Habitat Use by Native and Stocked Trout (Salmo Trutta L.) in Two Northeast Streams, Portugal

Abstract

Habitat use by stocked and native brown trout (Salmo trutta L.) was assessed in two headwater streams of North-eastern Portugal. Underwater observations were made during the summer season in three successive years to evaluate the effect of supplemental trout stocking. Multivariate analysis techniques applied to data sets on microhabitat use were exploited to identify the focal elevation (distance of fish from the bottom), total depth and cover as the variables that contribute most to the discrimination between stocked and native trout. Preference curves computed for native and stocked trout of the same age (1 + ), showed a distinct pattern in their ability to explore the available microhabitat resources. Stocked trout tended to occupy deeper pools (total depth > 100 cm vs. 60-100 cm for native trout), holding higher focal elevations (140-160 cm vs. < 20 cm for native) with lower water column velocities (< 10 cm.s -1 vs. 10-20 cm.s -1 for native) and no specific preference for cover. In contrast, native trout displayed a clear preference for microhabitats with coarse substrate (particle size > 22.5 cm) and cover (combination of boulders and overhanging vegetation or undercut banks). Furthermore, a high poststocking movement of 80% hatchery-reared fish was verified just one month after their release, suggesting that stocking did not contribute to the sustainable populations in either stream, and is far from being an adequate management technique. Key-words:Salmo trutta, snorkelling, restocking, microhabitat, preference curves. UTILISATION DE L'HABITAT PAR LA TRUITE COMMUNE (SALMO TRUTTA L.) SAUVAGE ET CELLE D'ÉLEVAGE, DANS DEUX RIVIÈRES DU NORD-EST DU PORTUGAL RÉSUMÉL'utilisation de l'habitat par la truite de repeuplement et par la truite commune (Salmo trutta) a été évaluée dans deux rivières du Nord-Est du Portugal. Des observations en plongée ont été faites en période estivale pendant trois années successives pour évaluer l'efficacité des repeuplements. Des techniques d'analyses multivariées appliquées à l'ensemble des données du microhabitat ont permis d'identifier la position Article available at

Interactive effects of cover and hydraulics on brown trout habitat selection patterns

“…These adverse environmental conditions make pools and visually isolated areas increasingly preferred as trout age, the selection of protected areas at river margins increasing with growing river width, and younger individuals selecting boulder sheltered positions. This pattern matches with observations from other southern brown trout populations (Vismara et al, 2001;Teixeira et al, 2006), although not with northern populations where adult trout select pool habitats but avoid river margins, and younger individuals prefer instream vegetation at river margins over boulder sheltered positions (e.g. Greenberg et al, 1996;Mäki-Petäys et al, 1997;Heggenes, 2002).…”

“…Greenberg et al, 1996;Mäki-Petäys et al, 1997;Roussel and Bardonnet, 1997;Teixeira et al, 2006). Despite physical habitat is the major determinant of spatial variations in the abundance and distribution of most salmonid populations , the distribution of younger individuals at a reach scale is affected by older fish through intercohort competition or predation (Bult et al, 1999;Vehanen et al, 1999;Nordwall et al, 2001;Vik et al, 2001).…”

“…Surprisingly, the number of studies in the literature describing brown trout habitat selection patterns, either HSCs or RSFs, in rivers characterized by a Mediterranean hydrological regime is scarce (e.g. Vismara et al, 2001), and inexistent in the Iberian Peninsula (but see Teixeira et al, 2006 for Iberian Atlantic rivers).…”

Combining Radio and PIT-Telemetry to Study the Large and Fine-Scale Movements of Stocked and Wild Brown Trout (Salmo trutta L.) in a Northeastern Stream, Portugal

“…This study also confirmed previous observations following distinct methodologies (e.g. snorkelling, electrofishing), which detected, just one month after, a low proportion of stocked brown trout in the stream segment where they had been released (Cortes et al, 1996;Teixeira et al, 2006). The potential negative impacts of stocking on wild population seemed to be limited in time and space and were demonstrated by the monitoring of fish movement (e.g.…”

Functional response and size‐dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)

“…A few studies have observed that the diets of large trout have higher proportions of terrestrial invertebrates than the diets of small fish and thus demonstrate an ontogenetic shift in diets (P. Gustafsson, unpublished data; Montori et al 2006;Teixeira et al 2006;Dineen et al 2007a;Er} os et al 2010). A few studies have observed that the diets of large trout have higher proportions of terrestrial invertebrates than the diets of small fish and thus demonstrate an ontogenetic shift in diets (P. Gustafsson, unpublished data; Montori et al 2006;Teixeira et al 2006;Dineen et al 2007a;Er} os et al 2010).…”