Conservation through Research, Awareness and Education

UK Registered Charity Number: 1145387

A pregnant female reef manta ray cruises along the reef at the remote Jarvis Island.

Project Goals:

To study the population sizes and migratory patterns of the manta rays within the remote Line Islands. To investigate the degree of genetic variation and isolation within and between these populations and to undertake a comparative study to determine the impacts of human inhabitation upon the local reef manta ray populations.

Why this is important:

Due to the remote location of the Line Islands and the vast distance they span, very little is known about the mantas that inhabit the waters around them. Genetic assessments of these animals can help us determine how populations interact and whether or not the Line Islands mantas are genetically special to their counterparts worldwide. By establishing population sizes and recognizing migratory patterns, we can better understand how human settlements affect manta aggregations.

Project Overview:

Located in the middle of the Pacific Ocean, the Line Islands are a chain of eleven atolls spread out over almost 2,400 km. Three islands are territories of the United States, while the remaining eight belong to the nearby island nation of the Republic of Kiribati. The Kiribati natives in the Line Islands inhabit only three of their eight islands and have a population under 9,000 with about half of the people living on Christmas Island. This mix of low human occupancy and remote location has attributed to relative anonymity and a thriving marine ecosystem.

Reef manta rays chain feed in the shallow water’s of Christmas Island’s lagoon in the Republic of Kiribati.

Manta rays have been regularly sited along the Line Islands for decades by the few dive shops in the area and passing research vessels. In recent years, gill netting for bone fish has seemingly heavily impacted a thriving manta population around Christmas Island with reported sightings decreasing in the past five years. This project has a rare opportunity to compare the amount of human interaction on populations of manta rays in this region due to the limited number of inhabited islands in the Line Islands chain. By comparing Christmas Island (human population of 5,100) to Jarvis Island (small settlement that was removed in the 1940s) to Kingman Reef (never had inhabitants), we can better understand the anthropogenic impacts, accidental or otherwise.

Palmyra, one of the US territories on the northern end of the Line Islands, was established as a National Wildlife Refuge in 2001. Several institutions have done isolated studies on the resident manta ray, but to date there has been no coordinated effort to study the manta ray populations in detail. We would like to increase awareness for the necessity of manta research in the Line Islands in order to bring together those in the area to collaborate. Working in conjunction with the National Oceanic and Atmospheric Administration, the Nature Conservancy, universities, other governmental organizations, and NGO’s we hope to use photo-identification and genetic sampling to get an idea of the population demographics, life history strategies and overall abundance. We also aim to build on previous acoustic and satellite tagging to show movement around and between the islands.

Main Objectives:

  1. To identify manta populations and distributions throughout the Line Islands.
  2. To use genetics to determine possible distinct populations and hybrids of Manta alfredi and Manta birostris.
  3. To discover the migration patterns, if any, of manta rays along the 2,400 km chain.
  4. To compare population densities around inhabited and uninhabited islands and identify potential anthropogenic impacts.

Partners & Sponsors:

Without the generous support and sponsorship we receive we would not be able to achieve our work in the Line Islands. We are grateful to the National Oceanic and Atmospheric Adminstration Pacific Islands Fisheries Science Center (NOAA/PIFSC) and the Shark Savers organisation for their support.

© 2017 Manta Trust