Fish Population Survey Report

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Fish population survey report

The River Great Ouse - Brackley and Newport Pagnell [September / November 2016] This report provides a summary of results from the 2016 fish population surveys conducted on the River Great Ouse between Brackley and Newport Pagnell. The surveys were carried out to assess the health of the river and enable successful management of our principal fisheries.

Image 1: A specimen barbel from the River Great Ouse at Manor Farm, Cosgrove. Summary  Ten sites on the River Great Ouse were surveyed by electric fishing and drag down Seine netting between the 5th of September and the 1st of November.  The 2016 survey is the second round conducted in the new triennial survey cycle. Prior to 2010 many Great Ouse sites were sampled annually.

 A total of 1695 fish of 17 species were recorded.

 Dace, roach and perch were the most numerous species captured.

 Average density and standing crop estimates derived from the ten sites surveyed equate to 6.71 fish per 100m² and 1193 grams per 100m² respectively. www.gov.uk/environment-agency

Introduction to Environment Agency fisheries surveys The Environment Agency has a statutory duty to maintain, improve and develop fisheries. Our policy is to do this in a way that maximises the social, recreational and economic benefits arising from the sustainable exploitation of the fish stocks that underpin fisheries. To help deliver this duty, we have a National Fisheries Monitoring Programme (NFMP) to describe the status of our fish populations and inform our fisheries management to meet international (WFD, Eel regulations, ICES reporting), national and local data needs. Sites are regularly reviewed to maintain a representative sample of fish populations and the water body as a whole in order to retain a comparable dataset. Sites designated for the national fisheries monitoring programme cannot be altered, unless there is a valid health and safety concern, access is no longer possible or there has been a review of policy during the monitoring period. Survey site locations

Site Name Site ID Site Name Site ID Brackley 31487 Mill Farm 4630 Westbury 4622 Passenham 4631 Water Stratford 4623 Manor Farm Cosgrove 4635 Buckingham 4625 D/s Wolverton Mill 36762 Thornborough Mill 4627 Mill Farm Gayhurst 4637

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Survey methodology Nine sites on the Great Ouse were sampled using electric fishing methodology and one site was surveyed by drag down seine netting. Electric fishing is a survey technique that uses the physiological effect of an electric field in water to attract and immobilise fish. Electrodes, immersed in the water, stimulate the fishes nervous system so that it swims towards the operator, or is unable to swim away, and can then be caught with a hand net. In shallow rivers and streams it is generally possible to wade upstream within the river channel using generator-powered equipment, which is towed within a small boat. When rivers deepen or site depth is variable, electric fishing from within a flat-bottomed boat is generally the preferred method. The boat is manoeuvred downstream on long ropes by an operative on either bank controlling the speed, direction of travel and in-channel positioning. Image 2 (below) shows the typical components of an electric fishing system. Stop nets are positioned across the channel to isolate the survey site and prevent fish from migrating into and out of the survey area. The electric fishing operation is repeated until a 50% reduction in the total number of fish caught has been achieved. Captured fish are measured to the nearest millimetre (to the fork of the tail) and scales are taken for age, growth and other statistical analyses at the National Fish Laboratory in Brampton. Density and standing crop results are reported utilising fish greater than 99mm in length as electric fishing methodology has been shown to loose capture efficiency on fish below this length. Numbers of juvenile fish and small species such as minnow and bullhead should therefore be viewed as a minimum estimate only.

It is not currently possible to discuss population trends other than at site level as the long-term data set is incomplete due to historic changes to survey schedules and the need to discontinue surveys at some locations (due to loss of access etc.) Some historic sites have subsequently been reinstated to increase survey coverage and the survey programme is now designed to sample a variety of the habitats present, both good and bad, to represent the river reach as a whole. These sites were chosen where historic data was present, where access was good and was likely to remain so and at sites where the survey can be carried out as efficiently as possible allowing maximum confidence in the data possible. Recent improvements to collection of channel width data revealed that field measurements were lower than the historic width values used to calculate population estimates. This means that population estimates will be underestimating stock present. The values in this report have been calculated using the historic width values to allow easier comparison with historic data; however, future reports will compare sites using the updated width data. The difference in population density derived from these new width measurements is given as Figure 15 in the appendices of this report. The Wolverton Mill site is most affected by this improved width accuracy with the 2016 density estimate increasing by around a third when the more precise channel dimension data is used. Results

• Ten sites on the River Great Ouse were surveyed by electric fishing and drag down Seine netting between the 5th of September and the 1st of November.

• A total of 1695 fish of 17 species were recorded.

• Dace, roach and perch were the most numerous species captured.

• The average density and standing crop estimates derived from the ten sites surveyed equate to 6.71 fish per 100m² and 1193 grams per 100m² respectively.

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Table 1: Total number and largest (mm) fish captured for key species during the 2016 survey.

Chub Dace Roach Perch Brown Trout / Barbel

Site Number Largest Number Largest Number Largest Number Largest Number Largest

Brackley 0 - 39 229 1 116 31 241 21 441

Westbury 15 485 35 254 17 176 17 213 15 414

Water Stratford 0 - 11 210 34 205 9 224 25 518

Buckingham 1 403 50 252 61 316 3 301 1 521

Thornborough Mill 1 132 19 156 8 152 1 270 0 -

Mill Farm 0 - 3 139 2 80 4 265 0 -

Passenham 0 - 10 116 14 77 4 190 0 -

D/S Wolverton Mill 18 557 21 183 53 230 25 315 0 -

Manor Farm Cosgrove 30 517 54 231 68 153 13 311 1/14 248/764

Mill Farm Gayhurst 7 496 67 236 29 193 6 263 0 -

Tables 2-3: Density estimate and Standing crop estimate for fish >99mm

Table 2: Results Table for Density (Ind./100m2) >99mm

Water Thornborough D/s Wolverton Manor Farm Mill Farm Brackley Westbury Buckingham Mill Farm Passenham Species Stratford Mill Mill Cosgrove Gayhurst Mean

05/09/2016 07/09/2016 08/09/2016 03/10/2016 10/10/2016 11/10/2016 11/10/2016 24/10/2016 31/10/2016 01/11/2016 Dace 4.22 2.52 0.91 2.75 0.97 0.13 0.53 0.77 3.52 3.10 1.94 Roach 0.11 1.53 3.00 3.43 0.12 0 0 4.69 3.58 1.25 1.77 Perch 3.67 1.44 0.82 0.29 0.06 0.04 0.08 1.31 0.65 0.20 0.86 Brown trout 2.11 1.62 2.36 0.10 0 0 0 0 0.05 0 0.62 Chub 0 1.35 0 0.10 0.06 0 0 1.39 1.68 0.35 0.49 Gudgeon 1.44 0.18 0.82 0.10 0 0.04 0.53 0.08 0.71 0.40 0.43 Pike 0.11 0.27 0.18 0.88 0.61 0.22 0.08 0.31 0.43 0.90 0.40 Barbel 0 0 0 0 0 0 0 0 0.76 0 0.08 Bleak 0 0 0 0 0 0 0 0 0.60 0.10 0.07 Brook lamprey 0.11 0 0 0.10 0 0 0 0 0 0 0.02 Bullhead 0 0 0.09 0 0.06 0 0 0 0 0 0.02 Roach x chub 0 0 0 0 0 0 0 0 0.11 0 0.01 Common bream 0 0 0 0 0 0 0 0 0.05 0 0.01 Total 11.78 8.92 8.18 7.75 1.88 0.44 1.21 8.54 12.14 6.30 6.71

Table 3: Results Table for Standing Crop (g/100m2) >99mm

Water Thornborough D/s Wolverton Manor Farm Mill Farm Brackley Westbury Buckingham Mill Farm Passenham Species Stratford Mill Mill Cosgrove Gayhurst Mean

05/09/2016 07/09/2016 08/09/2016 03/10/2016 10/10/2016 11/10/2016 11/10/2016 24/10/2016 31/10/2016 01/11/2016 Chub 0 816.7 0 82.9 2.1 0 0 1489.9 1560.4 296.1 424.8 Pike 30.7 19.2 13.6 372.8 270.6 28.4 4.5 284.1 232.0 389.8 164.6 Roach 2.7 154.8 176.8 378.3 4.5 0 0 293.9 249.4 81.8 134.2 Brown trout 354.3 310.6 462.3 106.5 0 0 0 0 8.3 0 124.2 Dace 270.2 249.9 48.3 97.4 25.5 3.3 8.5 25.3 172.5 206.9 110.8 Barbel 0 0 0 0 0 0 0 0 1084.0 0 108.4 Perch 218.3 131.5 110.2 135.7 24.0 14.6 9.5 288.9 112.2 32.1 107.7 Gudgeon 58.5 5.0 21.4 1.6 0 0.9 7.9 1.6 18.7 11.1 12.7 Roach x chub 0 0 0 0 0 0 0 0 40.2 0 4.0 Bleak 0 0 0 0 0 0 0 0 13.3 1.3 1.5 Bullhead 0 0 1.3 0 1 0 0 0 0 0 0.2 Brook lamprey 1.1 0 0 1.0 0 0 0 0 0 0 0.2 Common bream 0 0 0 0 0 0 0 0 0.8 0 0.1 Total 935.9 1687.8 834.0 1176.2 327.6 47.2 30.3 2383.7 3491.8 1019.1 1193.4

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Mean density estimate and standing crop by species 2016 Figure 1 shows the mean density estimate for the 2016 survey broken down to species level. This shows that dace were dominant by density with a population estimate of 1.9 Ind./100m2 and roach were subdominant (1.77 Ind./100m2). Both species were recorded at all sites sampled, albeit in low numbers at some locations. Surprisingly, brown trout ranked fourth by mean density thanks to good catches made in the Upper River and sporadic representation at sites as far downstream as Cosgrove. Figure 2 shows that although chub ranked fifth in terms of density, being caught at six of the ten survey sites, the species was principle in terms of biomass recorded and a prevalence of large fish meant that chub accounted for 36% of the standing crop estimate. By comparison, the next most important species in terms of standing crop (pike) represented just 14% of the mean biomass recorded. Barbel ranked sixth in terms of standing crop and, although limited in terms of numbers caught and distribution, the high average size of these fish means that the species formed almost 10% of the standing crop estimate.

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Site level results Site No. 31487 Site name: Brackley Date of survey: 05/09/2016

Species present (All lengths) Minimum Maximum Mean Species Length Length Length Number caught Bullhead [Cottus gobio] 28 84 69 147 Dace [Leuciscus leuciscus] 90 229 166 39 Perch [Perca fluviatilis] 114 241 148 31 Brown / sea trout [Salmo trutta] 91 441 220 21 Gudgeon [Gobio gobio] 132 185 147 9 Stone loach [Barbatula barbatula] 76 82 79 2 Roach [Rutilus rutilus] 116 116 116 1 Pike [Esox lucius] 327 327 327 1 Brook lamprey [Lampetra planeri] 152 152 152 1 Population Composition by density (>99mm) The river at Brackley averaged a little over 4 meters wide with an average depth of 0.36 meters and shallow run and glide

habitat dominant. Riffle and pool habitat was also present with a maximum pool depth of 0.86 meters. The substrate was predominantly coarse sand and gravel and the site possessed moderate shading.

The 2016 survey recorded nine species and a fish density

estimate similar to that previously found in 2013. Dace remain dominant at this site with a 36% share of the density estimate although the most numerous fish captured of all lengths was the bullhead.

Some change had occurred at species level with fewer dace in 2016 and an increased number of perch recorded. Brown trout populations have slowly increased over successive surveys raising from 1.63 Ind./100m2 in 2008 to 2.11 Ind./100m2 in

2016 and the species currently composes 18% of the density estimate.

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Site No. 4622 Site name: Westbury Date of survey: 07/09/2016

Species present (All lengths) Minimum Maximum Mean Species Length Length Length Number caught Dace [Leuciscus leuciscus] 72 254 165 35 Roach [Rutilus rutilus] 133 223 176 17 Perch [Perca fluviatilis] 63 213 164 17 Brown / sea trout [Salmo trutta] 210 414 258 15 Chub [Leuciscus cephalus] 156 485 329 15 Bullhead [Cottus gobio] 34 92 67 14 Minnow [Phoxinus phoxinus] 48 64 53 7 Pike [Esox lucius] 187 246 211 3 Gudgeon [Gobio gobio] 128 133 131 2 Population Composition by density (>99mm) The river at Westbury was a little over 5 meters wide and averaged 0.43 meters deep. Shallow run and glide habitat was dominant with a coarse sand and gravel substrate. Moderate shading was present. The 2016 survey found nine species present and recorded a fish density estimate comparable to that made in 2013. Dace were the dominant species by density with a 29% share of a population that appears to have been relatively steady since 2013, falling just 0.3 Ind/100m2 between the two survey cycles. Roach density has halved since the previous survey while brown trout density has increased six fold to 1.62 Ind./100m2. The increase in numbers of this sensitive species means that whatever the reason for the reduction in roach, it is not due to water quality at this location. Species richness remains

similar to that observed during the past three survey cycles and is much improved over that found in surveys conducted during the 1990’s.

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Site No. 4623 Site name: Water Stratford Date of survey: 08/09/2016

Species present (All lengths) Minimum Maximum Mean Species Length Length Length Number caught Roach [Rutilus rutilus] 92 205 142 34 Minnow [Phoxinus phoxinus] 42 84 63 28 Brown / sea trout [Salmo trutta] 139 518 245 25 Bullhead [Cottus gobio] 29 102 65 18 Dace [Leuciscus leuciscus] 41 210 144 11 Gudgeon [Gobio gobio] 113 146 127 9 Perch [Perca fluviatilis] 113 224 191 9 Stone loach [Barbatula barbatula] 84 93 89 2 Pike [Esox lucius] 205 229 217 2 Population Composition by density (>99mm) The Ouse at Water Stratford averaged 4.2 meters wide and 0.5 meters deep. Deep run and glide habitat was dominant with riffle and pool features also noted. The maximum pool depth was 1.25 meters, shading was light and the channel substrate was composed chiefly of coarse sand and gravel. The 2016 survey found nine species present and species richness was less than recorded in 2012 (11 species) but was an improved result over 2006 (7 species). In terms of density there was a slight decline noted since 2012, however that survey result had been influenced by poor survey efficiency that overestimated the gudgeon population present. Roach and dace density was broadly similar to that recorded in 2012, but brown trout density had doubled and this result represents the second highest population of the species to be recorded at this site. The current density estimate 8.18 Ind./100m2 is above the long term average of 5.18 Ind./100m2. In terms of biomass the 2016 result is comparable to that recorded in the previous survey cycle with brown trout contributing >50% of the standing crop estimate.

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Site No.4625 Site name: Buckingham Date of survey: 03/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Number caught Roach [Rutilus rutilus] 21 316 118 61 Dace [Leuciscus leuciscus] 41 252 109 50 Minnow [Phoxinus phoxinus] 41 64 54 36 Pike [Esox lucius] 191 465 343 7 Bullhead [Cottus gobio] 61 88 77 6 Gudgeon [Gobio gobio] 76 106 92 4 Perch [Perca fluviatilis] 261 301 283 3 Rudd [Scardinius erythrophthalmus] 64 64 64 1 Brown / sea trout [Salmo trutta] 521 521 521 1 Chub [Leuciscus cephalus] 403 403 403 1 Brook lamprey [Lampetra planeri] 142 142 142 1 The survey site at Buckingham was heavily shaded with deep run and glide habitat and a gravel and coarse sand substrate dominant. Submerged vegetation was absent, presumably due to the degree of shading. The 2016 survey found eleven species present with roach dominant by density (44%) and dace subdominant (36%). Overall density is down on the previous survey result and a little below the long-term average but remains higher than recorded between 2002 and 2009. The main reason for the decline in density is a reduction in roach captured, the density estimate for this species falling by almost two thirds. The majority of the roach captured were small individuals, but a number of larger fish were present which included an individual of over 300mm in length (Image 4). Dace density has continued to increase at this site and the current population estimate of this species is the second

highest on record. The 2016 survey was the latest in the year that this site had been sampled (October) and the survey followed a period of higher flow, which may have influenced stock distribution. The highest catch (1997) was made in the earliest survey undertaken (March) also meaning that this result may have been influenced by winter shoaling.

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Site No. 4627 Site name: Thornborough Mill Date of survey: 10/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Number caught Dace [Leuciscus leuciscus] 74 156 120 19 Pike [Esox lucius] 177 556 347 10 Roach [Rutilus rutilus] 63 152 87 8 Minnow [Phoxinus phoxinus] 42 52 48 3 Gudgeon [Gobio gobio] 54 82 68 2 Chub [Leuciscus cephalus] 132 132 132 1 Ruffe [Gymnocephalus cernuus] 91 91 91 1 Bullhead [Cottus gobio] 100 100 100 1 Perch [Perca fluviatilis] 270 270 270 1 The Ouse at Thornborough averaged over 10 meters wide and a little under 1 meter deep. Run and glide habitat was dominant with a bed substrate primarily composed of coarse sand and gravel. Shading was described as light to moderate although a fallen tree provided a large amount of cover in the middle reaches of the survey area. The sampling team stated that they considered the survey was probably quite inefficient due to the presence of the fallen tree, which while appearing to offer excellent habitat, made survey conditions difficult. Despite the team’s suspicion that fish evaded them, they did manage to achieve a good catch depletion suggesting that this result is a reasonable representation of stock present. The 2016 survey a produced a density estimate roughly half of that recorded in 2013, but slightly higher than that observed in 2010. The decline in density noted in this survey cycle has been caused by a reduction in roach and gudgeon captured.

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Site No. 4630 Site name: Mill Farm Date of survey: 10/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Numbers caught Minnow [Phoxinus phoxinus] 37 53 44 420 Bullhead [Cottus gobio] 42 61 55 6 Pike [Esox lucius] 227 268 256 5 Perch [Perca fluviatilis] 71 256 119 4 Dace [Leuciscus leuciscus] 111 139 126 3 Roach [Rutilus rutilus] 74 80 77 2 Gudgeon [Gobio gobio] 71 118 95 2 The river at Mill Farm was just over 8 meters wide with an average depth of 0.73 meters. Deep run and glide habitat was dominant with no riffle or pool features noted. The channels bed substrate was chiefly composed of coarse sand and gravel and shading was light. The 2016 survey was a disappointing catch dominated numerically by minnows (all fish) and Pike (>99mm). Historic data indicates that population density at this site declined following the 1997 survey and has not recovered subsequently. The site has little shade or cover with the exception of some beds of club rush and there is little flow diversity present either, glide habitat being dominant throughout the survey length. The absence of habitat data from historic survey cycles make it difficult to draw any conclusions

why roach have left this site, a photograph taken in 1994 seems

to indicate that little has changed in terms of bankside cover, in fact there is more cover in terms of club rush in recent survey cycles. It is apparent that far better habitat, in terms of riparian shading, is available a short distance downstream of the survey

site and it may be that this is where the bulk of fish populations now reside.

Further investigation will likely to be required at this location to assess fish populations present around alternative habitat types.

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Site No. 4631 Site name: Passenham Date of survey: 11/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Numbers caught Roach [Rutilus rutilus] 47 77 60 14 Gudgeon [Gobio gobio] 72 107 98 11 Dace [Leuciscus leuciscus] 72 116 103 10 Perch [Perca fluviatilis] 72 190 103 4 Pike [Esox lucius] 203 203 203 1 Bullhead [Cottus gobio] 61 61 61 1 Spined loach [Cobitis taenia] 63 63 63 1 The 2016 survey continued the pattern boom-bust of survey results recorded at this location over the past eight cycles. The river at this location is 11 meters wide with an average depth of 1.2 meters. Deep glide habitat is dominant with a bed substrate reportedly composed predominantly of coarse sand and gravel. Riparian shading is absent. This survey area appears to be used only intermittently by fish stocks with roach generally heavily dominant when present. Roach have a very close affinity with overhanging tree cover (of which this site is lacking) but there is much-improved habitat available nearby both upstream and downstream of the survey area such habitat offers increased security for shoaling species. Migration of stock into and out of areas such as Passenham is likely dictated by environmental conditions, such as channel turbidity,

and is likely replicated elsewhere at locations with a similar scarcity of habitat. There is some question in the value of retaining this site, as the results have become so variable; however, it has some value to represent the changeability of a fish population within a shade

deficient river reach.

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Site No. 4631 Site name: Downstream of Wolverton Mill Date of survey: 11/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Numbers caught Roach [Rutilus rutilus] 76 230 140 53 Perch [Perca fluviatilis] 71 315 163 25 Dace [Leuciscus leuciscus] 65 183 102 21 Chub [Leuciscus cephalus] 142 557 403 18 Pike [Esox lucius] 350 555 463 4 Minnow [Phoxinus phoxinus] 29 29 29 1 Gudgeon [Gobio gobio] 117 117 117 1 Spined loach [Cobitis taenia] 58 58 58 1 The river at Wolverton Mill was a little over 6.5 meters wide with an average depth of just under a meter. Deep run and glide habitat was predominant with light shading present. The channel substrate was predominantly coarse sand and gravel. The 2016 survey recorded eight species in a population chiefly composed of roach. This was the second survey to be conducted at this location and recorded a sharp decline in density since the initial sampling due to a fall in numbers of dace, roach and perch captured. Although the population estimate of shoaling species is reduced, chub density has increased slightly and the standing crop estimate for this species has increased by almost three times. The 2016 survey found that the population was mainly composed of large individuals, although a handful of smaller samples were also captured and the largest of the fish captured, pictured later in this report, weighed almost six

pounds (Image 5). This area currently offers some excellent angling potential for the species. Chub are omnivorous and will predate upon smaller fish and so the presence of this population of larger individuals (averaging over 40cm) may be responsible for the reduced dace population seen in 2016. Similar interaction between these two species has been observed on the River Ivel at Henlow

when increases in chub populations saw corresponding dips in numbers of dace resident.

www.aterforum.co.uk/index.php/reports-ea-bc/item/187-river-

ivel-survey-report-2016

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Site No. 4635 Site name: Manor Farm Cosgrove Date of survey: 13/10/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Numbers caught Roach [Rutilus rutilus] 60 214 152 68 Dace [Leuciscus leuciscus] 48 231 140 54 Chub [Leuciscus cephalus] 142 517 388 30 Barbel [Barbus barbus] 176 764 435 14 Gudgeon [Gobio gobio] 100 141 126 13 Perch [Perca fluviatilis] 68 311 175 13 Bleak [Alburnus alburnus] 110 153 127 11 Pike [Esox lucius] 128 688 300 8 Bullhead [Cottus gobio] 50 61 56 2 Brown / sea trout [Salmo trutta] 248 248 248 1 Common bream [Abramis brama] 100 100 100 1 Roach x chub hybrid 297 307 302 2 The survey site at Manor Farm has a mix of riffle (No=2) and pool (No=4) habitat and offers a greater range of habitat and flow variation than observed at some locations sampled on the upper river. The channels substrate was predominantly coarse sand and gravel and shading was light. The 2016 survey found a total of eleven species and one hybrid with roach dominant numerically. In terms of population estimate (>99mm) roach and dace both contribute 29% to the density with chub ranked third at 14%. This site is also marked the first capture of barbel during this cycle with the species composing 6% of the density estimate thanks to a catch of 14 individuals to specimen size. Chub and barbel standing crop estimates have both increased and this catch comfortably recorded the highest standing crop estimate to be made at this location. A photograph of one of the barbel captured is on the front of this report. (Image 1) Also of interest were specimen chub and the capture of two large hybrids, which appeared to be a cross between chub and roach. (Image 6)

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Site No. 4637 Site name: Mill Farm Gayhurst Date of survey: 01/11/2016 Species present (All lengths) Minimum Maximum Mean Species Length Length Length Numbers caught Dace [Leuciscus leuciscus] 41 236 154 67 Roach [Rutilus rutilus] 74 193 141 29 Pike [Esox lucius] 157 631 294 14 Gudgeon [Gobio gobio] 96 141 125 9 Chub [Leuciscus cephalus] 178 496 370 7 Perch [Perca fluviatilis] 69 263 156 6 Bleak [Alburnus alburnus] 103 116 110 2 Bullhead [Cottus gobio] 54 54 54 2 Minnow [Phoxinus phoxinus] 32 41 37 2 The 2016 survey at Mill Farm recorded deep glide habitat prevalent with a substrate principally composed of coarse sand and gravel. Riparian shading was light with cover provided by tree roots, branches and logs, submerged vegetation and undercut banks. The survey found dace dominant by density and pike primary by standing crop representing 50% and 38% of these population estimates respectively. The current density estimate appears higher than the previous 2013 result however; these surveys are not directly comparable as the single catch methodology used in 2013 means that this result was only a minimum estimate of stocks present. In terms of density, the 2016 result is more comparable to the 2011 result and, although below the long-term average is much improved over population estimates derived from data collected between 2002 and 2005. The decline in population density at this site appears to have been predominantly driven by a reduction in numbers of silver fish species (roach, bleak, gudgeon

and dace) with the most significant loss occurring between 1988 and 2001. This site will be discussed further later in this report.

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Species distribution at site level 2016 Figures 3 & 4 (below) show population density and standing crop estimates for key fish species >99mm in length at site level. Species distribution shows that brown trout are, perhaps unsurprisingly, generally restricted to sites the upper river where habitat and flow suits this sensitive species’ needs. This species population has increased since 2013 with a current density estimate that is one of the highest recorded from the Upper Ouse and exceeds the long term mean at site level in all instances. Other rheophillic species such as dace, chub and gudgeon are present in the upper river and more generalist species such as roach and perch also make an important contribution to the overall population. The lowest density and standing crop estimates were recorded through the middle reaches of the river length with Thornborough Mill, Mill Farm and Passenham sites all giving particularly disappointing results in 2016. At Passenham this poor catch is easily explained, the site does not possess any form of riparian tree cover, is predominantly uniform glide habitat and the fish population has historically shown ‘boom and bust’ results between survey cycles as fish move into and out of this area with habitation dictated by environmental conditions at the time of survey. Much improved habitat is available nearby, particularly upstream, and it is likely that the majority of fish reside in this area for the much of the time. This considerable variation in stock also makes this site problematic to use in long-term analysis as the capture of large aggregations, or indeed the absence of fish, at this location can significantly influence the mean population estimate of this river length as a whole. The final three sites between Wolverton and Mill Farm Gayhurst saw density and standing crop estimates improve once again and this is likely to be a result of the improved habitat present at these locations. The complex riffle pool features at Cosgrove show the importance of morphological diversity to both species composition and population density with this site producing the surveys largest catch of chub, the only representation by barbel and the second largest catch of roach and dace.

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Comparison of population estimates derived from 2013 and 2016 surveys conducted downstream of Buckingham shows that, although both density and standing crop estimates derived from the 2016 survey is lower than in 2013, the pattern of stock distribution is remarkably similar (the result at Passenham being a major exception). Figure 6 also shows that although standing crop estimates have fallen at Mill farm and Passenham, improvements at Wolverton Mill and Cosgrove means that the mean standing crop estimate is remarkably close to the previous survey result.

Habitat Habitat availability and typology is likely to be a major factor influencing a population at site level; those sites with a higher quality of habitat, particularly those possessing cover, a diversity of flow types and varied channel form have generally retained a higher (and in some cases an increased) fish population. Species composition is also closely linked to suitability of habitat at site level with riffle and pool sites such as Manor Farm offering larger catches of rheophillic (flow loving) species such as dace, chub and barbel. Unfortunately, riffle / pool & depth data supplied by the sampling team is incomplete and so it is hard to draw any more conclusions on this. Collection of detailed habitat parameters at site level is an area of data acquisition that requires further effort and improvement as robust habitat data will allow a more detailed analysis of stock at site level.

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The survey at Thornborough Mill threw up an unusual result in 2016 in that the cover present was reported as 70%, a figure that seems unusually high when compared to the “sparse” descriptor previously used in 2013 and yet despite the high aggregate cover present at this location, the catch was actually very poor. Cover is generally thought of as an important habitat type that most fish species of many life stages will utilise. Roach and barbel have a close affinity with overhanging structure and all anglers know that chub will frequently be found around overhanging trees, weed rafts, bridges and boats. The aggregate percentage of cover present can be seen to increase at the lower three survey sites and whilst the percentage of cover at Buckingham is low, this is likely mitigated by shading from riparian trees. The loss of a tree or bushes from a survey site can make a significant impact on fish stocks present, and the collection of habitat data in recent survey cycles, although not perfect, is much improved over historic surveys when few notes were ever collected at the time of sampling. This means that with the exception of scant photographic evidence it is hard to determine how a site has changed over time in terms of habitat present. An example of the prevalence of shoaling fish around areas of cover can be seen in the following video on the Environment Agencies YouTube page. This footage was attained by local fisheries staff using an ARIS acoustic camera on the River Delph. https://youtu.be/Tx5nN24UkyM Survey notes collated during 2016 indicate that all but one site possessed a slight turbidity at the time of sampling and conversation with fisheries staff tells that this was due to heavy rain in the catchment and increased river flow prior to the surveys commencing. These high flows are a potential factor for the reduced number of roach captured in 2016, the distribution of this generalist species potentially changing to sheltered areas when faced with increased flows. Habitat at site level is given below as Table 4.

Table 4 Habitat assesment sheet for the River Gt Ouse between Buckingham & Newport Pagnell Key = A (Absent) S (Scarce 0-5%) C (Common 5-20%) F (Frequent 20-50%) D (Dominant >50%) NC = Not collected.

Channel Survey conditions Flow Features Site Name Turbulent Run glide Max pool depth Width Depth Flow Turbidity Shade Turbulent deep Run glide deep Slack deep Slack Shallow Riffles (No) Pools (No) shallow shallow (M)

Brackley 4.38 0.36 Normal Slight Moderate A S F D A C 2 3 0.86

Westbury 5.1 0.43 Normal Clear Moderate A A C D S C 1 2 1.25

Buckingham NC NC Normal Slight Heavy A A D F S C 0 0 -

Water Stratford 4.27 0.51 Normal Slight Light A S D F S A 1 2 1.25

Thornborough Mill 10.7 0.92 Normal Slight Light/Moderate A A D C S S 0 0 -

Mill Farm D/s 8.1 0.73 Normal Slight Light A A D C S A 0 1 1.14

Passenham 11.1 1.2 Normal Slight None A A D S S A 0 3 2.4

D/s Wolverton Mill 6.7 0.94 Normal Slight Light A C D S C S NC NC NC

Manor Farm NC NC Normal Slight Light A A D C S S 2 4 NC

Mill Farm Gayhurst NC NC Low Slight Light A A D F A C NC NC NC

Substrate (%) Sources of cover (%) Invasive species Site Name Gravel / coarse Submerged Boulders and Tree root Branches and Other submerged Overhang Artifical Boulder Cobbles Fine sand / silt Clay Undercut banks Species name sand vegetation cobbles systems logs cover within 0.5m

Brackley S A S D C A 0 2 2 3 0 0 5 Signal crayfish

Westbury A A A D C A 10 0 3 5 1 0 0 Signal crayfish

Water Stratford A A S D S A 40 1 1 5 0 0 1 Signal crayfish

Buckingham S A A D F A 0 2 1 2 0 0 15 Signal crayfish

Thornborough Mill A A A D C A 25 0 5 22 0 0 20 Signal crayfish

Mill Farm D/s A A A D C A 5 1 1 0 0 20 0 sIgnal crayfish

Passenham A A C D S A 15 0 2 1 5 0 2 Signal crayfish

D/s Wolverton Mill A A A D C S 10 0 2 3 0 15 1 Signal crayfish

Manor Farm A A A D F A 10 0 2 4 20 0 5 Signal crayfish

Mill Farm Gayhurst A A A D C A 30 0 5 5 10 0 10 Signal crayfish

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Barbel: Mill Farm Gayhurst & Manor Farm Mill Farm Gayhurst, known to anglers as Adams Mill, will always be associated with barbel due to a small population of fish that became resident, grew to a high average size and culminated in the capture of more than one British record. The 2016 survey did not find barbel present at Gayhurst and this will be a disappointment to both the angling community and the EA fisheries staff who have spent considerable effort to assist the species with gravel jetting, habitat improvement works and an ongoing, long-term stocking programme. This report is intended merely as a summary of fish caught in the 2016 survey cycle; however, the popularity of barbel and their importance to the Great Ouse fishery means it is worth discussing the status of this species further. Long-term standing crop and density estimates for barbel at Mill Farm and Manor Farm is given as Figures 7 and 8 overleaf. At Mill Farm standing crop can be observed slowly increasing between 2001 and 2005 whilst the density estimate initially drops a little and then remains comparable, suggesting a (smaller) population of increasingly large fish becomes established. Surveys at Mill Farm ceased during the warm drought summer of 2006 at the request of the controlling angling club (in agreement with the EA) due to the apprehension that sampling may cause undue additional stress on this population of elderly fish. Surveys resumed in 2011 due to concerns about the state of the barbel fishery and routine monitoring was later reinstated on a 3-year rolling programme. The cessation of routine surveys means that the period of decline was not captured within the dataset, but it may still be possible to surmise what happened to this fish population. Scale reading samples collected during the 2005 survey found that the barbel stock at Mill Farm was composed entirely of elderly individuals, the National Fisheries Laboratory concluding “All of the fish recorded were over 15 years old, however these ages represent an approximate and minimum estimate as each scale revealed multiple annuli close to the scale margin making accurate ageing extremely difficult. It is therefore likely the barbel were older than their scale features suggested”. When this site was revisited in 2011 the ‘original’ population, last recorded in 2005, would have needed to be exceeding twenty years old to be recaptured and if these fish had not been recruiting successfully then population loss due to old age and predation was inevitable. The single barbel caught in 2011 was a younger individual of six years old and the 2013 survey also found a small number of barbel present, with four larger fish (between 594mm and 737mm) and two juvenile samples. The ongoing stocking programme has meant it is difficult to distinguish between stocked fish and naturally recruited fish unless scale reading can observe early patterns of growth suggesting a farmed origin. Despite the absence of barbel at Mill Farm in the 2016 survey there have been reports of captures by anglers and it is important to note that the recent survey excluded an area of riparian tree growth at the lower extent of the site. This area was a known barbel (and chub) holding area and the loss of this habitat from the survey length may have led to the omission of some fish, the catch at Manor Farm demonstrating how localised distribution can be with all 14 barbel caught in one comparatively small pool feature. The results of the Manor Farm survey will be particularly important to understand and investigate further as although based on a small number of surveys and fish captured the limited dataset does tentatively suggest an increasing barbel density at this location. The species has not been introduced in this vicinity since 2003 (at Haversham) and the aged subsample of fish caught in 2016 were found to be between 3 and 7 years old. Therefore, these aged fish could not have been stocked individuals. It will be important for fisheries staff to carry out a larger scale investigation of the river at this location to understand what makes this site able to support a recruiting population. This investigation should examine habitat present, hydro-morphological diversity, the availability and composition of spawning gravels and both sediment input & sediment loading of gravels. A large-scale electric fishing survey should be conducted at Mill Farm to assess the barbel population remaining and at Manor Farm to find whether the 2016 catch represents a small aggregated pocket of fish, or if the species is more widespread in this river length. Concerns about the stability of the Great Ouse barbel population has led to the EA funding two PhD students (2009- 2013 Dr Karen Twine- Hull International Fisheries Institute, and 2012-2017 Tea Basic – Bournemouth University) to examine the barbel fishery in detail. The most recent of these projects (Basic) has examined interaction of barbel with other fish species, investigated the relationship between stocked barbel and the ‘resident’ population and has identified bottlenecks to population growth. The impacts of signal crayfish and sediment, long suspected as significant pressures on the Great Ouse, are also detailed. The findings of these phD’s have greatly increased our understanding of this species within the river and the results will be made available in 2017 with outputs used to assess feasible measures, form working partnerships and drive the action required to improve population of this species. This report will be updated with key outputs from these projects when available.

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Roach With the exception of Cosgrove, many sites downstream of Buckingham have shown reduced roach catches when compared to that found in 2013 and this is unusual as a decreased population is in stark contrast to the much improved silver fish stocks and excellent catches reported by both pleasure and match-anglers further downstream between Newport Pagnell and Bedford. A site which generally produced a catch of several hundred roach was situated on ‘Toombs Meadow’ at Stoney Stratford but unfortunately this site was discontinued following the 2013 survey as the combination of deep margins and riparian tree growth extending into the channel meant that the section could no longer be surveyed safely or efficiently. Angling reports from the Milton Keynes Angling Association www.mkaa.co.uk tell of good catches of perch and some good, but occasionally localised nets of roach and other silver fish around Stoney Stratford, with location of fish holding habitat and ‘hot pegs’ important to success. The 2016 survey found roach to a maximum age of 16 years old and displayed slow growth at 84% of standard suggesting competition is limiting this species success, this may be from fellow roach & other dominant fish species such as chub or signal crayfish.

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Chub The dataset for chub shows some interesting trends (Figures 9 and 10). In the 20-year period that this dataset covers the site at Westbury gained a chub population, which at first was composed of smaller fish but latterly contained larger individuals with a stable standing crop estimate. Buckingham shows a declining chub population, Thornborough mill has had sporadic low-density representation throughout this period, whilst Mill Farm and Mill Farm Gayhurst sites both show a declining standing crop with declining density also observed at Mill Farm Gayhurst. The 2016 survey cycle at Mill Farm Gayhurst recorded seven individuals, which is less than half the long-term average recorded at this site. The larger dataset actually indicates that the density estimate for this species had increased between 2001 and 2011 but fell over the last two cycles. There has been little representation from smaller fish and younger year-classes at this site and of the 211 chub recorded; only 28 were below 20cm in length. If recruitment is also an issue for chub then work to address degraded habitat and spawning substrate for barbel will also have a positive effect for this species as chub also predominantly utilise gravel as a spawning media with eggs deposited onto riffle areas and adhering to the bed substrate. It is interesting to note that the chub population at Manor Farm Cosgrove has remained comparable over the last three survey cycles with an increasing standing crop estimate and a population composed of individuals between 4 and 17 years old. Overall, the 2016 survey found that chub captured exhibited average growth at 103% of standard and were aged to a maximum of 18 years old. Note that the large standing crop and density estimates at Mill Farm Gayhurst in 1997 are due to a very poor catch depletion with wide confidence limits and as such, population estimates from this survey may be an overestimation and should be viewed with some caution. The absence of chub at Mill Farm (Beachampton) in 2016 was only the second time that chub had not been found at this location since surveys began in 1988 (the previous being in 1991) but this recent instance was not just a poor result for chub, but a disappointing catch of all species.

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Match Catch Database Fish catches by rod and line are a valuable source of information about fishery performance and can be a sound indicator of the status of the exploited stock. The match catch database allows the storage of match results in a way that permits easy analysis of angler catches over time and is a way for anglers to support their fishery and have their say on the quality of sport they are experiencing. The data provided by anglers not only underpins and validates the survey data but in some cases also adds to it by including details of species which have not been caught in surveys. By collecting & providing the EA with match catch data an angling club can also know that if it has a concern about the sport experienced at its fishery, there will be a record of fishery performance against which this may be compared. An example of the usefulness of match catch can be summarised simply by the poor representation by Common Bream in the 2016 survey cycle (just one individual at Manor Farm Cosgrove). The shoaling and migratory nature of this species means that it is easy to miss during routine, fixed point sampling, however angling reports from Toombs Meadow at Old Stratford shows that common bream (to a large average size) are present in this section of river with individuals to over 6lb caught in bags of multiple fish. Output from the match-catch database is given below for the Great Ouse between Newport Pagnell and Bedford and is derived from data that has been kindly provided by Olney and Clifton Fishing Association. http://www.olneyfishing.co.uk This simple output shows a breakdown of match catches between January 2005 and January 2017 and shows that the average weight caught per angler and average weight per hour caught are a little down on 2015, but overall, catches have increased significantly over the past six years and these combined results all attain and ‘A` rated classification. This data also shows that the increased angler success is also translating into fewer dry nets with above an average number of competitors weighing in over the past three years. More detailed analysis of this dataset is possible and this will be included in the 2017 Newport Pagnell to Bedford Survey Report. Table 5: Match weights (lb/oz) on the Great Ouse – Newport Pagnell to Bedford.

 If clubs fishing the upper Great Ouse wish to provide such data for analysis and inclusion in subsequent reports then this is encouraged and will be welcomed.  A blank match return form & instructions for completion are included at the rear of this report.

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Image 3: Brown Trout from the Upper river.

Image 4: A quality roach caught at Buckingham.

Image 5: A large chub of almost 6lb from below Wolverton Mill.

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Image 6: A large chub / roach hybrid captured at Manor Farm Cosgrove.

Non-native species Signal crayfish are widespread throughout the River Great Ouse and the detrimental effect of this species on a rivers ecology is well known. This may be through competition for food, direct predation of fish eggs and fry and by mobilisation of sediment by foraging and causing bank collapses when burrowing. It is possible that the slow growth rates exhibited by roach and dace are at least partly due to increased competition from this species. Chub, which are quite capable of eating even moderately sized adult crayfish are faring better and showing average growth. Perch also prey on the younger life stages of crayfish and although growth analysis was not conducted on this species, they were present to a large size. Another non-native species noted was the plant Himalayan Balsam Impatiens glandulifera. When established this plant can quickly dominate and shades out native species completely changing the appearance of riverbanks with its large attractive flowers. When the shallow rooted plant dies back during the winter months it leaves riverbanks bare which may then be susceptible to increased erosion. When excess sediment enters a river channel from sources such as bank erosion, cattle poaching and crayfish activity, the increased fine sediment load may infiltrate or smother the important gravel substrate. Overlaying sediment may stop fish from using these areas, whilst sediment accumulation amongst the gravel will reduce through flow of oxygenated water to eggs, preventing development. Reducing sediment input and infiltration and keeping key gravel areas clean can therefore help contribute to increased productivity of the river and help improve fish populations in the local area. The invasive shrimp Dikerogammarus haemobaphes has been found in the Rivers Tove and Ouzel, and is thought to have colonised these via the Grand Union Canal over spillways. The shrimp has subsequently migrated down these tributaries and into the Great Ouse. In an attempt to prevent upstream migration of this invasive shrimp a baffle was constructed on the crest of Wolverton Weir, a structure that would otherwise have been easily surmountable for this species. It is very important that the spread of this species be controlled as it can have significant impacts on the native invertebrate ecology. (Image 7 below). Anglers can help stop the spread of invasive non-native species by using the check, clean & dry protocol, details of which are included at the back of this report or by visiting: http://www.nonnativespecies.org/checkcleandry/biosecurity-for-anglers.cfm Owners of smartphones could also help track the location of non-native species by using the Plant tracker App available for both Android and iPhone.

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Image 7: Wolverton Weir with shrimp baffle visible at the crest.

Habitat projects The following habitat enhancement works have been conducted on the Great Ouse since the last report written in 2013: 1. Riffle enhancements at Adams Mill, Sherington & Newport Pagnell. This work saw the introduction of fresh gravels into the river in an attempt to improve the spawning media present for species such as barbel, chub and dace. (Image 8) 2. A weir removal project in Buckingham. This project saw the removal of Chandos Weir in Buckingham. The weir was failing, having been undercut by floodwaters in 2016 and the removal of this structure protected public safety and enabled fish passage at this location. A riffle was subsequently created following removal to manage water levels upstream. (Images 9 and 10 overleaf) 3. A restored backwater channel at Stony Stratford. This project had multiple outcomes, providing enhanced habitat for the rivers wider ecology, off river habitat providing shelter for juvenile fish of all species and provided fish passage around the Stoney Stratford Weir structure. A fish survey conducted in June 2016 found that fish were already utilising the channel and the catch that included a fish population composed of 11 species including over 100 dace. 4. Riffle enhancement, bank erosion repairs, tree planting & flow deflectors at Adams Mill. Further habitat enhancements at Adams Mill including riffle enhancement work to improve spawning and flow deflectors to keep riffles clean. Bank repair were conducted using woody material to stop collapse and introduction of sediment into the watercourse.

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Image 8: Fresh spawning gravels introduced at Adams Mill.

Image 9: Chandos Weir Buckingham: Before removal.

Image 10: Chandos Weir Buckingham: After removal.

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Summary conclusions • The mean density estimate has fallen since the previous survey in 2013 due to a reduction in roach and dace at some sites. This is in contrast to the river reaches below Newport Pagnell where anglers have been experiencing good sport due to a resurgent silver fish population. • The standing crop estimate for this river reach remains comparable to the 2013 result due to increased numbers & size of chub and barbel captured. • Specimen fish of several species are a realistic target; particularly chub and perch, with areas of increased habitat complexity most likely to be most productive. Large barbel remain present to be caught if successfully located. • The absence of barbel at Adams Mill was particularly disappointing; however, the barbel population at Manor Farm offers some encouragement being composed of several year classes and the result of natural recruitment. Further investigation will be required to assess the size and extent of this population and understand the reason for its apparent success. • The findings of the Barbel phD’s have greatly increased our understanding of this species and the pressures limiting its success within the Great Ouse. The results of the most recent phD will be made public in early 2017 and its findings will be used to shape the action required to improve sustainable population of this species

Justin Mould Analysis and Reporting (Fish) 17.03.2017

Next survey due: Spring/summer 2019

Image 11: A specimen chub caught by this report’s author near Wolverton Mill in March 2017.

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Additional information

If any angling matches are held throughout this river length then angling clubs are encouraged to provide match results to feed into the Environment Agencies Match Catch Database which analyses angler catches to assess fishery performance. The output of this database can also be used as supporting evidence to assist analysis of routine survey results. Match return cards and more information on the Match Catch Database can be obtained from FBG Officer Chris Middleton. [email protected] Anglers can also keep up to date with all things fisheries & enforcement related by following the local Angling Trust Eastern Region and Lower Ouse & Fenland Fisheries Consultative Association (LOFFCA) Facebook pages.

https://www.facebook.com/AnglingTrustEastEnglandRegion/ https://www.facebook.com/LOFFCA/

For information regarding the Fisheries Improvement Programme, please follow the link below: https://www.gov.uk/government/news/fisheries-projects-needed-to-improve-the-environment

For information regarding the Angling Improvement Fund (AIF) administered by the Angling Trust, please follow the link below: http://www.anglingtrust.net/landing.asp?section=1094§ionTitle=Angling+Improvement+Fund

Before you go fishing don’t forget:

Environment Agency rod licence and permission from the fishery owner;

fisheries byelaws;

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 0800 80 70 60 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 0800 555 111 or https://crimestoppers-uk.org/give-information/give-information-online/.

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Environment Agency Match Record (Please complete after each match and return by email to [email protected])

Name of angling club: Date of match:

River: Venue:

Section / peg fished: Number of competitors:

Match start time: Match duration (hrs):

Number of anglers weighing-in:

Total weight caught: (lbs/oz) or (g) delete as appropriate

Winning weight: (lbs/oz) or (g) delete as appropriate

2nd weight: (lbs/oz) or (g) delete as appropriate

3rd weight: (lbs/oz) or (g) delete as appropriate

Species Caught In: Greatest number:

Second greatest number:

Other species present:

River Conditions:

Level Colour Condition River Temp

Low Clear Falling Cold

Normal Coloured Steady Normal

High Green Rising Warm

Weather Conditions:

Brightness Wind Rain

Dull Still Dry

Changeable Light Drizzle

Bright Moderate Light

Strong Heavy

Hail

Sleet

Snow

Any other comments:

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Appendix: Figures 11- 14: Growth rate graphs for key species

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Figure 15: Comparison of population density