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  • By Pacific island Times News Staff

Increased human traffic disturbs Guam manta ray habitat

Guam manta rays have been showing distressed behavioral changes over the past month as a result of increased disturbance to their natural habitats, according to scientists working with the Micronesian Conservation Coalition.

MCC said the growing number of curious residents and visitors in the habitat area indicates the enthusiasm for the Guam mantas. However, the researchers have witnessed and documented excessive chasing and touching of the mantas, which have resulted in distressed behavioral changes in such a short time.

“We are very concerned about the increased traffic of people in the mantas’ habitat, as this introduces an unnatural interference. The mantas target certain fish spawn in the area, which are also disturbed by excessive human presence,"said Julie Hartup, MCC executive director.

"The mantas are unable to feed unobstructed or even perform natural mating . When people dive down to take photos, this cuts off the unique ‘mating chain,’ as male mantas pursue a single female manta," she added.

According to MCC, Guam's manta rays have a micro-population with only 53 different individuals documented over the past 10 years. A typical “small” population is around 300 individuals, so Guam's manta ray population is comparably very small, making i highly susceptible to any threat, either man-made or natural. Because of certain physical features, Guam manta rays are thought to be a possible hybrid between the reef and pelagic manta rays, said MCC, which is actively researching the local local species.

Concerned over the increased disruption, the scientists are seeking support from the island community to preserve the habitats of the small population of Guam manta rays.

The impact includes the noticeable departure of members of this very small group of manta rays. More importantly, these undue interactions are changing the natural mating and feeding behaviors of the Guam mantas.

The organization and its supporters are respectfully appealing to recreational ocean enthusiasts to please avoid the manta rays’ habitat area. Snorkelers or paddles boards congregating at one time creates a “hard surface” on the water. This negatively impacts the mantas as they feed around the reefs and cruise along the ocean surface to feed.

Also, human presence impacts mating patterns, as they move from the ocean deep to the surface, sometimes involving individual mantas leaping out of the water.

Creating a “hard surface” on the water makes it impossible for mantas to exhibit natural behaviors in smaller, shallower areas.


"The organization’s plea is to respect and not disturb these areas to help maintain the ecosystem mantas need to survive,"MCC said. "Swimmers, divers, paddlers and motor operated ocean vessels are asked to please understand and help protect the sensitive, unique and small population of Guam mantas rays."

The MCC research team is made up of trained local scientists, using guidelines set out by the international NGO Manta Trust on how to study and approach manta rays as researchers.


MCC has issued the following guidelines for visitors:

- Keep your distance (safely 33 feet from a manta ray).

- Do not swim or dive down directly straight at the manta ray. This naturally forces them to turn and move away.

- Never touch a manta ray. They have a mucus covering to protect them from bacteria and forms of microbes. Touching mantas scrapes off the protective covering, which makes them susceptible to infections.

- If mantas approach you on their terms, stay still.

Do not chase, splash, or scream. They might stick around longer to check you out. Since mantas have the biggest brain for fish, they do display curiosity.

- Do not use any flash photography strobes or video lights. Guam manta rays are not used to this, as it creates agitation and is very disruptive.

- If you come across a MCC research team in the water (wearing attire displaying the MCC logo), and they are not busy on the surface, you are welcome to ask them questions you may have about the mantas.

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