Seattle’s marine environment, the Puget Sound, hosts a resident shark population, dispelling the misconception that the Pacific Northwest waters are too cold for large marine predators. These animals are not the surface-dwelling species often associated with warmer coastal areas. Instead, they are deep-dwelling creatures that thrive in the Sound’s unique underwater geography and cold temperatures. The presence of these sharks is a testament to the biological richness of the region’s inland sea.
Defining Seattle’s Shark Population
The two most prominent species in the Seattle area are the Bluntnose Sixgill Shark and the Pacific Spiny Dogfish, which represent vastly different sizes. The Bluntnose Sixgill Shark (Hexanchus griseus) is the largest shark in Puget Sound, with females often reaching lengths of 14 to 16 feet. This massive, ancient species is easily identified by its six gill slits, a feature that distinguishes it from most sharks that possess only five.
The Sixgill shark has a heavy, bulky body, a broad, blunt snout, and a single dorsal fin positioned far back near its tail. Its lower jaw holds distinct, saw-like comb-teeth, while its large eyes often have a fluorescent green appearance, an adaptation for its low-light habitat. Most individuals sighted within the Sound are sub-adults, suggesting that this protected inner sea may serve as a nursery area for the species.
In contrast, the Pacific Spiny Dogfish (Squalus suckleyi) is the most abundant shark in the Sound, yet it rarely exceeds three to four feet in length. These smaller sharks are identifiable by a sharp, venomous spine located directly in front of each of their two dorsal fins. The dogfish are schooling predators, often seen in large groups, and are characterized by a slender body, dark gray coloration, and scattered white spots. The dogfish is a notably long-lived species, with some individuals surviving for up to 80 years.
Where Seattle’s Sharks Reside
Puget Sound’s physical characteristics create an ideal, cold-water refuge for these shark species. The Sound features deep, glacially carved trenches that plunge to depths of over 600 feet in many areas. The water temperature remains consistently cold, typically ranging between 52 and 54 degrees Fahrenheit.
Sixgill sharks are primarily deep-water inhabitants, with adults preferring depths greater than 300 feet. They engage in diel vertical migration, moving to shallower waters closer to the surface at night to feed before returning to the dark depths during the day. This keeps them out of sight from the average surface observer.
The Spiny Dogfish, while more common and sometimes found in shallower coastal waters during the summer months, also prefers deeper environments. These sharks often form large schools and are frequently encountered by bottom-trawling fishermen in the deeper parts of the Sound. The low-light environment and the abundant deep-sea prey allow both species to thrive far from human activity.
Assessing the Risk to Swimmers and Boaters
Encounters between the resident shark species and humans are extremely rare, largely because the sharks inhabit deep water. The Bluntnose Sixgill is a sluggish and docile animal, posing virtually no threat to swimmers or recreational boaters. Despite their large size, they are not known to be aggressive toward humans, and there has never been a recorded fatality involving this species.
The Spiny Dogfish possesses a defensive mechanism in the form of a venomous spine, but its small size makes it non-lethal. Injuries from a dogfish are typically limited to accidental punctures and toxic wounds sustained by fishers handling them after they are incidentally caught. The official safety assessment confirms that the threat of an unprovoked shark attack in Seattle’s waters is statistically negligible.
Historical records show only two non-fatal, unprovoked shark incidents in all of Washington state since 1837, neither of which occurred in Puget Sound. The biggest risk to sharks in the Sound comes from fishing gear, where they are often accidentally caught as bycatch. For humans, other hazards, such as the water’s extreme cold and strong currents, present a far greater concern than any of the deep-dwelling sharks.