Do Lemon Sharks Attack Each Other? | SharkFest

NARRATOR: The cannibal sharks investigation heads to Bimini in the Bahamas. The mangrove swamps here are a precious nursery for lemon sharks. Every year, scores of pregnant females return to these shallow waters where they were born to give birth. But in a Machiavellian twist that surprised scientists, someone was eating the kids.

TRISTAN GUTTRIDGE: Of 100 newborn sharks born in June of one year, by June the next year, around 50 are left. So 50% of the cohort in every year are eaten or die from starvation.

NARRATOR: This pup is less than two feet long, one of a litter of up to 17 pups. Scientists from the Bimini Shark Lab have been studying the lemons here for more than 20 years. They found the pups can stay up to eight years here, learning to hunt and hide among the twisted mangrove roots. But the shock discovery was the pups' biggest threat comes from their own.

TRISTAN GUTTRIDGE: Everything seems to kick off at high tide. As the water rises, it basically gives access to shallow water areas for big predators to come in as well. That's when these big lemon sharks come in and start patrolling and cruising the outskirts of those mangroves.

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NARRATOR: The young are on high alert. They instinctively hug the mangrove roots which offer some protection. But if they stray too far, the hunt is on.

TRISTAN GUTTRIDGE: For a baby lemon shark that's in close proximity to a big adult, if they haven't seen it before it's seen them, they've got no chance. They can burst attack very quickly and ambush really effectively. I've seen firsthand bite marks. I've seen adults chasing juveniles. You know, we know it's happening.

NARRATOR: It's clear evidence shark cannibalism goes on in the wild. But why would you eat your own?

TRISTAN GUTTRIDGE: The one great advantage that an adult lemon shark has is insider knowledge on where the juveniles are hiding and what tactics they use to avoid predators, because it's been one itself. And that gives it an extra advantage, and probably why they then pick off the juveniles of their own species. What's happening here in Bimini isn't unique. Throughout the world in other nursery areas, big sharks are eating little sharks. It comes down to needing to eat. Why would they not take advantage of that resource?

NARRATOR: And now, new research suggests this has been happening for millennia.