Oceanic manta rays-often thought to take epic¹ migrations²-might actually be homebodies, according to a new study. A Scripps Institution of Oceanography at the University of California San Diego-led research team studied satellite-tracked manta rays to shed light on the lives of these mysterious ocean giants. Manta rays (Manta birostris) spend much of their lives swimming in remote open-ocean environments, such as on seamounts and offshore³ islands, in search of tiny free-floating plankton⁴, their main source of food. They can live for over 40 years and reach a wingspan of up to seven meters (23 feet).

 

The findings, published in the journal Biological Conservation, have important implications for the conservation of the threatened species.

 

To better understand their travels, the researchers tagged and collected muscle tissue samples from the rays at four different sites in the Indo-Pacific separated by 600-13,000 kilometers (373-8,078 miles), to see if the local aggregations⁵ of mantas were in fact a network of highly connected subpopulations. 

 

Using the tagging information, which included up to six months of data on their movements, along with genetic⁶ and stable isotope⁷ analyses on the collected tissues, the researchers found that manta rays remained close to their tagged location, and are very likely distinct subpopulations with very limited connectivity between regions.

 

"These animals are showing a remarkable⁸ degree of residency behavior compared to the migrations we were expecting," said Scripps Oceanography PhD candidate Joshua Stewart, a researcher in the Scripps Gulf⁹ of California Marine¹⁰ Program and the study's lead author. "While mantas do make the occasional long-distance movement, it appears that the norm is to stay put. This means that any one population of mantas is highly susceptible¹¹ to fisheries and other human impacts, but that local populations are also more easily protected."

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