By Katrina Mueller, Ph.D.
Chinook salmon grow to great sizes and are highly sought by anglers. Paul Dicarlo caught this Chinook salmon near Juneau, Alaska.
Credit: Andy Wink
American author and journalist Tim Egan famously described the Pacific Northwest as "any place salmon can get to." In the same breath he captured the iconic status of a genus and underscored the gravity of very real extirpations and declines. For him and others, Pacific salmon—especially Chinook salmon—and the character of North America's west coast are inextricably linked. Recognized as the state fish of Alaska and Oregon, Chinook are part of the fabric of human life throughout their range, supporting long-valued traditions and economies associated with subsistence, personal use, commercial, and recreational fisheries.
The Chinook is the largest of the Pacific salmon, with adults commonly exceeding 30 pounds, and, in rare cases, 100 pounds. It becomes quickly apparent why they are called "Kings." A Kenai River King salmon that topped the scales at 97.25 pounds currently holds the sport fishing world record. The largest commercially caught fish weighed 126 pounds.
Besides King, other monikers—spring salmon, June hog, blackmouth—describe the timing of spawning migrations or distinguishing physical characteristics. In fact, the genus Oncorhynchus is derived from the Greek onkos (hook) and rynchos (nose), in reference to the pronounced kype or snout on spawning males. The species name, tshawytscha can be traced back to the native people of Kamchatka, Russia.
In North America, Chinook once ranged from Point Hope, Alaska, to the Ventura River in southern California. They were introduced to the Great Lakes in 1967 and have since catalyzed a robust sport fishery there.
Like other Pacific salmon, Chinook typically return to their river of origin, and possibly to the same local area, to spawn. Alevin emerge in spring from the gravel—specifically from a redd (nest) dug deep enough by the powerful tail of a spawning female to protect incubating eggs from scouring spring flows. The act of redd construction cleans the gravel of silt, ensuring that buried eggs are bathed in cold, well-oxygenated water throughout winter.
Stream-type" Chinook—like those originating from Alaska's Yukon River—spend a significant portion of their life cycle in the headwater streams of large river systems and tend to have a longer freshwater residency and migrations compared to their "ocean–type" counterparts. This makes them particularly vulnerable to freshwater habitat fragmentation and loss, or the drying, thawing, and rising water temperatures associated with changing climatic conditions in the Arctic.
Before smolts migrate to sea, they make their living among a wide variety of freshwater habitat types including main-stem rivers, side channel braids, headwater streams, and lower gradient streams with pools and wood for cover. A Yukon River Chinook may move hundreds of miles from their natal stream and travel among these different habitat types to find what it needs to survive the different seasons and environmental conditions typical of Interior Alaska. A barrier caused by a seemingly mundane culvert placed where a gravel road crosses a stream and not designed to pass fish can prevent or delay juveniles from reaching overwintering grounds or some other key resources needed for survival.
For a Yukon River Chinook, completing each life stage requires avoiding different sets of predators and contending with the dynamic nature of one of the last largely uncontrolled large rivers in the world (save for a dam at Whitehorse, Yukon). That includes ice and a dynamic environment shaped by the millions of tons of sediment moving towards the sea, and a discharge that exceeds a hundred thousand cubic feet of water per second.
Destined for the rich waters of the Bering Sea, and perhaps, ultimately, the North Pacific, juvenile Yukon River Chinook make their way downriver one or more years after hatching (after spring thaw) and transform from parr into smolts for the transition into saltwater. At sea, they'll acquire the strength and size needed to swim thousands of miles up the Yukon where the beginning of a new cohort's life cycle will mark the end of theirs—but not typically before spending several years pursuing and growing fat off the ocean's smorgasbord of prey—like herring, sandlance, and squid.
Just as juveniles are camouflaged with parr marks to break up form and avoid predation in freshwater, smolts and adults wear a color phase more suited for pelagic environments. If you were to fly over Chinook swimming near the surface at sea, you would see the blue-green-purple hues of their backs, speckled with black spots; from the side, chrome; and from below looking up, white, to match the lighter sky above.
Worldwide, less than two dozen rivers are longer than the Yukon, and Yukon River Chinook migrations are likewise some of the longest of any salmon in the world. Originating in the Canadian Province of British Columbia, this river flows through the Yukon Territory before crossing the U.S.-Canada border. Flowing east to west across the entirety of Alaska, it finally fans out across the Yukon-Kuskokwim Delta (roughly the size of Oregon) before draining into the Bering Sea. The amount of energy needed to migrate upriver makes Yukon kings highly prized for their oily flesh. Yukon River Chinook are the preferred food source for Alaska Natives that have co-existed with and subsisted on Chinook and other Pacific salmon species since time immemorial.
Today, Chinook populations south of northern California's Sacramento River have been extirpated, and a number of other populations outside Alaska are considered Endangered, Threatened, Candidates for Listing, or Species of Concern. These declines are largely the result of human activities having significantly reduced access to inland habitats and the quality and quantity of those remaining. Even in Alaska, Chinook populations are showing signs of stress: 11 are currently considered Stocks of Management or Yield Concern and statewide returns are down.
Maintaining broad diversity of river-specific, thus genetically distinct, populations of Chinook salmon throughout their range is key to the resiliency and stability of the species as a whole and associated fisheries. Broad genetic diversity is undoubtedly linked to the varying habitats and stream conditions within and among rivers to which they are adapted. Because Chinook migrations cross state and international boundaries, many stakeholders are involved with their conservation and management—as well as understanding and addressing declines. Keeping people connected to rivers and the fish is incredibly important in maintaining the relevance of this species.
Katrina Mueller, Ph.D., is an outreach specialist for the U.S. Fish and Wildlife Service, stationed in Anchorage, Alaska.