Effects of Sea-Ranching and Family Background on Fitness Traits in Brown Trout Salmo trutta Reared under Near-Natural Conditions

• Published in: The Journal of applied ecology 2003-04, Vol.40 (2), p.241-250
• Main Authors: Dannewitz, Johan, Petersson, Erik, Prestegaard, Tore, Järvi, Torbjörn
• Format: Article
• Language: English
• Subjects: Anadromous fishes; Applied ecology; domestication; Ecological genetics; Eggs; Fish; Freshwater fishes; growth; life histories; microsatellites; Salmo trutta; Salmon; Salmon smolt; salmonids; Special Profile: Current Issues with Fish and Fisheries; Streams; survival; Trout
• ISSN: 0021-8901; 1365-2664
• DOI: 10.1046/j.1365-2664.2003.00779.x

1. Many threatened populations of salmonids depend on supplemental releases of hatchery-produced fish. Laboratory studies suggest that altered selection regimes in the hatchery may result in evolutionary changes of traits connected to fitness. Such changes can have profound effects on the performance of the hatchery fish following release in the natural environment, and may also affect the genetic characteristics of locally adapted wild populations. However, surprisingly few studies have looked at the ability of hatchery fish to compete with wild conspecifics under natural conditions. 2. We studied growth, survival and life-history adoption of a wild and a multigeneration sea-ranched strain of brown trout Salmo trutta in a semi-natural stream. The fish were planted in the stream as eyed eggs and their family and strain origins were later revealed by microsatellite markers. 3. In the first experiment, in which the experimental fish originated from a full-sib mating design, there were strong family effects on both growth and survival over the first growth season. In the second experiment, in which the experimental fish originated from a half-sib mating design, there were significant male and female effects on growth parameters but not on survival over the first growth season. 4. When family and male-female effects were accounted for, there were no differences between wild and sea-ranched trout in body size and condition factor after the first growth season, or in survival up to this stage. Nor was there any difference between the groups in the proportions that metamorphosed into the migratory smolt phase at 1 year of age. 5. Synthesis and applications. Our results suggest that wild-born trout of sea-ranched origin can successfully compete with trout of wild origin under semi-natural conditions. This indicates that the impact of hatchery selection on the performance of sea-ranched fish in the wild may not be as pronounced as previously thought. It is suggested that for salmonid populations that depend on supplemental stocking, more effort should be paid to minimizing negative environmental effects during hatchery rearing. The observed differences in fitness characters between families suggest that family effects should be taken into account in stocking programmes because the amount of genetic variation maintained within populations is related to the variance in family performance.