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Gillnet test fishing and radiocaesium (Cs-137) of brown trout (Salmo trutta) and Arctic char (Salvelinus aplinus) 2008 and 2009 from 20 Central Scandinavian lakes: Occurrences


Brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) were sampled in 20 lakes located along an altitudinal gradient (36 - 850 m.a.s.l.) in central Scandinavia. 10 of these lakes where trout only populations (allopatric) and in 10 trout and char co-existed. In addition, Three spined stickleback (Gasterosteus aculeatus L.) and European eel (Anguilla Anguilla L) co-occurs in most lakes below the marine transgression line. However, these species where not collected using the present gill-net series. Also, two of the lakes (Slipstikken and Grisbakktjørna) had a scares population of burbot (Lota lota L.) (catch of burbot not recorded). The sympatric lakes, with the exception of Kjerråtjønnin were sampled three times (spring 2008 – autumn 2008 – spring 2009), and the allopatric lakes were sampled two times (autumn 2008 – spring 2009). Autumn samples were collected just before ice formation and spring samples in 2008 somewhat after and 2009 just after ice breakup. At each sampling period fish were sampled with bottom gill nets (1.5 m x 25 m) with bar mesh sizes of 12.5 – 16 – 19.5 - 24 – 29 – 35 mm. Three and three nets were linked together making chains with alternating mesh sizes in order to represent all mesh sizes at different depths in each lake at each sampling period. Depths were measured at the start and end of each net. The gillnet chains were set perpendicular to the shore in the evening and hauled the next morning. The fish were frozen in plastic bags and stored at -25 °C. In the laboratory, wet mass (precision 0.1 g), fork length (precision 1 mm), sex, parasite load and maturation stage (Dahl 1917) were determined. Scale (trout) and otolith (char) samples were taken and used for age determination. In a subsample of the fish the contents of the oesophagus and the stomach were identified to various taxonomic levels and grouped into seven categories: surface insects, chironomidae, mollusca, benthic insects, benthic crustaceans, zooplankton and fish. Stomach contents and each individual fish were dried, and homogenized before quantifying 137Cs by gamma counting the samples in an integral, well-type, NaI-scintillation detector (LKBWallac Compugamma). Due to current restrictions with the DwC-A format, data and associated measurements on individual fish ((this dataset) is published separately from gill-net events and associated measurements. This dataset gives occurrence part of the dataset. Data on gill-net sampling, effort and temperature recordings are given in a separate dataset ("Gillnet test fishing and radiocaesium (Cs-137) of brown trout (Salmo trutta) and Arctic char (Salvelinus aplinus) 2008 and 2009 from 20 Central Scandinavian lakes: Events" (UUID: a6cc334b-036a-43d0-ae68-3f84a08e8d97, Alternative Identifier: http://gbif.vm.ntnu.no/ipt/resource?r=gillnet_fishing_from_20_central_scandinavian_lakes_events)