Salmon Scales
There are circular rings called ciculi on the outer surface of a salmon's scales. Rapid growth of the salmon results in a zone of widely-spaced rings. During the freshwater life of a young Atlantic salmon, growth is rapid from May to October when the water is warm, and slower from December until spring when the water is cold. The young salmon become smolts and migrate to the sea during the spring. Seasonal growth patterns are also evident on the scales while salmon are at sea, but growth is more rapid than in fresh water and the rings are more widely-spaced. The sea is colder during the January-March period and a zone of closely-spaced rings is formed at that time.
Adult salmon do not feed as they come onshore and migrate up our rivers to spawn. This period of starvation results in the loss of the recently-formed rings near the outer edge of the scales. If the adult salmon survives spawning and returns to the sea, the rings that have been lost are replaced by a scar or mark. Scale growth continues by the usual process while at sea, but the spawning mark does not disappear. Because scale growth is proportional to the growth of the salmon, growth patterns on a scale reflect the length of the salmon at different times of its life.
Sample Scales:
Scale 1
- Migrated to sea as a 15 cm smolt after living in fresh water for two years.
- Grew to a length of 49 cm after one winter at sea.
- Returned to spawn in fresh water as a 59 cm grilse then migrated back to sea the following spring.
- Returned to spawn a second time at a length of 83 cm after spending another year at sea.
Scale 2
- Migrated to sea as a 19 cm smolt after living in fresh water for three years.
- Grows to a length of 50 cm after one winter at sea.
- Spent a second winter at sea then returned to fresh water to spawn as a 73.5 cm salmon.
|
