A long-term study of the impact of the invasive species Eurasian minnow Phoxinus phoxinus on brown trout Salmo trutta production in a high mountain lake, Southern Norway

2024-03-11T21:23:47+00:00

The shallow Lake Skjerja was originally one of the most outstanding brown trout lakes on the Hardangervidda mountain plateau. During the period 1973–1985, the annual yield was on average 3.35 kg ha^-1. In the mid-1980s, Eurasian minnow established a dense population in the lake. Since 1994, 5304 kg of Eurasian minnow have been removed with baited traps, which correspond to an annual mean catch of 177 kg year^-1 or 1.12 kg ha^-1. The competition for food, in addition to longer food chains, has had a strong negative impact on the brown trout production, with an annual yield reduced to 1.07 kg ha^-1, or 32% of the historical catches (1973-1985). The total removed biomass of the two fish species correspond to 65% of the brown trout yield before the invasion of the Eurasian minnow. In Lake Skjerja, the two crustacean species Gammarus lacustris and Lepidurus arcticus, have historically been staple food items for brown trout. Fishing with baited traps on the minnows, and the presence of a large fraction of predatory brown trout, may have reduced the predation pressure on the two crustacean species, and they are still a part of
the brown trout diet. The availability of fish as food has resulted in a significant increase in the presence of large individuals of brown trout with maximum weights above four kg. Despite reduced annual yield of brown trout, Lake Skjerja is still a popular fish destination with nearly 200 big-sized brown trout (mean annual weight 1065 grams) landed annually. On Hardangervidda, an increase in air temperature has been observed since the 1980s, with a corresponding change in water temperature which may benefit Eurasian minnow. In warm summers, water temperature approaches 14°C which has proved to be near to the upper thermal threshold for Lepidurus arcticus.

Brachiopods of the northern North Atlantic and Arctic, with a focus on Norwegian fauna

2023-12-07T07:11:38+00:00

Ten species of Brachiopoda have been found living around Norway, including the Arctic Svalbard and Jan Mayen, while 26 are recorded here for the region extending from the Arctic Ocean in the North to the northernmost North Atlantic and Celtic Sea in the South. This paper provides an identification key and short descriptions for all species, including the new species Xenobrochus islandicus n. sp. from southwest of Iceland and the new East Atlantic species Dallina lusitanica n. sp. The distributions of all species have been reviewed and were generally found to follow the oceanic temperature, salinity and depth gradients of the region. Also organic enrichment had some influence on distribution. Some species have shown a possible ongoing northward shift of their biogeographic boundaries over the last two centuries, including the Arctic to subarctic species Hemithiris psittacea.

Fauna norvegica

A long-term study of the impact of the invasive species Eurasian minnow Phoxinus phoxinus on brown trout Salmo trutta production in a high mountain lake, Southern Norway

Brachiopods of the northern North Atlantic and Arctic, with a focus on Norwegian fauna