What the Tiger Shark Ate (and Why it Matters)

The headline read: “Tiger Shark Regurgitates Echidna.” I clicked the link so fast, I should have burned my fingers.

Tiger shark? Regurgitated echidna? I had so many questions.

The first being: Wait? Echidnas can swim? Yes, they can. In fact, I learned that echidnas—small monotremes (egg-laying mammals) native to Australia and New Guinea—swim quite well. Which, for this particular echidna, turned out to not be such a great thing, since it ended up temporarily, but fatally in the gullet of a tiger shark off the coast of northern Queensland.

To be fair, the scientist who discovered the regurgitated echidna, Nicolas Lubitz, was also startled by this find. It happened when he and some colleagues from James Cook University were tagging sharks near Orpheus Island. In this case, a tiger shark they’d just caught regurgitated the still-largely-intact echidna and Lubitz managed to snag an image that made headlines around the world.

It was practically a recipe for headlines because (as I discovered) the internet hive mind seems obsessed with stories of what tiger sharks may or may not have eaten. That echidna was merely the latest entry in a very long list. No one had ever documented a tiger shark eating an echidna, so it qualified as weird. Still, while the things tiger sharks eat make for great click-bait (sorry) headlines, they can also tell us important things about the state of the world’s oceans.

By paying to attention to these wide-ranging apex predators, including what they eat, scientists are mapping habitats, attempting to discover emerging threats, and even gauging the health of marine ecosystems around the world.

Things Tiger Sharks Eat in Three Broad Categories

Over the years, scientists have catalogued a large, we’ll call it an “assortment,” of items recovered from tiger shark bellies (or regurgitated). They tend to fall into three broad categories:

Category A—Things that Shouldn’t be There

Chicken coops, automobile tires, license plates, iron horseshoes, potato chip bags, condoms, jars of mayonnaise. It can be a really long list and a grim reminder of how much human trash ends up in the ocean. Tiger sharks are often called “garbage cans of the sea,” which has always struck me as deeply unfair. They wouldn’t be swallowing tires, chicken coops or jars of mayonnaise if those things weren’t in the oceans in the first place.

Category B—Things that Should be There

Tiger sharks are at the top of the marine food chain, but scientists have also found that they are what one paper called “adaptable generalists,” meaning they exploit a wide variety of prey. Their regular menu includes fish, seals, rays, other sharks, bits of whale, and, of course, sea turtles. Tiger sharks seem especially fond of sea turtles. In turn, sea turtles have developed an interesting defense against such predation. Basically, they keep an eye on the tiger shark and keep their back to its large head. It can look like a very strange and oddly graceful underwater ballet. With very high stakes.

If the sea turtle gets the angle wrong—gets horizontal to the tiger shark essentially—one bite can shear it in half. Shell and all.

Category C—Things that Make Scientists Go “Hmmm….”

Which brings us to Exhibit A from this story, that regurgitated echidna. Besides that unlucky monotreme, tiger sharks have been found with songbirds, clapper rails, crocodilians, monitor lizards, and blue duikers in their stomachs (or regurgitated therefrom). In the case of the songbirds, further research revealed that, rather than being an opportunistic one-off, birds more common to backyard feeders than oceans and beaches, seem to be a dietary staple of juvenile tiger sharks that swim near the routes of migratory birds.

Maybe more research will reveal something similar about echidnas. The point is, these more or less unexpected meals raise questions and offer insights into where tiger sharks are traveling, and what they’re encountering—and eating—along the way.

To answer those questions and probe those insights, scientists are turning to each other and to technology.

Tales Tiger Sharks Tell

In one notable experiment, scientists attached 360-degree cameras equipped with biologgers to tiger sharks in the Bahamas to see what they could learn. Turns out, they learned a lot and showed that tiger sharks are potentially excellent oceanographers.

Biologgers are, essentially, small, sensor‑equipped devices—often including tools like accelerometers, depth and temperature sensors, and cameras—attached to marine animals to record fine‑scale data that reveal how they navigate, forage and function underwater. Unlike camera-only tracking, the biologgers in this work captured everything around the shark, revealing not just its movements, but the entire underwater landscape.

Over a single hour-long swim, one biologger-tagged shark surveyed more than 22,000 square meters of seafloor, logging things like habitat type, swimming speed and behavior. The results, published in 2021 in Frontiers in Marine Science, also showed tiger sharks spending much of their time over seagrass meadows, which are vital for carbon storage and marine life, including sea turtles.

Another study examined how warming oceans are shaping tiger shark movements in the western Atlantic. By stitching together nine years of satellite tracking with nearly 40 years of capture records, researchers showed that tiger sharks are migrating north and arriving earlier in northern waters during warmer years.

Tiger sharks tend to prefer a temperature range between 26 and 28C. As sea surface temperatures rise, those ranges expand toward the poles. The study, published in Global Change Biology, showed that for every 1C rise in temperature, tiger sharks may extend their range roughly four degrees of latitude north and show up about two weeks earlier than previous records report.

This matters because tiger sharks are apex predators. Shifts in their distribution ripple through the prey populations and can change overall ecosystem dynamics. If their ranges expand, it also may push them beyond the bounds of existing marine protected areas. Understanding how climate change effects the movements and diets of marine species—not just tiger sharks—is important for ensuring the lasting effectiveness of the world’s network of marine protected areas.

Sharks as Ocean Sentinels

When tiger sharks start showing up in new locales or swallowing unexpected prey—like echidnas—it may signal that something fundamental is changing. It could be a shift in ocean temperature, a decline in the availability of traditional prey, or a sign of other changes showing up in the tiger shark’s world.

That echidna made headlines because it seemed weird. But tiger sharks have been eating, swimming and migrating through the world’s oceans long before we had cameras and satellites to follow them. What looks like an oddity to us might just be Tuesday for a tiger shark. In a changing ocean, “weird” is data. What the tiger shark ate has always mattered. We’re just learning how much it might matter to us.