Morphological measurements of manta rays (Manta birostris) with a description of a foetus from the east coast of Southern Africa

Abstract

Descriptions and morphological measurements from manta rays (Manta birostris) caught in bather-protection nets in eastern South Africa are presented and compared to a M. birostris foetus from southern Mozambique. Specimens examined from South Africa had disc widths ranging between 2230–2370 mm and were immature. The foetus was 1328 mm in disc width. External examination of the foetus revealed the presence of teeth on the lower jaw and spot patterning on the ventral surface. The ventral spot patterning, which is commonly used in photo-identification studies, was similar in style and colour to the patterning recorded in both the examined juveniles and free-swimming manta rays. The presence of a distinctive ventral spot arrangement in this foetus establishes that spot patterns develop before birth. Morphological differences between the foetus and the juvenile specimens are attributed to the folded position of the foetus’s pectoral fins in utero and its developmental state. The presence of 1300–1700 mm DW free-swimming individuals from the southern Mozambican area suggests that the foetus was near-term. This study on western Indian Ocean specimens provides the first diagnostic description, morphometric measurements and photographs of M. birostris from this region.