CONNECTED

SEAS

To help conserve life in the ocean, researchers

are following marine organisms’ movements.

BY CATHERINE OFFORD

W

hen it comes to telling manta

rays apart, Asia Armstrong is

an expert. The University of

Queensland PhD student is studying popu-

lations of Mobula alfredi, the reef manta, in

the Great Barrier Reef Marine Park off the

northeast coast of Australia, and has spent

countless hours poring over photos of the

fish—snapped by citizen scientists as well as

by Armstrong and her colleagues over several

decades—with the aim of identifying indi-

viduals. “Manta rays have a unique spot pat-

tern on their ventral surface—smudges, dots,

stripes,” she explains. In a database of around

1,300 individual animals, “I’d probably recog-

nize half of them now.”

For the past few years, researchers have

been working under the assumption that

local manta populations are split between

two main regions, a northern one and a

southern one, separated by hundreds of kilo-

meters. But a video Armstrong received last

June from a dive site off the coast of north-

ern Queensland in between the two sup-

posed ranges threw that assumption into

doubt. The video showed two manta rays that

Armstrong immediately recognized as mem-

bers of a population inhabiting the southern

region. Indeed, the rays had last been seen

some 1,150 kilometers south of the dive site—

a distance almost double that of the longest

recorded movement for a reef manta. Pho-

tographs submitted a few weeks later con-

firmed the find: one of the two mantas had

been spotted again swimming around the

same site.

“Until this point, everything we had [on

the mantas] from northern Queensland

didn’t match anything from southern

Queensland... and we didn’t have anything

in between,” says Queensland marine scien-

tist Christine Dudgeon, who coauthored

the study documenting the finding in July.^1

Although it’s unclear whether the northern

and southern populations overlap, the new

data extend the southern population’s range

by hundreds of kilometers to the north, she

says. This information could help research-

ers devise better plans for worldwide con-

servation of manta rays, whose numbers are

decreasing in part due to the many threats

they face from humans, including harvest-

ing for use in traditional Chinese medicine.

The findings are a surprise to local manta

researchers, but they hammer home the

importance of considering marine organisms’

movements through the world’s oceans when

trying to protect them. Research suggests

that lots of animal species, many of them

commercially, culturally, and ecologically

important, could regularly traverse much

larger areas than previously realized, whether

as swimming adults, or, more often, at other

life stages such as larvae or juveniles swept

along by or propelling themselves within

ocean currents. Until now, most species have

been managed and conserved locally, often in

marine protected areas (MPAs)—from strict

“no-take” zones to areas with more-nuanced

rules—overseen by national or regional gov-

ernments. But the constant traffic of individ-

uals from one place to another means that

animals are often moving between areas with

different levels of conservation protection

and administrative oversight. Unless such