Many readers will be aware that in 2004 with great foresight the Spey Fishery Board initiated a genetic monitoring programme to try and establish the contribution of the Spey hatchery programme to the rod catch in the river. From 2004 onwards the female and male broodstock stripped to provide the eggs and milt used in the Spey hatcheries were DNA sampled by collecting fin clips for future genetic analysis. Records of all crosses made in the hatcheries (the Spey hatchery pedigree record) were maintained, even though at the time there appeared to be no mechanism by which the genetic analysis could be undertaken.
In subsequent years Spey gillies collected DNA from rod caught fish for genetic profiling against the baseline information on the hatchery broodstock. With the development of the FASMOP (Focussing Atlantic Salmon Management on Populations) project genetic analysis capability became available within the RAFTS network and the analysis of the Spey hatchery and rod caught fish commenced.
The fry derived from the 2004 broodstock were stocked in 2005 as fry or 0+ parr. Very few smolts in the Spey leave the river as one year olds so the earliest expected returns from the 2005 stocked fish would be 2008 with grilse derived from 2 year old smolts. In subsequent years a wider range of older smolts as well as MSW salmon could feature in the rod caught returns.
Significant numbers of broodstock were utilised to supply the Spey hatcheries, averaging around 500 fish annually during the period 2004 to 2007.
The results from the first two years rod caught fish genetic analysis had already been published but the results for rod caught fish from 2010 to 2012 are now available. The full Spey Hatchery genetic analysis report is awaiting formal clearance for publication but we are now in a position where the results can be published.
Based on the rod catch in each year the total number of hatchery origin fish featuring in the rod catch can be calculated. We have no definitive exploitation figures for the Spey salmon rod fishery but using an assumed figure an estimate of the total number of hatchery fish returning to the river in each year can be made. In the example above the figure of 15% rod exploitation has been used, although it could be higher or lower depending on factors such as total stock levels and angling conditions.
It is then interesting to compare the assumed total number of hatchery origin fish with the number of broodstock used to produce them. The ratio between the number of broodstock and returning adults is shown in the right hand column in the table above. In 2011 and 2012 it appears that for every two broodstock stripped in the hatchery four adults returned to the river with much lower numbers in the first three years. The overall mean over the five years studied was 106%, i.e. just over two fish returning for every pair stripped in the hatchery.
The key question then is how many returning adults would naturally be expected if those fish had been left to spawn in the wild? This would appear to be a very simple and straightforward question to answer, but it turns out not to be so. This issue will require a blog post of its own! The point is that hatchery fish are not “free” fish, broodstock used in the hatchery are denied the opportunity to spawn naturally, with the mate(s) and in the location of its choice.
This is only a brief summary of the full Spey hatchery genetic report which will be published on this website soon. The results will be presented in full at the public meeting in Aberlour on the 5th September.