The broad scale aims of this project are to implement a long-term study of the Mariana Islands reef-associated manta ray (Manta alfredi) population which will result in effective conservation management practices and facilitate outreach programs for this species in the region. Through robust study methods we aim to gain new insight into the dynamics of the smaller populations of these animals with a specific focus on previously undocumented feeding behaviours.
- Identify Areas of Key Habitat
- Estimate Population Size
- Population Structure
- Investigate Feeding Behaviours
- Natural and Anthropogenic Threats
Project Start Date:
Why this is important:
Even with increased research into manta rays in recent years, we still have much to learn about the overall ecology of these majestic animals. Most studies currently being undertaken on the feeding behaviour of manta ray populations globally focus on large populations, such as the Maldives, which have brought to light complex behavioural dynamics during the manta’s feeding aggregations. In the Mariana Islands the population of reef manta rays is small, however, the unique feeding behaviours exhibited by this population are a testament to the adaptability of this species. By understanding mechanisms by which these animals are able to exploit new feeding opportunities here in the Mariana Islands we hope to better understand how manta rays dispersed and colonised the tropical oceans of the world, and which underlying factors drove the speciation of this genus. Understanding these driving forces is essential to implementing effective conservation management plans globally and locally in the Mariana Islands. The implementation of effective conservation measures are increasing important due to the growing anthropogenic threats facing manta rays; tourism, habitat decline, bycatch and targeted fishing are all taking their toll on these species globally.
The 15 Mariana Islands form an arc-shaped archipelago which is perched upon the summits of fifteen volcanic mountains. Situated in the north-western Pacific Ocean they are part of the Pacific sub-region of Micronesia. Composed of two U.S. jurisdictions: the Commonwealth of the Northern Mariana Islands and, at the southern end of the chain of islands, the territory of Guam. The Mariana Islands lie in close proximity to the global central ‘hot-spot’ of coral reef biodiversity so the island’s coral reefs are some of the most species rich in the world. To the people of the Mariana Islands the oceans and their inhabitants have always been extremely important culturally and economically; providing goods and services from tourism, fisheries, and recreation. In the more populated islands, such as Guam and Saipan, scuba diving and snorkelling with manta rays is also fast becoming a growing attraction. However, very little is known about these populations; their size, distributions and possible migration patterns between the islands are all still unknown. Therefore, one of the primary goals of this project is to create a baseline of data gathered from photo-Identification of the individual manta rays which will be used to estimate population size and structure throughout the region. The project will also be focusing on the newly documented feeding behaviours of manta rays in Guam which target fish spawning aggregations, feeding upon their gametes released on mass at specific times of the lunar calendar each month and year. A more comprehensive study of targeted feeding events is needed to improve our understanding of the behaviour and population dynamics that most likely occur at these events. Using photo identification to document the individual mantas present at each of these spawning event over time will allow us to study the social structure of the population. This data will also allow the project to identify the areas of crucial habitat utilised by manta rays around Guam and throughout the Mariana Islands. Acoustic and satellite tagging methods and DNA analysis, coupled with this photo-ID, work will enable the project to build a much clearer understanding of the resident population of manta rays throughout this archipelago.
- Identify manta ray distribution throughout the Marianas Islands.
- Document and examine different feeding behaviors, particularly mantas targeting fish spawning aggregations.
- Study manta population dynamics at targeted spawning events.
- Access and determine local manta ray threats, both natural and anthropogenic.
- Use DNA analyses to determine population structures of the Marianas manta rays.
- Create and initiate community outreach programs throughout the Marianas Islands to educate and bring awareness of manta ray ecology and biology.
- Facilitate the implementation of protective legislation for manta rays within the Common Wealth of the Northern Mariana Islands and Guam to reduce the negative impacts of boat traffic, watercrafts, dive operators, fisheries, scuba divers and snorkelers.
Partners & Sponsors:
Without the generous support and sponsorship we receive we would not be able to achieve our work in the Mariana Islands. We are grateful to the University of Guam Marine Lab, the Dive Force on Guam and in Micronesia (MDA) and Saipan’s premier dive shop, for their support.