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Pacific Sleeper Shark

Somniosus pacificus

iNaturalist Wikipedia

Meet the ghost of the abyss, a massive deep-sea predator that thrives in the freezing darkness of the North Pacific. The Pacific Sleeper Shark is a mysterious giant, combining a sluggish demeanor with the heart of a versatile hunter.

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Quick Identification

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Size

Reaches lengths of 3.7–4.4 m (12–14 ft) and weights up to 880 kg (1,940 lbs), though some individuals may grow larger.

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Colors

Uniform dark gray, slate-brown, or blackish-violet with no distinctive spotting or saddle marks.

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Key Features

Large, heavy cylindrical body
Small, low dorsal fins without spines
Short, blunt snout with a small mouth
Eyes often harbor pinkish parasitic copepods
Gill slits are small and located low on the head

When You’ll See Them

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Activity pattern Active day and night

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Peak hours Variable; often rises to shallower depths during dark hours (10 PM - 4 AM)

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Season Year-round

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Diet A generalist carnivore and scavenger that eats giant squid, rockfish, flounder, salmon, and marine mammals like seals or cetacean carrion.

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Habitat Benthic and pelagic zones of the deep ocean, ranging from the continental shelf to depths of over 2,000 meters.

Behavior

Despite its sluggish appearance and name, the Pacific Sleeper Shark is a highly versatile and effective predator. It is known for its slow, energy-conserving swimming style, which allows it to glide through the dark, cold depths of the abyss undetected. This shark is a master of vertical migration, spending its days in the crushing pressures of the deep sea and occasionally rising toward the surface at night to follow prey. It possesses high concentrations of urea and trimethylamine oxide in its tissues, which act as biological antifreeze and pressure stabilizers.

While often characterized as a scavenger feeding on whale carcasses, recent studies reveal it is an active hunter capable of capturing fast-moving prey like giant squid and even harbor seals. Socially, they are solitary wanderers, rarely encountered by humans due to their extreme habitat preferences. They are remarkably non-aggressive toward divers in the rare instances they meet in shallow northern waters, though their sheer size and powerful jaws demand extreme caution.

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Camera Tips

Capturing a Pacific Sleeper Shark on camera is a significant challenge that requires specialized deep-sea equipment rather than a standard backyard camera. For coastal residents in Alaska or the Pacific Northwest, the most effective method is using a Baited Remote Underwater Video System (BRUVS). This involves a high-pressure waterproof housing and a sturdy frame that can be lowered to the seafloor or suspended at depth. Because these sharks inhabit high-pressure environments, ensure your housing is rated for at least 300 meters if deploying near the continental shelf break.

Bait is essential for attracting this species. Use highly oily fish with a strong scent profile, such as mackerel, salmon heads, or squid. Secure the bait in a perforated container or 'bait bag' attached about one meter in front of the lens. This encourages the shark to linger and bump the bait, providing clear identification of the snout and tooth structure. Since the deep ocean is pitch black, you will need powerful external LED lights. Using red filters or lower-intensity red light can sometimes prevent the 'startle response' in deep-sea creatures, though Sleeper Sharks are generally unfazed by artificial light.

Timing and location are everything. Deploy your camera near steep underwater drop-offs or submarine canyons where upwelling occurs. In high-latitude regions like the Gulf of Alaska, you may have luck in shallower waters (50-100m) during the winter months when surface temperatures drop. Set your camera to record in high-definition with a wide-angle lens, as these sharks can reach 14 feet in length and may pass very close to the rig. Use a high-capacity SD card and set your camera to record on a timer—for example, 2 minutes of footage every 10 minutes—to maximize the battery life during long deployments.

Similar Species

Species that look similar or are commonly confused with Pacific Sleeper Shark.

Greenland Shark

Nearly identical in appearance but primarily restricted to the North Atlantic and Arctic Oceans.

Sixgill Shark

Has six gill slits instead of five and a single dorsal fin located much further back on the body.

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Frequently Asked Questions

Pacific Sleeper Sharks are active around the clock, but they exhibit vertical migration patterns. They are most likely to be found in shallower waters during the night and at dawn, retreating to the darker, deeper ocean during the brightest parts of the day to avoid light and maintain their preferred temperature.

To attract this species, you must use strong-smelling, oily bait such as squid or fish carcasses. Because they are both scavengers and hunters, the scent of decaying organic matter or fresh oils trailing through the current is the best way to bring them within camera range in the vastness of the deep sea.

Their diet is incredibly varied; they consume bottom-dwelling fish like rockfish and flatfish, cephalopods including the Giant Squid, and have been known to eat marine mammals such as seals. They are also significant scavengers, feeding on whale falls that sink to the seafloor.

In most of their range, they are deep-water specialists found far offshore. However, in subarctic regions like Alaska or the Bering Sea, they are known to enter shallower coastal bays and fjords, especially during the colder winter months when the surface water matches their preferred temperature.

Visually, they are almost identical. The best way to distinguish them is by location: the Pacific Sleeper Shark is found in the Pacific and Southern Oceans, while the Greenland Shark is restricted to the North Atlantic and Arctic Oceans. Genetic testing is often required for definitive identification where their ranges might overlap in the Arctic.

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