Photo identification (Photo ID) is the term used to track individual animals based on their unique body patterns. Photographs of animals showing these provide a data record of when and where the animal was sighted. Manta rays have unique body patterns on their ventral surfaces (bellies). They are born with these markings and keep them through their lives. Therefore photo-ID provides a ‘natural tag’ so that individual animals can be followed in space and time. Manta rays are curious animals and if they do not feel threatened they will spend considerable time around scuba and free divers in the water while generally undertaking their normal feeding or cleaning behaviours. This gives divers a great opportunity to photograph manta rays and to take those informative belly shots.
Discovery from photo identification
Photo-ID methods are used in many different research applications. The most common application is for estimating population size of mantas using an approach called mark-recapture. In this case the animals are not physically marked but rather the photo provides the initial mark record for that individual. Subsequent resightings and photos of those animals provide the recaptures.
Photo-ID has been used to estimate the size of manta rays populations at several locations across the world including Mozambique, Japan, Indonesia and Lady Elliot Island in the Great Barrier Reef, Australia, where an estimate of 500 reef manta rays visit Lady Elliot Island reefs during winter each year (Couturier et al. 2011).
Photo-ID data has also been used for investigating movement of individual manta rays between different locations. On the east coast of Australia, individual manta rays have been shown to move between Lady Elliot Island and North Stradbroke Island in southern Qld, as well as between North Stradbroke Island and Byron Bay in northern NSW (Couturier et al. 2014).
Global photo-ID databases have been developed for manta rays including MantaMatcher and the Manta Trust databases to examine large scale movements, particularly across international borders.
Photo-ID has been a great tool for following individual mantas in the wild to find out how old they are and how often they produce pups. Meet Taurus. He was first recorded by Project Manta in 2009 at Lady Elliot Island by Kathy Townsend. Since then we have recorded him almost every year including June 2016.
Photo credit: Lydie Couturier
We were able to obtain old photos of mantas from Peter Allen and were able to match Taurus from 1985 when he was already a mature male. That means that Taurus is at least 40 years old and definitely a resident of eastern Australia as he has been sighted at Lady Elliot Island a total of 39 times.
Research directions
Project Manta currently uses photo-ID data to address several major research aims:
Obtaining population size estimates for key aggregation sites in Western Australia (Coral Bay) and Eastern Australia (North Stradbroke Island, Lady Elliot Island) as well as a total, Australia-wide estimate.
Examining the movement patterns of manta rays around key aggregation sites in Australia as well as comparing with global databases to look for movement across international borders.
Examining the importance of key sites. Manta rays visit aggregation sites to feed, visit cleaning stations and mate among other reasons. Photographs of mantas at key aggregations sites can provide critical information on the frequency that mantas use different areas as well as the behaviours they are displaying.
