ABSTRACT A management regulation applied in some recreational Atlantic salmon ( Salmo salar ) fisheries is a moratorium on harvest of female fish, which can only be effective if recreational anglers can consistently discriminate females from males. We used molecular methods to compare angler‐reported sexes of salmon captured in Norwegian populations with the true sexes of the same individuals. We made this comparison (i) among rivers that were subject to female no‐take policies or not within the same year; and (ii) within rivers before and after a female no‐take regulation was instituted. Sex was misclassified for ca. 25% of salmon that were true females, especially those that were large or captured early in the season. Furthermore, true females were misclassified more often when a female no‐take regulation was in effect. We conclude that a management regulation aimed at protecting female salmon in recreational fisheries may be less effective than expected.

ObjectiveSurveillance fishing surveys can be performed to estimate the proportion of farmed salmon represented in the spawning stock of native Atlantic Salmon Salmo salar populations. These surveys take place after the recreational fishing period and therefore closer to the spawning period than the open recreational fishing season. Although catch-and-release angling has been demonstrated to affect salmon migration during the summer months, surveillance fishing that is conducted close to the spawning time could have more severe effects.MethodsTo test this, the migration distance of Atlantic Salmon (n = 74) caught in the Orkla River, Norway, was tracked by use of radiotelemetry. One group was tagged during the regular fishing season in the summer (control group), whereas another group was tagged in autumn during surveillance fishing (surveillance group).ResultSixty-one salmon remained for analysis after we excluded fish that were recaptured, died, or migrated to other rivers. Relocation of the salmon during autumn (October 11-31) was used to compare movements and test for differences in migration using negative binomial regression because distances were nonnegative integers. During the tracking period, the surveillance group moved 12 +/- 14 km (mean +/- standard deviation) and the control group moved 13 +/- 15 km; both groups moved 1 +/- 2 km/day on average. There was no evidence that surveillance fishing impacted movement of the salmon compared to controls. However, one salmon died after tagging and three were not released due to injuries; total mortality of 9% during surveillance fishing could be unsustainable for smaller populations. Consequently, factors such as surveillance sample size, the status of the salmon population, and the population size should be assessed for each river individually when deciding the necessity of and approach to surveillance fishing.ConclusionThe results support existing recommendations to use careful handling and to end surveillance at least 2 weeks prior to the expected onset of spawning, thus providing a sufficiently long period for recovery after surveillance fishing. Impact statement Surveillance fishing is a method to determine the number of farmed salmon in a river. Capture and release of wild salmon during an autumn surveillance period may negatively impact these important spawners, but we found that movement of surveillance-captured fish was not different from a control group.

Although 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 investigated 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 >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. Environ Toxicol Chem 2022;41:771-780. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Abstract Genetic methods for the estimation of population size can be powerful alternatives to conventional methods. Close‐kin mark–recapture (CKMR) is based on the principles of conventional mark–recapture, but instead of being physically marked, individuals are marked through their close kin. The aim of this study was to evaluate the potential of CKMR for the estimation of spawner abundance in Atlantic salmon and how age, sex, spatial, and temporal sampling bias may affect CKMR estimates. Spawner abundance in a wild population was estimated from genetic samples of adults returning in 2018 and of their potential offspring collected in 2019. Adult samples were obtained in two ways. First, adults were sampled and released alive in the breeding habitat during spawning surveys. Second, genetic samples were collected from out‐migrating smolts PIT‐tagged in 2017 and registered when returning as adults in 2018. CKMR estimates based on adult samples collected during spawning surveys were somewhat higher than conventional counts. Uncertainty was small (CV < 0.15), due to the detection of a high number of parent–offspring pairs. Sampling of adults was age‐ and size‐biased and correction for those biases resulted in moderate changes in the CKMR estimate. Juvenile dispersal was limited, but spatially balanced sampling of adults rendered CKMR estimates robust to spatially biased sampling of juveniles. CKMR estimates based on returning PIT‐tagged adults were approximately twice as high as estimates based on samples collected during spawning surveys. We suggest that estimates based on PIT‐tagged fish reflect the total abundance of adults entering the river, while estimates based on samples collected during spawning surveys reflect the abundance of adults present in the breeding habitat at the time of spawning. Our study showed that CKMR can be used to estimate spawner abundance in Atlantic salmon, with a moderate sampling effort, but a carefully designed sampling regime is required.