Salmon embark on one of nature’s most remarkable journeys, migrating from ocean feeding grounds back to their natal freshwater streams to spawn. This listicle explores what salmon eat during this migration period, focusing on the specific prey and feeding behaviors that sustain them along the way. Whether you’re a fisheries biologist, angler, or nature enthusiast, understanding salmon diet during migration offers insight into their survival and the ecosystems they traverse.
Marine Zooplankton
During the early ocean phase of their migration, juvenile salmon heavily consume marine zooplankton such as copepods and euphausiids (krill). These tiny crustaceans are abundant in coastal waters and provide essential proteins and lipids that fuel rapid growth. Zooplankton’s high caloric density makes them a vital energy source before salmon transition to larger prey.
Small Pelagic Fish
As salmon grow and migrate through marine environments, their diet shifts toward small pelagic fish like sand lance (Ammodytes spp.), anchovies, and juvenile herring. These fish are rich in omega-3 fatty acids, which are crucial for salmon’s energy reserves during long-distance travel. Sand lance, in particular, are a preferred prey due to their schooling behavior and high availability in North Pacific waters.
Amphipods and Other Benthic Crustaceans
Salmon often feed on benthic amphipods such as Parathemisto pacifica, especially in estuarine and nearshore zones during migration. These crustaceans inhabit the seafloor and are a dense protein source, helping salmon maintain muscle mass. Their presence in both fresh and saltwater transitional zones makes them a reliable food item during migration.
Cephalopods (Squid and Octopus)
In deeper oceanic stages of migration, salmon consume small squid species like Gonatus spp. and juvenile octopuses. These cephalopods offer high levels of fat and protein, supporting the energetic demands of extended swimming. Their swift movements also provide salmon with challenging prey that enhances hunting skills.
Insects in Freshwater Systems
Once salmon enter freshwater rivers and streams, their diet shifts to include aquatic insects such as mayflies (Ephemeroptera), caddisflies (Trichoptera), and stoneflies (Plecoptera). These insects are abundant in clean, oxygen-rich waters and provide critical nutrients during the final migration stages before spawning. Feeding on insects also helps salmon maintain strength after ocean fasting.
Other Fish Species (Including Conspecifics)
Some larger salmon, particularly Chinook (Oncorhynchus tshawytscha), exhibit piscivory by preying on smaller fish, including juvenile salmon of other species. Cannibalism or predation on other fish like sculpins and smelt helps supplement their diet with high-protein meals. This behavior is more common in ocean and estuarine phases where prey diversity is greater.
Planktonic Crustaceans (Euphausiids and Mysids)
Krill (Euphausiacea) and mysid shrimp are common planktonic crustaceans consumed by migrating salmon. These prey items are rich in lipids, essential for building fat reserves needed to endure freshwater migration where feeding decreases. Their swarming behavior makes them easy targets during nocturnal feeding.
Algae and Detritus (Incidental Consumption)
While primarily carnivorous, salmon sometimes ingest algae and organic detritus, particularly when feeding in estuarine environments where plant matter is abundant. Although not a significant nutritional source, incidental consumption of detritus can introduce beneficial microbes and aid digestion. This behavior is more common in juvenile salmon adjusting to changing salinities.
Amphibians and Small Invertebrates
In freshwater migration stages, some salmon opportunistically feed on small amphibians like frogs or aquatic invertebrates such as freshwater shrimp and snails. These prey provide additional protein and nutrients, especially where insect populations fluctuate seasonally. This dietary flexibility supports salmon’s adaptability in diverse freshwater habitats.
Energy Reserves and Fasting Periods
Interestingly, many salmon species reduce or cease feeding altogether during the final upstream migration to spawning grounds. They rely heavily on stored fat and muscle tissue accumulated during ocean feeding. This fasting period preserves energy for reproductive activities but also means prior diet quality directly impacts migration success.
How to Choose
When considering what salmon eat during migration, the key factors are life stage, habitat, and energy demands. Juvenile salmon focus on small zooplankton and insects to fuel growth, while adults shift to high-fat prey like small fish and cephalopods to build reserves. Freshwater feeding is opportunistic and often limited, with many species fasting entirely before spawning. Understanding these dietary shifts helps fisheries managers support habitat conservation and anglers anticipate salmon behavior.
Frequently Asked Questions
Q: Do salmon eat during their entire migration?
Not always. Many species reduce or stop feeding during the final freshwater migration to conserve energy for spawning.
Q: What is the most important food for salmon in the ocean?
Small pelagic fish like sand lance and juvenile herring are critical for building fat reserves required for migration.
Q: How do salmon find food during migration?
Salmon use keen vision and olfactory senses to locate prey, often feeding during low-light conditions to avoid predators.
Q: Does diet vary between salmon species?
Yes, species like Chinook tend to be more piscivorous, while sockeye focus more on zooplankton and insects.
Q: How does water salinity affect salmon feeding?
Salmon adjust their diet as they move from saltwater to freshwater, shifting from marine prey to aquatic insects and small invertebrates.
Q: Can salmon survive without eating during migration?
Many survive by relying on stored energy, but adequate feeding beforehand is essential for successful migration and spawning.
Final Thoughts
Salmon diets during migration are dynamic and closely tied to their developmental stage and environment. From tiny zooplankton in the ocean to insects in freshwater streams, their varied prey supports the immense energy demands of one of nature’s most challenging journeys. Understanding these feeding habits is vital for conserving salmon populations and the ecosystems they connect. Whether studying salmon ecology or simply appreciating their life cycle, recognizing what salmon eat during migration reveals much about their resilience and adaptability.
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