4. River fish
We are proposing to revise the river fish classification system for Scotland by changing the method by which results are aggregated at the waterbody level. Further technical details about changes to the assessment method are available from UKTAG.
The current tool for classifying river fish in Scotland for River Basin Management Planning is FCS2 (Scotland). The tool relates the number of salmon and trout caught in a survey to the predicted abundance and prevalence of the species at the specific site. For multiple sites within a single waterbody, it currently calculates status class using a Bayesian statistical approach implemented using specially developed software. The method is described in detail in the UKTAG method statement produced for the second RBMP.
For multiple sites within a single waterbody we propose applying a simple arithmetic mean to amalgamate individual results provided by the FCS2 (Scotland) tool, rather than using the current approach. This will provide a clearer reflection of the overall ecological quality across multiple sites.
Implications of the proposal
Based on an assessment of 517 waterbodies, which have multiple sites available, Table 4.1 summarises the effect on river fish classification.
|Class||Existing assessment method||New proposed assessment method||Net change|
Using the new proposed assessment method 85 waterbodies would be downgraded in river fish classification, while 43 waterbodies would be upgraded.
Out of the 85 instances in total where the fish status would drop in class only 21 of these would result in the overall waterbody lowering in status to below good; whereas out of the 43 waterbodies upgraded in river fish class only 3 would result in the overall waterbody status being raised to good status or better.
For those 21 waterbodies which would be newly downgraded to below good more evidence would be needed on the underlying causes of these impacts before determining whether any regulatory action is appropriate.