What Do Leatherback Sea Turtles Eat?

Leatherback sea turtles eat jellyfish. That is not a simplification or a headline-friendly shortcut; it is genuinely the core of their diet. Unlike every other sea turtle species, leatherbacks are gelatinous-prey specialists, feeding almost exclusively on jellyfish and closely related soft-bodied organisms like comb jellies and salps. What makes this remarkable is the sheer scale of it: animal-borne camera studies have recorded individual leatherbacks consuming an average of roughly 330 kilograms of jellyfish per day, and the physiology that lets a 450-kilogram reptile thrive on something that is more than 95 percent water is one of the more unusual feeding stories in the ocean.

Which Jellyfish Species They Target

Leatherbacks are not picky about the specific species of jellyfish they eat, but they do show preferences that vary by ocean region and what is locally abundant. In the North Atlantic, animal-borne video cameras attached to foraging leatherbacks off Nova Scotia documented 601 prey captures, with lion’s mane jellyfish making up 83 to 100 percent of the diet, along with some moon jellyfish.¹ In Chesapeake Bay, an autonomous underwater vehicle tracked leatherback feeding behavior and found that about 95 percent of prey captures were Atlantic sea nettles, with feeding rates topping 30 jellyfish per hour.²

Over in the Pacific, the picture shifts. Stable isotope analyses of leatherbacks in the California Current found that carnivorous sea nettles were the largest dietary contributor, followed by thaliaceans, a group that includes salps and pyrosomes. These filter-feeding organisms are not jellyfish in the strict taxonomic sense, but they are gelatinous and soft-bodied, fitting neatly into the leatherback’s feeding niche.³ The common thread across all ocean basins is that leatherbacks eat gelatinous zooplankton and essentially nothing else. They do not eat fish, crustaceans, seagrass, or algae.

The Quantities Are Staggering

Jellyfish are roughly 95 percent water and extremely low in calories compared to fish or squid. To survive on such dilute food, leatherbacks eat extraordinary amounts. The video-camera study from Nova Scotia estimated that the turtles consumed an average of 73 percent of their own body mass in jellyfish every day, translating to about 261 individual jellyfish daily. Some individuals ate far more, with the highest recorded intake reaching around 840 kilograms in a single day. Daily energy intake averaged about 66,000 kilojoules, with the most voracious feeders pulling in nearly 168,000 kilojoules, representing three to seven times their estimated daily metabolic needs.¹

Those peak numbers reflect gorging behavior when prey is abundant. Modeled estimates for what adults need to simply maintain their weight put the figure lower, at roughly 65 to 117 kilograms of jellyfish per day for a turtle weighing between 250 and 450 kilograms.⁴ The difference between maintenance feeding and the observed gorging makes sense: leatherbacks need to build up massive energy reserves in the form of blubber to fuel their long migrations and sustain themselves through breeding seasons when they eat little or nothing.

Over an entire lifetime of roughly 40 years, a single leatherback is estimated to consume more than 1,000 metric tonnes of jellyfish, or about 3,000 times its own adult body mass. Just to reach sexual maturity at around 16 years old, it must eat more than 310 tonnes.⁴ The Pacific population alone has been estimated to consume around 2.1 million tonnes of jellyfish per year, with juveniles aged two to seven accounting for over half of that total.

How Leatherbacks Find Their Food

Jellyfish do not stay in one place, and neither do leatherbacks. These turtles undertake some of the longest migrations in the animal kingdom, crossing entire ocean basins between tropical nesting beaches and temperate or subarctic feeding grounds. Where they choose to feed is tightly linked to where jellyfish aggregate. Research in the Northwest Atlantic found strong spatial correlations between jellyfish biomass and leatherback density. On the Scotian Shelf off eastern Canada, the correlation between jellyfish weight and leatherback concentration was very strong, with a similar pattern in the Gulf of St. Lawrence and the Bay of Fundy.⁵ In other words, map the jellyfish blooms and you will find the turtles.

Leatherbacks also adjust their diving behavior to match the vertical movements of their prey. Many jellyfish species migrate up and down in the water column on a daily cycle, rising toward the surface at night and sinking during the day. Satellite-tagged leatherbacks at high-latitude feeding grounds forage around the clock, but their diving patterns shift when they begin migrating south: daytime dives become shallower while nighttime dives become longer and deeper, tracking the changing distribution of prey at different latitudes and seasons.⁶ This flexibility is important because jellyfish populations are patchy and ephemeral: a bloom may appear in one area for a few weeks and then vanish.

What Juveniles Eat

Hatchling and juvenile leatherbacks start eating gelatinous prey almost immediately, but the specific organisms they encounter differ from what adults target because the youngest turtles feed in warm surface waters rather than making deep dives in cold northern seas. Observations of juvenile leatherbacks in the Florida Current documented them feeding throughout the water column on moon jellyfish, comb jellies, and unidentified gelatinous egg masses.⁷ As they grow and develop the ability to dive deeper and tolerate colder water, they gain access to different prey assemblages. This behavioral trajectory sets leatherbacks apart from green sea turtles very early in life: the two species may share surface waters as hatchlings, but their ecological niches diverge rapidly.

Juveniles also carry a disproportionate share of the species’ total food demand. Because they are actively growing while adults have essentially stopped, the two-to-seven-year age class accounts for more than half of total population-level jellyfish consumption in the Pacific, even though adults are far larger as individuals.⁴ Adults, by contrast, account for less than 9 percent of total population intake. This means that the survival of juveniles and their access to productive foraging areas is disproportionately important for the population as a whole.

The Salt Problem and How They Solve It

Eating hundreds of kilograms of jellyfish every day means ingesting enormous quantities of seawater and marine salts. For most reptiles, this would be a lethal osmoregulatory problem. Leatherbacks handle it with oversized lachrymal salt glands, located near the eyes. These glands are the reason sea turtles appear to “cry” when they come ashore to nest, though the tears are actually concentrated salt secretion, not emotion.

In leatherbacks, the salt glands are exceptionally large. CT scanning of an adult revealed glands weighing about 0.62 kilograms in a 450-kilogram turtle, roughly three times the relative size of salt glands in other sea turtles. The glands produce a secretion with an osmolality of about 1,800 milliosmoles per kilogram, which is far more concentrated than seawater. Modeling based on known jellyfish salt and water composition, metabolic rate estimates, and measured gland capacity suggests that a leatherback can consume up to 80 percent of its body mass in lion’s mane jellyfish each day without overwhelming its salt-excretion system.⁸ Divalent ions like calcium and magnesium are dealt with separately, excreted through the gut rather than the salt glands. This physiological toolkit is what makes a jellyfish-only diet viable for a warm-blooded-feeling reptile that maintains a body temperature well above the surrounding ocean.

Why They Mistake Plastic for Prey

A floating plastic bag drifting in the current bears an unfortunate resemblance to a jellyfish, and leatherbacks pay the price for it. A study that examined autopsy records of 408 leatherback turtles spanning more than a century, from 1885 to 2007, found plastic debris in the gastrointestinal tract of 34 percent of the animals examined.⁹ That is roughly one in three turtles carrying synthetic material in their gut.

The problem is not just visual similarity. Leatherbacks feed by engulfing prey whole, using backward-pointing spines (papillae) lining their esophagus and throat to grip slippery jellyfish and prevent them from escaping. This anatomy is well suited to soft, gelatinous prey but poorly suited to rejecting inedible objects once they enter the mouth. A sheet of plastic caught in those spines is not easily expelled. Ingested plastic can block the gut, reduce the turtle’s ability to absorb nutrition from real food, and in severe cases cause internal injury or death. Given that plastic pollution in the ocean has increased dramatically since the mid-twentieth century, this problem is almost certainly worse now than the historical average suggests.

Balloon releases are a particularly well-documented source of leatherback-targeting debris. The latex or Mylar fragments, once deflated and waterlogged, float at the surface in a shape and movement pattern that closely resembles jellyfish. Conservation groups have pushed for bans on mass balloon releases partly on this basis.

How Researchers Figure Out What Leatherbacks Eat

Studying the diet of an animal that spends most of its life in the open ocean and dives hundreds of meters deep is not straightforward. Researchers use several complementary approaches, and the picture has become much richer over the past two decades as technology has improved.

Animal-borne cameras, attached to the turtle’s carapace with suction cups, provide direct video evidence of prey capture events. This method produced the detailed feeding data from Nova Scotia, where researchers logged nearly two hours of footage per turtle on average and documented 601 individual prey captures.¹ Autonomous underwater vehicles have also been deployed to follow turtles and record feeding behavior externally, capturing footage of prey identity and feeding rates without attaching anything to the animal.²

Stable isotope analysis offers a different kind of evidence. By measuring the ratios of carbon and nitrogen isotopes in turtle tissue and comparing them to potential prey species, researchers can infer what a turtle has been eating over weeks or months, not just during the brief window of camera deployment. This approach confirmed that leatherbacks in the California Current feed on a mix of carnivorous scyphozoan jellyfish and filter-feeding thaliaceans, and that their trophic position has been relatively stable over time even as ocean conditions have fluctuated.³ Necropsy data, satellite tracking, and aerial surveys round out the toolkit, each filling in different pieces of the puzzle.

Fishing Gear and Foraging Grounds

The places where jellyfish aggregate are often the same places where commercial fishing operations concentrate, which creates a deadly overlap. Leatherbacks foraging near the surface can become entangled in gillnets, longlines, and trap lines. A review of leatherback sightings in southeastern Australian waters found that out of 605 documented sightings, about 12 percent were of dead individuals, mostly washed ashore, with fishing gear entanglement the likely cause in most cases.¹⁰

This is not a problem limited to Australia. Leatherback populations have declined sharply in the Pacific over the past several decades, and bycatch in fisheries is widely considered one of the primary drivers alongside egg harvesting and habitat loss on nesting beaches. Because leatherbacks must travel vast distances between nesting and feeding grounds, they cross through the territorial waters and exclusive economic zones of many nations, making coordinated protection especially difficult. A turtle that nests in Indonesia and feeds off California passes through waters governed by dozens of different fisheries management regimes.

The dependence on jellyfish also raises questions about climate change. Warming oceans and overfishing of jellyfish predators like sunfish and certain fish species may be increasing jellyfish populations in some regions, which could theoretically benefit leatherbacks. But the relationship is not simple. Shifting ocean currents can move jellyfish aggregation zones, potentially forcing turtles to travel farther or forage in less productive areas. And if important foraging hotspots shift into regions with higher fishing pressure, the net effect on leatherbacks could still be negative.

The “Trophic Dead End” Debate

For a long time, biologists puzzled over how leatherbacks could sustain their large body size, active metabolism, and long migrations on jellyfish, which were assumed to be nutritional dead ends in the food web. The reasoning was that jellyfish occupy a low trophic level and contain so little organic matter that they could not possibly support a large, warm-bodied predator. This was sometimes called the “trophic dead end” framing: energy flows into jellyfish and then largely stops there, contributing little to higher trophic levels.

Research over the past 15 years has largely overturned this view. The isotope work in the California Current explicitly addressed this question, showing that the leatherback food web has a coherent and realistic trophic structure: thaliaceans sit at the bottom, scyphozoan jellyfish in the middle, and leatherbacks at the top.³ The key insight is that leatherbacks compensate for the low caloric density of each individual jellyfish by eating enormous volumes. With daily consumption regularly exceeding half their body weight, they extract sufficient energy even from a prey source that is mostly water. Their enlarged salt glands, unique insulating blubber layer, and efficient foraging strategies all evolved in concert to make this diet viable. Jellyfish are not a dead end for the food web if something is adapted to exploit them at massive scale.

The energy surplus observed in the Nova Scotia camera studies reinforces this point. Turtles feeding on abundant lion’s mane jellyfish were taking in three to seven times their estimated daily metabolic requirements, meaning they were actively building fat reserves.¹ The “dead end” label said more about how biologists had underestimated gelatinous prey than about what leatherbacks could actually do with it.

1
PubMed Central. Jellyfish support high energy intake of leatherback sea turtles (Dermochelys coriacea): video evidence from animal-borne cameras
2
Frontiers in Marine Science. TurtleCam: A “Smart” Autonomous Underwater Vehicle for Investigating Behaviors and Habitats of Sea Turtles
3
Marine Ecology Progress Series. Re-examining trophic dead ends: stable isotope values link gelatinous zooplankton to leatherback turtles in the California Current
4
PLOS ONE. Resource Requirements of the Pacific Leatherback Turtle Population
5
PubMed Central. Jellyfish distribution in space and time predicts leatherback sea turtle hot spots in the Northwest Atlantic
6
Canadian Journal of Zoology. Changes in diel diving patterns accompany shifts between northern foraging and southward migration in leatherback turtles
7
Journal of Herpetology. Ontogeny of Diving and Feeding Behavior in Juvenile Seaturtles: Leatherback Seaturtles (Dermochelys coriacea L) and Green Seaturtles (Chelonia mydas L) in the Florida Current
8
PubMed. Crying a river: how much salt-laden jelly can a leatherback turtle really eat?
9
PubMed. Leatherback turtles: the menace of plastic
10
Marine Biology. A review of the importance of south-east Australian waters as a global hotspot for leatherback turtle foraging and entanglement threat in fisheries