|Zooplankton, amphipods, insects, squid
|5 – 15 pounds (2.3 – 7 kg)
|0.6–0.84 meters (2 to 2.8 feet)
|Chordata, Actinopterygii, Salmoniformes
|Pacific coasts of Asia and North America (some small landlocked populations father inland)
The Sockeye Salmon
The sockeye salmon is immediately recognizable by the bright red color it takes on during spawning.
The name sockeye originates from a rough translation of the word suk-kegh found in the Coast Salish language of British Columbia.
Suk-kegh appropriately means “red fish.”
The sockeye salmon’s iconic appearance is fitting for such a distinctly important Pacific species.
This fish is an essential keystone species in western North American ecosystems.
Likewise, the sockeye is a keystone of the continent’s fisheries.
The sockeye’s importance as a food source has a rich history, with many indigenous peoples of North America holding it in particular cultural reverence for feeding so many.
Sockeyes are notable for their anadromous life cycle.
Those who manage to evade the many sets of jaws with a taste for salmon embark on the journey of a fish’s lifetime.
Adult sockeyes migrate from their ocean habitat up freshwater rivers to spawn.
Stunningly, these salmon are often destined for the exact river of their birth.
Even more astonishing is that this journey can be made over distances up to 3000 km!
The adult dies after returning home and spawning.
The sockeye’s epic odyssey is then carried on by the new generation, who will spend their juvenile years in freshwater before their passage to the ocean.
In this article, we’ll dive into the fascinating world of sockeye salmon; from their physical characteristics, habitats, diet, behaviors, ecological importance, and cultural significance.
Taxonomy and Classification
The sockeye salmon is otherwise known by its scientific name; Oncorhynchus nerka.
This species is part of the kingdom Animalia, within the phylum Chordata.
It is a ray-finned fish of the class Actinopterygii.
The sockeye is part of the family Salmonidae, the only extant family in the order Salmoniformes.
Fish in this family are referred to as salmonids.
These are fish that inhabit the cold temperate or subarctic waters of the Northern Hemisphere and undergo a migration to freshwater during spawning.
This family is not limited to only “true salmon,” such as the Atlantic and Pacific salmon variants, but includes species like trout, char, and graylings among others.
The genus Oncorhynchus contains 6 extant species of Pacific salmon, one of which being the sockeye, along with 6 extant species of Pacific trout.
This genus evolved around 10 million years ago, probably from freshwater ancestors.
Around 25 million years ago the northern Pacific Ocean began a 15 million year long cooling process.
These colder waters were nutrient-rich, increasing productivity.
Resultantly, the ancestral freshwater species began making feeding trips into the brackish water of estuaries.
Through the evolution of salt pumps in the gills, this freshwater species eventually adapted to the oceanic environments sockeyes inhabit today.
Sockeyes will typically range from 60 to 84 cm in length (2 ft 0 in – 2 ft 9 in).
Most individuals weigh between 5 and 15 pounds (2.3 – 7 kg).
Although sockeyes are known for their bright red color, throughout most of their life sea-going individuals display silver flanks with a bluish top.
This feature earned them the nickname “bluebacks.”
It is only upon returning to their spawning grounds that sockeyes will take on their famous red body, green head combination.
Like all salmonids, the sockeye has a relatively primitive body structure.
This is seen with the far back placement of the pelvic fin and the presence of an adipose fin on the back.
The tail fin exhibits a forked shape.
Their body is slender and covered in rounded scales.
One distinguishing feature of this species is their gill rakers.
Sockeyes display sexual dimorphism.
Sexually mature males are easily identifiable by their humped backs and hook-shaped jaws.
The jaw contains a single row of sharp, clearly visible teeth.
Habitat and Distribution
Sockeye are usually born on the gravel beds of creeks.
A variety of freshwater environments can serve as early-life habitats for sockeye.
These include lakes, streams, and wetlands near estuaries.
As adults, sockeyes migrate downstream of a tributary river to the Pacific Ocean.
Sockeyes return to the aforementioned freshwater habitats at the end of their lives.
A small segment of sockeyes spend their entire lives in freshwater.
In the Pacific Northwest, these non-anadromous salmon are known as “kokanee.”
Kokanee are smaller than their migratory counterparts, rarely growing over 1.2 feet in length.
These fish inhabit landlocked bodies of freshwater.
Sockeye are most prolific on the west coast of North America.
In North America, the species’ range extends from the Klamath River in Oregon up to Point Hope in northwestern Alaska.
Sockeye are most common in Alaska.
The farthest inland that the anadromous sockeye ranges on the continent is Redfish Lake, Idaho.
Sockeye can also be found on Asia’s Pacific coast.
The farthest this species extends westwards is the Anadyr River in Siberia.
Sockeyes prefer colder temperate or even subarctic waters.
Behavior and Distribution
The sockeye’s most notable behavior is of course the spawning migration.
Folklore has long held that the sockeye will return to the exact river its parents once migrated up during spawning.
There are various scientific theories regarding what makes this possible.
Some believe that chemical and geomagnetic cues guide them back to their birthplace.
Others think that the salmon’s strong sense of smell takes an imprint of its home at birth, allowing it to return later.
Sockeye salmon are semelparous, meaning they die a few weeks after spawning.
Overall, the sockeye’s migration is one of the most extreme in the entire animal kingdom.
Sockeyes employ various strategies to reduce the likelihood of predation during feeding.
They can alter their position in the water column, the length and time of their feeding sessions, and their target prey.
Sockeye salmon travel in schools which can change formation for defense purposes.
These behaviors also contribute to the sockeye’s success as a predator.
Sockeye salmon form hierarchical groups.
Reproductive success varies amongst males and is dependent upon body size and shape.
Generally, males with a larger and more distinct hump will see greater reproductive success.
Non-reproducing males act as subordinates to their reproducing counterparts.
The non-reproducing male will follow a mating pair.
When the opportunity arises, they will quickly swim into the nest and release their sperm.
Aggressive behavior in sockeyes is most prevalent among dominant males.
These conflicts are the result of one intruding on another’s territory.
Aggressive interactions between females are also important as they determine which individuals get access to the best quality nest sites and larger mates.
Sockeyes sometimes compete with each other for food while living in freshwater.
Occasionally, they may even compete with other species in their environment.
Diet and Feeding
Sockeyes primarily feed on zooplankton while in salt and freshwater.
This dietary preference distinguishes them from other species of Pacific salmon.
In freshwater, a smaller component of their diet consists of amphipods and insects.
In saltwater, they will occasionally feed on juvenile and small adult fish.
Rarely, they will feed on squid.
Sockeyes employ the diel vertical chronology.
This feeding strategy sees the fish move to the upper layers of a body of water during the night to feed, returning to the bottom during the day.
Patterns of movement like this one are designed to combat the risk of predation during feeding.
This is essential for the sockeyes’ survival, as they are an important prey species for many larger animals.
In the ocean, sharks, lampreys, and marine mammals all prey on sockeye.
While in freshwater sockeye are preyed on by bears, eagles, and occasionally wolves.
The sockeye salmon migration occurs in autumn.
This makes it an important feeding opportunity for animals like bears that hibernate through winter.
Reproduction and Life Cycle
Male sockeyes will select a breeding partner based on her size and readiness to spawn.
A larger body indicates that the female can lay a greater amount of eggs.
The female will alter her breeding rate depending on the size of the male, spawning faster with a larger male.
Females are also entirely responsible for parental care.
They choose and defend a nest site, known as a redd, for the remaining weeks of their lives.
Sockeyes stop feeding as soon as they enter freshwater during the spawning migration.
The embryos are nourished purely through endogenous food supplies, those nutrients already contained within the adult.
Reproduction and the associated migration is a massive energy investment, resulting in the death of the reproducing sockeye.
Sockeyes hatch 8 to 20 weeks after fertilization.
One female can lay 2000 to 5000 eggs.
Only 1 in 1000 eggs will live long enough to return to freshwater for spawning.
Newly hatched salmon stay in the gravel and rely on their yolk sacs for nourishment until the spring.
They are called alevins during this first stage.
When the juvenile is no longer reliant on the yolk, it enters the fry stage.
During this time they will spend 1 to 3 years in freshwater.
Next they reach the smolt stage, migrating to the ocean.
Sockeyes typically reach sexual maturity at the age of 5.
Mature males develop a large hump and snout.
Females undergo gonad enlargement.
Fully fledged adults soon embark on the migration, making the sockeye’s natural life span around 5 years.
Ecological Role and Interactions
The sockeye salmon is a keystone species in western North America.
As a prey species, the sockeye provides nutrients essential for the over-winter survival or migrations of predators.
Even dead salmon have a huge impact on their surrounding ecosystem.
Salmon carcasses are a substantial source of nitrogen and phosphorous.
Because of this, the salmon run acts as a giant nutrient pump.
Their migration pushes marine nutrients into rivers with otherwise low productivity.
The sockeye salmon run in southwest Alaska has been found to contribute 170 tons of phosphorous annually to Lake Illiamna.
These nutrients then integrate into the food chain of a river and its surrounding landscape.
Brown bears will spread these nutrients into nearby forests, facilitating the growth of trees lining freshwater streams.
These trees will then protect the stream from erosion.
In southeast Alaska, sockeyes provide nearly 25% of the nitrogen found in tree foliage.
Resultantly, trees affected have growth rates about three times greater than those in areas without spawning salmon.
The increased nutrients in the river also help the salmon themselves, improving the survival and growth rates of newly hatched individuals.
Conservation Status and Threats
The IUCN Red List designates sockeye salmon as a species of Least Concern.
This means that the global sockeye population is not at risk of extinction.
However, 4 evolutionarily significant units of sockeye are considered endangered.
An evolutionarily significant unit, or ESU, is a specific population of a species that presents distinct conservation concerns.
Two of these ESUs are located in the United States; Ozette Lake in Washington, and Snake River in Idaho.
The other two are found in the Canadian province of British Columbia at Cultus Lake and Sakinaw Lake.
With the example of the Sakinaw Lake population, unique characteristics like an early river-entry time, longer lake residency pre-spawning, and the small size of adults put them at heightened risk of extinction.
While sockeyes are not at immediate risk of extinction, their populations across North America have been in decline for over a century.
The primary risk to sockeye numbers is the degradation of spawning habitat.
This may be the result of land development, logging, or other forms of resource extraction.
Conservationists have employed various techniques in their attempts to reverse the declining trend.
These include captive rearing in hatcheries, removing dams that block salmon runs, and restoring damaged habitats.
One notable conservation plan is the Puget Sound salmon recovery effort in Washington.
This project is a collaboration of federal, state, and local governments with nonprofit organizations aimed at restoring Pacific salmon habitat.
Overfishing has also contributed to the sockeye’s decline over the last century.
Global warming has become a threat to sockeye, as they perform poorly in warmer waters.
Unique Adaptations and Survival Strategies
A key adaptation of sockeyes is their gill rakers. Gill rakers are thin bony projections of a fish’s gill arch.
They allow for the suspension feeding of small prey animals.
Since the sockeye’s diet consists mainly of zooplankton, gill rakers are essential for feeding.
They can also be used to catch very small fish.
Gill rakers in sockeye are serrated and particularly lengthy. A sockeye will generally have 30-40 rakers.
During the smolt stage, sockeyes rely on camouflage for protection.
The developing fish’s scales are coated with silver to make them less visible in the water.
Cultural Significance and Human Interactions
Sockeye salmon have been harvested by First Nations peoples in North America for centuries.
These groups rely on the fish for both food and ceremonial purposes.
As a result, the salmon has an important place in the art of Northwestern indigenous peoples.
It is regarded as a symbol of perseverance, self-sacrifice, prosperity, and regeneration.
In Indigenous art, the male salmon is distinguishable by a curved beak-like mouth.
Females are depicted with circles on their bodies, representing eggs.
In certain Pacific Northwestern Indigenous mythologies, salmon are immortal humans that live in villages under the water.
These humans dress up as fish in the spring to offer themselves as food.
Due to this belief, these peoples often place the full skeletons of consumed salmon back into the river so the salmon peoples’ spirits can rise again.
Since the 19th century, sockeyes have been harvested by commercial fisheries.
These operations employ gill nets, purse seines, trolling gear, and handlines.
Sockeyes caught via these methods are considered a sustainable food source.
Commercial sockeye operations in Alaska alone create 15,000 jobs and bring in $990 million annually.
The sockeye was the first species of Pacific salmon to be harvested and canned in significant quantities.
Overfishing can be a significant threat to sockeye populations that are already experiencing the pressure of habitat loss.
It is essential to ensure the sustainable use of this important natural resource.
Future Prospects and Research
The effect of global warming on sockeye populations is already being observed in British Columbia.
The province has seen a high degree of fluctuation in sockeye run size.
This fluctuation is speculated to be the result of changing water temperatures.
In the Fraser River, the resident sockeyes vary in their thermal tolerance.
On the other hand, most individuals in the Chilko River sockeye population show the ability to maintain cardiorespiratory function at higher temperatures.
This adaptation will prove crucial to surviving the province’s warming waters.
One experiment sought to determine the cause of this adaptation.
It took juveniles from the Chilko River alongside those from Weaver Creek and reared them alongside each other at temperatures of 5 °C and 14 °C.
The experiment found the different sockeyes do not diverge in their heart’s force-frequency response or cardiac pumping capacity.
Therefore, the cause of the Chilko River population’s thermal tolerance has not yet been determined.
The sockeye is an anadromous species of Pacific salmon with a distinct red coloration during spawning.
It inhabits both bodies of freshwater, most prolifically on North America’s west coast, and the Pacific Ocean at different stages of its life.
This fish mainly relies on zooplankton as a food source.
Its epic spawning journey is a key feeding opportunity for a variety of predators.
A keystone species, the sockeye’s nutrient contribution to freshwater environments far outweighs its biomass.
The sockeye has long served a significant role in First Nations cultures.
Likewise, it is an important species for the commercial fishing industry.
Sockeye populations have been declining for over a century.
With the effects of habitat degradation, overfishing, and now global warming all taking a toll on the sockeye, it is critical that we continue to protect this species.
- https://wildsalmoncenter.org/why-protect-salmon/#:~:text=Salmon%20runs%20function%20as%20enormous,per%20 year%20to%20 Lake%20 Iliamna.