Teresa C. Borges

Trophic relationships in deep-water fish communities off Algarve, Portugal

A preliminary investigation was made of the trophic relationships of three species of cartilaginous fish and 12 species of bony fishes along the upper part of the continental slope off the Algarve. These fish, from the by-catch of crustacean bottom trawlers fishing between 190 and 650 m, were sampled for stomach content analysis. Three major predator assemblages were identified. Group 1 consumers preyed upon zooplankton, particularly euphausids, and micronekton usually associated with the deep scattering layers. Group 2 consumers were larger predators that fed largely on fish, particularly those of group 1, and several penaeid and pandalid shrimps. Group 3 consumers had a stronger benthic affinity, and their most important prey items were isopods, followed by crabs and shrimps. The euphausid Meganyctiphanes norvegica seems to play a key role in this food web. The results are discussed from a biogeographic perspective. The deep-water fishery off Algarve seems to be characterised by large technological (multi-fleet) and biological (multi-species) interactions.

Reproductive biology of the blackmouth catshark, Galeus melastomus (Chondrichthyes: Scyliorhinidae) off the south coast of Portugal

the reproductive biology of 1045 female (9.5–67 cm (total length (tl)) and 1007 male (9.4–64.3 cm tl) blackmouth catsharks, galeus melastomus , was investigated. the sharks were caught off southern portugal by bottom crustacean trawlers at depths from 209 to 754 m. the sex ratio was 1:1, and this species is sexually dimorphic with males approaching maturity at smaller size than females. sexual segregation appears to be given for the stock within the study area. sexual maturity was reached at a total length above 49 cm in males and above 56 cm in females. mating and egg-deposition take place all year round, with two reproductive peaks of activity, in winter and summer. egg capsules are, on average, 54 mm long and 21 mm wide, with a maximum of 63×25 mm encountered. morphometric measurements of claspers, testes, ovaries, and oviducal glands were suitable for determining sexual maturity of blackmouth catshark.

Feeding ecology of conger eels ( Conger conger ) in north-east Atlantic waters

In order to understand how marine ecosystems function, it is essential to study the trophic interactions among the community members, particularly from poorly known regions. In this study, the feeding ecology and diet of conger eels, Conger conger , an abundant fish species with commercial interest, was examined in the north-east Atlantic, off Algarve (southern Portugal) between May 2005 and August 2006. The diet was characterized by species composition, size and mass of prey. Conger eels are opportunistic feeders, cannibalistic, feeding on benthopelagic/pelagic prey (67% by mass and 71% by number) but also benthic prey (32% by mass and 29% by number). Fish (67.8±4.7% in mass) are the main prey of conger eels, followed by cephalopods (16.5±3.8%) and crustaceans (15.6±3.7%). The most numerous (identifiable) fish consumed were Capros aper , occurring in 90% of the stomach samples that contained food and representing 1.4% in mass, and Scomber japonicus , the most important fish in mass (21.1%), which occurred in 4.2% of the stomach samples that contained food. The present study shows that octopodids can play a more important role in the diet of conger eels than previously thought. Of the species preyed upon by conger eels, six species (21% of the total prey taxa) are caught commercially (Trachurus trachurus, Scomber japonicus, Micromesistius poutassou, Helicolenus dactylopterus and Conger conger) by local fisheries. As discards by local trawl and longline fisheries do not correspond with the diet of C. conger , it is likely that most prey of C. conger in rocky areas were caught actively in that study region.

Diet of the cuttlefish Sepia officinalis (Cephalopoda: Sepiidae) off the south coast of Portugal (eastern Algarve)

The diet of Sepia officinalis was studied by examining the stomach contents of 522 specimens caught off the coast of the Algarve, Portugal. A total of 49 different prey items, belonging to six taxa (Polychaeta, Cephalopoda, Teleostei, Bivalvia, Crustacea and Gastropoda) was found, indicating opportunistic feeding behaviour. The diet was examined in relation to season, sex and size. The diet of males and females were similar. For small S. officinalis, crustaceans were more important in weight, whereas for larger specimens, fish were dominant. Seasonal differences in the diet were apparent but were shown to be possibly influenced by the cuttlefish size.