One out of every six dolphins in The Bahamas has been bitten by a shark

by • August 8, 2014 • Dolphin News, Dolphin Science, Nature/ConservationComments Off9339

According to a recent study, one out of every six dolphins that live off of the island of Bimini in The Bahamas is sporting some kind of scar from a failed shark predation attempt. Scientists were able to recognize the scars on these Atlantic spotted dolphins as shark bites due to their telltale crescent shape. Oh, and the occasional shark teeth that get embedded in the dolphin’s skin (see below image).

Yes, those are shark teeth embedded in the dolphin's skin.

Yes, those are shark teeth embedded in the dolphin’s skin.

No shark bite scars were found on the dolphins’ heads for this study, with most scars located on the belly, back, and fins. This observation jives with the idea that sharks typically don’t approach their prey from the front, instead preferring the ‘ambush-from-underneath’ technique that results in those shots of great whites flying out of the sea while hunting seals, or this cool footage of sharks sneaking up on and power-chomping the REMUS SharkCam from below.

Although a sizable percentage of the spotted dolphins near Bimini have shark bite scars, there are other dolphin populations that are much more battle-worn. In the aptly named Shark Bay in western Australia, an astonishing 74% of  the local bottlense dolphins are sporting some kind of shark bite scar. This doesn’t necessarily mean that Shark Bay is a hotbed of shark-dolphin predation. In fact, it could be the opposite.

“Even though the Bimini spotteds show fewer scars than bottlenose in other parts of the world it does not mean sharks are less likely to attack a dolphin in Bimini; perhaps the sharks in Bimini are successful more often,” suggest Kelly Melillo-Sweeting of the Dolphin Communication Project, and lead author on the article.

The actual rate of dolphin mortality due to shark predation is difficult to establish, since we only have evidence of shark predation for those dolphins that didn’t get eaten.

Despite dolphins being famous for their ability to fend off sharks, and protect human swimmers from sharks (a controversial topic), dolphins’ primary strategy where sharks are concerned is to avoid them. Predator avoidance likely dictates a lot of dolphins’ behavior, including their choice of habitats, and social/group living. The Bimini dolphins spend most of their time in the shallow sandy bank just offshore, where it’s harder for a predator to sneak up on them.

“They zip over to the deep Gulfstream water to feed and zip back to the bank for everything else. We know from the research coming out of the Bimini Biological Field Station that there is a healthy number of big sharks near Bimini so it seems likely the dolphins would make habitat choices to reduce their risk,” suggests Melillo-Sweeting.

Has anybody seen my dorsal fin? Bruce?

Has anybody seen my dorsal fin? Bruce?

Unfortunately for the Bimini dolphins, it seems that the younger/smaller dolphins receive a fair amount of unwanted attention from sharks. This study found that of the ten dolphins whose ages were known at the time they were bitten, only one was an adult. The rest were chomped on as young animals, with seven of them being calves. Although this means that smaller dolphins are being targeted by sharks, it’s also a sign that the youngsters are able to hold their own. “The fact that we saw more scars on calves tells us, at the very least, that some calves get away,” says Melillo-Sweeting.

No newborn dolphins (neonates) have yet been seen with shark bite scars around Bimini. For some dolphin populations, almost half of newborn dolphins don’t survive the first year of life, and it’s possible that many of them end up in a shark’s belly. Itsy bitsy dolphins are certainly cute, but they are also shark-bite-sized. It’s difficult to say what the lack of scarred neonates tells us about shark-dolphin interactions around Bimini given the lack of data on neonates to begin with.

“It is intuitive to say that a neonate, or even a calf, is more likely to be targeted and killed by a shark than a larger dolphin both because of size and inexperience (and, possibly, speed). But, neonates and calves have their mothers protecting them, so that’s something in their favor,” argues Melillo-Sweeting.

Although many of the shark-bite scars on the Bimini dolphins look gruesome, dolphins are known to be quick healers, so recovering from a nasty shark bite is all in a day’s work. Check out this image (below) of an Indo-Pacific bottlenose dolphin calf that had a huge section behind his dorsal fin removed by a hungry shark. This same dolphin was seen a year later having completely healed from this seemingly fatal injury.

Dolphin Calf Shark Bite

Ouch ouch ouch ouch ouch!

It’s worth pointing out that just because the Bimini dolphins appear to encounter (and get munched on) by sharks on a regular basis, this does not mean that “shark attacks” (a controversial phrase) are common around Bimini. Especially where humans are concerned. In fact, in the many years that researchers have been swimming alongside these dolphins, studying their behavior (and counting their shark bite scars), they have never once seen a shark interact with a dolphin, let alone a human.

“Only once have I seen a dolphin group and a tiger shark even remotely near each other, and even this was still at a distance,” says Melillo-Sweeting.

Dolphins and sharks live together in the same environment, and even though dolphin meat is certainly on the menu for many species of sharks, dolphins and sharks spend most of their time swimming in relatively close proximity without eating/attacking each other. And sharks (and dolphins) spend even less time attacking/eating humans. So you, like 85% of the Bimini dolphins, could spend a lifetime swimming in Bahamian waters with almost zero chance of getting shark teeth embedded in your skin.

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