Drift diving: A quick and accurate method for assessment of anadromous salmonid spawning populations

The accuracy of drift diving surveys of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L., was evaluated by comparing the abundance and size distribution with catches in a fish trap over 6 years in the River Etneelva, western Norway. The population count from drift diving accounted for on average 96.3% of the salmon in the trap after accounting for the catches during fishing. Size structure registered during drift diving corresponded with trap catches of salmon, but the number of small salmon (<3 kg) appeared to be somewhat underestimated, while large salmon (>7 kg) were overestimated in drift diving. For sea trout, the match between drift diving counts and trap registrations was poorer (average 76.3%), but may have been affected by the surveys being performed too late with regards to sea trout spawning time. The study illustrates the utility of drift counting for estimating the entire population of anadromous salmonids in a river.     

Morphological and genetic comparison between naturally produced smolts of Atlantic salmon,brown trout and their hybrids

Morphological characters were compared between smolts (standard length 110–220 mm) of Atlantic salmon Salmo salar L., anadromous brown trout Salmo trutta L. and their hybrids captured in River Driva, western Norway. Morphological discrimination between S. salar, S. trutta and their hybrids was correct for 93% of the individuals (correct form was determined genetically). Morphological discrimination of hybrids was incorrect with 9.1% (n = 7) classified as S. salar and 1.3% (n = 1) as S. trutta, suggesting that the hybrids were morphologically more similar to S. salar than S. trutta despite a bias towards S. trutta mothers (7 of 8 cases). The largest morphological differences were found in head (notably maxilla length) and caudal peduncle morphology. Hybrids between S. salar and S. trutta had the longest pectoral and pelvic fins. This indicates that precise discrimination based on morphological traits can be made between S. salar, S. trutta and their hybrids.     

Microsatellite analysis in domesticated and wild Atlantic salmon (Salmo salar L.): allelic diversity and identification of individuals

Samples of wild and domesticated salmon in Norway were genotyped at 12 microsatellite loci to compare allelic variability and investigate the potential of microsatellite markers for identification of individuals. The following loci were amplified: Ssa20, Ssa62NVH, Ssa71NVH, Ssa90NVH, Ssa103NVH, Ssa105NVH, SsaF43; Ssa20.19; Ssa13.37; SsOSL85; Ssa197; Ssa28. All domesticated strain samples displayed reduced variability compared to wild salmon. On average 58% of the allelic richness observed within the four wild stocks were present in the samples taken from domesticated strains. No systematic differences in heterozygosity were observed between samples representing the two groups.

Pairwise genetic distances, as estimated by Fst values and Nei [1978] was 2–8 times higher among domesticated strains than among wild strains. Among the wild stocks, the highest genetic distances were observed between the river Neiden, located in northern Norway, and the other wild stocks located in the southwest of Norway.

Assignment tests indicated that the wild and domesticated salmon could be distinguished with high precision. Less than 4% of domesticated salmon were misassigned as wild salmon, and less than 3% of wild fish were misassigned as domesticated salmon. Fish from individual domesticated strains were identified with similarly high precision. Assignment to wild salmon stocks was less accurate, with the exception of the sample taken from the river Neiden, for which 93% of the individuals were correctly assigned.