Manta alfredi Krefft 1868

Manta alfredi (Krefft, 1868).

Selected synonymy. Manta fowleri Whitley, 1936 (see Fowler 1927); Manta pakota Whitley, 1936.

Common names. Manta ray, inshore manta ray, Alfred manta, Prince Alfred’s ray.

Diagnosis: Disc approximately 2.2–2.4 times as broad as it is long. Maximum disc width size approximately 5500 mm. Slender whip-like tail approximately 123% of disc length if intact. No distinct caudal spine or cartilaginous mass present at base of tail. Some specimens have small hump at the base of the tail on the dorsal surface, while other specimens have a slight depression and groove on the dorsum of the tail immediately posterior to the posterior margin of the dorsal fin. Small, knob-like dermal denticles evenly distributed on both the dorsal and ventral surfaces, with ventral surface having slightly larger denticles. Dental ligament with small cusped teeth on the lower jaw measuring roughly 22% of total disc length with approximately 6–8 rows, 142–182 files across entire width of the tooth band. Total tooth counts of 900–1500 for entire tooth band. Top jaw lacks rows of enlarged denticles.

Morphometrics. See Table 1 for complete measurements of M. alfredi. See Table 2 for morphometric comparison of M. alfredi to M. birostris.

Colouration. Dorsal surface black in colouration (Fig. 9 a). Pale to white coloured shoulder patches, with or without dark spots within them, present on the dorsal supra-branchial region (Fig. 9 a, 10a–h). Anterior margin of shoulder patch initially emanates posteriorly from spiracle before curving medially, a diagnostic feature of M. alfredi colouration (Fig. 10 a–h). Towards the midline, colouration again begins to radiate out posteriorly continuing down over the supra-branchial region in variably sized shoulder patches (Fig. 10 a–h). Anterior distal side of the shoulder patch may present as an anterior facing hook. Pale colouration may be present along the distal margin of the pectoral fin tips (Fig. 9 a). Pale chevron shaped patch typically stretches anteriorly from the insertion point of the dorsal fin.

Ventral surface predominantly cream to white in colouration with variable dark markings (Fig. 9 b). Mouth white to light grey in colouration (Fig. 9 b, 11a–h). Blue-grey to black spots of variable size can occur across most of the ventral surface (Fig. 9 b, 11a–h). The most diverse spot patterns typically occur medially to the five pair of gill slits, centrally on the abdomen and across the posterior half of the pectoral fins (Fig. 9 b, 11a– h). A small black semi-circular spot is typically located immediately posterior to the fifth gill slit on each side of the body (Fig. 9 b). Pale to dark charcoal-coloured bands are present on the posterior edge of each pectoral fin, typically stretching mid-way down the length of the fins from the pectoral fin tip (Fig. 9 b).

A melanistic form of M. alfredi occurs that is entirely black on the dorsal surface and predominately black on the ventral surface except for a variably sized white blaze along the mid-line (Fig. 12 a,b). Manta alfredi ’s distinctive ventral spot patterning is often visible on the abdominal region and between the gill slits (Fig. 12 a,b). A rare white, or leucistic, colour morph also exists in this species, in which the normally very darkly coloured dorsal surface appears almost entirely white (Fig. 12 c,d). The ventral surface may also appear lighter in overall colouration. This leucistic colour morph appears to be rare, with less than twenty observed specimens documented worldwide.

Dentition. Tooth band on lower jaw comprising 54.2–77.4% of total jaw width (Fig. 13 a). Tooth band containing 6–8 rows of small cusped teeth (approximately 1–2 mm in length) and 142–182 files across entire width of the tooth band (Fig. 13 b,c). Total tooth counts range from 918–1456 for entire tooth band. Morphology of individual teeth are variable and may be dimorphic between sexes. General tooth morphology is shown in figure 13(d). Each tooth has a bulbous root that is embedded in the dental ligament, a freestanding stalk that ends in a curved cusp that forms the occlusal surface and is oriented to face the lingual side of the jaw (Fig. 13 b). Teeth in the tooth band do not overlap (Fig. 17c). Upper jaw edentate with no enlarged denticle bands present.

Denticles. Denticles are small, non-overlapping and uniformly distributed along the dorsal and ventral surfaces (Fig. 14 a,b). Each denticle comprises a stellate base (which is embedded in the skin, Fig. 14 c,d) with a dorso-laterally elongated emergent knob (Fig. 14 c,d). Denticles on the ventral surface are larger than those on the dorsal surface, but all are of similar overall morphology (Fig. 14).

Manta alfredi Manta birostris

Size. The smallest individuals observed in the wild were approximately 1500 mm DW and a single examined near-term foetus was 1300 mm DW (Marshall et al. 2008). Dissected specimens of M. alfredi measured up to 3420 mm DW but estimates of the largest individuals sighted in southern Mozambique were slightly over 5000 mm DW. Size at maturity may vary slightly throughout its range, but males in southern Mozambique mature at approximately 3000 mm DW (Marshall, 2009), while females in southern Africa mature at approximately 3900 mm DW (Marshall, 2009).

Habitat and distribution. Commonly sighted inshore, within a few kilometres of land. Found around coral and rocky reefs as well as along productive coastlines with consistent upwelling, tropical island groups, atolls and bays. This species is widespread in the Indian Ocean, with images and sightings of M. alfredi from the Red Sea in the north to Durban, South Africa in the south, and from mainland Thailand in the north to waters off Perth, Australia in the south. In the eastern and south Pacific, M. alfredi occurs from the Yaeyama islands, Japan in the north to the Solitary Islands, Australia in the south and is sighted as far east as French Polynesia south of the equator and the Hawaiian islands north of the equator. Two reports and photographs of M. alfredi from the north Atlantic off the Canary Islands and the Cape Verde Islands and historical reports and photos of M. alfredi off the coast of Senegal in north west Africa (Cadenat 1958) are the only evidence of populations of M. alfredi in Atlantic waters (Fig. 8).

Material examined (n = 11). Juvenile male caught in bather protection nets on 11 April 2006 off Margate beach, Durban, South Africa (2230 mm DW, mass 71 kg). Juvenile female caught in bather protection nets on 17 July 2006 off Karridene beach, Durban, South Africa (2370 mm DW mass, 75 kg). Juvenile female caught in bather protection nets on 28 April 2006 off Sunwich Port beach, Durban, South Africa (2330 mm DW, mass 71 kg). Mature male caught in Mozambique on 15 January 2004 off Paindaine Beach, Inhambane, Mozambique (3420 mm DW). Juvenile male caught in bather protection nets on 14 June 2004 in Umhlanga Beach, Durban, South Africa (2520 mm DW, mass 107 kg). Juvenile female caught in bather protection nets on 21 June 2004 off South Port, Durban, South Africa (2440 mm DW, mass 101 kg). Juvenile male caught in bather protection nets on 10 August 2004 off Durban, South Africa (2320 mm DW, mass 85 kg). Juvenile male caught in bather protection nets on 15 September 2004 in South Broom, Durban, South Africa (2470 mm DW, mass 105 kg). Near-term male foetus caught in Mozambique on 15 October 2004 in Paindane Beach, Durban, South Africa (1328 mm DW, mass 15 kg). Mature male sampled on 20 March 2006 off the coast of Inhambane, Mozambique (skin sample only). Mature female sampled on 15 September 2007 off the coast of Inhambane, Mozambique (skin sample only).