Shark Week Night Six: Are some great whites monogamous?

On night six of Shark Week, one team made a startling discovery about great white mating habits while another searched for Jaws Jr. off Long Island.

One of the coolest parts about Shark Week is that as commercial as it tries to be, satisfying outcomes are never guaranteed. Sharks can’t be controlled, and experiments don’t always yield the results the scientists had hoped for.

Night six proved both of those points, but it also proved that experiments can yield surprising silver linings and generate new research questions. Here’s a look at what went down when two teams studied West Coast and East Coast North American great whites.

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The West Coast team set out to get DNA from great white pups in Baja California, Mexico and adult great whites in Guadalupe in the hopes of finding genetics links. Though great white pups had never been seen in Baja waters, the team had theorized that it could be a nursery.

That theory was swiftly proven correct. The scientists were able to get DNA samples from 15 pups of different sizes, meaning they were born in different years.

Getting DNA samples from the adults proved to be trickier. Females, in particular, have very thick skin because males bite them while mating in order to hold on. Great white mating has never been filmed, but the scarring on females is evidence enough.

To get the adults’ DNA, Toby decided to try doing biopsies using a speargun. The technique proved successful, so all they had left to do was wait for the results to prove that Guadalupe great whites give birth in Baja.

The team had also tagged three pregnant females in Guadalupe, hoping to see them travel to Baja, but that turned out to be a bust. Unlike most satellite tags, these were designed to relay data in real-time but only if the sharks surfaced. The sharks proved to be hilariously uncooperative because they stayed in the depths.

Thus, the team had to rely on the DNA testing to link the two great white populations, but the results were also a bust. None of the eight adult sharks they tagged are related to the 15 pups. So, Baja is likely a nursery for another Pacific white shark population.

There was an upside to the team’s efforts, though. The DNA proves that some of the pups are related to each other. There are two siblings pairs (meaning they were born in the same litter): a brother and a sister who were only a few months old as well as two brothers who were at least two.

Even more shocking was the discovery all four of the pups are related to each other. They all have the same mother… and the same father!

Though shark mating behavior, especially among great whites, has not been extensively studied, scientists have long assumed that sharks never mate for life. The team’s finding throws that assumption into question.

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The East Coast team explored the waters off Long Island and Cape Cod in search of “relatives” of the massive great whites that inspired Jaws. They didn’t do DNA testing because they have nothing to compare it to. They were basically just looking huge great whites and wanted to a flashy episode title.

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That being said, Jaws does have another connection to the real world. As everyone knows, the blockbuster film inspired a wave of hysteria. Like the characters, people along the eastern seaboard began hunting great whites. It got so bad the species was protected in 1997 in East Coast waters.

Fortunately, great whites have been recovering. The team was disappointed to only find juveniles off Long Island, though. They traveled up the coast to Chatham, Massachusetts, which has a large seal population and managed to find the massive white sharks they’d been looking for. However, they also realized they’d discounted something important about Long Island.

According to Greg, who they met up with in Chatham, great whites along the East Coast are all part of the same migrating population. That theory was backed up by migratory data from an adult they tagged. Montauk may, therefore, be a nursery.

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