Life History Analysis and Identification of Potential Nursery Grounds for Juvenile Manta Rays

Abstract

Manta rays are zooplankton consuming filter-feeders that have a global distribution across tropical, subtropical, and temperate waters. There are two recognized species of manta – the Giant Oceanic Manta, Mobula birostris, and the recently resurrected Reef Manta, Mobula alfredi – as well as a putative third species, Mobula sp. cf birostris. Their conservative life history traits, including late sexual maturity, relatively long lives, and exceptionally low fecundity, increase manta vulnerability to environmental stressors and substantially diminish their resiliency. Currently listed as “Vulnerable” by the IUCN Red List, mantas are facing increasing anthropogenic pressure from targeted and bycatch fisheries that harvest their gill rakers for use in eastern medicine. Despite their perception as charismatic megafauna, much is still unknown about the biology, ecology, and life history of mantas, particularly relating to the juvenile life stage. Therefore, this research synthesized knowledge from published literature and identified a widespread lack of data, including glaring gaps regarding sexual maturation and fecundity, lifespan, and the occurrence of and mortality rates associated with natural predation. These gaps, and many more, were especially prevalent within non-adult life stages. From the available data, the following characteristics were isolated and sampled from a known manta ray nursery ground (Flower Garden Banks): water depth, water temperature, productivity, and proximity to deep water environments. These characteristics were applied within the Gulf of Mexico with limited results, though should form the basis for future, more in-depth studies.