No abstract

The structure of the demersal assemblages (fish, crustaceans and cephalopods) of the continental shelf and upper slope of Angola (ca 5 to 17's) was studied based on the trawl survey of the RV 'Dr. Fridtjof Nansen' in February and March 1989, by means of an ordination technique, Detrended Correspondence Analysis (DCA), implemented by the computer program DECORANA and a classification technique, Two-Way Indicator species Analysis (TWIA), implemented by the computer program TWINSPAN. Correlation of DCA axes with the environmental variables showed that the thermal, depth-dependent stratification explains the main groupings, while bottom type and latitudinal gradients are the main factors within each depth stratum. A major latitudinal faunal shift takes place in the area Tombua-Cunene (Angola) and is related to the southern limit of Equatorial Water for the shallow-water assemblages and to the frontal area between the warm, southward-flowing Angola Current and the northward-flowing cold Benguela Current for the subthermocline shelf assemblages. Highest biomass densities (from bottom trawl catches) were found in correspondence with the upper slope, consisting mainly of the bony fish Synagrops microlepis (Norman).

The structure of demersal assemblages (fish, crustaceans and cephalopods) of the continental shelf and upper slope between the Gulf of Tehuantepec and the Gulf of Papagayo was studied from data obtained in the course of surveys carried out by the RV 'Dr. F. Nansen' in 1987, by means of an ordination techmque, Detrended Correspondence Analysis (DCA) implemented by the program DECORANA, and a classification technique, Two-Way Indicator Species Analysis (nVIA) implemented by the program TWINSPAN. Three major groups of species were identified: those distributed above the thermocline, those within the range of the thermocline and a thud group below the thermocline, where oxygen content is extremely low. Highest biomass densities were found below the thermochne, consisting mainly of the galatheid crustacean Pleuroncodes monodon (H. Milne Edwards, 1837) Correlation of DCA Axis 1 with depth, temperature, salinity and oxygen showed that depth is the main gradient along which fauna1 changes occur.

Many of the world’s fish stocks are depleted as a result of overexploitation, pollution and habitat loss. The 2002 World Summit on Sustainable Development (WSSD) sets a target for fisheries to maintain or restore stocks to levels that can produce the maximum sustainable yield (MSY) by 2015. We assessed the global stock status and found that 68% were at or above the MSY level in 2008 and that the 2015 target is unlikely to be met. We compiled data for eight indicators to evaluate the sustainability of fisheries and the gap to meet the WSSD target. These indicators show that the overall condition of global fisheries is declining, long‐term benefits are being compromised, and pressures on fisheries are increasing despite fisheries policy and management actions being taken by coastal States. We develop a bio‐economic model to estimate the costs and benefits of restoring overfished stocks. Our results show that the global fishing capacity needs to be cut by 36–43% from the 2008 level, resulting in the loss of employment of 12–15 million fishers and costing US$96–358 billion for buybacks. On the other hand, meeting the WSSD goal will increase annual fishery production by 16.5 million tonnes, annual rent by US$32 billion and improve biodiversity and functioning of marine ecosystems. However, progress towards rebuilding has been hindered by an unwillingness or inability to accept the short‐term socio‐economic consequences associated with rebuilding fisheries. Thus, there is a pressing need for integration of rebuilding plans into national political and economic decision‐making.

The structure of the demersal assemblages (fish, crustaceans and cephalopods) of the continental shelf and upper slope off Congo and Gabon (from about 1 to 5" S) was studied based on the trawl survey of the RV 'Dr Fridtjof Nansen' in January-February 1989, by means of an ordination technique, Detrended Correspondence Analysis (DCA), implemented by the computer program DECORANA and a classification technique, Two-Way Indicator species Analysis (TWIA), implemented by the computer program TWINSPAN. Major fauna1 discontinuities were found between the shelf and the slope assemblages and, on the shelf, between the suprathermocline and the subthermocline assemblages. Correlation of DCA Axes 1 and 2 with the environmental variables showed in fact that temperature was most highly correlated with DCA Axls 1. The lack of any correlation wlth Axis 2 indicates that other factors (e.g. bottom type) also play an important role in explaining the various groups. Highest biomass densities (from bottom trawl catches) were found on the deeper shelf off Gabon and in the intermediate shelf off Congo.