CR 18:119-126 (2001)  -  doi:10.3354/cr018119

ABSTRACT: Estuarine fish communities are usually used in an ecological monitoring context to infer the environmental changes ocurring in estuarine environments. In the present paper several analytical tools, namely community analysis indices, species-ranking methods and multivariate ordination techniques, were applied to time series data for the Tagus fish community for 2 periods: 1979 to 1981 and 1995 to 1997. Assessment of the relative importance of anthropogenic versus naturally induced fluctuations is made difficult by the range of natural short-term variations. For the Tagus case study, multivariate ordination techniques, rather than the ranking methods and indices analyzed, provide a good indicator of long-term changes. The major trends in the changes observed in this fish community were a decrease in abundance for several species that use the estuary as a nursery area and an increase in some resident species, namely Gobius spp. and Halobatrachus didactylus. Several species with southern European affinities have increased their importance within the Tagus estuarine fish community.

KEY WORDS: Fish community · Environmental changes · Assessment methods · Tagus estuary · Portugal