Hampshire Avon salmon ( Salmo salar L.) smolt investigations 2012-13. 1. Acoustic tracking through the catchment. 2. Smolt quality assessments. Dr Chris Gardner (Environment Agency & Ahern Ecology) Dr Andy Moore (CEFAS)
Hampshire Avon compliance with conservation limit (CL) CEFAS (2012) Annual Assessment of Salmon Stocks and Fisheries in England and Wales 2011.
RST Winkton Sea
1. Acoustic tracking. Objectives • Determine the duration of smolt migration in the Hampshire Avon, taking account of a range of environmental variables e.g. flow, temperature. • Assess mortality rates during migration. • Assess migratory delays / loses associated with barriers i.e. hatches, abstractions, water meadows & fish farms and efficacy of screens at abstractions to prevent entrainment. • Assess the efficacy of current acoustic deflectors used to prevent smolt entrainment into Water Meadow systems.
Method • Rotary Screw Trap (RST) operated by EA was used to catch actively migrating salmon smolts at Bemerton Bridge ~3km d/s Nadder-Wylye confluence u/s of Salisbury. Ran the trap from the beginning of April for three nights a week, for three weeks in 2012, five/six weeks in 2013. • Actively migrating salmon smolts had acoustic tags (VEMCO V7) surgically implanted under ASAP licence; n=40 in 2012 and n=33 in 2013. Fish migration was monitored with fixed receivers (VR2 and VR2W). • However, in 2012 only a few receivers in the lower catchment were capable of receiving the tag signal due to technical error by the supplier. Therefore in year 1 receiver coverage was lacking in upper/middle reaches. But only objective 3 (migratory delays at every barrier) was compromised by this. • Receiver coverage was complete in 2013.
2013 2012
2012 Results – Limited receiver coverage – Data analysis ongoing. • The downstream movement of smolts occurred when temperatures had exceeded 10°C and during periods of elevated flow. Fish migrated at night early on but switched to movement during both day and night as the season progressed. Smolts were generally delayed 2-3 days post tagging, then migrated covering 50+km in 3-4 days, quicker during higher flows. • 21/40 fish made it to The Estuary – Suggesting 52% mortality in freshwater. However, only 9 fish were detected at the exit to Christchurch Harbour, possibly due to poor detection in this large noisy environment? • In freshwater, steady attrition rate suggesting that loses were due to predation. • Limited receiver coverage, but did allow assessments of delays at a fish farm at Britford d/s Salisbury – receivers were placed u/s and d/s, 18 fish were recorded u/s, 19 d/s. Of these fish 2 or 3 were delayed for periods up to 8 hours, but none were entrained or lost. • Acoustic deflectors – one tagged fish was detected d/s of one of the deflectors, but this fish successfully migrated past this point.
2013 Results – Data analysis ongoing. • Previous studies reviewed by Thorstad et al. (2012) give mortality rates of 0.3 – 7.0% km -1 within river migrations. • So Hampshire Avon giving about 1% km -1 isn't bad given the Avon is atypical; lower reaches being lowland coarse fishery, whereas published work is often from freestone rivers.
2013 Results – Data analysis ongoing. • Acoustic deflectors – one tagged fish was detected d/s of one of the deflectors, but this fish successfully migrated past this point. • Fish farm at Britford d/s Salisbury – only 4 fish were recorded u/s but 21 d/s. Of the 4 fish detected both u/s and d/s all were delayed for 8-33 minutes (mean 23 minutes). • Poor u/s detection makes for inconclusive results… Bickton Trout Farm delays 9 (out of 25 fish that attempted the Bicton barrier) were 'delayed' = 36% No. Fish Delay Daytime or Nighttime? u/s or d/s Dets? Successfully passed Barrier? 1 8896 06:41:42 DT&NT evening u/s and d/s y 2 8888 06:31:59 DT u/s and d/s y 3 8889 17:15:00 DT & NT u/s and d/s y 4 8886 01:45:15 NT u/s and d/s y 5 8880 06:48:57 DT u/s and d/s y 6 8878 08:11:59 DT u/s and d/s y 7 8879 05:59:04 DT morning u/s and d/s y 8 8876 09:58:38 DT u/s and d/s y 9 8874 09:30:03 DT just u/s y Average 08:04:44
2. Smolt quality assessments 2013. Objectives & Method • Determine the level of saltwater adaptation of smolts about to enter the estuary; blood and gill samples were analysed to investigate if wild fish captured near the bottom of the catchment were compromised in their ability to adapt to saltwater.
Trout Farm Effluent Research Waring, C.P., Moore, A., Best, J.H., Crooks, N., Crooks, L.E., (2011) Do trout farm effluents affect Atlantic salmon smolts? Preliminary studies using caged salmon smolts, Aquaculture, doi: 10.1016 • CEFAS and EA sampling of wild smolts (10-15 fish) at Winkton in the spring 2013, utilising an operational eel rack to capture fish.
2. Smolt quality assessments 2013. Results • Blood samples showed all fish had full saltwater adaptation, gill samples yet to be analysed.
Discussion of tracking results. • Existing studies reviewed by Thorstad et al. (2012) give mortality rates of 0.3 – 7.0% km -1 within river migrations, which is consistent with the data presented here. Literature suggests predation rates are much higher in Estuaries, however the Avon is atypical lower reaches being lowland coarse fishery, whereas published work is often from freestone rivers. • Hampshire Avon smolts migrating out of the Wylye and Nadder have to travel through a large lowland system – good habitat for predators and unlike neighbouring chalk streams. • Predation rates increased habitat features; lakes / reservoirs / impoundments (Jepsen et al. 1998 & 2000; Aarestrup et al. 1999), tail race of hydropower scheme (Koed et al . 2002), areas of dramatic depth change (Jepsen et al. 2006).
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