Details

Autor(en) / Beteiligte

• Vinagre, Catarina Maria Batista

Titel

Ecology of the juveniles of the soles, Solea solea (Linnaeus, 1758) and Solea senegalensis Kaup, 1858, in the Tagus estuary

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2007

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• The soles, Solea solea (Linnaeus, 1758) and Solea senegalensis Kaup, 1858, are among the most valuable commercial fish in Portugal. Two important nursery areas for the juveniles of these species have been identified in the upper area of the Tagus estuary. The present work aimed at investigating the ecology of these species in the Tagus estuary nursery areas. Habitat use was analysed at different spatial scales, using spatial modelling, isotopic analysis and a complex sampling program accounting for the diel and lunar cycles. Prey abundance proved crucial in the prediction of high densities of juveniles. The stable isotope approach revealed low connectivity between nursery areas and different levels of dependence upon the freshwater energy pathway. A diel and semi-lunar activity pattern was detected for S. senegalensis. Experimental work on gastric evacuation and feeding behaviour and its application to the wild populations allowed the estimation of food consumption by juvenile soles. Temperature, salinity and predation pressure were found to affect prey consumption. Otolith daily increments and RNA-DNA ratio analyses, showed that growth rates and condition variation reflects estuarine colonization patterns. The Tagus estuary soles were found to be in good overall condition and their growth rates were higher than at higher latitudes. The use of these methodologies for habitat quality monitoring was discussed. Estimation of spawning time through back-counting of otolith daily increments and comparison with other areas revealed a latitudinal variation in S. solea spawning in that it tends to occur earlier with decreasing latitude. Investigation on the effect of climate and hydrodynamics upon migrating sole larvae emphasized the importance of river drainage in this process. The magnitude of the mortality caused by fishing conducted within the nursery areas was considerable for S. solea and lower for S. senegalensis. Several management measures were suggested and discussed. Future studies were proposed.