Salmon spawning report 2010

Transcription

1 Salmon spawning report 21 Midlands Region, West Julie Cowley, April 211

2 We are the Environment Agency. It's our job to look after your environment and make it a better place - for you, and for future generations. Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier. The Environment Agency. Out there, making your environment a better place. Published by: Environment Agency Rio House Waterside Drive, Aztec West Almondsbury, Bristol BS32 4UD Tel: enquiries@environment-agency.gov.uk Environment Agency All rights reserved. This document may be reproduced with prior permission of the Environment Agency.

3 Contents Contents... i Summary Introduction Results Fish Counters Afon Tanat River Teme Electric Fishing Surveys HabScore Rod Catches Discussion Conclusions Recommendations References i

4 Summary Data from the Environment Agency resistivity counter at Carreghofa on the Afon Tanat and the Vaki counter at Ashford on the River Teme have been analysed and compared to flows. An appraisal of trends has also been carried out. Electric fishing data interpretation has also been undertaken. There has been a general decline in the number of migratory salmon recorded through the fish pass at Carreghofa since 23. Juvenile salmon recorded during the surveys has also decreased since 25 on both the Afon Tanat and Afon Rhiew ( control river) although it is not possible to determine the cause/s of this decline, partly due to inconsistencies with data as a result of flow conditions and/or site access. Utilisation of habitat by juvenile salmon has also been assessed and shows that available habitat is not being fully exploited at any of the sites. Continued monitoring of the juvenile salmonid populations is recommended to show if the decrease is continuing. Investigation into the possible causes of this trend should also be undertaken and internal consultation with Fisheries, Recreation and Biodiversity (FRB) should direct any future work. Data for the River Teme shows movement of salmon through the pass and results from the Salmon Action Plan six yearly survey at Downton (21) indicate the site is used as a nursery area by juvenile salmonids. Afon Tanat at Carreghofa (Environment Agency) - 1 -

5 1 Introduction This is the 7 th Salmon Spawning report (Midlands Region, West), providing analysis and interpretation of results for the fish counter at Carreghofa on the Afon Tanat, and juvenile salmon electric fishing surveys. Data for the fish counter at Ashford on the River Teme have also been analysed. Map 1 shows the location of both counters. Habitat quality has also been assessed using HabScore software to determine whether available habitat is being fully utilised by the fish. The Habitat Quality Score (HQS) values are derived from habitat and catchment features and are expressed as the long-term average density of fish per 1m 2 (NRA, 1995). The Habitat Utilisation Index value (HUI) is derived from the difference between the observed density and the HQS (pristine conditions) and is a measure of the extent that salmonid species use the habitat available (NRA, 1995). Table 1 shows the data analysed for the purposes of this report. Previous reports are available via the Analysis and Reporting Team, West Area and also include data on salmon redd counting (this programme was terminated in 21). Table 1. Summary table of sites used for data analysis and interpretation. Fish Counter Electric Fishing HabScore Tanat, Pedair-fford Carreghofa Tanat, Langedwyn Carreghofa Rhiew, New Mills Rhiew, RVLR Teme, Downton Ashford 21 - The Afon Tanat catchment is significant for migrating salmon in the River Severn, both as a spawning river and a nursery for juvenile salmon. However, movement of salmon to spawning areas can be restricted by weirs, and the weir at Carreghofa is impassable to salmon even at high flows. Therefore all fish moving upstream have to do so through the fish pass. A resistivity counter has been installed on the fish pass to count the number of migrating salmon accessing the catchment. This measures changes in conductivity within the water column. It can also detect whether movement of fish is upstream or downstream. To provide evidence of the success of the pass a programme of juvenile salmonid fish surveys are carried out in autumn on the Afon Tanat. The Afon Rhiew, a tributary of the River Severn and accessible to migratory fish, is also surveyed as a control river. Migratory fish counting on the River Teme is also undertaken at Ashford Carbonell, where a Vaki counter has been installed. This records fish movement through the counter as silhouettes through infra red beams. The weir at Ashford is passable by salmon during high flows. Data for 21 has been analysed as there are currently no long term data available for this counter. Data for 29 has been interpreted in the Salmon Spawning Report 29 (Environment Agency, 21). A programme of juvenile salmonid fish surveys has also been undertaken in

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7 Jan-1 Feb-1 Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Flow (Ml/d) 2 Results 2.1 Fish Counters Afon Tanat Monthly up counts for 21 in relation to flow are shown in Figure 1. The main run of fish can be observed in October, with the spring run fish passing through the counter predominantly in June. The peak period of fish movement is 27 and 28 October, as flows increased. The number of fish recorded through the pass is consistent with previous findings whereby during periods of very high flows the count is reduced. It would appear this is demonstrated further in the long term temporal response in upcounts compared to flow (Figure 2). Whereby flows below approximately 2Ml/day do not inhibit the ability of salmon to move through or be detected within the fish pass at Carreghofa. Comparison of upcounts against flow January to December Flow (ml/d) Figure 1. Comparison of up counts against flows (Ml/d) during

8 Jan-3 Apr-3 Jul-3 Oct-3 Jan-4 Apr-4 Jul-4 Oct-4 Jan-5 Apr-5 Jul-5 Oct-5 Jan-6 Apr-6 Jul-6 Oct-6 Jan-7 Apr-7 Jul-7 Oct-7 Jan-8 Apr-8 Jul-8 Oct-8 Jan-9 Apr-9 Jul-9 Oct-9 Jan-1 Apr-1 Jul-1 Oct-1 Jan-6 Apr-6 Jul-6 Oct-6 Jan-7 Apr-7 Jul-7 Oct-7 Jan-8 Apr-8 Jul-8 Oct-8 Jan-9 Apr-9 Jul-9 Oct-9 Jan-1 Apr-1 Jul-1 Oct-1 Flow (Ml/d) 5 Temporal response in counts to flow (Ml/d) 26 to Flow Figure 2. Temporal response in up counts in relation to flow (Ml/d) for the period 26 to 21. The annual average of salmon up counts has declined over time (Figure 3) and in both 29 and 21 the actual number of salmon counted has decreased considerably. Salmon upcounts for Carreghofa, 23 to upcounts 23=837 upcounts 24=131 upcounts 25=893 upcounts 26=115 upcounts 27=767 upcounts 28=334 29=55 21= Annual Average 3 25 missing data Figure 3. Atlantic salmon up counts recorded from the fish counter at Carreghofa on the Afon Tanat, 23 to

9 Jan-1 Feb-1 Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 Stage (m) River Teme Monthly up counts have been compared to river levels for the period January to December 21 (Figure 4). The main run of fish has been recorded in November, with a number of fish also moving through the pass in early spring (217 between March and May compared to 374 between October and December). It is evident that fish movement is related to flow although it should be noted that during periods of high flow the weir is passable by migrating salmon. Early November was the peak period of movement, with 332 fish passing through the counter during the whole of November. 6 Comparison of upcounts against river levels January to December Stage (m) Figure 4. Comparison of up counts against river levels (m) on the River Teme, during Electric fishing surveys The programme of juvenile salmon surveys has been reduced over time and in 21 just 2 sites: Pedair-fford and Llangedwyn were surveyed. The numbers of + salmon recorded for the period 25 to 21 across the programme of surveys are shown in Figure 5. Specifically for 21, Pedairfford recorded 19 fish/are (Are is 1m 2 ), although this is a decline compared to numbers in 25 and 26 (>38/Are). The second site at Llangedwyn has experienced a similar downward trend (.15/Are) although it is not directly comparable to previous years due to a change in site location

10 density of + salmon (Nos/Are) density of + salmon (Nos/Are) Density of + salmon, Afon Tanat Eirth Llangynog Glan Hafen Penybont fawr Pedair-fford Llangedwyn Glan Tanat Isaf Linear (Eirth) Figure 5. Density of + salmon (Nos/Are) on the Afon Tanat, 25 to 21. The number of + salmon recorded on the Afon Rhiew has fluctuated over time (Figure 6) across the sites; however the number of sites surveyed has been reduced to 2 in salmon captured at both New Mills and RVLR were down on previous years with RVLR numbers similar to that of Density of + salmon, Afon Rhiew Llety Gwilym Isaf Baxters Mill Dol Gwyn Felin Llanllugan New Mills Manafon RVLR Refail Figure 6. Density of + salmon (Nos/Are) on the Afon Rhiew, 24 to 21. The site at Downton on the River Teme was surveyed in July 21 as part of the Salmon Action Plan (6 yearly semi quantitative survey). Results are shown in Figure 7 and there is evidence that juvenile salmon are using the river as a nursery area

11 Actual Abundance at Downton, River Teme salmon 1+ salmon Eel Figure 7. Actual abundance of fish caught at Downton, River Teme in Habscore There are considerable differences between the observed density and the HQS for both + and >+ salmon (numbers per 1m 2 ) at all of the sites. The HUI scores are less than 1 and this suggests that the observed populations are less than what would be expected for the habitat. Expressed as a percentage >+ salmon are just 9% and 2% respectively at the Tanat sites, and 13% and 14% respectively at the Afon Rhiew sites (Table 2). + salmon are also under-utilising the sites on the Rhiew. Data from Pedair-fford (Tanat) are not included due to poor catch efficiency during the fish survey. Table 2. Summary table of HQS and HUI values for the Afon Tanat and Afon Rhiew. HUI HQS Site + salmon >+ salmon + salmon >+ salmon Pedair-fford (Tanat) Not analysed (.97) Pont Langedwyn (Tanat) (.14) 7.9 (.14) New Mills (Rhiew) (7.28) 12.9 (1.66) RVLR (Rhiew) (14.73) 1.28 (1.49) (Scores in italic in brackets = Observed density) 2.4 Rod Catches declared salmon rod catches for 21 on the River Severn and Vyrnwy were 23, of which 131 were released (57%). Figure 8 and Figure 9 respectively show the number of salmon caught and released during the Open season for both the River Severn and the River Vyrnwy

12 Declared salmon rod catches for the River Severn during 21 Oct Sept Aug Jul Jun May Apr Mar No of salmon Captured Released Figure 8. Declared number of salmon rod catches (caught and released) for the River Severn during 21. Declared salmon rod catches for the River Vyrnwy during 21 Oct Sept Aug Jul Jun May Apr Mar No of salmon Captured Released Figure 9. Declared number of salmon rod catches (caught and released) for the River Vyrnwy during

13 3 Discussion For Water Framework Directive purposes the Afon Tanat and Afon Rhiew have an overall Ecological Classification of Moderate and specifically the Fisheries Classification Scheme (FCS2) for is Good/High. For the River Teme the Ecological Classification is Good and although the FCS2 classification is more varied (between Poor to High) these data have not been validated and status is unconfirmed. There is a continuing downward trend in the number of adult salmon returning to the Afon Tanat to spawn as recorded through the Carreghofa fish counter. As discussed in the Salmon Spawning Report 29 (Environment Agency, 29) the effect of flow on salmon movement and data capture can compromise these data and clearly there is a fine balance between an attracting flow and high flows. Despite high flows in 29 Pedair-fford shows a similar number of juvenile fish recorded during the electric fishing surveys in both 29 and 21. However total numbers are approximately 65% less than when the site was surveyed in both 25 and 26 with this decline experienced across the age populations (+ and >+) of salmon. The habitat for juvenile salmonids at this site would appear to be generally good however they are clearly under-utilising available habitat. In this instance HabScore results should be used with caution, in particular a high variance value for Pedair-fford meant that data analysis was not possible for + salmon (of which 97 actual fish were captured of this age). Furthermore, poor capture efficiency as a consequence of higher than normal flow/spate conditions does not allow for a more accurate representation of the quality of the site. Nevertheless, juvenile salmon and salmonid species generally are underperforming within this section of the Afon Tanat and recruitment into the populations has declined over time. The site at Llangedwyn has become increasingly difficult to fish and was eventually relocated for the 21 survey. The results for the new site approximately 1km downstream were poor with just single numbers of salmonids. There is some discrepancy with the expected long-term density of fish (HQS), suggesting that habitat quality scores better than observed on the day. The site was dominated by gravels within a shallow glide/run; not typical habitat of + salmon, and the number of fish recorded reflects this. Unfortunately access to the river along this stretch is a problem and as a consequence the quality of the surveys is compromised and does not necessarily reflect the status of the juvenile salmonid populations within this section of river. The Afon Rhiew has seen a reduction in the number of sites surveyed for juvenile salmonids thus comparison of data between years to provide an assessment of the general condition of the Afon Rhiew as a spawning river is not possible. As a consequence although the site at New Mills shows a drop in numbers of fish caught in 21 compared to 29 it is not possible to determine if this decrease occurred throughout the river, has been a localised

14 change, or is a natural occurrence within the complex life cycle of salmonid species. HabScore data suggests that brown trout fully utilise both sites. Whilst salmon density is expected to be higher than trout they are not exploiting this habitat and trout are potentially out-competing salmon within this section of the river. On the River Teme during 21 the main movement of salmon upstream to spawn was experienced during the autumn months, and as the weir is passable during high flows numbers may be more than recorded. Furthermore, there are in-efficiency s with this type of counter and only good images are recorded thus numbers quoted are a minimum. The six yearly fish survey carried out in July pertains to the 29 spawning season and has been included to demonstrate that the main river is also used as a nursery by juvenile salmon. Declared rod licence capture and release for 21 were slightly up on 29 (212) overall (Environment Agency, 29b). However, they are nearer to the lower levels reported pre 23 (Environment Agency, 29c). The annual report on stock and fisheries assessment for 21 will provide comprehensive interpretation of salmon in England and Wales. The 29 report suggests that rod catches reflect flow with a higher catch rate during periods of higher flows (Environment agency, 29c). Unfortunately there are insufficient declared rod catch data for the River Vyrnwy to provide evidence of this, or to provide further insight into the status of returning salmon into the Tanat catchment. 4 Conclusion There is a continuing decline in recorded adult fish movement within the Afon Tanat The juvenile salmon populations recorded in both the Afon Rhiew, and more sharply in the Afon Tanat, are continuing a downward trend however as the regularity of sites surveyed has varied between years it is not possible to determine within/between species cyclical patterns, if there is a localised change, or a more general decline The River Teme is a migratory river for Atlantic salmon and is also used as a nursery area for juvenile salmonids. 5 Recommendations To enable assessment of the River Vyrnwy catchment and in particular the Afon Tanat as a salmonid river continued juvenile salmonid fish monitoring is recommended. A review of the number of sites surveyed and location may be appropriate at this stage, particularly as Llangedwyn has become increasingly difficult to survey. These surveys will complement the long-term data being compiled from the fish counter at Carreghofa. On the River Severn at Shrewsbury a video imagery system has been installed and special motion - 2 -

15 detection software can be used to detect fish movement through the pass. Since installation some images of fish have been recorded which shows the pass being used by a number of different species, but due to technical difficulties data for 29/21 are not available. In the future these images will be analysed to enable comparison between them and the respective counts at Carreghofa, and also rod catches. A secondary element to these data interpretation will be to validate the use of the pass at Shrewsbury as being accessible to all fish species. The weir at Shrewsbury is passable by salmon in high flows although the attracting flow is limited. The success of the River Teme as a spawning river is also worthy of further investigation. Methods and techniques are available for assessing its status and consultation with FRB is recommended to establish an appropriate strategy for future monitoring. 6 References Environment Agency, 29a. Salmon Spawning Report. Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, Bristol, BS32 4UD. Environment Agency, 29b. Fisheries Statistics Report 29. ( Environment Agency, 29c. Annual assessment of salmon stocks and fisheries in England and Wales, 29. ( NRA, Rivers House, Waterside Drive, Almondsbury, Bristol, BS12 4UD. WRc plc R&D Note