Catch & Release Impacts on the River Dee

The report below was compiled by the River Dee Trust’s fishery biologist Dr Lorraine Hawkins and was submitted as part of an Aquaculture & Fisheries Bill Consultation.

Survival after catch and release

The (Aberdeenshire) River Dee has a voluntary total catch and release policy for salmon and sea trout. As part of a three-year study to investigate the released salmon’s ability to survive and migrate to spawning grounds as a result of extending the angling season by two weeks into October, 140 salmon were radio tagged by the River Dee Trust between 2008 and 2010. All 140 salmon were caught by paying anglers who were fishing in the autumn period (mid Sep – mid Oct), i.e. they were the regular clientele of the river. This was a necessity of the study as we needed to mimic the ‘normal’ fishery to assess potential effects of angling on the fish. Once caught, the fish were put into keep nets and held in the river until staff arrived to tag the fish. The fish that were tagged were not selected for and so represented the typical rod catch on the river, with the exceptions that: (1) fish showing signs of significant damage were excluded and (2) fish under 55 cm length were excluded. The latter was to avoid any harm to the fish when inserting the radio tag (the tag length was 5 cm and was pushed into the fish’s stomach).

118 (84%) of the fish were tracked through their spawning period (late Nov – Jan), which contributed to the study’s conclusion that catching and releasing salmon in October made no difference to the fish’s ability to survive to spawn compared to catching and releasing fish in September (full reports can be viewed at River Dee Trust & Dee District Salmon Fishery Board: Home: Welcome). Of the 22 fish that it was not possible to track through their full spawning migrations, 16 of these fish were tracked moving upstream (minimum of 1 km, average 12 km) and were all tracked for a minimum of 22 days (average 46 d). This confirms that these fish survived being caught and released. A further six fish were tracked for a period of 27 – 75 days after they were captured and released but during that time only migrated downstream. This downstream migration behaviour was considered ‘normal’ because over the three years an additional 15 fish showed only downstream migration but remained in the river throughout the spawning period, suggesting that some fish originally migrate above their intended spawning grounds. It was concluded that these six fish also survived capture, tagging and release.
All of the remaining 22 (16%) salmon were therefore accounted for after they were released and so it was concluded that survival release post-release was 100%. In addition though, there were a total of eight fish (5.7%) which although they were tracked throughout the study, showed no movement. It is thought that in all of these cases the tag was regurgitated and remained on the river bed through the tracking period. This is surmised because no carcasses were found or reported and if a fish had died then the carcass would eventually be washed downstream and tracking would have detected this movement. In addition, a study by Environment Agency (Gowans 2004) found a regurgitation rate of 9% in 302 salmon that were radio tagged, which is in line with our estimate of 5.7%.

Gowans (2004) estimated that 2.4% of salmon (five out of 208 tagged fish) caught by anglers died immediately from the effect of capture trauma and a further 2.4% died soon after being tagged and released. In the last four years, 98% of salmon caught on the Dee have been released for the whole angling season. The retained 2% is mostly explained by mortality during capture/handling of the fish, which is in line with the estimate of Gowans (2004). For the Dee, a mortality of 2% of the total rod catch in the last four years equates to an average of 160 salmon per year. In 2004 it was estimated that angling tourism brings in £11.5 million each year to the Deeside economy (Radford et al 2004).
The River Dee was one of the first rivers in the UK to introduce catch and release (in 1994) and in 1996 the survival of these released fish was assessed by Webb (1998). In this study, 25 salmon that were caught by anglers between March and June 1996 were radio tagged. Of these 25 fish, 21 were successfully tracked until spawning at the end of the year. A further two fish were lost from the study, after being tracked for 83 and 90 d and showing upstream migration of 7 – 37 km. One fish was recaptured 69 d later and killed by the angler. The remaining one fish died 31 d after release with evidence of disease. As it cannot be ruled out that angling contributed to this disease, the study shows a maximum mortality relating to angling of 4%.

References
Gowans A (2004). Radio-tracking of Atlantic salmon on the River Eden, Cumbria: spawning distribution and survival to spawning. Environment Agency.
Radford A, Riddington G, Anderson J & Gibson H (2004). The Economic Impact of Game and Coarse Angling in Scotland. Report prepared for Scottish Executive Environment and Rural Affairs Department. Scottish Executive, Edinburgh.
Webb JH (1998). Catch and release: the survival and behaviour of Atlantic salmon angled and returned to the Aberdeenshire Dee, in spring and early summer. Scottish Fisheries Research Report 62. 16 pp

For further information about the report please contact Lorraine@riverdee.org