Tracking manta movements

On Wednesday, we had a visit on the Carolyn Chouest by Emma Hickerson and Rachel Graham who are conducting their research on another boat, the M/V Spree. Between live broadcasts, I had a chance to ask Rachel about the progress of her work on manta rays. Rachel and another researcher, Dan Castellanos, are interested in finding out how and why mantas move from place to place. 

Rachel described the work they had accomplished on their first scuba dive the previous day. The dive had two objectives: the first was to place acoustic tags on manta rays they found.The tags send out sound waves that can be detected and recorded by underwater acoustic receivers, allowing Rachel and Dan to collect data on mantas and their movements. The second objective was to retrieve an acoustic receiver they had placed earlier on West Flower Garden Bank, so that they could download any data the receiver had recorded.

During the dive, they saw two manta rays. The first one measured 10 ft (3m) across. They were excited to see that this ray had one of their acoustic tags, but interestingly, when they retrieved their acoustic receiver data they found that the manta's tag had not been recorded. They concluded that they must have tagged the animal back in 2004 and that the battery inside the acoustic tag had died. The second manta was smaller and had no tag. Unfortunately the currents in the water were too strong for them to tag the animal.

The acoustic receiver at West Flower Garden Bank did contain data on three mantas that had been tagged in 2005. Two of the mantas had been tagged on East Flower Garden Bank, 12 mi (19 km) away. The third manta was tagged at Stetson Bank almost 40 mi (64 km) away. This shows that the manta rays are moving between the different banks in the sanctuary. The question is why. One hypothesis is that the banks are important habitats for young mantas because all of the mantas that have been tagged and recorded have been relatively small.

While the evidence shows that manta rays are moving between the banks, scientists still don't know how far mantas really travel. Do they stay in the area of the Flower Garden Banks, or does their range extend much farther? More research is needed.

And with that update, Rachel and Emma headed back to the Spree. Meanwhile the team on the Carolyn Chouest continued the survey of East Flower Garden Bank and the exploration of the brine seeps.