Secrets of manta ray behavior revealed

Reef mantas (Mobula alfredi) are among the largest and most iconic of marine species. They are widely distributed in the tropical and subtropical waters of the Indian and west Pacific Oceans, where they mostly frequent shallow waters along the coastal reefs of continents and oceanic islands. Because of their beauty and graceful behavior, these manta rays are hugely popular with divers and snorkelers, who travel from afar to places where the rays congregate, in order to view them underwater. 

The Komodo National Park in Indonesia is just such a place. Mantas are present all year round in the waters of this National Park, which is itself a UNESCO World Heritage Site where the famous Komodo dragons are protected. Dive tourists come to view the mantas, which grow up to 5m in length, as they feed in the shallow waters, visit ‘cleaning stations’ on the coral reefs to have parasites removed by small fish, or even display courtship ‘trains’ as part of their reproductive behavior. 

Dr. Andrea Marshall, principal scientist and co-founder of the Marine Megafauna Foundation saw the potential to engage the public with data collection on these threatened and understudied marine animals and worked with software company WildMe to develop an online wildlife database platform (MantaMatcher.org) to match and catalog manta rays in different populations around the world.

Scientists from the Marine Megafauna Foundation and Murdoch University approached local dive operators to promote the development of a data bank of the manta rays in the waters of the Komodo National Park. They asked that visitors take photographs of the mantas they encountered, and then submit them to MantaMatcher.org for identification and analysis. In this way, the scientists hoped to monitor the movement patterns and demographics of the mantas in the area. 

“People love manta rays – they are one of the most iconic animals in our oceans. The rise of the number of people engaging in SCUBA diving, snorkeling and the advent of affordable underwater cameras meant that photos and videos taken by the public during their holidays could be used to quickly and affordably scale data collection,” said Marshall, who was co-author of the study.

Individual mantas can be identified by the unique patterns of dark marks on their ventral surface and so the photos could be used to track individuals and monitor their movements. The project ran for 5 years, between 2013 and 2018, during which time   3,941 sightings were submitted by citizen scientists and 1,085 different reef mantas were identified. The photographs, along with time and location information, were used to construct siting histories of individual manta rays, which could then be analyzed with statistical movement models. 

The results, published today in the open-access scientific journal PeerJ, indicate that some manta rays moved mostly within the area of the Park, whereas others traveled as far as the Nusa Penida MPA (more than 450 km to the west). Interestingly, most of the mantas had favorite spots that they inhabited within the Park. 

“I found it very interesting how some manta rays appear to prefer spending their time in some sites more than others, even when sites are 5 km apart, which are short distances for manta rays,” said study lead author Dr. Elitza Germanov. “This means that manta rays which prefer sites where fishing activities continue to occur or that are more popular with tourism will endure greater impacts.” 

Mantas in the Komodo NP are threatened by two major factors. Although fishing activities have been prohibited in many coastal areas within Komodo NP since 1984, illegal operators and the movements of mantas out of the Park and into heavily fished waters, have continued to take their toll. About 5% of Komodo’s manta rays have permanent injuries that are likely the result of encounters with fishing gear. 

In addition, tourism activity in the Komodo NP continues to increase. During the study period the researchers recorded a 34 percent increase in the number of tourist boats visiting manta ray sites.  The associated disturbance from divers and snorkelers can have a negative impact on manta rays and their habitats. In 2019, the Komodo National Park Authority introduced limits on the number of boats and people that visit one of the most famous manta sites. 

“This study shows that the places where tourists commonly observe manta rays are important for the animals to feed, clean and mate. This means that the Komodo National Park should create measures to limit the disturbance at these sites,” said Mr. Ande Kefi, an employee of the Komodo National Park involved with this study. “I hope that this study will encourage tourism operators to understand the need for the regulations already imposed and increase compliance,” he adds. 

The authors of the study also recommend limiting the number of tourist boats allowed at one time at all manta ray aggregation sites, and enforcing codes of conduct for divers that ensure minimum impact from tourism. In this way they hope that Komodo’s large ray aggregations will be protected into the future. The study also highlights that marine protected areas that are large enough to host important manta ray habitats are a beneficial tool for manta ray conservation.

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By Alison Bosman, Earth.com Staff Writer