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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–September when the fish on average were c. 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18°C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, this appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence the later growth as reported earlier from the studies of Atlantic salmon Salmo salar. [ABSTRACT FROM AUTHOR]

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 modified body shape and fin size when temperatures averaged 2.6 vs. 5.6 °C. This temperature difference simulates increases predicted in climate change scenarios. Based on previous studies, we hypothesized that salmon originating from eggs subjected to cold incubation temperatures would have slimmer bodies and larger pectoral and dorsal fins than salmon from eggs that experienced warmer temperatures. After hatching, the juveniles were raised for 1 year under identical temperatures, after which we measured their body shape and fin areas. We found no support for our hypothesis regarding body shape. Indeed, we found the opposite, with cold-incubated salmon having deeper bodies than warm-incubated salmon. For fin size, the pectoral fins of cold-incubated salmon were larger than for warm-incubated salmon as predicted, but there was no difference in dorsal fin size. These results suggest that global warming may lead to altered body shape and fin size, possibly affecting swimming performance, and thus raise questions about the ecological consequences of the changes. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 timing caused by climate change and for cultivation and release of S. salar. [ABSTRACT FROM AUTHOR]

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). During 2006-2012, migrating smolts descending the southern Norway River Storelva were caught in a rotary screw trap located at the river mouth. The date of 50% cumulative smolt descent correlated significantly with the date when the river temperature exceeded 8°C for both Atlantic salmon and sea trout smolts. In 2010, smolts of both species were passive integrated transponder (PIT)-tagged, and the diel timing of their migration was precisely documented. The degree of night migration decreased in both species as the river temperature rose, and at temperatures above 12-13°C, more smolts migrated during day than during night. A multinomial model was fitted for estimating temperature and species effects on probabilities of migration during night, daytime, dusk and dawn. Atlantic salmon smolts preferred migrating under lower light intensities than sea trout smolts during early, but not late spring when both species migrated during bright daylight. In accordance with the early-season tendency to migrate at night, Atlantic salmon smolts migrated more during darker hours of the day than sea trout. In both species, smaller smolts migrated under dark conditions than during light conditions. Most of the findings on thermal, light and temporal effects on the observed smolt migration pattern can be explained as adaptations to predation avoidance. [ABSTRACT FROM AUTHOR]

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 was best described by a multiplicative model and increased with the fecundity of the females as proxy for number of eggs deposited and the minimum water flow in August towards the end of the first growth season. Mean monthly water temperature, or water flow in any other month during the first year, had no significant effect on number of smolts produced. At sea, there was an almost linear relationship between number of emigrating smolts and returning adults, possibly because population abundance of Atlantic salmon is low relative to the carrying capacity in the ocean. Thus, both number of eggs spawned and minimum water flow in late summer influenced population abundance in the present river. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater ('parr') stage to the migratory stage where they descend streams and enter salt water ('smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 °C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5 days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The migration of wild and hatchery Atlantic salmon ( Salmo salar) postsmolts of different origins was monitored using ultrasonic tags and arrays of acoustic receivers across the Bay of Fundy (BoF), Canada. Postsmolts from outer BoF populations migrated rapidly into the Gulf of Maine (GoM) and did not return, and most were classified as distant migrants (77%-100%). In contrast, postsmolts from inner BoF populations were usually classified as coastal migrants that returned to the BoF for the summer (30%-90%). They used well-defined migration corridors, close to shore, associated with prevailing surface currents. An Akaike information criterion (AIC) evaluation of migration models identified region and watershed, date of river exit, and migration speed as important predictive variables for coastal residency. A late or slow migration increased residency, as did delaying hatchery releases. The BoF provided returning postsmolts with a summer thermal refuge (8-14 °C) encircled by warm water (>20 °C), but extended residency in this coastal habitat increased exposure to sources of mortality absent further at sea. This reduced marine survival of inner BoF salmon to almost nothing. It is likely that the different migratory strategies of inner and outer BoF salmon populations influenced their relative marine survival and endangered status. [ABSTRACT FROM AUTHOR]

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)., We enhanced growth rates by increasing temperature and ratio of lipids to proteins in the food for groups of Atlantic salmon. Both treatments gave higher percentages of early mature and therefore smaller adults in contrast to the proposed Berrigan- Charnov puzzle. There was a difference between sexes in that males could attain maturity 1 year younger than females when reared under similar environmental conditions., Males that matured during the first year in sea water were smaller than similar aged immature males. The probability of that Atlantic salmon attained maturity for the first time during their second year in sea increased with growth rate during the preceding winter and if fed a high-lipid diet. Increased summer temperature exhibited no additional effect., Similar aged fish reared at elevated temperature and fed high-lipid diet attained maturity at a larger body mass and exhibited higher mass-length-ratios than those reared at natural temperature and fed a low-lipid diet, indicating that structural growth has priority over lipid deposits., Increased growth rate before the onset of maturation, whether this is owing to enhanced lipid content in food or increased water temperature, decreased age and therefore size at maturity. Enhanced lipid relative to protein content in food, but not temperature, had an additive positive effect on early maturation probability, likely due to increased amounts of reserve energy. These results may be general for ectotherm organisms. [ABSTRACT FROM AUTHOR]

Summary 1. 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, but not with the size of the catchment. The summer biomass of age-0 brown trout and Atlantic salmon was smaller than that of age-1 and constituted 27.4 and 25.7%, respectively, of the total biomass of the two groups. 3. Mean production of brown trout from July to September varied between streams, but in most cases it was below 2 g 100 m−2 day−1. Yearly cohort production from age-0 in July to age-1 in July was 10 g m−2 or less, with mean annual production of 1.32 g 100 m−2 day−1, equivalent to 4.8 g m−2 year−1. The corresponding annual cohort production of Atlantic salmon was 0.38 g 100 m−2 day−1 or 1.4 g m−2 year−1. Annual production to biomass ratio ( P/ B) for brown trout of the same cohort in the various streams was between 1.47 and 4.37; the overall mean (±SD) for all streams was 2.25 ± 0.94. Mean turnover rate of Atlantic salmon was 2.73 ± 0.24. 4. Production of 0+ brown trout during the summer correlated significantly with the percentage of agricultural land and forest/bogs in the catchment, with maxima at 20 and 75%, respectively. Age-0 brown trout production also correlated with concentration of nitrogen and calcium in the water, with maxima at 2.4 and 14 mg L−1, respectively. 5. The results support the hypothesis that brown trout parr production reflects the quality of their habitat, as indicated by the dome-shaped relationship between percentage of agricultural land and the concentration of nitrogen and calcium in the water. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When cultured Atlantic salmon are released into nature, they compete with wild fish for food, space, and breeding partners. As a result of morphological, physiological, ecological, and behavioural changes that occur in hatcheries, their comp etitive ability often differs from that of wild fish. These changes are partly phenotypic and partly genetic. Cultured juveniles'' faster growth rate influences age and size at smolting and maturity, reproductive output, and longevity. Fast-growing parr tend to smolt younger, produce more but smaller eggs, attain maturity earlier, and die younger. Juvenile learning influences a number of behavioural traits, and differences in early experience appear to affect feeding and spawning success, migratory behaviour, and homing ability. Genetic change in hatcheries is chiefly the result of natural selection, with differential mortality among genotypes and broodstock selection based on production traits such as high adult body mass and fast growth rate. Experimental evidence has revealed that cultured parr''s greater aggression often allows them to dominate wild parr, although smaller cultured parr can be subordinated if they co-occur in fast-flowing water and if wild smolts have established prior residence. During spawning, the fitness of wild salmon is superior to that of cultured conspecifics. Cultured males are inferior to wild males in intra-sexual competition, courting, and spawning; cultured females have greater egg retention, construct fewer nests, and are less efficient at covering their eggs in the substratum than their wild counterparts. In rivers, the early survival of cultured offspring is lower than that of their wild counterparts. The lifetime reproductive success of farmed fish has been estimated at 17% that of similar-sized wild salmon. As a result of ecological interaction and through density-dependent mechanisms, cultured fish may displace wild conspecifics to some extent, increase their mortality, and decrease their growth rate, adult size, reproductive output, biomass, and production. [Copyright &y& Elsevier]

Climatic conditions experienced by Atlantic salmon (Salmo salar) in their early development appear to affect parr size at the end of the first growth season and age at emigration from the nursery river. North Atlantic Oscillation indices (NAOIs) correlated positively with water temperature (degree-days) and discharge in the River Imsa during winter (January–April) 1976–2002, indicating a significant oceanic influence on the winter conditions in the river. Specific growth rate of Atlantic salmon parr during the first year of life and the proportion of one-year-old smolts correlated positively with water temperature, flow, and NAOI during February–April during the winter of egg incubation, but only NAOI was significant when cross-correlating the two series using a time difference of 1 year. Water temperature correlated significantly with the proportion of salmon cohorts smolting and migrating to sea at age-1. Such long-term effects of climate during early development may be more important than generally recognized. [ABSTRACT FROM AUTHOR]

This paper reviews recent advances in our understanding of factors influencing the marine production of wild Atlantic salmon (Salmo salar). Population abundance has declined during the last 30 years because of decreased marine growth rate, survival-rate, and production of multi-sea-winter fish. Mortality appears density-independent, indicating that the marine abundance is beneath the carrying capacity for the species. Correlations between the North Atlantic Oscillation winter index for the post-smolt year and production variables indicate that unfavourable climatic conditions are partly responsible for the decline. Low sea temperature may be the ultimate reason for the poor salmon production, whereas predation is one proximate mortality factor, which is probably both size and temperature dependent. Low growth rate during cold years was associated with low sea age at maturity and small salmon, contrary to the common observation that fast growth leads to young age at maturity. It is suggested that low water temperature may stimulate lipid storage relative to protein production and that the energy density needed to attain sexual maturity is lower in small than in large salmon. Future research should focus on the relationships between smolt age and (or) size and adult age and (or) size, and the association among water temperature, growth rate, growth efficiency, and age at sexual maturity. [ABSTRACT FROM AUTHOR]

Summary 1. Catches of Atlantic salmon Salmo salar L. decreased in the 1980s and 1990s over its entire area in the North Atlantic and smolts were often released for stock enhancement. However, there are questions about their survival and performance relative to fully wild fish. This paper reports on the survival and sea growth of River Imsa salmon released from 1981 to 1999 as 1- and 2-year-old hatchery and wild smolts. 2. Survival was significantly higher for wild than hatchery fish. Hatchery salmon released as 2-year-old smolts had lower survival, were captured more in coastal than freshwaters, grew more slowly and attained maturity younger than corresponding 1-year-old smolts. 3. The survival rate of hatchery fish released as 2-year-old smolts, but not 1-year-olds and wild smolts, decreased during the 1980s and 1990s. Growth rates at sea, adult size and the proportion of multi-sea-winter fish of all three groups also decreased over time. 4. Catches in coastal relative to freshwaters were higher for two- than one-sea-winter fish. Salmon captured in coastal water were greater in length than those captured in rivers. Mean specific growth rate at sea was similar for wild and hatchery salmon released as 1-year-old smolts, and higher than in hatchery fish released as 2-year-olds. 5. The proportion of two-sea-winter salmon correlated positively with the specific growth rate in the first year at sea. Total capture of wild adult salmon in rivers and Norwegian home waters each year correlated positively with the specific growth rate in the first year at sea. The same correlation held for hatchery fish released as 2- but not 1-year-old smolts. 6. Synthesis and applications. The coastal fishery was size-selective in reducing the size and age of salmon. Releases of 1-year-old smolts were financially more profitable than those of 2-year-olds. Decreasing production of River Imsa salmon since 1981 was chiefly caused by reduced sea-age at maturity and growth rate at sea of both hatchery and wild fish. A counteracting measure would be to reduce the size selectivity of the salmon fisheries. [ABSTRACT FROM AUTHOR]

Presents a study which described relationships between energy density and body length which varied life-history stages of Atlantic salmon by power functions. Advantage of natural selection to energy partitioning; Materials and methods; Sematic energy density and tissue composition.

SUMMARY 1. Annual energy, carbon, nitrogen and phosphorus fluxes across the river mouth by Atlantic salmon were estimated for 18 years (1976–94) in the Norwegian River Imsa. The total energy content of the emigrating smolts in each year varied considerably with a mean value of 237 × 103 kJ. That of returning adults also varied between years with a mean value of 141 × 104 kJ. One-sea-winter salmon (grilse) made up 65% of the total energy content of the spawners in the river. Dead carcasses remaining in the river after spawning were estimated to have a mean annual energy content of 175 × 103 kJ. 2. The net annual energy flux from the sea to the river varied between 48 × 103 kJ (1987) and 152 × 104 kJ (1989) with a mean of 616 × 103 kJ, and a coefficient of variation of 67%. Average net marine import of the returning adults was 83 × 104 kJ year-1 with a coefficient of variation of 52%. Mean annual export of C, N and P to sea by the smolts was 595, 131 and 22 kg, and by kelts 1535, 352 and 70 kg, respectively, whereas gross import via the adults was 3176 kg C, 735 kg N and 132 kg P. The annual flux across the river mouth was 1046 kg C, 253 kg N and 39 kg P. The net marine import were 1585 kg C, 371 kg N and 60 kg P. The net flux was estimated at 0.2% for nitrogen and 5% for phosphorus of the total river load. 3. The energy flux caused by Atlantic salmon spawning in the River Imsa was relatively high because the general nutrient load in the river is low. Thus, even though most Atlantic salmon survive spawning, their contribution to the nutrient flux in the river is significant. [ABSTRACT FROM AUTHOR]

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 were monitored from 1976 through 2013, and since 1982, supportive breeders spawning in the river were also monitored. The supportive breeders were first‐generation salmon, reared for 1—2 years in a hatchery before being released at the mouth of the river so they could migrate to sea (i.e., sea‐ranching). Wild and sea‐ranched salmon live in the ocean for 1—2 years before they return to the river for spawning. In years when only wild adults were present, mean number of smolts produced per 100 m2 river area and female breeder was 0.47. When there were 5% wild females, the mean production was only 0.088 (19%). The gradual decrease in offspring production with decreasing proportion of wild females (r2 =.41) indicates that the reduced offspring production was caused by inferior spawning behavior of hatchery females or reduced survival of their offspring in nature. Previous experimental evidence suggests that wild males fertilize the eggs of wild but also hatchery females. It is discussed how epigenetic effects caused by hatchery environments influence the developing juveniles, lead to phenotypic changes that may reduce their fitness in nature even after free ranging for a year or more in the ocean before they return and spawn. [ABSTRACT FROM AUTHOR]

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 warming moves its thermal niche northwards. We analysed long-term catch data (1949–2013) from a salmon fishery in northern Spain, and examined its relationship with local and global indicators of temperature and hydrological change. CPUE data, analysed by ARIMA time-series models, exhibited a significant negative trend and a marked decrease since 1973–1974, possibly triggered by overfishing at sea and a sudden outbreak of disease. Temperature increased in the same period, particularly so since 1986–1988, being negatively correlated with CPUE. A significant change in magnitude and duration of extreme water conditions occurred from 1970s onwards. Indicators of hydrological shift were also significantly correlated with CPUE of returning salmon. The best ARIMAX models indicated however, that the decrease in salmon CPUE was mainly driven by temperature trends. This indicates that both local (temperature and flow in the river) and global (ocean temperature) factors have contributed to the decrease in salmon numbers, and that temperature has played the major role. Despite a strong reduction in fishing pressure after the 1970s widespread collapse, our study population did not recover to previous abundance levels. This suggests the operation of additional factors, being climate warming and changes in food webs of the North Atlantic the most likely reasons. [ABSTRACT FROM AUTHOR]