Interesting for manta-loving divers visiting the Philippines – and significant for focusing conservation efforts – is the compilation of a national population database that has identified four ray hotspots.
The new collaborative scientific study was led by the Large Marine Vertebrates Research Institute Philippines (LAMAVE) in collaboration with the UK-based Manta Trust, other research bodies and citizen-scientists.
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The database was compiled from a combination of sightings by LAMAVE researchers and partners, contributions from dive-centres, submissions on digital platforms such as Manta Matcher and reports on Facebook, Instagram, YouTube and other social media.
Of the 2,659 sightings analysed by the team, 499 individual mantas were able to be photo-identified using their unique belly spot patterns. Reef mantas (Mobula alfredi) and oceanic mantas (Mobula birostris) were seen distributed between 22 sites, with both species observed at half of these locations.
The four hotspots where aggregations occurred hosted 89% of all the individual manta rays, with cleaning, courtship and feeding behaviours observed there. They were the protected Tubbataha Reefs Natural Park in Cagayancillo, Palawan – already well-known by international scuba divers – San Jacinto in the Ticao-Burias Pass Protected Seascape and two unprotected areas, Puerto Princesa City and TayTay, both also in Palawan.
“Ticao Pass is one of the Bicol region’s key marine biodiversity areas, known to be home of filter-feeding megafauna like whale sharks, megamouth sharks and mobulas,” commented senior fishing regulations officer Nonie P Enolva, explaining that the area was particularly rich in planktonic nutrients. “The protection of this important fishing ground would also mean the protection of the many marine species that are dependent on it.”
Insight into movements
The data on 107 individual oceanic mantas provided an insight into their movements. The first recorded movement of an oceanic manta between Philippines sites came with a female first sighted in Daanbantayan, Cebu in 2009, seen again in San Jacinto in 2014 and then again back in Daanbantayan in 2017. Another individual made a similar journey that same year, covering a distance of more than 80 nautical miles in five days.
Other records from Daanbantayan also revealed the longest resighting interval, for two individuals that were seen in the area again after eight years. Six other individuals were sighted there in at least two different years.
A total of 392 individual reef mantas were identified between 2004-2020, and more than 90% of these favoured San Jacinto, Taytay and Cagayancillo. In these areas, 66-80% of the mantas identified were seen more than once, most often at cleaning stations.
However, a quarter of the San Jacinto and Taytay rays displayed fishery-related injuries such as damaged or missing fins or severe cuts. An abundance of fishing gear was also noted to be entangled in the reef at the San Jacinto cleaning sites.
Sightings of oceanic mantas in Daanbantayan dropped from 73 between 2006-2012 to only 16 between 2013-2019, despite increased scuba diving in the area, while San Jacinto showed a similar trend with 15 sightings between 2013-2014 but only three between 2017-2019.
The report attributes this “alarming 80% decline” to fishing in the rays’ assumed range, such as in the Bohol Sea. It urges the urgent adoption of conservation strategies such as marine protected areas and fishing-gear regulations at the hotspot sites, especially the currently unprotected Taytay and Puerto Princesa City.
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