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5th International Conference on Environmental Future: Climate change and the future state of the world\u27s aquatic ecosystems
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Predicting indirect effects of fishing in Mediterranean rocky littoral communities using a dynamic simulation model
No full textModelling may significantly enhance our understanding of the potential impacts of fisheries at larger spatial scales and on groups that would otherwise be very difficult to study. An aggregated biomass-based simulation model of a Mediterranean infralittoral zone was developed and used to carry out fishing \u27experiments\u27 where fishing intensity and catch selection were varied. The model was constructed for the Bay of Calvi, Corsica, using the Ecopath with Ecosim software, and was composed of 27 compartments, including seabirds, 11 groups of fish, 12 groups of invertebrates, 2 primary producers, bacteria and detritus. Several instances of indirect fishing effects (\u27trophic cascades\u27 and \u27keystone predation\u27) have been proposed from anecdotal evidence in the western Mediterranean. Model outcomes provided little support for the widely accepted paradigm that fishing, by removing invertebrate-feeding fish, allows increases in the biomass of sea urchins and as a consequence the formation of overgrazed \u27barrens\u27 of bare substrate. Simulated harvesting of sea urchins by humans did, however, results in an increase of macroalgal biomass as reported previously. Intensified fishing pressure on \u27macrocarnivorous\u27 fish resulted in a \u27release\u27 of small fish species (e.g. blennies), and as a consequence a decline in the biomass of some small invertebrates on which they feed (e.g. amphipods). Increased fishing on large \u27piscivores\u27 resulted in increases in other small fish groups and consequential effects on other benthic invertebrate groups (e.g. polychaetes). Depletion of piscivorous fish resulted in a dramatic increase in the biomass of seabirds, which apparently compete with piscivores for small demersal and pelagic fish. An intensification of fishing pressure overall resulted in an increase in cephalopod biomass. Responses of target species to increased fishing pressure were most marked within the first 5 years of the new fishing regime. Indirect responses exhibited varying degrees of inertia, and biomasses of many groups did not assume a new equilibrium within the first 20 years of the simulation. The Mediterranean infralittoral rocky-bottom ecosystem was predicted to be relatively resilient to pulses of increased fishing and exhibited a high degree of detritus recycling. However, the speed and magnitude of ecosystem responses was shown to depend greatly on the extent of \u27top-down\u27 or \u27bottom-up\u27 control assumed for components within the system. Crown Copyright \ua9 2003 Published by Elsevier B.V. All rights reserved
Preliminary analyses of overarching issues effecting the 21 marine and freshwater ecosystems
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Using informal knowledge to infer human-induced rarity of a conspicuous reef fish
No full textThere have been few contemporary extinctions in the sea, which suggests marine species are either less vulnerable to extinction than terrestrial species, or marine extinctions may have gone unnoticed. We consider whether a large conspicuous reef fish, the giant humphead parrotfish (Bolbometopon muricatum), is likely to have declined across much of its geographical range. Informal knowledge was used to determine the status of the giant humphead parrotfish. We first surveyed fishers\u27 knowledge of this parrotfish at 12 lightly exploited islands in the Lau group, Fiji and then compiled a global inventory of available information. In the Lau islands, Fiji, fishers reported this parrotfish as previously abundant, but it had not been caught at six islands since at least 1990 and was considered rare at another four islands. The parrotfish had been captured recently (since the 1990s) at three islands where fishers did not target parrotfishes regularly. A compilation of giant humphead parrotfish records provided by local scientists at 39 locations in 31 Indo-Pacific nations suggested this fish is locally common only inside areas where fishing is prohibited and that it is currently globally rare. Local densities of the giant humphead parrotfish were negatively correlated to a categorical scale of fishing pressure across six Indo-Pacific locations. The retrospective discovery of local disappearances and global rarity of a distinctive and formerly prominent reef fish is consistent with the hypothesis that the capacity to detect disappearances of exploitation-vulnerable species in the sea is lower than expected. \ua9 2004 The Zoological Society of London
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