Post by fishdee on Nov 21, 2009 8:46:10 GMT
A Fine day Redd counting
Assembled prior to commencing Redd count survey
It was a crisp cold morning when Ed, Mark, Danny and I met at the Dinnet office to go on a Redd count in the upper Dee catchment. A Redd is a “nest” that a female salmon excavates to deposit her eggs that are fertilised at the moment of release by a male salmon. The female then swims slightly upstream and turns on her side and beats gravel and stones, which are carried by the current and cover the newly fertilised eggs. This is the culmination of its life journey that has taken the salmon from that area where it was born 5 years earlier, on an epic migration to the seas off the Faeroes, or perhaps even further to the west coast of Greenland to feed and grow. It then is seized by an instinct to return to the river of its birth to produce another generation of offspring. The journey back to the river is something that salmon must do as they cannot spawn in salt water.
Lochnagar bathed in early morning sunlight
We travelled to an upper tributary of the River Dee and arranged to cover 15 kilometres of water and record salmon redds that were identifiable. We split into teams of two and left vehicles at the middle and lower points of the survey areas. We set off on our surveys walking carefully along wild riverbanks where there were no paths with the ground conditions being very frosty. There had been a very hard frost over night bringing temperatures down to -8 degrees providing glorious views but tricky walking conditions. There were tremendous numbers of Red Deer grazing on the hill sides with the good numbers of Buzzards, Grouse and Dippers. There had been recent high water that left a debris line some 5 foot above the river level. This recent high flow would have levelled out a good number of redds as you normally want to see a depression excavated with a mound of gravel just behind it. There have been 2 periods of really high water levels in the last month.
The frost lingers in areas untouched by warm sunlight
In a tributary with a width of 10 metres you would want to see 2 redds per kilometre of river length, which will give a minimum fry density to sustain a natural population for that area. The more redds there are provides a higher density of fry, with a greater increase in competition for food ensuring only the strongest survive. The returning salmon are highly selective in choosing the gravels that they will spawn in, where the gravel and water flow have to provide optimum conditions for this process. If the gravel is too firm or too loose to use then the fish will not utilise this. There whole life culminates in getting this process right and the salmon will spend a considerable period of time choosing the exact spot that will ensure the best survival of the fry produced. The area we were surveying had excellent nursery areas for the juvenile offspring with plenty of cover provided by rocks and stones. Over the fifteen kilometres we surveyed we counted 123 identifiable redds and we discounted others where we couldn’t guarantee 100 % that they were redds. This was a good count with ideal conditions for carrying out the survey. We also spotted 69 salmon in the river and 8 fish that had been taken by otters. The fish in the river were in excellent condition with very little Saprolegnia skin disease apparent, which in cold water conditions can be a common occurrence with salmon.
The survey being carried out
As we carried out the survey we were able to look out for signs of pollution, bank erosion and poaching activity which are all detrimental to the production of juvenile salmon. The river was in first class condition with no visible signs of any major problems to affect the salmon spawning in the survey area. The water was flowing crystal clear with the river bed in excellent condition showing no signs of pollution or silt that could harm the salmon redds. These surveys are carried out annually during the month of November when the spawning activity peaks in the upper catchment providing river levels are low enough to allow counts to be made accurately.
The midday sun bathing the valley
It was a very enjoyable survey in an excellent area for producing juvenile salmon. There were good numbers of salmon on the gravels with some ready to spawn and some really quite fresh and not ready to spawn.There was a good mix of sizes present from grilse to large MSW salmon. This is an important activity that is carried out throughout the whole catchment throughout November through December. This allows you to keep a record of findings on computer GIS software where you can see maps and the survey results highlighted on a year to years basis. All salmon and redds found are mapped out carefully to ensure you have an accurate picture of what is going on and monitor it properly on an annual basis.
