My fly fishing club in North Yorkshire belongs to something called the Riverfly Partnership, whose main aim is to protect the UK’s rivers. Part of this involves monitoring invertebrates in the rivers. This provides information about the ecology of the water and is also an important way to detect if the water quality is improving or deteriorating. A friend and I do regular sampling on a site on the Pickering Beck upstream of the town.
Sampling involves taking what is known as a three-minute kick sample. Basically you get in the water and face downstream. You then place a sturdy, flat-bottomed net onto the bed of the river in front of you and vigorously agitate your feet to disturb the bottom. Clouds of silt, sand, sediment, gravel, weed etc – basically whatever it is you are disturbing – billow up and get caught in your net. Together with all the bugs that are living there. You do this for a total of three minutes and empty the contents into a bucket. You then put this into a tray and count different classes of critter.
Here’s our sampling spot:
And this is the kit:
We’re looking for six types of beast: freshwater shrimp, cased caddis, caseless caddis, and the nymphs of the mayfly, a couple of types of olive, stonefly and something called Heptageniidae, whose adult form is something I can’t remember. Anyhow, it’s all very interesting for the fly fisherman, who can get a first-hand look at the larder from which Mr Trout takes his pickings. In the small patch that we sample, typically we might get a total of anything between 300 and 500 invertebrates in our three-minute kick.
Here is a very impressive mayfly nymph that showed up in the bucket today:
This is a Hepta:
This is a stonefly nymph with half of one of its tails half missing:
And this is a caseless caddis:
Here’s the puzzle though. With all that food around, why are the fish in this beck so small?