The image, taken on Christmas Day, was posted on Facebook by Edwin Pittman who asked if anyone could identify the animal.
Many suggested that it was a sea snake, but the good news for herpetophobes (those with an aversion to reptiles) is that experts say they are not found in the waters around Rarotonga and believe the creature is probably a snake eel.
According to scientist Kirby Morejohn of the Ministry of Marine Resources, a dorsal fin is clearly visible in the image.
“Sea snakes don’t have dorsal fins which automatically rules them out and leads me to believe it is an eel. Due to the low resolution of the photograph, I’d have to guess based on the colour - a terrible trait to ID fish - and would put my money on a peppered moray or a crocodile snake eel,” he says.
“The reports of a flattened head may be explained by the loose tissue that can bulge outward around an eel’s throat and gills.”
His assessment is backed up by Cook Islands biologist Gerald McCormack, who also believes that it was an eel.
He says the behaviour of the creature is in keeping with that of an eel. It had been feeding on shellfish thrown into the water before it was pictured swimming away. The photographer also said it appeared aggressive.
“Snakes only hunt live prey,” says McCormack. “And the idea that it acted aggressively is also completely unsnakelike.”
McCormack says the question of whether sea snakes are found in the Cook Islands is a common one. But he explains that snake eels, which are fish, can easily be confused with sea snakes, which are reptiles.
“Inshore sea-snakes are common on and around the reefs of Fiji, Samoa, Tonga and Niue, but have never been recorded in the Cook Islands. The snake-like creatures in our lagoons are scaleless fish in the snake-eel family.”
Although Niue is well-known for its population of inshore sea snakes, or sea kraits to be precise, they are not found any further east.
Ocean-going sea snakes are found throughout the Pacific, says McCormack, but they do not come into shallow waters. There have been cases of these snakes being found washed up on beaches in the Cook Islands, but there has never been a recorded stranding in Rarotonga, he adds.
Meanwhile, there are several species of snake eel, and other types of eel, found in the lagoons of the Cook Islands.