For the first time, an international team of researchers has used satellites to track the movements of manta rays, providing valuable new information about the massive rays, which are considered “vulnerable” to extinction by the International Union for Conservation of Nature. The preliminary findings for the Atlantic mantas showed that they traveled as far as 680 miles over a one- to two-month period searching for food, sticking close to the coastline. They also spent considerable time in shipping lanes, which rendered them vulnerable to being hit by freighters.
The manta ray, Manta birostris, is the largest of the rays, reaching as big as 25 feet across. Although they are closely related to sharks and are often called “devilfish” because of their frightening appearance, they are actually harmless to humans. The animals are filter feeders, straining large volumes of water through their mouths to extract zooplankton and fish eggs. They are considered vulnerable because fisherman often capture them to use as bait for sharks. Their gill rakers (fingerlike structures that filter out prey) are also used in traditional Chinese medicine.
A team headed by Rachel T. Graham of the Wildlife Conservation Society in Punta Gorda, Belize, attached transmitters to six individuals -- four females, one male and one juvenile -- off the coast of Mexico’s Yucatan peninsula. They reported in the journal PLoS One that they monitored the rays for periods ranging from 27 to 64 days, until the transmitters fell off.
Although the rays traveled as far as 680 miles, they spent most of their time within Mexico’s territorial waters -- that is, within 200 miles of the coastline. Only about 11.5% of the areas they traversed, however, were within marine protected areas, and the majority of their locations were within shipping lanes. The coastal regions they traversed were rich in zooplankton and fish eggs, explaining the rays’ presence there, the team said.
“Studies such as these are critical in developing effective management of manta rays, which appear to be declining worldwide,” said marine biologist Howard Rosenbaum, director of the Wildlife Conservation Society’s Ocean Giant Program.