A place where reef manta rays thrive

In rare good news from the marine world, scientists have found a place where reef manta rays are thriving.

In a decade, populations have increased dramatically in the Raja Ampat archipelago in Indonesia, highlighting the importance of long-term conservation and management measures such as marine protected areas (MPAs) and well-enforced fishing regulations. , explains researcher Edy Setyawan, from the University of Auckland. Institute of Marine Sciences.

This is the first published evidence populations of reef manta rays are increasing all over the world, he says. “Despite the global decline of oceanic sharks and rays due to overfishing over the past 50 years, the manta rays on the reefs of Raja Ampat have recovered and are thriving,” Setyawan said.

The scientist and his colleagues studied reef manta rays (Mobula Alfredi) in two of the largest MPAs in Raja Ampat, Dampier Strait and South East Misool. They used sightings of rays, each individually identified by photograph, to assess population dynamics from 2009 to 2019. In Dampier Strait, the estimated population increased to 317, a compound annual gain of 3.9%, while South East Misool’s estimated gain at 511 was 10.7. % on the same basis.

The increase in population size resulted from high survival rates (up to 93% of individuals in each group survived each year) and high recruitment rates (generally groups received a 20% annual increase new members). While conservation measures greatly reduced fishing pressures, another reason populations thrived was the climate cycle of the El Niño Southern Oscillation, which boosted plankton numbers. This led to larger and more frequent aggregations of manta rays to feed, which in turn provided more mating opportunities.

A watch list of threatened species, the International Union for Conservation of Nature’s ‘Red List’, lists the reef manta ray as a ‘vulnerable’ species with declining populations throughout its range in the United States. ‘Indo-Pacific, based on an assessment in 2018.

Today, it is estimated that 16,000 to 18,000 of these creatures may survive, with the Maldives hosting the highest number, at least 5,000 individuals, followed by Indonesia with at least 3,500. “Unfortunately, the manta rays of the Reefs are generally in decline, such as in Mozambique where they have been continuously caught in targeted fisheries, or simply holding steady, such as in Australia and the Maldives,” says Setyawan.

Around the world, more well-enforced MPAs are needed to protect the critical habitats of the creatures, along with strong commitments from governments to protect the species and restrictions on fishing gear such as banning gillnets and nets. longlines, he said. Manta rays are known for their intelligence, graceful swimming and traits such as somersault feeding, a technique to keep moving while staying in one place to gorge on plankton or krill. Manta rays must keep moving to stay alive.

The reef manta ray has a wingspan of up to five meters. This slow-growing species begins to mature between the ages of nine and 13 (male) and between 13 and 17 (female). An adult female gives birth to a single young every two to six years, after 12 to 13 months of gestation. Late maturation and low fecundity make the species particularly vulnerable to population declines.

The research, published in Marine Science Frontiers, was carried out with the help of researchers from the Raja Ampat MPA Management Authority, Konservasi Indonesia, Conservation International Aotearoa and Waipapa Taumata Rau, University of Auckland. “Since the end of the study, the reef manta rays seem to be doing well and the populations continue to grow,” Setyawan says. “Large feeding aggregations have often been observed and reported. Over the past three years, we have identified over 300 new manta rays. Not to mention the hatchlings and juveniles living in the Wayag lagoon and the nursery areas of the Fam Islands that we discovered recently.

– This press release was originally published on the University of Auckland website

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