The energy budget of the brown trout population of øvre Heimdalsvatn

Abstract

Energy pathways of a natural brown trout Salmo trutta population were constructed. The main subjects taken into account were: the biomass, calorific values and production of the population, natural mortality and annual yield, energy intake, calorific values and composition of the food, efficiency of food absorption, spawning and migration of young trout. The specific energy value of trout increased with increasing weight of the fish. An energy decrease of almost 50% was demonstrated for the spawning trout of both sexes, and the calorific values prior to spawning were not reached before the next summer. Energy intake was estimated to 6.87, 10.31, 8.42 and 9.15 kcal m−2 lake surface for the years 1969, 1970, 1971 and 1972 respectively. Although a great number of food items were found in the trout stomachs, the four groups Gammarus lacustris, Lepidurus arcticus, Trichoptera and Chironomidae accounted for 2/3 of the total consumption. The efficiency of food absorption varied between 42 and 53%. The mean age of trout entering the lake from the nursery streams was ca. 3 yr. The annual amount of this immigration was estimated to be 0.28 and 0.24 kcal m−2 lake surface for 1969 and 1970 respectively. Annual production of trout in the take was estimated to be 1.46 and 2.66 kcal m−2 respectively for the same years. For both these years balance was found between biomass at the beginning of the year plus immigration of young and total production, minus catch by man, natural mortality and spawning on the one hand and biomass at the end of the year on the other hand.

Energy allocation in polymorphic Brown Trout

“…) used the equations of Elliott (1976) when reconstructing the energy content of the fish. Moreover, Lien (1978) reported a mean energy content of spent Brown Trout from the Lake Øvre Heimdalsvatn (situated 1090 m above sea-level in southern Norway), of 489 kJ per 100 g, which is only 2% different from the present anadromous trout. In Atlantic Salmon from the River Imsa, south-western Norway, mean somatic energy content of the spawners was c. 500 kJ per 100 g somatic tissue (Jonsson, Jonsson & Hansen 1991b), which is within 5% of our results.…”

“…In the present species, the figures may be similar (cf. Lien 1978). Although not fully measured, it is reasonable to assume that the reproductive effort of residents will be smaller than that of migrants, as the available energy reserves of residents are small.…”

Long-term changes in the littoral benthos of a Norwegian subalpine lake following the introduction of the European minnow (Phoxinus phoxinus)

“…Gammarus lacustris was an important part of the diet for brown trout population in the period 1969-1972, especially during autumn and winter (Lien 1978). By 1975-1977 the amount of G. lacustris in the trout diet had declined considerably, and the amount of Chironomidae had increased.…”

Cannibalism governing mortality of juvenile brown trout,Salmo trutta, in a regulated stream

“…Consumption in terms of energy as well as growth is unaffected by assumptions about prey-fish energy density because we specified energy intake in terms of p. Because the samplings have taken place in periods with none or few seatrout present, most fish greater than 17 cm sampled in Øyreselv were mature males. Spawning brown trout males have been reported to lose between 10% (Berg et al, 1998) and 44% (Lien, 1978) of their energy content. To explore the effect of spawning on simulated growth and consumption, we simulated energy intake and growth in a fish of initial length 17 cm for specific spawning losses between zero and total energy loss.…”