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 Lincolnshire & Northamptonshire Analysis & Reporting Team Author(s) Jake Reeds Date February 2018 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 100 - 200m 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. 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 0.916 0.666 6.984 10.600 7.000 5.833 0.5 0.571 0.649 - - - Size range 146 - 291 69 - 198 171 - 294 74 - 363 77 - 392 77 - 417 81 - 449 175 - 479 171 - 489 - - - Chub Density - - - - - 0.667 0.1 1.429 3.052 1.900 0.0342 0.063 Size range - - - - 111 - 442 345 93 - 516 114 - 387 79 - 381 93 - 236 201 C Bream Density - - - - - - - - - - - - Size range - - - - - - - - - - - 46 - 81 Dace Density - - - - 1.4 1 - 0.952 2.208 - - 0.125 Size range - - - - 78 - 213 81 - 226 - 79 - 188 111 - 193 - - - Eel Density - - - - 0.1 - 0.1 0.667 0.39 0.05 0.598 - Size range - - - - 620 - 635 425 - 675 390 - 495 230 285 - 410 - Gudgeon Density - - - - - - - - 0.519 0.205 1.282 - Size range - - - - - - - - 108 - 124 88 - 109 101 - 118 - Grayling - - - - - 1.333 0.7 1.429 - - - - Size range - - - - - 79 - 275 95 - 249 153 - 246 - - - - Perch Density - - - - - 0.6667 - 0.952 - 0.05 1.197 0.375 Size range - 216 - 264 - 246 - 364 - 326 95 - 248 64 - 175 Pike Density - - - - - 1.677 0.1 0.286 272 - 724 0.085 0.085 0.188 Size range - - - - - 290 - 455 553 334 - 536 - 236 - 652 582 157 - 229 Roach Density - - - - - 1.000 0.2 0.19 3.701 3.200 - 13.428 Size range - - - - - 141 - 198 127 - 128 115 - 151 134 - 212 42 - 199 89mm 45 - 199 Tench Density - - - - - - - - - - 0.085 0.063 Size range - - - - - - - - - - 173 169 Species 3SS, 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 present 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 Upper River fish density per site (fish>99mm): 20 18 16 14 12 10 8 Fish density density (fish/100mˉ²) Fish 6 4 2 0 Easton Park Cringle Brook Great Ponton Paper Mills U/S Syston Sleeper Marston U/S Foston Claypole U/S Haddington U/S Weir Bridge Bridge Ford Bridge Beckingham Bridge Bracebridge Bridge 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 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 14 12 10 8 6 Number of fish of Number 4 2 0 65 80 95 110 125 140 155 170 185 200 215 230 245 260 275 290 305 320 335 350 365 380 395 410 425 440 455 470 485 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 110 - 140mm 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. Good size trout taken from the Witham (artistically held to look big, note the concentration). Chub 10 9 8 7 6 5 4 Number of fish of Number 3 2 1 0 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 360 375 390 405 420 435 450 465 480 495 510 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.