Eel Management plans for the United Kingdom Thames River Basin District

Transcription

1 Eel Management plans for the United Kingdom Thames River Basin District Date published: March 2010

2 Contents 1. Introduction 2. Description of the Thames River Basin District 2.1 The Thames River Basin District 2.2 Current eel population 2.3 The Fishery 2.4 Silver eel escapement 2.5 Eel mortality and available habitat 3. Restocking 3.1 Habitat to be restocked 3.2 Past restocking 3.3 Potential restocking in the Thames RBD 3.4 Eels to be restocked in Compliance with restocking requirements in the Regulation 4. Monitoring 4.1 Assessment of silver eel escapement 4.2 Price Monitoring and reporting system 4.3 Catch and effort sampling system 4.4 Traceability of live imported and exported eels 5. Measures 5.1 Measures to meet Escapement Objective 5.2 Measures taken 2007 to Measures to be taken 2009 to Measures to be taken beyond 2012 to achieve Escapement Objective 6. Control and Enforcement 6.1 Control and enforcement measures 7. Modification of Eel Management Plans Eel management plan for the Thames River Basin District Page 2

3 1. Introduction This Eel Management Plan for the Thames River Basin District (RBD) aims to describe the current status of eel populations, assess compliance with the target set out in Council Regulation No 1100/2007 and detail management measures to increase silver eel escapement. This will contribute to the recovery of the stock of European eel. 2 Description of the Thames River Basin District 2.1 The Thames River Basin District The Thames River Basin District covers an area of 16,133 km 2 and encompasses the River Thames and tributaries from its source in Gloucestershire through London to the North Sea. The district also includes the Medway catchment which drains north Kent, joining the Thames Estuary in its outer reaches. The numbers and areas of four main water body types, as defined by the Water Framework Directive, are shown in Table 2.1 (Defra 2005). Water body type Number present Length/Area Rivers with catchments greater than 4,474 km 10 km (ha) Lakes with areas greater than km 2 km (ha) Transitional water bodies km 2 Coastal water bodies km 2 Table 2.1 Water bodies in the Thames RBD. The Thames RBD includes the rural areas of Wiltshire, Oxfordshire and parts of Kent and Essex, as well as heavily urbanised areas, such as Reading, Slough, Luton, London and the Medway towns. Dominated by Greater London, the eastern and northern parts of the RBD are heavily urbanised, but considerable areas of rural land remain. The western parts of the catchment are predominantly rural but include larger towns such as Oxford and Swindon. Eel management plan for the Thames River Basin District Page 3

4 Figure 2.1 The River Thames RBD. Throughout the RBD, two factors have combined to reduce access for eel to freshwater habitats: flood defence engineering and weir construction. Many of the rivers in the RBD have been extensively managed to control flooding, particularly in the lower and tidal reaches where low-lying land has been reclaimed for agriculture, housing and urban areas. Flood control tidal flaps and pumped drainage removes water from large areas of potential habitat in the Marsh Dykes, Romney Marshes and many other low lying areas. The Thames RBD also has considerable areas of navigable waters, including the River Thames and parts of the River Lee, River Wey and River Kennet. Navigation locks and weirs are maintained to ensure boat passage. Whilst fish passes have been installed on many of these structures, little is known about the effectiveness of these passes for eels and very few specific eel and elver passes are currently provided. There are still many obstructions on tributaries that are not open to navigation. Major tributaries such as the Medway, Wandle, Lee and Colne all have large barriers close to their confluence with the River Thames that restrict migration of fish Some information has been gathered on the obstructions to fish movement in the Thames RBD (Figure 2.2). No assessment has been made of the passability of these obstructions to the movement of eels upstream. The list is neither complete nor comprehensive and there are important tributaries such as the Lee, Cherwell and Thame catchment where there is currently no definitive list of obstructions. Eel management plan for the Thames River Basin District Page 4

5 Figure 2.2 Barriers to migration in the Thames RBD 2.2 Current eel population Glass eel recruitment There is no glass eel fishery and little fishery-independent monitoring of glass eel recruitment in the Thames RBD. Some attempts have been made to measure elver and glass eel numbers. Traps were set at six weirs on the lower River Thames between 1983 and Over 10,000 pigmented elvers and yellow eels were caught, but no glass eels. Very few one-year-old eels were caught and it was suggested this might be because most eels spent their first year in the estuary or the lower river (Naismith & Knights 1988). In recent years a programme of juvenile eel monitoring has been initiated as a partnership between the Environment Agency and Zoological Society of London (ZSL). Traps have been positioned at up to six sites on the main river and tributaries (Table 2.2). River Site Distance from tidal limit (km) Total Catch Darent Acacia Weir Roding Passingford Bridge Weir Roding Redbridge Roundabout Wandle Merton Abbey Mills Mole Zenith weir Thames Molesey Weir Table 2.2 Location and results from eel trapping at weirs in the Thames RBD Eel management plan for the Thames River Basin District Page 5

6 Catches of eels are very variable between years, sites and tributaries. Results from the Redbridge Roundabout site on the River Roding in 2005 in relation to date, river temperature and dissolved oxygen levels are shown in Figure 2.3. Eels caught Temperature Dissolved Oxygen Eels caught May 17-May 31-May 14-Jun 28-Jun 12-Jul 26-Jul 09-Aug 23-Aug 06-Sep Date 0 Temp. (oc)/do (mg/l) Figure 2.3 Eels caught at Redbridge Roundabout, River Roding, 2005 The eels caught in these traps are all pigmented elvers or yellow eels. The length distribution of eels caught on the River Roding at Redbridge Roundabout in 2005 is shown in Figure Eels caught Length category (mm) Figure 2.4 Length frequency of eels caught at Redbridge Roundabout, River Roding, Yellow Eel Distribution Within the Thames RBD, 109 sites are monitored for fish on a six year rolling programme (i.e. around 18 are sampled each year). An additional 209 sites are Eel management plan for the Thames River Basin District Page 6

7 sampled on an annual basis and a further 40 sites are surveyed at least every six years as part of the Water Framework Directive programme of monitoring. All these 358 sites are multi-species surveys and may therefore underestimate the true density of eel (Knights et al., 2001). There have been no eel-specific electric fishing surveys in the Thames RBD. The eel population in the Thames RBD has been monitored since the 1960s. A variety of methods have been used ranging from routine electric fishing sites in the tributaries; boom boat electric fishing in the main river; trapping and fyke netting in freshwater and estuary; and continued sampling of the screens at power station intakes. The distribution of eels found at electric fishing survey sites is shown in Figure 2.5. This shows that eels are present throughout the estuary (based on fyke netting), and the lower river but there is a general limit to eel migration around 60 km from the tidal limit and they are largely absent in the main river and tributaries above Goring, a town between Reading and Oxford. Though there are some populations further upstream along the River Thames catchment, for example in the Dickler, these are likely to be the result of previous stocking with small eels. There appear to be some key migration barriers on all the major tributaries of the Thames, the River Darent and the River Medway. Figure 2.5 Distribution of eel in the Thames RBD ( survey data combined). Eel management plan for the Thames River Basin District Page 7

8 2.2.3 Abundance and Biomass in the Thames RBD Main River surveys The main River Thames has been surveyed by fyke net surveys, boom boat electric fishing, and estuarine power station sampling. The information from these surveys is briefly considered below. Fyke net surveys in the Thames estuary and the freshwater river show high catches per net end per day near to the tidal limit, but reducing seawards, and in freshwater reducing rapidly after about 20 km of the tidal limit (Figure 2.6 after Knights 2005) CPUE (N end -1 day -1 ) CPUE Length Length (cm) Distance (km) Figure 2.6 River Thames fyke net data (reproduced from Knights 2005), the vertical line represents the tidal limit Results from the boom boat electric fishing surveys between 1995 and 2004 are shown in Figure 2.7 (reproduced from Knights 2005). The information on catches is shown as the number of eels caught per minute of electric fishing. There are some fluctuations in these data between years, but there is a strong general trend towards increasing catches from 10 km to 50 km above the tidal limit at Teddington in London and then a decline to the top reaches of the system. In general, large eels are found in backwater and impounded areas in the lower freshwater main river, rather than in weir pools, with occasional large catches in the margins where there are pockets of suitable habitat. Eel management plan for the Thames River Basin District Page 8

9 CPUE N min Mean River km Figure 2.7 Thames main river boom boat catches Eels were also sampled on the intake screens of West Thurrock Power station between 1974 and the station s closure in This power station is on the north bank of the Thames Estuary, 36 km downstream of London Bridge. Samples were taken fairly regularly and the results considered by Knights et al. (2001). The information gathered was very variable but with general peaks in numbers in June and October and troughs in February. Those data gathered from this sampling cannot be used for robust statistical analysis. In 2006 the Zoological Society of London began a programme of sampling at Tilbury Power Station each month in collaboration with the Environment Agency. Fish washed off the intake screens over a 5 hour period are sampled twice a month. The number of fish sampled per month in for the 12 months from March 2006 to February 2007 is shown in Figure 2.8. The number of eels caught is dependent upon abstraction rates and flow, and there will also be a diurnal effect on catches, however a crude extrapolation of these data suggests that 3,800 eels could be entrained each year. Eel management plan for the Thames River Basin District Page 9

10 Number eels trapped Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Month Figure 2.8 Eels sampled from the intake screens of the Tilbury Power Station from March 2006 to February Electric Fishing in Thames Tributaries A large number of electric fishing surveys have been carried out on the tributaries of the Thames and the Medway. These are multi-species surveys and will underestimate true population densities. The information gathered from these (between ) was analysed and reported by Knights (2005). On the Thames there is a decline in eel densities with increasing distance upstream, from around 4 eels per 100 square metres of habitat at the tidal limit to less than 0.5 eels/100m 2 habitat 50 km upstream. Biomass follows a similar trend, and the average length of the eels increases. On the Medway, the density and biomass show similar trends, but with lower densities and biomass, and the average length of eel remains static throughout the range (Figure 2.9). Eel management plan for the Thames River Basin District Page 10

11 Log. (All Tribs) 4 Density N 100m All tribs y = Ln(x) R2 = Medw ay y = Ln(x) R2 = Log. (Medway) Biomaas g 100m All tribs y = Ln(x) R2 = Medway y = Ln(x) R2 = Length cm All tribs y = Ln(x) R2 = Medway y = Ln(x) R2 = Distance rkm Figure 2.9 Mean density, biomass and body length for eels sampled from the River Thames and River Medway Eel management plan for the Thames River Basin District Page 11

12 2.2.4 Population size structure in the River Thames There is little available information on the sizes of eels in the Thames. The eel length data shown in Figure 2.9 has been estimated from average eel biomass for a survey site and using standard weight-length relationships to estimate the length (Bark, Knights and Williams, unpublished data). Length data can be important in identifying whether there is an issue of limited recruitment or migration. Eel length can also be a useful guide as to the sex of the eel. Males tend to mature, silver and migrate to sea whilst still less than 45 cm long. There are some individual eel length data available from the boom boat electric fishing surveys. These are shown in Figure y = Ln(x) R 2 = Length cm Distance rkm Figure 2.10 Average eel length from main river boom boat surveys (reproduced from Knights, 2005). All of the information presented shows an increasing average length of eel with increasing distance from the tidal limit. Eels less than 45 cm long dominate the higher density regions of the upper estuary, larger eels longer than 60cm (and therefore female) dominate the river 80 km upstream. This was the case for all of the tributaries except for the River Medway, where large female eels dominated throughout the system. There is some information available on eel growth rates in the River Thames from work undertaken by Naismith & Knights (1993). This showed fastest growth in estuarine and tributary populations, slowest in the main Thames. These growth rates probably reflect differences in habitat, favourable temperature regimes and the length of the growing season. It is expected that estuarine populations would mature and Eel management plan for the Thames River Basin District Page 12

13 emigrate after about 7-8 years, the main river populations after years, although some may be much older Estimation of silver eel output. Eel specific surveys were undertaken on two catchments with the Thames RBD, the Wandle and Darent at 12 and 13 sites, respectively. The probability model estimated silver eel output for the Wandle to be 10.6 kg/ha and for the Darent 34.5 kg/ha. Using the mean output from the Darent and Wandle the estimated silver eel output from the Thames RBD is 309 t / yr. 2.3 The Fishery Introduction There are records of an eel fishery in the River Thames going back to the Domesday Book of 1086, and written reports of eel catches at eel bucks throughout the catchment up to the 20 th century. There are also historical records of very large elver runs into the Thames. Eel recruitment into the Thames all but ceased following the gross pollution of the Thames through London during the Industrial Revolution and continuing through to the 1960s. During this period a very small eel population was retained in the freshwater Thames by a number of elver releases into tributaries. Following the removal of the chemical pollution barrier in the lower Thames, eel recruitment increased in the river and a fishery developed during the 1980s consisting of fyke nets and pair trawling. Licences to fish for eels and glass eels commercially are issued by the Environment Agency on a Regional basis. The Thames RBD is located within the Thames and Southern Environment Agency Regions. The eel fishery in the Thames RBD is extensive. The number of licenses issued from 2005 to 2007 for the two Regions that contain parts of the Thames RBD is shown in Table 2.3. Two important points should be considered when looking at these data The number of licences issued is not the same as the number of fishermen. One fisherman is able to set many traps and fykes. The only fishing gears operated by a single person are dip nets, fixed traps, and Gloucester Wing Nets. The number of licences issued does not equal the number of fishermen within the Thames RBD. There are extensive fisheries outside of the Thames RBD and within the South East RBD. Eel management plan for the Thames River Basin District Page 13

14 Fishing Method Licensed instruments Region Thames Southern Year Elver Dip Nets Gloucester Wing Nets Small Wingless Traps Winged Traps/Fykes Fixed Traps Table 2.3 Numbers of eel licences issued by the Thames and Southern Environment Agency Regions, 2005 to The elver (glass eel) fishery There is no glass eel fishery in the Thames RBD Yellow and silver eel fisheries Recreational Fishery The recreational fishery for eels within the Thames RBD is small. The vast majority of eel are captured whilst anglers are fishing for other coarse and game species and, in these circumstances, eel are usually returned to the water. In 2007 a total of 321,598 fishing licences were sold in the Environment Agency Thames Region and the North East Area of Southern Region. These encompass the Thames RBD but also small areas outside of the RBD. A survey of anglers carried out in the 1990s indicated that the average distance travelled to fish by a licence holder was 20 miles and that 35% fished predominantly on rivers (National Rivers Authority 1995). Assuming that each angler catches one eel per season (Appendix 4) then approximately 112,000 eels are caught by recreational anglers each year. The level of post release mortality has not been assessed. Commercial Fishery The commercial eel fishery in the Thames RBD operates between Tower Bridge and the Yantlet line (the historic downstream boundary of the City of London). Catches are shown in Table 2.4, these represent around 30% and 9% of the declared yellow and silver eel catches for England and Wales respectively. The fishery comprises a few fishermen that work most seasons, with new ones occasionally entering, but then leaving after a few seasons. The total value of the fishery in 1999 was estimated to be around 124,000 (Knights 2001), an average income of around 25,000 per licence holder. A pair trawling fishery operated in and around the Medway and Swale from the 1980s until recently. The Medway estuary also has a small fyke net fishery. The declared catch data from 2005 to 2007 are shown in Table 2.3 for different rivers in the RBD. The distribution of catches through the months in 2005 to 2007 are shown in Figure 2.11 and Eel management plan for the Thames River Basin District Page 14

15 River Declared catch (kg) Yellow eels Silver eels Thames 7,175 5,688 6,801 1, Warden Point Medway Stillwater Total 7,175 5,818 6,966 1, Table 2.4 Declared yellow and silver eel catches for rivers in Thames RBD, 2005 to Declared catch (kg) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 2.11 Declared monthly catches of yellow eels in the Thames RBD, 2005 to Declared catch (kg) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Figure 2.12 Declared monthly catches of silver eels in the Thames RBD, 2005 to Eel management plan for the Thames River Basin District Page 15

16 Data on catches and fishing effort for the Thames fyke net fishery were analysed by Knights (2005), and are shown in Figure CPUE (kg end-1 day-1) CPUE Effort Fyke days year Year Figure 2.13 Analysis of Thames fyke net fishery (after Knights, 2005) Although eel catch returns are known to be of poor quality, the general trend in catches between 1981 and 2003 is reasonably stable. Effort varied quite widely over this period, with declines in the late 1980s and 1990s. The low number of netting days in the late 1980s coincided with poor catch return rates in Thames Region, and health warnings about residues of dieldrin in Thames eels, which had a negative impact on local sales. Throughout the period, the weight of eels caught per fyke net end per day (CPUE) has remained reasonably constant. This suggests that the Thames estuary has a stable eel population and that the fyke net fishery is not having a major impact on stocks. 2.4 Silver eel escapement There was no direct measure of silver eel escapement in the Thames RBD before anthropogenic influence on stocks and there has been none carried out in recent years. Eel specific surveys were undertaken on the Wandle and Darent, the probability model estimated silver eel output for the Wandle to be 10.6 kg/ha and for the Darent 34.5 kg/ha. For the Wandle to be non-compliant the pristine escapement would need to be in excess of 25 kg/ha. A comparison with other rivers (Table 1; in Eel Management Plan overview for England and Wales) would that the Wandle and the Eel management plan for the Thames River Basin District Page 16

17 Darent and by association the Thames RBD is compliant with the 40% escapement target. Analysis of multi-species electric fishing data, for the Thames and Medway (gathered between 1993 and 2004) have also been applied to the Reference Condition Model (RCM: Appendix 3) to assess compliance (Figure 2.14 and 2.15). It is accepted that there is low confidence in the results from this analysis. Comparison of the Thames data (area under the curve) with that estimated by the RCM suggests that the potential production of silver eels from the Thames represents 99% of the reference ( pristine ) conditions. For the Medway, the current data suggests 61% compliance with Reference conditions. In its basic form, the RCM assumes uniform habitat available upstream of the tidal limit. If it is weighted according to the amount of habitat available to eel at various distances from the tidal limit then the Thames population is estimated at 100% of reference conditions and the Medway at 65% of reference conditions Eel density (# 100m-2) Predicted y = 1.129e x Observed y = e x r 2 = Distance (km) Figure 2.14 The predicted (dotted line) and observed rate of decline in eel density for the River Thames Eel management plan for the Thames River Basin District Page 17

18 Eel density (# 100m-2) Predicted y = 0.446e x Observed y = 0.446e-0.05x r 2 = Distance (km) Figure 2.15 The predicted (dotted line) and observed rate of decline in eel density for the River Medway 2.5 Eel mortality and available habitat Eel Habitat The development of London and the other towns and cities on the River Thames over the past 200 years has lead to the steady loss of eel habitat as the main river and tributaries have been constrained by flood defences, and weirs constructed. Many low lying areas have been drained for agriculture and building urban areas, and navigable rivers dredged to allow the passage of boat traffic. The Thames RBD now bears very little relation to how it would have looked before the Industrial Revolution. There are however still large areas of eel producing habitat that can be utilised and it is essential that this loss of habitat is quantified and any shortfall made good by creating more Barriers to migration The legacy of an industrial history is that the natural hydrology of many of the rivers in the Thames RBD have been significantly changed by weirs, sluices, bridges and dams. These can create barriers to fish migration, including the upstream movement of eels. A recent assessment has identified 514 obstructions within the river basin (Table 2.5). This list is not comprehensive and there are several tributaries not included. Large areas of low lying marshland in the Thames tideway such as the Marsh dykes, that would once have been connected to the Thames and provided excellent eel habitat, are now drained and pumped preventing eel migration. In the east of the River Basin, the Darent, the Cray and the Medway have been identified Eel management plan for the Thames River Basin District Page 18

19 as having structures that prevent upstream movement. These include Chipstead Lake Dam on the Darent, Vitbe Mill on the Cray and Allington Weir on the Medway. River Obstructions identified Colne 38 Churn 12 Coln 2 Kennet 96 Leach 10 Pang 6 Thames 44 Windrush 94 Wye 11 Loddon 33 Wandle 19 Wey 124 Mole 25 Total 514 Table 2.5 Obstructions identified within the Thames River Basin District It is probable that the cumulative effects of each of the barriers within the Thames RBD is increasing the general effect of low recruitment to the river, reducing density dependent upstream migration and restricting the range of eel in the system. A definitive list of all the barriers to migration in the Thames RBD, and some indication of their passability, would be a useful starting position for further targeted work. From this, and a better understanding of the eel populations, bottlenecks can be identified and action taken. Measures to address this will be implemented in the first phase of this EMP. A number of eel and elver passes have already been built on the River Thames. This has mostly been where there has been an opportunity rather than according to a strategic plan. Passes currently exist on: Barking Barrage, River Roding Sunbury Weir, Shepperton Weir, Marsh Weir and Abingdon Weir, River Thames Cobham Mill, River Mole Stoke Mill, River Wey Staines Lino Mill, River Colne. The effectiveness of these passes is not known Entrainment and Hydropower There are nine raw water intakes on the main River Thames between the tidal limit at Teddington and Windsor. Together these have a licensed abstraction of approximately 7,000 megalitres a day. The screening on these intakes generally Eel management plan for the Thames River Basin District Page 19

20 consists of a coarse trash screen and a behavioural sound screen barrier, neither of which would offer particular protection for juvenile or adult eels. A recent extensive investigation considered juvenile entrainment of all fish species at these intakes. Sampling was carried out throughout the year, but concentrated around the summer period. No eels were caught in these investigations (D Clifton- Dey, Environment Agency, pers. comm.). Other, smaller abstraction points are also present as well as pumping stations for land drainage purposes. The entrainment of eels in these has not been assessed. Concern at the potential loss of migrating silver eels at these abstraction points has lead to the initiation of an Environment Agency project in 2008 to look at abstraction at one raw water intake using a dual frequency identification sonar (DIDSON ) 1 ; no results have been published to date from this work. In the estuarine River Thames there are a number of abstractions for commercial purposes and cooling water. No assessment has been made on the entrainment of eels at these, except at Tilbury Power Station where it has been estimated that up to 3,800 eels are entrained each year (Section ) Eels are known to be present in the water supply reservoirs to the West of London. The most probable route of entry is that these are entrained from the main river and then live and grow in the reservoir. Potentially these large waterbodies constitute a useful area of habitat that could produce spawning eels. A recent report commissioned by the Environment Agency considered the potential for using these London reservoirs to rear eels for the Thames. This concluded that although potentially a useful contribution to the spawning stock, there is no easy route for silver eels from the reservoir back to the main river (APEM 2008), and therefore limited potential to enhance silver eel escapement from the RBD at the moment. There are only three hydropower installations known to be operating in the Thames RBD: at Sonning Mill on the River Thames, Guildford on the River Wey, and at Betchworth on the River Mole. The mortality of eel at these installations has not been estimated. A number of other sites have also been identified by developers as suitable for hydropower and turbines will be installed at Romney weir in These will be Archimedean screw turbines, which experiments at a site on the River Dart in Cornwall seem to suggest does not cause damage or mortality to downstream moving fish, including eels (Fishtek consultation report 2008). There is no information on the effect of screw turbines on upstream eel migration Predation The Thames RBD comprises 11% of the freshwater and lake habitat in England and Wales (A Walker, CEFAS, pers. com.), and may expect to constitute 11% of eel consumption by cormorants: 3.3 to 4.8 tonnes (Appendix 6). With the average length of eel taken at cm (Carss and Marzano 2005) or g this suggests 16,000 to 32,000 eels consumed by cormorants within the Thames RBD each year. Predation of eel by other species is considered in Section of the Overview. 1 Sound Metrics Corporation Eel management plan for the Thames River Basin District Page 20

21 2.5.5 Water quality and pollution Water quality in the Thames has probably been an issue for eel and elver migration since the start of the Industrial Revolution in the 1800s. The pollution from the rapidly expanding and developing City of London washed into the Thames and created a chemical barrier that prevented all migratory fish from getting upstream for most months of the year. This pollution caused populations of salmon, shad and lamprey to become extinct and probably stopped elvers from getting upstream. Even after the building of the London sewerage system in the late 19 th century, the river remained heavily polluted below the outfalls. By 1920 it was noted that no fish could survive in the 30 mile stretch of tideway between Fulham and Tilbury docks. Water quality improved after the construction of sewage treatment works in the 1960s and fish species returned. The first elvers to be found in the Thames in the 20 th Century were caught in Intermittent water quality problems remain an issue in the Thames through and below London, particularly following summer storms and the discharges from storm sewage overflows into the river. These have become a fairly regular summer event in the Thames. There is evidence of these killing eels that are resident in the tideway and fyke netsmen have reported increased catches during storm sewage discharge events, suggesting that eels are pushed further downstream by poor water quality. The River Medway has also suffered from urban pressures, but to a much lesser extent than the Thames. Water quality was never the barrier that it became in the Thames for over 100 years, although the river is modified and open to boat traffic along part of its length. In 2007 samples of 12 eels from the freshwater Thames and 36 from the tideway were collected for contaminant analysis. No results have been received from this work to date. The 2005 GQA chemistry and biology assessments of the Thames RBD are shown in Figures 2.16 and These suggest that the freshwater Thames River Basin District is generally of water quality that is suitable for eel to thrive. Eel management plan for the Thames River Basin District Page 21

22 Figure 2.16 GQA Chemistry for the Thames RBD, 2005 Figure 2.17 GQA Biology for the Thames RBD, 2005 Eel management plan for the Thames River Basin District Page 22

23 Pathogens and parasites The first reported incidence of Anguillicoloides (Anguillicola) crassus in the Thames RBD was in the late 1980s and it is now considered to be prevalent throughout the catchments. Results of eel samples examined in 2007 are shown in Table 2.6 (D. Clifton-Dey, Environment Agency, pers. comm.). Sample Thames estuary, Woolwich Area Freshwater Thames, Walton area No. eels examined % A. crassus presence Additional comments 1-7 adult or juvenile individuals found, no larval stages adult or juvenile individuals found, no larval stages. Table 2.6 A. crassus presence in River Thames, Restocking The European Eel Regulation allows for the use of captured eels and glass eels for restocking areas of habitat in order to increase silver eel escapement and work towards meeting the compliance target. At present in the Thames RBD there is little evidence to suggest that the basin is failing the 40% silver eel escapement target, The confidence in these estimates is low but no major eel stocking will be carried out until monitoring supports a more robust assessment of silver eel production and prioritises potential areas for effective stocking. 3.1 Habitat to be restocked This has yet to be quantified, but guidelines for stocking are described in Appendix Past restocking There has been extensive restocking of the Thames in the past, particularly during the Second World War when the Ministry of Agriculture took temporary control over the then German-owned trapping station on the River Severn. A policy of stocking British waters with the catch resulted in the release of several million elvers on the Thames in 1942, 1943, 1944 and 1946, principally in Oxfordshire. In 1944 alone 1,000,000 elvers were released at Letchlade, Bablock Hythe and Abingdon (Naismith 1992). Further releases occurred in 1981 and in Knights (2005) reported evidence of the survival and augmentation of natural populations, presumably by the 1993 stocking (Figure 3.1). Eel management plan for the Thames River Basin District Page 23

24 Figure 3.1 Distribution of eels in the Thames catchment. Core occupied area is delineated by heavy dotted line. River reach colours correspond to FCS classes for eels red = A, orange = B; green = C; light blue = D; dark blue = E; no colour = absent, F. Yellow coloured reaches are ones with evidence of stocking in Brown colours indicate distributions in the estuary and main river. Reproduced from Knights (2005) 3.3 Potential restocking in the Thames RBD Knights (2005) identified 720 km of Thames tributary that contained eels and 1,880 km where they were found occasionally or not all. Past stocking of eel into the Mole, Lee, Wey and upper tributaries have been shown to have increased populations and so stocking is definitely an option for increasing the escapement of eel from the Thames RBD. Knights (2005) estimated that stocking at a density of 1.0 glass eel per 100 m 2 yr -1 would increase the stock by 9,400 eels and increase the production of breeding eels by 60%. These would mostly be large fecund females each capable of producing more than 1 million eggs. The cost is estimated at more than 300,000 per year. 3.4 Eel to be restocked in 2009 There are no plans to carry out large scale eel restocking within the Thames RBD at present. Population density evidence does not suggest that it is needed to meet the silver eel escapement target. Eel management plan for the Thames River Basin District Page 24

25 3.5 Compliance with restocking requirements in the Regulation This is addressed in Appendix 7. 4 Monitoring In the Thames RBD the rivers Wandle and the Darent will be monitored biennially for yellow eel at 10 sites within each catchment (Figure 4.1). This will be supported with: Better eel data from multi-species surveys. Monitoring of juvenile eel migration at 6 sites. Collation of Anguillicola crassus presence on any eel health checks for removals or releases. Programme to measure levels of contaminants in eel flesh from the freshwater and estuarine population. Monitoring of growth rates and age at migration Monitoring of the commercial fyke net fishery through catch returns, monitoring of import and export data, and targeted enforcement patrols in the Thames estuary. Figure 4.1. Eel index monitoring sites within the Thames RBD. Eel management plan for the Thames River Basin District Page 25

26 4.1 Assessment of silver eel escapement Ongoing work to improve the assessment of compliance with the silver eel escapement target is described in Section of the Overview Price monitoring system This is addressed in Appendix Catch and effort sampling system This is addressed in Appendix Origin and traceability of live eels This is addressed in Appendix Measures The available data on eel populations in the Thames is inconsistent. The populations do not appear to be at the levels assumed to be present before the Industrial Revolution, but there is no evidence that it has changed significantly over the past 30 years. The commercial fyke net fishery is extensive in the estuary, but catches have been consistent and this fishery appears to operate at a sustainable level. Recruitment of glass eels to the Thames is at low levels. This is because of the distance of the Thames from the Continental Shelf, tending to produce low densities of eels within rivers on the East Coast and those entering into the North Sea. At present the numbers of eels immigrating into the river appear sufficient to sustain production in the estuary and around 80 km of the lower freshwater river and tributaries. The results must be interpreted with care, as eel population data from freshwater is from surveys where eels were not the target species. The Probability Model has been used to assess whether the Thames RBD meets the target of 40% of the silver eel escapement that would be produced under undisturbed conditions. The indications are that, overall, the Thames RBD is complying with the 40% escapement target. There is low confidence in this assessment and it is accepted that it does not relate compliance in the absence of anthropogenic mortality. The main anthropogenic issues thought to be affecting eel populations in the Thames RBD are: Barriers to migration River channelisation and habitat removal Eel management plan for the Thames River Basin District Page 26

27 5.1 Measures to meet Escapement Objective Reduction of the fishery pressure. The yellow and silver eel fisheries in the River Thames estuary are considerable, comprising 30% and 9% of the total declared catches for England and Wales respectively. However they comprise less than 3% of the estimated silver eel output from the Thames RBD. The CPUE have remained consistent however for around 30 years, since the recovery of the River Thames from pollution, suggesting that the fishery is not having a significant impact on the local population. However, it is essential that exploitation is sustainable and it is important that the Environment Agency works closely with the industry to ensure awareness of the eel issue and the need to deliver the 40% escapement target. Whilst more information is being collected and a better assessment of the eel fishery is made, the fishery should be kept within its existing limits by not allowing the number of instruments to be increased nor the range of where they are currently set. This would be as a precaution until more detailed information is gathered on stocks and the fishery. Improving access and habitat. This is addressed in Section of the Overview, and detailed below. Some easy and quick improvements might be to consider eel migration on all weir renovation and rebuilding works and to investigate the replacement of estuarine flap gates with ones that are more suitable for juvenile and silver eel migration into and from the habitat behind. Stocking of glass eel This is addressed in Section of the Overview and in Appendix 7. There is no evidence to suggest that large scale stocking of the Thames RBD is necessary, although small scale targeted releases may be effective. It is certainly evident that there is a considerable amount of habitat available (Figure 3.1) to eel that is presently underutilised. Predator control No action will be taken to control predators (see Overview Section 1.4.4). 5.2 Measures taken 2007 to 2009 The following measures have already been implemented or will be implemented in the period up to July 2009 Eel management plan for the Thames River Basin District Page 27

28 Monitoring Improved quality of eel data collected during multi-species electric fishing surveys at 358 sites. Carried out eel specific surveys at 5 sites on each of the Rivers Hogsmill and Wandle Continued to monitor juvenile eel migration at Molesey weir on the River Thames, Red Bridge Roundabout on the River Roding, Zenith weir on the River Mole, and Acacia weir on the River Darent. Investigated sites for monitoring of the silver eel migration, including the reinstatement of the Horton eel trap on the River Colne. Investigated eel growth rates in the Beverly Brook and River Quaggy by the release of PIT tagged eels and their recapture in future years. Investigated freshwater and estuarine preference in Thames eels by otolith analysis. Investigated estuarine and freshwater eels for the presence of A. crassus infection. Investigated eel contaminants from samples taken in freshwater and the Thames estuary. Improving access and habitat Installed eel passes on the River Mole at Molember, and on the River Thames at Teddington and Molesey. Commissioned a study of the Cray, Len and Loose (Tributaries of the Medway) to identify and prioritise structures for installation of eel passage solutions. Stocking of glass eel Investigated the potential use of the water supply reservoirs in the River Thames as possible sites for stocking and growing eels to maturity. Reducing the impact of entrainment Continued to monitor the eels entrained at the Tilbury power station and working to reduce eel entrainment when the Tilbury B power station is replaced by Tilbury C. Investigated the entrainment of silver eels at water intakes on the lower River Thames during their downstream migration using DIDSON. 5.3 Measures to be taken 2009 to 2012 The following measures will be implemented from July 1 st 2009 Eel management plan for the Thames River Basin District Page 28

29 Monitoring Continue monitoring of eel populations via multi-species electric fishing surveys and eel-specific surveys. Continue juvenile eel trapping in collaboration with Zoological Society of London. Investigate feasibility of eel monitoring at Vitbe sluice on the Cray. Install remote monitoring at Allington Lock eel pass. Continue to monitor commercial eel fisheries through catch returns and through the assessment of import and export data. Illegal exploitation of yellow eel and glass eels will be targeted by enforcement teams Improving access and habitat In 2009/2010 it is proposed to install 15 passes in Thames RBD (Figure 5.1). Figure 5.1 Location of eel passes to be installed in Thames RBD in 2009 / Install eel passes at Allington Lock on the River Medway and at Vitbe Sluice on the Cray, via flood defence projects and maintenance works. Eel management plan for the Thames River Basin District Page 29

30 Continue to target priority sites for eel passage in the RBD, including the tidal weir at the confluence of the River Wandle with the River Thames, and Bulldogs Island weir at the confluence of the River Wey with the River Thames. Complete a thorough assessment of the obstructions and habitat for eels in the Thames RBD. The Programme of Measures for the Water Framework Directive will be a good opportunity for improving habitat and access for eel populations. All opportunities should be taken to influence waterbodies for the benefit of eel populations. Stocking of glass eel Further consideration will be given to stocking within the Thames RBD and a stocking plan for the release of glass eels will be produced. This will include pre and post stocking surveys to identify the effectiveness of glass eel releases on silver eel escapement. Reducing the impact of entrainment All abstraction points in the RBD will be assessed for their likely impact on eel populations and appropriate screening suggested. All hydropower installations in the RBD will be assessed for their likely impact on eel populations and appropriate screening suggested. All pumping stations in the RBD will be assessed for their likely impact on eel populations and appropriate screening suggested. Stakeholder engagement An Eel Management Plan Implementation Group will be convened comprising representatives of the Environment Agency Area Teams with responsibility for the Thames RBD. This will make decisions on best use of limited resources. All of these actions will be subject to resources being available. The actions proposed in the period from 2009 to 2012 are detailed in Table 5.1. Measures that will have a DIRECT effect on silver eel escapement are qualified in terms of their presumed benefit, where short = <5 years, medium = 5-15 years and long = > 15 years. Note that only the shortest term is given and that the classification is for the time to effect silver eel escapement and not the time for the measure to be implemented. Eel management plan for the Thames River Basin District Page 30

31 Issue Actions to be carried out (subject to resources being available) Timescale Exploitation Monitor commercial eel fisheries through catch returns and the assessment of import and export data. Illegal exploitation of yellow eel and glass eels will be targeted by enforcement teams Initiate a price monitoring and reporting system for eels less than 12cm long. Initiate a system to ensure the traceability of all live eels imported or exported from the UK If necessary bring in byelaws to limit fisheries and protect stocks Habitat Produce maps of available & potentially available eel habitat within the River basin district, identify significant areas for habitat restoration works Use the Environment Agency s consenting of works on rivers and stillwaters and their own works programme to improve eel producing habitat Identify waterbodies within the Water Framework Directive Programme of Measures with significant opportunities for improving eel habitat Identify all surface water abstraction points and hydropower installations within the RBD and quantify their impact on eel populations Passage Produce plan of priority actions for facilitating eel passage throughout the RBD, taking into account area of available upstream habitat and cost. Ease barriers to eel migration on the Thames, Mole, Wey, Cray and Medway River systems Research into the potential for replacing tidal flap gates with structures that will allow eel passage into the drain systems in lower rivers and estuaries Identify waterbodies within the Water Framework Directive Programme of Measures with significant opportunities for improving eel passage Stocking Identify areas for restocking within the RBD Undertake pilot study with effective pre and post stocking evaluation to determine the contribution that stocking makes to the spawning stock If economically and scientifically justifiable produce plan for wider RBD Monitoring Continue to gather information on yellow eel density and biomass throughout the RBD. Continue eel trapping at four sites to assess recruitment. Continue to investigate the loss of eels at tidal power stations Investigate sites for silver eel monitoring, including the Horton eel trap on the River Colne. Further development of models to assess compliance with target (RCM and SMEP) Monitor success of novel eel passage solutions Resources Obtain funding: through partnerships with other organisations; bids to the Agency s project pot (~ 150k annually); from the European Fisheries Fund and from Interreg short short medium medium Table 5.1 Proposed actions Measures beyond 2012 to achieve the Escapement Objective It is intended that, in the period 2009 to 2012, actions will be reviewed in response to improved information on the effectiveness of the measures identified above. Eel management plan for the Thames River Basin District Page 31

32 6 Control and Enforcement 6.1 Control and enforcement measures These are addressed in Appendix 12. Illegal activities that have the potential to seriously impact on elver stocks such as fishing from boats and the use of fixed engines will be targeted. Liaison with the elver fishing community will be encouraged, through forums and consultative groups to promote understanding of the byelaws and reporting of illegal activities. 7 Modification of Eel Management Plans EMPs will be updated as and when new data become available. New data will feed into the ICES / EIFAC Eel Working Group country report for the UK and will be reviewed for the next reporting round in Eel management plan for the Thames River Basin District Page 32