The brown trout (Salmo trutta) in the lake, Øvre Heimdalsvatn: long-term changes in population dynamics due to exploitation and the invasive species, European minnow (Phoxinus phoxinus)

Abstract

Studies of the brown trout (Salmo trutta) population in the Norwegian subalpine lake, Øvre Heimdalsvatn, over a 50-year period have revealed major changes in population dynamics.

Diet overlap between introduced European minnow (Phoxinus phoxinus) and young brown trout (Salmo trutta) in the lake, Øvre Heimdalsvatn: a result of abundant resources or forced niche overlap?

“…The biomass of sexually mature minnows in Øvre Heimdalsvatn was estimated to be 4.7 and 2.1 kg ha -1 in 1999 and 2000, respectively. Compared with the estimated biomass of brown trout (C4 years) during the period 1993-2006, which ranged from 7.3-14.1 kg ha -1 , the minnow biomass can be seen as modest, although it constituted as much as 37% of the total fish biomass in the lake in 1999 Borgstrøm et al, 2010). However, the minnow population mainly occupies habitats at depths \1 m for most of the ice-free season, resulting in a biomass of up to 31 kg ha -1 in these habitats of the lake , while the majority of the brown trout population occupies deeper areas over a large part of the lake (Lien, 1978).…”

“…The increase in the population size of minnows, which was followed by a considerable reduction in individual growth rates, strongly indicated intraspecific competition and density dependent growth of minnows in the lake (Lien, 1981;Museth et al, 2002). Borgstrøm et al (2010) found a negative correlation between biomass and individual growth of brown trout during the period 1993-2006, which also indicated density dependent growth of brown trout at biomasses ranging from 7.3 to 14.1 kg. Since both minnows and young brown trout occupy the shallower parts of the littoral zone of the lake, and to a large extent utilize the same food resources, it is also likely that the high biomass of minnows in this habitat negatively affects the individual growth of brown trout.…”

“…Hence, diet analyses of sympatric minnow and brown trout populations alone cannot provide definitive conclusions concerning competitive interactions between the two species. However, reduced abundance of brown trout populations in sympatry with minnows compared to allopatric populations (Museth et al, 2007), and reduced recruitment of brown trout after minnow introductions (Borgstrøm et al, 1996(Borgstrøm et al, , 2010 strongly indicate negative interactions between the two species. The change from a dominance of large macroinvertebrates (EPT taxa and G. lacustris) to smaller benthic prey (Chironomidae) is an additional indication of heavier predation on benthos in the shallow parts of the littoral zone (Ware, 1972;Newman & Waters, 1984;Tate & Hershey, 2003).…”

The development of new algorithms for remote sensing of snow conditions based on data from the catchment of Øvre Heimdalsvatn and the vicinity

“…The snow cover algorithm is evaluated for application in a global climate monitoring system for snow variables. The early warning of the start of snowmelt and the extent of snow cover have the potential to be useful tools in detecting the timing of major hydrological processes in remote areas, such as ice break and the spring flood (Kvambekk & Melvold, 2010), which again are crucial to the seasonal development of lake biological production and food chains (Larsson et al, 1978(Larsson et al, , 2010Borgstrøm et al, 2010).…”

The Norwegian reference lake ecosystem, Øvre Heimdalsvatn

“…In 1969, the first specimens of the European minnow were observed in the lake (Lien, 1981). The population of minnows subsequently increased substantially (Lien, 1981) and they had, and still have, a major impact on the lake ecosystem, especially brown trout dynamics (Borgstrøm et al, 1996;Museth et al, 2002;Borgstrøm et al, 2010;Museth et al, 2010) and the benthic community (Naestad & Brittain, 2010). With the knowledge of trout dynamics and the benthic community composition prior to the introduction of minnows, scientists have been able to elucidate the impact of the introduction of an alien species into a subalpine lake in which brown trout were previously the sole fish species (Fig.…”