Does global change increase the risk of maladaptation of Atlantic salmon migration through joint modifications of river temperature and discharge?

In freshwater ecosystems, water temperature and discharge are two intrinsically associated triggers of key events in the life cycle of aquatic organisms such as the migration of diadromous fishes. However, global changes have already profoundly altered the thermal and hydrological regimes of rivers, affecting the timing of fish migration as well as the environmental conditions under which it occurs. In this study, we focused on Atlantic salmon ( Salmo salar ), an iconic diadromous species whose individuals migrate between marine nursery areas and continental spawning grounds. An innovative multivariate method was developed to analyse long-term datasets of daily water temperature, discharge and both salmon juvenile downstream and adult upstream migrations in three French rivers (the Bresle, Oir and Nivelle rivers). While all three rivers have gradually warmed over the last 35 years, changes in discharge have been very heterogeneous. Juveniles more frequently used warmer temperatures to migrate. Adults migrating a few weeks before spawning more frequently used warm temperatures associated with high discharges. This has already led to modifications in preferential niches of both life stages and suggests a potential mismatch between these populations' ecological preference and changes in their local environment due to global change.

Characterization of feeding and downstream migration of juvenile chum salmon in the Kichiga river (north-eastern kamchatka)

Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.

Evaluation of oregano (Origanum vulgare) essential oil supplementation on growth performance, digestive enzymes, intestinal histomorphology and gut microbiota of Black Sea salmon, Salmo labrax

This study aimed to determine the effect of dietary oregano (Origanum vulgare) essential oil (EO) on the growth performance, digestive enzyme activity, intestinal histomorphology, and intestinal microbiota of the Black Sea salmon juvenile (Salmo labrax). Fish fed with diets have at different levels oregano EO such as 50, 100, 200, and 400 mg kg−1. For this purpose, a total of 675 fish were distributed randomly in triplicate into 5 experiment groups in 15 experiment tanks. Fish with average initial weights of 3.52±0.01g were fed by hand 3% level of live weight for 90 days. At the end of the study, feeding with oregano EO supplementation didn’t significantly affected the growth performance of fish. Except for pepsin, there were no significant differences in the activity of digestive enzymes among the control and oregano EO groups. Besides, oregano EO at the doses of 50 or 400 mg kg−1 may have the potential to increase the surface area required for digestion by increasing intestinal villi length. Moreover, all doses of oregano EO showed antimicrobial properties by decreasing the count of lactic acid bacteria in the intestine. Supplementation with 100 and 200 mg kg−1 oregano EO in diets decreased the total coliform, Escherichia coli and lactic acid bacteria counts when compared to the control group. The results showed that oregano EO may affect positively digestion and absorption without adverse effects on the growth performance of Black Sea salmon juvenile.

Coherent population dynamics associated with sockeye salmon juvenile life history strategies

Although the importance of diversity to maintaining metapopulation stability is widely recognized, the ecological characteristics that lead to synchronous dynamics within population aggregates are often unclear. We used a constrained dynamic factor analysis to explore patterns of covariance in productivity among 16 Fraser River sockeye salmon (Oncorhynchus nerka) conservation units (CUs). Specifically, we tested whether coherent trends in productivity covaried with five distinct ecological attributes: physical characteristics of nursery lakes, large-scale management interventions, genetic similarity, adult migration phenology, or juvenile migratory traits. The top-ranked model had two trends based on nursery lake characteristics and juvenile migratory traits. One trend represented the dynamics of CUs that rear in nursery lakes prior to ocean entry and undergo relatively rapid marine migrations. The second included a sea-type CU, Harrison River, which enters the marine environment without rearing in a nursery lake and migrates more slowly. The uniform response of lake-type CUs, as well as Harrison River CU’s unique life history, suggests that coherent trends are structured by traits that covary with broad life history type, rather than fine-scale characteristics. Furthermore, we document substantial temporal variability in the strength of synchronous dynamics among Fraser River CUs. Greater synchrony in recent years suggests that the importance of shared regional drivers, relative to local processes, may have increased.

EVALUATION OF THE RIVERS VILNIA AND SIESARTIS ECOTOXICOLOGICAL STATE BASED ON MORPHOLOGICAL INDEXES OF JUVENILE ATLANTIC SALMON (SALMO SALAR L.) / SIESARTIES IR VILNIOS UPIŲ EKOTOKSIKOLOGINĖS BŪKLĖS ĮVERTINIMAS PAGAL ATLANTINĖS LAŠIŠOS (SALMO SALAR L.) JAUNIKLIŲ MORFOLOGINIUS RODIKLIUS

Objective of the study – to evaluate ecotoxicological state of two probably differently polluted salmon rivers: the Vilnia and Siesartis based on Atlantic salmon (Salmo salar L.) juvenile’s morphological indexes. Statistical analysis of estimated fish morphometric parameters and morphological indexes showed that the Vilnia and Siesartis Rivers’ salmon juveniles differ significantly. Condition factor (CF) and the gills-somatic index (GSI) were found to be the most sensitive biomarkers reflecting the physiological state of the fish. The Vilnia River salmon juvenile CF and GSI value was significantly different as compared with the Siesartis River’s salmon juvenile indexes, apparently, due to the increased water pollution. Since according to the classical physico-chemical parameters, both rivers’ water was very similar [no significant differences were found (p > 0.1)], it was suggested that here exist other non-specific chemical factors (pollutants) in water, which determine fish physiological and indicate river ecotoxicological states. Tyrimo tikslas – įvertinti dviejų galimai skirtingai užterštų lašišinių upių Vilnios ir Siesarties ekotoksikologinę būklę pagal atlantinės lašišos (Salmo salar L.) jauniklių morfologinius rodiklius. Statistiškai apdorojus ir apskaičiavus žuvų morfometrinius parametrus bei morfologinius rodiklius, nustatyta, kad tirtos Vilnios ir Siesarties žuvys gerokai skiriasi. Žuvų įmitimo koeficientas (IK) ir žiaunų somatinis indeksas (ŽSI) – jautriausi biožymenys, atspindintys žuvų fiziologinę būklę. Vilnios upėje lašišų jauniklių IK ir ŽSI vertės gerokai skyrėsi, lyginant su Siesarties upės lašišų jauniklių rodikliais, tikriausiai dėl didesnės vandens taršos pirmojoje upėje. Kadangi pagal klasikinius fizinius ir cheminius vandens parametrus upės buvo labai panašios [patikimų skirtumų nenustatyta (p > 0,1)], galima teigti, kad egzistuoja kiti, nespecifiniai cheminiai veiksniai (teršalai) vandenyje, kurie lemia žuvų fiziologinę bei indikuoja upių ekotoksikologinę būklę.

Advancing an Ecosystem Approach in the Gulf of Maine

<i>Abstract</i> .—The marine survival of Atlantic salmon <i>Salmo salar </i> stocks in the Gulf of Maine area has declined as sea surface temperature in the coastal ocean has increased; in part, this change in recruitment can be attributed to a phenological mismatch between the timing of smolt migrations and initial conditions postsmolts find during their early marine phase. Salmon juvenile migrations to the ocean are released by photoperiod and spring transitional freshwater temperatures, neither of which have changed significantly in recent decades, thus actuating the migrations at nearly the same time each year. However, ocean water temperatures have increased during the spring transition period, suggesting that smolts have entered the ocean under varying physical and biological conditions. The phenological effect observed in the Gulf of Maine is consistent with the relationship observed for the North American stock complex. In light of recent findings related to the growth of postsmolts, the contrast in recruitment for North American salmon, and Gulf of Maine stocks in particular, appears to be the result of mortality that occurs during the first months at sea. This mortality covaries with the thermal changes in the coastal ocean, which we suspect is associated with variation in the predator field.

Recycling of Elements Transported Upstream by Runs of Pacific Salmon: II. δ15N and δ13C Evidence in the Kvichak River Watershed, Bristol Bay, Southwestern Alaska

Biota δ15N and δ13C values (deviations from recognized isotope standards) from lliamna Lake (a major anadromous sockeye salmon (Oncorhynchus nerka) nursery lake supporting peak-year runs > 10 million) and several other anadromous-salmon-free lakes in the Kvichak River watershed, Bristol Bay, southwestern Alaska, were compared to determine the significance of marine-derived nitrogen (MDN) delivered by returning adult salmon. Biota in lliamna Lake had higher δ15N compared with control lakes, verifying a mixing model correlating δ15N with MDN. Periphyton δ15N values reflected localized input from populations of spawning salmon. Juvenile sockeye MDN varied in response to escapement size, suggesting the importance of large escapements (> 10 million) for maintaining a predominantly MDN lacustrine N pool. Other resident fishes showed shifts in δ15N between years of high and low escapement. The dual-isotope approach, using δ15N and δ13C together, suggested that fish production is primarily dependent on limnetic primary and secondary production. The dual-isotope approach indicated that the coast range sculpin (Cottus aleuticus) was the only fish with an appreciable dietary component consisting of salmon eggs or emergent fry.