Saturday, 13 December 2008

Manta & Whale Shark Research Centre, Mozambique - Manta ray research

POPULATION ECOLOGY OF MANTA RAYS (Manta birostris)

OVERALL OBJECTIVES

The manta rays are the largest living ray in the ocean. Measured by their wingspan, individuals have been known to reach over 7m in disc width. Like many other large marine megafauna, manta rays are planktivores, feeding on small marine invertebrates and occasionally small fish.

As human pressures increase worldwide manta ray populations have declined in many areas where they were once common. There is a notable contrast between the few reasonably protected populations, such as in Yap and the Hawaiian Islands, where economically valuable ecotourism and dive operations exist, and populations in areas where fisheries target the species, such as along the coast of Africa, South East Asia, and in Mexico. Sadly, due to many of their life history traits mantas are highly vulnerable to over-fishing, and there looms a genuine threat of localised extinction of certain populations.
Currently there are no comprehensive management programs for manta rays anywhere in the world, yet they are listed by the IUCN as ‘near threatened’ or ‘vulnerable’ to extinction throughout their distribution. Acquiring accurate information on population dynamics, lifespan, reproductive parameters, growth rates and natural mortality rates is crucial to understanding the conservation requirements of a species. Additional information on the life history of manta rays is sorely needed to supplement the paucity of existing data.

Site fidelity, movement patterns and habitat usage are also essential pieces of information needed to properly manage a species. This type of information can highlight an animal’s potential susceptibility to fishing pressures and help determine critical habitats and seasonal migration routes. Once biological and ecological information has been acquired however, real efforts need to be made to protect these identified areas.Beyond this, fishing, diving, etc. must be regulated to some degree in order to ensure the sustainability of fisheries and eco-tourism in specific locations that might otherwise receive intense anthropogenic pressure.

Manta & Whale Shark Research Centre, Mozambique - Manta ray research

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