Wednesday, November 18, 2009

Salmon Fishing Scotland Atlantic Salmon Key Facts.

Salmon Fishing Scotland Atlantic Salmon Key Facts.

Salmon Facts

Salmon Biology
How do salmon navigate?

Salmon navigation is one of the marvels of nature. While the full answer is not yet clear, a number of mechanisms may guide salmon at sea. These include guidance by the stars as well as use of receptors sensitive to local differences in the earth's magnetic field. Ocean currents may also play an important role. Near the coast and in the rivers, salmon are guided by a chemical memory which apparently allows them to recognise and home to substances, including pheromones, present in the water in very minute traces.
Do salmon always return to their own river?

Atlantic salmon return to their native river with amazing accuracy. Although some may stray to other rivers, the majority ascend their home river.

Can male and female salmon easily be identified?

When they arrive fresh from the sea it is difficult to distinguish the sex of salmon externally. Later the head of the male becomes elongated and grows a protuberance called a "kype" from the tip of the lower jaw. At this stage male and female are easily distinguished.
When do salmon spawn?

Spawning time varies between rivers and may be influenced by the water temperature and amount of daylight. Generally spawning will occur during the period November-December in Great Britain and Ireland but may extend from October until late February in our larger rivers.
Do all salmon die after spawning?

About 90-95% of all Atlantic salmon die following their first spawning, but some survive to spawn two or three times: as many as four spawnings have been reported. The survivors, predominantly female, return to sea to feed between spawnings.
How many eggs does an Atlantic salmon deposit?

Female salmon in most areas produce 450-750 eggs per pound of body weight but the number may rise, for example in Iceland, to 900.
Where are the eggs deposited?

They are laid in depressions called "redds" excavated by the female fish in the gravel of the river bottom. After the eggs are deposited they are immediately fertilised by an accompanying sea-run male, and often by mature male parr, and then covered with gravel by the female.
When do the eggs hatch?

The incubation time depends upon the water temperature. Hatching usually occurs in early spring and the young fish (called "alevins") remain in the redd for a few weeks., nourished by the attached yolk sac. When they emerge from the gravel in April or May, they are about one inch in length. As they grow, the young fish develop prominent markings on their sides and are then known as parr.
How long do young Atlantic salmon stay in the river?

This is dependent upon the water temperature and the availability of food. The length of stay varies very much, from one year in the southern portion of the salmon's range to five or more years in the more northern, colder regions.
When do they leave the river?

The young fish, now called "smolts", leave the rivers during the late spring. Most will be gone by June.

Where do they go?

Smolts are believed to move in schools while heading off to deep-sea feeding areas. While the best-known feeding locations are in the Norwegian Sea and the waters off Southwest Greenland, there are known to be many other sub-arctic feeding areas. Salmon that remain at sea for more than one winter undertake the longest migrations, but grilse tend not to travel beyond the Faroe Islands and the southern Norwegian Sea.
What are grilse?

A grilse is an Atlantic salmon which has spent only one winter at sea before returning to the river.
How long do salmon stay at sea?

They remain in the ocean from just over a year to three or four years. Salmon feeding off Greenland generally stay at sea for two or three years.
What are the salmon's natural enemies?

At different life stages, the principal predators of salmon are goosanders and red-breasted mergansers, cormorants, gulls, pike, pollack, cod, sharks, seals and otters.
How high can a salmon jump?

The highest jump a salmon has been known to make in Scotland is a vertical one of 12ft (3.7m) at the Orrin Falls in Ross-shire. The height a salmon can achieve depends upon the relative depth of the water at the foot of the fall and the position of what is referred to in engineering terms as the "standing wave" or hydraulic jump.

What influences the upstream movement of salmon in a river?

A number of factors affect the movement of salmon up the river. In the spring, water temperature is of great importance, and until the water temperature reaches 42ºF (5ºC) there is little upstream movement of fish over obstacles. Later in the season movement is affected by river flow and climatic conditions.
What are the survival rates at various stages in the life cycle of the salmon?
Stage No. of Individuals % Survival
Mean Range
Egg 5,000 - -
Alevin/Fry 4,700 94
Fry End 1st Year* 360 8 5-14
Parr (1+ yrs old)† 140 43 28-53
Parr (2+ yrs old)† 77 } 52 smolts 57 44-67
Parr (3+ yrs old)† 39 } 55 47-65

Mean survival rate from egg to smolt is 1%

Sea % Survival from smolt stage
Adults returning to coastal
waters as grilse and 2-5
sea winter fish 10 3-20

* 88% of total mortality occurs between March and July.

† A proportion of these migrate to sea as smolts in the spring.

These figures have been compiled from the work of David Hay on the Girnock Burn and David Piggins on the Burrishoole Fishery.
How does one know the age of a salmon?

The concentric rings of the scales of a salmon can reveal the age of a fish. When the young salmon first emerges from the gravel it has no scales, but very soon papillae start to appear along each side and develop quickly into small calcareous plates which, as they grow, lay down rings or 'circuli' at regular intervals. During periods of rapid growth occurring in the warmer months, when the fish are feeding more actively, the rings are widely spaced, but during the winter months when feeding activity is reduced, the circuli are laid down close together, giving the appearance under the microscope of a dark band, known as an 'annulus'.

The annulus is complete by the end of the period of little or no feeding in the winter. Once feeding recommences in the late spring the circuli are again more widely spaced. So by counting the 'annuli' or winter bands, the age of the fish can be determined.

Example of a grilse scale

Here is an illustrated example of a grilse scale
(from an Atlantic salmon in Scotland)

Age 2.1+ (two years in the river and over one year in the sea)

R = River life
S = Sea life
F = Focus of scale or nucleus

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1 comment:

Anonymous said...

Excellent Bob your an absolute mine of information.The Tay Oracle!!!

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