Each year perform our timed electrofishing surveys during the same weeks each season. Timed surveys enable us to rapidly assess spawning success and survival from the previous winter’s salmon spawning activity. These are salmon fry surveys and while we catch other year classes and species, it is 0+ year class of salmon that we focus on and there’s a mixture of habitat assessed raging from optimal to sub optimal. It is not a case of cherry picking the best sites but rather assessing productivity across all habitats. On each of the 4 DSFB controlled rivers in Ayrshire we visit the same sites each year and electrofish for 5 minutes across the same habitat. What that means is 5 minutes of passing electricity through the water with fish handling and processing additional to the time spent actually fishing. That allows us to compare results from previous years with the current year.
Struan and Cameron counting and recording the catch
Timed surveys are the least accurate survey methods we use but being a rapid assessment, they allow us to cover the catchments quickly and generally where we see one river performs well, more often than not, all the rivers perform well and vice a versa. Of course that doesn’t always hold true as each river is different with their own unique salmon populations and therefore they may be subject to localised influences that affect fish production and spawning survival such as weather, pollution and levels of predation, but more often than not, they perform similarly although they can’t be compared directly as the habitat is distinct and unique. We can also therefore assume that external influence often play a part in the results we achieve such as marine survival as our river’s juvenile salmon populations very often rise and fall in unison. It should go without saying that all the fish we catch are returned unharmed to the river after we have recorded and measured them.
We record and measure eels too as they are another species currently in critical decline
This season we are well underway with these surveys and the Ayr and Lugar’s are complete. The Doon has one site to finish and the Girvan is half done. Tomorrow should see the Girvan finished and the team will move onto the Stinchar afterwards. By Friday evening, all timed surveys should be finished. I’ll hold off from giving any details of our results this year until the full suite of surveys are compiled and analysed but we we are always keen to share some information as it can be encouraging to anglers and anyone interested to see that we still have our share of juvenile trout and salmon stocks and other species too; often contrary to what some fishermen may say.
Trout and salmon parr captured during one of the timed surveys
Next week, we continue with more detailed surveys techniques in areas where we have questions to answer or lack data. Semi quantitative or fully quantitative surveys are used and these allow us to calculate densities within fished areas. Using electrofishing techniques we can identify bottlenecks and barriers to migration, not just for salmon and trout but eels and lamprey too as their distribution can be severely limited by obstacles.
Watch this space for an update on results and findings coming next week.
