Gulper eels (Eurypharynx pelecanoides) are fascinating creatures, found in the depths of temperate and tropical oceans around the globe at depths from 500 m to 7,625 m.
The gulper eel was first named in 1882. Leon Valliant, a French zoologist, describes its discovery off the coast of Morocco during the Travailleur expedition. On this expedition, the gulper eel was dredged from the ocean at a depth of 2,300 m.
Although we have known of its existence for over 135 years we know relatively little about the gulper eel. Recent footage captured by research vessel EV Nautilus, owned by the Ocean Exploration Trust, shows the gulper eel deflating itself and appearing to shrink in size. It ‘shape-shifts’ from a large and bloated organism to a sleek, thin, traditionally eel-like creature.
As can be seen in the footage, one of the most fascinating features of this creature is its mouth. The jaw of the gulper eel is a quarter of the length of its body and resembles a pelican’s throat pouch, leading it to be commonly referred to as the ‘pelican eel.’ Despite its huge mouth, E. pelecanoides is thought to mostly eat small creatures such as shrimp, crustaceans, squid and other small invertebrates. The gulper eel expels water taken in with food through its gill slits. While it has been suggested it could potentially consume creatures much larger in size, its very small teeth would suggest it typically consumes small prey.
A large open jaw may conjure up images of filter feeders such as the blue whale which could lead you to believe that the gulper eel is a very large creature. On the contrary, it is generally 0.47 m to 0.75 m long.
Despite their name, they are not true eels – though they are related. Gulper eels lack scales and swim bladders. A swim bladder is a gas-filled internal organ which allows fish to stay at a particular water depth. As pressure increases with depth, a swim bladder would be a disadvantage and may hamper movement vertically through the ocean.
Perhaps unsurprisingly, the gulper eel has small eyes. The only light at this depth in the ocean is that produced by animals: this is known as bioluminescence. Instead of relying on sight, the gulper eel has lateral line sensors. These multi-directional sensors allow it to sense movement and pressure changes in its environment.
Finding food in the depths of the ocean is difficult, so the gulper eel has developed an ingenious method of attracting prey. At the end of its long tail it has an organ known as a photophore which can produce glowing pink or red light. In the deep dark depths of the ocean the gulper eel is thought to use its tail, held above its open mouth, as a lure. Prey are presumably meant to be attracted to the light and swim straight into the gulper eel’s large jaws.
Little is currently known about how the gulper eel reproduces but it is believed to be semelparous – in other words, it dies after reproducing and is eaten by predators such as the lancet fish.
The International Union for Conservation of Nature (IUCN) lists E. pelecanoides as a species of ‘least concern’ with ‘no major threats’. However, very little is known about trends within their population.
The depth at which they are found makes them very difficult to study. Improved technologies and growing interest in our oceans will allow us to view and learn more as there is still so much to find out about these and other fascinating deep sea dwelling creatures.
Image credit: Olyngo via Wikimedia Commons