Monday, May 28, 2012

Phew what a scorcher!

Fly fishing in this country would be a fairly straightforward enterprise if it weren't for the bloody climate! After a spring which got off to a warm start and was then followed by weeks of cold north-biased airstreams, we now have to contend with heatwave conditions during which the average daily temperature has risen by some 18C in a matter of days.
Perhaps unsurprisingly it seems to have knocked the invertebrate and subsequent fish activity right off balance, and with hindsight I was always going to be up against it when I spent the middle portion of the day on the river recently. The fish showed no real inclination to feed in the bright sunlight and even nymphing the streams proved disappointingly ineffective. A couple of fish were nobbled on the dry fly, but that really is about all there is to report on this occasion.

On the invertebrate front, we saw a few mayfly, uprights and pale wateries/small dark olives (I can't tell females of those last two buggers apart); lots of gnats and a few large caddis. First thing in the morning, there were a few medium olive spinners knocking around and it was interesting to turn a few stones and see the females egg laying underneath. It never fails to surprise me when I see 'fully formed' adult flies creeping about underwater, but this is what Baetis vernus does for a living - unlike say, the blue wing spinners, females of the medium olive crawl sub surface by whatever means necessary (including the wading anglers' legs) to deposit their treasure on the underside of stones. Here she crouches, swinging her abdomen slowly side to side, to form a small fungal-looking patch of eggs:

This stone was taken from right in the margins and bears tens of thousands of baetis eggs. Its very top was above the surface and it is this dry landing pad which the spinners had used to access the water.

Herein lies a problem: if the dry weather continues for too much longer, then ultimately this stone - and countless others like it - will end up totally above the waterline and its precious cargo lost.......thousand of little olives we will never get to meet. When I returned this stone, I put it back a few feet further out in deeper water. I know one or two other anglers who have done the same.

Of course, the hydrological characteristics of our spate rivers is different now to a few decades ago. Where once they responded to rainfall and its subsequent run-off in a fairly stable manner, these days rapid urban growth and artificial drainage of impermiable surfaces has caused our rivers to exhibit a much more 'flashy' regime, that is 'quick to flood, quick to fine down'. As more and more natural farmland is replaced by road gullies, culverts and agricultural land drainage, rainfall is into the system in a flash, and out just as quick without the buffer of constant infiltration from surrounding meadows.

I wonder if this is one of the reasons for the perceived decline in abundance of some species. Just over two weeks ago a 6 foot flood raged down the Eden near Langwathby; now it is down to below normal summer level again. What hope do our egg laying friends have in such conditions?

1 comment:

Polly said...

I'm very pleased you posted that picture. Before you showed me yesterday I would have thought it was slime!