Some basic biology today with two invertbrate samples collected from the mainstem at the Brae Water. For interest I took one sample from an area of bright river bed – relatively mobile substrate in fast flow, and another from an area of dark or “black” river bed where the more stable substate had allowed algae to become well established. The bright sample was taken in the run above Auldearg on Brae Water 3 beat.
Sampling here was easy, the riverbed was quite loose and the cobbles turned over readily. Iain Tennant, the beat ghillie was impressed by the amount of life in the tray.
The vast majority of the mayfly nymphs were of Rhithrogena family, of which there are two species in the UK. Apparently it is difficult to tell the two species apart at this stage but anglers will know them as March Browns and Medium Olives. The relative size of the nymphs gives a good clue as to which is which. The large one on the top left is almost certainly a MB, whilst the smaller ones will be the olives. It looks as if there will be a good hatch of both this spring. Stoneflies and a few caddis were also identifiable in the tray. I wanted to do a full count and identification of this sample so they were preserved in alcohol for sorting later.
The sample from the dark river bed was taken below the Rock Pool on Beat 2 (looked fantastic today and no-one fishing!) Here the more stable riverbed proved harder to sample but by working between the boulders a good sample was gathered. When I tipped the net into the tray it was obvious that the population was quite different with more Baetid mayflies (Large Dark Olives etc) and caseless caddis. This sample was also preserved for further analysis.
It doesn’t take long to collect a sample, 3 minutes to be precise, but the sorting and the identification takes a lot of time. Back at the office and 2.5hours later I still hadn’t finished sorting all the bugs from the first sample. Another half hour in the morning will finish the sorting of the first sample then there will another hour or two for the count and identification. This detailed work is time consuming but essential for me to learn what it present in the Spey. In Ayrshire we developed a quick bankside assessment method based on the Riverfly Partnership technique that provides a score based on the pollution tolerance of the bugs present plus abundance. We will use that method most of the time at electrofishing sites etc.
Whilst sorting the sample I spotted a small shrimp like bug that wasn’t familiar. I checked this one under the microscope and I’m confident it was Crangonyx pseudogracilis see http://www.brc.ac.uk/gbnn_admin/index.php?q=node/326. This is considered a non-native although now widespread in the UK. The SEPA invertebrate data I have access too shows they had recorded it twice before on the Spey, once near Fochabers and at Kingussie, so it looks well spread out in the Spey. No Killer Shrimp thankfully!
By the end of play tomorrow I should have the samples sorted and part identified, I’ll post the results next week. It will be interesting for me to compare the results from the different habitat types.