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 · PortugalResale or republication not permitted without written consent of the publisher

SUMMARY: The diets and the trophic niche overlap between seven flatfish species were studied in a coastal nursery adjoining to the Tagus estuary (Portugal). Fish were sampled monthly, from March to November 1999, using a beach seine. Arnoglossus imperialis (Rafinesque, 1810), Arnoglossus laterna (Walbaum, 1792) and Arnoglossus thori Kyle, 1913, fed mainly on crustaceans. The diets of Buglossidium luteum (Risso, 1810) and Dicologoglossa cuneata (Moreau, 1881) were mainly composed of Bivalvia and Polychaeta, while for Scophthalmus rhombus (Linnaeus, 1758) the main food items were Mysidacea and Teleostei. The diet of Pegusa lascaris (Risso, 1810) was mainly composed by Cumacea, Bivalvia, Decapoda and Amphipoda. Based on diet similarities two main groups were identified: one composed of A. imperialis, A. laterna, A. thori and S. rhombus, and the other grouping B. luteum, P. lascaris and D. cuneata. For the most common flatfishes, a similar pattern of diet seasonal variation was found, such that Amphipoda presented higher indices values in the period from March to June, while from July to November, Decapoda were more abundant. Although high values of diet overlap were obtained among some of the species, the main items in the diet of flatfishes are probably the most abundant prey in this coastal area, which suggests a generalist and opportunistic utilization of these food resources. Furthermore, niche overlap between these species is probably minimized by differences in resource use in other niche dimensions, namely time and space.Key words: niche overlap, feeding ecology, flatfish, nursery, coastal areas. RESUMEN: SOLAPAMIENTO DEL NICHO TRÓFICO EN UN ÁREA DE CRÍA EN LA COSTA PORTUGUESA. -Se estudiaron las dietas y el solapamiento de nicho trófico de siete especies de peces planos en un área costera adyacente al estuario del río Tajo (Portugal). Los peces se muestrearon mensualmente, de marzo a noviembre de 1999 usando un arte de cerco de playa. Arnoglossus imperialis (Rafinesque, 1810), Arnoglossus laterna (Walbaum, 1792) y Arnoglossus thori Kyle, 1913, se alimentan principalmente de crustáceos. La dieta de Buglossidium luteum (Risso, 1810) y Dicologoglossa cuneata (Moreau, 1881) estuvo compuesta, principalmente, por bivalvos y poliquetos, mientras que para Scophthalmus rhombus (Linnaeus, 1758) el principal alimento fueron misidáceos y teleósteos. La dieta de Pegusa lascaris (Risso, 1810) estuvo compuesta, principalmente, por cumáceos, bivalvos, decápodos y amfípodos. En base a las similaridades de la dieta se identificaron dos grupos: uno compuesto por A. imperialis, A. laterna, A. thori y S. rhombus, y el otro por B. luteum, P. lascaris y D. cuneata. Se encontró una pauta similar de variación estacional de la dieta para los peces planos más comunes, destacando que los amfí-podos presentan índices más altos en los periodos de marzo a junio, mientras que los decápodos fueron más abundantes en las dietas de julio a noviembre. Aunque se obtuvieron altos valores de solapamiento en las dietas entre algunas de las espec...

SUMMARY: The sand goby Pomatoschistus minutus (Pallas, 1770) and the common goby Pomatoschistus microps (Krøy-er, 1838) are among the most abundant fish species in estuaries, lagoons and along the Atlantic shores of Europe. In the Tagus estuary these species are particularly important in the food web. Fish samples were taken monthly in the upper estuary, and the gut contents of a total of 431 P. minutus and 382 P. microps were analysed in order to study preferences and seasonal changes in their diets and to understand intra-and interspecific relations between these two congeneric gobies. The sand goby had no dominant prey, although mysids were particularly important in the diet of this species. Shrimps and polychaetes were also common prey. P. microps preferentially ingested polychaetes, with isopods, amphipods, bivalves and copepods as secondary prey items. Significant seasonal variations in the ingestion of the main prey groups of both species were obtained, which reflect variations in prey availability. During the reproductive season there were differences in the food consumed by males and females, mainly for P. minutus, reflecting the different activity pattern exhibited by males and females during the breeding season, since parental care is supported by the former. The smallest classes from P. minutus increased their niche widths as they grew. Due to the different length reached by each species, the degree of interspecific overlap decreased with increasing body size. (Krøyer, 1838) están entre las especies más abundantes de peces de estuarios, lagunas y a lo largo de las orillas atlánticas de Europa. En el estuario del Tajo estas especies son particularmente importantes en la cadena alimentaria. Muestras de los pescados fueron tomadas mensualmente en la parte superior del estuario, y el contenido de la tripa de un total de 431 P. minutus y de 382 P. microps fue analizado con la finalidad de estudiar las preferencias y cambios estacionales en sus dietas y comprender las relaciones intra e ínter específicas entre estos dos gobios congéneres. El cabuxino no tenía ninguna presa dominante, aunque los misidáceos eran particularmente importantes en la dieta de esta especie. Los camarones y los poliquetos eran también presa común. Los P. microps injirieron preferencialmente poliquetos, con isópodos, anfípodos, bivalvos y copépodos como presas secundarias. Fueron obtenidas variaciones estacionales significativas en la ingestión de los grupos principales de la presa de ambas especies, lo que refleja variaciones en la disponibilidad de la presa. Durante la estación reproductiva había diferencias en el alimento consumido por los varones y las hembras, principalmente para el P. minutus, reflejando la diferencia en el patrón de la actividad exhibido por los machos y las hembras durante la estación de cría, puesto que el cuidado parental es llevado a cabo por los primeros. Las clases más pequeñas del P. minutus aumentaron el tamaño de sus nichos mientras crecían. Debido a la diversidad de longitud alcanzada por cada e...

No abstract

No abstract

The spatio–temporal abundance pattern of 0-group sea bass, Dicentrarchus labrax, was investigated between April 1995 and November 1996 by beam trawl surveys. The highest densities of D. labrax were recorded in shallow areas. Dicentrarchus labrax density was also significantly related to water temperature and salinity, but the variation pattern was not linear. The 0-group individuals of this species first occurred on the nursery ground in May and the highest densities were recorded in June. Diet of 0-group D. labrax was mainly composed of crustaceans, the most important food items being Decapoda, Mysidacea and Isopoda. Feeding activity increased during summer. Short-term variations were related to the period of the day and tidal cycle. The growth rate determined for 0-group D. labrax was higher than those reported for the UK and northern France, and was similar to those obtained in eastern Mediterranean.

Among the stomach contents of 609 individuals of Solea solea and 1104 of S. senegalensis the main food items of S. solea were Corophium spp. and Hediste diversicolor, and of S. senegalensis were Corophium spp., H. diversicolor and Scrobicularia plana. For both species, the importance of larger prey items in the diet, namely H. diversicolor and Crangon crangon, increased with fish size. Feeding activity of S. solea and S. senegalensis increased in spring and summer. Short-term variations were particularly related to the tidal cycle and the two species fed in intertidal areas. Dietary differences between the two nursery areas reflected prey availability mainly. Although intra-and interspecific length classes overlapped in diet, potential interspecific competition was probably minimized by a differential habitat use pattern. 2000 The Fisheries Society of the British Isles

No abstract