A glance at the temporal progression of the Hampshire Avon gives rise to major concerns related to the historic weed cutting policy adopted by the EA. The EA now recognise the potential adverse impact of their actions and are endeavouring to minimise the extent of their cut. Nevertheless the deliberate lowering of water level however "minimal" cannot fail to impact on the natural regime of the river.
The natural progression of events in the calendar of the Avon will see the salmon fry emerging in March and April, dace, pike and perch spawning, first major hatches of fly, (Grannom) in a channel hopefully scoured clean after winter flood events. Cyprinid juveniles are still in the main channel margins, side channels and flood relief areas, sheltering from the winter floods. Weed has yet to establish vigorous growth; high flows are still present after winter rains and groundwater recharge from upper catchment springs.
Early May will normally see the freeboard at its maximum and the ranunculas beginning a phase of rapid growth. The main channel is still not a suitable, safe habitat for juvenile cyprinids, flow rates flushing food and juveniles downstream. Throughout this period the flow gradually reduces, the water and air temperature slowly rise and the turbidity of the water changes in proportion to the weed mass present. Roach, chub, barbel spawn as water temperatures and flow rates reach the desired levels.
Ranunculas growth is determined by flow and substrate, areas of greatest flow attract heaviest growth which in turn coffer the channel forcing the flow to the opposite side of the channel, adopting the route of least resistance. The primary unimpeded flow under natural conditions follows the outside of a bend as this route becomes choked with ranunculas the water level rises and the exposed clean gravel bars of May on the inside of bends become the route of greatest flow and a new generation of ranunculas springs into life. These new clean shallows provide clean habitat ideal for salmonid juveniles just at a time when flows are diminishing and winter habitat is reduced.
Rising water in the main channel backs water into associated ditches and side channels that provide shallow, warm water rich in zooplankton ideal for juvenile cyprinids. Older juvenile cyprinid year classes migrate from the side channels into the reduced flow of the main channel taking advantage of the reduction of flow rate over much of the channel profile.
As we have already mentioned water coffered behind dense beds of ranunculas is forced to flow over the shallow gravel bars on the inside of bends. Through the increased head of water flow is also forced beneath the dense weed fronds at an increased rate over the bed of the river. This increased flow along the bed in shaded conditions, provided by dense overhead growth, acts to maintain clean gravel and provide and oxygenated benthic layer. This clean gravel is similarly demonstrated by the large marginal growth of floating vegetation such as cress which when flushed after the first frosts and floods of winter leave huge areas of sparkling clean gravel. The flow beneath the weed cover also appears to be at a reduced temperature (salmon retention carriers Somerley 95) which now appears to have relevance for the maturation of salmon within the freshwater period of migration.
Into this natural scene we now introduce the EA mechanical weed cut, the reasons for and the arguments against will come later but we initially must consider the impact.
The objective appears to simply increase the freeboard to enable farmers to get second cut silage, prolonged grazing and allow heavier modern machinery access to the water meadows. To that end channels are cut through the weed in varying patterns and channels. Irrespective of the pattern or depth of cut the desired result is a drop in water level. Associated ditches and carriers suffer a similar drop in levels with the loss of vital habitat for, amphibians, breeding waders and juvenile cyprinids. Current year and 1+ juveniles risk being swept with the flow downstream losing vital year class structures, upstream cyprinid migration is impossible on the Avon.
Flow is dissipated across the width of the main channel with an almost total loss of juvenile salmonid habitat. Dissipated flow is no longer sufficient to encourage EU designated Ranunculas to grow and undesirable vegetation such as Sagittaria, Elodea and Potamogeton are encouraged. Apart from the direct effect of encouraging undesirable plant species cutting also generates regrowth of ranunculas at an unseasonal period when sufficient flow returns. A problem arises when fresh luxuriant growth is present when the winter floods that should lift out and clear the spent plant lifecycles of summer cannot scour this vigorous new material more akin to May. Whilst the scale of the problem is uncertain complete weed cuts such as those practiced by the EA undoubtedly have implications for the natural cycles within the river; flow deviation, invertebrate habitat, juvenile salmonid and cyprinid habitat and food sources disrupted. Without a full assessment of the possible detrimental impact of this extreme change of regime the “precautionary principle” should be adopted.
Given the high nutrient inputs of the Avon, a low spring macrophyte biomass will result in larger plankton blooms and that this applies to a greater extent later in the year, when algae grow more rapidly. As well as the physical trapping of suspended algae and sediments by weedbeds, the extremely abundant larvae of river flies (associated intimately with the Ranunculus habitat) include filter-feeders and scrapers that convert algae to energy-rich prey for fish, invertebrates and even birds! The indigestible components are converted to faecal pellets that settle more readily than algae and lead to clearer water.
The nutrient filter algal platform is removed allowing increased levels of nutrient, combined with sunlight, algal blooms increase. Light penetrates to the gravel bed with the potential for algal growth to colonise the stones creating oxygen imbalance and concretion of the gravels. (In light of the three, one hundred year probability flood events in the last fifteen years which surely would provide gravel as clean as any historically found in the Avon, consideration of weed cutting being a major contributor to the concreted gravel malaise should be considered.) Somerley where weed has not been cut for in excess of a decade does not have a problem with gravel quality, seatrout numbers using this same gravel appear at record levels.
Vital cover and food sources are removed causing adult coarse fish to be subject to higher risk of avian predation. Migration of coarse fish populations to deeper water, in search of cover throughout daylight hours, creates a serious loss of amenity for anglers. Drifting weed, long associated with the weed cut, also gives rise to a serious loss of amenity as does the serious loss of water depth. Newly hatched 0+ cyprinid larval stages from spawning sites within the main channel risk being swept through the system if the migrations of this life stage are as indicated on the roach studies from Europe.
The above is a brief summary of events throughout the river, closer scientifically based scrutiny would provide answers to some of the questions raised but until such time the authorities have a statutory obligation to adopt the precautionary principle regarding future weed cutting.
Whilst I appreciate the difficulties the Environment Agency have in attempting to balance the conflicting demands. As stated at the beginning of my response I similarly appreciate the current attempts to reach an agreement to limit further damage to the angling amenity. I would point out that the local angling community are charged in the region of 300000 GBP annually by the Environment Agency, 21 GBP million nationally. For that charge I believe the angling community might quite rightly expect their interests to be upper most when it came to consideration of objectives. If that is not to be the priority I think the case for making the charge becomes questionable. Added to the sum charged by the Environment Agency is the equally considerable sum paid to landlords and the dependency of the professional fishery staff, the tackle trade and the tourism value
How do the EA equate their weed cutting practices with the *EU life bid* funding which specifies Ranunculas as a directed species to be encouraged and supported? Perhaps that is a question for Europe
Is the loss of amenity suffered by the angling community taken into consideration when establishing weed cutting policy? At a conservative annual estimate of 10k per mile and the impact of weed cutting creating loss for periods in excess of six weeks. Is it conceivable for either the EA, or those deemed beneficiaries of the weed cut by the EA, to compensate those angling rights affected? On a simply weekly pro-rata basis a figure of 1000ukp per mile might be considered reasonable.
Prior to 1952 the majority of hand cutting was restricted to the side channels and shallows in the main river (Pers.Com. Mr W.Cabey, Severals riverkeeper 1930’s-50’s. Mr T Sampson, Mr H Goulding, Somerley Tenants 1920’s-90’s) The increased efficiency and range of the mechanical cut coincides with the recorded decline of the MSW fish and concern related to the state of the coarse fish population, concerns which persists to this day. Within the EA protocol "a need to demonstrate weed cutting will contribute to conservation of the Avon Valley" and under the Habs.Dir. The precautionary principle should be adopted where actions may potentially have adverse impact.
Interestingly the species chosen to measure or reflect the potential impact of the weed cutting in the EA Biological Report was the roach (Rutilus rutilus), a species giving rise to considerable concern at the present time. It clearly emphasises the importance of shallow, weedy areas for both spawning and subsequent fry stages (Schindler 1957, Bagenal 1973, and Wheeler 1969). Areas weed cutting is specifically aimed at draining with the potential to strand or displace the population away from spawning areas described in the report as historic (Rudd 1943). The inability for upstream migration of cyprinids within the Avon potentially risks distinct species populations within the SAC. I believe para 7.57 of the report so encapsulates my concerns that I feel it needs restating and to that end I have scanned it in;
7.57 Throughout all the studies reviewed, a general picture of the vital importance of water weed to the spawn- ing and early life-history stage of roach is evident The cutting of weed at the wrong time and wrong place could disturb spawning, destroy eggs, destroy newly hatched young, remove cover for young fish and, as the below extract (Yorkshire River Authority, 1974) explains, drastically interfere with the feeding of young fry:
"The abundance of rotifers is affected by the abundance of diatoms and these depend in turn upon the availa- bility of plenty of surface area, for instance aquatic plants A weed cut during this phase would not only rob the fry of cover, but it would also deprive them of the base of their food chain".
Can the EA give assurances that the publicly funded weed cut will not have any detrimental impact on the EU designated species of the Avon Valley and River Avon SSSI/SACs? (Particularly re salmon and lamprey in the event of low summer river flow) No they cannot.
The publicly funded Agri/Env schemes in the Avon Valley used to pay in the region of 350,000.00 GBP per annum to the farmers in an attempt to help restore the valley to a favourable status by 2010. Added to this the EA spend a further 30,000.00 GBP in weed cutting in an effort to enable farming in as ecologically damaging way as possible to continue. Hopefully the public money that will be paid into the agricultural community under the new ELS and HLS farming schemes will insist on greater consideration for the Riverine SSSI.
Trying to get to grips with the socio-economic value of the Avon fishery is an enormous task. The trout fisheries of the higher catchment are internationally recognised, as is the coarse fishery of the middle and lower river. Added to this the salmon fishery was valued in its heyday at six to ten fold the value of the coarse fishery. Add in the river keepers, tackle industry, accommodation and knock on expenditure the final figure would be colossal. I believe the value put on angling in our neighbouring river, the Test, is in excess of three million; the Avon would probably be greater when all the disciplines are considered.
What is somewhat paradoxical is that the anglers pay in licence fees alone a figure not that far removed from what is paid the agricultural community in subsidies from the public purse. For their money the Avon angler gets next to nothing yet the farmers receive a further 30k a year from the EA weed cutting budget to destroy the fishery.