Carlos A. Assis

Do eel grass beds and salt marsh borders act as preferential nurseries and spawning grounds for fish? An example of the Mira estuary in Portugal☆

Abstract The fish communities of the Mira estuary (Portugal) have been studied as a whole since 1986. It was possible to identify two different types of habitat that act as nursery areas and spawning grounds for a large number of fish species — the eel grass beds and the salt-marsh-bordered zone. The importance of these habitats is due, not only to the number of species present, but also to their abundance. However, as the eel grass beds only extend over a small surface in the Mira estuary, the salt marshes become of vital importance for the marine fish, especially those with economical value. As several major modifications are planned for the Mira estuarine bed and valley in the near future, suggestions are given in order to preserve the estuarine ecosystem equilibrium.

Trophic relationships in the community of the upper Tagus estuary (Portugal): A preliminary approach

The diet of 25 invertebrate and fish species occurring in the upper Tagus estuary are compared. Multivariate methods are used to define trophic groups and identify key prey species, fundamental links in the understanding of the estuarine food web. Four trophic groups are described: microalgae, macroinfauna, mysid and fish and decapod eaters. It was found that the food web of this area heavily relies on the polychaete Nereis diversicolor and the crustacean Crangon crangon .

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 blue marlin, Makaira nigricans, off the south coast of Portugal

Abstract The blue marlin, Makaira nigricans (Istiophoridae), is a large, top predator with a worldwide distribution whose feeding ecology is still unknown in the northeast Atlantic. The stomach contents of 24 Atlantic blue marlin, caught by the Big Game fishing fleet (between 2007 and 2010) off the south coast of Portugal, were studied. All marlin fed exclusively on pelagic fish, with a total of 180 prey items recorded, belonging to 6 identified species. The most important family in the blue marlin diet was Scombridae, representing 70% of the total prey items. Among the Scombridae, the chub mackerel, Scomber colias, was the most important prey species (47.9% by weight, 51.1% by number, 58.3% by frequency of occurrence). The length of prey found in the stomachs ranged from 136 to 727 mm in length, and a significant positive correlation was found between prey and blue marlin size. Our results suggest that in this geographical area (NE Atlantic) marlin feed on a small spectrum of species, with a preference for foraging on seamounts.