Fisheries catches and the carrying capacity of marine ecosystems in southern Brazil

The carrying capacity of marine shelf ecosystems in southern Brazil for har vestable species is analyzed by (1) quantifying the amount of available pri mary production appropriated by fisheries catches, (2) evaluating the trend in the mean trophic level of fisheries, and (3) simulating the ecosystem e ffects of "fishing down the food web" in an intensively exploited shelf reg ion. Fisheries utilize ca. 27 and 53% of total primary production in the so uthern and south-eastern shelf regions, respectively. Regional variation in the carrying capacity appropriated by fisheries results from differences i n the primary production, catch volume and trophic transfer efficiencies. O verall, fisheries landings do not display a trend of decreasing trophic lev el with time due to the collapse of the sardine fishery and the recent incr easing of offshore fishing for higher trophic level species, mainly tunas a nd sharks. However, the simulations show that fishing down the food web thr ough fisheries that target small pelagic planktivorous fishes, while at fir st increasing catches in intensively exploited regions, has the potential o f decreasing yields, by interrupting major energy pathways to exploited, hi gh-trophic level species. The consequences of these results to the design o f precautionary measures for future fishing policies are discussed. (C) 200 1 Elsevier Science B.V. All rights reserved.