Swell Shark

Fascinating facts about the Swell Shark

• When threatened, a swell shark can double its girth by gulping water or air, turning its body into a balloon that predators can’t easily bite, an instant armor that lets it stay in the same spot without fleeing.
• Most swell sharks linger just 5–37 m (16–121 ft) above rocky, algae-covered bottoms, but they’ve been recorded as deep as 457 m (1,499 ft), showing a surprising vertical range for a shallow-water dweller.
• A newborn pup emerges from its egg at only about 15 cm (5.9 in) long, already equipped with a double row of enlarged dermal denticles that act like tiny wedges to help it break free from the egg case.
• With around 55–60 teeth each bearing three to five smooth cusps, the swell shark can sense electric fields from prey as small as 20 cm away, letting it hunt bony fish and crustaceans in total darkness.
• First noted in 2014, the species glows with a species-specific biofluorescent pattern produced by brominated kynurenine pigments, a trait that may help sharks talk to each other or hide among fluorescent reef lights.

At a glance

About the Swell Shark

The swell shark, Cephaloscyllium ventriosum, glides through the rocky, algae-clad reefs of the eastern Pacific with a sleek, flat head and a canvas of yellow-brown mottled with brown and white spots. Adults reach about 90 cm, with some growing to 110 cm, their large gold eyes framed by nictitating lids that flicker in the dim light of crevices where they spend daylight hours. Their small, tight gill slits and a mouth bristling with 55–60 three-cusped teeth hint at a nocturnal predator that relies on electric fields to locate bony fish, molluscs and crustaceans, often sucking prey in or lying in wait with an open mouth like a silent trap. A single, surprising trait sets them apart: when threatened they gulp water (or air) into a distensible stomach, swelling to roughly double their diameter, a defensive puff that makes them hard to bite and even produces a dog-like bark as they expel the air. At night, these sociable sharks emerge from their rock hideouts, sometimes sleeping side-by-side, to hunt along depths of 5 to 37 m, though they can be found as deep as 457 m. Their reproductive strategy is oviparous, laying two amber-green, tendril-attached egg cases that cling to kelp or reef, with embryos feeding solely on yolk for 9–12 months before hatching as self-sufficient 15 cm pups. Their biofluorescent glow, first reported in 2014, paints them with species-specific patterns that may aid in communication and camouflage, adding a hidden splash of color to their already remarkable biology

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