Salmon are migratory predators known for their remarkable life cycle, spanning from freshwater streams to the ocean. These Pacific fish (Oncorhynchus) undergo a significant transformation as they move from their natal rivers to a marine environment. Their diet shifts dramatically during this anadromous journey, moving from insects and small invertebrates in the rivers to a diverse range of marine organisms at sea. The specific composition of their diet in the ocean phase is largely determined by their species, size, and the particular oceanic region they inhabit. This adaptability in feeding is fundamental to how salmon grow to maturity and store the energy reserves necessary for their eventual return to spawn.
Consumption of Cephalopods by Salmon
Yes, certain species of salmon, particularly the larger types like Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch), do consume cephalopods, which include squid and small octopus. This is an opportunistic feeding behavior that occurs when cephalopods are abundant in a salmon’s foraging range. For example, studies near West Coast Vancouver Island have shown that squid can comprise a substantial portion of the diet for both Chinook and Coho salmon in that area. The direct observation of a salmon’s diet in the open ocean is difficult, leading scientists to rely heavily on stomach content analysis of captured fish. This method has confirmed that adult Chinook salmon feed on squid, alongside various fish species, as they mature in saltwater, and Pink salmon have also been documented to consume squid as they grow larger.
The Primary Forage Base
While squid can be a part of the diet, the majority of a salmon’s caloric intake during its ocean phase comes from schooling forage fish and various macro-crustaceans. Small, energy-dense fish are a dominant food source for mature salmon, providing the high-fat and high-protein nutrition required for rapid growth. Key prey fish include Pacific herring, capelin, sand lance, and age-0 pollock. The other major component of the salmon diet is made up of invertebrates, particularly macro-crustaceans like krill (euphausiids), amphipods, and crustacean larvae. Krill, a small, shrimp-like organism, is a particularly important food source for many species, including Sockeye salmon, which have a diet almost entirely composed of zooplankton and krill. These tiny organisms, though individually small, form dense patches that allow salmon to feed efficiently and meet their high metabolic needs.
Environmental Drivers of Salmon Diet
The diet of a salmon is highly variable and is dictated by a complex interaction of environmental and biological factors. Species-specific differences are pronounced; Sockeye salmon, for instance, are primarily planktivores with long gill rakers adapted for sieving small zooplankton, whereas Chinook are more fish-focused predators. Migration patterns also influence feeding, as a salmon’s specific oceanic zone determines the available prey community. Oceanographic conditions, especially water temperature, play a significant role in dictating dietary shifts. During periods of warmer ocean conditions, salmon tend to exhibit increased piscivory, meaning they consume a greater proportion of other fish, while conversely, colder conditions are often associated with an increase in the consumption of large crustacean zooplankton. These environmental shifts affect the distribution and abundance of both the salmon and their prey, leading to opportunistic feeding on whatever nutrient-rich organisms are most accessible.