Today we surveyed a lot of sites in the Back Burn in Rothes. The Back Burn is a tributary of the Rothes Burn and was subject to considerable engineering works as part of the flood alleviation programme. Sites were surveyed from the confluence with the Rothes Burn for over 1km upstream. The first site set the scene with high numbers of salmon and trout fry. In a site measuring 20m2 we captured 63 salmon fry and 1 parr with 21 trout fry and 1parr, as well as 3 eels.
Salmon numbers declined as we went upstream but the trout were very consistent averaging 28 in each of the small sites surveyed.
The fry were large in the lower two sites, much larger than we had seen at other sites surveyed so far this summer, however the reason was soon apparent. The water temperature in the lower site was 13+oC, whilst at the third site upstream it was 11+oC, the difference was due to a discharge of what must be cooling water, it was over 21oC! Artificially high water temperatures such as these may enhance fish growth but a situation could easily arise in hot weather whereby lethal temperatures could occur resulting in a fish kill. However earlier studies by the Spey Foundation in the Fiddich, which is also affected by above normal water temperatures, found that juvenile fish growth was enhanced but the fish returned from the sea at expected times of year and sea ages.
When I compared the number of fish caught today with the previous study we found 7 times as many trout fry and 2.5 times the number of salmon fry, although our survey today was completed earlier in the year. In my experience not every year is a good year for trout spawning but I was impressed by the number of trout fry found today…. it didn’t look too bad for salmon either.