The salmon shark, scientifically known as Lamna ditropis, is a powerful predator that inhabits the cold, subarctic, and temperate waters of the entire North Pacific Ocean. This heavy-bodied species belongs to the family Lamnidae, also known as the mackerel sharks, which includes the great white shark. The species is highly migratory, ranging from the Sea of Japan in the west to the Gulf of Alaska and down to Baja California in the eastern Pacific. As an apex predator in its ecosystem, the salmon shark’s diet plays an important role in regulating the populations of the fish and other marine life it consumes.
Staple Foods of the Salmon Shark
The diet of the salmon shark is diverse, consisting primarily of pelagic (open ocean) and schooling bony fishes. True to its common name, various species of Pacific salmon, including Sockeye, Pink, Chum, and Coho, form a significant portion of its intake, especially during the annual salmon runs. This predation pressure can be substantial, with one study in Prince William Sound, Alaska, estimating that the sharks consumed a notable percentage of the total annual salmon run in that area during certain years.
Beyond salmon, the shark’s menu regularly features other energy-rich, cold-water species. These staples include Pacific pollock, herring, sablefish, and mackerel, all of which aggregate in large, manageable schools. Cephalopods, such as squid, are also a routinely consumed food source across their vast range.
While their diet is dominated by fish, salmon sharks are known to prey on other vertebrates when the opportunity arises. They have been documented consuming both marine birds and sea otters, though these items are generally considered secondary. The composition of their diet reflects a reliance on the availability and concentration of prey in the wide-ranging pelagic environment they inhabit.
Endothermy and Active Hunting Strategies
The salmon shark’s ability to hunt fast-swimming, cold-water prey is supported by endothermy. Unlike most fish, which are cold-blooded, this shark can maintain a body temperature significantly warmer than the surrounding water, with internal core temperatures recorded up to 20°C above the ambient environment. This physiological feat is accomplished through a specialized network of blood vessels called the rete mirabile, or “wonderful net.”
This counter-current heat exchange system allows the shark to retain metabolic heat in its swimming muscles, eyes, and brain. Warm muscles contract more quickly and powerfully, granting the shark enhanced speed and agility. The high metabolic rate required to maintain this internal warmth is substantial, necessitating a high-volume diet.
A salmon shark must consume approximately 8% of its body weight in food each day to fuel this warm-blooded lifestyle. This constant need for energy makes them highly active pursuit predators, often attacking from below and relying on bursts of speed to secure their meal. While they often hunt alone, they have also been observed aggregating in feeding groups of several dozen individuals when concentrating on dense schools of migrating salmon.
Regional and Developmental Diet Differences
The salmon shark’s diet shifts based on geography and the shark’s life stage. Geographically, sharks that spend significant time in coastal areas, particularly during the summer months, show a higher concentration of Pacific salmon in their diet. Their seasonal migrations are closely linked to the availability of these high-calorie fish near the coastlines of Alaska and other northern regions.
In contrast, those individuals inhabiting the open ocean and southern parts of their range rely more heavily on other pelagic species. Their diet in these offshore areas tends to feature a greater proportion of squid, Pacific pollock, and other schooling fish that are abundant in the deeper, more temperate waters. Studies looking at tissue composition have shown that long-term dietary trends can differ from what is consumed in recent, localized feeding events.
Developmental stage also influences the food choices of Lamna ditropis. Smaller, juvenile sharks exhibit a wider trophic niche, meaning they consume a broader variety of smaller fish and invertebrates. As the sharks grow and mature, their diet often narrows and specializes to focus on the larger, more energetic prey, such as full-grown salmon and other large schooling species. This size-based segregation also results in larger, mature sharks migrating farther north to access the richest feeding grounds.