Laksebestanden i Skjern Å 2016

In this report both the actual and the maximal potential population population of young-of-the-year (y-o-y) and older salmon parr present in 2016 in the Skjern Å river system. From these the recruitment status (actual population relative to the maximal potential) was calculated. Information on salmon densities and on river habitat quality were collected during late summer / autumn 2016, supplemented with information from a regular monitoring program (Fishcare management programme) and information provided by Denmark’s Center for Wild Salmon.

The calculated number of naturally produced y-o-y salmon was 192,500 (68,100-277,000) and 62,100 (32,300-91,700) parr. The number of stocked one-year-old and older salmon present in the river, was 57,500 (25,200-91,300). Due to model restrictions and considerable variation in stream morphology the theoretical maximal population of y-o-y was calculated only for the upper parts of the streams.

With the prevailing (2016) habitat conditions the highest possible population number was 461,000 (385,900-543,300) in these parts of the river system. Accordingly, the recruitment status was 28.7% within the upper parts of the river system holding salmon in 2016. If all parts of the river system with suitable habitat conditions had been populated by salmon (i.e. including areas presently not holding salmon), the river system could house additionally 255,700 (199,700-318,400) y-o-y salmon, resulting in an estimated recruitment status of 18.5% for the entire river system.

Smolt production was calculated using literature values for the smoltification rate. The calculated smolt production from the population naturally produced young salmon (y-o-y and older parr combined), was 50,900 (21,500-72,600) assuming a 20% smoltification-rate (Koed et al. 2006) and 22.900 (9.600-32.600) assuming 9 % smoltification-rate (Kennedy et al. 2012).

The estimated number of smolt from stocking was 40,300 or 22,900 (9,600-32,600) depending on the smoltification-rate (calculated from the number of stocked y-o-y, 1-year old parr and smolt). Assuming a stable population of salmon parr during the years before the investigation, the estimated sea survival (calculated from the size of 2016 spawning run) was approx. 3.4 % for multi sea winter (MSW) salmon and approx. 6.7% for grilse, assuming a 20 % smoltificationrate.

With a 9% smoltification-rate the estimated sea survival was approx. 7.5% for MSW salmon and approx. 14.8% for grilse. For stocked salmon, the average sea survival (MSW and grilse combined) was estimated to be approx. 3.4% or 7.1% depending on the smoltification-rate. The calculated number of eggs spawned in 2015, was approx. 21.3 (18.1-24.5) million.

From this, and from the number of naturally produced y-o-y salmon, the survival from egg to ½-year old salmon was calculated to be approx. 0.9 (0.36-1.72)%.