Each year the Spey ghillies collect DNA samples from some of the rod caught fish along with a few scales to allow the fish to be aged. Steve Burns has just finished aging the 2013 rod caught scale samples along with any other scales which we collected ourselves when the opportunity arose.
There were only 89 readable sets of salmon scales for 2013, a smaller sample than normal. Another facter to be borne in mind is that the scales were collected when available so the sample colected is not necessarily representative of the whole population. Many of the scale samples collected in 2013 were from fish caught in May with late season fish under-represented; much the same as in previous seasons.
Here the results of the 2013 salmon scale samples are presented along with a comparison with recent seasons and historic data from the Spey scale reading report produced by G.H. Nall in 1921 on behalf of the Fishery Board for Scotland.
The sea ages of the 2013 fish are shown in the graph below.
For comparison here is the same graph but showing the fish from 2012.
It can be see from the graph above that the one sea-winter year class occurred much more frequently in our 2010 samples than in any pre- or succeeding years. This does actually reflect well what happened in that year as there was a big run of grilse. These grilse were from the 2009 smolt run, a year class where marine survival was good all across Scotland. The impact of that strong year class was also evident in 2011 and 2012.
So in a period of generally low marine survival the 2009 smolt year class did very well. As this was almost universal across Scotland (that same year class produced the record catch of 23,000 in the Tweed in 2010), the success of those smolts is likely to have been due to improved marine survival rather than the size of the smolt run. The reasons for the improved marine survival that year are not understood although interestingly it did coincide with the much improved sea trout run in 2010. The 2010 sea trout catch on the Spey was the best in the last ten years. The factors affecting marine survival of salmon and sea trout are almost certainly not the same, but good inshore feeding conditions during the smolt run would obviously benefit both species.
3.4% of the salmon aged in 2013 were previous spawners. All these fish were spring fish, one had been caught in February.
From the scales we can also derive the river (smolt) age of the smolts providing the scales are not replacements, in which case the early history of the fish will be missing. The graph below shows the river age of the fish sampled.
From this rather limited (and flawed) comparison there would appear to have been little change in the age composition of salmon run in the Spey in the years studied. Sea and river ages of the 1921 sample and the recent years are similar, although the recent samples are not as representative as the 1921 collection. The 1921 samples were taken from the Spey nets throughout the season. We have a vast archive of scales and other analysis have been undertaken. I will try and pull it all together sometime.
We are grateful to the ghillies and anglers who continue to supply scale samples. Understanding the age composition of the Spey salmon run is of fundamental importance.