Activity, distribution and microhabitat use by the imperilled mira chub Squalius Torgalensis

Tese de doutoramento, Biologia (Ecologia), Universidade de Lisboa, Faculdade de Ciências, 2014Understanding habitat selection and use by stream fishes increasingly requires the analysis of the relationships between fish and their environments in terms of individual fitness. However, such mechanistic approaches are still uncommon for cyprinids, and remain to be evaluated and tested for Mediterranean species. This thesis addressed activity, distribution and microhabitat use by Mira chub Squalius torgalensis, an imperilled cyprinid native to Mediterranean streams in SW Portugal. This was analysed using a mechanistic approach, including direct observations of fish and habitat in two reaches of the Torgal stream, in spring 2009 and 2010, and laboratory experiments on foraging success under variable velocities. Daily activity patterns were variable at the individual level and shaped by extrinsic and intrinsic factors. Foraging changed from drift to benthic on an annual-basis and with shoal size, and time spent cruising vs. searching was influenced by temperature and body size. Chub displayed an aggregated distribution apparently in association with patchily distributed and autocorrelated physical resources, such as debris, roots and aquatic vegetation. Microhabitat use was influenced by substrata, cover and depth, but random at the focal level, and little variable throughout ontogeny. Contrary to expectations, microhabitat use was generally unrelated to velocity, probably because prey capture success was high at the low velocities prevailing in study reaches. Nevertheless, the proportion of fish capturing prey and capture success decreased at high velocities. Results indicate that chub may display high flexibility in activity and habitat use, which may be important to cope with the high variability of physical conditions in Mediterranean streams, with maintenance of patches with variable substrata, cover and depth likely favouring local persistence. Moreover, this thesis shows that mechanistic fitness-based criteria may be crucial for understanding habitat selection by Mediterranean cyprinids.Fundação para a Ciência e a Tecnologia (FCT