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The growth of many organisms is seasonal, with a dependence on variation in temperature, light, and food availability. A growth model proposed by Somers (Fishbyte 6:8-11, 1988) is one of the most widely used models to describe seasonal growth. We point out that three different formulae (beyond numerous typographical errors) have been used in the literature referring to Somers (Fishbyte 6:8-11, 1988). These formulae correspond to different curves and yield different parameter estimates with different biological interpretations. These inconsistencies have led to the wrong identification of the period of lowest growth rate (winter point) in some papers of the literature. We urge authors to carefully edit their formulae to assure use of the original definition in Somers (Fishbyte 6:8-11, 1988)Financial support for this research was provided by the Spanish Ministry of Science (projects CGL2009-12877-C02-01 and Consolider-Ingenio 2010 CSD2009-00065)

The effects of hydrological alterations on thermal regimes due to small water provisioning schemes are poorly understood. We studied the alteration of thermal regimes in a Mediterranean stream, where a weir and a water abstraction have been previously shown to severely affect the flow regime (e.g.frequency and duration of drought) and fish assemblage. Compared to non-impacted sites, the daily water temperature was more variable downstream of the weir, where water flow was reduced and drying occurred every summer. However, water temperature variation was smaller in a nearby downstream site dominated by effluents from a wastewater treatment plant. In addition, compared to all other sites, the times of the day to reach minimum and maximum water temperatures were markedly different in this site receiving the wastewater plant effluents and occurred earlier in the day in the site below the weir. The relationships between air and water temperatures were tight downstream but became looser and anomalous at the sites affected by water abstraction and effluent inputs. Overall, our results show that water temperature regimes in small streams are abruptly disrupted with water provisioning schemes with unknown consequences for aquatic organisms and ecosystems. Effects may be particularly stressful in Mediterranean-climate streams, where water is scarce and hydrological alterations pervasiveThis research was financially supported by the Spanish Ministry of Economy and Competitiveness (projects CONSOLIDER-INGENIO SCARCE, CSD2009-00065 and CGL2013-43822-R), the Government of Catalonia (ref. 2014 SGR 484), and by the Catalan Water Agency and Sant Celoni town council (‘Observatori de la Tordera’ project, led by Dr. M. Boada). MJB benefited from a postdoctoral grant from the European Commission (Erasmus Mundus Partnership ‘NESSIE’, 372353-1-2012-1-FR-ERA MUNDUS-EMA22

Water flow is a fundamental characteristic required for the ecological integrity of stream ecosystems. However, populations of many freshwater fishes in the Mediterranean region are threatened by man-induced drought due to water diversion.Mark-recapture methodology is an effective tool for estimating fish abundance and survival probability, but it has been seldom used with Mediterranean freshwater fish.We tagged over 2,400 individuals of two threatened cyprinids (Mediterranean barbel Barbus meridionalis and Catalan chub Squalius laietanus) inhabiting an Iberian streamaffected by water diversion, and used mark-recapture methods to evaluate the effects of flow, temperature and depth on their apparent survival and abundance at hydrologically altered and perennial reaches. Based on estimates over the summer drying season, survival of Mediterranean barbel was more than six times higher in an upstream reach with permanent flow than a middle reach impacted by water diversion.Water depth was the most important habitat feature accounting for differences in survival, with both barbel and chub exhibiting higher survival and abundance at permanent sites farther downstream where flow had been restored and in an unaltered tributary. Our results show clear negative impacts of water diversion on fish populations. Both species, but particularly barbel, have life-cycle characteristics that may allow populations to recover quickly if natural streamflow was restored by conserving water and reducing water diversion. K E Y W O R D SBarbus meridionalis, Cyprinidae, hydrologic alteration, mark-recapture study, population density, Squalius laietanus

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