River Ythan Trust

...protecting the River Ythan for all our futures

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Scale sampling

Life histories from salmon and sea trout scales

SALMON

When a salmon is landed, diagnosis particularly if it has recently arrived in the river, its life history while it has been in the ocean can usually be identified by visible features. However for some fish these features can be misleading. Also the indicators of the early life history of the fish, before the small juvenile fish left the river for the ocean, are hidden from unaided vision.

Helpfully the scales of a salmon grow throughout its life with many concentric lines laid down as the scale expands. Most critically these rings are spaced more widely whilst the fish is growing faster. Growth is normally slower during the winter than the rest of the year. Thus, using an appropriate magnification, both the freshwater years and the ocean years of a salmonís life can be identified. Should an adult salmon survive a winterís spawning and return to repeat the process this leaves a characteristic feature on the scales. A lengthy spell between ceasing feeding and the scale being inspected also shows up on rim of the scales as does a period of checked growth whilst at sea.

At the present time salmon are encountering varied conditions in the ocean with some fish growing well while others, elsewhere in the ocean one presumes, fail to grow as might be expected. In these circumstances the RiverYthan Trust has started a program of scale collection by anglers and the reading of these by an expert. The first results of this program come from salmon landed from the river during 2011 when scales from forty five fish were obtained over August to October.

Forty four of these fish were on their first return to the river and one on its second return. Of the forty four, one fish had spent three winters in the ocean, twenty one of them two winters in the ocean and twenty two of them one winter in the ocean. The second return fish had been one winter at sea, then spawned the following winter and was back in the river to spawn the next winter. Fish which have spent one winter at sea before spawning the following winter are called grilse while fish which spend two or more winters at sea before returning to spawn are rather confusingly simply called salmon or technically multi sea winter fish.

The smallest fish, at 3lbs, was the second return fish while the largest was the three sea winter fish at all of 32lbs. The range of growth rates experienced by salmon is exemplified by two fish with identical life histories but weights of 5lbs and 20lbs.

Of the 45 fish, one had migrated to sea one year after hatching, thirty nine two years after hatching and five three years after hatching.

The sample of 45 fish is only about one in seven of the salmon landed by anglers during 2011 but the sample contained one surprise. No less than three of the fish, including the large one, were spring salmon, ie they showed no summer growth and might well have been in the river before June. Scaling up to the river as a whole, were there that many salmon in the river before the summer?

Also notable was how small some of the two sea winter fish were and similarly the near lack of the large one sea winter fish, grilse, which were not uncommon in the 1980s and into the 1990s.

We have asked anglers to continue to co-operate in collecting scale samples in 2012 going forward, so that the distribution of life histories of salmon entering the Ythan can be further established and any marked changes in the mix of life histories identified. Such information is crucial in safeguarding the welfare of salmon in the Ythan.

SEA TROUT

We are also involving anglers in collecting scales from sea trout in order to learn more about Ythan fish. In 2011 we only managed to get the scale sampling project set up late in the summer, too late for many sea trout scales to be obtained. We are now fully prepared to collect sea trout scale samples in 2012 and have them read in order that we can provide life history information.

Sea trout are not dissimilar to salmon in their life histories in that they spend their earliest years in freshwater and the bulk of their growth takes place at sea. However very few of them migrate to distant Northern seas as all salmon do and a higher proportion of them survive to spawn more than once. Many, called finnock in NE Scotland, also make forays into estuaries and upriver before adulthood. When sufficient sea trout scales have been read it will be instructive to see what mix of life histories characterises sea trout presently being caught in the Ythan and how this compares with data from the past. Fish from the estuary are likely to include fish destined to spawn in other rivers. If the work currently being devoted to linking salmon to individual rivers by genetic typing is extended to sea trout then it may transpire that the home rivers of such fish can be identified.

SALMON

When a salmon is landed, particularly if it has recently arrived in the river, its life history while it has been in the ocean can usually be identified by visible features. However for some fish these features can be misleading. Also the indicators of the early life history of the fish, before the small juvenile fish left the river for the ocean, are hidden from unaided vision.

Helpfully the scales of a salmon grow throughout its life with many concentric lines laid down as the scale expands. Most critically these rings are spaced more widely whilst the fish is growing faster. Growth is normally slower during the winter than the rest of the year. Thus, using an appropriate magnification, both the freshwater years and the ocean years of a salmonís life can be identified. Should an adult salmon survive a winterís spawning and return to repeat the process this leaves a characteristic feature on the scales. A lengthy spell between ceasing feeding and the scale being inspected also shows up on rim of the scales as does a period of checked growth whilst at sea.

At the present time salmon are encountering varied conditions in the ocean with some fish growing well while others, elsewhere in the ocean one presumes, fail to grow as might be expected. In these circumstances the RiverYthan Trust has started a program of scale collection by anglers and the reading of these by an expert. The first results of this program come from salmon landed from the river during 2011 when scales from forty five fish were obtained over August to October.

Forty four of these fish were on their first return to the river and one on its second return. Of the forty four, one fish had spent three winters in the ocean, twenty one of them two winters in the ocean and twenty two of them one winter in the ocean. The second return fish had been one winter at sea, then spawned the following winter and was back in the river to spawn the next winter. Fish which have spent one winter at sea before spawning the following winter are called grilse while fish which spend two or more winters at sea before returning to spawn are rather confusingly simply called salmon or technically multi sea winter fish.

The smallest fish of the forty five, 3lbs, was the second return fish while the largest was the three sea winter fish at all of 32lbs. The range of growth rates experienced by salmon is exemplified by two fish with identical life histories but weights of 5lbs and 20lbs.

Of the forty five fish, one had migrated to sea one year after hatching, thirty nine two years after hatching and five three years after hatching.

The sample of forty five fish is only about one in seven of the salmon landed by anglers during 2011 but the sample contained one surprise. No less than three of the fish, including the large one, were spring salmon, ie they showed no summer growth and might well have been in the river before June. Scaling up to the river as a whole, were there that many salmon in the river before the summer?

Also notable was how small some of the two sea winter fish were and similarly the near lack of the large one sea winter fish, grilse, which were not uncommon in the 1980s and into the 1990s.

We have asked anglers to continue to co-operate in collecting scale samples in 2012 going forward, so that the distribution of life histories of salmon entering the Ythan can be further established and any marked changes in the mix of life histories identified. Such information is crucial in safeguarding the welfare of salmon in the Ythan.

SEA TROUT

We are also involving anglers in collecting scales from sea trout in order to learn more about Ythan fish. In 2011 we only managed to get the scale sampling project set up late in the summer, too late for many sea trout scales to be obtained. We are now fully prepared to collect sea trout scale samples in 2012 and have them read in order that we can provide life history information.

Sea trout are not dissimilar to salmon in their life histories in that they spend their earliest years in freshwater and the bulk of their growth takes place at sea. However very few of them migrate to distant Northern seas as all salmon do and a higher proportion of them survive to spawn more than once. Many, called finnock in NE Scotland, also make forays into estuaries and upriver before adulthood. When sufficient sea trout scales have been read it will be instructive to see what mix of life histories characterises sea trout presently being caught in the Ythan and how this compares with data from the past. Fish from the estuary are likely to include fish destined to spawn in other rivers. If the work currently being devoted to linking salmon to individual rivers by genetic typing is extended to sea trout then it may transpire that the home rivers of such fish can be identified.

SALMON

When a salmon is landed, particularly if it has recently arrived in the river, its life history while it has been in the ocean can usually be identified by visible features. However for some fish these features can be misleading. Also the indicators of the early life history of the fish, before the small juvenile fish left the river for the ocean, are hidden from unaided vision.

Helpfully the scales of a salmon grow throughout its life with many concentric lines laid down as the scale expands. Most critically these rings are spaced more widely whilst the fish is growing faster. Growth is normally slower during the winter than the rest of the year. Thus, using an appropriate magnification, both the freshwater years and the ocean years of a salmonís life can be identified. Should an adult salmon survive a winterís spawning and return to repeat the process this leaves a characteristic feature on the scales. A lengthy spell between ceasing feeding and the scale being inspected also shows up on rim of the scales as does a period of checked growth whilst at sea.

At the present time salmon are encountering varied conditions in the ocean with some fish growing well while others, elsewhere in the ocean one presumes, fail to grow as might be expected. In these circumstances the RiverYthan Trust has started a program of scale collection by anglers and the reading of these by an expert. The first results of this program come from salmon landed from the river during 2011 when scales from forty five fish were obtained over August to October.

Forty four of these fish were on their first return to the river and one on its second return. Of the forty four, one fish had spent three winters in the ocean, twenty one of them two winters in the ocean and twenty two of them one winter in the ocean. The second return fish had been one winter at sea, then spawned the following winter and was back in the river to spawn the next winter. Fish which have spent one winter at sea before spawning the following winter are called grilse while fish which spend two or more winters at sea before returning to spawn are rather confusingly simply called salmon or technically multi sea winter fish.

The smallest fish of the forty five, 3lbs, was the second return fish while the largest was the three sea winter fish at all of 32lbs. The range of growth rates experienced by salmon is exemplified by two fish with identical life histories but weights of 5lbs and 20lbs.

Of the forty five fish, one had migrated to sea one year after hatching, thirty nine two years after hatching and five three years after hatching.

The sample of forty five fish is only about one in seven of the salmon landed by anglers during 2011 but the sample contained one surprise. No less than three of the fish, including the large one, were spring salmon, ie they showed no summer growth and might well have been in the river before June. Scaling up to the river as a whole, were there that many salmon in the river before the summer?

Also notable was how small some of the two sea winter fish were and similarly the near lack of the large one sea winter fish, grilse, which were not uncommon in the 1980s and into the 1990s.

We have asked anglers to continue to co-operate in collecting scale samples in 2012 going forward, so that the distribution of life histories of salmon entering the Ythan can be further established and any marked changes in the mix of life histories identified. Such information is crucial in safeguarding the welfare of salmon in the Ythan.

SEA TROUT

We are also involving anglers in collecting scales from sea trout in order to learn more about Ythan fish. In 2011 we only managed to get the scale sampling project set up late in the summer, too late for many sea trout scales to be obtained. We are now fully prepared to collect sea trout scale samples in 2012 and have them read in order that we can provide life history information.

Sea trout are not dissimilar to salmon in their life histories in that they spend their earliest years in freshwater and the bulk of their growth takes place at sea. However very few of them migrate to distant Northern seas as all salmon do and a higher proportion of them survive to spawn more than once. Many, called finnock in NE Scotland, also make forays into estuaries and upriver before adulthood. When sufficient sea trout scales have been read it will be instructive to see what mix of life histories characterises sea trout presently being caught in the Ythan and how this compares with data from the past. Fish from the estuary are likely to include fish destined to spawn in other rivers. If the work currently being devoted to linking salmon to individual rivers by genetic typing is extended to sea trout then it may transpire that the home rivers of such fish can be identified.

 

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