The River Carron: understanding the role of stocking in the restoration of salmon catches Eric Verspoor Bob Kindness Matthew Curran Rivers and Lochs Institute Inverness College University of the Highlands and Islands

Is this a convincing argument that eating more chocolate will win you a Nobel Prize? Is it a convincing argument that it won’t?

A ssociation of recovery in the salmon catch on the River Carron, Wester Ross, with stocking of native fish Is this a convincing argument that stocking will restore the salmon run in your river? Is it a convincing argument that it won’t?

Associations do not prove causality, they may be spurious!

- A three year research project ( ) to carry out an objective scientific assessment of the impact of stocking on the recovery of the River Carron salmon stock and on the catches of salmon in the river Project Aim: - to determine whether existing data and information, combined with new information that can be collected, can provide compelling evidence for the actual impact of stocking (negative, neutral or positive) on salmon abundance, or whether the evidence is inadequate and results in an “unproven” verdict. Project Methodology: Review of historical information Monitor contribution of contemporary stocking using molecular markers Assess historical character of Atlantic salmon stock Conduct modelling assessments of the capacity of the stock to recover with and without stocking inputs Assess the contribution of catch and release to increased catch levels

Talk Outline The River Historical stock levels Salmon stock collapse Postulated cause Management Response Salmon stock recovery Cause of collapse Cause of recovery Overview of current work Conclusions??

River Carron Wester Ross, Scotland

Historical stock levels From the study of sea trout in Loch Dughaill 1936, During 3 visits to the loch. – 1,614 sea trout and finnock netted. – All fish tagged and scale sampled. – 112 salmon caught as a by-catch. 4 th visit in November – 1,136 finnock and 411 adult sea trout (50 over 7 lbs, 1/3 over 4 lbs) were netted. – Only 5 tagged fish were recaptured prompting the conclusion that the fish tagged were a small proportion of the total stock.

Salmon stock collapse Rod catches of salmon and sea trout collapsed through the 1990’s 1999 – Rod catch of 5 salmon/grilse, 1 sea trout, 1 finnock 5-year average for salmon to 2001 was only year average for sea trout to 2000 was only 11.2

Postulated cause Spates and redd washout?

Management Response

Salmon stock recovery 5- year average for salmon for was > figure is 416 (138 salmon and 278 grilse) 2013 figure is 131 (93 salmon and 38 grilse)

A ssociation of recovery in the salmon catch on the River Carron, Wester Ross, with stocking of native fish Stocking

C omparison of catch statistics with those in other rivers

What does this tell us about the cause of the decline? the cause of the recovery and increase?

Investigation of the cause of collapse Possibility A: cyclical fluctuations due to various, multiple natural factors Possibility B: higher episodic marine mortality associated with environmental changes in food, fish farm impacts Possibility C: higher episodic freshwater mortality due to environmental change e.g. spates, redd wash out Absence of robust analysis/evidence related to all of these but…. Natural fluctuations do occur and can be cyclical Exceptional episodic marine factors are known that could potentially depress populations Exceptional episodic freshwater factors are known that could potentially depress populations Occurrence of extreme flood events and river bed erosional events: R. Tipping, Stirling University

Investigation of the cause of recovery Possibility A: wild population has not recovered but catches are sustained by stocked fish Possibility B: wild population has recovered on its own Possibility C: wild population recovery was facilitated by stocking and stocking makes minor contribution to catches with no detriment Possibility D: wild population recovery occurred but the long-term sustainability is compromised by stocking Mark and recapture Genetic Identification Computer Modelling None of these possibilities can be ruled out at this point. Gathering and assessing the evidence under way.

Survival of stocked fish

Since 2005, rod caught salmon have been marked using a panjet before being released to assess possible subsequent captures 2005 – 34 marked, 3 caught twice 2006 – 79 marked, 11 caught twice 2007 – 120 marked, 13 caught twice 1 caught 4 times 2008 – 75 marked, 11 caught twice 5 caught 3 times 2009 – 54 marked, 15 caught twice 2 caught 3 times Information on multi-captures is vital if using rod catches to assess the overall run of salmon in a river Recapture rates of angled fish

Demographic modelling -Individual based stochastic model (Gilbey and Verspoor, submitted) -Successfully recreates Girnock Burn demographic dynamics

Genetic Tagging of stocked fish -programme underway: genetically tagged fish have been stocked in 2012 and Proportions of stocked fish among juveniles, smolts and returning adults will be assessed

Conclusions Watch this space!