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Determining the mechanisms driving range-wide reductions in Atlantic salmon marine survival is hindered by an insufficient understanding of their oceanic ecology and distribution. We attached 204 pop-up satellite archival tags to post-spawned salmon when they migrated to the ocean from seven European areas and maiden North American salmon captured at sea at West Greenland. Individuals migrated further north and east than previously reported and displayed increased diving activity near oceanographic fronts, emphasizing the importance of these regions as feeding areas. The oceanic distribution differed among individuals and populations, but overlapped more between geographically proximate than distant populations. Dissimilarities in distribution likely contribute to variation in growth and survival within and among populations due to spatio-temporal differences in environmental conditions. Climate-induced changes in oceanographic conditions will alter the location of frontal areas and may have stock-specific effects on Atlantic salmon population dynamics, likely having the largest impacts on southern populations. [ABSTRACT FROM AUTHOR]

Climate change is expected to affect the flow regime, cause loss of habitat, change community composition and behavioural habits of fish. This study assessed the impact of climate change on ecologically relevant streamflow conditions for fish migration and spawning in the Vistula and the Odra river basins. Streamflow simulations obtained with the Soil and Water Assessment Tool (SWAT) for the historical period and two future horizons were driven by nine bias‐corrected EURO‐CORDEX Regional Climate Models under two greenhouse gas concentration trajectories. This study identified a subset of Indicators of Hydrological Alteration (IHA) that are relevant for pike, Esox lucius L., chub, Squalius cephalus (L.), and Atlantic salmon, Salmo salar L. IHA indicators were calculated and compared for different scenarios. An index‐based framework identified that all considered species will be impacted by climate change, with Atlantic salmon facing the largest impact. The model's uncertainty was addressed through an aggregation method that assessed inconsistencies in the model's response. [ABSTRACT FROM AUTHOR]

Atlantic salmon populations appear to fluctuate stochastically through time. It is suspected that both density‐dependent and density‐independent factors cause these fluctuations but the relative importance of each, and the life stages at which they operate, is not well known. In this study, a long‐term data set on Atlantic salmon migrants returning to the Foyle catchment, Ireland, was used to determine the role of density‐dependent and life stage‐specific environmental factors regulating population size. A Ricker density‐dependent model showed that spawning adult population size significantly predicted variation in the resultant filial generation; however, a large amount of variation (ca. 68%) remained unexplained. It was shown that environmental factors were significant in explaining some of the remaining variance and that these influences were linked to specific life stages. Three life stages—spawning and incubation, fry emergence and marine survival—were shown to have significant environmental effects that resulted in changes in the returning cohort strength. It is concluded that these life stage‐specific environmental effects are likely to contribute to the stochastic variation in population size resulting from the application of traditional stock–recruitment models. The identification and quantification of these effects should allow improved model accuracy. [ABSTRACT FROM AUTHOR]

The risk of mortality associated with a long-distance migration will depend on an animal's physiological state, as well as the prevailing ecological conditions. Here, we assess whether juvenile telomere length, which in endotherms has been shown to be a biomarker of physiological state and expected life span, predicts whether wild Atlantic salmon Salmo salar successfully complete their marine migration., Over 1,800 juvenile fish were trapped, measured, passive integrated transponder tagged and a tissue biopsy taken when migrating as juveniles down-river towards the sea. Survivors of the marine phase of the life cycle were then re-trapped and re-sampled when returning to the river to spawn as sexually mature adults, 1.5-2.5 years later. Most individuals experienced a reduction in telomere length during the marine migratory phase of their life cycle. While the relative rate of telomere loss was greater in males than females, telomere loss was unrelated to growth at sea., Contrary to expectations, salmon that had the shortest telomeres at the time of the outward migration had the greatest probability of surviving through to the return migration. This effect, independent of body size, may indicate a trade-off between investment in readiness for marine life (which favours high glucocorticoid levels, known to increase telomere attrition in other vertebrate species) and investment in telomere maintenance. Survival was also significantly influenced by the seasonal timing of outward migration, with the fish migrating downstream earliest in the spring having the highest probability of return., This study reveals that telomere length is associated with survival, although in ways that contrast with patterns seen in endotherms. This illustrates that while telomeres may be universally important for chromosome protection, the potential for telomere dynamics to predict performance may vary across taxa., A is available for this article. [ABSTRACT FROM AUTHOR]

Atlantic salmon ( Salmo salar) often survive spawning and migrate back to the sea to feed, either shortly after spawning in autumn or the following spring. We conducted a 4-year observational field study using telemetry to evaluate the determinants of migration timing in Atlantic salmon postspawners (kelts). We found that individuals with low energy reserves migrated early to the risky but productive marine habitat, whereas individuals with greater energy reserves stayed in the safe but less productive river habitat until staying became energetically more costly than migrating. For males, the likelihood of overwintering in the river instead of migrating in autumn increased 27-fold with each increase in body condition index, whereas almost all females overwintered in the river. Among spring migrants, body condition was the strongest determinant of migration timing, and females left the river about 5 days later than males. Our study suggests that migration timing in Atlantic salmon kelts is the outcome of adaptive state-dependent habitat use, related to individual and sexual differences in energy allocation during spawning. [ABSTRACT FROM AUTHOR]

Pop-up satellite archival tags identified differences in oceanic migration of Atlantic salmon ( Salmo salar) kelts from three distinct Canadian populations. Kelts from two endangered populations were restricted to coastal areas near home rivers, whereas kelts from a persisting nearby population migrated to the Labrador Sea and towards the Flemish Cap. Kelts spent most time near the surface (0-5 m), but coastal migrants undertook repeated daytime dives (10-40 m), associated with feeding, upon marine entry and progress was slow (8-23 km·day−1). Distant migrants moved rapidly along the continental shelf (10-50 km·day−1) against prevailing ocean currents, remaining near the surface, except for deep dives (100-1000 m) when crossing ocean channels and at the shelf edge. Home range water temperatures (0-15 °C) indicated that kelts avoided warmer adjacent areas in summer. Kelts did not avoid cold coastal habitat (0-5 °C) in winter, but avoided the surface layers. Kelt migration mimicked that of postsmolts of similar origins, with water temperature acting as a directive or controlling factor. Containment of kelts from endangered populations in coastal habitat was probably responsible for the disappearance of repeat spawners. [ABSTRACT FROM AUTHOR]

- Programmes of habitat restoration usually assume that the targeted populations will readily colonise the newly provided habitat. However, this assumption may not always hold, and the success of restoration may be impaired if the individuals are driven to aggregate in areas of the habitat already available instead of spreading to new ones. We investigated how weirs situated along a river could drive Atlantic salmon ( Salmo salar) to aggregate their redds and tested whether aggregation intensified at low fish density. For this, we applied spatial point pattern analysis to a data set consisting on the distribution of salmon redds in a small river over 15 years (1992-2006). Within the habitat suitable for spawning, redds were significantly aggregated, especially in the first 15 morphodynamic units below weirs. Our results suggest that the constraint imposed by obstacles on redd distribution should be considered when conducting habitat restoration. [ABSTRACT FROM AUTHOR]

Hubley, P. B., Amiro, P. G., Gibson, A. J. F., Lacroix, G. L., and Redden, A. M. 2008. Survival and behaviour of migrating Atlantic salmon (Salmo salar L.) kelts in river, estuarine, and coastal habitat. – ICES Journal of Marine Science, 65: 1626–1634.The downstream migration of 30 Atlantic salmon (Salmo salar) kelts tagged with acoustic transmitters was monitored using 26 underwater receivers at eight locations from April to October 2006 in the LaHave River and Estuary. In all, 27 tags were detected as they left the coastal environment by the middle of May, 5 weeks after release, indicating a possible 90% kelt survival to coastal departure. Two missing tags and one dropped tag were assumed to be attributable to natural mortality in the estuary. Migration time from release to the outermost coastal receivers 24 km below the tide limit took an average of 14 d, but varied from 3 to 32 d. Some 40% of the kelts lingered and were active in the lower estuary. Five kelts monitored with depth transmitters migrated mostly at the surface in all habitats, with occasional brief descent to the bottom. A consecutive spawning salmon returned after 79 d outside the outermost array. The low rate of returns is consistent with the historical repeat spawning schedule for this river, and more precisely documents the temporal and spatial habitat use of migrating kelts. [ABSTRACT FROM PUBLISHER]

Spawning migration timing of maiden Atlantic salmon Salmo salar and previous spawners was analysed in the catches in 1989–2004 in the large subarctic River Teno in the northernmost parts of Finland and Norway. The hypothesis was that the migration timing of previous spawners and their maiden counterparts is similar, with the migration timing similar between sexes. In most cases, however, previous spawners were observed to migrate into the River Teno and its tributaries earlier than their maiden counterparts. The difference in run timing was especially evident between maiden one-sea-winter (1SW) Atlantic salmon and the corresponding group of previous spawners [1S1, 1 year at sea (1) followed by first spawning (S) and reconditioning period of 1 year (1) at sea and second spawning run] for both sexes in the River Teno and in its two tributaries. The same was also evident between 2SW maiden and 2S1 previous spawning female Atlantic salmon in the River Teno. Females showed earlier spawning migration than males both in previous spawners and maiden Atlantic salmon. Different maiden sea-age classes also showed differences in run timing as multi-sea-winter fish (2–4SW) ascended earlier than 1SW fish but the timing of 1S1 and 2S1 previous spawning females coincided. The results suggest that run timing of Atlantic salmon may not be strictly genetically fixed as previous spawners ascend earlier than they did on their first spawning migration as maiden fish, and indicated that the closeness of the reconditioning area of postspawners to the river of origin resulted in an early ascent. Run timing of different sea-age groups has major management implications if the populations are heavily exploited with numerous fishing methods in different periods of the fishing season, as in the River Teno system. [ABSTRACT FROM AUTHOR]

The return of Atlantic salmon ( Salmon salar ) to their home river for spawning coincides with drastic skeletal alterations in both sexes. Most prominent is the development of a kype (hook) at the tip of the lower jaw in males. Salmon that survive spawning have to cope with the kype throughout their life, unless it disappears after spawning, as was suggested in the early literature. To understand the fate of the kype skeleton, we compared morphological and histological features of kypes from pre-spawned mature anadromous males (grilse) with post-spawned males (kelts). The kype of male grilse is supported by fast-growing skeletal needles that differ from regular dentary bone. In kelts, growth of the kype skeleton has stopped and skeletal needles are resorbed apically by osteoclasts. Simultaneously, and despite the critical physiological condition of the animals, proximal parts of the kype skeleton are remodelled and converted into regular dentary bone. Apical resorption of the skeleton explains reports of a decrease of the kype in kelts. The conversion of basal kype skeleton into regular dentary bone contributes to the elongation of the dentary and probably also to the development of a larger kype in repetitive spawning males. [ABSTRACT FROM AUTHOR]