Disentangling individual movement between populations from effective dispersal in the facultative anadromous Salmo trutta L.

Abstract

Gathering information on both individual movement and gene flow is rarely possible when studying dispersal among populations in fish species. It is, however, possible to assess both at a reasonable cost in Salmo trutta L. on the Atlantic coast of Europe where the facultative anadromous species is composed of discrete populations of brown trout residents occupying distinct river systems, but exchanging phenotypically distinguishable sea trout migrants. We performed two kinds of genetic analyses using individual microsatellite genotypes: the stock identification of sea trout entering each corridor and the estimates of effective dispersal through each corridor. We observed that individual movement (nonlocal individuals of each source population ranging from 4% to 35% of the sea trout run) never translates into effective dispersal except in one of four migratory corridors examined. The likely origin of this uniquely detected gene flow event is discussed in the light of well-documented migratory fish management actions undertaken in the past in the studied area. K E Y W O R D Sbrown trout, effective dispersal, homing, sea trout, straying

Water level influences migratory patterns of anadromous brown trout in small streams

“…Furthermore, the effective straying rate may not be higher than 1%-3% per generation to explain the genetic differentiation that exists among anadromous trout populations in the North Sea area (Ferguson, 2006;Knutsen et al, 2001;Masson et al, 2018). Sea lice appear not to be problematic for trout from the present systems.…”

“…However, runs of that size appear adequate to maintain viable populations of anadromous brown trout, as reported by Thomson and Lyndon (2018) from the Orkney, UK. Anadromous trout sometimes visit lower parts of rivers other than their home stream (Euzenat, 1999;Jensen et al, 2015;King et al, 2016;Masson et al, 2018;Solomon, 2006). The effective straying rate, however, may be low as immature first-time migrants tend to enter other streams more often than the mature veteran migrants do.…”

“…Trout that enter streams outside the regular upstream migration period from late September to early November, may have returned to freshwater to feed, avoid osmotic stress, find shelter or get rid of marine ectoparasites, such as sea lice (Lepeophtheirus salmonis) (Wells et al, 2006). Anadromous trout sometimes visit lower parts of rivers other than their home stream (Euzenat, 1999;Jensen et al, 2015;King et al, 2016;Masson et al, 2018;Solomon, 2006).…”

“…Degerman et al (2012) reported straying rates between 3% and 43% among Swedish populations of anadromous brown trout, with 16% as the average figure, but few of the strays may actually leave offspring (Masson, Lepais, Manicki, Prévost, & Chat, 2018). Degerman et al (2012) reported straying rates between 3% and 43% among Swedish populations of anadromous brown trout, with 16% as the average figure, but few of the strays may actually leave offspring (Masson, Lepais, Manicki, Prévost, & Chat, 2018).…”

“…Like other migratory salmonids, anadromous brown trout tend to return to their home stream for spawning, but a variable proportion, called strays, reproduce in foreign rivers. Degerman et al (2012) reported straying rates between 3% and 43% among Swedish populations of anadromous brown trout, with 16% as the average figure, but few of the strays may actually leave offspring (Masson, Lepais, Manicki, Prévost, & Chat, 2018). The variable proportion may be associated with varying migration routes, migration timing and possibly varying accessibility of the home stream (Jensen, Diserud, Finstad, Fiske, & Rikardsen, 2015).…”