Effects of sea trout stocking on the population genetics of landlocked brown trout, Salmo trutta L., in the Conwy River system, North Wales, U.K.

Abstract

The effect of the introduction of fry of anadromous sea trout, Sulmo rrurta L., on the genetic integrity of landlocked brown trout populations was evaluated. Samples were taken from six brown trout populations from streams above impassable waterfalls in the Conwy river system (North Wales, U.K.) in 1989 and 1990. Three ofthese streams had no known stocking history and three had been stocked with sea trout fry from the lower Conwy system over the last few years. Representatives of these sea trout were collected from two streams in the lower Conwy system and from a hatchery. Allele frequencies at 13 loci, six ofwhich were polymorphic, were determined by starch gel electrophoresis.The stocked populations were intermediate in their allele frequencies between unstocked brown trout and sea trout samples. A principal component analysis suggested significant numbers of hybrids in all of the stocked streams. This shows that some of the introduced sea trout did not migrate down the falls to the sea, but stayed in fresh water and hybridized with the local population. The significance of this finding for the conservation of the genetic resource of brown trout stocks is discussed.

Allozyme variability of brown trout (Salmo trutta L.) populations across the Rhenanian–Danubian watershed in southwest Germany

“…There are no populations left for which stocking in the past or immigration by released fish can be totally excluded. Our results indicate genetic introgression of hatchery brown trout into natural populations which also has been reported from France (Barbat-Leterrier et al, 1989), Ireland (Taggart & Ferguson, 1986) and Britain (Hauser et a!., 1991). The intensively stocked populations clearly exhibited elevated genetic variability within the populations which is in accordance with expectations based on the varied origin of the hatchery stocks.…”

Origins and relationships of native populations of Salmo trutta (brown trout) in Spain

“…The 'Atlantic' subdivision is proposed to extend to unglaciated areas of the southern British Isles and Brittany based on the predominance of the CKA1*115 allele and the LDHC*1OO allele (the marker allele of the 'ancestral race') reported in unstocked populations in these areas (Krieg & Guyomard, 1985;Hauser et at., 1991). The 'Mediterranean' subdivision is proposed to extend eastward through the Black and Caspian Seas based on the predominance of CKA1*1OO and LDHC*1OO throughout this area (Krieg & Guyomard, 1985;Osinov, 1988;Barbat-Leterrier et a!., 1989;Karakousis & Triantaphyllidis, 1990).…”

Can the lost migratory Salmo trutta stocks be compensated with resident trout stocks in coastal rivers?

“…In a new environment, the stocks follow their inherited migration pattern in migration distance and direction (Jonsson, 1982;Jonsson et al, 1994;Brannon, 1984;Hansen et al, 1993;Kallio-Nyberg et al, 2000). There are, however, cases where a resident stock has evolved from an anadromous one when the barriers in a stream have prevented the feeding migration (Hindar et al, 1991;Hauser et al, 1991). Skrochowska (1969) observed that a resident type may evolve from an anadromous type, and vice versa.…”