Fisheries Survey Report of the River Great Ouse: Brackley to Newport Pagnell 30 of July to the 20 August 2013
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Fisheries survey report of the River Great Ouse: Brackley to Newport Pagnell 30th of July to the 20th August 2013 SUMMARY The 2013 survey cycle recorded a number of exceptional specimen fish and some strong, if localised, roach populations were also found. The increased population of silver fish has meant that stock density has improved at most locations since the previous survey cycle. Perhaps unsurprisingly catches were linked to habitat quality with those sites offering riffle and pool habitat such as Manor Farm, Mill Farm Gayhurst and Wolverton Mill offering the greater catches of rheophillic (flow loving) species such as dace, chub and barbel. The slower glide and slack reaches produced stronger roach catches and occasional common bream. Standing crop has decreased at some locations due to the absence of large common bream found in 2010 and fewer chub being recorded at some sites. RESULTS Seventeen species and one hybrid were recorded over the ten sites sampled. List of species caught: Roach [Rutilus rutilus] Spined loach [Cobitis taenia] Gudgeon [Gobio gobio] Barbel [Barbus barbus] Dace [Leuciscus leuciscus] Roach x common bream hybrid [Rutilus rutilus x Abramis brama] Perch [Perca fluviatilis] Brown / sea trout [Salmo trutta] Bullhead [Cottus gobio] Ruffe [Gymnocephalus cernuus] Minnow [Phoxinus phoxinus] 3-spined stickleback [Gasterosteus aculeatus] Chub [Leuciscus cephalus] Tench [Tinca tinca] Pike [Esox lucius] Brook lamprey [Lampetra planeri] Stone loach [Barbatula barbatula] Common bream [Abramis brama] Density and standing crop pie charts with % values and colour key Species composition by density of fish >99mm Species composition by standing crop of fish >99mm The average density (number of fish in a given area) of all species (>99mm) over all sites equates to 12.2 Ind./100m2 Total average standing crop (weight of fish in a given area) of all species (>99mm) over all sites equates to 1102 g/100m2. The largest fish recorded during the survey included a barbel of 730 mm (13lb) from Mill Farm Gayhurst and a chub of 534mm (6lb 8oz) from Manor Farm. The largest individual (mm) and estimated number of fish (>99mm) are recorded for barbel, chub, perch and roach at site level (Table 1). Table 1: Numbers recorded (all fish) and largest length (mm) for selected species. Trout Chub Roach Dace Barbel Largest Largest Largest Largest Largest No. (All) No. (All) No. (All) No. (All) No. (All) Site (mm) (mm) (mm) (mm) (mm) Westbury 3 416 16 415 35 238 29 242 - - Buckingham - - 2 146 300 279 25 191 - - Thornborough Mill - - 6 162 67 170 6 162 - - Mount Mill Farm - - 2 198 11 176 14 181 - - D/s Mill Farm - - 5 477 45 210 5 162 - - Passenham - - 1 94 431 200 34 202 - - Old Stratford - - 7 117 327 184 33 173 - - D/s Wolverton Mill - - 17 530 154 259 114 200 1 168 Manor Farm - - 30 534 58 186 40 204 7 677 Mill Farm Gayhurst* - - 11 478 49 173 9 163 6 704 *Single catch minimum estimate Table 2: Survey Sites Survey Site Name Reference Date Grid reference Catch Strategy Catch Method Area (M2) Westbury 4622 07/08/2013 1110 SP6216435534 CATCH DEPLETION ELECTRIC FISHING Buckingham 4625 08/08/2013 1020 SP6985833956 CATCH DEPLETION ELECTRIC FISHING Thornborough Mill 4627 14/08/2013 1650 SP7368835432 CATCH DEPLETION ELECTRIC FISHING Mount Mill Farm 4628 05/08/2013 1400 SP7628937592 CATCH DEPLETION ELECTRIC FISHING D/s Mill Farm 4630 13/08/2013 2250 SP7743338410 CATCH DEPLETION ELECTRIC FISHING Passenham 4631 02/08/2013 960 SP7838639304 CATCH DEPLETION SEINE NETTING Old Stratford 4633 30/07/2013 1040 SP7815040692 CATCH DEPLETION SEINE NETTING D/s Wolverton Mill 4635 20/08/2013 1750 SP7973241309 CATCH DEPLETION ELECTRIC FISHING Manor Farm 36762 06/08/2013 1845 SP8079742435 CATCH DEPLETION ELECTRIC FISHING Mill Farm Gayhurst 4637 31/07/2013 2000 SP8562445154 SINGLE CATCH ELECTRIC FISHING 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, 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. METHODOLGY: Ten sites were surveyed on the river Great Ouse between the 30th of July and the 20th of August 2013. The sites were sampled using a combination of electric fishing and drag down seine netting methodology depending on the nature of the site. Electric fishing: This survey technique uses the physiological effect of an electric field in water to attract and immobilise fish. Electrodes, immersed in the water, stimulate a fishes nervous system so that it swims towards the operator, or is unable to swim away, and can be caught. Image 1 shows the typical components of an electric fishing system. In shallow streams it is generally possible to wade upstream within the channel using generator powered equipment towed within a small boat, (Image 1). When rivers deepen or site depth is variable, electric fishing from a boat using generator powered equipment is often the preferred method. The boat is manoeuvred downstream on ropes by an operative on either bank controlling the speed, direction and channel positioning. Stop nets are positioned across the channel isolating the survey site preventing fish from migrating Image 1. 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 (catch depletion). Seine netting: Stop nets are positioned across the channel to isolate the survey site and prevent fish from migrating into and out of the survey area (seine 3 & 4 on image 3 below). A catching net is set at the lowermost extent of the survey site (seine 2) and a heavily weighted net is then laid across the channel (seine 1) which is drawn downstream driving fish into the catching net. The catching net is drawn into the bank to encircle the driving seine which is then removed. Fish are then trapped within the catching net which may be hauled in. The netting operation is repeated until a 50% reduction in the total number of fish caught has been achieved. The nets are constructed from 10mm knotless mesh which is relatively soft and helps to minimize fish damage. Floats are attached along the top edge and a lead-line along the bottom edge so that the net hangs vertically within the water column. Image 3. Fish captured by both techniques are measured to the nearest millimetre and scale samples are taken for age and growth analysis. Results are reported primarily utilising fish greater than 99mm as both methods have been shown to lose efficiency on fish below this length. Supporting evidence is also presented using total catch figures i.e. fish of all lengths. These figures are likely to be an underrepresentation of stock and where included should be viewed with caution. COMBINED SURVEY RESULTS The average density (number of fish in a given area) of all species (>99mm) over all sites equates to 12.2 Ind./100m2 Total average standing crop (weight of fish in a given area) of all species (>99mm) over all sites equates to 1102 g/100m2. Roach were the most common fish (>99mm) over the ten sites surveyed with a mean density estimate of 6.1 individuals for every 100m2 of river surveyed, or a 50 % share of the population. Dace populations were subdominant representing a 21% share of the total population with an estimated mean density of 2.5ind./100m2. Figure 1. Mean density of fish (>99mm) in the River Great Ouse 2013 (Mill Farm excluded) Chub were the dominant species’ by weight with a mean standing crop estimate of 317.8 g/100m2 and representing 29% of the total weight of fish captured. Roach populations were subdominant by weight at 281.7 g/100m2 (26% of standing crop), Pike were the third most important species with an estimated 209.1g/100m2 representing a 19% share of the total weight of fish caught, the comparatively low numbers caught does not point to a predator prey imbalance. Figure 1a. Mean standing crop of fish (>99mm) from the River Great Ouse 2013 (Mill Farm data excluded) Figure 2: Density of species >99mm at site level 2013 Figure 2 shows the numerical prevalence of roach which were generally either the dominant or the subdominant species at each site sampled, the notable exceptions to this being the Mount Mill Farm and Manor Farm sites. Site 4631 (Passenham) provided the highest density recorded with a population estimate of 29.4 ind./100m2 which was chiefly comprised of roach. Figure 2a indicates the importance of chub and roach to the overall standing crop estimate, the capture of large barbel at Manor Farm is also apparent. Figure 2a: Standing crop of species >99mm at site level 2013 SITE LEVEL DATA Site No. 4622: Westbury Species present (All lengths) Species Number Species Number Bullhead [Cottus gobio] 59 Perch [Perca fluviatilis] 12 Roach [Rutilus rutilus] 35 Stone loach [Barbatula barbatula] 4 Dace [Leuciscus leuciscus] 29 Brown / sea trout [Salmo trutta] 3 Chub [Leuciscus cephalus] 16 Gudgeon [Gobio gobio] 3 Minnow [Phoxinus phoxinus] 16 3-spined stickleback [Gasterosteus aculeatus] 2 Population Composition Density (Lengths >99mm) In 2013 the fish population at Westbury was dominated by roach and dace.