Bror Jonsson

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• Dr.philos.
• Consultant at Norwegian Institute for Nature Research

Simple Summary Otoliths, which are calcium carbonate structures found in the inner ears of fish, can be used to describe the use of freshwater and saltwater habitats during the lifespan of fish. This is performed by looking at the ratio of strontium to calcium along the radius of an otolith, where a high ratio indicates the use of saltwater and a l...

Changes in the number, structure, and function of mitochondria during the early life stages of animals can play an important role for an organism’s metabolic rate, growth, and health. Previous studies have shown that juvenile brown trout (Salmo trutta) subjected to elevated temperatures during the embryonic stage respond phenotypically with a reduc...

Climate warming is a serious threat to many organisms, such as cold-adapted ectotherms [...]

Through a phenotypic plastic response, early temperatures have knock-on effects on later appearing traits of organisms such as stream-spawning salmonids. Moderately warmer water during embryonic development has carry-over effects to later developing life history characters such as body shape, metabolic rate, growth rate, egg and gonad sizes. Also,...

Personality varies among individuals and is influenced by the environment. Here, we tested the hypothesis that egg incubation temperature had carry-over effects on swimming activity of juvenile brown trout, Salmo trutta. Eggs from different crosses involving anadromous and lacustrine-adfluvial parents were incubated under two temperature regimes, u...

Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salm...

Environmental factors influencing parents or offspring during embryogenesis can have knock-on effects at later life stages of the offspring. These effects may prepare the progeny for conditions that they may encounter as larvae, juveniles and/or adults. Here, we give examples on how knock-on effects of temperature and predator cues can affect pheno...

The present experiment tested if temperature during embryogenesis and parental heritage affected the migratory behaviour of young brown trout Salmo trutta. Two parental forms were used, a freshwater resident form and an anadromous form, both from the same river system but geographically isolated since 1993–95. Four groups of young S. trutta were pr...

Temperature during egg incubation and early development influences later life stages of fishes, potentially influencing survival. Throughout its distribution, Atlantic salmon (Salmo salar Linnaeus, 1758) have experienced population declines, and in view of ongoing global warming, we tested if temperature during the earliest developmental stages mod...

In this study, individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway, was estimated. The juveniles were incubated until hatching at two temperatures (±s.d.), either 4.4 ± 1.5°C or 7.1 ± 0.6°C. Growth rate was estimated for 22 days in August–Sept...

Citation: Durtsche, R. D., B. Jonsson, and L. A. Greenberg. 2021. Thermal conditions during embryogenesis influence metabolic rates of juvenile brown trout Salmo trutta. Ecosphere 12(2): Abstract. The projected climate change and increase in thermal conditions in northern latitudes over the next 60 yr has the potential to alter the metabolic scope...

When rehabilitating and reintroducing trout Salmo trutta in rivers, it is a goal that as many as possible survive, home and form self‐sustaining populations. Hatchery‐reared, anadromous S. trutta have significant lower ability to return to the area where they were raised if (a) transported in a closed tank to sea and released 5 km from the River Im...

This paper reviews the life history of brown trout and factors influencing decisions to migrate. Decisions that maximize fitness appear dependent on size at age. In partly anadromous populations, individuals that attain maturity at the parr stage typically become freshwater resident. For individual fish, the life history is not genetically fixed an...

Wild Atlantic salmon (Salmo salar) are in decline over the entire distribution area, and populations are enhanced by supportive breeding. Parental fish are sampled in rivers, crossed and the offspring reared in hatcheries until smolting when released, ready for ocean migration. Naturally reproducing salmon entering the River Imsa from the ocean wer...

Temperature during embryonic development affects ecological traits and influences the ability to rapidly adapt to the prevailing conditions in changing environments. Here, we review examples of how these developmental effects are manifested in life-history traits from studies of various fish species, with examples of impacts on somatic growth, age...

The consistency of the global declining trend of Atlantic salmon (Salmo salar) populations suggests that climate-driven reduced survival and growth at sea are the main driving factors. The southernmost populations have experienced the greatest declines, consistent with harsher conditions in natal fresh waters. We analyzed temporal trends in Spanish...

Here, we show that adult Atlantic salmon Salmo salar returned about 2 weeks later from the feeding areas in the North Atlantic Ocean to the Norwegian coast, through a phenotypically plastic mechanism, when they developed as embryos in c. 3°C warmer water than the regular incubation temperature. This finding has relevance to changes in migration tim...

Using a national perspective, Mo et al. (2018) described and expressed concern over the recent invasion into Norwegian rivers of adult pink salmon Oncorhynchus gorbuscha (Walbaum 1792), which were counted in thousands in 2017.

Habitats modify the population ecology of species. Here, we show how low water level influences abundance and size of adult anadromous brown trout (Salmo trutta) entering a small, South Norwegian stream for spawning. After smolting, the fish appear chiefly to feed within 10 km of the home stream. In the autumn, South Norwegian streams typically flo...

The abundance of Atlantic salmon is declining throughout its geographical area. Fisheries and global warming were assumed as main drivers of the decline, and recent studies suggest that habitat changes in freshwater is a third contributor. Southern populations experience the greatest decline, and face the highest risk of extinction as global warmin...

Habitat use and life histories are central issues in the ecology of species. There are close associations between how individuals and populations exploit, compete for, and share habitats and food resources in time and space, and their ability to grow, survive and reproduce (i.e. their fitness). Individuals exploiting rich habitats can grow larger a...

The timing of smolt migration is a key phenological trait with profound implications for individual survival during both river descent and the subsequent sea sojourn of anadromous fish. We studied relationships between the time of smolt migration, water temperature and light intensity for Atlantic salmon (Salmo salar) and sea trout (Salmo trutta)....

In southern Norway, 22 acidified rivers supporting anadromous salmonids were mitigated with lime to improve water quality and restore fish populations. In 13 of these rivers, effects on Salmo trutta and Salmo salar densities were monitored over 10-12 years, grouped into age 0 and age ≥ 1 year fish. These rivers had a mean annual discharge of betwee...

Occurrence of domesticated organisms in nature is a major biological issue. Many can survive and reproduce with wild conspecifics, but little is known about the ecology of hybrid offspring. Here, we investigated recapture, homing and growth of released offspring of farmed (domesticated), and wild Atlantic salmon Salmo salar and their crosses. The f...

Populations are retained at reduced levels by resource competition and environmental stochasticity. In the Norwegian River Imsa, the relationship between fecundity of Atlantic salmon (Salmo salar) spawners and number of smolts per unit river area was investigated for cohorts spawned from 1976 to 2011. Annual number of smolts produced per unit area...

Long-distance migratory species can reduce mortality risks by synchronizing the migration event and create confusion by swamping predators with high densities. To reduce confusion, predators are known to primarily select aberrant prey. We hypothesized that at the start of their sea sojourn, particularly small and large Atlantic salmon (Salmo salar...

Interbreeding between domesticated and wild animals occurs in several species. This gene flow has long been anticipated to induce genetic changes in life-history traits of wild populations, thereby influencing population dynamics and viability. Here, we show that individuals with high levels of introgression (domesticated ancestry) have altered age...

This study gives the probabilistic reaction norm for length at different ages of smolting before seaward migration of Atlantic salmon Salmo salar, spawning in the Norwegian River Imsa. The reaction norm was compared with the optimal length at smolting estimated as the product of survival and female fecundity on the return, given their length at smo...

Effect of increased temperature during egg maturation on the mass of single eggs produced by the offspring was investigated experimentally in Atlantic salmon Salmo salar. Mass of eggs produced by next-generation females was larger when their mothers experienced warmer water during the last two months of egg maturation, relative to those that experi...

Fish often migrate between habitats, and by that, fitness is improved. We estimated population parameters and studied possible migration of brown trout Salmo trutta between a Norwegian river and a tributary under two different regulated water flow regimes. In the 1970s, the main stem had high winter flows and reduced summer flows. Since 1981, the r...

The precision of growth estimates based on fish scales often remains uncertain because of withinindividual variation in scale size and scale patterns, and also due to measurement errors. Based on scale readings of Atlantic salmon, we show that errors decreased with number of times and number of scales read per fish. The annual number of scale circu...

Annual mean total length (LT) of wild one-sea-winter (1SW) Atlantic salmon Salmo salar of the Norwegian River Imsa decreased from 63 to 54 cm with a corresponding decrease in condition factor (K) for cohorts migrating to sea from 1976 to 2010. The reduction in LT is associated with a 40% decline in mean individual mass, from 2 to 1·2 kg. Hatchery f...

Fennoscandian rivers were colonized postglacially. Early colonization was from the sea and through the Baltic Ice Lake. Salmonids, cottids, smelts Osmerus eperlanus, three-spined sticklebacks Gasterosteus aculeatus, roach Rutilus rutilus and European minnow Phoxinus phoxinus were early immigrants. The species diversity varies among countries and wi...

Fennoscandian rivers were colonized postglacially. Early colonization was from the sea and through the Baltic Ice Lake. Salmonids, cottids, smelts Osmerus eperlanus, three-spined sticklebacks Gasterosteus aculeatus, roach Rutilus rutilus and European minnow Phoxinus phoxinus were early immigrants. The species diversity varies among countries and wi...

Anadromous trout Salmo trutta exhibits sexual size dimorphism (SSD ); females were larger than males in populations where male mean total length (LT ) at maturity was below 49 cm and females were smaller than males when mean male LT was above 49 cm, the slope of the regression of female on male LT was 0·59. In streams with mean annual discharge bel...

Surface ice in rivers and lakes buffers the thermal environment and provides overhead cover, protecting aquatic animals from terrestrial predators. We tested if surface ice influenced the behavior (swimming activity, aggressive encounters, and number of food items eaten) and stress level (coloration of eyes and body) of stream-living brown trout Sa...

Linking embryonic temperature with adult reproductive investment Bror Jonsson*, Nina Jonsson, Anders G. Finstad *Email: bror.jonsson@nina.no ABSTRACT: The expression of fitness-related traits, such as egg and gonadal size, often varies among habitats and exhibits clinal variation along climatic and latitudinal gradients. The mechanisms allowing...

The expression of fitness-related traits, such as egg and gonad size, often varies among habitats and exhibits clinal variation along climatic and latitudinal gradients. However, the mechanisms allowing such variations are obscure and have been ascribed to both phenotypic plasticity and genetic adaptation. We experimentally tested whether variation...

We tested whether marine survival and migration pattern differed between naturally and hatchery produced European trout Salmo trutta of different origins. The hatchery fish were released 150 m above the river estuary of the southwestern, Norwegian River Imsa, the home of the local population. Recaptures were used as proxy for survival. Wild and loc...

Conditions fish encounter during embryogenesis and early life history can leave lasting effects not only on morphology, but also on growth rate, life-history and behavioural traits. The ecology of offspring can be affected by conditions experienced by their parents and mother in particular. This review summarizes such early impacts and their ecolog...

Whether time of seaward migration of young Atlantic salmon Salmo salar influences their subsequent survival and growth was investigated in the River Imsa, south-western Norway. Salmo salar were tagged when moving downstream through a trap near the outlet between 1976 and 2010 and recaptured on their adult return. Most descended as smolts in April a...

Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo...

1. The reaction norm between growth rate, age and size at maturity in ectotherms is widely debated in ecological literature. It has been proposed that the effect depends on whether growth is affected by food quality or temperature (called the Berrigan–Charnov puzzle). The present experiment tested this for Atlantic salmon (Salmo salar). 2. We enhan...

Field studies have revealed that many ectotherms mature younger and smaller in warmer environments although they grow faster. This has puzzled ecologists because the direct effect of factors that accelerate growth is expected to be larger, not smaller size. We tested this experimentally for Atlantic salmon (Salmo salar) at two winter temperatures a...

We explored the mechanisms of density-dependent growth in Arctic char (Salvelinus alpinus) by comparing the energetics of growth, consumption, and activity obtained under three replicated density treatments in a large-scale enclosure (90 m² surface area) experiment. The enclosures permitted the entry of zooplankton and allowed char to feed on the b...

This study investigated the importance of competition with brown trout Salmo trutta as a driver of the morphological and behavioural divergence of two morphs of Arctic charr Salvelinus alpinus. The morphs originated from two lakes differing in absence or presence of the competitor. The bioenergetics and behaviour of S. alpinus were quantified in re...

Interspecific variations in thermal growth performance of ectotherms have received considerable recent interest fueled by the focus on ecological climate change effects. Amongpopulation variations in growth are commonly observed in field studies. However, the role of pheno typic plasticity in shaping this variation is largely unexplored in teleost...

There has been a growing recognition that single species responses to climate change often mainly are driven by interaction with other organisms and single species studies therefore not are sufficient to recognize and project ecological climate change impacts. Here, we study how performance, relative abundance and the distribution of two common Arc...

We tested the importance of thermal adaptations and energy efficiency in relation to the geographical distribution of two competing freshwater salmonid fish species. Presence–absence data for Arctic char and brown trout were obtained from 1502 Norwegian lakes embracing both temperature and productivity gradients. The distributions were contrasted w...

Destruction of habitat is the major cause for loss of biodiversity including variation in life history and habitat ecology. Each species and population adapts to its environment, adaptations visible in morphology, ecology, behaviour, physiology and genetics. Here, the authors present the population ecology of Atlantic salmon and brown trout and how...

This chapter describes important elements of the parr-smolt transformation (smolting) in Atlantic salmon and brown trout. Smolting is a preparatory physiolo­gical adaptation, which occurs in spring prior to the seaward migration. It includes morphological transformation, and changes in salinity tolerance, visual pigments, buoyancy, metabolism and b...

In this chapter, we first treat density regulation of populations. The abundance of all populations varies with time, but the magnitude of the fluctuations differs among populations and species. The variation is influenced by both extrinsic and intrinsic factors. If only environment affected population densities, there would be nothing that prevent...

At what age do Atlantic salmon and brown trout become sexually mature, and which factors and mechanisms determine the seasonal timing of maturation and spawning? How are resources allocated to the development of sexual characters and reproduction, and how do they maximize their reproductive output? This chapter reflects on these issues.

Habitat use is a central aspect in the ecology of a species. There are close associations between how individuals and population exploit, compete for, and share habitats and food resources in time and space, and their ability to survive and reproduce (Kramer et al. 1997; Cuthill and Houston 1997). For instance, individuals exploiting rich habitats...

In this book we review and synthesize ecological aspects of Atlantic salmon and brown trout with special emphasis on their life histories in relation to their habitat uses. We draw general conclusions when possible and identify gaps in knowledge. In this final chapter, we draw some main conclusions about life history consequences of present habitat...

Habitat is a template, which influences life histories, behaviour and physiology of organisms, and is the origin of intraspecific variation (Southwood 1977, 1988; Poff and Ward 1990). This is a useful concept for considering relationships underlying demographic patterns observed in fish populations. As habitats differ geographically and temporally,...

This chapter reviews possible effects of expected climate change in view of current knowledge on consequences of water temperature and flow for Atlantic salmon and brown trout in their endemic range. Population-level effects influencing life-history variables, recruitment, mortality and production are especially emphasized, but also behaviour chan...

Migration is long-distance movements made by many individuals more or less in the same direction and at the same time of the year (Endler 1977). The movements are normally followed by a return migration. Migrations are under genetic control (Northcote 1981; Svärdson and Fagerström 1982; Jonsson 1982; Kallio-Nyberg et al. 2002), but are also modulat...

In this chapter, we describe systematics and geographical distribution of Atlantic salmon and brown trout and factors important for their success in natural systems. Both are cold water species from the northern hemisphere, but due to human aquaculture and stocking, they now occur in most parts of the world offering suitable habitats.

Farmed Atlantic salmon escape unintentionally from hatcheries and fish farm and occur both in the Atlantic and the Pacific Oceans. These fish exploit natural feeding areas in fresh water and at sea, introgress natural populations (Fleming et al. 2000; O’Reilly et al. 2006; Castillo et al. 2008), and reduce the survival of wild populations that are...

Summary1. We estimated the biomass and production of juvenile anadromous brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) (parr) in 12 streams in the Skagerrak area of Norway to identify controlling environmental factors, such as land‐use and water chemistry.2. Production estimates correlated positively with fish density in early summer...

A common environment experiment was conducted to assess the magnitude of the difference in growth, consumption, activity rate, and spatial and temporal patterns of habitat use between morphologically different populations of Arctic char (Salvelinus alpinus) originating from two Norwegian lakes. These two lakes contrasted sharply in terms of surface...

The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life-history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wette...

Restoration ecology, the study of renewing degraded, damaged or destroyed ecosystems and populations, is a rapidly growing field, stimulated by new know­ledge about population and community ecology, behavioural ecology, genetics and evolution. With the advancement of modern technology, the human ability to destroy habitats and use and overexploit p...

The aim of the paper was to study sea migration, growth and survival of brown trout Salmo trutta of the River Imsa, 1976-2005. The migratory S. trutta were individually tagged and fish leaving or entering the river were monitored daily in traps located near the river mouth. The mean annual duration of the sea sojourn was 6-9 months for first-time m...

Using thermal growth data from eight populations of anadromous and lake-feeding brown trout Salmo trutta, hypotheses of adaptation to local optima and countergradient variation in growth were tested. The adaptation to local optima hypothesis suggests that natural selection can shift optimal performance temperatures to match the prevailing temperatu...

1. Population regulation was studied for seven consecutive years (1992–98) in five rivers at the periphery of the distribution of Salmo trutta , where the fish were living under environmental constraints quite different from those of the main distribution area. 2. Recruitment is naturally highly variable and the populations had been earlier classif...

Jonsson B and Jonsson N. 2008. Thinlip grey mullet Liza ramada (Mugilidae) caught in a smallNorwegian stream. Fauna norvegica 26/27: 31-33. Two individuals of thinlip grey mullet Liza ramada were collected in a southern Norwegian brook(58° 22’ N, 8° 37’ E) on 12th September 2007. The fish were 8.7 and 9.0 cm in total length, 6 and 7 g in total mass...

To what degree are population differences in resource use caused by competition and the occupation of adjacent positions along environmental gradients evidence of competition? Habitat use may be the result of a competitive lottery, or restricted by competition. We tested to what extent population differences in habitat use of two salmonids, cutthro...

Activity rate of Arctic char (Salvelinus alpinus) held in 90m² littoral enclosures were estimated using bioenergetic (with consumption estimated using stable caesium, ¹³³Cs) and behavioural approaches (with fish movements quantified using video cameras). We found no statistically significant difference between values of activity rate obtained using...