As adults, sand tiger sharks are known to be relatively non-aggressive. But when they were babies, these animals were involved in a cannibalistic war with dozens of their brothers, only one of them was alive.
It’s all part of a natural phenomenon known as intrauterine cannibalism. Sand tiger sharks are probably one of the most famous species. This shark is ovoviviparous, which means that the offspring grow in the eggs in the shark’s uterus until they hatch, and then they go out into the ocean.
“It’s survival of the fittest. The strongest will emerge,” Lizeth Webster, curator of fish and invertebrates at the Long Island Aquarium in New York told CBS News. “The healthiest person will absorb all the nutrients, not enough for others, so they will consume others in the womb.”
NOAA/Sand Tiger Shark Embryo Reproduction and Development, Odontaspis Taurus (Rafinesque)
Sand tiger sharks are known to have two uteri. In each one, the female shark will have between 16 and 23 fertilized eggs. But shortly after teething, the largest and most advanced embryo which is often the first to hatch will kill and eat all its uterine siblings, as well as the remaining yolk sac. After being in the womb for eight to nine months, two pups – one from each uterus – will make their way out to sea.
“That’s how we get top predators,” Webster said. “The strong will survive.”
NOAA/Sand Tiger Shark Embryo Reproduction and Development, Odontaspis Taurus (Rafinesque)
Shark scientists have known about this process for decades. In research published in the NOAA Fisheries Bulletin in 1983, he even provided a visual representation of the process.
In one case, he saw “a large hatched embryo (100 mm) that attacked and severely damaged (puncture wounds and torn intestines) a 51 mm embryo. … It is possible that the 51 mm embryo had not hatched before attacking.”
NOAA/Sand Tiger Shark Embryo Reproduction and Development, Odontaspis Taurus (Rafinesque)
The cannibalism, however, stops when the shark is officially born. Sand tiger sharks, also known as ragged-tooth sharks and gray nurse sharks, tend to eat herring, eels, squid, crabs and lobsters, among other animals.
And no, humans are not on the list. The animal is known to be non-aggressive towards humans, although it will become defensive if necessary. After growing up, Webster described the animal as “quiet.”
“Usually in the wild, they swim in big packs,” he said. “…When there’s a big group like that, they tend to be calmer because they have to swim together with other sharks. They look like they’re floating and calm.”
And while eating their siblings helps ensure that strong pups are born, the species also has a hard time surviving.
The shark, which can grow up to 10 feet and 500 pounds, according to the Long Island Aquarium, has the lowest reproductive rate of all shark species. According to the Aquarium of the Pacific, they only give birth every two years. And this poses a major problem because the species has reached a critical status.
According to the IUCN Red List, populations have declined worldwide, with the Mediterranean population “probably locally extinct”, as there have been no records of sharks in the area since 2008. Overall, researchers with the group believe the species has been spotted. a decline of more than 80% in the past 74 years “due to the level of exploitation.” Urban and industrial development, overfishing, climate change and severe weather affecting their habitat remains the biggest threat to the species.
