Biological Aspects, Stock and Conservation Status of Giant Oceanic Manta Ray, Manta birostris in the Indian Ocean

Abstract

The giant oceanic manta ray (Manta birostris) is a ray species of the Family Mobulidae, the largest type of rays in the world. A study on Manta rays from the Indian Ocean was conducted from April 2001 to August 2005 at Cilacap-Central Java and Tanjungluar-East Lombok fish landings. Catch data of Cilacap fishing port from 2006 to 2011 are also presented in this paper. The methodology utilized was direct observations and data collection by enumerators. The results show that Manta rays were caught as by-catch of tuna gillnet and tuna longline fishing in the Indian Ocean. There were three age groups (cohorts) of the Manta birostris caught in the Indian Ocean, i.e. size class between 200-300 cm disc width (DW) as a young group, 301-400 cm DW (subadult group), and 401-500 cm DW (adult group), respectivelly. The sex ratio of males to females of Manta birostris was 1:1 (P>0.05). Monthly production of Manta birostris during six years (2006-2011) indicated that the highest production occurred in the period between May and September. Almost all of the body of this species were utilised, for instance, the gill plates and cartilages were used for medicines, and meat for consumption. Based on IUCN Red List, the conservation status of Manta birostris is near threatened and vulnerable in South-East Asia.