Comparison of field- and GIS-based assessments of barriers to Atlantic salmon migration: a case study in the Nore Catchment, Republic of Ireland

Abstract

SummaryIn Ireland, the Water Framework Directive (WFD) Freshwater Morphology Programme of Measures and Standards (POMS) identified barriers to fish migration as one of the principal issues placing channels Ôat riskÕ in terms of failing to achieve hydromorphology status. To quantify the degree of risk posed, and to develop methods to appraise and quantify risk associated with barriers, the POMS undertook a pilot study on the River Nore catchment. This provided an opportunity to compare the outcomes of an intensive fieldbased qualitative assessment of barriers to fish migration with a rules-based appraisal of risk, based on layers of georeferenced data, in a Geographical Information System (GIS) analysis. The underlying aim of this risk-based assessment was the restoration of the fisheries resource, in the context of WFD, grounded on knowledge-based assessment. The comparison focused on the Atlantic salmon (Salmo salar L.). A rapid-assessment field survey compiled a geo-referenced inventory of 508 structures (497 artificial and 11 natural) and classified each with regard to presumed risk of preventing the upstream migration of adult Atlantic salmon. This inventory was then subjected to a rigorous GIS-based analysis, using field-generated datasets on Atlantic salmon ecology in the Nore catchment. The rules-based analysis provided a very substantial re-classification of artificial barriers with a major reduction in the numbers classified as impassable or high-risk. It confirmed that no Ôhigh riskÕ barriers to adult salmon occurred on the R. Nore main stem but identified clusters of high risk barriers in the Dinin subcatchment and a series of moderate risk obstructions in the KingÕs River system. The GIS-based approach enabled an examination of the costs and benefits of stepwise removal of barriers, in terms of additional wetted habitat and salmon spawning area made accessible upstream of each barrier. A multi-species approach was then explored, examining the risk to upstream passage for eel (Anguilla Anguilla L.), sea lamprey (Petromyzon marinus L.) and Twaite shad (Alosa fallax Lace´pede). Substantial clustering of sea lamprey spawning effort was reported downstream of the lowermost weirs on the R. Nore. A combination of barriers identified from a salmon perspective and via the multispecies approach provided a listing of priority barriers for attention. The strategy of step-wise removal or modification of artificial barriers in an upstream direction would provide optimal conservation value for the relevant species. The study identified the primacy of the field survey in geo-referencing site locations. However, it also identified the shortcomings of the qualitative, Ôexpert-judgementÕ approach to risk category allocation of the barriers and, hence, the need for more rigorous criteria in implementing a field-based rapid assessment.

An eDNA assay for Irish Petromyzon marinus and Salmo trutta and field validation in running water

“…Weirs can present a major barrier to P . marinus passage in Ireland (Gargan et al , ), therefore sampling both above and below the weir could provide useful information on the success of recent barrier mitigation measures, introduced at the Annacotty Weir in 2011 as part of the EU LIFE Nature project MulkearLIFE (http://www.mulkearlife.com). Two locations in the river were each sampled eight times between 13 May and 11 July 2013.…”

A toolkit for optimizing fish passage barrier mitigation actions

“…A large number of barrier passability assessment methods have been developed (Taylor & Love 2003;WDFW 2009;Gargan et al 2011). Despite the varied impact that structures can have on different fish (Ovidio & Philippart 2002;MacPherson, Sullivan & Foote 2012), few methodologies account for multiple species and structure types and even fewer consider downstream movements (Kemp & O'Hanley 2010).…”

The value of a desk study for building a national river obstacle inventory

“…Physical obstacles to fish migration were recorded during the bankside surveys of the Nore and Dodder catchments, mentioned above. The River Nore was walked in winter 2007–2008 by Inland Fisheries Ireland (Gargan et al, ). The Dodder catchment was walked in summer 2016 by the research team in University College Dublin.…”

“…Surveys and field dataPhysical obstacles to fish migration were recorded during the bankside surveys of the Nore and Dodder catchments, mentioned above. TheRiver Nore was walked in winter 2007-2008 by Inland FisheriesIreland(Gargan et al, 2011). The Dodder catchment was walked in summer 2016 by the research team in University College Dublin.Obstacles recorded included any physical structures in the river channel that the field surveyors judged to have the capacity to prevent or delay the upstream movement of fish, including Atlantic…”