The diets and trophic ecology of the dominant fish species from the marine coastal region of Aveiro (north-western Portugal) caught during a summer survey were studied. Mysids were the most important prey group for the fish assemblage analysed. As a consequence, there was a high dietary overlap between species and a low incidence of piscivory. Nevertheless, a clear segregation of trophic niches was observed, with one group (comprising the species Chelidonichthys cuculus, Callionymus lyra, Dicologlossa cuneata and Pomatoschistus lozanoi) showing a stronger preference for infaunal epibenthic prey, such as polychaetes and amphipods, another group (including Arnoglossus imperialis, Arnoglossus laterna, Chelidonichthys obscurus, Chelidonichthys lucernus, Echiichthys vipera, Pagellus acarne and Trisopterus luscus) preying mostly upon suprabenthic prey, mainly mysids, and a third group (Engraulis encrasicolus and Trachurus trachurus) feeding largely on planktonic prey like copepods. Some species, including A. imperialis, C. lyra, E. vipera, T. trachurus and T. luscus, showed ontogenic diet shifts that may be related to the habitat occupied by different size-classes and/or to their ability to capture prey of different size.

Piscivorous birds consume diets which are rich in highly-polyunsaturated n-3 fatty acids; these play vital roles in embryonic development but are very susceptible to oxidative damage. The effects of such diets on the fatty acid composition and antioxidant content of the yolk were investigated in the northern gannet Morus bassanus, the great skua Catharacta skua, the American white pelican Pelecanus erythrorhynchos and the double-crested cormorant Phalacrocorax auritus. The phospholipid fraction of the eggs of these four species contained high proportions of the n-3 fatty acid, docosahexaenoic acid, which formed 7.5–11.3% (w/w) of the fatty acids of this fraction. The presence of eicosapentaenoic and docosapentaenoic acids also contributed to the total n-3 content of the phospholipid. The n-6 polyunsaturate, arachidonic acid, formed between 8% and 19% (w/w) of the phospholipid fatty acids. For the pelican and cormorant, this is consistent with the consumption of freshwater fishes in which arachidonic acid may be a significant acyl constituent. This finding is, however, more difficult to explain for the gannet and skua which largely consume marine fish with a low arachidonic acid content. The yolks of all four species contained relatively high concentrations of vitamin E (90.2–302.3 μg g−1 wet yolk) which was mainly present as α-tocopherol. The eggs of the pelican and cormorant were especially enriched in carotenoids (150.9 and 115.7 μg g−1 wet yolk, respectively).