Counting fish at night using artificial light: transect survey of common bream Abramis brama and northern pike Esox lucius abundance as an example.

Visual transect counting of large-bodied fish using artificial light at night in a shallow littoral zone (<1 m water depth) is introduced as a complementary survey method for fishes such as common bream Abramis brama and northern pike Esox lucius that are under-represented in standard gillnet surveys. The results suggest that transect counting at night and applying necessary corrections for environmental variables could provide a simple and repeatable method to assess the presence and abundance of large-bodied fishes in lakes with satisfactory water clarity.

Seasonal acclimation of the moss Polytrichum juniperinum Hedw. to natural and enhanced ultraviolet radiation.

Short- and long-term changes in the methanol-extractable UV-absorbing compounds and biomass of the pioneer moss Polytrichum juniperinum in response to natural and enhanced UV radiation were studied. Under natural conditions, the compounds were found to fluctuate seasonally. In summer these compounds correlated negatively with irradiation.

Environmental specimen bank samples of Pleurozium schreberi and Hylocomium splendens as indicators of the radiation environment at the surface.

Pleurozium schreberi (Brid.) Mitt. and Hylocomium splendens (Hedw.

UV-absorbing compounds in subarctic herbarium bryophytes.

The UV-B-absorbing compounds of herbarium specimens of 10 subarctic bryophyte species collected during the years 1926-1996 and available at the Botanical Museum, University of Oulu, were studied. We studied whether herbarium specimens reflect changes in the past radiation climate through their methanol-extractable compounds. The order of gametophytes based on the average amount of total compounds (sum of A280-320 nm) per mass from the lowest to the highest was Polytrichum commune, Pleurozium schreberi, Hylocomium splendens, Sphagnum angustifolium, Dicranum scoparium, Funaria hygrometrica, Sphagnum fuscum, Sphagnum warnstorfii, Sphagnum capillifolium and Polytrichastrum alpinum, and the amount of UV-B-absorbing compounds per specific surface area correlated with the summertime daily global radiation and latitude.