It is easy to check if the fish you have just landed is a grilse or a salmon by reading scales taken from the fish. Thats okay if your have access to the right equipment and have the experience required to “read scales”, but if you don’t then the handy ready reckoner produced by the The University of Strathclyde may be useful. A grilse is of course the name given to salmon which have been to sea for one year only, salmon that have been to sea for two years are known as “two-sea winter” then “three-sea winter” etc.
The Strathclyde age calculator is based on scale readings taken from 186,000 salmon, mainly from the east coast of Scotland but has been found to be accurate for west coast fish also. A few years ago I caught a 7lb salmon on the River Ayr in late May. Before returning the fish I took a couple scales which showed it to be a two-sea winter fish. But before I read the scales I had figured it wasn’t a grilse, you just don’t get grilse of that size so early in the season, although by the end of the season grilse can be up to 12lb.
By researching the size and time of capture the Strathclyde scientists were able to come up with a calculator that enables the age of a fish to be predicted with a high degree of confidence. See http://www.mathstat.strath.ac.uk/outreach/salwrd/index.php for details of the calculator. The calculator can be changed from length to weight measurements and from imperial to metric. It is easy to age individual fish using the calculator here or you can look at a monthly predictor here.
Now there was a 26lb fish caught on the Stinchar on Friday. The calculator predicts with 98% probability that it is a two-sea winter fish. This is the same age class of fish that has provided such good sport in Ayrshire this year, although they were only 9-14lb in May/June. There is every likelihood that more of these big two-sea winter fish will be caught before the season ends, with a 30lb fish a distinct possibility.