Numerous scuba divers in places like Australia’s imperiled Great Barrier Reef have reported what they interpreted as unprovoked attacks from venomous sea snakes, especially the olive sea snake which can reach lengths of around six feet. Divers say the snakes, which breathe air but spend their entire lives in the ocean, sometimes come hurtling out of the blue swimming in rapid zig-zags straight at the person. These encounters almost never result in recreational divers getting bitten, but the apparent aggression from animals packing deadly neurotoxic venom is enough to alarm most who experience it firsthand.
Now, new research reveals that these charging sea serpents likely harbor no malice toward the humans visiting their home. Instead, the paper, published today in the journal Scientific Reports, suggests these underwater dust ups are actually cases of mistaken identity, with the understandably shaken divers having been caught in the crossfire of the sea snake’s urgent quest to find love during the winter mating season.
“Wild animals don’t attack people without good reason,” says Rick Shine, evolutionary biologist at Macquarie University in Australia and the study’s senior author. “Snakes on land almost never attack people but there were all these stories about sea snakes doing it. Why the hell would a sea snake race towards a person underwater?”
Shine’s co-author Tim Lynch, a scientist with Australia’s Commonwealth Scientific and Industrial Research Organization, happened to be sitting on an unpublished data set with the potential to answer that very question. Back in 1994, Lynch had spent 250 hours scuba diving around the Keppel Islands in the southern Great Barrier Reef to study olive sea snake behavior for his PhD thesis. Lynch would record how many snakes he encountered as well as whether they approached him and for how long within individual 30-minute periods.
Shine recalls reviewing the completed thesis with interest but the results weren’t published in a peer-reviewed journal at the time. Then, more than 20 years later when the Covid-19 pandemic grounded virtually all field research, Shine approached Lynch about dusting off his data and giving it a fresh analysis.
Shine and Lynch found that out of 158 encounters, 74 included the snake approaching the diver and that these interactions were more common during the olive sea snake’s mating season between May and August. Only 13 of these interactions involved full on charges towards the diver. The onrushing snakes were split almost fifty-fifty by sex, with seven males and six females comprising the group.
At the time, Lynch made some crucial observations about the circumstances of these apparent moments of aggression that ultimately helped him and Shine clarify what might be occurring.
First, all the charges occurred in the thick of the sea snakes’ breeding season. Second, all the charges by male snakes occurred right after the male had been squaring up with a rival male or if the male snake had lost track of a female he had been chasing around the reef in hopes of mating with her. Some of these male snakes even appeared to be getting slightly amorous with Lynch’s flippers—coiling around his fins the way sea snakes do each other during courtship. Finally, all the female snakes that charged Lynch underwater were being chased by hopeful male snakes.
Shine explains that these details, combined with prior research showing that olive sea snakes likely can’t see that well underwater, suggest that the jarring interactions between divers and sea snakes are most likely cases of mistaken identity.
“Male sea snakes have trouble locating females in the first place,” says Shine. “And if the girl runs away and the boy loses touch with her, he might go hurtling over towards any shape he sees in the water. Then once the snake gets there it takes him a little while to realize the large object isn’t the girl he was pursuing.”
In the case of females being chased by males, the divers might have looked like a good place to take refuge such as a hunk of coral. Male sea snakes can be quite persistent, so fleeing for cover is sometimes a female’s best option to ditch an undesirable suitor.
“People almost universally interpreted these behaviors as aggression,” says Shine. “Snakes are often seen as these malevolent beings intent on mayhem, but in this case really they’re just looking for love.”
Lynch and Shine say their findings offer practical information for scuba divers who might encounter olive sea snakes or even other species of sea snakes. “Sea snakes can swim faster than you, so it’s a complete waste of time to try to swim away,” says Shine. “Don’t try to hit the snake or fend it off because that could upset it. Just give the snake a chance to figure out who you are and once they do they will likely head off.”
Despite the fact that bites from sea snakes are rare among divers, Vinay Udyawer, a sea snake researcher at the Australian Institute of Marine Science who was not involved in the study, says these findings provide “very useful information for recreational divers that can help minimize the chances of a negative interaction.”
Providing an explanation for the behavior and clear instructions might also help divers override what for some remains a reflexive fear of a potentially dangerous animal moving rapidly in their direction.
“I know now from enough time spent with snakes that they bear no ill will towards me but it’s one thing to know that and it’s another to feel it when a snake comes racing towards you,” says Shine. “But our work shows you just need to hang in there, stay calm and let the snake work out that you’re not a sea snake or a piece of coral.”