Ole Kristian Berg

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Digestibility, growth and nutrient utilisation of Atlantic salmon parr (Salmo salar L.) in relation to temperature, feed fat content and oil source

Condition dependence and adaptation-by-time : breeding date, life history, and energy allocation within a population of salmon

Correlations between breeding date and the life history or energy stores of individuals might stem from a combination of two different mechanisms. The conventional view is that individual size and condition influence breeding date (i.e., condition dependence). A different view is that heritable maturation schedules allow temporally separated population components to adapt to selective regimes associated with particular breeding times (i.e., adaptation-by-time). Considering each of these hypotheses, we examined a population of sockeye salmon (Oncorhynchus nerka) for evidence of correlations among life history traits (age, body size, egg size, and reproductive life span), patterns of energy allocation (somatic energy stores and gonadal investment), and breeding date. Life history traits were measured for 705 individually tagged adult salmon monitored from the onset of breeding until death. Energy stores were quantified for 60 fish collected when they entered the stream and 46 fish collected at death. Multiple regression models revealed that most of the variation could be explained by simple linear relationships among traits; older fish were larger, and larger lish had larger gonads, larger eggs, and more available energy when they started breeding. Condition dependence did not appear relevant to breeding date because fish that started breeding early were similar in size and did not have more stored energy than fish that would breed later. Similarly, adaptation-by-time had little influence on variation in body size or egg size (predicted relationships were significant but very weak). In contrast, adaptation-by-time appeared very important to variation in reproductive life span and patterns of energy allocation. Early-breeding fish lived considerably longer than late-breeding fish (females, R 2 =0.525; males. R 2 =0.533). This pattern arose because late-breeding fish expended more energy before breeding, and because late-breeding females invested more energy into egg production and retained less for metabolism during breeding. Adaptation-by-time may play an important role in life history evolution within some species, particularly those with breeding systems characterised by semelparity, capital breeding, and heritable breeding times.

Adaptive variation in senescence: reproductive lifespan in a wild salmon population

The antagonistic pleiotropy theory of senescence postulates genes or traits that have opposite effects on early–life and late–life performances. Because selection is generally weaker late in life, genes or traits that improve early–life performance but impair late–life performance should come to predominate. Variation in the strength of age–specific selection should then generate adaptive variation in senescence. We demonstrate this mechanism by comparing early and late breeders within a population of semelparous capital–breeding sockeye salmon (Oncorhynchus nerka). We show that early breeders (but not late breeders) are under strong selection for a long reproductive lifespan (RLS), which facilitates defence of their nests against disturbance by later females. Accordingly, early females invest less energy in egg production while reserving more for nest defence. Variation along this reproductive trade–off causes delayed or slower senescence in early females (average RLS of 26 days) than in late females (reproductive lifespan of 12 days). We use microsatellites to confirm that gene flow is sufficiently limited between early and late breeders to allow adaptive divergence in response to selection. Because reproductive trade–offs should be almost universal and selection acting on them should typically vary in time and space, the mechanism described herein may explain much of the natural variation in senescence.

Growth and survival rates of the anadromous trout,Salmo trutta, from the Vardnes River, northern Norway

SynopsisThe anadromous brown trout,Salmo trutta L., from the Vardnes River feed in coastal waters during the summer, but spend the winter in freshwater. Mean increase in weight during the sea sojourn ranged from 125 g for first time migrants to 704 g for the largest fish. A loss in weight, increasing with fish size, occurred during the winter residence in freshwater. Growth was positively correlated with the duration of the sea sojourn, which was generally longer in years when higher sea temperatures prevailed. The mean growth rate of the females during the sea sojourn, was generally higher than that of the males. About 37% of first time migrants survived the sea sojourn (mean duration 70 days), compared to 56%–68% of repeat migrants. Minimum estimates of the survival rate in freshwater (duration about 290 days) lay between 66% and 74%. Annual minimum survival was 25% for first time migrants, 37% for second time migrants, and 50% for older fish. The survival rates of the males of both the first- and the second-time migrants were generally higher than those of the respective females. Prolongation of the sea sojourn, due to low water-level in the river at the normal time of ascent, resulted in a further decrease in the survival rate over and above that resulting from the increase in residence time per se.

The duration of sea and freshwater residence of the sea trout,Salmo trutta, from the Vardnes River in northern Norway

SynopsisThe sea trout,Salmo trutta, from the Vardnes River generally stays in freshwater during winter. The results from 11 years of tagging experiments showed that the mean annual duration of the feeding migration in the sea was 68 ± 21 days (yearly means ranging between 54 and 88 days). A pronounced variation was found with size, sex and time of migration of the fish and between the different years. The males stayed for a shorter time in the sea (mean 66 days) than the females (mean 69 days) and they usually descended later and ascended earlier. Those fish that descended first stayed for the longest period in the sea. The mean annual duration of stay in the sea for first and second time migrants to the sea was positively correlated with the mean sea temperature in May (r2 > 0.5). A positive correlation was also found between the annual duration of stay in the sea for the sea trout above 33 cm and the mean temperature in the river in July (r2 > 0. 6). Prolonged mean yearly sea sojourn was generally correlated with higher sea temperatures. Water temperature-salinity effects are discussed.

Diel Periodicity and Environmental Influence on the Smolt Migration of Arctic charr, Salvelinus alpinus, Atlantic salmon, Salmo salar, and Brown Trout, Salmo trutta, in Northern Norway

We caught smolts of Arctic charr, Salvelinus alpinus (L.), Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a trap situated at the mouth of the river Halselva (70° N 23° E), northern Norway during a 5-year period. Salmon and charr were the first to leave freshwater at the end of May, while most trout left freshwater about 14 days later. Whereas the midnight sun shines continuously during the downstream migration period, the light intensity has a diel intensity pattern. The majority of the descending migrants were recorded during the night. The number of descending fish was relatively low at water temperatures below 3°C. The increase in water level was largely caused by snowmelt and thus correlated with lower water temperatures. The number of migrants of all three species increased with increasing water level and decreased with increasing water temperature, with the exception of trout, which increased with water temperature. Notably, the increase in number of migrants was also correlated with the increase in water level the following day, indicating that fish movements represent an early response to a later spate. There was no significant relationship between the number of migrants and the daily change in water level or temperature. The three species were highly synchronised in their daily number of migrants. The strongest synchronisation was found between Arctic charr and Atlantic salmon, followed by Arctic charr and brown trout.

Adaptive winter survival strategies: defended energy levels in juvenile Atlantic salmon along a latitudinal gradient

Current knowledge suggests that patterns of energy storage and depletion in animals are governed by behavioural trade-offs between risks associated with feeding and future energy demands. However, the length of adverse periods varies over geographical or climatic gradients. To explore the potential for genotypic sources of variation in behavioural trade-offs, we compared the winter energy-depletion patterns among 13 wild populations of juvenile Atlantic salmon (Salmo salar L.) along a latitudinal gradient (58–70°N) and performed common-environment experiments of energy-state-dependent feeding. In the wild, winter lipid-depletion rates were lower for northern than for southern populations. The variation in spring lipid levels among the population was lower than autumn variation, with storage lipid levels clustered close to critical limits for survival. In semi-natural stream channels with natural food supply, hatchery-reared fish originating from northern populations showed a positive scaling of feeding activity with decreasing energy levels, whereas southern populations did not. In conclusion, juvenile Atlantic salmon from northern populations defend their energy levels more strongly than fish from southern populations. Adaptive variation in feeding activity appears important for this difference. Thus, the present study shows a link between geographical patterns in storage energy trajectories and adaptive differences in state-dependent feeding motivation.

Duration of sea and freshwater residence of Arctic char (Salvelinus alpinus), from the Vardnes River in northern Norway

Abstract Nine years of tagging experiments in the Vardnes River show that mean duration (± s.d.) of residence in the sea of the anadromous Arctic char (Salvelinus alpinus) was 47.7 ± 15.6 days (annual means range 38–57 days). Females stayed in the sea for a significantly (P

The seasonal pattern of growth of the sea trout (Salmo trutta L.) from the Vardnes river in northern Norway

Abstract The growth pattern of sea trout in the sea was studied by measurement of 2787 tagged individuals before and after their stay in the sea while corresponding measurements of 2180 individual fish ascertained the growth pattern in fresh water. In the sea, there was a period of particularly rapid growth just before the beginning of July. The greatest rate of growth in fresh water was recorded for those sea trout that ascended the river relatively early on, or left the river late the following year. This result may explain the relatively simultaneous timing in northern areas of the migration to the sea of several species of salmonids in spring, and also the high degree of variation seen in the timing of the return migration to fresh water.

Direct and indirect climatic drivers of biotic interactions: ice-cover and carbon runoff shaping Arctic char Salvelinus alpinus and brown trout Salmo trutta competitive asymmetries

One of the major challenges in ecological climate change impact science is to untangle the climatic effects on biological interactions and indirect cascading effects through different ecosystems. Here, we test for direct and indirect climatic drivers on competitive impact of Arctic char (Salvelinus alpinus L.) on brown trout (Salmo trutta L.) along a climate gradient in central Scandinavia, spanning from coastal to high-alpine environments. As a measure of competitive impact, trout food consumption was measured using 137Cs tracer methodology both during the ice-covered and ice-free periods, and contrasted between lakes with or without char coexistence along the climate gradient. Variation in food consumption between lakes was best described by a linear mixed effect model including a three-way interaction between the presence/absence of Arctic char, season and Secchi depth. The latter is proxy for terrestrial dissolved organic carbon run-off, strongly governed by climatic properties of the catchment. The presence of Arctic char had a negative impact on trout food consumption. However, this effect was stronger during ice-cover and in lakes receiving high carbon load from the catchment, whereas no effect of water temperature was evident. In conclusion, the length of the ice-covered period and the export of allochthonous material from the catchment are likely major, but contrasting, climatic drivers of the competitive interaction between two freshwater lake top predators. While future climatic scenarios predict shorter ice-cover duration, they also predict increased carbon run-off. The present study therefore emphasizes the complexity of cascading ecosystem effects in future effects of climate change on freshwater ecosystems.