Fish population survey report The Lower Great Ouse August 2016 This report provides a summary of results from recent fish population surveys on the River Great Ouse between Brampton and Earith. The surveys were carried out to assess the health of the river and enable successful management of our principal fisheries. Summary Image 1: The River Great Ouse at Portholme Meadow, Huntingdon. Five sites on the River Great Ouse were surveyed by Seine netting between the 26 th of September and the 1 st of October 2016. A total of 2275 fish of fifteen species including one non-native species were recorded. Roach were the most numerous species captured (1815 Individuals) followed by perch. The average density and standing crop estimates derived from the five sites surveyed equate to 8.12 fish per 100m² and 277.5 grams per 100m² respectively.
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 or there has been a review of policy during the monitoring period. Survey locations Map 1: Survey sites sampled on the Lower Great Ouse Table 1: Site Name Site ID Date Length (M) Width (M) Area (M2) NGR Catch Method Portholme Meadow 4758 29/09/2016 70 35 2450 TL2315770539 Seine netting Houghton 4764 27/09/2016 65 30 1950 TL2850071500 Seine netting U/s Dolphin Meadow 4768 28/09/2016 70 24 1680 TL2984671527 Seine netting Holywell 4781 26/09/2016 60 35 2100 TL3447470525 Seine netting Pike & Eel 4783 01/10/2016 50 40 2000 TL3615871423 Seine netting 2 of 23
Survey methodology Five sites on the River Great Ouse were sampled by Seine netting. Seine netting is our primary survey technique utilised on lowland watercourses where depth and width of the river channel precludes the use of electric fishing. The netting process starts by staff positioning stop nets across the river channel to isolate the survey area and prevent fish from migrating in and out of the site. A 100-meter long seine net is then laid by boat to encircle the entire survey area. The Seine net is constructed from 10mm knotless mesh, which is soft to help minimize fish damage. Floats are attached along the top edge and a lead line along the bottom to ensure that the net hangs vertically within the water column. This catching net is hauled in by hand and fish are removed and retained in floating keep- cages. The netting operation is repeated until a 50% reduction in the total number of fish caught in the first catch has been achieved. The captured fish are measured to the nearest millimetre (to the fork of the tail) and scales are taken from a sub sample of these fish for age, growth and other statistical analyses, which occurs at the National Fish Laboratory in Brampton. Density and standing crop results are derived using Carle and Strub depletion methodology and reported utilising fish greater than 99mm in length as electric fishing methodology has been shown to lose capture efficiency on fish below this length. Numbers and population estimates of juvenile fish and small species such as minnow and bullhead should therefore be viewed as a minimum estimate only. Results Five sites on the River Great Ouse were surveyed by Seine netting between the 26 th of September and the 1 st of October 2016. A total of 2275 fish of fifteen species including one non-native species were recorded. Roach were the most numerous species captured (1815 Individuals) followed by perch. The average density and standing crop estimates derived from the five sites surveyed equate to 8.12 fish per 100m² and 277.5 grams per 100m² respectively. Table 2: Total number and largest (mm) fish captured for key species during the 2016 survey. Site Roach Perch Dace Bleak Number Largest Number Largest Number Largest Number Largest Portholme Meadow 460 235 35 245 6 162 43 120 Houghton 257 166 24 110 16 168 - - Upstream Dolphin Meadow 716 135 83 233 23 167 6 104 Holywell 356 166 7 117 55 160 7 120 Pike and Eel 26 136 - - - - - - 3 of 23
Table 2: Results table for density (>99mm) >99mm Survey Site Reference Number Species Portholme Houghton US Dolphin Meadow Holywell Pike & Eel Mean 29/09/2016 +/-CI 27/09/2016 +/-CI 28/09/2016 +/-CI 26/09/2016 +/-CI 01/10/2016 +/-CI Roach [Rutilus rutilus] 11.18 0.85 4.97 0.08 9.82 0 3.10 0.02 0.40 0 5.89 Dace [Leuciscus leuciscus] 0.08 0 0.62 0.03 1.13 0.06 2.33 0.37 0 0.83 Perch [Perca fluviatilis] 1.22 0.64 0.21 0.14 1.43 0.36 0.05 0 0 0.58 Bleak [Alburnus alburnus] 1.18 0.42 0 0.18 0 0.33 0.04 0 0.34 Gudgeon [Gobio gobio] 0.69 0.63 0.21 0.06 0 0 0 0.18 Pike [Esox lucius] 0.29 0.03 0.21 0.00 0.12 0.12 0.14 0.07 0.10 0 0.17 Rudd [Scardinius erythrophthalmus] 0.16 0 0 0.06 0 0 0 0.04 Chub [Leuciscus cephalus] 0.16 0 0 0 0 0 0.03 Silver bream [Abramis bjoerkna] 0.04 0 0 0.06 0 0 0 0 0.02 Brook lamprey > ammocoete [Lampetra planeri] 0 0 0.06 0 0 0 0.01 Common bream [Abramis brama] 0 0 0.06 0 0 0 0.01 Ruffe [Gymnocephalus cernuus] 0.04 0 0 0 0 0 0 0.01 Total 15.06 1.30 6.21 0.18 12.92 0.38 5.95 0.38 0.50 0 8.13 Table 2a: Results table for standing crop (>99mm) >99mm Survey Site Reference Number Species Portholme Houghton US Dolphin Meadow Holywell Pike & Eel Mean 29/09/2016 +/-CI 27/09/2016 +/-CI 28/09/2016 +/-CI 26/09/2016 +/-CI 01/10/2016 +/-CI Roach [Rutilus rutilus] 351.6 26.6 132.4 2.0 214.8 0 73.8 0.6 9.9 0 156.5 Pike [Esox lucius] 77.2 9.3 143.9 0 5.7 5.5 52.7 25.7 11.5 0 58.2 Perch [Perca fluviatilis] 66.2 34.4 3.7 2.6 67.7 17.0 1.2 0 0 27.8 Dace [Leuciscus leuciscus] 2.7 0 18.0 0.9 31.7 1.6 66.5 10.7 0 23.8 Bleak [Alburnus alburnus] 13.6 4.8 0 1.8 0 4.6 0.6 0 4.0 Gudgeon [Gobio gobio] 10.9 9.9 3.7 1.1 0 0 0 2.9 Rudd [Scardinius erythrophthalmus] 7.1 0 0 1.4 0 0 0 1.7 Chub [Leuciscus cephalus] 8.3 0 0 0 0 0 1.7 Ruffe [Gymnocephalus cernuus] 2.2 0 0 0 0 0 0 0.4 Silver bream [Abramis bjoerkna] 0.9 0 0 1.1 0 0 0 0 0.4 Common bream [Abramis brama] 0 0 0.8 0 0 0 0.2 Brook lamprey > ammocoete [Lampetra planeri] 0 0 0.3 0 0 0 0.1 Total 540.7 45.8 301.7 3.6 325.2 18.0 198.8 27.8 21.5 0 277.6 Table 3: Results table for density (All fish) All Fish Survey Site Reference Number Species Portholme Houghton US Dolphin Meadow Holywell Pike & Eel Mean 29/09/2016 +/-CI 27/09/2016 +/-CI 28/09/2016 +/-CI 26/09/2016 +/-CI 01/10/2016 +/-CI Roach [Rutilus rutilus] 20.08 0.80 13.33 0.23 42.62 0.03 17 0.11 1.3 0.09 18.87 Perch [Perca fluviatilis] 2 1.24 1.54 0.80 5.24 0.46 0.33 0 0 1.82 Dace [Leuciscus leuciscus] 0.25 0.04 0.82 0.03 1.37 0.05 3.10 0.78 0 1.11 Silver bream [Abramis bjoerkna] 1.47 0.13 0 0.95 0 0.57 0.03 0 0.60 Bleak [Alburnus alburnus] 1.92 0.33 0 0.36 0 0.33 0.04 0 0.52 Gudgeon [Gobio gobio] 1.22 0.76 0.21 0.06 0 0 0 0.29 Bitterling [Rhodeus sericeus] 0 0 0 1.33 0.18 0.05 0 0.28 Pike [Esox lucius] 0.29 0.03 0.21 0 0.12 0.12 0.14 0.07 0.1 0 0.17 Rudd [Scardinius erythrophthalmus] 0.16 0 0 0.06 0 0 0 0.04 Common bream [Abramis brama] 0 0 0.18 0 0 0 0.04 Chub [Leuciscus cephalus] 0.16 0 0 0 0 0 0.03 Ruffe [Gymnocephalus cernuus] 0.08 0 0.05 0 0 0 0 0.03 Spined loach [Cobitis taenia] 0 0 0.12 0 0 0 0.02 Brook lamprey > ammocoete [Lampetra planeri] 0 0 0.06 0 0 0 0.01 Bullhead [Cottus gobio] 0 0 0.06 0 0 0 0.01 Total 27.63 1.70 16.15 0.83 51.13 0.48 22.81 0.81 1.45 0.09 23.84 Table 3a: Results table for standing crop All Fish Survey Site Reference Number Species Portholme Houghton US Dolphin Meadow Holywell Pike & Eel Mean 29/09/2016 +/-CI 27/09/2016 +/-CI 28/09/2016 +/-CI 26/09/2016 +/-CI 01/10/2016 +/-CI Roach [Rutilus rutilus] 422.84 16.80 218.94 3.83 466.20 0.29 202.02 1.31 17.77 1.20 265.56 Pike [Esox lucius] 77.16 9.26 143.94 0 5.66 5.55 52.74 25.68 11.51 0 58.20 Perch [Perca fluviatilis] 78.33 48.53 12.85 6.67 91.94 8.03 3.03 0 0 37.23 Dace [Leuciscus leuciscus] 4.35 0.67 20.14 0.65 33.92 1.31 77.69 19.46 0 27.22 Bleak [Alburnus alburnus] 19.27 3.34 0 3.18 0 4.63 0.56 0 5.42 Silver bream [Abramis bjoerkna] 9.23 0.83 0 7.38 0 4.00 0.20 0 4.12 Gudgeon [Gobio gobio] 16.62 10.30 3.70 1.11 0 0 0 4.07 Rudd [Scardinius erythrophthalmus] 7.11 0 0 1.36 0 0 0 1.69 Chub [Leuciscus cephalus] 8.33 0 0 0 0 0 1.67 Bitterling [Rhodeus sericeus] 0 0 0 7.30 1.01 0.25 0 1.51 Ruffe [Gymnocephalus cernuus] 2.88 0 0.10 0 0 0 0 0.60 Common bream [Abramis brama] 0 0 1.56 0 0 0 0.31 Brook lamprey > ammocoete [Lampetra planeri] 0 0 0.30 0 0 0 0.06 Bullhead [Cottus gobio] 0 0 0.18 0 0 0 0.04 Spined loach [Cobitis taenia] 0 0 0.12 0 0 0 0.02 Total 646.1 53.3 399.7 7.8 611.8 9.8 351.4 32.3 29.5 1.2 407.7 4 of 23
Density and Standing Crop estimate by species (>99mm) Population estimates derived from the 2016 survey cycle show that roach are dominant by density representing 73% of the population (5.89 Ind./100m 2 ) and the species is also primary by standing crop with 56% of the biomass estimate (156.5 g/100m 2 ). Dace were subdominant by density representing 10% of the density estimate (0.8 Ind./100m 2 ) whilst pike ranked second by standing crop with 21% of derived biomass (58.2 g/100m 2 ). See Figures 1 & 2 below. Common bream were poorly represented in the 2016 survey cycle with just 3 individuals to 100 mm in length captured (at Dolphin Meadow) and therefore do not appear at species level in either standing crop or density estimate, instead being combined in the others category. The whereabouts of bream during this survey cycle is uncertain, but the nomadic and shoaling nature of this species means that populations can be very localised and because of this, hard to sample efficiently with fixed point monitoring. The widespread absence of juvenile bream is unusual and the status of this species may need further clarification. Angler results posted on the website of controlling angling clubs show that some large catches of bream are remain possible when these fish are located. 5 of 23
Density and Species Composition at site level (>99mm) Figures 3 & 4 (below) give population estimates by species at site level and clearly shows the dominance of roach populations in the 2016 survey cycle. The sites at Portholme and Dolphin Meadow produced the highest density estimates whilst Houghton and Holywell gave comparable density estimates, albeit with differing species composition, both roughly half of that observed at Portholme and Dolphin meadow. The final and lowermost Pike and Eel site produced a very limited catch of just 0.5 Ind./100m 2. In terms of standing crop (Figure 4) Portholme Meadow still ranks highest with a population estimate of 540 g/100m 2 which was predominantly comprised of roach with some representation from pike and perch. The standing crop estimate at Dolphin Meadow (325 g/100m 2 ) is comparable to that recorded at Houghton, although in terms of contribution by species Dolphin meadow was predominantly composed of roach (214 g/100m 2 ) and perch (67 g/100m 2 ) whilst standing crop Houghton was primarily pike (143 g/100m 2 ) and roach (132 g/100m 2 ). The highest dace population was noted at Holywell and this may be due to the confluence with the Marley Gap Brook a short distance upstream of the survey area. This small tributary of the Great Ouse has only limited survey coverage but reasonable catches of dace, chub and roach have all been made near St Ives where habitat suits these species requirements. 6 of 23
Density estimate of the Great Ouse 1996 2016 Population estimates derived from successive and comparable survey cycles is given below as Figure 5. This data shows that the current density estimate is below the long-term average (LTA) for this section of river. Historic data shows that between 2003 and 2006 the rivers density estimate was steadily rising, (peaking in 2006) and this was likely brought about by environmental conditions over the years preceding this survey. While the bulk of fish captured in 2006 were small individuals from the 2005 year-class, strong representation was also seen from fish spawned in 2004. The Great Ouse experienced low winter river flows in both of these years, which will have allowed increased survival of young of the year. Good representation was also noted from 2002 and 2003 year-classes and scale reading by the National Fisheries Laboratory found that the fish caught in 2006 also showed the second highest growth rates recorded for this river length. The subsequent 2007 survey recorded very poor catches and this was likely due to a number of reasons. The extensive flooding experienced prior to the survey had the potential to displace fish stocks (particularly younger year classes), disrupt spawning and also meant that the survey was postponed until late in the year, which increased the risk of winter shoaling influencing stock distribution and decreased confidence in the data collected in this cycle. The 2008 result seemed to defy expectations of the wash out suggested by the 2007 data and produced an above average mean density figure, although it was observed that density was much reduced at both Portholme and Dolphin Meadow and unusually high at the Pike and Eel site which may suggest downstream displacement of fish stock had occurred. See figure 5a. Following a second year of summer flooding (in 2008) the 2009 estimate was significantly lowered and less than 400 roach recorded were recorded with only five of these exceeding 99mm in length. The subsequent two surveys saw a return to an increasing density estimate, which exceeded the LTA in 2013. The current population estimate marks a decline below the LTA which is comparable with the 2010 result. Length frequency data from the 2016 survey indicates that populations of smaller individuals remain broadly comparable with that observed in 2013 and the fall in density (and standing crop) between these survey cycles has been caused poor representation by older year classes. (Figure 5b overleaf) This will be discussed later in this report. Standing crop estimate of the Great Ouse 1996 2016 Examination of historic standing crop data shows that the 2016 result is below the LTA for this section of river. It should be noted that the while the outlier standing crop estimate in 2006 did include good catches of roach at both Portholme and Dolphin Meadow it was also boosted by the capture of 40 common bream at Holywell which have not been recorded in similar numbers since. As mentioned previously, the cause in the decline between the 2013 and 2016 survey cycles has been brought about by poor representation from larger fish. 7 of 23
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Site level discussion Site No: 4758 Site name: Portholme Meadow Date of survey: 29/09/2016 Minimum Maximum Mean Numbers Species Length (mm) Length (mm) Length (mm) Caught Roach [Rutilus rutilus] 65 235 104 460 Bleak [Alburnus alburnus] 92 120 101 43 Silver bream [Abramis bjoerkna] 64 110 76 35 Perch [Perca fluviatilis] 64 245 115 35 Gudgeon [Gobio gobio] 72 111 100 23 Pike [Esox lucius] 224 476 301 7 Dace [Leuciscus leuciscus] 91 162 106 6 Chub [Leuciscus cephalus] 120 176 148 4 Rudd [Scardinius erythrophthalmus] 116 145 135 4 Ruffe [Gymnocephalus cernuus] 98 144 121 2 Population Composition by density (>99mm) The 2016 survey at Portholme Meadow recorded ten species with roach dominant by both density and standing crop contributing a 74% and 65% share of these values respectively. The current density estimate of 15 Ind./100m 2 is quite comparable to the long term average for this site (16.7 Ind./100m 2 ). The long-term dataset also shows that roach have frequently been the dominant species at this site. This catch provided the highest standing crop and density estimates recorded on the Great Ouse in the 2016 survey cycle. 9 of 23
Site No: 4764 Site name: Houghton Date of survey: 27/09/2016 Minimum Maximum Mean Numbers Species Length (mm) Length (mm) Length (mm) Caught Roach [Rutilus rutilus] 69 166 101 257 Perch [Perca fluviatilis] 64 110 81 24 Dace [Leuciscus leuciscus] 94 168 121 16 Gudgeon [Gobio gobio] 104 117 111 4 Pike [Esox lucius] 305 546 410 4 Ruffe [Gymnocephalus cernuus] 52 52 52 1 Population Composition by density (>99mm) The 2016 survey at Houghton recorded a limited catch of just six species with roach primary by density. Whilst this is not the smallest catch to be made at this location, the recent density estimate is around half of that recorded in 2013 and is well below the long-term average for this monitoring point. In terms of total catch, more roach were present in 2016 than 2013; however, the average size in 2016 was smaller (by 20mm) than recorded in the previous survey and this led to a large proportion of these fish being discounted from the population estimate. Very little historic data exists for this site to allow comparison & analysis; however that which is available shows roach have been dominant by density over all survey cycles to date with subdominant contribution by dace, bleak and gudgeon. 10 of 23
Site No: 4768 Site name: US Dolphin Meadow Date of survey: 28/09/2016 Minimum Maximum Mean Numbers Species Length (mm) Length (mm) Length (mm) Caught Roach [Rutilus rutilus] 52 135 89 716 Perch [Perca fluviatilis] 63 233 92 83 Dace [Leuciscus leuciscus] 89 167 123 23 Silver bream [Abramis bjoerkna] 52 106 80 16 Bleak [Alburnus alburnus] 90 104 98 6 Common bream [Abramis brama] 76 100 87 3 Pike [Esox lucius] 134 224 179 2 Spined loach [Cobitis taenia] 48 64 56 2 Rudd [Scardinius erythrophthalmus] 114 114 114 1 Bullhead [Cottus gobio] 62 62 62 1 Brook lamprey > ammocoete [Lampetra planeri] 104 104 104 1 Population Composition by density (>99mm) The 2016 survey at Dolphin Meadow found eleven species present with roach dominant by density and representing 76% of the population estimate. Over 700 roach between 52mm and 135mm in length were captured and in terms of fish of all lengths, this constituted the largest catch of the 2016 survey cycle and the fifth largest catch of the species at this location. The sites 2016 density estimate is a more modest 12.9 Ind./100m 2 a result which ranks second highest in the 2016 cycle. This population estimate reflects the low average size of the dominant roach stock in 2016, which meant a large proportion of these fish were not used to derive the population estimate. The current population estimate is almost half of the long-term average for this site, this figure being boosted by excellent catches of roach made in 2005 & 2006. 11 of 23
Site No: 4781 Site name: Holywell Date of survey: 26/09/2016 Minimum Maximum Mean Numbers Species Length (mm) Length (mm) Length (mm) Caught Roach [Rutilus rutilus] 38 166 92 356 Dace [Leuciscus leuciscus] 88 160 122 55 Bitterling [Rhodeus sericeus] 56 99 62 27 Silver bream [Abramis bjoerkna] 70 88 80 12 Bleak [Alburnus alburnus] 100 120 111 7 Perch [Perca fluviatilis] 60 117 82 7 Pike [Esox lucius] 222 467 322 3 Population Composition by density (>99mm) In terms of total catch (all lengths) the 2016 result was above average numerically, but due to the small average size of these fish (only 65 of the 365 roach captured were >99mm in length) the current density estimate is around two thirds of the long term average for this location (8.5 Ind./100m 2 ). The survey team observed a large shoal of around 200 gudgeon, but these were tucked away in a shallow bay and unfortunately were not captured by the seine net meaning that this species was not recorded in the survey. The long-term dataset for this site shows particularly poor survey results in 2007 & 2009 and a very changed species composition in 2010 when dace were heavily dominant. The poor 2007 result is likely to be linked to high flows & summer flooding experienced preceding this survey. These high flows also postponed the survey cycle until November, increasing the risk of winter stock aggregation of influencing the catch further still. 12 of 23
Site No: 4783 Site name: Pike and Eel Date of survey: 01/10/2016 Minimum Maximum Mean Numbers Species Length (mm) Length (mm) Length (mm) Caught Roach [Rutilus rutilus] 61 136 94 26 Pike [Esox lucius] 229 268 249 2 Bitterling [Rhodeus sericeus] 63 63 63 1 The 2016 survey at the Pike and Eel produced a very disappointing catch of just 29 fish with only a third of these fish over 99mm in length. Habitat details collected during sampling indicates that the survey was undertaken during a period of high river clarity and bright sunshine and this combination of factors is likely to have influenced stock distribution, particularly when better habitat is present nearby which fish are more likely to utilise during such conditions. Habitat availability in the lower river and its influence on fish distribution will be discussed later in this report. 13 of 23
Species level discussion Roach are the most numerous species likely to be encountered by anglers on the lower Great Ouse and are therefore an important indicator of fishery performance. Common bream are another key angling species but the shoaling nature of this fish means that they are often encountered infrequently on routine survey. Angler reports suggest that shoals of large bream are present in the lower river and details of catches are provided on the websites of controlling angling clubs. Roach were the dominant species by density representing 73% of the overall population estimate and several hundred individuals were caught at all but one of the sites sampled. As already mentioned previously in this report, the average size of roach caught in 2016 was somewhat small and of the 1815 roach captured only 582 were >99mm in length, a little over thirty percent. A sub sample of these fish were aged using scale samples collected at the time of survey. The results of this work revealed that the maximum age of the roach sampled was 6 years old and these fish were exhibiting a slow growth rate at 84% of standard. This growth rate is lower than observed in previous three survey cycles where the percentage standard growth was around 90% (average growth). Scale reading showed that the large majority of fish captured in 2016 were fish of one and two years old+ and spawned in 2014 & 2015. Examination of historic data (Table 4) shows that the current growth rate is not outside of the range of that which has been observed previously. Historic data also shows that these surveys have also recorded fish from a limited number of year classes. In the 2015 survey of the Great Ouse between Bedford and Brampton roach growth was observed to be slower still at just 78% of standard growth and fish were aged to 8 years old. Table: 4 2003 2004 2005 2006 2007 2008 2009 2010 2013 2016 P.S.G 87 82 89 92 101 86 90 91 90 84 Maximum roach age 8 4 6 7 6 7 3 6 8 6 Data from previous survey cycles also show a pattern in roach distribution in the lower river and it is apparent that Portholme Meadow and Dolphin Meadow have been the most consistent survey sites with the rivers population density generally decreasing at sites further downstream. Table 5 and 5a show the percentage of the total catch of roach (derived from numbers captured) at each survey site over successive survey cycles. When average figures are calculated for roach >99mm it is apparent that Portholme Meadow has, on average, produced 52% of the roach catch (although this varies widely between just 15% and 100% of the catch) Dolphin Meadow ranks second at 26% followed by Holywell 12% and the Pike and Eel site 9%. When data for ALL fish is examined the average figures still indicate that the bulk of fish has been caught at Portholme (43%) followed by Dolphin Meadow (25%) whilst in the lower river the ranking of sites has changed with Pike and Eel third with 18% and Holywell fourth at 15%. See table 4 and 4a (Below). Table 5: >99mm 1992 2003 2004 2005 2006 2007 2008 2009 2010 2013 2016 Average Portholme 41 73 62 15 34 100 45 80 31 45 51 52 Us Dolphin Meadow 19 8 4 72 48 0 8 0 56 37 34 26 Holywell 16 19 27 7 10 0 12 20 1 12 13 12 Pike and Eel 24 0 7 7 8 0 35 0 13 6 2 9 Table 5a: All Fish 1992 2003 2004 2005 2006 2007 2008 2009 2010 2013 2016 Average Portholme 47 45 61 29 32 67 33 56 37 33 30 43 Us Dolphin Meadow 12 23 5 43 47 17 8 2 49 23 46 25 Holywell 12 27 21 7 11 0 18 1 1 37 23 15 Pike and Eel 29 5 13 20 9 17 41 41 12 7 2 18 14 of 23
Examination of site photographs and habitat data collected at the time of survey indicates that complexity of habitat at site level is likely to be responsible for the stock distribution observed. The sites at Portholme and Dolphin Meadow for example are fortunate to retain stands of riparian tree cover, some of which are close to, and indeed within, the routine survey areas overhang the channel and providing a source of woody material and creating good fish-holding habitat. Although the routine site at Holywell provided a relatively modest catch in 2016, a member of EA fisheries staff regularly angled near here during the summer and when targeting where tree cover was present experienced brisk sport and some good catches of both roach and dace. Images 2 to 5 show aerial photographs of the four survey sites and it is apparent that the amount of riparian cover within the sample area diminishes in the downstream sites. The lowermost Pike and Eel site has very scarce cover present within the survey area, however less than 200 meters upstream a marina provides extensive overhead cover, which is more likely to attract and hold fish stocks. It is interesting to see that in 2008 & 2009 there were much-improved catches of roach at the Pike and Eel site and these coincided with particularly poor results at Dolphin Meadow. Catches of this magnitude have not been repeated at the Pike and Eel site in subsequent surveys, which raises the possibility that the fish observed at Pike and Eel in 2008 & 2009 had been displaced from the upstream reach by the extensive summer flooding which occurred in 2007 and again in 2008? The marina would certainly offer an area of refuge from high flows for fish to utilise. 15 of 23
Image 2: Site 4758 Portholme Meadow Image 3: Site 4764 U/S Dolphin Meadow Image 4: Site 4768 Holywell Image 5: Site 4783 Pike and Eel 16 of 23
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 allows 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 worries about the state of its fishery, there will be a record of fishery performance against which these concerns may be compared. If clubs fishing the 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. Conclusions The 2016 survey recorded a fish population with a density and standing crop estimate below the long-term average for this section of river. This has been brought about by poor representation from larger fish in this survey cycle. Growth rates have slowed and generally this would suggest a larger population remains present with no reduction in pressure on food resource, but the whereabouts of larger fish is currently uncertain. Of course, the slow growth rates these fish exhibit means that the average length of 3 year old fish is currently below 99mm (standard growth would be 111mm long) this means that fewer fish are present to count towards the population estimate due to their small average size. Scale reading data also noted that growth rates for roach increase once the species reaches 4 years old suggesting competition is most effecting younger year-classes. It is important to remember that these surveys are only a snapshot of what was in the survey area at the time of the survey and the high river clarity experienced at the time of the survey may have caused fish to move to areas with improved habitat and cover. The lack of any input from match catch data and inability to conduct large-scale hydroacoustic surveys due to the rivers physical characteristics mean that the results of these fixed point monitoring surveys cannot be validated and may be influenced by stock movement in response to environmental conditions. Management Options: The ARIS acoustic camera is an imaging sonar capable of creating detailed underwater images in completed darkness or turbid conditions using high frequency pulses of sound and when mounted on a boat this technology can allow long river lengths to be covered, locating fish stocks present and in some cases also identifying the species. Images 6 & 7 (overleaf) show examples of footage collected by the EA using the ARIS camera and show a large shoal of roach (Image 6) and two large common bream (Image 7) the latter clearly identifiable by the shape of the acoustic shadow behind them. The following footage on the EA YouTube page shows a previous example of footage attained when the ARIS camera was used to find shoaling fish on the Ouse Washes. https://youtu.be/tx5nn24ukym It is suggested that the ARIS camera could be used on the Great Ouse to investigate the utilisation of marinas as offchannel habitat and be used to assess fish populations in the river around Holywell and Pike and Eel to investigate whether increased fish populations are present around areas of riparian cover. It is also suggested that ARIS survey could occur around the Earith area to investigate fish stocks in this locality and on the tidal river where large shoals of fish have been observed recently. This report will be updated with details and results of this survey and images when this survey has been undertaken. Some tree planting has occurred between the Pike and Eel Public House and Brownshill recently with a small number of willow and alder trees introduced. If the ARIS investigation finds elevated fish stocks around the remaining riparian cover on the lower river then it is suggested that a larger scale programme of tree planting is investigated. The reintroduction of riparian cover in key locations, with landowner consent, would likely increase stock distribution but would obviously not be a quick fix. 17 of 23
Image 6: Roach on the River Delph. Image 7: Two large common bream Non-native species Floating Pennywort: In its native range, floating pennywort (Hydrocotyle ranunculoides) occurs in slow-flowing warm and nutrient rich water in Argentina, Brazil, Paraguay and southern states of the USA. It is an invasive weed in North Western Europe and was first naturalised in the UK in 1990 as an introduction from garden ponds. Since then it has become widespread in the south and east of England and is spreading rapidly north and westwards. Floating pennywort is found in and around canals, lakes, rivers, streams, ditches and ponds. It roots along waterbody margins, growing up to a rate of 20cm per day, and spreads out onto the water as dense interwoven mats above and beneath the surface. These dense mats can quickly overwhelm a waterbody and impede water flow. Very large infestations may interfere with navigation, prevent angling access and increase the risk of flooding. Another important consideration is the detrimental effect of floating pennywort on native plant and animal species. The dense growths result in native plants being shaded out and may obstruct native air-breathing insects from reaching the water surface. In addition, the water beneath mats can become deoxygenated resulting in fish mortality and changes to the invertebrate community. On the River Great Ouse, floating pennywort has been identified from Bedford downstream to Hemingford including some minor tributaries of the main river. The infestation was identified in 2015 and initial herbicide work was undertaken to control growth, this was followed by a mechanical removal programme in 2016 with approximately 100 tonnes of floating pennywort removed from the river. Floating pennywort is usually spread by vegetative propagation, with very small fragments of the plant able to form new colonies. Landowners are responsible for undertaking swift and effective action to control floating pennywort on their land. Under the provisions of the Wildlife and Countryside Act (1981) it is illegal for landowners to allow floating pennywort to spread from their property. Anglers should adhere to the check, clean, dry protocol to help avoid spreading this plant on their equipment such as landing nets and keep-nets. Anglers using weed rakes should be particularly careful not to disturb or break up clumps of pennywort as this could cause the spread of fragments, which may then root elsewhere. If you think you have found floating pennywort please report it to anglian-invasive@environment-agency.gov.uk providing a photograph and detail of the location, preferably including a grid reference. Owners of smartphones could also help track the location of non-native species by using either the Plant Tracker or Aqua Invader Apps available for both Android and IPhone. For more information, please see: http://www.nonnativespecies.org/checkcleandry/biosecurity-for-anglers.cfm 18 of 23
Image 8: Floating pennywort. Image 9: Floating pennywort showing detail of leaf structure. 19 of 23
Graphs showing growth rates for key species Figure 8: Roach growth rate 2016 20 of 23
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 Fisheries Biodiversity and Geomorphology (FBG) Officer Chris Middleton. chris.middleton@environment-agency.gov.uk 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; ns 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 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/. Justin Mould Fisheries Analysis and Reporting Officer 23.01.2017 Carle, F. L. & Strub, M. R. (1978) A New Method for Estimating Population Size from Removal Data. Next survey due Summer 2019 21 of 23
Environment Agency Match Record (Please complete after each match and return by email to chris.middleton@environment-agency.gov.uk) Name of angling club: River: Section / peg fished: Match start time: Date of match: Venue: Number of competitors: Match duration (hrs): Number of anglers weighing-in: Total weight caught: Winning weight: (lbs/oz) or (g) delete as appropriate (lbs/oz) or (g) delete as appropriate 2 nd weight: (lbs/oz) or (g) delete as appropriate 3 rd 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: 22 of 23
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