“Salar was not feeding, he was not hungry; but he was enjoying remembrance of this river-life with awareness of an unknown great excitement before him. He was living by the spirit of running water. Indeed, Salar’s life was now the river: as he explored it higher, so would he discover his life.”
from Salar the Salmon by Henry Williamson
Introduction
The Atlantic Salmon (Salmo salar) is a remarkable species of fish that undergoes a fascinating life cycle. From its birth as a tiny egg to its triumphant return as a mature adult, the journey of the Atlantic Salmon is a tale of survival and adaptation. In this webpage, we will explore the various stages of the Atlantic Salmon’s life cycle, following its remarkable journey from freshwater to the vast ocean and back to its natal river to spawn.
Stage 1: Spawning
The life cycle of the Atlantic Salmon begins with spawning. This process typically occurs during the late autumn and early winter months when adult salmon return to their natal rivers to lay their eggs. These natal rivers can be located hundreds or even thousands of miles away from the open ocean. The female salmon, known as a hen, uses her tail and body to create a shallow depression in the gravel of the riverbed, called a “redd.” She then releases her eggs into the redd whilst the male fish, known as a cock, attend close by to fertilize them with his milt (on the redds, there often is fierce competition amongst the cock fish to fertilise a hen’s eggs, and it is not rare to find that sexually immature parr can sneak in under the radar to fertilise, whilst their larger relatives are busy sparring!. Once the fertilization is complete, the female uses her tail to cover the eggs with gravel to protect them from predators and being lost in the current. A hen fish carries approximately 800 eggs per pound of body weight, so maybe think about the potential for increased numbers of fish if you are tempted to take one home! A 20lb hen “fish of a lifetime” killed and taken home deprives the river of a potential 16,000 eggs!
Stage 2: Egg Incubation
The fertilized eggs are now left in the gravel to incubate over the following weeks and months. The temperature of the water determines the speed at which the eggs develop – as with so many living creatures, evolution has organised itself to coincide the hatching of the eggs with the onset of new invertebrate life, a primary food source for the growing juvenile fish. Generally, it takes several weeks to a few months for the eggs to hatch, depending on environmental conditions. During this incubation period, the eggs remain vulnerable to disturbances such as sedimentation and pollution, which can affect their survival rate.
Stage 3: Alevin
Once the eggs hatch, the tiny salmon that emerge are called alevin. At this stage, they remain hidden in the gravel, absorbing the remaining yolk sac attached to their bodies for nourishment. Alevin are highly sensitive to light and will often hide in the safety of the substrate to avoid predators. As they grow, the yolk sac depletes, and they start to develop pigmentation.
Stage 4: Fry
As the alevin exhaust their yolk sacs, thereby becoming more mobile, they transform into fry. At this point, they emerge from the gravel and remain relatively close to the hatching areas, on the lookout for food, competing with other juvenile fish, in a typical Scottish river, principally trout. Fry are typically about 2 to 3 inches long, depending on the supplies of food and are still relatively vulnerable to predation, particularly by larger trout and ducks such as goosanders and mergansers.
The large pectoral fins which distinguish salmon fry and parr from their Salmo Trutta cousins enable them to hold station in faster flowing water, thereby a modicum of extra protection.
Stage 5: Parr
As the fry continue to grow and adapt to their surroundings, they develop a distinctive pattern of “fingerprint” markings. At this stage, they are referred to as parr. These markings provide excellent camouflage in the freshwater streams, helping them hide from predators. Parr feed on larger invertebrates, small fish, and even some plant matter.
Stage 6: Smolt
After spending a year or two in freshwater, the parr undergo a significant transformation known as smoltification. Smoltification is triggered by various environmental factors, including changes in day length and water temperature. During this process, the salmon undergo physiological changes that enable them to adapt to a saltwater environment. Their body colour changes to a silvery hue, and they become more streamlined for life at sea.
Stage 7: Migration to the Sea
Once smoltification is complete, the young Atlantic Salmon begin their migration to the open ocean. This journey can be arduous, as they navigate through rivers, estuaries, and coastal waters, facing various challenges such as predators, dams, fish farms and pollution. However, those who successfully reach the ocean have access to a vast feeding ground that offers them an abundance of food.
Stage 8: Ocean Life
During their time at sea, which can last from one to several years, Atlantic Salmon feed on a diet of sandeels,fish, squid, and crustaceans. They grow significantly during this period, sometimes reaching impressive sizes. Their time at sea also exposes them to numerous dangers, including fishing nets, predators, and changes in ocean conditions.
Stage 9: Return to Natal River
As the adult Atlantic Salmon approach maturity, they experience an innate urge to return to their natal rivers to spawn. This incredible homing instinct guides them back through hundreds or thousands of miles of treacherous ocean and coastal waters to the same river where they were hatched.
Stage 10: Spawning Reprise
Upon reaching their natal river, the adult salmon repeat the same spawning process that initiated their life cycle. The hens create redds, lay their eggs, with the cock fish alongside to fertilize the eggs as they are deposited.
Unfortunately, this arduous journey, together with the stresses of spawning, take a toll on the adult salmon, and the mortality rates, particularly amongst the cock fish, can be high. Numbers of post-spawning adults, however, do survive, and will gradually make their way back towards the sea. At this stage of their life cycle, they are referred to as “kelts”. Fish that do survive gradually will regain their silvery sheens, and all too readily will take a fly or other bait – often causing an increase in the heartbeat of an angler, who may be out looking for a prized Spring Salmon in the early parts of the new season! A kelt may look silvery, but will tend to be “skinny” and have greyish gills (rather than the pink of a ‘yet to spawn’ fish). By law, all kelts must be returned to the water unharmed.
Conclusion
The life cycle of the Atlantic Salmon is a remarkable journey of adaptation, perseverance, and instinct. From the tiny, vulnerable eggs hidden in the riverbed to the majestic adults that battle back to their natal rivers, each stage of their life cycle is an awe-inspiring testament to the resilience of nature. However, the Atlantic Salmon faces numerous challenges in the modern world, including habitat destruction, pollution, overfishing, and climate change. It is crucial that we understand and appreciate their life cycle to ensure the preservation of this iconic species for future generations.