Scottish Marine and Freshwater Science Vol 7 No 30
Salmon fry densities on the river Dee were estimated from juvenile electrofishing data using a capture probability model initially developed in 2015. The resulting density estimates were compared to two potential reference levels that also varied by habitat; (1) a mean National Reference, and (2) a Dee Reference. Despite the limitations of the current approach, it provides useful insights into status of salmon on the River Dee and with future developments will offer a useful assessment to complement those based on adult returns.
Data and Resources
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2015-01-01 to 2016-12-01
UK Open Government Licence (OGL)
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The biological reality of the different reference levels was assessed by determining whether observed fry densities were above or below the reference levels in the Girnock Burn for each year between 2001 and 2016 and comparing this to an independent measure of catchment health (Smax: that indicates whether maximum emigrant production is likely to be sustained) obtained from stock-recruitment data. The local Dee Reference was found to be in greater agreement with assessment made using Smax than the National Reference which was considerably too low for the Girnock Burn. When salmon fry densities across the whole Dee catchment were compared to the Dee Reference, it was found that the catchment was close to maintaining maximum production in 2012 (a high spawner return year), but considerably below reference in 2016. A number of limitations of the current data, models and monitoring are identified and discussed alongside future developments and directions.
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Marine Scotland Science
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