Temporal and environmental influences on the variation in Atlantic salmon smolt migration in the Burrishoole system 1970–2000

Abstract

The relationships between a number of environmental variables and the number of Atlantic salmon Salmo salar smolts migrating in the Burrishoole system, western Ireland, were examined over a 30 year period from 1970 to 2000. The number of Atlantic salmon smolts recorded migrating downstream decreased significantly from an annual mean of 11 579 in the 1970s to a mean of 6272 in the 1990s. The primary factor in the decline in Atlantic salmon numbers was a consistent decline in the number of returning adults from the 1970s until the mid 1990s. Timing of the smolt migrations (runs) was consistent throughout the three decades. The mean durations of the smolt runs were 102Á1, 92Á6 and 103Á2 days for the 1970s, 1980s and 1990s respectively. Mean surface water temperatures at key points in the smolt run for the three decades were also similar. Mean water temperature values were 5Á4, 5Á1 and 5Á3 C at the start of the smolt runs and 15Á2, 14Á9 and 15Á3 C at the end of the smolt runs in the 1970s, 1980s and 1990s respectively. Multivariate analysis identified two groups of environmental variables which had a significant influence on the daily smolt catch. One group of variables dominated by photoperiod and temperature operated prior to the smolt run and was considered to regulate the development of smoltification. The second group of variables dominated by total light and water level operated within the smolt run and was considered to control daily smolt migration.

Adult recaptures of farmed Atlantic salmon post-smolts allowed to escape during summer

“…In the Burrishole system in western Ireland, the majority of the smolts leave the river within a period of 4 wk from April to June (Byrne et al 2003). Furthermore, the time of smolt entrance into the sea is up to 6 wk later in northern than southern Norwegian rivers (Hvidsten et al 1998), and high returns of wild smolts that migrated in early August have been observed in cold rivers in the north of Iceland (Antonsson & Gudjonsson 2002).…”

“…The onset of migratory behaviour in wild fish is typically timed with the season and/or some physiological factor that triggers migration to feeding or spawning grounds (Smith 1985). Wild smolts in western Europe usually leave rivers in spring and early summer (Hvidsten et al 1998, Byrne et al 2003). The recapture rates of adults released as smolts and post-smolts have been in accordance with the timing of the migration of wild smolts to the open sea.…”

Links between patterns of marine growth and survival of Atlantic salmon Salmo salar, L.

“…Scales from one sea winter (1SW) Atlantic salmon were sampled from fish returning to the Burrishoole catchment, in western Ireland. Migration movements in fresh water for this population are entirely monitored by permanent upstream and downstream trapping facilities (Byrne et al , 2003). The upstream traps are also used to capture returning fish that have previously been released as smolts from the local hatchery.…”

Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions

“…The experiment was undertaken in the Burrishoole system, which is situated in County Mayo on Ireland's western sea board (McGinnity et al ., 1997, 2003; Byrne et al ., 2003). This system consists of a freshwater lake (Lough Feeagh) and a number of afferent rivers (Fig.…”