Patterning can be used to identify individuals
Their inky backs boldly patterned with white spots, spotted eagle rays are among the most graceful and photogenic fish in the sea. However, new research has revealed these striking patterns are not only beautiful but unique.
Conducted by Maria del Socorro González-Ramos, a doctoral candidate at Mexico’s Instituto Politécnico Nacional, scientists analyzed images of 192 individual spotted eagle rays from the Chacahua Lagoon in Oaxaca, Mexico, an area believed to be a nursery for the species.
To keep track of individual rays, researchers fastened a unique tag to each fish. Socorro González-Ramos and her team then utilized photo identification software to calculate how reliably a ray’s spots could be used to identify it. They discovered a ray could be accurately identified from a photo 88.2 percent of the time.
As a scientific technique, photo identification is best known for its applications for studying humpback whale tail flukes. However, other animals also have identifying traits including: polar bears’ whiskers, great white sharks’ dorsal fins, and whale sharks’ spots.
Simon Pierce, a marine biologist with the Marine Megafauna Foundation not involved with the study, emphasized that when the study was performed carefully and correctly, photo identification is a fickle technique. It is imperative to determine individuals do possess unique markings and that remain stable over time.
If the technique is used improperly, individuals appearing multiple times may be misidentified as multiple individual animals. “That could inflate estimates of population size and lead to individuals appearing more transient than they really are, and that’s bad news for management and conservation,” says Pierce. “You could think that there are more animals left than there really are, or that they are less likely to be impacted by local human activities than is really the case.”
With assistance from tourists acting as citizen scientists, photo identification allows researchers to accumulate substantial volumes of data. Tens of thousands of tourists ‘photographs have identified more than 8,000 individual sharks. “Anyone with a camera—scientists or non-scientist—can help with population monitoring in these species,” said Pierce.
Now that photo identification has been validated for spotted eagle rays, Socorro González-Ramos is optimistic it can be utilized to obtain additional data on ray populations, as they are often caught as fisheries by-catch in Mexico.
“The spotted eagle ray population at Chacahua Lagoon still has many things to show us about the biology, reproduction, and demography of this species,” added Socorro González-Ramos. Despite promising results, “so many things remain unknown.”