Fish are commonly sedated to render them immobile and thus easier to handle for research, veterinary, and aquaculture practices. Since sedation itself imposes a significant challenge on the targeted fish, the selection of sedation methods that minimize physiological and behavioral disturbance and recovery time is essential. Two popular sedation methods include the chemical tricaine methanesulfonate (MS‐222) and electrosedation. Although many studies have already investigated the physiological consequences of these methods, there is limited research examining the latent behavioral effects on fish. Using Largemouth Bass Micropterus salmoides as a model species, we compared the postsedation behaviors of fish that were sedated with either MS‐222 or electrosedation to those of a control group exposed to the same handling protocol. Immediately after sedation, fish exposed to either treatment demonstrated lower reflex scores than the control group. Time to resume regular ventilation did not differ between chemically sedated and electrosedated fish; however, electrosedated fish regained equilibrium faster (mean ± SE = 154 ± 20 s) than fish that were exposed to MS‐222 (264 ± 30 s). Locomotor activity and swimming performance were assessed at 5‐, 30‐, or 60‐min intervals, beginning after individuals had recovered from sedation sufficiently to regain equilibrium. For all postsedation intervals, locomotor activity was two times greater in the electrosedated group than in the control and MS‐222 groups. Other behavioral measures (refuge emergence time, activity level, and flight initiation distance) and swimming performance did not differ at 5, 30, or 60 min postrecovery for any of the treatment groups. Our results indicate that while both chemical and electrical sedation methods result in impairment (i.e., sedation) immediately after treatment, these behavioral effects do not persist beyond 5 min postrecovery, and the two methods have similar impacts on Largemouth Bass. However, we caution that these results cannot be extrapolated to other fish species without further study. Received September 27, 2016; accepted January 17, 2017 Published online April 3, 2017
Background: Manual tracking has been used since the 1970s as an effective radio telemetry approach for evaluating habitat use of fish in fluvial systems. Radio tags are often located by continually reducing the gain when approaching the tag along a watercourse to estimate its location, termed here as the 'Gain Reduction Method'. However, to our knowledge the accuracy of this method has not been empirically evaluated and reported in the literature. Here, the longitudinal and lateral positional errors of radio tags are assessed when applying the Gain Reduction Method in a small stream environment. Longitudinal and lateral positional errors (i.e. the difference between the estimated and actual radio tag location) were evaluated based on the distance from the actual tag position, the gain recorded when estimating the tag position and a number of environmental parameters (i.e. stream depth, velocity, stream width and specific conductivity). Results: The manual tracking trials produced an average lateral positional error of 0.91 m (± 1.4) and a longitudinal positional error of 0.66 m (± 0.87). A larger degree of longitudinal positional error was documented when the gain was higher (t = 2.21, p < 0.05). Larger lateral positional error was recorded when the tag was farther across the stream (t = 2.27, p < 0.01) and due to greater inaccuracy in longitudinal positioning (t = 3.2, p = 0.001). In addition, greater rates of lateral positional error were found when specific conductivity levels were higher (t = 2, p < 0.05). Longitudinal and lateral positional errors were not influenced by stream width (m), depth (m) or velocity (m/s). Conclusions: Although the Gain Reduction Method is commonly used to estimate habitat use of stream fishes, there appears to be a paucity of information in the literature that addresses the accuracy for obtaining fine-scale positioning of tagged fishes. This study is aimed to address this knowledge gap by identifying sources of locational error with the Gain Reduction Method. Overall, habitat variables were deemed to be unlikely to have a significant effect on estimating fish position in small streams. Researchers should be aware that error in the longitudinal direction will translate into larger errors in the lateral position. Further exploration of positional accuracy using this active tracking approach is recommended for larger and deeper fluvial systems.
Sustainable management of exploited populations benefits from integrating demographic and genetic considerations into assessments, as both play a role in determining harvest yields and population persistence. This is especially important in populations subject to size‐selective harvest, because size selective harvesting has the potential to result in significant demographic, life‐history, and genetic changes. We investigated harvest‐induced changes in the effective number of breeders (Ntruêb) for introduced brook trout populations (Salvelinus fontinalis) in alpine lakes from western Canada. Three populations were subject to 3 years of size‐selective harvesting, while three control populations experienced no harvest. The Ntruêc decreased consistently across all harvested populations (on average 60.8%) but fluctuated in control populations. There were no consistent changes in Ntruêb between control or harvest populations, but one harvest population experienced a decrease in Ntruêb of 63.2%. The Ntruêb/Ntruêc ratio increased consistently across harvest lakes; however we found no evidence of genetic compensation (where variance in reproductive success decreases at lower abundance) based on changes in family evenness (trueFÊ) and the number of full‐sibling families (Ntruêfam). We found no relationship between trueFÊ and Ntruêc or between Ntruêfam/Ntruêc and trueFÊ. We posit that change in Ntruêb was buffered by constraints on breeding habitat prior to harvest, such that the same number of breeding sites were occupied before and after harvest. These results suggest that effective size in harvested populations may be resilient to considerable changes in Nc in the short‐term, but it is still important to monitor exploited populations to assess the risk of inbreeding and ensure their long‐term survival.
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