What do salmon eat in the sea? While many people hold a vague understanding of this question, the reality is that our knowledge on the matter remains limited. Science can only offer a partial glimpse into the life of Atlantic Salmon at sea.
Above: A pioneering figure in high-seas salmon exploration, the late Mr. Flemming Madsen, proudly displays an Atlantic salmon caught in the Baltic Sea near Ystad.
Marine biologists propose that salmon are opportunistic feeders, and research has not definitively concluded on their food selection, feeding behavior, and foraging habits, particularly concerning the Atlantic Salmon species.
What do salmon eat in the sea?
At sea, Atlantic salmon primarily feed on fish such as capelin, sprats, sand eels, and large zooplankton organisms, notably euphausiids and amphipods.
According to surveys of salmon stomach contents, fish may constitute the majority of the diet by weight, while shrimps could represent up to 95% of the food by number.
Left: Pictured is the author with a 20-kilo, 120-centimeter (44 lb. and 47 inches) Atlantic salmon caught in the Baltic Sea. It was hooked at a depth of 135 feet over 200 feet of water using a salted sprat. The fight lasted 55 minutes. Inside the salmon’s stomach were found 13 sprats and a small sea trout, while the sea trout itself contained three sticklebacks.
Note the impressive silver tail of this apex deep-sea predator.
Baltic salmon is on a protein-rich diet
In a study from 1968 (Throw 1968), researchers examined Baltic salmon and found that individuals longer than 60 centimeters (23.6 inches) consumed a minimum of 50 grams of food daily.
Additionally, it is estimated that the entire population of Atlantic salmon in the Baltic Sea would collectively consume over 16,000 tons of sprats annually.
Pictured is the Common European Sprat (Sprattus sprattus), the primary food source for Atlantic salmon residing in the Baltic Sea. These sprats typically grow to a size of 14 to 15 centimeters.
What do salmon eat in the sea?
Shrimps: a sought-after meal
* Studies into salmon feeding at high seas in the North-East Atlantic by biologists Jacobsen J. A. and Hansen L. P. (2001) show that shrimps accounted for 95% of the food in number but only about 30% by weight.
By weight, 66% of the stomach content was fish, particularly mesopelagic fish. Some larger pelagic fish, such as herring, blue whiting, and mackerel, were also part of the diet. Fish and crustacean prey accounted for 96% of the weight of all prey taken by salmon, but
Left: The Frances fly is one of the most successful salmon flies ever made -most likely interpreted by salmon as a shrimp.
Odd finding in salmon stomacs at high sea
the report also mentions a small percentage of birds and bird remains… being part of the salmon stomach content !!
With this biological survey from 2001, we plunged into the depths, meticulously examining the contents of thousands of salmon stomachs to identify some of the most common critters that salmon consume.
The repport we used to learn what do salmon eat in the sea?
Read the interesting report by Mr. Jan Arge Jacobsen and Lars Petter Hansen
Important crustaceans from the Jacobsen and Hansen survey
Studies into salmon feeding at high seas in the North-East Atlantic show that shrimps accounted for 95% of the food in number, but only about 30% by weight
Above: Crustaceans of the genus Thermistor libellula one of the crustaceans salmon, had eaten in the sea north of the Faeroe Islands. Along with other crustaceans, this food source was found in high numbers during the survey conducted during late autumn. Photo Mr Claude Nozères, World Register Of Marine Species
Above: Thermisto libellula in comparison to its cousin: Themisto abyssorum. Photo Mr Kwasniewski Slawomir, World Register Of Marine Species
Above: Meganyctiphanes norvegica swimming with a Thermisto libellula (see above) – Both important animals in the zooplankton food chain. Both are 30 – 45 millimetres big. Photos Mr Claude Nozères, World Register Of Marine Species
Above: Sergestes arcticus (top of photo), another type of shrimp. Below in the same photo is a Nothern krill, Meganyctiphanes norvegica. Photo Mr Claude Nozères, World Register Of Marine Species
Above: Paraeuchaeta norvegica. A marine planktonic copepod 6 – 7 millimetres long – The blue sack at the rear is eggs. Photo © ®Fisheries and Oceans Canada, Jean-François St-Pierre, 2011
Above: Crustaceans of the genus Themisto abyssorum – another important food source found during the survey. Photo Mrs Joanna Legeżyńska, World Register Of Marine Species
Above: From top to bottom: Thermisto libellula, Themisto abyssorum and Thermisto compressa. Three crustaceans were found in great numbers in the survey conducted in the North-East Atlantic. Photo Mr A. Kraft, Alfred-Wegener-Institut
Above: Meganyctiphanes norvegica A krill commonly known as the Northern Krill. A crustacean that is a central figure in the zooplankton mass and an important course of food for whales, birds and fish in the North Atlantic. Photo: © & ® Øystein Paulsen
Above: Hymenodora glacialis Brilliant blood-red shrimp growing to 19 – 20-millimetre. Photo Mr Russ Hopcroft, World Register Of Marine Species
Above: Eusirus holmi – A 40 – 50-millimetre big Gammaridea. Photo Mr Russ Hopcroft, World Register Of Marine Species
Important fish and squid from the Jacobsen and Hansen survey
By weight, 66% of the stomach content was fish, particularly mesopelagic fish. Some larger pelagic fish such as herring, blue whiting and mackerel were also part of the diet.
Above: Maurolicus muelleri: Pearlside. A small silver fish with pigment spots. Size: 40 – 80 mm – a species that lives (mesopelagic) from 20 – 400 meters deep. It lives at greater depth during the daytime and rises toward the surface when it gets dark. Photo Mr Jim Ellis, World Register Of Marine Species
Above: lampanyctus crocodilus or Jewel lanternfish. A small fish that feeds on zooplankton found from 45 – 4000 meters depth – fully grown it will stay between 700-1,000 meters during the day and 4000-1,000 meters at night. Photo Mr Costa, F, Discoverlife
Above: Myctophum punctatum. Its common name is spotted lanternfish. Just like Notoscopelus kroeyeri it lives to the depth of 1000 meters during the daytime but may come to the surface during nighttime Photo Mrs Daphne Themelis, World Register Of Marine
Above: Clupea harengus Linnaeus. Commonly known as herring belonging to the family Clupeidae (herrings, shads, sardines, menhadens), which consists of some 200 species, A large family of fish of great importance to marine life also in the North Atlantic. It feeds on copepods, crustaceans and fish eggs. Prefer relatively shallow waters 1 – 200 meters.
Above: Gaidropsarus argentatus. Commonly known as Arctic rockling, it is a genus of lotid fishes. (Here, a juvenile specimen). Found offshore at depths of 150- 2000 meters on soft bottoms. Photo Mr Claude Nozères, World Register Of Marine Species
Left: Scomber scombrus. The Atlantic mackerel is a pelagic schooling species on both sides of the North Atlantic Ocean. The species is also called Boston mackerel or just mackerel. The mackerel is, in its own right, a ferocious predator that can grow to a length of 50 centimetres – but like most fish, they start out being sizable prey to salmon that roam the same waters as the mackerel. The mackerel strain is growing strong these years, and the species is migrating further north into the Arctic Ocean – Some say that they have become a potent adversary to the Atlantic salmon, who will have to fight for the same food as the Atlantic mackerel – New surveys on this hot topic will surely be worth reading.
bove: gonatus fabricii or Boreoatlantic gonate squid or boreoatlantic arm hook squid, is a squid in the family Gonatidae. (Here is a juvenile specimen) It occurs in the northern Atlantic Ocean from Canada to the Barents Sea. Grows to 30 cm in length. This tiny beautiful squid was well represented in the Norwegian team’s late autumn and winter surveys. Photo Mr Claude Nozères, World Register Of Marine Species
Above: Arctozenus risso – A long fish of the baracudinas family, occurring singly or in small schools mainly at 200-1000 meters depth. Grows to 29-centimetre. Photo Mr Henk Heessen, World Register Of Marine Species
Above: Notoscopelus kroeyeri, Another deep sea fish that lives to the depth of 1000 meters during the daytime but may come to the surface during nighttime – Grow to 17 centimetres. It has glowing dots along the body that help disguise the fish’s outline when seen from below. Photo Mr Henrik Carl, Fiskeatlas –
Above: Benthosema glaciale. Commonly known as Glacier lanternfish. Also, a small migrating deep-sea fish that surges to 700 – 1000 meters at day time to return close to the surface at night time Photo Fisheries and Oceans Canada, World Register Of Marine
Above: mallotus villosus capelin: The capelin or caplin is a small fish of the smelt family found in the Atlantic and Arctic oceans – A important food source for the Atlantic salmon. Photo Mr Claude Nozères, World Register Of Marine Species
Above: Micromestistius poutassou. Commonly known as Blue Whiting, belonging to the cod family. Found over the continental slope and shelf to more than 1000 meters, but more common at 300-400 meters. Blue whiting can grow to a length of more than 40 centimetres. Photo Mr Henk Heessen, World Register Of Marine Species
Above: Belone belone. Commonly known as garfish. Yet another ferocious predator that the Atlantic salmon will feed on when they find them in the correct size. The garfish, or sea needle, is a pelagic, oceanodromous needlefish found in brackish and marine waters of the Eastern Atlantic, the Mediterranean Sea and the Baltic Sea. The garfish is a long and slender fish that grows to about 50 to 75 centimetres – They hunt in packs near the surface, Photo Mr Pillon Roberto, World Register Of Marine Species
Above: Gasterosteus aculeatus or three-spined stickleback. Lives in marine, brackish, fresh. Most populations are anadromous (they live in seawater but breed in fresh or salty water). Among the larger sticklebacks, it is usually 5 cm (2 in) long.
Still curious? - Read the whole report!
Read the interesting report by Mr. Jan Arge Jacobsen and Lars Petter Hansen
What do salmon eat in the sea? - Facts from other surveys on salmon feeding
Science will tell us that adult salmon will prey on whatever organisms are present
86 % of the food was Caplin
A survey from 1952 done at the Faroese Islands showed that pre-grilse had eaten amphipods (thermistor gaudichaudi) – and squid (Brachioteuthis riisei), while another study from 1967 done by Shearer and Balmain off Greenland showed that salmon had been taking mainly 86 % Capelin mallets Villousus
Right: mallotus villosus capelin: The capelin or caplin is a small fish of the smelt family found in the Atlantic and Arctic oceans – An important food source for the Atlantic salmon. Photo Mr Claude Nozères, World Register Of Marine Species
Salmon inhabiting the coastal waters of Greenland predominantly feed on fish.
According to Reddin’s research in 1988, salmon off West Greenland primarily consume Capelin and sand eels (also known as sand lance) in coastal waters. In the Labrador Sea, their diet includes herring, barracuda (Parallels coregonides borealis), amphipods, euphausiids, and squid, which collectively form a significant portion of their food intake.
Left: Pictured is Hyperoplus immaculatus, commonly known as the Sand eel or sand lancer, names used for numerous species of fish. Sand eels prefer habitats near the seabed floor, particularly areas with smooth gravelly sand bottoms. They serve as a vital food source for many fish, birds, and whales.
Salmon in the Grand Banks region predominantly feed on Capelin and sand eels
According to Templeman (1968), Lear (1972), and Lear and Christensen (1980), as cited by Redding (1988), salmon caught over the Grand Banks were observed feeding on Capelin and sand lance (sand eel). Additionally, it was noted that salmon in the oceanic depths to the east of the Grand Banks were consuming barracuda, black smelt, and amphipods.
Right: Pictured is Hyperoplus immaculatus, commonly known as the Sand eel or sandeel.
Young cod is on the menu in Labrador
In the coastal waters of Newfoundland, salmon feed mainly on herring, capelin and sand eels, while in Labrador; pteropods, sand eels, young cod and capelin are the primary food (Lear, 1972b.). Reddit (1988) concludes from this wide variety of prey species that adult salmon are opportunistic feeders and prey on whatever organisms are present. Similar conclusions could also be made from examining salmon stomachs from fish caught in the North-east Atlantic.
left: Gadus morhua. Common name cod. Here is a trio of tiny cod. Photo Mr Claude Nozères, World Register Of Marine Species
Caught on sprats, but their primary food sources were small krill and tiny crustaceans
Research by Strtuhers (1970-71) highlighted sea animals such as amphipods and euphausiids as the main dietary components.
Fish caught on longlines baited with sprats supported these findings. Another survey conducted at the Faroese Islands also utilized longlines and discovered amphipods (parathemisto spp.), euphausiids, * myctophidae (Lantern fish), capelin, and Maurolicus muelleri (pearlsides).
Right: Pictured are ** myctophidae, fish of the Lanternfishes family, typically found offshore at depths ranging from 300 to 1200 meters during the day and between 10 and 100 meters at night. Photo credit: Mr. Henk Heessen. World Register Of Marine Species
Squid served as a significant food source in the deep sea.
A separate survey conducted in 1985, examining 1145 salmon stomachs, was carried out by Hanson and Pethon off the shelf of Helgeland/Trøndelag (Norway) and in the oceanic waters of Andenes (Norway). The results revealed that essential food items varied between locations.
At the shelf of Helgeland/Trøndelag, euphausiids and hyperid amphipods were predominant, whereas in Andenes, myctophid Benthosema glacial and the squid Gonatus fabric, along with euphausiids, were the most frequently found food items in the stomachs of caught salmon.
Scottish salmon have been observed feeding on ragworms
Some Scottish salmon, caught in drift nets, were found to have consumed polychaete worms (Nereis spp.), amphipods, euphausiids (Meganyctiphanes norvegica), as well as herring, sprats, whiting, and sand eels (Fraser, 1987).
Photo on the right: Polychaete worms, commonly known as Ragworms (Nereis spp.), are inhabitants of soft and muddy bottoms, where they dwell in a network of burrows. They emerge from their hiding places to spawn and are sought after as prey by various marine animals. Photograph Copyright © 2008 Field Studies Council.
How do salmon get to the food out at sea ?
Flowing with the currents
Sea currents, including gyres, play a crucial role in transporting small salmon parr from rivers and fjords to their feeding grounds. These young salmon appear to migrate towards waters with optimal temperatures for growth, adjusting their movements to follow the cyclical patterns of their prey within the vast water column as sea temperatures fluctuate throughout the seasons. (Image source: sciencelearn.org)
Spanning the oceans
Atlantic salmon exhibit extensive oceanic migrations, seeking out areas where oceanographic conditions foster the distribution of zooplankton, a primary food source for smaller fish, shrimps, and crustaceans. Remarkably, tagged salmon have been documented traveling on intercontinental journeys, with individuals tagged in the United Kingdom later being recaptured in North America, while others tagged in North America have been caught in Norway.
Climate changes may alter the life at sea – and stocks of Atlantic salmon
Certain scientists have proposed that the notable shifts observed in sea-surface temperatures across the North Atlantic might have played a role in heightened mortality rates among young salmon, often referred to as post-smolt. It is theorized that these temperature variations could be linked to the pronounced decline witnessed in Atlantic salmon populations over recent decades.
Studies by Cushing (1983) and Dunbar (1981) have demonstrated that climate changes can exert significant impacts on the distribution and abundance of various marine fish species. Alterations in climate can affect surface water temperatures, the intensity of ocean currents, and, by extension, the salinity of seawater due to increased ice melting. Any of these factors have the potential to influence food availability, survival rates, growth patterns, maturation processes, and overall activity levels within marine ecosystems.
Read our 2023 newsletter issue on climate changes and salmon fishing
