Alaska, a region often associated with icy landscapes and frigid waters, might seem an unlikely habitat for sharks. However, Alaska’s vast and diverse marine environment supports a surprising array of shark species. These waters provide a rich ecosystem where sharks thrive, adapting to the challenging North Pacific conditions. Their presence highlights the complexity and biodiversity of Alaska’s underwater world.
Sharks Common to Alaskan Waters
The most frequently encountered sharks in Alaskan waters are the Pacific Sleeper Shark, Salmon Shark, and Spiny Dogfish. Each occupies a specific niche within the marine ecosystem.
The Pacific Sleeper Shark (Somniosus pacificus) is a large, deep-water species reaching up to 14 feet, with unconfirmed reports of 23 feet or more. These sharks are dark gray to black with a cylindrical body and a short, rounded snout. Their diet primarily consists of bottom-dwelling organisms like octopuses, flounders, pollock, and cephalopods. Larger individuals may also prey on marine mammals such as harbor porpoises and Pacific salmon. They are found on continental shelves and slopes, from the surface to 6,600 feet deep, in both Arctic and temperate waters.
The Salmon Shark (Lamna ditropis) is a powerful, fast-swimming predator often compared to a small great white shark. They typically grow 6.5 to 8 feet long and can weigh around 485 pounds. Named for their primary prey, Pacific salmon, their varied diet also includes herring, squid, sablefish, and pollock. They are highly migratory across the North Pacific, from Japan to the Bering Sea and Baja California, inhabiting cool temperate waters. They are frequently observed in the Gulf of Alaska, particularly Prince William Sound, during annual salmon runs.
The Spiny Dogfish (Squalus acanthias) is a smaller shark, with males growing up to 3.3 feet and females up to 4 feet. They have gray or brown bodies with white spots and sharp, venomous spines in front of each dorsal fin. Spiny Dogfish are opportunistic feeders, consuming squid, crabs, shrimp, and various fish. They are found in coastal waters from Alaska to Baja California and travel in large schools, sometimes numbering in the thousands.
Unique Adaptations to Cold Environments
Sharks in Alaskan waters possess adaptations allowing them to thrive in cold, deep, and sometimes icy conditions. These traits enable them to maintain body functions and hunt effectively where many other marine species would struggle.
The Salmon Shark is endothermic, maintaining a body temperature higher than the surrounding water. This is achieved through a specialized network of blood vessels called a rete mirabile, or “wonderful net,” which acts as a countercurrent heat exchanger. This system allows them to retain metabolic heat, raising their internal body temperature up to 15.6°C (28°F) above ambient water temperatures, and sometimes up to 21°C (38°F). This ability provides increased speed and agility in cold water, allowing for rapid acceleration and sustained swimming, beneficial for ambushing fast-moving prey like salmon.
The Pacific Sleeper Shark, unlike the Salmon Shark, exhibits different adaptations for its deep, cold habitat. Its liver oil contains low-density compounds (diacylglyceryl ethers and triacylglycerol) instead of squalene, which would solidify in frigid temperatures. These compounds help maintain the fluidity of the liver oil, contributing to buoyancy. They also have a slow metabolism, conserving energy where food can be scarce. Their large mouth allows them to feed by suction, inhaling prey, and their teeth are structured for cutting.
Rare and Transient Visitors
While some shark species are regular inhabitants, others are rare or transient visitors, occasionally venturing into these northern territories. These species typically have broader ranges extending into warmer latitudes but may appear in Alaska due to migratory patterns, prey availability, or unusual oceanographic conditions.
The Blue Shark (Prionace glauca) is one occasional visitor, known for its extensive migrations. Though not a common resident, Blue Sharks can travel long distances and may stray into Alaskan waters. Their presence is less frequent and predictable than resident species, as their core habitats lie in more temperate and tropical regions.
Human Encounters and Conservation
Human interactions with sharks in Alaska are uncommon, and these sharks generally pose little threat. While there have been reports of shark-related injuries to marine mammals, direct attacks on humans are rare in Alaska’s cold waters. The species found in Alaska, particularly the deep-dwelling Pacific Sleeper Shark, are not typically associated with human encounters.
Sharks play a role in the marine ecosystem, acting as apex predators that help regulate prey populations and contribute to ocean health. They can influence the behavior of other marine species and maintain biodiversity. For example, Salmon Sharks consume a significant portion of marine life in the Gulf of Alaska, impacting the food web.
The Salmon Shark is listed as “Least Concern” by the IUCN Red List, with stable populations. Commercial fishing for Salmon Sharks in Alaska has been banned, and recreational fishing is heavily regulated.
The Pacific Sleeper Shark is categorized as “Near Threatened” on the IUCN Red List. This species is often caught as bycatch, and its slow maturation and reproduction rates make its populations vulnerable. Conservation efforts for the Pacific Sleeper Shark include tagging and releasing to study their movements and habitat preferences.
Spiny Dogfish are sustainably managed in U.S. waters, though they are frequently caught as bycatch. The presence and health of these shark populations in Alaska are indicators of a functioning marine environment.