Production of juvenile salmonids in small Norwegian streams is affected by agricultural land use

• 1. We estimated the biomass and production of juvenile anadromous brown trout (Salmotrutta) and Atlantic salmon (Salmo salar) (parr) in 12 streams in the Skagerrak area ofNorway to identify controlling environmental factors, such as land-use and waterchemistry.2. Production estimates correlated positively with fish density in early summer, but notwith the size of the catchment. The summer biomass of age-0 brown trout and Atlanticsalmon was smaller than that of age-1 and constituted 27.4 and 25.7%, respectively, of thetotal biomass of the two groups.3. Mean production of brown trout from July to September varied between streams, but inmost cases it was below 2 g 100 m)2 day)1. Yearly cohort production from age-0 in July toage-1 in July was 10 g m)2 or less, with mean annual production of 1.32 g 100 m)2 day)1,equivalent to 4.8 g m)2 year)1. The corresponding annual cohort production of Atlanticsalmon was 0.38 g 100 m)2 day)1 or 1.4 g m)2 year)1. Annual production to biomass ratio(P⁄B) for brown trout of the same cohort in the various streams was between 1.47 and 4.37;the overall mean (±SD) for all streams was 2.25 ± 0.94. Mean turnover rate of Atlanticsalmon was 2.73 ± 0.24.4. Production of 0+ brown trout during the summer correlated significantly with thepercentage of agricultural land and forest⁄bogs in the catchment, with maxima at 20 and75%, respectively. Age-0 brown trout production also correlated with concentration ofnitrogen and calcium in the water, with maxima at 2.4 and 14 mg L)1, respectively.5. The results support the hypothesis that brown trout parr production reflects the qualityof their habitat, as indicated by the dome-shaped relationship between percentage ofagricultural land and the concentration of nitrogen and calcium in the water.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

biomass

nitrogen

parr

Salmo salar

Salmo trutta

turnover rate

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)