Green Lake National Fish Hatchery is a large-scale cold-water hatchery located in Downeast Maine. Built in , the mission of the hatchery has changed from supplementing Atlantic salmon populations in the Penobscot, Merrimack and Connecticut rivers , to a conservation hatchery dedicated to raising river-specific strains of endangered Atlantic salmon for Gulf of Maine rivers.

Three out of every four Atlantic salmon returning to U. waters come from Green Lake National Fish Hatchery. Nashua National Fish Hatchery was established in and is one of the oldest national fish hatcheries still operating today.

Programs at the hatchery support Atlantic salmon, Landlocked Atlantic salmon, American shad, and other aquatic species restoration efforts in many New England waterbodies.

Hatcheries serve as a living gene bank for future recovery. The brood populations originate from rivers like the Penobscot, Machias, Narraguagus, Sheepscot, East Machias, Dennys, and Pleasant rivers. These populations are kept genetically distinct as a safety net to prevent extinction and provide genetic resource needed to produce the next generation of Atlantic salmon.

The mission of the U. Fish and Wildlife Service is working with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. Whether you are an angler, a nature enthusiast, or have heritage ties that connect deeply with this species, this recovery effort is made so that Atlantic salmon and the benefits they provide to the environment will be available for future generations.

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Life Cycle of Atlantic Salmon. The King of Fish. Image Details. Edited By Holly Richards. Migratory Species. Facilities Craig Brook National Fish Hatchery. Green Lake National Fish Hatchery. Nashua National Fish Hatchery. Other Story Credits Bryan Drew. Latest Stories.

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Salmon spawning can be affected by a wide range of environmental and man-made conditions in our rivers and streams, including habitat degradation. For example, deposition of sediment in the gravel used by spawning salmon can reduce spawning success, embryo survival and juvenile salmon production.

Investigations have demonstrated that such impacts can be mitigated by the cleaning of spawning gravels, the use of bankside incubators or the establishment of riparian buffer zones to limit sediment input.

Longer term solutions require improved catchment management based on understanding the source of sediments and their subsequent dynamics in rivers. Understanding the requirements of salmon and the challenges they face at each life stage is vital for managing stocks effectively.

Recent investigations have highlighted the following important issues for spawning salmon:. Atlantic Salmon Spawning Reference List PDF, KB.

Atlantic salmon bury their eggs in gravel nests known as redds to protect them from predation, light, low temperatures and wash-out during high flows. The burial depth, typically less than 30 cm varies with the size of the female fish and the river bed composition. Salmon eggs are relatively large, and incubation is relatively long, with the resulting embryo known as an alevin relying on a yolk sac for a lengthy period before emergence from the gravel and first feeding.

Egg and alevin development are influenced strongly by temperature and this provides the best predictor of when eggs will hatch. Egg burial depth can also influence development, in part by affecting the temperature of the eggs themselves, but also by affecting oxygen content.

Burial depth can also be critical in preventing exposure of the eggs during low flows. Other factors also influence development, and therefore the timing of hatching and emergence, such as the composition of the gravel, stream bed conformation and hydraulics, patterns of river discharge, and mechanical shock.

Such factors can arise as a result of natural variations, but also through human impact. Egg survival can also be affected by the changing climate e. through more frequent storms risking the wash-out of eggs. Emergence from the redd occurs when the alevin is no longer reliant on its yolk sac food reserves and when fry need to start feeding.

It is generally accepted that the timing of adult spawning has evolved in response to local conditions so that the fry emerge at the best time to take advantage of increasing food supplies.

Marked changes in temperature, for example arising from climate change, oxygen levels, or reduced water flow through the redd due to sedimentation or concretion of the gravels during egg and alevin incubation can therefore affect the timing of emergence.

This, in turn, can create a mismatch between emergence and optimum environmental conditions for first feeding resulting in increased levels of mortality.

An unusually warm period in December is believed to have contributed to very poor levels of fry abundance observed in many rivers in England and Wales in Understanding the requirements of salmon and the challenges they face at each life stage is vital to manging stocks effectively.

Recent investigations have highlighted the following important issues for salmon eggs and alevins:. Eggs and alevins Reference List PDF, KB. The period between fry emergence and dispersal from the spawning redd and the establishment of defended feeding territories is a critical period in the life cycle of the Atlantic salmon and populations experience high mortality during this time.

The timing of fry emergence in the spring is determined by environmental conditions during the development of the egg and resulting embryo. The main factors are water temperature and dissolved oxygen concentration, both of which can be affected by natural variations, but also by human impacts as well as the effects of a changing climate.

In pristine habitats, a combination of adult spawning date and the temperature-dependent rate of egg and alevin development, effectively determine when emergence will occur.

The dispersal of fry from spawning redds occurs principally at night. This is generally accepted to be a predator avoidance tactic, so any disruption to this timing is likely to increase levels of mortality. Fry dispersal is predominantly downstream and may be an important means of maximizing use of available habitat.

Subsequent survival and growth can be influenced strongly by competition, as the first fry to arrive in a resource rich habitat defend these territories, with later arrivals often forced to occupy less-suitable locations.

Recent investigations have highlighted the following important issues for salmon fry:. Fry Reference List PDF, KB. Once feeding territories have been established, salmon parr need to grow as quickly as possible, without getting predated upon, so that they are ready for the next stage of their life-cycle in the marine environment.

Growth is primarily controlled by temperature and resource availability, both of which can be affected by natural variations, but also by human impacts as well as the effects of a changing climate.

The rate of parr growth increases with the temperature of the water up to an optimum ~°C. Above this, growth rate is reduced and if the water gets very warm °C the fish are likely to become stressed and seek refuge in cooler areas.

Growth is also regulated by food availability and habitat quality. Parr will grow fastest in rich habitats containing lots of suitable resources , where food intake can be maximised at a minimum energetic cost. In practice, habitat quality varies markedly and can be significantly degraded by human impacts and other factors, and parr will expend energy defending territories and seeking refuge from predators to avoid being eaten.

Various factors thus affect survival and the rate at which salmon parr grow and this, in turn, can affect the age at which parr become smolts and migrate to sea. In addition, evidence is mounting that intrinsic factors carried over from parr freshwater life-history stage i.

smolt quality are important determinants of subsequent marine survival rates. Recent investigations have highlighted the following important issues for salmon parr:.

Parr Reference List PDF, KB. The smolt stage is when the juvenile salmon move from freshwater to the feeding grounds in the sea. It is a period of significant change for the fish involving modifications to the body shape and colour, behaviour and physiology which pre-adapt them to a life in the ocean.

The juvenile salmon become smolts after they have spent at least a year feeding in freshwater and when they have attained a length of 10 cm and above. River temperature and day length all have a role in controlling the development of parr to smolts. Smolts have evolved to migrate to sea in the spring when the sea temperatures and food availability are best for survival and growth.

Smolts become adapted to a life in the sea whilst they are still in freshwater and the need to move to survive is thought to be one of the main factors initiating migration.

Smolts generally migrate to sea at night, although fish migrating later in the spring may move during both day and night, often shoaling together during daylight hours to confuse predators. The smolts also move through the river estuary at night and use the ebbing tide to assist their seaward migration.

Movement is therefore rapid and, under the cover of darkness, the smolts are less visible to predators. Once in the sea the fish are known as post-smolts and they continue to migrate rapidly to their oceanic feeding grounds.

Smolt migration can be affected by a wide range of environmental and man-made conditions in our rivers and estuaries. For example, changes in flow and temperature regimes associated with climate change, and barriers to migration such as weirs, renewable energy schemes and barrages may delay the movement of smolts into the sea.

Artificial light and noise may also delay or inhibit smolt migration. All these factors have the potential to mean that conditions in the sea when the smolts arrive may be less favourable and might affect their subsequent survival.

Understanding the requirements of the salmon smolts and the challenges they face during their seaward migration is vital for manging stocks effectively. The use of tags and tracking to follow the movements of smolts from freshwater to the marine environment has been as important tool in the research on smolt migration.

Further information on recent investigations related to salmon spawning are available here. Smolts and Smolt Migration Reference List PDF, KB. Populations have been declining in most places and, in some cases, stocks have disappeared.

Declines have generally been greatest at the southern extent of the range and have occurred despite significant reductions in the numbers of fish removed by fishing. The main reason for the decline has been a marked increase in the natural mortality of salmon at sea.

As a result, stocks have seen a sharp fall in the proportion of fish that survive between their seaward migration as smolts and subsequent return to freshwater as adult fish.

On first entering the sea, young salmon become post-smolts and face a range of new challenges. The fish undertake extensive migrations and may stay at sea for a little over one year returning as adult one-sea-winter salmon or grilse , or for two or more years to return as larger multi-sea-winter salmon.

It has typically been assumed that mortality of salmon in the sea is highest in the early stages of marine residency, since predation is likely to be one important factor. Small fish are vulnerable to a larger range of predators than large fish and more predators occur on the continental shelf than in oceanic areas.

However, numerous factors can affect the survival of salmon in the sea, although their relative impact and the interactions between them are poorly understood. The movements of post-smolt and the distribution and habits of salmon while they are at sea are poorly understood.

Thereafter, the distribution of the fish likely varies both with the time fish might spend at sea before returning and their region of origin. Much of our current understanding of the ocean distribution of Atlantic salmon comes from the recapture of tagged fish and this has confirmed that salmon undertake long migrations to oceanic feeding areas.

We are thus aware that some salmon from England and Wales can migrate as far as the west coast of Greenland, although this is restricted to older fish that spend more than one-winter at sea before returning home to spawn. Recaptures of different sea-age fish have also been reported from fisheries that previously operated north of the Faroes winter months and around the Irish coast summer months indicating that fish range quite widely around the North Atlantic.

Of course, the recapture of tagged fish only occurs in areas where there are fisheries and does not provide precise information on the migration routes between the marking site and the point of subsequent recapture. New tagging technologies are starting to shed further light on salmon movements at sea, but none of these are suitable for all purposes and all sizes of fish, particularly smolts.

The wide geographical extent of the changes in salmon marine survival, and the common patterns that have emerged, have long been considered to indicate that broad-scale changes in the marine environment are the main cause of the observed decline.

The yolk sac continues to provide nutrients as the alevins grow. For a few months, alevins rely on their yolk sac and cover from the surrounding gravel until they are large enough to swim away from the redd. After alevins have fully absorbed their yolk sac, they become fry.

Once fry have left their redd, they search for food and try to avoid being eaten. During this stage, fry may begin moving from freshwater to saltwater.

Each species may spend a different amount of time developing before begining migration from freshwater to saltwater. At some point, fry pick up environmental cues and begin their migration to the ocean.

At this stage, the salmon are called smolts. They grow new scales, giving them a silvery color. This is the last time salmon will be in freshwater until they are ready to spawn. Now in saltwater, salmon continue to look for food.

and closely related to Brown trout Salmo trutta. Atlantic salmon can be found throughout the North Atlantic Ocean. In North America, their range extends from the northeastern United States Maine to northern Quebec Ungava Bay.

Atlantic salmon are commonly found in rivers throughout the island of Newfoundland and southern Labrador. Atlantic salmon are a cold water migratory species that require different habitats for each life stage. The term anadromous refers to this type of migratory behavior.

They head for dark pools in protected spots e. When they feel the urge, they begin their migration toward the ocean see Species for the different migratory patterns that characterize each species. To manage the transition between freshwater and saltwater, salmon fry must go through a physical change known as smolting.

Smolting begins in freshwater and sees the young salmon through the estuaries and into the ocean when it is time. Smolts have a silvery coating over their scales to camouflage them from predators and shield their bodies from fresh to saltwater. Salmon enter the ocean as young, or juvenile, adults and leave it as mature adults, ready to spawn.

The length of time salmon spend in saltwater depends on how old they were when they entered, their species, marine conditions, and other factors. Their travels in the ocean are similarly variable, and one of the least understood parts of their lives. When they are sexually mature, salmon follow their homing instinct and travel back to their natal streams to spawn.

It is an arduous journey, and only the toughest and luckiest salmon complete it. Salmon fry are vulnerable to predation as they develop into fry. Juvenile Adults.