The viability of the crustacean Eurycercus lamellatus (Branchiopoda, Cladocera) in a high mountain area in southern Norway

Abstract

The branchiopod Eurycercus lamellatus is widely distributed in Norwegian lakes, ranging from coastal to alpine areas. On the Hardangervidda mountain plateau in southern Norway, E. lamellatus was searched for in 144 lakes in 11 catchments in the western and 16 catchments in the central and eastern areas. Their occurrence is mainly based on the diet of brown trout Salmo trutta. Eurycercus lamellatus was recorded in 25% and 70% of the lakes in these two areas, respectively. This may be due to striking differences in the environmental conditions, with more dilute water and lower water temperatures in western areas, and hence shorter growing seasons. The occurrence of E. lamellatus in central and eastern catchments increased with lake size, being found in 65% and 85% of lakes with a surface area of <2.0 and ≥2.0 km2, respectively. In the western area, E. lamellatus occurred less frequently in lakes above 1000 m a.s.l. That was not the case for lakes in central and eastern catchments. In this central part of Hardangervidda, the relative abundance of E. lamellatus in the diet of brown trout was obtained from five different lakes, showing that they were preyed upon throughout the growing season (June to October). When the two big crustaceans Gammarus lacustris and Lepidurus arcticus are at low densities in these lakes, E. lamellatus became the staple food item for brown trout, except for larger fish (>400 mm). However, under high predation pressure, E. lamellatus also contributed significantly to the diet of larger fish. The abundance of E. lamellatus seems to vary highly on a yearly basis in one of the lakes (Sandvatn). Even though E. lamellatus is described as a typical littoral species, it was common down to depths of 15 m.

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

“…Some of the surveys contain population characteristic analyses of the population. The individual growth rate of brown trout average 3.35 kg ha -1 which is a high yield compared to other lakes on the plateau (Qvenild 2022). All of these 13 yearly catches from Lake Skjerja are in the uppermost part of this fish yield statistics.…”

“…During the period 2017-2023 the average water temperature in Lake Skjerja was 3.67°C (range 3.23-4.26°C) above the lake air temperature, compared to 3.23°C (range 2.77-3.74°C) in Lake Dargesjåen for the same period. Water temperatures in the The climatic conditions have proved to be important for production of brown trout on Hardangervidda (Qvenild 2022). In this context, the winter precipitation and summer air temperature and its significance to water temperature, is of special interest.…”

“…Hardangervidda is the most extensive mountain plateau in Europe, where the brown trout Salmo trutta Linnaeus, 1758 is mainly the only fish species present. The lakes on Hardangervidda are rated among the best brown trout lakes in Norway, hosting large fish of high quality (Sømme 1941;Qvenild 2022). Lake Skjerja, situated on the northeastern part of the plateau, is known as one of the most outstanding lakes providing high brown trout yields of large fish (Qvenild 2004).…”

“…Since the 1980s, the climate on Hardangervidda has changed, owing to the secular trend in global climate. Both annual winter precipitation and temperature has increased (Qvenild 2022). The intrinsic relationship with air temperature makes mountain lakes very sensitive habitats to changes in climate.…”

Impacts of reduced Lepidurus arcticus availability on brown trout life history traits in a mountain reservoir

“…Although E. lamellatus is known as brown trout prey and can account for between 31 and 41% of age-1 + brown trout diet, consumption tends to fall in fish larger than 150 mm (Hesthagen et al 1992). In lakes at the Hardangervidda mountain area in Norway, E. lamellatus is the main prey for small brown trout and is consumed by larger individuals (> 400 mm) if large-sized crustaceans (Lepidurus arcticus and Gammarus lacustris) are absent or scarce (Qvenild and Hesthagen 2020). However, the highest E. lamellatus abundances occur later in the growing season, e.g.…”