Fauna norvegica 2020-03-31T11:27:42+00:00 Fauna norvegica Open Journal Systems <p>Fauna norvegica is an international journal focusing on Nordic fauna. In addition to faunistic studies, contributions concerning systematics and taxonomy, biogeography, biodiversity in order to describe abundance and distribution, as well as methodological development, are welcome. Submitted manuscripts will be considered for publication after peer review. There are no page charges for manuscripts accepted for publication.</p> The freshwater shrimp Gammarus lacustris (Malacostraca, Amphipoda) in lakes on the Hardangervidda mountain plateau, southern Norway: distribution and environmental requirements 2020-03-31T11:26:59+00:00 Tore Qvenild Trygve Hesthagen, TH Arne Fjellheim <p>The distribution of the amphipod <em>Gammarus lacustris</em> on the Hardangervidda mountain plateau was mapped by&nbsp;screening published data from 245 lakes in 11 and 16 catchments in western and central/eastern areas, respectively.&nbsp;These data are primarily based on stomach analyses of brown trout <em>Salmo trutta</em>. In central/eastern areas, <em>G.&nbsp;lacustris</em> was recorded in 79% of all the lakes examined, while there are only two former records (4%) in the western&nbsp;area. The distribution pattern of <em>G. lacustris</em> on Hardangervidda appears to be related to environmental conditions.&nbsp;The apparent absence of <em>G. lacustris</em> in the western area may be explained by a combined effect of cold water due to&nbsp;higher deposits of snow and water with low ionic strength as a consequence of its bedrock of Precambrian gneisses&nbsp;and granites with little or no moraine cover. However, lakes in central/eastern areas sustain <em>G. lacustris</em> in spite of&nbsp;dilute water, as <em>G. lacustris</em> has been recorded in 89 lakes of which 28% had calcium concentration &lt;1.0 mg L<sup>-1</sup>, eight&nbsp;of them with pH &lt;6.0. The lower lethal threshold for calcium concentration seems to be ~0.5 mg L<sup>-1</sup>. <em>Gammarus&nbsp;lacustris</em> was found in lakes at altitudes of 832 to 1396 m a.s.l. Furthermore, their occurrence increased significantly&nbsp;with lake size, being 69% in lakes &lt;1.0 km<sup>2</sup> and 97% in larger lakes. The number of refugia with better water quality&nbsp;is likely to increase with lake size. <em>Gammarus lacustris</em> is highly searched for as prey by all size groups of brown&nbsp;trout (15-45 cm). Access to proximity refugia that reduce predation pressure from fish may also increase with lake&nbsp;size. Climate changes are now in progress in this mountain area, and detailed mapping of <em>G. lacustris</em> is important&nbsp;in order to trace future range changes.</p> 2020-03-16T00:00:00+00:00 ##submission.copyrightStatement## The viability of the crustacean Eurycercus lamellatus (Branchiopoda, Cladocera) in a high mountain area in southern Norway 2020-03-31T11:27:42+00:00 Tore Qvenild Trygve Hesthagen <p>The branchiopod <em>Eurycercus lamellatus</em> is widely distributed in Norwegian lakes, ranging from coastal to alpine areas. On the Hardangervidda mountain plateau in southern Norway, <em>E. lamellatus</em> 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 <em>Salmo trutta</em>. <em>Eurycercus lamellatus </em>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 <em>E. lamellatus</em> in central and eastern catchments increased with lake size, being found in 65% and 85% of lakes with a surface area of &lt;2.0 and ≥2.0 km<sup>2</sup>, respectively. In the western area, <em>E. lamellatus</em> 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 <em>E. lamellatus</em> 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 <em>Gammarus lacustris</em> and <em>Lepidurus arcticus</em> are at low densities in these lakes, <em>E. lamellatus</em> became the staple food item for brown trout, except for larger fish (&gt;400 mm). However, under high predation pressure, <em>E. lamellatus</em> also contributed significantly to the diet of larger fish. The abundance of <em>E. lamellatus</em> seems to vary highly on a yearly basis in one of the lakes (Sandvatn). Even though <em>E. lamellatus </em>is described as a typical littoral species, it was common down to depths of 15 m.</p> 2020-03-31T07:33:31+00:00 ##submission.copyrightStatement##