Abstract

TEIXEIRA, Amílcar; FONSECA, Telmo  and  OLIVEIRA, João. Habitat Improvement and Restocking of Salmonid Streams in Northeastern Portugal. Silva Lus. [online]. 2013, vol.21, n.Especial, pp.185-200. ISSN 0870-6352.

Passive integrated transponder (PIT) technology was used to study the behaviour of fishes during the summer season of 2010 in the River Penacal, a salmonid headstream of northeastern Portugal. A total of 60 PIT tags (12.0 mm long x 2.1 mm diameter) were surgically implanted into the intraperitoneal cavity of fish. Three trout populations were considered: 1) native brown trout of different age classes (8.0-16.0 cm L_T, 4.5-29.8 g) (n= 20 individuals, previously captured by electrofishing in the study site) and 2) stocked trout, age 1+ (12.5-18.1 cm L_T, 16.8-59.9 g) reared in different conditions 2a) traditional cement raceways (n=20) and 2b) natural (land) tanks (n=20). Eight independent antennae, connected to a multi-point decoder (MPD reader) unit, were placed in different microhabitats, selected randomly every three days, during the observation period (7 weeks). Fish habitat improvement was made recurring to blocks and vegetation in order to promote refugee. The results confirmed this method as a suitable labour efficient tool to assess the movement and habitat use of stocked and native trout populations. About 80% of stocked and 60% of native PIT tagged trout were detected. Multivariate techniques (NMDS, dbRDA) showed a separation in habitat use between the three sympatric populations. Stocked trout, reared in conventional raceway tanks with high densities used, mainly, the microhabitats located in the middle of the channel with higher depths and without cover. Furthermore, these fishes displayed a greater mobility and a different activity pattern in comparison with the native and the acclimated trout populations, which displayed a better adaptation to the aquatic environment, namely to the habitat improvement promoted.

Keywords : Salmo trutta; habitat improvement; stocking; PIT-telemetry.

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