Differential changes in growth patterns of anadromous brown trout and Atlantic salmon from the River Etneelva over a 25-year period

Abstract

Freshwater and marine growth of anadromous brown trout (Salmo trutta) and Atlantic salmon (Salmo salar) from the River Etneelva was analysed in relation to river, fjord and ocean temperatures during the periods 1976Á1982 and 2000Á2007. Anadromous brown trout grew more slowly through their first and second summers in the sea during the last observation period compared to the first period, and there were more growth checks in the scales sampled from the last period. The reduced growth in length corresponds to a weight reduction of about 20Á40%. In fresh water, there was no change in growth rate of the trout parr, while in Atlantic salmon, growth rates of both parr and post-smolts increased from the first to the second period, possibly due to the corresponding increase in temperatures in the river and the marine environments. Anadromous brown trout stay in the fjord during the whole marine feeding period, and therefore the reduced growth in the sea must be caused by factors operating in the fjord environment. Although changes in food availability may also play a part in the observed changes, the negative trend for anadromous brown trout is most likely related to the high infection levels of salmon lice (Lepeophtheirus salmonis) observed in the central and outer parts of the Hardangerfjord.

Evidence for long‐term change in length, mass and migration phenology of anadromous spawners in French Atlantic salmon Salmo salar

“…In contrast, recreational hook-and-line fisheries are operating in almost all rivers across the species' distribution range. Thus, when available, catch data provide the broadest spatio-temporal sampling of S. salar populations across several countries (Bacon et al, 2009;Valiente et al, 2011;Fjørtoft et al, 2014). Here, time trends in S. salar life-history traits were analysed using catch data from both recreational and commercial freshwater fisheries.…”

Exocrine glands of Lepeophtheirus salmonis (Copepoda: Caligidae): Distribution, developmental appearance, and site of secretion

“…Lice infestation can be detrimental to fish as it disturbs the osmotic balance and stress the fish increasing the susceptibility to other pathogens (Grimnes and Jakobsen ; Finstad et al, ; Tort ). An increased occurrence of resistance to antiparasitic treatments and the consecutive impact on wild salmonid fish (Besnier et al, ; Fjørtoft et al, ; Vollset et al, ; Aaen et al, ), underscores the importance of a better understanding of this parasite to enable the development of new countermeasures.…”

Aquaculture and environmental drivers of salmon lice infestation and body condition in sea trout

“…A number of studies also record impaired swimming performance (Wagner et al 2003) and feeding activity in lice-infested fish, typically once the salmon lice have moulted to the pre-adult and adult stages (Dawson et al 1998, Wells et al 2006. Fjørtoft et al (2014) demonstrated that sea trout growth was slower during the first and second summers at sea when salmon farming was active, with the growth reduction after the first summer in the sea corresponding to a body mass reduction of 20 to 40%. This compares to a 14% reduction in the weight of a sea trout of mean length in the present study.…”