Discharge can directly or indirectly regulate the quality and quantity of habitat available for aquatic species, including socio-economically important species, such as Atlantic salmon ( Salmo salar L., hereafter salmon) and trout ( S almo trutta L.) (Pennell & Prouzet, 2009), and thereby their distributions and abundances (Bunn & Arthington, 2002). Inter-annual variation in discharge is essential for maintaining the structure, function and ecological integrity of rivers (Poff et al., 1997). Therefore, a strategic review of juvenile salmonid monitoring programmes integrating environmental data collection is recommended.įreshwater discharge is a “master variable” in rivers (sensu Power, Sun, Parker, Dietrich, & Wootton, 1995) that influences many environmental factors, such as geomorphology, sediment delivery, water temperature and dissolved oxygen (Arthington, 2012). However, overall, only equivocal evidence was found regarding which discharge aspects affect juvenile salmonid densities. High discharges might increase spawning site availability for salmon and decrease egg-to-fry survival for trout. More frequent high discharges between spawning and emergence were positively and negatively associated with 0+ salmon and trout densities, respectively. All hydrological variables had weak associations with 0+ salmonid densities. Associations between these densities and nine hydrological variables representing the magnitude, frequency and duration of discharge events were evaluated using historical monitoring data from 36 sites on five rivers in England and Wales.
This study developed Bayesian hierarchical mixed-effects models relating 0+ Atlantic salmon ( Salmo salar L.) and trout ( S almo trutta L.) densities to different aspects of river discharge.
Understanding salmonid discharge requirements can help inform management to conserve wild populations in a changing climate.
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