July 16, 2023 —The following was released by NOAA Fisheries:
New research shows that manta rays in Hawaiʻi live in isolated, island-specific, and genetically distinct populations. A team of researchers from NOAA’s Pacific Islands Fisheries Science Center, the Hawai‘i Association for Marine Education and Research, and the University of Miami conducted the first genetic study of reef manta rays in Hawaiʻi. The results were published in BMC Ecology and Evolution. The researchers used genome scans to investigate population differences between reef manta rays of Hawaiʻi Island and Maui Nui (the four-island complex of Maui, Molokaʻi, Lānaʻi, and Kahoʻolawe). Their work reveals that Hawaiʻi Island and Maui Nui populations are made up of only a few hundred individuals each and should be considered distinct and separate. Small and isolated animal populations are vulnerable to disease and extinction. Each island may need separate management strategies to ensure the rays’ long-term stability.
Mantas Stay Close to Home
Reef manta rays are strong swimmers and could easily travel the tens of miles to different islands. However, this study found that these reef manta rays stay close to home and rarely cross the deep channels between islands. Researchers compared differences in the genes inherited by both parents and those inherited only from mothers to better understand migration differences between males and females. They found that females only reproduce at the island where they were born. Migration rates are equivalent to one female moving between island groups every 1,300 years and one male only about every 64 years.
“We offer the first direct evidence that female reef manta rays reproduce close to their birthplace, which leads to strong genetic isolation of populations,“ said Dr. Jonathan Whitney, an ecologist at NOAA’s Pacific Islands Fisheries Science Center and lead author of the study. “Ultimately, this means that each island population is demographically on its own. So if the manta population in West Hawaiʻi declines, they are unlikely to be repopulated by the neighboring islands.”