Two spotted eagle rays have set off into the big blue, fitted with new acoustic tags that will help us learn more about the species. 

Scientists at Mote Marine Laboratory successfully tagged the pair of large rays, a 57-pound male and 77-pound female, before releasing them off Florida's Longboat Key recently. 

The tags* work by sending an ultrasound signal to one of many hydrophones scattered throughout the Gulf. The Mote team can then download this information once a month to help paint a clearer picture of the rays' movement and behaviour as they cruise local waters. 

Since the project began back in 2009, biologists have tagged and released around 540 eagle rays – and although a fair bit of intel has come through in recent years, we still don't know much about the rays' distribution, migration, feeding habits, growth rates and reproductive biology. 

"In order to conserve them we need to understand where they go and what they eat," explains Mote Marine Laboratory senior biologist Kim Bassos-Hull. "And we can do this by using various techniques such as satellite and acoustic tagging, new technologies that were not available to researchers 20 years ago."

With wingspans of up to ten feet and a maximum length of 17 feet nose to tail, spotted eagle rays are some of the largest, most recognisable fish in Florida waters. They are also protected here, and Mote scientists have found rays of every age, from pups to adults.

But in federal waters, these fish aren't so lucky. The Mote team hopes the tags will provide clues about where the species is overlapping with fisheries in nearby Mexico and Cuba, where eagle rays are still caught for food.

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Image: Mote Marine lab

The study is the first of its kind in the Gulf of Mexico, and also has potential to uncover the secrets of spotted eagle ray reproduction, and to give us a clearer picture of their strongholds. "This information is crucial, because spotted eagle rays are a good indicator of the overall health of the ecosystem," says Bassos-Hull.  

The rays' large snouts are the perfect tool for sniffing out prey on the silty ocean floor. Special electro-receptors within the bulbous appendage help spotted eagle rays locate prey, and crushing jaw plates just behind the snout make light work of tough mollusc shells.   

Because these rays feed primarily on a diet of small molluscs like snails and clams, a drop in ray populations could have a top-down effect on the rest of their habitat. "Understanding how they impact this resource is important for safeguarding the health of our oceans," adds Bassos-Hull.

* For those of you wondering, the tags do no hurt the rays. Designed to pop off on their own over time, they are fitted during a quick workup, which lasts just a few minutes.