Glyphosate in fisheries management

Abstract

Glyphosate is the active ingredient of the broad-spectrum, translocated herbicide ‘Roundup’. Glyphosate is cleared for safe use in or near watercourses, being rated virtually non-toxic by the World Health Organisation. Trials in and alongside Irish fishery watercourses first commenced in 1989 and are continuing to date. The aim of this work is to evaluate the product’s efficacy in clearing nuisance ‘reed’ species in recreational fisheries. The longevity of control and impact on the habitat and its fauna is also investigated. Trials in canal fisheries have demonstrated the capacity of glyphosate to remove obstructive stands of reeds (mainly Schoenoplectus lacustris, Glyceria maxima, Phragmites australis, Sparganium erectum and Typha latifolia), so creating reed-free areas and swims for anglers. These swims remained open for three years following a single application. In 1992 a trial over a 3 km length of the River Boyne, a renowned salmonid fishery, was undertaken. The results clearly demonstrated the ability of glyphosate to provide long-term control of dense (354 shoots m⁻²) Schoenoplectus infestations in a large watercourse. In the year following, less than one shoot per m² was present in the channel. In 1994 a small increase in density (7.6 shoots m⁻² was recorded, so enabling unobstructed angling in a stretch of river that had been virtually unfishable for years. Trout (Salmo trutta L.) and salmon (Salmo salar L.) also used the newly exposed gravels for spawning in the winter of 1993, thereby improving fish recruitment and production in the fishery.