Manta birostris ( Walbaum, 1792 )

Marshall, Andrea D., Compagno, Leonard J. V. & Bennett, Michael B., 2009, Redescription of the genus Manta with resurrection of Manta alfredi (Krefft, 1868) (Chondrichthyes; Myliobatoidei; Mobulidae), Zootaxa 2301, pp. 1-28 : 4-11

Manta birostris ( Walbaum, 1792) .

Selected synonymy. Brachioptilon hamiltoni Newman, 1849 (see Beebe and Tee-van 1941, as Manta hamiltoni ); Ceratoptera ehrenbergii Müller and Henle, 1841 .

Common names. Giant manta ray , Pacific manta ray , devilfish, chevron manta, pelagic manta, oceanic manta.

Diagnosis. Disc approximately 2.2–2.3 times as broad as it is long. Maximum disc width over 7000 mm. Slender whip-like tail. Reduced caudal spine predominantly encased in a calcified mass present on the dorsum of tail immediately posterior to the dorsal fin. Dermal denticles situated on long, sagittally oriented, raised ridges in the dermis that extend down the length of both the dorsal and ventral surfaces. Dental ligament embedded with small cusped teeth on the lower jaw measuring roughly 25% of total disc length with approximately 12–16 rows, 220–250 files across entire width of the band. Total tooth counts of 3000–4000 for entire tooth band. Upper jaw contains at least two rows of enlarged denticles that span the same width of the upper jaw as the tooth band on the lower jaw.

Morphometrics. See Table 1 for complete measurements of Manta birostris . A total of ten nonoverlapping proportional measurements were identified that could be used to separate Manta birostris from Manta alfredi (highlighted in Table 2 ).

Colouration. Dorsal surface black, with large, conspicuous, white shoulder patches in the supra-branchial region, with or without black spots within them ( Fig. 1 a, 2a–h). Shoulder patches, which occur on either side of a dark midline, are distinct and approximately triangular in shape with hook shaped lateral extensions ( Fig. 2 a–h). Anterior edge of shoulder patches runs medially from spiracle in an approximately straight line parallel to the edge of the upper jaw, a diagnostic character of this species ( Fig. 2 a–h). Pale to white chevron shaped patch, of variable size, extends anteriorly from the anterior insertion point of the dorsal fin ( Fig. 1 a). Small blazes of white colour are also often visible on the dorsal tips of the pectoral fins ( Fig. 1 a).

Mouth black to charcoal grey in colouration ( Fig. 1 b). Dark colouration around mouth often extends posteriorly on the ventral surface from the base of the cephalic fins to the anterior edge of the first gill slits ( Fig. 1 b, 3a–h). Ventral surface largely cream to white with dark grey to black spots and patches most commonly occurring on the abdominal region between gill slit openings and anterior to the opening of the cloaca ( Fig. 1 b). Spots do not occur medially between the five gill slits or on the pectoral fins lateral to the body cavity ( Fig. 3 a–h). Medium to large black semi-circular spots posterior to the fifth gill slits are present ( Fig. 1 b). Posterior third of disc charcoal-coloured forming a V-shaped margin along the posterior edges of the pectoral fins ( Fig. 1 b, 3a–h), a diagnostic feature for M. birostris .

A melanistic form 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 ventral mid-line. Typical spot patterns are often visible along the white portion of the midline, which are centralised on the abdominal region and absent medially between the gill slits ( Fig. 4 a,b). A whitish, or leucistic, colour morph has also been documented which exhibits increased white colouration on the dorsal surface, a near white or completely white face and mouth and light ventral colouration, including an interrupted charcoal-coloured pectoral fin margin ( Fig. 4 a,b). This leucistic colour form appears to be rare, with less than a dozen observed specimens documented worldwide. All other morphological and meristic characters were the same as other examined individuals of M. birostris .

Dentition. Tooth band on lower jaw comprising 64.76–69.65% of total jaw width ( Fig. 5 a). Tooth band containing 12–16 rows of small cusped teeth (approximately 1.5 mm in length) and 220–250 files across entire width of the band ( Fig. 5 b). Total tooth counts range from 3000–4000 for entire tooth band. Morphology of individual teeth variable and may be dimorphic between sexes. Each tooth has a bulbous root, which is embedded in the dental ligament and 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. 5 b-d). Teeth in the tooth band slightly overlap ( Fig. 5 c). Tooth band absent in upper jaw but two irregular bands of enlarged denticles extend along the upper jaw for a distance equivalent to the length of the lower tooth band ( Marshall 2009).

Denticles. Prominent dermal denticles present on both the dorsal and ventral surfaces are randomly distributed along sagittally oriented ridges in the skin ( Fig. 6 a,b), a diagnostic feature of M. birostris . Denticles on the dorsal and ventral surfaces are similar in appearance and distribution, with slightly larger denticles on the ventral surface ( Fig. 6 a,b). Denticles have pronounced bifid cusps ( Fig. 6 c) that give the skin a much rougher texture than that of M. alfredi . The morphology of the most common denticle form on both the dorsal and ventral surfaces is shown in Fig. 6 c,d.

Caudal spine. A calcified mass with an embedded spine is located on the dorsum of tail immediately posterior to dorsal fin ( Fig. 7 a). The calcified mass rests just under a thin layer of dermis, lacks attachment via collagenous connective tissue to tail and detaches easily if skin is removed ( Fig. 7 b). Spine with serrated lateral edges is embedded in a large mass of highly mineralised cartilage, similar to that described for Mobula japonica (Notobartolo-di.Sciara 1987) ( Fig. 7 c). Spine appears to have an enameloid exterior and is slender in shape, approximately 3.5% of the width of the calcified cartilage mass. Tip of spine projects approximately 3 mm out from the surrounding mass ( Fig. 7 c). A sagittal plane CT scan clearly shows the spine embedded one third of the way into the calcified mass ( Fig. 7 d). Visual examinations in the field suggest that the size of the calcified mass is positively correlated with disc width. The calcified masses extracted from the two rays examined (male 3850 mm DW/ 1785 mm DL and female 3765 mm DW/ 1645 mm DL), were similar in overall shape and were 5.98% and 6.69% of the total DL of the rays respectively.

Size. Dissected specimens of M. birostris measured up to 4695 mm DW but estimates of the largest individuals sighted in the field (southern Mozambique and Mexico) were slightly over 6000 mm DW. Manta birostris reaches disc widths of at least 7000 mm, with anecdotal reports up to 9100 mm ( Compagno 1999). Size at maturity for M. birostris may vary slightly throughout its range, but males in southern Mozambique mature at approximately 4000 mm DW ( Marshall 2009). In Indonesia, the only mature male examined was 3850 mm DW. Additional fisheries data from Lombok, Indonesia suggest male M. birostris mature at 3750 mm ( White et al. 2006). The only mature females observed or examined (n = 3) in southern Mozambique were in excess of 4695 mm DW. In Indonesia, female M. birostris up to 3800 mm DW were immature. Additional fisheries data from Lombok, Indonesia suggest females mature by approximately 4130 mm DW ( White et al. 2006).

Habitat and distribution. Manta birostris occurs in tropical, sub-tropical and temperate waters around the globe ( Fig. 8 ). Commonly sighted along productive coastlines with regular upwelling, oceanic island groups and particularly offshore pinnacles and seamounts ( Compagno 1999; Rubin 2002). Manta birostris has been documented to occur as far north as southern California and Rhode Island on the United States west and east coasts, Mutsu Bay, Aomori, Japan, the Sinai Peninsula, Egypt and the Azores Islands in the Northern Hemisphere and as far south as Peru, Uruguay, South Africa and New Zealand in the Southern Hemisphere. In some locations, including Mozambique M. birostris is sympatric with M. alfredi ( Fig. 8 ). When they do occur together M. alfredi and M. birostris typically exhibit different habitat use and movement patterns ( Marshall 2009).

Material examined (n = 11). Mature male caught in gill net on 13 May 2007 in the Alas Strait south of TanJung Luar, Lombok (3850 mm DW). Juvenile female caught in gill net on 13 May 2007 in the Alas Strait south of TanJung Luar, Lombok (3765 mm DW). Juvenile female caught in gill net on 13 May 2007 in the Alas Strait south of TanJung Luar, Lombok (3800 mm DW). Juvenile female caught in gill net on 13 May 2007 in the Alas Strait south of TanJung Luar, Lombok (3568 mm DW). Mature female caught in gill net on 13 May 2007 in the Alas Strait south of TanJung Luar, Lombok (4695 mm DW). Mature female killed in June 1949 in Bimini, Bahamas (approx. 4500 mm DW) examined at the Harvard Museum of Comparative Zoology ( MCZ 37006). Mature female sampled on 26 September 2007 off the coast of Inhambane, Mozambique (skin sample only). Mature male sampled on 23 December 2006 off the coast of Inhambane, Mozambique (skin sample only). Mature female sampled on 12 October 2007 off the coast of Inhambane, Mozambique (skin sample only). Mature female (melanistic morph) sampled on 24 November 2007 off San Benedicto Island, Mexico (skin sample). Mature female sampled on 24 November 2007 off San Benedicto Island, Mexico (skin sample).

Figures

FIGURE 1. Natural colouration patterns in Manta birostris: (a) dorsal surface, arrows pointing to the shape and colouration of the shoulder patches and the colouration on the pectoral fins, box showing chevron shaped marking anterior to dorsal fin; (b) ventral surface, box showing region of highest spot density and distribution, arrows showing size of spot anterior to the 5 th gill slit, colouration of mouth region, and colouration of the pectoral fin margin.

FIGURE 2. Variation in dorsal supra-branchial shoulder patch markings on Manta birostris shown on individuals from: (a) Inhambane, Mozambique; (b) Inhambane, Mozambique; (c) Lombok, Indonesia; (d) Inhambane, Mozambique; (e) Brothers Islands, Red Sea; (f) Revillagigedo Archipelago, Mexico; (g) Ogasawara Islands, Japan; (h) Lombok, Indonesia.

FIGURE 3. Variation in ventral markings on Manta birostris from: (a) Inhambane, Mozambique; (b) Inhambane, Mozambique; (c) Revillagigedo Archipelago, Mexico; (d) Revillagigedo Archipelago, Mexico; (e) Inhambane, Mozambique; (f) Inhambane, Mozambique; (g) Ogasawara Islands, Japan; (h) Inhambane, Mozambique.

FIGURE 4. (a-b) Examples of the melanisic form of Manta birostris from the Revillagigedo Archipelago, Mexico and (c-d) examples of the white, or leucistic, colour morph of Manta birostris from southern Mozambique and the Revillagigedo Archipelago, Mexico.

FIGURE 5. Dentition and tooth morphology in Manta birostris: (a) lower jaw with elongated tooth band; (b) section of teeth mid-band; (c) embedded teeth of male ray; (d) view of single embedded female tooth.

FIGURE 6. Skin and denticle morphology in Manta birostris: (a) superior view of dorsal skin in male ray; (b) superior view of ventral skin in female ray; (c) lateral view of single denticle; (d) superior view of single denticle.

FIGURE 7. Views of calcified mass with embedded spine from Manta birostris (entire structure was 106.7 mm total length, 42 mm wide, and 46.7 mm in height and has a mass of 112.5 grams and a density of 1.324 g / cm ^ 3): (a) lateral view of the dorsal fin and calcified mass with embedded spine; (b) superior view after the skin was peeled back to expose the calcified mass; (c) lateral view; (d) sagittal plane CT scan showing the embedded spine.

FIGURE 8. Worldwide distribution of Manta from preliminary analysis (n = 2231 images from over 100 aggregation sites and sighting records).

Tables

TABLE 1. Morphometric measurements of Manta alfredi from South Africa and Manta birostris from Lombok, Indonesia.

Location South Africa	South Africa	South Africa	Lombok	Lombok	Lombok	Lombok
Sex Female	Male	Female	Female	Female	Female	Male
Disc Width (mm) 2370	2330	2330	3765	3800	3568	3850
%DL	%DL	%DL	%DL	%DL	%DL	%DL	_
Disc Length 100.00	100.00	100.00	100.00	100.00	100.00	100.00
Disc Width 237.00	220.79	220.79	228.88	228.23	227.26	215.69
Anterior Projection 40.00	39.60	39.60	36.78	35.74	35.67	34.73
Rostrum to Pelvic Fin 99.00	99.01	99.01	101.52	101.32	100.76	100.28
Pre-dorsal Length 87.00	85.15	85.15	83.89	82.28	79.62	79.55
Pre-cloacal Distance 85.00	84.16	84.16	79.03	82.28	76.11	78.15
Disc Thickness 20.00	24.75	22.77	23.10	28.83	29.30	25.21
Pectoral Length 1 93.00	92.08	89.11	92.16	90.09	90.76	85.71
Pectoral Length 2 122.00	113.86	112.87	112.46	110.51	112.74	102.52
Pectoral Length 3 94.00	96.04	93.07	98.78	97.30	94.27	96.92
1st Gill Slit Length 21.00	22.77	22.77	20.97	22.52	22.29	21.01
2nd Gill Slit Length 24.00	23.86	23.76	24.01	24.02	23.57	22.13
3rd Gill Slit Length 25.00	23.76	23.76	22.98	23.48	22.29	21.29
4th Gill Slit Length 23.50	20.79	21.78	20.36	20.30	19.75	18.82
5th Gill Slit Length 18.00	17.33	17.82	15.50	14.83	14.97	15.52
Distance Between 1st Gill Slits 27.00	23.76	25.74	25.65	24.92	23.25	23.53
Distance Between 5th Gill Slits 14.00	13.86	14.85	12.58	12.61	12.42	11.76
Rostrum to 1st Gill Slit 20.00	19.80	19.80	18.30	19.22	19.75	17.65
Rostrum to 5th Gill Slit 43.50	42.08	42.57	44.07	42.94	42.99	41.46
Cephalic Fin Length 26.00	26.73	22.77	27.36	28.23	28.34	26.89
Cephalic Fin Width 12.00	12.38	11.88	13.37	14.11	11.46	11.76
Diameter of Eye 2.40	2.97	1.98	3.95	4.50	4.20	3.47
Cranial Width 54.00	51.49	52.48	58.36	56.76	58.28	51.82
Head Length 35.00	32.67	31.68	32.83	34.29	32.48	31.09
Mouth Width 37.00	30.69	33.66	38.30	37.54	36.94	34.17
Lower Toothband Length 21.50	23.76	23.76	24.80	24.44	25.73	25.21
Internarial Distance 34.00	30.69	30.69	34.04	31.83	32.48	30.81
Spiracle Length 4.10	2.18	2.28	2.92	2.98	3.69	3.31
Interspiracle Distance 45.00	44.55	44.55	50.46	48.05	47.13	45.10
Dorsal Fin Base 17.00	14.36	15.84	13.37	12.91	13.69	12.89
Dorsal Fin Height 11.00	10.40	9.90	8.81	7.87	8.34	8.40
Dorsal Fin Anterior Margin 10.30	14.85	15.84	14.29	13.21	13.38	12.89
Width Across Pelvic Fin Base 22.00	19.80	20.79	16.72	18.32	17.20	17.09
Pelvic Fin Length 28.00	23.76	21.78	25.41	22.52	24.20	24.93
Pelvic Fin Anterior Margin 17.00	18.81	17.82	13.37	12.31	11.46	10.92
Clasper Inner Length N/A	15.84	N/A	N/A	N/A	N/A	24.65
Tail Length 113.00	97.03	102.97	89.06	N/A	89.17	N/A
Tail Width 2.10	1.49	1.58	1.58	N/A	1.53	N/A
Tail Height 2.20	2.18	2.08	1.64	N/A	1.66	N/A