The Salisbury & District Angling Club controls over 30 miles of first class angling on the ‘Five Rivers’ of Wiltshire and, with over 2000 members, it is the largest game fishing club in the country. The quality of any fly fishing water is dependent upon its Riverfly populations and compared to the declines seen on many other rivers, the Wiltshire Avon has remained relatively good, but we can’t afford to be complacent; if we are to conserve our Riverflies, we need to know a lot more about them. Since the club was designated as a ‘Centre for Riverfly Conservation’ we have been involved in a number of important initiatives and this report gives an update on this work and our plans for the future. As the River Avon is a Special Area of Conservation (SAC) we work closely with Natural England and the Wiltshire Wildlife Trust.

Courses run at the Club’s headquarters

All of the equipment previously used at The John Spedan Lewis Trust’s field centre at Leckford has now been transferred to our newly equipped field centre at the Club’s headquarters alongside the river Avon near Salisbury. To supplement the monitoring team, one ARMI monitoring course has been run together with two identification courses, and a further ID course may be run to meet demand. Preparations are also in hand for a new ‘Species Level Identification Course’ to run from 2015 and a meeting of interested parties was held in October 2014 at the Wiltshire Wildlife Trust’s centre at Langford Lakes to take this forward.

‘App’s for Riverflies

The Matchahatch app is available for download in the Google Android store and Apple Store.

This app. will provide a visual aid for fly fishermen on the river bank to identify the adults of each species on the water; this will include size, flight period, a short ecology and a suitable artificial pattern.

 

Research work on the Blue Winged Olive (Serratella ignita)

Weekly sampling of growth rates and population densities has shown changes in emergent patterns such that large numbers of adults are now emerging well into the late autumn, together with a small overwintering population of larvae. This appears to be due to: (1) rather than going into diapause, some eggs are hatching immediately to produce a second generation; and (2) some eggs from the previous year are staying in diapause

for a longer period. This shift in emergent pattern has also been recorded in the upland rivers of Derbyshire (pers. comm. Dr Nick Everall (Aquascience).

Serratella ignita – River Avon (West Amesbury) 2011

The accumulation of silt on developing eggs appears to undermine the adhesive qualities of the eggs causing large numbers to become dislodged and lost downstream. As the eggs of this species enter diapause for up to eight months, they are obviously more vulnerable than eggs that do not have a diapause period and this could be why this species is far more sensitive to siltation (PSI score ‘A’).

Research work over a two year period has shown that Blue Winged Olive (and Mayfly) eggs can be safely incubated (and therefore quarantined) in domestic tap water giving a considerable amount of bio-security when moving eggs between river systems.

Establishing a Mayfly (E. Danica) population on the River Wandle in South London.

Once declared as one of the most polluted rivers in England, and with the colour of water often matching the dye being produced in the local factories, the river Wandle was virtually devoid of any aquatic life for over 200 years. However, subsequent clean-ups over the last 30 years or so have improved the water quality dramatically such that gin clear water now flows over vivid green beds of Ranunculus; wild brown trout have returned together with good populations of freshwater invertebrates, but no mayflies. In line with the Riverfly Partnership protocol for the restoration of a Riverfly species, approximately seven million eggs were ’stripped’ from females returning to the club’s water on the Wiltshire Avon, incubated (in tap water) and then moved to the River Wandle in an attempt to establish a population.

The eggs were introduced at development stage 6/7, and tiny nymphs were starting to hatch after three days. Routine monthly invertebrate monitoring, carried out by the Wandle Piscators, will now keep a close watch on their progress over the next two years.

This initiative was recorded by a film unit from Bristol for the BBC ‘One Show’ and will be shown at some time in the future. Once the date is confirmed this will be published on the News page.

Grannom (Brachycentrus subnubilus)

Whilst this species has seriously declined on some of our chalk streams, large populations still remain on the Hampshire/Wiltshire Avon below Salisbury, but only sparse populations are found above the City. This gives a unique opportunity to study this species in detail and to investigate why there are such low populations on the club’s extensive fisheries above Salisbury where this species could provide good early season dry fly fishing at a time when few other species are emerging.

During the flight period in April/May, females deposit large numbers of eggs in the aquatic vegetation and it is thought that the early season weed-cut above Salisbury during this period has, over a long period, resulted in large numbers of eggs carried downstream on the cut weed to the Environment Agency weed boom below Salisbury. The numerous bridges in the city appear to be acting as an optical barrier to upstream migration of the adults; huge numbers can often be seen turning left at the Harnham Bridge and following the main road thinking it’s the river.

The obvious solution was to move large numbers of eggs upstream to re-establish populations above the City, and to modify the early season weed-cut.

 

Whilst the collection of eggs using traditional fly boards provided some success, a new method was initiated this year using a wooden post (females like to crawl down posts in the river) with a cross section on which a fabric is attached to simulate a weed bed. These proved to be highly successful and within a short period huge numbers of eggs had been collected. The eggs develop and hatch in about 21 days and were moved upstream at development stage 6. Further modifications to this system are planned for next year.

As routine riverfly monitoring is carried out at the release site, the growth and population size can be recorded and compared with populations at other S&DAC monitoring sites further upstream.

River Wylye invertebrate survey

In conjunction with Aquascience and other angling clubs, a full invertebrate survey is being carried out at four sites on the river Wylye in order to obtain a ‘Biological Fingerprint’ of the river. This will highlight any organic pollution problems together with sedimentation and phosphate levels. The results of this survey were presented at the October meeting in 2014 and form part of our move towards monitoring down to species level.

Gravel Jetting

As this important service is no longer provided by the Environment Agency, the club has acquired the equipment and is carrying out this task to ensure that Salmon & Trout spawning sites remain in good order.

As it was also important to know what effects blasting the sediments with high pressure hoses had on the invertebrate populations, a detailed survey was carried out at one of these sites.

Both fully quantitative (Surber) and 3 minutes kick samples were taken just before jetting, 3 hours after and then 1/2/4/8/16 and 32 days after. After a significant drop, there was a large increase in the population size of all groups except cased caddis flies, which returned to their original size.

Effect

 

Dr Cyril Bennett MBE
Salisbury & District Angling Club
(Centre for Riverfly Conservation)
June – 2014