Radiotelemetry was used to investigate seasonal movement and home range of brown trout Salmo trutta (size range 188-420 mm fork length, N = 30) in two reaches of the Noguera Pallaresa River (Ebro Basin, north-east Spain) subjected to different flow regulation schemes. NP-1 reach is a bypassed section with near natural flow conditions, whereas the downstream reach NP-2 is subjected to daily pulsed flow discharge (i.e., hydropeaking) from an upstream hydropower station. Significant differences in home range size (95% kernel estimates) and seasonal movement pattern between study reaches were found. Mean home range size was (μ ± SE) 112.1 ± 11.5 m in the bypassed reach NP-1 and increased significantly in the hydropeaking reach NP-2 up to 237.9 ± 37.2 m. There was a large individual variability in fish home range size within reaches. Most of the seasonal differences in fish movement among reaches were associated with the spawning season. Pulsed discharge events in NP-2 during daytime in summer (lasting about 3 hr and increasing water flow from 1 to 20 m 3 /s) did not cause significant displacements in either upstream or downstream direction during the duration of the event. Our results highlight the importance of habitat connectivity in hydropeaking streams due to the need of brown trout to move large distances among complementary habitats, necessary to complete their life cycle, compared with unregulated or more stable streams.

SummaryThe influence of pulsed discharges associated with hydroelectric power generation (i.e. hydropeaking) on feeding activity and diet composition of adult brown trout (Salmo trutta) was studied during summer by comparing two sites: upstream (control site) and downstream from a power plant (hydropeaking site). Twenty fish were captured from each study site by electrofishing at four-hour intervals for two consecutive days and stomach contents were collected with pulsed gastric lavage. Hydropeaking events affected brown trout feeding behaviour as well as prey availability. Feeding intensity, measured by the stomach Fullness Index, showed pronounced variations with maximum values after flow pulses, which were linked to variations in prey availability because of increased drift rates of invertebrates. In contrast, brown trout living at the control site showed smoother variations of feeding activity not linked to invertebrate drift. Overall, brown trout at the hydropeaking site had higher food consumption rates and a more generalist and heterogeneous diet than trout from the control site, indicating an opportunistic feeding behaviour during flow pulses. Therefore, the hydrological disturbance caused by hydropeaking did not appear to cause direct negative impacts on feeding of adult brown trout. However, reduced trout density and imbalanced size structure in the hydropeaking site were detected, requiring further research to clarify the spatial influence of hydropeaking on other factors that could negatively affect brown trout populations.

Dispersal is a critical determinant of animal distribution and population dynamics, and is essential information for management planning. We studied the movement patterns and the influence of habitat and biotic factors on Mediterranean brown trout (Salmo trutta) by mark-recapture methods in three headwater streams of the Ebro Basin (NE Iberian Peninsula). Fish were sampled by electrofishing on five occasions over 18–24 months and movements of over 3,000 individually tagged trout (age 1+ onwards) were recorded. Most of the tagged fish exhibited limited movement and were recaptured within 100 m from the initial capture section. Small seasonal differences in the movement pattern were observed, but in two of the streams, displacement distances increased prior the spawning period in autumn. The frequency distributions of dispersal distances were highly leptokurtic and skewed to the right and fitted well to a two-group exponential model, thus trout populations were composed of mobile and stationary individuals, the latter being the predominant component in the populations (71.1–87.5% of individuals). The mean dispersal distances, for fish captured at least in three sampling events, ranged 20.7–45.4 m for the stationary group and 229.4–540.5 m for the mobile group. Moving brown trout were larger than non-moving individuals and exhibited higher growth rates in two of the streams. Habitat features were not consistently linked to movement rates, but there were some interaction effects between stream and habitat characteristics such as depth, cover and water velocity.

-The status of Pyrenean sculpin Cottus hispaniolensis was assessed in the Spanish part of the Garonne drainage on the basis of its distribution and abundance from 2001 to 2016. Population trends showed a progressive reduction in range extension and density, exacerbated by a severe spate occurred in 2013. However, C. hispaniolensis was resilient to this natural disturbance by compensating for mortality with increasing recruitment. Both occurrence and density of Pyrenean sculpin showed a positive correlation with coarse substrates. Riverine habitat deterioration, mainly channelization, presence of dams and flow regulation are the main factors threatening sculpin populations. Several management measures are proposed.Keywords: abundance / catastrophic spate / conservation measures / Cottus hispaniolensis / Garonne Résumé -Tendances et état actuel de la population du chabot pyrénéen menacé Cottus hispaniolensis dans la partie espagnole du bassin de la Garonne. Le statut du chabot pyrénéen Cottus hispaniolensis a été évalué dans la partie espagnole du bassin de la Garonne sur la base des données de distribution et d'abondance au cours de la période 2001-2016. Les tendances de la population ont montré un déclin progressif de l'extension de répartition et de la densité, exacerbé par une crue sévère survenue en 2013. Cependant, C. hispaniolensis a montré une résilience à ce type de perturbation naturelle en compensant la mortalité par un recrutement accru. L'occurrence et la densité du chabot pyrénéen ont montré une corrélation positive avec les substrats grossiers. La détérioration des habitats rivulaires, principalement la canalisation des cours d'eau, la présence de barrages et la régulation des débits, sont les principaux facteurs potentiels qui menacent les populations de chabots. Plusieurs actions de gestion sont proposées.

† Don't speak too soon, for the wheel's still in spin, and there's no telling who that it's naming (Bob Dylan, The times they are a-changing).