Life History Of Atlantic Salmon Research Articles

Long term effects of smolt production strategy and early seawater phase rearing environment on mortality, growth, sexual maturation, and vertebra deformities in farmed Atlantic salmon (Salmo salar L.)

The life history of Atlantic salmon is plastic and determined by factors such as daylength and temperature. In aquaculture, artificial long days during smolt production maximize growth and allows for early sea-transfer, occurring between the first summer and autumn after hatching. However, the impact of such intensive rearing strategies on the salmon's welfare is not well understood. In this study, we follow underyearling (0+) juvenile salmon through two different smolt production regimes, either dietary induced seawater tolerance (fed with SuperSmolt®) under continuous light (LLS), or light-induced seawater tolerance, where for six weeks the photoperiod was lowered to 12 h light and 12 h darkness and then increased again to continuous light (LD-LL). Next, the LD-LL and LLS salmon were distributed into indoor seawater tanks where they experienced light and temperature conditions simulating either an August (AUG) or an October (OCT) sea transfer scenario lasting 2 months, after which all fish were transferred into a sea cage and reared there until reaching harvest size (10 months). Welfare parameters were mortality, growth, vertebra deformities (radiology), and sexual maturation. LLS grew faster than LD-LL smolts up until seawater transfer, while LD-LL post-smolts grew faster during the early seawater phase, resulting in equal harvest weights. The simulated AUG transfer gave higher harvest weights than the simulated OCT transfer regardless of smolt production strategy. Mortality during the first period in sea cages was higher in the LD-LL compared to LLS fish within the AUG scenario. At harvest, male sexual maturation was significantly higher in the LLS AUG (21%) group compared to the other groups (∼10%), while the occurrence of fish with vertebra deformities (1 ≥ deformed vertebrae) was highest among LD-LL fish within the AUG scenario (31%). Only the LD-LL fish had severely deformed individuals (fish with >10 deformed vertebrae): 2.8% in AUG and 5.6% in OCT. The present study shows that the incidence of male sexual maturation and vertebral deformities is lower in dietary- and photoperiod-induced smolts, respectively, by transferring them to seawater in autumn rather than summer. However, such a strategy could be expected to reduce the harvest weight of both LD-LL- and LLS-induced smolts.

Na+/HCO3- cotransporter 1 (nbce1) isoform gene expression during smoltification and seawater acclimation of Atlantic salmon.

The life history of Atlantic salmon (Salmo salar) includes an initial freshwater phase (parr) that precedes a springtime migration to marine environments as smolts. The development of osmoregulatory systems that will ultimately support the survival of juveniles upon entry into marine habitats is a key aspect of smoltification. While the acquisition of seawater tolerance in all euryhaline species demands the concerted activity of specific ion pumps, transporters, and channels, the contributions of Na+/HCO3- cotransporter 1 (Nbce1) to salinity acclimation remain unresolved. Here, we investigated the branchial and intestinal expression of three Na+/HCO3- cotransporter 1 isoforms, denoted nbce1.1, -1.2a, and -1.2b. Given the proposed role of Nbce1 in supporting the absorption of environmental Na+ by ionocytes, we first hypothesized that expression of a branchial nbce1 transcript (nbce1.2a) would be attenuated in salmon undergoing smoltification and following seawater exposure. In two separate years, we observed spring increases in branchial Na+/K+-ATPase activity, Na+/K+/2Cl- cotransporter 1, and cystic fibrosis transmembrane regulator 1 expression characteristic of smoltification, whereas there were no attendant changes in nbce1.2a expression. Nonetheless, branchial nbce1.2a levels were reduced in parr and smolts within 2days of seawater exposure. In the intestine, gene transcript abundance for nbce1.1 increased from spring to summer in the anterior intestine, but not in the posterior intestine or pyloric caeca, and nbce1.1 and -1.2b expression in the intestine showed season-dependent transcriptional regulation by seawater exposure. Collectively, our data indicate that tissue-specific modulation of all three nbce1 isoforms underlies adaptive responses to seawater.

Deterrents and nudges improve compliance in Greenland's Atlantic salmon (Salmo salar) fishery

Abstract Fishers reporting all of their catch is key to estimating population viabilities of vulnerable, highly migratory fish stocks. However, fishery managers find it difficult to ensure that this reporting behavior takes place consistently. Wild Atlantic salmon (Salmo salar) are a highly migratory and internationally contested species with a threatened conservation status. Greenland manages a fishery for Atlantic salmon, and its coastline serves as a key feeding ground in the life history of Atlantic salmon. However, salmon catch is underreported by fishers, even though they are required to report. Deterring noncompliant behavior with penalties and sending short message service (SMS) messages have been shown to increase compliance, but no known studies test their effect on compliance with catch reporting requirements. We evaluated two interventions for their effect on salmon catch reporting behavior among Greenland's salmon fishers. Salmon fishers were 41% more likely to report (p < 0.00) once a deterrence-based intervention was implemented. Fishers who received SMS reminders were 6% more likely to report salmon catch (p < 0.1). These results highlight the complementarity of nudges and command-and-control interventions to increase compliance with catch reporting requirements.

Salient Needs for Conservation of Atlantic Salmon

A short review is presented on the major factors contributing to recent precipitous declines in populations of wild Atlantic Salmon Salmo salar, with the approach of describing the major needs for stabilizing or enhancing factors to conserve and reverse the decline of salmon populations and incidentally of other salmonid species. Some aspects of physiology and required habitat characteristics through the life history of Atlantic Salmon are reviewed that determine responses to degradation of habitats. Anthropogenic developments, including obstructions to migration and degradation of freshwater habitats, are major reasons for declines in the resource. Thus, habitat is a primary factor to be considered in conservation and restoration. Socioeconomic considerations may override ecological and public interest concerns, and examples are given from Canada, where environmental regulations have been relaxed in favor of economic interests. Public education and awareness and advocacy in order for political “will” for better conservation of the resource are required to slow, and eventually stop, the decline in Atlantic Salmon populations.

Origin and life history of Atlantic salmon (Salmo salar) near their northernmost oceanic limit

138 Atlantic salmon (Salmo salar) captured in the Advent Fjord off Svalbard were genetically assigned to two main clusters of European salmon. Two-thirds were assigned to salmon rivers in Finnmark (the northernmost county in Norway) and the rest to salmon rivers further south in Norway. The genetic assignment was based on genetic profiles from 60 Norwegian rivers. The two clusters correspond to two larger genetic groupings: the Barents–White seas and Atlantic groupings. Thus, we cannot rule out other populations from these groupings as sources of Atlantic salmon at Svalbard. Svalbard salmon assigned to the two genetic groupings differed in ecological and phenological traits, with highest smolt age and lowest postsmolt growth in the Finnmark salmon cluster. High smolt ages in both groups, however, suggest a northern origin of most individuals in the sample. Although Atlantic salmon have sporadically been observed in the Arctic Ocean at earlier times, the high abundance outlined here seems to be a recent phenomenon, suggesting a northward penetration caused by climate change.

Smolt Emigration and Survival to Adulthood in Two Icelandic Stocks of Atlantic Salmon

AbstractAtlantic salmon Salmo salar smolts were sampled at weirs from two Icelandic rivers (Ellidaár and Vesturdalsá) for a 15‐year period to test four hypotheses: (1) longer smolts (i.e., at the high end of the length‐frequency distribution) will have higher survival to adulthood than shorter smolts (i.e., in the middle and lower parts of the distribution); (2) plumper (i.e., higher condition factor) smolts will have higher survival to adulthood than leaner (slim or average) smolts; (3) middle‐age smolts (i.e., in the middle part of the freshwater age distribution) will have higher survival rates than fish at the extremes of the age distribution; and (4) fish in the middle portion of the smolt run will have higher smolt‐to‐adult survival than smolts emigrating early and late. Among the three length‐groups, significant differences were found in smolt‐to‐adult survival in each river. In pairwise comparisons, long smolts had significantly higher survival rates than middle‐sized and short smolts for both rivers. Among the three condition groups, significant differences were found in smolt‐to‐adult survival for the Ellidaár but not for the Vesturdalsá. Ages of smolts in the Ellidaár ranged from 1 to 5 years, and more than 98% of smolts were age 2–4. Smolts in the Vesturdalsá ranged in age from 2 to 7 years, and more than 99% of smolts were age 3–5. Among the dominant three age‐groups for each river, significant differences were found in smolt‐to‐adult survival. Among the three migration timing groups, significant differences were found in smolt‐to‐adult survival in both rivers. In pairwise comparisons for the Ellidaár, late‐migrating smolts had significantly higher survival rates than middle and early smolts. In the Vesturdalsá, late‐migrating smolts had significantly higher survival than early and middle smolts, which did not differ from each other. These results are placed in the context of optimization of life history strategies and ideas about the process of smoltification in Atlantic salmon life history.

Atlantic salmon (Salmo salar) smolt production: the relative importance of survival and body growth

The complex life history of Atlantic salmon ( Salmo salar ) coupled with interacting abiotic and biotic factors leads to extreme demographic variability across the species’ range. Our goal was to evaluate the relative importance of survival and body growth in determining smolt production across space and time. We used passive integrated transponder tags and capture–mark–recapture analyses to estimate survival, emigration, and growth for six cohorts of presmolt Atlantic salmon in two streams (three cohorts per stream) in New England, USA. We observed remarkable among-cohort consistency in mean monthly survival during a 17-month period from age-0+ autumn to age-2+ spring yet high variability in monthly survival over shorter time intervals (seasons). Despite this latter variability, survival did not translate into among-cohort differences in proportions of age-2+ versus age-3+ smolts. Alternatively, the high variability across seasons and cohorts in mean individual growth rate did lead to differences in within-cohort proportions of age-2+ versus age-3+ smolts (regardless of stream). We conclude that in our two small study streams, variability in growth and size impacted smolt age and, ultimately, smolt production. Density-dependent effects on growth at the scale of the entire study site represent a possible mechanism underlying our observations.

Life history changes in Atlantic salmon from the River Dee, Wales

The change in life history of Atlantic salmon (Salmo salar L) on the River Dee over the last 60 years is described. Over the last 60 years, salmon have shown a change in run timing, the majority currently entering the liver between August and October compared with prior to June. This has coincided with a change in the sea age composition, which was dominated by multi-sea winter salmon prior to the 1980s after which the proportion of 1sea-winter fish increased until they now dominate the mature population. Growth rates of salmon in fresh water remained relatively stable until the mid-1980s and then increased. By the end of the 1990s juvenile salmon were, by the end of their first and second year, respectively, ∼60 and ∼19%, on average, larger than they were between the late 1930s and mid-1980s. This has been reflected in a change in the age composition of smolts where the mean smolt age has declined from ∼2 years prior to the 1980s to ∼1.6 years in the late 1990s. There was no observed trend in post-smolt (marine) growth for salmon. Size at return for 1SW salmon appeared stable while there is some evidence of an increase in mean length of 2SW salmon at the end of the 1990s. A steady state life history model was developed which suggests an increase in the instantaneous rate of mortality by 2.9% from 1.495 year−1 in 1937/1938 to 1.538 year−1 in 1967/1969 and by 21.6% to 1.870 year−1 in 1997/1999. This is considered to explain the shift in mean age at maturity from 5.2 to 4.8 to 3.9 years for the three periods examined. There is close argeement between the observed mean age at maturity and that predicted by the model suggesting optimal lifetime reproductive success.

Importance of ontogenetic habitat shifts to juvenile output and life history of Atlantic salmon in a large subarctic river: an approach based on analysis of scale characteristics

Importance of ontogenetic habitat shifts to juvenile output and life history of Atlantic salmon in a large subarctic river: an approach based on analysis of scale characteristics

Importance of ontogenetic habitat shifts to juvenile output and life history of Atlantic salmon in a large subarctic river: an approach based on analysis of scale characteristics.

Juvenile and adult scale characteristics were used to compare two juvenile groups of Atlantic salmon in a large subarctic river in northern Scandinavia: individuals that have migrated from the main stem into small tributaries and those which remain in the main stem. Body size and scale measurements indicated enhanced growth in migratory parr as compared to their resident main stem counterparts. Analysis of adult salmon scale characteristics using maximum likelihood estimators revealed that 20% of the adults had been in the tributaries before the end of their second year of life, and more than 30% more had moved into the tributaries in the third year. Tributary fish matured at a smaller size and younger age (one-sea-winter salmon) than those rearing in the main stem which included a higher proportion of multi-sea-winter salmon. In addition, when smolt ages and ages at maturity were compared, older female smolts often resulted in smaller spawners and younger smolts, larger spawners. Small female spawners were more likely to survive to become repeat spawners.

Atlantic Salmon in the Sea

The main facts about the life history of Atlantic salmon have been known for a surprisingly long time. Neill (1946) gives an account of early writings on this subject which makes it clear that, for over four hundred years, it has been known that salmon breed in fresh-water, that they spend a period there before migrating to the sea and that, once in the sea, they undertake long migrations. These earlier writers tended to underestimate the period of time spent in the sea (e.g. they thought it likely that salmon returned to fresh water in the same year that they migrated to sea) but, otherwise, their knowledge of the life history of salmon was remarkably complete and accurate.