Implications of modifying the current WFD1112a passability assessment protocol to adopt an automated version based on the French ICE protocol (Baudoin etal., 2015)

Abstract

This document describes proposed modifications to the current WFD111 2a “Rapid assessment method for assessing riverine barriers to fish passage”, informed by feedback from users and instructed by the modelling of fish swimming performance and methodology proposed by the ONEMA ICE protocol ((Baudoin etal, 2015). The field surveying approach to the assessment of various passage routes for fish across structures, and the collection of data remains largely unchanged from version 1, but version 2 is now presented in a user-friendly Excel formatted spreadsheet, where guidance is provided, and users enter measurements and complete the relevant fields. Passability scores (0, 0.3, 0.6, 1.0) are produced for a number of elements for each structure, or section of structure being assessed, and presented in a set of final tables for inclusion into output reports. In version 2 the “Salmon” and “trout” groups have been split to accommodate a wider range in body length and swimming abilities. Three groupings for salmonids are now included: “large” body length individuals (MSW salmon or ferox trout: > 60cm body length) , “migratory trout/ grilse” (adult sea trout and grilse : 30-60cm body length) and “small resident brown trout” (< 30cm body length) . The thresholds for swimming, water depth and jumping ability are presented for the mean body size of an individual within each group. The “lamprey” group has been split to represent “Sea lamprey” and “River lamprey” groups. The “cyprinid”, “juvenile salmonid” and “juvenile lamprey” groups have all been removed as they were considered to be of limited value. In order to account for the capacity for some species to produce very high short burst swimming speeds, and the re-grouping of fish size categories, modified thresholds for swimming speed are presented in version 2. These thresholds are applicable to the feature being assessed and species and mean size of fish in a category, and are evidenced by the extensive modelling results provided in the ONEMA ICE protocol (Baudoin et al, 2015). The limiting water depth in the current WFD 111 2a methodology was produced using a combination of initial literature evidence and expert judgement. In version 2 minimum water depth thresholds for swimming have been modified with a water depth > 1.5x the mean body depth of the fish in each category being adopted as optimal. This value is proposed as the absolute limiting threshold depth in the ONEMA ICE protocol (Baudoin etal, 2015) and all water depths shallower than this will result in complete blockage to fish passage. In version 2 this absolute threshold approach towards water depth is not utilised. As recorded water depth reduces incrementally below this optimal value, the associated passability scores are reduced to reflect that some fish are still able to swim through water depths that expose a section of their caudal fin (Clough & Turnpenny, 2001), even if swimming performance is not always optimised. The vertical leaping height thresholds applied in the current WFD 111 2a methodology are conservative, with the height of 1.4m given as the maximum jumping height for adult Atlantic salmon and 1.0m for adult trout. The ONEMA ICE protocol (Baudouin etal., 2015) provides values for vertical jumping height calculated using the equations of Videler (1993) and incorporating modelled maximum burst swimming speeds for fish of certain lengths. These values are higher than those used in the WFD 111 2a method, with adult salmon upper jumping limit being > 2.5m, and large trout / grilse upper jumping limit being > 2.0m.