Manuela Azevedo

Temporal and local variations in biochemical composition of Crassostrea gigas shells

Abstract The objective of this work was to find relations between organic and inorganic shell components. Crassostrea gigas shells were analysed from live specimens collected at five different stations: the Lima estuary (1), the Ria de Aveiro (2, 3), and the Mondego estuary (4, 5), Portugal. About 30% of the oysters, from stations 1, 2 and 3 had shell-thickness-index values ≤10, indicating a severe thickening. Oysters from the Mondego estuary contained mud blisters due to Polydora infestations. Oysters from station 3 had thicker shells and showed a higher Pb content in shell and tissues than oysters from the other stations. Amino-acid composition changed mainly according to the modified protein (jelly-like substance) probably produced by the presence of TBT (tributyltin) in the water; in particular, we observed an increase in glutamic acid and threonine and a decrease in major amino acids such as aspartic acid, serine and glycine. Elemental shell composition was mainly associated with environmental conditions: shells from stations in open areas had higher Li, Cd, Cr and Ca and lower Mn levels than those from semi-enclosed areas (fish farms). Discriminant analyses against the three kinds of shell observed (normal, thick and infested), using chemical elements and amino acids as discriminant variables, showed the infested group to have the biggest differences. There was no correlation between amino-acid and chemical-element patterns in shell composition. Observed changes in amino-acid pattern, probably due to TBT, did not imply a simultaneous change of elemental composition.

Structural and functional trends indicate fishing pressure on marine fish assemblages

pressure on marine fish assemblages Sofia Henriques*, Miguel P. Pais, Rita P. Vasconcelos, Alberto Murta, Manuela Azevedo, Maria J. Costa and Henrique N. Cabral Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal; Instituto Português do Mar e da Atmosfera, Av. de Bras ılia, 1449-006 Lisboa, Portugal; and Departamento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal

A statistical analysis of black monkfish catch rates in ICES Division IXa

Abstract An analysis of variance was undertaken to compare the black monkfish catch rates by depth strata and year observed between 1990 and 1992 off the Portuguese southwest coast (Alentejo) and off the south coast (Algarve). This study is also used to emphasize the importance of controlling Type I and Type II errors when using ANOVA to interpret results. The data were collected during Portuguese bottom trawl surveys and provide information on the abundance of the black monkfish stock of ICES Divisions VIIIc and IXa. A main effect ‘year’ was found in the Alentejo zone and a main effect ‘strata’ in the Algarve zone. Post hoc paired comparisons were made on these main effects. A post hoc statistical power analysis shows that the probability of having committed a Type II error is in the range 43–69% for the ‘year’ effect in Algarve, and is very low for the ‘strata’ effect in Alentejo. It is concluded that the abundance of black monkfish has decreased between 1990 and 1992 in the Portuguese southwest coast, though a decrease in the south zone may be masked by a low power experiment. At the same time, the Portuguese trawl fishing effort increased and the catch per unit effort decreased. Therefore, the decrease in abundance of black monkfish may be a consequence of the fishing mortality increase and reflect a stock abundance decrease. It is also concluded that this species presents different distribution patterns in ICES Division IXa, occurring preferentially on the continental shelf in the Portuguese south zone (Algarve) which may be due to the relation between the nature of the bottom and the bathymetric characteristics of this zone and the species behaviour.