Beschreibung: We compared several large marine ecosystems in terms of species numbers of fishes, sea birds, marine mammals, and cephalopods. We examined how these numbers were distributed by trophic level, from herbivores to top predators. We created group-specific trophic signatures as plots of number of species by trophic level, and used these to identify similarities and discrepancies between taxonomic groups and ecosystems. Preliminary results suggested that trophic signatures are similar for ecosystems previously known to share major features, and different for dissimilar ecosystems. In the Mediterranean, as well as in the other large marine ecosystems, fish clearly dominate the predatory trophic levels above 3.0. Preliminary signatures for cephalopods, marine mammals, and sea birds in the Mediterranean and in the North Sea indicate that these groups are restricted to trophic levels above 3.0, and are represented by many fewer species than are predatory fish. Notably, cephalopods are the only invertebrates present at higher trophic levels (〉= 4). Invertebrates other than cephalopods are restricted to trophic levels below 3, with very few exceptions. Trophic signatures appear to be useful tools for better understanding of the roles that different groups of organisms play in different ecosystems. We also applied free-scale network theory to analyse the food web created by trophic links of fishes. Our preliminary results indicated that Mediterranean fishes are, on average, only two trophic links away from each other.

Beschreibung: Birds are the most conspicuous, wide-ranging, and easily studied organisms in the marine environment. They can be both predators and scavengers, and they can be harmed by and can benefit from fishing activities. The effects of fishing on birds may be direct or indirect. Most direct effects involve killing by fishing gear, although on a lesser scale some fishing activities also disturb birds. Net fisheries and hook fisheries have both had serious negative effects at the population level. Currently, a major negative impact comes from the by-catch of albatrosses and petrels in long-lines in the North Pacific and in the Southern Ocean. High seas drift nets have had, prior to the banning of their use, a considerable impact on seabirds in the northern Pacific, as have gillnets in south-west Greenland, eastern Canada, and elsewhere. Indirect effects mostly work through the alteration in food supplies. Many activities increase the food supply by providing large quantities of discarded fish and wastes, particularly those from large, demersal species that are inaccessible to seabirds, from fishing vessels to scavengers. Also, fishing has changed the structure of marine communities. Fishing activities have led to depletion of some fish species fed upon by seabirds, but may also lead to an increase in small fish prey by reducing numbers of larger fish that may compete with birds. Both direct and indirect effects are likely to have operated at the global population level on some species. Proving the scale of fisheries effects can be difficult because of confounding and interacting combinations with other anthropogenic effects (pollution, hunting, disturbance) and oceanographic factors. Effects of aquaculture have not been included in the review