Fish population summary report

Transcription

1 Fish population summary report River Witham, 2017 This report provides a brief summary of results from recent fish population surveys on the River Witham between Easton Park upstream of Grantham and Boston at the rivers tidal limit. The surveys were carried out to assess the health of the river and enable successful management of our principal fisheries. Aubourn weir rock ramp fish pass (part of several habitat improvements on the upper river). Originating team Author(s) Lincolnshire & Northamptonshire Analysis & Reporting Team Jake Reeds Date February 2018

2 Summary Twelve fisheries survey sites were surveyed during 2017 along the Witham above Lincoln. Surveys consisted of a mixture of netting and electric fishing. The wide river downstream of Lincoln was surveyed using hydroacoustic technology during the night when fish are more active. This was supplemented with side scan and multibeam sonar surveys during winter to look at fish aggregations around available habitat. Nineteen species of fish were recorded and a total of 1740 fish were captured for measurement in the upper river survey sites. Brown Trout the most widespread species in the upper river followed by chub and pike, being recorded at nine and seven sites respectively. The river downstream of Lincoln holds good numbers of adult bream and roach but the fish are difficult to find. Site locations: Sites varied between m in length, each site was isolated using stop nets at the upstream and downstream limit. It was then electric fished twice with fish being placed in a recovery tank immediately after capture. All fish are then identified for species, measured to fork length and returned to the river. The river downstream of Lincoln is surveyed using different types of sonar. Split beam sonar is undertaken at night from a boat to look at fish densities over greater distances. Multibeam sonar is used to look at how fish shoal up in winter in locations that offer suitable habitat. Side scan sonar was used to assess large shoals of bream that are present in the river downstream of Bardney.

3 Survey results - summary Fish density for fish greater than 99mm in length (fish/100mˉ²) from the survey sites undertaken is shown below. Fish lengths (mm) for all sizes are given to indicate the overall size range found at the site. Easton Cringle Paper U/S Syston Sleeper U/S Foston Claypole U/S Beckingham Haddington U/S Bracebridge Great Ponton Marston Park Brook Mills Weir Bridge Ford Bridge Bridge Bridge Bridge Brown Trout Density Size range Chub Density Size range C Bream Density Size range Dace Density Size range Eel Density Size range Gudgeon Density Size range Grayling Size range Perch Density Size range Pike Density Size range Roach Density Size range mm Tench Density Species present Size range SS, BH, MN, 3SS, BH, MN. 3SS, BH, MN, 3SS, BH, MN, 3SS, BH, MN, 3SS, BH, MN, STL, 3SS, BH, MN, STL, BL, RUF, RU BH BH, STL BH, STL BH, MN, STL STL STL STL STL STL SPL SPL Key: 3SS = Three Spined Stickleback, BH = Bullhead, STL = Stone Loach, SPL = Spined Loach, MN = Minnow, BLE = Bleak, RUF = Ruffe, RU = Rud

4 Fish density (fish/100mˉ²) Upper River fish density per site (fish>99mm): Easton Park Cringle Brook Great Ponton Paper Mills U/S Syston Weir Sleeper Bridge Marston Bridge U/S Foston Ford Claypole Bridge U/S Beckingham Bridge Haddington Bridge U/S Bracebridge Bridge Bleak Brown trout Chub Common bream Dace European eels Grayling Gudgeon Perch Pike Roach Rudd Ruffe Tench Small fish in general are difficult to catch efficiently using standard electric fishing techniques, it is highly likely that fish under 100mm in length are underrepresented in survey results. The potential voltage difference during electric fishing over small fish can be minor, meaning they are not necessarily captured when fishing. Due to the mesh size used in fish capture they can sometimes evade being picked up in a survey. Density estimates are configured using fish above 99mm in length, this gives more accurate results when looking over long term trends. The density results show a textbook shift in the fish population as the survey sites move downstream. Sites from Easton Park down to Sleeper Bridge are dominated by brown trout, the river being shallower, faster flowing with a greater habitat diversity. Coarse fish populations increase as the river becomes more traditionally lowland, with slower velocities, increased width and depth and higher levels of nutrient rich sediment. Roach numbers increase in the lower sites with the population at Bracebridge Bridge being dominated by them. Common bream and tench are all present in the sites further down towards Lincoln in small numbers but are underrepresented due to their transient shoaling nature which makes them more difficult to locate in standard surveys. Trout density was highest at Paper Mills just upstream of Grantham, traditionally this has been a good survey site with the fish seeming to prefer the fast flowing water as the river comes over the weir upstream. A good range of adult and juvenile trout were caught at the site showing available habitat is present for a diverse age structure. Great Ponton produced a good catch of trout, over 20 adult brown trout were captured in the length of just over 100m, numbers here and in sections downstream may have been influenced by past stockings. The sites at Syston and Sleeper Bridge continue to produce good density figures with adult fish to 40cm present at both. Easton Park was

5 Number of fish affected by a pollution event in April 2012, the population present there now contains adult trout that are of spawning size and age. Densities at the site now are on average with historical data, this would suggest that the section has recovered to some extent. Grayling start to appear in the river around Syston and are present in good numbers down to the Long Bennington area but are not picked up at Claypole or Beckingham. The largest grayling caught was at Syston being almost 30cm in length. Upper River length frequency results: The figures below are combined numbers of fish per species from across all survey sites graphically representing how many fish are present in a particular size range. This allows for a visual overview of the age structure and population size throughout the upper Witham. Brown Trout Fish Length (mm) Good numbers of brown trout were caught during surveying throughout sites in the upper river, the largest was in the 485mm size range from Claypole Bridge. The site in the Cringle Brook at Great Ponton provides most of fish between 65-95mm indicating that the juveniles are using it as shelter habitat before they become large enough to move out downstream into the main river. It is likely the Cringle Brook is an important spawning location for the wild trout in the river, the site there consistently produces baby trout when electric fished. Future work could look into winter redd counting surveys looking at spatial and numerical locations between the main river and the brook. Few fish were caught between the mm size ranges which could indicate a weak year in recruitment a couple of years ago. Numbers increase as the fish become larger and more mature but past stockings may be affecting the distribution, there will be wild fish in the age structure within the adult population that will help aid natural recruitment. Hydrology and habitat will be a key factor in enabling a healthy trout population in the river, the improvements made to the river led by the local Fisheries, Biodiversity and Geomorphological team will go some way to address this and is illustrated later in the report.

6 Number of fish Good size trout taken from the Witham (artistically held to look big, note the concentration). Chub Fish Length (mm) The largest chub caught upstream of Foston Ford was in the 515mm size bracket which would represent a fish of around 5lbs. The smallest fish caught was 75mm which would have been spawned in Numbers of fish in the juvenile age range show that recruitment is taking place in the river, they are often underrepresented as small chub are not often found in great numbers when surveying, they seem to be expert at finding space in the river. Relatively good numbers are present through the low 20cm size range with fewer fully mature adult fish in the 30-40cm size bracket. There are still specimen fish present in the river to be fished for.

7 Number of fish Number of fish Dace Fish Length (mm) Few juvenile dace below 80mm were caught during surveying but this is often the case, they tend to favour habitat where they can t be caught easily and are underrepresented in most fisheries data sets. Most fish reside between 90mm and 130mm long and they are present in good numbers that should hopefully follow through into more adult fish being present in the future. The largest fish caught measured 226mm and would represent a fish of around 7 years old from Sleeper Bridge. Eel Fish Length (mm) Few eels were caught in the upper river. The decline in the species is most marked in relatively shallow watercourses towards the upper areas of rivers such as the Witham. Sections such as Claypole in the late 1980 s were returning almost 400 eels alone from one site. In 2017 just over 20 eels were caught from eleven electric fishing sites throughout the entire upper river. The most likely reason for this shallow water decline is the lack of recruitment at the tidal limits as lower numbers of elvers arrive after their journey across the Atlantic. Eel distribution within a river relies greatly on the density present, as does their sex, they arrive neither male nor female, higher densities produce males and lower densities females. As fewer elvers come into the Witham the lower density produces less of a migratory push to move up river meaning the upper sections of rivers are receiving fewer eels than they used to. This is shown in the sizes we caught, most were mature female eels living in low densities that would have been in the section for around ten years or over. The largest eel in the 675mm length distribution would be a female that would be starting to get to the size where they are ready to begin their seaward migration to spawn. A historical electrical fishing survey site at Blackmoor Farm on the Witham in 1987 caught 960 eels, this is one of the highest catches from a single survey site anywhere around the country. To move from those numbers to the levels we see now within a thirty year time scale indicates the huge decline that the species has undergone. Increased levels of bird and mammal predation combined with lower levels of recruitment has affected the species dramatically.

8 Number of fish Number of fish Grayling Fish Length (mm) Juvenile grayling were caught showing that natural recruitment is taking place in the river. In general grayling numbers were low, the spatial range within the river which they seem to reside in is around 12km long downstream of Grantham. New fish passes and habitat improvement schemes will hopefully go some way to addressing this and will allow for increased numbers. Relatively good numbers of fish are present as fish start to reach maturity with fewer larger adults present. Perch Fish Length (mm) Perch numbers are low within the upper river but the size being attained by some of the fish is worth being looked at. Numbers of fish reaching mature adulthood are small but the largest fish was in the 360mm bracket. This is a specimen fish of over 2lbs and well worth angling for. Foston Ford contained the highest level of big perch, a Grantham Angling Association club book is needed to fish this section. The upper river is well worth a go for a large fish.

9 Number of fish Roach Fish Length (mm) The majority of roach caught were from Bracebridge Bridge just upstream of Lincoln, the largest fish caught was at Claypole at just over 20cm. A similar maximum size was found at Bracebridge, Sleeper Bridge and at Beckingham. Predation is a large factor for roach growth in watercourses such as the upper Witham, the larger fish are an ideal size for avian predation was has no doubt impacted the success of the population in recent years. Roach of 30cm and over were a common feature of the survey results during the s and early 1990 s. These fish are no longer present as fish are being predated upon before they reach these sizes. Habitat improvements should help to negate these impacts as more shelter refuge is installed in the upper river. Recruitment is taking place, it is an issue of providing enough shelter for the fish to grown on to larger sizes.

10 Historical data: Data from three sites where we hold long term electric fishing records is shown below. Results are given in fish density/100mˉ² for fish greater than 99mm in length, fish smaller than this are unrepresented in the data due to their size making results from them inaccurate. 80 Fish density (fish/100mˉ²) Haddington Road Bridge Historical catch data, Haddington Road Bridge. Historical density results from Haddington Road Bridge are shown above. Figures fluctuate with high numbers of coarse fish present in some survey years. Since 2011 the density from Haddington has been below the long term average of 28 fish/100mˉ². This could be caused by environmental factors such as river flow or water temperatures. Both have the ability to move fish away from locations in order to seek out refuge when surveying is undertaken. It is likely that increased predation on the river will hamper density levels increasing to relatively high numbers but monitoring will be able ascertain how the river is responding. The improvements to habitat in the river being made will help to increase fish density by offering more shelter habitat, this will help with both recruitment, survival and the overall fecundity of the river.

11 Fish density (fish/100mˉ²) Foston Ford Historical catch data from Foston Ford. The river above Foston Ford averages just over 10 fish/100m ˉ². Recent years have been below this but results from 2010 were good with a large shoal of dace pushing the density figures up. In 2005 good numbers of dace and chub were found in the section which recorded the highest fish density since surveying began there in This section can suffer from very high flows during high rainfall events, it is heavily embanked and fish have limited shelter to take refuge in.

12 Fish density (fish/100mˉ²) Great Ponton Historical catch data from Great Ponton. The fish density at Great Ponton is likely to be affected by previous stockings by the trout fishing club so the figures are only representative of what is present in the section rather than any longer term trends. When density has been high it is likely to have been heightened by the presence of stocked fish. The club now operate a no stocking policy and catch and release policy. Surveying carried out in the future will be able to see how fish numbers are responding to this change. Future monitoring could include specific redd counting and egg survival investigations to be able to link this in with habitat improvement schemes.

13 Hydroacoustic data - Wide Witham: Witham results May Environment Agency copyright All rights reserved. Ordnance Survey licence number

14 The river below Lincoln was surveyed using a split beam sonar transducer during night time in May starting at 10pm. The survey ran from Stamp End Lock to Bardney Lock finishing at 1am, the next night from Bardney to Dogdyke finishing at 2am and then from Dogdyke to Boston for a similar duration on the third evening. The system detects fish in the water column and allows a density estimate to be mapped out against their location in the river. This is displayed in the map above, the larger the circle the higher the fish density. The Witham is surveyed in May because if it is left any later it becomes too weedy for the equipment to image the fish, a similar case on the Welland and Ancholme locally. Stamp End to Bardney: Fish distribution here was skewed towards the city end of the section, this is a common occurrence in lowland rivers where fish utilise habitat around human structure. The area downstream of Stamp End lock contained the highest densities, the trees on the right hand bank offer good refuge habitat. The river level here stays at a constant throughout winter and summer. This allows fish to utilise marginal habitat through all times of the year, in cold temperatures and in high flows. Numbers dropped off as the river moves out past Washingborough but picked up again under the boat moorings at Bardney Lock. Large echoes on the display indicated that larger fish species such as bream, tench and pike were present in this section, the ability for these to be identified and monitored in the future has been greatly increased by the acquisition of a side scan sonar. This will be embedded in our monitoring alongside future split beam work and is demonstrated in following pages. Bardney to Dogdyke: Fish were located around Bardney downstream to Kirkstead, this is often the case when the river is at summer retention level. The side channels such as Nocton Delph, the Sincil Dyke, Timberland Delph and Billinghay Skirth all become available as side channel habitat for spawning and foraging. This section of the river downstream of Bardney consistently held the most bream during the year when a tagging project was run on the river between In a highly modified channel such as the Lower Witham than side channels stand out as beacons to the fish present, they will help to hold the fish in the upper river. Dogdyke to Boston: The river downstream of Dogdyke to Boston had the lowest fish density in the wide Witham. In certain stretches no fish were located using the split beam transducer. The river is uniform, barren and has no suitable off channel habitat. Overwintering here for most species is hard work, the level is dropped removing all access to overhanging trees which are crucial for small fish to shelter in. Langrick Bridge is the only real area providing overhead cover and roach can be found under the bridge and around the boats but avian predation is constant here during winter. Side scan/multibeam survey results: Side scan surveys produce a bank to bank bird s eye view of the river bed, this allows fish to be imaged and the location they are present to be logged. While it may not produce density estimates it can give a very good indication as to why a fish population is behaving as it is. This method was used to assess fish numbers on the lower Witham for the first time during winter Firstly to establish bream shoaling in the main river and also to assess where fish are overwintering, this helps to highlight how habitat plays an important role in the fish population. Multibeam sonar uses over 100 beams working next to one another at very high frequencies. This gives back a highly detailed live video image under the water. It is a vital tool for looking into how fish utilise habitat and the need to protect bankside trees. This can see through darkness and high levels of turbidity in the water.

15 The side scan image produced while surveying. Multibeam sonar on a pan and tilt unit.

16 Sincil Dyke: The Sincil is a known overwintering location for bream shoals. If they aren t in it sheltering from high flows they sit in the basin where it joins the main river. The image below shows the bridge access to Bardney Lock, anytime from November through to March this section of the river is worth bream fishing. The Sincil itself can hold very large shoals, over 1000 adult fish were in a 100m survey site in 2010 about half a mile up from where it joins the Witham. The side scan survey imaged over 100 fish in the entrance in early February Bream shoal at the entrance to the Sincil Dyke. Marked fish on the right.

17 Directly adjacent to the entrance to the Sincil Dyke is Bardney Lock pit. The photo on the left shows the old railway bridge with the lock pit just above it. On the side scan image below left the stanchions for the bridge can be seen towards the bottom of the scan on the banks. A large bream shoal was present stretching from just above the bridge past the lock pit up towards the arm of the river that comes past Branston Island. This contained approximately 355 adult bream averaging around 4-5lbs. This is another favoured location for the fish as they can feed in the channel and move into either the lock pit or the Sincil Dyke if the flows in the river pick up. In early 2017 an experiment was undertaken to establish the importance of the willow trees along the Sincil Dyke for both adult bream and 0+ and 1+ fish juvenile fish during winter. A multibeam sonar was set up and the area was baited using ground bait. The photo below shows the location and set up. Within five minutes of baiting the area the sonar screen was full of adult bream and thousands of cyprinid fry and 1+ fish. The image to the left shows the adult bream and the thousands of fry present in the Sincil during winter when it is groundbaited. Because they are here during winter it can also be a prolific pike fishery.

18 Bardney Moorings The moorings at Bardney provide vital overhead cover for large roach during winter when macrophyte cover has died back in winter. There are often shoals in excess of ten thousand fish below them, the river either side can be devoid of large roach for mile at a time during winter retention level. The image from Bardney Moorings on the left illustrates the tightness of the shoaling Roach gather round moorings, under bridges and in Dogdyke marina in large numbers. The willow trees in the Sincil Dyke provide critical refuge habitat for them. At the entrance to the Kyme Eau at Chapel Hill fish can be seen under the moorings so tightly packed in the sonar cannot image between them. All display classic persecution behaviour. Predation by cormorants plays a large part in this shoaling behaviour. Winter shoaling is common amongst cyprinids but the extent to which the fish seek out and shoal in massive numbers is exacerbated by the efficiency of avian predation. When the colour falls out of the river the lower river is left with very little shelter habitat. If a roach spends time in open water in daylight there is a high chance it will be eaten, cormorants feed heavily at Langrick Bridge daily during the winter. Roach there have little or no other shelter habitat to escape this form of predation.

19 WFD Classification: Current WFD fisheries classification for the Witham system ranges from Poor to Good over 6 sites undertaken on the river throughout surveying years ( ). Classifications should be put in perspective as results can be heavily influenced by fish location and river conditions. Water body ID Sites in water body Fish status Reason Overall River status GB Witham - US EASTON PARK POOR GB Witham - DS GRANTHAM GOOD GB Witham - US LINCOLN POOR Low species numbers and low densities at EASTON PARK Driven by good catches at PAPERMILLS, MARSTON and CRINGLE BROOK. Driven by low catches at Bracebridge Bridge GB Witham - LOWER NA NA NA POOR GOOD POOR Water Framework Directive water bodies with classification status for 2016 (data based on catches from ). Health of fish population: Results from the upper river electric fishing sites provided good densities with some sites containing good numbers of fish and specimen chub and perch. Habitat improvements in this section by the Fisheries, Biodiversity and Geomorphology team will provide increased opportunities for spawning, refuge and foraging that will in the long term lead to higher densities and larger fish. The river upstream of Lincoln holds good numbers of roach and some bream, new technology will enable us to assess the impact that Brayford Pool has on the system, Lincoln and District Angling Association have the pool on membership and day ticket. At present we cannot estimate just how much of the population is present there, it is likely given the evidence for fish shoaling around human structure that it will be significant especially during winter. This is applicable to the bream that reside in the area. The lower river downstream of Bardney contains roach and bream in numbers but excessive weed growth in the summer can hamper catching them. The weed is driven by high levels of phosphate and nitrogen in the river, mixed with clear water and sunshine it is the perfect combination for large scale growth. Habitat is poor on the lower river, there is very little in the way of natural complex margins or trees that can provide vital cover for fish. This leads to the winter shoaling effect we see where the fish are not available to anglers because they are tightly bunched around key locations. The winter retention level and corresponding increased predation and loss of side channels is the key restriction to the fish population present. The removal of access to side tributaries, emergent vegetation and the condition of the delphs to the west of the river is discussed in the following pages. The Sincil Dyke and the shelter the willow trees along it provide are absolutely critical to the success of the entire fish population in the lower river. It needs the utmost protection.

20 Angling: Trout and grayling fishing in the upper river is good with certain stretches containing some good wild fish. These sections are fishable under a Grantham Fly Fishers membership only. Chub, dace and perch are worth fishing for around Foston and Long Bennington, these sections are available on a club book from Grantham Angling Association. For winter bream/roach/pike fishing the Sincil Dyke is the only place to fish. The fish have little option but to overwinter around this section. Summer on the lower river when the levels come up the bream can be highly mobile but the sections between Bardney and Tattershall Bridge will be likely spots, finding colour in the water during the summer will be key to this. Boston and District Angling Club have a section upstream of Tattershall including weedy bay. Roach will spread out from their overwintering areas into the main river during summer. Again the section from Bardney to Tallington is the best bet. They can pack in tightly to the willows on the Sincil dyke in winter, fish close to them. Habitat improvement work: Several habitat improvement schemes have been underway on the upper river over the past five years. All of them are aimed at increasing the available shelter, feeding and spawning habitat for fish in the river. This is combined with the benefits that are brought about by the fish passes being installed in the river to allow higher degree of movement. Some examples of the work carried out by the local FBG team are shown in the following pages. Off channel fish refuge at Chapel Hill on the Lower Witham.

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23 Winter retention level - Lower Witham: Each November the river downstream of Bardney Lock is dropped for five months to increase winter capacity for flood defence purposes. The lower Witham is very difficult to drain, it has low gradient, has no washlands downstream of Branston Island and is effective tide locked when the tide is in at Boston. The extra capacity added by lowering the river helps to negate against this but has significant impacts on the fish present. Fish during wintertime need marginal habitat to provide refuge from predation and high flows, this is especially important in the recent decade because of increased levels of predation. Lowering the river removes the most significantly important habitat in the river at a key time of year. Off channel habitat such as Nocton Delph should be a vital overwintering location for all species of fish both adult and juvenile. During winter retention levels it can average 20cm in depth. Nocton Delph during winter level. This effect is also present on the Kyme Eau, the Billinghay Skirth and the Timberland Delph. All would usually act as overwintering locations for the fish. However they do not hold the water levels necessary to do so. In Feb 2018 a side scan of the Kyme Eau was undertaken from Chapel Hill to Bottom Lock which is the first upstream barrier on the Eau. Not a single fish was recorded in the river, it averaged 40cm deep and is offering no shelter to any species of fish. This problem is confounded by the levels of sediment present in the side channels. Nocton Delph has in places over 1.5m of silt, combine this with a low winter level and 20cm of water is the result. To illustrate this some cross sectional transects of the tributaries of the lower river were carried out in 2014.

24 Depth (M) Depth (M) Two sites each were undertaken on the Kyme Eau, Billinghay Skirt, Timberland Delph, Nocton Delph and Sincil Dyke. The Kyme Eau is illustrated below, the light blue line is summer water level, the dark blue winter water level and the brown is the top of the sediment. Sediment is accounting for half the depth during summer and two thirds during winter. This was similar to all the other tributaries apart from the Sincil Dyke. 0 Kyme Eau The Sincil has an open connection to the Witham and is the most upstream of the tributaries to be affected by the winter retention. The difference in why fish chose to overwinter here is illustrated below, combine the depth that it retains during winter, the lack of sediment present and the overhead cover from trees and it offers real shelter habitat. Sincil Dyke The winter level is historic on the Witham and was in place during its angling height in the 1960 s and 1970 s so it is important to illustrate why it has become so important for fish and will be into the future. Firstly predation on fish populations has increased by a significant amount since then, having overhead cover wasn t as important as it is now. Without it fish are extremely vulnerable, this leads to heavy loses and large scale changes in behaviour which make them very hard to catch. Second is the level of sediment that has built up to render the side delphs uninhabitably when the level is dropped.

25 The middle section of Nocton Delph in This was an important off channel spawning site for bream, sediment build up colonised by emergent macrophytes has left it unfit for use for fish during summer and winter. The lower end of Nocton Delph, summer Nutrient rich sediment helps to drive large scale filamentous algal growth which causes poor water quality.

26 If possible mutually beneficial opportunities for both flood defence and fisheries arise in the future these will be looked at to try alleviate some the pressures acting on the fish present. Next survey year: 2020 Will look at changes in fish populations associated with the habitat improvement schemes in the upper river. Will look into the total bream population of Lower River, at present we only have snapshot of how many are there. Will look into fish populations in the Brayford pool to assess how significant it is to the section of the river upstream of Lincoln. If you would like to discuss the information presented in this report, please contact: Jake Reeds, Fisheries Officer, Analysis & Reporting Team, Spalding Before you go fishing don t forget: You must have a valid Environment Agency rod licence and permission from the fishery owner; You must comply with the fisheries byelaws; The coarse fish close season (15th March to 15th June inclusive) applies to all rivers, streams and drains in England and Wales but not most stillwaters. Stillwater fishery owners can still have their own close season and rules, so please check with them before setting out. Report illegal fishing: If you see any fishing, netting or trapping you think may be illegal, please do not tackle it yourself. Call us immediately on and tell us: Exactly where the alleged offence is taking place; What is happening; How many people are involved and their descriptions; The registration numbers of any vehicles involved. If you prefer to remain report an environmental crime anonymously call Crimestoppers on or