in fisheries in India, Bangladesh, Malaysia, Gulf of Thailand and Indonesia ( Annandale, 1908; 1909; Nair & Soundararajan, 1976; Mohsin & Ambak, 1998; Last & Compagno, 1999; White & Dharmadi, 2007), it is only occasionally observed and appears to be rare throughout much of its range. For example, only one individual of D. microps was recorded during a major 5-year survey of shark and ray fisheries in Indonesia in which>28,000 individual rays were examined ( White & Dharmadi, 2007).

The presence of D. microps in southern Mozambique represents a western range extension of more than 5000 km, indicating that it is likely to be more widespread in the Indo-Pacific than previously considered. The scarcity of recorded observations suggests that D. microps is rare and possibly patchily distributed. The species has been taken from estuaries, inshore coastal waters and from the lower continental shelf and has been assumed to be predominantly demersal. The distinctly broad disc of this species indicates that this species is likely to have a somewhat different swimming mode than most other dasyatids. Typical dasyatids, together with rajids (skates) and urolophids (stingarees), have an undulatory swimming mode, whilst gymnurids (butterfly rays), mobulids (devil rays), myliobatids (eagle rays) and rhinopterids (cownose rays) have an oscillatory swimming mode ( Rosenberger, 2001; Schaefer & Summers, 2005). This is physiologically apparent in the skeletal structure of the pectoral fins of these groups and physically is apparent in the very broad disc of oscillatory swimmers. The observations of this species in mid-water off Mozambique indicate that this species is possibly a semi-pelagic species which may also account for its rarity in catches throughout its range compared to other dasyatid species. The disc shape of D. microps is intermediate between that of a typical Dasyatis and a Gymnura , and it is possible that this represents a form of convergent evolution within the Myliobatiformes .

Figures

FIGURE 1. Smalleye stingray, Dasyatis microps from southern Mozambique: A) dorsal view showing pectoral fin morphology; B) ventral view; C) dorsal view showing tail morphology and colouration; and D) specimen speared off Tofo Beach, Mozambique. Photographs by A. D. Marshall.