The secret life of manta rays

Have you ever wondered what manta rays on the Great Barrier Reef do when we're not watching? World first research might have answered that question and many more - but not without a major team effort. Project Manta's Christine Dudgeon explains.

In a world-first, researchers fitted a manta ray with a satellite tag in the waters off Cairns.The collaborative effort between the Biopixel Oceans Foundation and UQ’s Project Manta then tracked the manta ray’s movements for six months.  The aim was to discover if the more elusive manta rays of northern Queensland might be a separate population to the more frequently sighted mantas living in southern Queensland waters.

Manta rays may seem like large, obvious animals, but finding one within the massive area of the northern Great Barrier Reef was a challenge in itself. Our search for a ‘host’ involved a plane, a boat, a drone and one brave snorkeller. An aerial survey supported by GSL Aviation located our manta ray among the coral reefs off Cairns, then radioed a boat-based research team which travelled to the reef to send up a drone pinpointing the position of the manta. Finally, a researcher snorkelled out to attach a tag to the manta ray. 

That 10cm tag with its 20cm antenna hitch-hiked with our manta ray for six months before detaching in waters north of Cooktown. Then came challenge number two – finding a veritable ‘needle in a haystack’.  Although the tag itself is worth a few thousand dollars, the data collected and stored in its memory over its travels is priceless. Tags do transmit some useful information for a while after detaching from their hosts, but the resolution is coarse and signals are often corrupted.  Our intrepid tag eventually washed up on a remote and rugged stretch of beach near Hope Vale, below the Cape Bedford peninsula. But that was only half the tale.

Image: Amelia Armstrong

Image: Amelia Armstrong

Retrieving the tag from the beach proved to be a four-day, six-person task. Our research team contacted the Elim Beach Campground, located on the other side of the Cape Bedford Peninsula.

Frank Lowie answered the call and for three days headed out of his beach buggy at low tide to search for the device, only to come home empty-handed each time.

Enter Biopixel’s Tai Inoue, who flew north with goniometer equipment borrowed from Cairns CSIRO. A goniometer is a manual tracking device with a sensitive directional antenna and receiver which decodes satellite transmissions. Tai joined forces with ranger Barry Lyon and his wife Shelley from Cooktown – keen beach fossickers familiar with the region. After two hours combing the beach in the fading afternoon light, Tai spotted a bright blue, 10 cent coin-sized object in the sand. It was nestled at the high-tide mark between a wetsuit and two mackerel lures. That small patch of blue was the only part of our tag that was visible.

Retrieving the tag allowed us to download amazingly detailed data that would otherwise have been lost – most excitingly, recordings of temperature, light level and depth every three seconds for its entire deployment. This information means we can estimate the manta ray’s position for the entire six months it was tagged. Preliminary results suggest that this manta remained a a north Queensland local,  moving between Townsville to the south and Cooktown in the north, as well as making several deeper dives down to 400m off the edge of the continental shelf.  Our data supports the idea that northern Queensland’s manta rays do indeed behave as a separate population to those further south.

Found it!

Found it!

Our needle in the haystack

Our needle in the haystack

A new round of tagging research will get underway later this year in North Queensland on both the eastern and western sides of Cape York. This work will accompany more photo-identification studies to compare individually identified animals between different Australian and regional sites.

There's still a lot more to learn about the habits of manta rays, so these studies offer researchers an exciting way to take those journeys with them.

Image: Amelia Armstrong

Image: Amelia Armstrong

The University of Queensland’s Project Manta is funded by an Australian Research Council-Linkage Grant, Austral Fisheries, TJ Kailis Marine Conservation Fund, and Lady Elliot Island Eco Resort.

The Biopixel Oceans Foundation and James Cook University Megamouths project is funded through the Run for the Reef Marathon.