Fisheries survey report of the Burwell Lode
Cambridgeshire and Bedfordshire – Fisheries Monitoring Programme 2014
Summary
Fish populations within Burwell Lode are currently at their lowest recorded estimates, with this deterioration primarily attributed to a reduction in the number of roach. Further monitoring should reveal whether this is due to a general downturn in fish stocks, or, as is possible simply the result of a poor survey year brought about by environmental factors such as clear water conditions influencing fish distribution and stock migration. Allowing for the ‘gin clear’ water clarity and the timing of historic surveys, either late winter or early spring, may help explain the fluctuating datasets and changes within the fish population. Supporting evidence in the form of angling match catch data seems to indicate that fish stocks are actually greater than our current survey data suggests.
Sixteen species plus one hybrid were recorded over the 3 sites surveyed, including bitterling a non native species. Species caught included:
Bitterling [Rhodeus sericeus] Perch [Perca fluviatilis] Bleak [Alburnus alburnus] Pike [Esox lucius] Bullhead [Cottus gobio] Roach [Rutilus rutilus] Chub [Leuciscus cephalus] Rudd [Scardinius erythrophthalmus] Common bream [Abramis brama] Ruffe [Gymnocephalus cernuus] Dace [Leuciscus leuciscus] Silver bream [Abramis bjoerkna] Stone loach [Barbatula barbatula] European eels [Anguilla anguilla] Gudgeon [Gobio gobio] Tench [Tinca tinca] Ro x Cb hybrid [Rutilus rutilus x Abramis brama]
Density and standing crop pie charts with percentage values and colour key:
Species density composition (>99mm) Species standing crop composition (>99mm)
Density and standing crop of individual fish species are calculated using the number / weight of fish in each site and then a mean (average) calculated for the reach, in this case five sites. Density is reported as the number of individuals of that particular species that might be found in 100m2 of the river. Similarly, standing crop is the weight, or grams, of that fish species that might be found in the same area.
The average density (number of fish in a given area) of all species >99mm over the three sites decreased from 30.12 Ind./100m2 in 2010 to 4.23 ind./100m² in 2014, a decline of 86%.
Total average standing crop (weight of fish in a given area) of all species >99mm also decreased from 2744.7 g/100m2 in 2010 to 808.4 g/100m² in 2014, a decline of 71%. Site locations
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 methodology
The sites were sampled using electric fishing methodology, which 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.
Image 1
In shallow streams it is generally possible to wade upstream within the channel using generator powered equipment towed within a small boat. 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 via an electric or petrol outboard engine or 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 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.
Fish are measured to the nearest millimetre and scales taken for age, growth and other statistical analyses at the National Fish Laboratory in Brampton. Results are reported utilising fish greater than 99mm as this method has been shown to be inefficient below 99mm. Current survey data
Total number and largest (mm) fish captured during the 2014 survey cycle for key species.
Roach Perch Common bream Rudd Pike Site Name No. Largest No. Largest No. Largest No. Largest No. Largest Burwell Village 46 162 67 191 - - - - 20 681 Cock-Up Bridge 78 166 8 141 2 457 - - 4 618 Upware 138 161 13 165 25 100 6 126 2 569
Roach were the most common fish over the three sites surveyed, with a maximum density estimate of 2.74 individuals for every 100m2 of river surveyed, equivalent to a 65% share of the total population. Eels were subdominant with 14%, followed by pike contributing 10% to the overall population.
Mean density of fish (>99mm) from Burwell Lode 2014
Pike were the dominant species’ by weight with a mean standing crop estimate of 336.1g for every 100m2 of the river or 42% share of the overall biomass. Eel were subdominant by weight at 292.3g/100m2, followed by roach with a standing crop estimate of 99.6g/100m2.
Mean standing crop of fish (>99mm) from Burwell Lode 2014 Historic survey data
Fish populations were seemingly at their strongest during the 1990’s, peaking in 1993 with a combined density estimate of 101.28 ind./100m². This data however should be viewed with caution as the inconsistent timing of the survey cycles, particularly during the 80’s and 90’s, may have increased the possibility of seasonal behaviour influencing these survey results.
Historic density of fish (>99mm) from Burwell Lode 1984 – 2014
Winter surveys, such as the 1990 survey cycle, can be “hit or miss” in nature and may produce lower catches than those recorded during summer months when fish populations are more evenly distributed. As temperatures decline shoaling species such as roach, rudd and bream tend to congregate in large numbers with this behaviour occasionally leading to very large catches if occurring within a survey area. Spring surveys, such as the 1993 and 1998 survey cycles, may also see fish aggregating or changing distribution as they migrate to areas of river which offer the most suitable habitat for spawning.
Whilst strong recruitment to the roach population was acknowledged as part of the reason behind the high density estimates recorded during the 90’s, the potential issue of stock aggregation and migration was also highlighted as a significant factor, with the corresponding fisheries reports concluding:
1990:
Overall biomass has increased by more than four-fold since the 1987 survey. This increase is almost entirely due to a rise in roach biomass and density and represents a winter aggregation phenomenon, coupled with strong recruitment. Burwell Lode is openly connected to Reach Lode and Wicken Lode and is also linked to the River Cam at Upware Lock and temporal and spatial distribution of fish populations between all of these water-bodies is likely to have an important influence on survey results.
1993:
During the 1990 survey a mean fish biomass estimate of 69 g/m² was recorded largely as a result of aggregation of fish at site 507 Burwell Village. This site again recorded the highest biomass estimate in April 1993 survey with a biomass of 86.5 g/m² with roach continuing to form the dominant component of biomass and density estimates. Recruitment has been excellent to the 1989, 1990 and 1991 year classes but one notable feature has been the change in growth rates since the 1990 survey. In 1990 growth rates were fast, however, the growth rate of the population in the 1993 survey was slow at 80% of the standard growth and is probably related to the very high densities of roach present in the Burwell Lode as a result of consistently high recruitment since 1989. In order to gain a realistic impression of fish distribution within the Burwell Lode it is therefore recommended that surveys be undertaken at times of the year when fish are more normally distributed to help avoid distortions caused by winter aggregations.
1998:
Biomass and density levels are now at the highest recorded on the Burwell Lode with the main reason for this improvement being an increase in the roach and common bream population. A large aggregation of roach was recorded at the Burwell Village site where approximately 6000 fish were captured. This phenomenon was also exhibited during the previous survey in 1993 and is probably the result of annual migrations towards the upper reaches prior to spawning.
Historically, the majority of fish caught during fish population surveys on Burwell Lode have been roach and in this respect 2014 was no exception however, density estimates for all fish and fish greater than 99mm have been steadily declining. Additional spatial surveys should reveal whether the 2014 result is due to a general downturn in the roach population, or, as is possible simply the result of a poor survey year influenced at the time by environmental factors such as clear water conditions and stock aggregation.
Historic roach density from Burwell Lode 1984 – 2014
Habitat data collected at the time of the surveys recorded water clarity as being ‘clear’ at all three sites sampled on Burwell Lode during 2014. Clear water can affect both fish behaviour and distribution with stocks often preferring to aggregate in areas where they feel less vulnerable. Fish in clear water may show a tendency to shoal around features which provide the most cover and protection from predators with areas such as bridges, pumping stations, moored boats and overhanging trees often utilised. The “fixed” nature of our survey sites mean we cannot move sites to accommodate shoaling behaviour and even if we chose to, these areas of refuge are, by their nature, generally not suitable for sampling with our survey techniques.
This is an occurrence recently observed on Soham Lode in 2013 and Bottisham Lode in 2012 as part of an investigation into the use of pumping stations as a place of refuge by fish. An investigation discovered more than 17,000 fish comprising of 12 species were utilising Soham Lode Pumping Station during daylight hours, only leaving the safety of the pump chambers once darkness had fallen.
Scale data received from the National Fisheries Laboratory shows roach populations within Burwell Lode at the Cock-Up Bridge survey site as having slow growth rates when compared to their species standard for roach in ‘Southern’ waters, with a Percentage Standard Growth value of 69%. This slow growth was common across all age groups, with the maximum age recorded for roach at this site at 6+.
No data analysis was performed for the two common bream at Cock-Up Bridge or for the roach captured at the remaining survey sites due to limited sample size submitted. However, the common bream were aged up to 11+, whilst the oldest roach caught from Burwell Village was aged at 7+. Both species exhibited slow growth similar to the roach at Cock-Up Bridge.
This data would seem to suggest that there is actually a far greater number of fish, particularly roach, present then was actually recorded during the three spatial surveys, as slow growth can potentially signify high fish densities.
When analysing the data collected from Burwell Lode, it is important to consider that stock migration around the Cam Lodes system is inevitable as there are no barriers preventing fish migration.
Site level survey data
Site: Burwell Village Survey Date: 05/06/2014
Species density composition (>99mm)
Despite being numerically dominant in 2014, almost all of the perch caught were less than 99mm in length. Whilst the inclusion of these juvenile fish is encouraging for future years and is evidence of recent recruitment to the population they are not used in the density estimate calculation.
Historic species density data (>99mm)
Site: Cock-Up Bridge Survey Date: 03/06/2014
Species density composition (>99mm)
Cock-Up Bridge was the only site surveyed in 2014 to record the presence of mature, adult common bream, albeit only two individuals. Due to the relative small survey areas and the roaming nature of this species, which are capable of travelling several kilometres a day, the chance of capturing large shoals are extremely low.
Historic species density data (>99mm)
Site: Upware Survey Date: 11/06/2014
Species density composition (>99mm)
In 2014, the site at Upware recorded both the greatest species composition and number of fish present. However the vast majority of fish caught were juveniles <99mm in length and not included within the density estimates. The population is currently dominated by roach (78%) with perch sub-dominant (9%) followed by eel (4%).
Historic species density data (>99mm)
Supporting evidence
Sawbridgeworth Angling Society and Cambridge Fish Preservation and Angling Society (CFPAS) have kindly provided match catch data from the Burwell Lode between 2013 and 2014. Roach were the most abundant species recorded over the 10 matches (all held at Upware) followed by rudd. Other species present included; perch, common bream, tench and eels.
The match held by Sawbridgeworth Angling Society on 24 August 2014 was won with 33lbs and comprised almost entirely of rudd, including several fish over 1.5lb. When analysing the historic survey data from all three sites, rudd rarely feature and have only ever been recorded in low densities since 1984. This match alone highlights the importance of angling match catch data as supporting evidence and is essential when analysing trends in fish populations.
This collated angler data seems to suggest that the 2014 survey cycle may not be an accurate reflection on the current fish population, particularly throughout the lower reaches of the watercourse.
Match Summary (01/01/2013 to 30/11/2014):
No. Anglers Total Weights Caught (lbs-ozs) Year No. Matches No. Anglers Total Weight Weighing-in 1st 2nd 3rd 2013 5 70 57 205-0-0 34-10-0 25-03-15 21-11-07 2014 5 64 61 329-1-8 68-12-0 39-7-0 34-9-0 Total 10 134 118 534-1-8 103-6-0 64-10-15 56-4-8
Match Returns (01/01/2013 to 30/11/2014):
No. Anglers Match Weights (lbs-ozs) Match Date No. Anglers Weighing-in Duration Total 1st 2nd 3rd 16/06/2013 19 9 5.00 5-8-0 1-4-0 1-1-15 1-1-0 01/09/2013 15 14 5.00 50-2-0 5-2-0 5-0-0 4-13-0 29/09/2013 19 19 5.00 67-8-0 9-4-15 5-8-15 4-14-7 20/10/2013 11 10 5.00 50-14-15 7-11-15 7-4-0 6-6-15 08/12/2013 6 5 5.00 30-14-15 11-3-0 6-4-15 4-7-15 09/03/2014 14 13 5.00 51-14-8 7-10-0 5-14-0 5-10-0 06/07/2014 15 15 5.00 53-0-0 6-12-15 6-6-0 5-5-0 24/08/2014 14 12 6.00 95-0-0 33-12-0 10-3-15 9-1-0 31/08/2014 10 10 5.00 55-13-0 8-14-0 8-3-0 6-9-0 28/09/2014 11 11 5.00 73-6-0 11-10-15 8-12-0 8-0-0
Pictures courtesy of Sawbridgeworth Angling Society 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 Analysis and Reporting Officer Chris Middleton [email protected]
Before you go fishing don’t forget: You must have a validEnvironment Agency rod licence and permission from the fishery owner; You must comply with thefisheries byelaws; The coarse fish close season (15th March to 15th June inclusive) applies to all rivers, streams and drains in England and Wales but not most stillwaters. Stillwater fishery owners can still have their own close season and rules, so please check with them before setting out. Report illegal fishing: If you see any fishing, netting or trapping you think may be illegal, please do not tackle it yourself. Call us immediately on 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 vehiclesinvolved. 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/.
Next survey
Summer 2020.