High mortality in introduced brown trout depressed potential gene flow to a wild population

• Published in: Journal of fish biology Vol. 61; no. 5; pp. 1085 - 1097
• Main Authors: Borgstrosm, R., Skaala, Ø., Aastveit, A. H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.11.2002; Blackwell
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; brown trout; Exploitation and management of natural biological resources (hunting, fishing and exploited populations survey, etc.); Fundamental and applied biological sciences. Psychology; gene flow; introductions; parr; survival; Norway; Europe; Salmonidae; Farming animal; Growth; parr; Anadromous species; Wild animal; Animal introduction; Survival; Young animal; Freshwater environment; Restocking; Vertebrata; Gene flow; Salmo trutta; Pisces; Stream; Intraspecific comparison; brown trout; introductions
• ISSN: 0022-1112; 1095-8649
• DOI: 10.1111/j.1095-8649.2002.tb02457.x

Hatchery reared 0+ year brown trout Salmo trutta, with 51 mm mean LT, were released in a sea trout stream in June 1991 to compare the survival of wild and introduced trout during the freshwater stage from age 0+ to 2+ years. The introduced brown trout were homozygous for a genetic marker, enabling released individuals and their offspring to be distinguished phenotypically from the local sea trout. The mean size of 0+ and 1+ year introduced parr was larger than 0+ and 1+ year wild parr, while 2+ year parr of both groups were of the same size. Half year survival rates of both introduced and wild parr increased with size up to c. 80 mm (1+ years), but then decreased, and could be described by a polynomial regression function, with the same shape for both groups. The introduced parr had, however, a significant lower survival rate than the wild parr. The number of the introduced cohort decreased from 2200 at release in 1991 to c. 20 in March 1994 (c. 1% of the original number). Between 1994 and 2000 no introduced individuals or offspring have been observed in the study area. High mortality at the parr stage and additional mortality until the spawning, give a low probability for a genetic impact on the local population as long as releases are restricted, both in time and number of fish.