Keeping tabs on manta rays

This is blog entry posted from the field during the 2012 Phoenix Islands Marine Protected Area (PIPA) Expedition. The Phoenix Islands are an isolated island chain more than 1,000 miles southwest of Hawaii. They are part of the island nation of Kiribati, which partnered with the New England Aquarium and Conservation International to create PIPA in 2008. Today it is one of the world's largest marine protected areas and a UNESCO world heritage site. This voyage is part of a regular series of scientific expeditions to investigate coral health and study ecosystems and biodiversity.

This post is from Kelton McMahon, post-doctoral fellow at WHOI and KAUST after the first day of diving near Kanton Island.

The “fish heads,” as Rob the owner of the Nai’a affectionately calls our group of fish ecologists, sat at the bow of the Nai’a as we pulled into the lagoon of Kanton Atoll. We discussed what we hoped to accomplish during our four day stay at Kanton, and at the top of everyone’s wish list was to see (and tag) at least one giant manta (Manta birostris).

A giant manta (Manta birostris) cruising past the channel of Kanton Atoll in the Phoenix Islands. 
(Kanton Island)

We arrived with just enough time to do a drift freedive through the channel into the lagoon before dinner. With a bit of optimism, or perhaps a fear of Murphy’s Law, we brought a GPS-enabled, pop-up satellite archival tag (PSAT) with us knowing that if we didn’t, we’d surely regret it. We tried our best to fight the impressive current as long as possible, but as the light began to fade we bobbed together at the surface chatting about our plans for the next day.

 Kelton McMahon and Camrin Braun (Woods Hole Oceanographic Institution scientists) examine manta dive profile data from a previous tagging expedition as preparation for the manta migration study conducted in the Phoenix Islands.  (Enderbury Island)

Almost as if on cue, a large manta emerged in the distance.  As the manta slid past us, hovering just above the reef, Mark “Sparky” Priest hovered into position above the ray to apply the tag. With nearly ten fin strokes for every flip of the manta’s wings, Sparky honed in on his target. In a split second, he administered the tag, and the dive ended in a torrent of adrenaline and huge smiles. During the rest of our stay, we tagged one or two mantas each day, including a last minute arrival on our final dive at Kanton. In total, we sent out seven tags, happily exceeding our initial goal of three.

A Giant manta (Manta birostris) recently fitted with a GPS-enabled satellite archival tag near the base of its tail. 
(Kanton Island)

The purpose of the tagging project is to understand the movement patterns of large pelagic fishes like giant mantas by implementing GPS-enabled, PSAT tags. These devices record and store temperature and depth every 10 seconds for a nine month deployment, in addition to logging GPS locations every time the manta visits the surface.

A GPS-enabled satellite archival tag that will record manta locations, dive depths, and water temperature for nine months before popping off and delivering data via satellite to researchers at Woods Hole Oceanographic Institution. 
(Enderbury Island) 

This information helps us understand how these fish move around these widespread South Pacific islands and, potentially, what influences these movements. [Learn about tracking currents in this part of the world in this recent expedition post.] Tracking mantas can also improve our understanding of the effectiveness of protecting large swaths of the ocean like here in the Phoenix Islands Protected Area. The tags are programmed to burn their tethers and “pop-up” around March 1, 2013. Until then, our fingers will be crossed that the tags and their tethers function as planned.

-- Kelton

1 comment:

  1. there was a school of 15 to 20 mantas in the passage at the right of the entrance riding the current behind the wreck.
    also a school of bottlenose dolphins seeing everyday, riding the bow waves of our dinghy.
    wondering if they are still there?