Anders Foldvik

Atlantic salmon Salmo salar is an anadromous species that exhibits a wide range of life history strategies. One of the least understood and documented strategies involves adult salmon ascending rivers in the autumn or early winter and remaining there without feeding for a full year before spawning. This study provides the first scientific documentation of year-early migratory salmon in Norway. About 5% of Atlantic salmon captured during tagging studies in the river Alta arrived a year prior to spawning. Tracking of 8 tagged fish in the river Alta showed that they entered the river a year prior to spawning and overwintered in the river after spawning. The longest recorded stay in freshwater was 21 mo (640 d). Scale analysis revealed that year-early migrants had smaller sizes at age during their ocean years but entered rivers with higher relative energy reserves. Genetic analysis showed that the year-early migrating fish belong to the river Alta and were not strayers from Russian populations. The factors shaping this strategy are still unclear but may involve balancing the loss of ocean growth and the costs of extended river residency against the advantage of escaping high ocean mortality rates.

Size at maturity is an important demographic characteristic due to its effect on fecundity. Synchrony in size at maturity across populations suggests similar environmental conditions, mainly through shared feeding grounds. We study such synchrony over 30 years across 187 populations using data from about 200 000 individual Atlantic salmon belonging to four geographic regions in Norway. Synchrony was high among the three southern regions, while the northernmost region had more independent fluctuations. Synchrony among closely separated populations was high, declined with distance, but was still present more than 1000 km apart. In all regions, the general pattern was that size at age was largest in the late 1980s and around 2000 and smallest between 2005 and 2010. Fulton’s condition factor was consistently largest in the North region. Overall, our results are consistent with the known marine distribution, including that the northernmost populations have a reduced migration distance to feeding areas and forage more northeast than the southern populations. The observed synchrony in size at maturity is anticipated to have large-scale demographic consequences by generating synchrony in egg deposition.

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone) is a widespread contaminant of emerging concern resulting from oxidation of 6PPD, which is an antidegradant substance added to tires. The recent identification of 6PPD-quinone as the cause of acute mortality in coho salmon has quickly motivated studies on 6PPD-quinone toxicity to other species. Subsequent findings have shown that 6PPD-quinone toxicity is highly species specific. Closely related species can differ widely in response to 6PPD-quinone from extremely sensitive to tolerant. Hence toxicity testing is currently the only way to establish whether a species exhibits 6PPD-quinone toxicity. We investigated the acute toxicity of 6PPD-quinone in pink salmon alevins (sac fry). This species has is the only Pacific salmon that so far has not been tested for 6PPD-quinone sensitivity. Fish were exposed in static water in eight treatments with initial concentrations ranging from 0.1 to 12.8 μg/L. Fish were observed for 48 h, and changes in concentrations of 6PPD-quinone were monitored throughout the experiment. No mortalities or substantial changes in behavior were recorded. Environ Toxicol Chem 2024;43:1332–1338. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

In many populations of Atlantic salmon, individuals return to rivers months or even a year prior to spawning. This premature arrival in fresh water by far exceeds the time needed for upstream migrations to spawning areas. Leaving the ocean early means forgoing substantial growth and incurring high metabolic costs of fasting in freshwater. Differences in timing of return migration has been shown to have a genetic basis, and different sea age classes return to rivers at different times. Previously suggested explanations regarding the cause for this behaviour have included both environmental factors and life history trade‐offs, but these hypotheses have not been tested. Here, we combine data on marine growth and mortality of Atlantic salmon with the calculations of energetic expenditures of fasting in freshwater to explore how timing of river entry affects the probability of survival and energy recourses available for spawning. Our results show that to maximize the product of survival until spawning and energy available at spawning, multi sea winter fish in general must enter rivers earlier than one sea winter fish. And that for a large range of sea survival rates, the optimum river entry date for multi sea winter fish is as early as possible. This strongly suggests that the phenomena of premature arrival in Atlantic salmon is adaptive behaviour.

Recent identification of 6PPD-quinone as the chemical causing acute toxicity in coho salmon has led to substantial concern regarding the toxicity of this contaminant for other aquatic species. Environmental occurrence of 6PPD-quinone is probably high, because it is an oxidation product of a common tire rubber additive. Research on 6PPD-quinone toxicity in fish has revealed a rather unusual pattern, with closely related species exhibiting responses ranging from extreme sensitivity to no effect. Of 11 previously studied fish species, 6PPD-quinone was toxic to four. The species-specific toxicity of 6PPD-quinone complicates urgently needed environmental risk assessment. We investigated the acute toxicity of 6PPD-quinone in Atlantic salmon and brown trout alevins (sac fry). These species have previously not been tested for sensitivity to 6PPD-quinone. The fish were exposed in static conditions in eight treatments with initial concentrations ranging from 0.095 to 12.16 µg/L. Fish were observed for 48 h, and changes in concentrations of 6PPD-quinone were monitored throughout the experiment. No mortalities or substantial changes in behavior were recorded in either Atlantic salmon or brown trout. This provides an important first step in assessing effects of 6PPD-quinone on these economically and culturally highly important species. Environ Toxicol Chem 2022;41:3041–3045. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sedimentation is one of the main eco-morphological and technological challenges associated with reservoirs. Sedimentation not only reduces the functional capacity of a reservoir by filling it, but also changes downstream sediment dynamics and habitat availability for the aquatic biota. Additionally, dams hinder free bi-directional fish passage, emerging as a major threat to species of migratory fish. In the past decades, mitigation measures aimed at reducing such environmental and technological impacts have been developed. Sediment bypass tunnels (SBTs) have been shown to successfully help prevent reservoir sedimentation, whereas fish passages have been found to be potential solutions to facilitate bi-directional passage of fish. However, the construction of such structures, in particular of SBT, can be extremely costly. The development of design solutions that can function both for downstream sediment transport and up- and downstream fish passage should be considered as they can mitigate ecological deficiencies of reservoir operations while accounting for economic feasibility. Possibilities and challenges of combining SBT and fish passage were explored by bringing together a team of interdisciplinary specialists on hydraulics, sediment transport and continuity, bypassing, hydraulic structures, hydropower engineering, aquatic biology, and fish passage in a two-day workshop. Here, we present potential solutions identified during the workshop for integrating SBT and fish passage.

While effects of acidification on salmonid fish are well studied and documented, effects of episodic high pH have rarely received attention. In the present study, we investigate effects of high pH events on Atlantic salmon (Salmo salar) using both field and laboratory data. Effects of an episodic high pH event on juvenile densities in a Norwegian river were studied using data from several electrofishing surveys conducted both before and after the event. Effects of high pH on survival of eggs were studied by exposing eggs to a range of high pH treatments for different durations. Juvenile densities from the field study showed that the high pH event had little or no effect on the cohort that had been exposed to pH 9.7-10.3 during the egg stage. This finding was in accordance with the laboratory experiment that showed no excess mortality on eggs until pH was above 12. The high pH event occurred in March during low winter flows, and densities of older juveniles in May were significantly lower in the affected area compared to controls upstream. In June and September the difference was not significant, but there was a clear spatial trend indicating that the event had a negative effect on densities of older juvenile salmon.

Traditional tagging methods for fishes can have issues relating to both animal welfare and economic costs. Biometric data such as iris patterns can be captured via digital cameras, which allows for non-invasive tagging and inexpensive and rapid analysis. The purpose of this study was to investigate if the iris of Atlantic Salmon (Salmo salar) is a suitable biometric template for long-term identification of individuals. Atlantic Salmon were individually tagged in the body cavity using PIT tags at the juvenile pre-smolt stage, and the left eye was photographed six times over a 533-day period. Changes in iris stability were assessed both qualitatively and using iris-recognition software. Identification of individual Atlantic Salmon using the iris was not successful over the entire period, as the iris pattern changed significantly with time. Over a shorter time period (four months) with frequent samplings, iris software was able to correctly identify individual fish. The results show that iris identification has potential to replace other methods for Atlantic Salmon over short timeframes.