B.W.O Supplementation Programme

B.W.O Supplementation Programme

Introduction to the Programme

Any fisherman who has fished the evening rise over several years cannot have failed to notice the steady decline in Serratella lgnita (Blue Winged Olives) , particularly the column of “Sherry Spinners ” flying upstream. Concerned by this, several angler/entomologists have decided to see if anything can be done to temporarily assist nature There maybe one , but more likely a combination of several reasons for the present situation ranging from low water flows,rising temperatures, agriculture practices and several more.
Re introduction of Ephemeroptera Danica (Mayfly) has been successfully achieved at one or more sites but the decline in these cases was due to different causes than that of the BWO.
However the Mayfly and the BWO have similar egg laying habits, so at three sites in Southern England ( Surrey,Wiltshire and Dorset) attempts are being made to instigate a supplementation programme until hopefully conclusions have been reached enabling a halt to this steady decline.
Rivers in the North of the country seem to have suffered far less than those in the South This project involves identifying an egg laying site, catching the “Sherry spinner”, removing her eggs and attaching them to a slide under controlled conditions.
The slides ( in Dorset, holding approximately two thirds of a million eggs) are then placed in the river and left for nature to take her natural course . Fly “egg farming” is in its infancy with no guaranteed results of success

Why bother ??
It has been estimated that under normal egg laying conditions the failure rate is extremely high (as with most things in nature extremely high numbers are produced to compensate for very high natural losses) The aim of this project is to try and ensure that losses are kept to a minimum with hopefully a success rate being increased by eighty per cent plus.
Obviously it will be some time before any results become known What improvements can be made to BWO habitat ? A question which at present we are searching for. There are many things that are not understood regarding fly life. Habitat may be one of the reasons for its overall decline Other ” Grey areas” include diapause in egg development towards the end of the hatching period. This is a natural process and eggs lay in diapause during the winter months in cold water emerging from this condition in March Water temperature can have a dramatic effect on fly eggs from perhaps a small rise in temperature causing a faster development of the eggs but possibly a smaller percentage successfully developing, There appears to be only a small window in water temperature where maximum success occurs.
After hatching, natural phenomina such as ” Natural Nymph Drift” may come into the equation Do Baetis nymphs and Serratella nymphs behave in the same manner ? What determines this behaviour ?are there other factors to take into account such as day or night drifts , diseased nymphs etc. etc. the questions seem endless !

Dr. Cyril Bennett of the Riverfly Partnership has been extremely helpful with both information and advice concerning the the Dorset project now underway.My thanks go to him. Any person concerned with Flylife and water quality in our rivers should be very gratefull for the existance of such an organisation and I hope to be able to provide them with relevant and useful information gained during this experiment in return for their support