What the world’s largest sharks, crocs, and spiders can tell scientists
The biggest animals of their kind often generate headlines, but these record-holders can also tell us a lot about an animal's biology.
Whether it’s awe, fear, or simply fascination, people love things that are big.
So it’s no surprise that Deep Blue, a 20-foot-long great white shark and the largest ever captured on camera, makes headlines anytime she’s spotted snacking on a dead whale. It’s the same reason the world knows the name Lolong, one of the biggest saltwater crocodiles ever recorded, who even had a few inches on Deep Blue.
And now, in a July 19 episode of National Geographic's SharkFest, scientists have set out to find Kamakai, a female tiger shark spotted in French Polynesia and thought to be one of the most colossal tiger sharks caught on film.
But beyond the sensationalism associated with such stories, experts say superlative giants have plenty of science to teach us too.
“Is there value in just telling a story about a big shark? No,” says Chris Fischer, founding chairperson of Ocearch, a data-collection organization that has tagged and tracked some of the largest great whites on Earth.
However, Fischer says that if such an animal is safely captured, sampled, tagged, and released, then it can be useful to science. Tracking a large female like Deep Blue, for instance, can reveal “where great white sharks mate, where they gestate, and where they give birth,” says Fischer.
And for a species vulnerable to extinction, such as the great white, this is crucial data for figuring out how to best protect the fish and boost its numbers, he says. (Read why great whites are still a mystery to us.)
A window into the past
There’s another good reason for documenting the biggest of the big: They can tell us about the past.
“Really big animals are really useful data points,” says Stephanie Drumheller-Horton, who studies ancient crocodile relatives at the University of Tennessee.
For instance, when trying to figure out what the 40-foot Sarcosuchus imperator—nicknamed SuperCroc—ate during the Cretaceous period, it’s helpful to study the diet of today’s largest crocs. Lolong, who died in captivity in the Philippines in 2013, likely dined on fish, birds, mammals, and even livestock in the wild. (Read more about the biggest ever freshwater croc fossil.)
“We can make predictions based off the living groups, and that includes looking at some of the biggest ones,” says Drumheller-Horton.
At the same time, today’s measurements can be used to show how living species have changed in response to hunting, fishing, and other human impacts.
“If you look at historical records for some of these animals, like manta rays and whale sharks, you’ll see that they used to be significantly larger than the ones we see presently in our oceans,” says Andrea Marshall, a National Geographic Society explorer and co-founder of the Marine Megafauna Foundation, which is based in California but also has a research center in Mozambique.
This means that we’ve “fished out all of the largest, oldest, most mature individuals out there,” says Marshall. And that means conservationists have some serious work to do to restore species back to their original state.
When being big is bad
Animals that survive to gigantic sizes are the products of a combination of factors, including good genetics and healthy ecosystems. But that success can also put a target on their backs.
Take the alligator gar, a prehistoric-looking freshwater fish of the U.S. South that can grow longer than eight feet and tip the scales at more than 300 pounds.
“Once they reach a certain size, there are very few predators that can eat them,” says Solomon David, an aquatic ecologist at Nicholls State University in Louisiana.
But even a full-grown alligator gar is no match for a human with a compound bow. David says far too many of the impressive fish are now being killed as trophies, and this has negative consequences for the species, which is considered rare and threatened in some parts of its range.
Scientists have already shown that hunting the largest bighorn rams can cause populations to have smaller horns, while poaching can lead to elephants born without tusks entirely.
“We’re targeting the biggest and the baddest of the given population,” David says. “So we’re actually removing those genes” that make them so big.
There’s another downside to the fascination with the largest animals: It can take attention away from the animals that aren’t outliers, some experts say.
There are about 500 shark species, including the lesser known—and smaller—epaulette sharks, angelsharks, and goblin sharks, says Melissa Cristina Márquez, a marine biologist and founder of the Fins United Initiative.
Angelsharks are especially in need of some attention, as these bottom dwellers have disappeared from more than 80 percent of their range over the last century and are now considered the second-most threatened family within sharks and rays.
“Just focusing on these big, ‘charismatic’ sharks like hammerheads, tiger sharks, or great white sharks does kind of overshadow all the other species,” Márquez says. (Read about six sharks you’ve never heard of.)
At the same time, superlatives like “largest” and “biggest” can be used to drum up interest for animals that usually get much less attention, says Stefano Mammola, an ecologist with the Italian National Research Council. In 2017, Mammola published a study that featured nearly a hundred record-breaking spiders.
They include the Goliath birdeater of South America, the heaviest spider, which weighs about as much as a hockey puck, and the giant huntsman spider of Laotian caves, which has the largest leg span at about a foot wide.
“If you can get people interested in cool features, which are a bit on the extreme side, then they will hopefully find [spiders] more appealing,” says Mammola. “And this may translate into better public awareness of these neglected organisms.”