A Vanishing Act: Maui’s Mysterious Manta Rays

By SERENE GUNNISON

The shallow channels between Maui Nui’s four islands attract scores of humpback whales every winter. But these waters are also a preferred habitat for another marine giant: hahalua, the majestic manta ray.

The four islands of Maui Nui are home to the largest known population of manta rays in the U.S., with more than 600 cataloged individuals. Unlike the conspicuous humpbacks, manta rays are far more elusive – and increasingly so.

When Lāhainā-based Mark Deakos, a researcher for the Hawai‘i Association for Marine Education and Research (HAMER), started studying Maui’s mantas in 2005, he averaged more than six manta sightings per dive.

Today, Deakos is lucky to spot one in 20 dives. “This could be an indication that population numbers are declining, or that they are no longer visiting the area,” Deakos said.

Twenty years ago, manta sightings were all but guaranteed at a “cleaning station” off West Maui. Here, mantas would congregate as cleaner wrasses nibbled away at parasites inside their gills and mouth. However, Deakos believes due to declining reef health, wrasses are not as reliably present at the cleaning stations, causing the mantas to abandon them. Where are they going? “We are trying to figure that out,” he said.

Deakos and his team are examining

18 years of data to better understand if the population is growing, stable or in decline. Based on genetic samples taken of mantas in Maui Nui and Hawai‘i Island, they discovered that these two populations are genetically isolated, meaning they don’t mix, furthering each population’s vulnerability.

Manta rays are a slow-growing species, with females giving birth to a single pup only once every three to seven years. The mantas’ slow birth rate coupled with an uptick in human-caused hazards could spell trouble for Maui’s manta population, Deakos said.

While some protections exist for mantas in Hawai‘i, they pale in comparison to the slew of regulations that safeguard threatened and endangered sea turtles, monk seals and humpback whales. More research is needed to properly protect Maui’s mantas, but Deakos says mitigating storm water runoff that threaten our reefs and establishing a marine protected area for manta critical habitat could be beneficial.

Divers who spot manta rays statewide can help with research by emailing photographs of the manta’s unique belly spot patterns to HAMER at reportmanta@mantatracker.com.

If you’re lucky enough to see a Maui hahalua, its graceful underwater ballet is sure to amaze, inspire and ignite hopes for the population’s utmost protection.

Adult manta rays living in the waters of Maui Nui have 12-foot wingspans and weigh 1,000 pounds. Manta rays are a slowgrowing species, with females producing a single pup only once every three to seven years.