Bacon, P. J., Palmer, S. C. F., MacLean, J. C., Smith, G. W., Whyte, B. D. M., Gurney, W. S. C., and Youngson, A. F. 2009. Empirical analyses of the length, weight, and condition of adult Atlantic salmon on return to the Scottish coast between 1963 and 2006. – ICES Journal of Marine Science, 66: 844–859. Sea age, size, and condition of adult Atlantic salmon (Salmo salar) are prime determinants of individual, and hence population, productivity. To elucidate potential mechanisms, 151 000 records of salmon returning to six Scottish coastal sites over 44 years were analysed for length, weight, and condition, by site, sex, sea age, and river age. After correcting for capture effort biases, all sites showed seasonal increases in length and weight for both 1 sea winter (1SW) and 2SW fish. However, whereas condition increased slightly with season for 2SW, it decreased notably for 1SW. Sites showed common decadal trends in length, weight, and condition. Within years, length and weight residuals from trends were coherent across sites, but residuals from condition trends were not. Rates of seasonal condition change also showed decadal trends, dramatically different between sea ages, but common across sites within sea-age groups. Longer salmon were disproportionately heavy in all seasons. 1SW condition was markedly lower in 2006. Detrended correlations with oceanic environmental variables were generally not significant, and always weak. A published correlation between the condition of 1SW salmon caught at a single site and sea surface temperatures in the Northeast Atlantic could not be substantiated for any of the six fisheries over the wider time-scales examined.

Todd, C. D., Friedland, K. D., MacLean, J. C., Whyte, B. D., Russell, I. C., Lonergan, M. E., and Morrissey, M. B. 2012. Phenological and phenotypic changes in Atlantic salmon populations in response to a changing climate. – ICES Journal of Marine Science, 69: 1686–1698. Atlantic salmon (Salmo salar) of southern European origin migrating to the Norwegian Sea currently encounter anomalously high sea-surface temperatures, and returning adults are of low mean condition factor. For the River North Esk (Scotland), time-series changes in river age-structure of emigrant smolts and returning one- and two-sea-winter (1SW and 2SW) adults are assessed. A comparison of the river age-structure of returning adults (1977–1999) with that of their respective annual emigrant smolt cohorts shows no evidence of river age-related bias in survivorship at sea. Evidence is presented of a possible transgenerational, or maternal, influence (poor somatic condition of spawners) driving reduced quality of emigrant S2 smolts in the North Esk. This effect is concurrent with an influence of freshwater climate as indicated by the North Atlantic Oscillation Index (NAOI). The maternal influence and NAOI variation in the winter immediately prior to smolt migration jointly explain approximately 29 (S2) and 17% (S3), respectively, of the variation in the mean size of smolts over the period 1975–2010. Run-timing of 1SW adult cohorts returning to Scotland shows recent delays. Variation in river flow did influence mean return date for the River Tweed, but adult condition factor, which itself shows temporal trends likely to be associated with ocean climate change, was the primary significant explanatory variable for run-timing in the rivers North Esk and Tweed. Overall, in years of poorer adult condition, 1SW salmon stay at sea longer.

A method of dating the marine growth circuli on Atlantic salmon (Salmo salar L.) scales is presented. Data were available for 54 salmon, intercepted as smolts at the completion of their downstream migration in the River North Esk, Scotland.Smolts were tagged, released, and recaptured as return adults after either one (1SW) or two (2SW) winters at sea. Dating of circuli was achieved by fitting a simple quadratic model to the circuli pertaining to fixed points on the scale. For 1SW fish, the latter were the dates of river emigration and completion of marine migration, and the midpoint circulus (equal to the winter solstice) of the winter annulus. For 2SW salmon, these were the date of emigration and the two winter annulus midpoints. A key assumption is that winter annulus formation arises from constraints of light availability on foraging, and hence, reduced growth rate.Comparative analyses indicate the method to be robust and effectively transferable to salmon of known capture date -but of unknown smolt emigration date -by assuming a fixed date of emigration; in such cases, circuli could still be allocated with confidence to a calendar month.Résumé : Une méthode de datation des stries de croissance en mer sur les écailles de saumon atlantique (Salmo salar L.) est décrite. Des données étaient disponibles pour 54 saumons interceptés au stade de saumoneau à la fin de leur avalaison dans la rivière North Esk, en Écosse. Les saumoneaux ont été marqués, relâchés, puis repris en tant qu'adultes à leur retour après un (1SW) ou deux (2SW) hivers en mer. La datation des stries a été effectuée en calant un modèle quadratique simple sur les stries reliées à des points fixes sur l'écaille. Pour les poissons 1SW, ces points étaient les dates de l'émigration de la rivière et de la fin de la migration marine, ainsi que la strie médiane (égal au solstice d'hiver) de l'anneau hivernal. Pour les saumons 2SW, il s'agissait de la date d'émigration de la rivière et des stries médianes des deux anneaux hivernaux. La méthode repose notamment sur l'hypothèse voulant que la formation des anneaux hivernaux soit causée par des restrictions à l'alimentation associées à la lumière disponible et, donc, à une réduction du taux de croissance. L'analyse comparative indique que la méthode est robuste et peut être appliquée avec succès à des saumons dont la date de capture est connue (mais dont la date d'émigration en tant que saumoneaux est inconnue) en postulant une date d'émigration fixe; dans ces cas, les stries peuvent quand même être affectées avec confiance à un mois précis. [Traduit par la Rédaction]

Caligid ectoparasitic copepods are major pathological pests on cultured Atlantic salmon Salmo salar L., and their population biology has been well studied in the farm environment. The ecology of caligid infestations of wild salmon is, by contrast, rather poorly understood. We monitored return migrant one sea-winter wild Atlantic salmon in Scotland annually for infestations of 2 caligids, Lepeophtheirus salmonis (Krøyer) (between 1998 and 2005) and Caligus elongatus Nordmann (between 1999 and2005). Prevalence of L. salmonis was 100% in all years, whereas C. elongatus prevalence ranged from 90 to 100%. Abundances fluctuated markedly between years and L. salmonis mean abundance (min. to max.: 17.4 to 31.0) was significantly greater than for C. elongatus (min. to max.: 2.9 to 23.8) in all except one year. A positive association in abundance of the 2 species, for individual fish within any one year, indicates weak or absent competitive effects on abundances for individual hosts. Individual fish within any one year appeared similarly vulnerable to infestation by either species, although Taylor's power regression showed clear differences in density-related patterns of overdispersion amongst hosts for the 2 species. Host condition factor (expressed either as Fulton's index, K, or the relative mass index, W R ) showed significant variation among years. Parasite species abundances were not, however, determined by host condition factor, and poor condition fish were no more likely to carry high infestations than were high condition fish.