ABSTRACT. The structure of the demersal fish assemblages of the Gulf of Salamanca, Colombian Caribbean Sea, was studied based on 4 trawl surveys carried out in December 1995, April and August 1996, and February 1997. Multivariate analysis revealed the presence of 2 distinct assemblages, one belonging to the continental shelf (150 m depth) and the other belonging to the upper slope (>50 m depth). The continental shelf assen~blage showed significantly more biomass per tow but not more individuals or species It is typified by specles of interest for the artisanal fishery, like Lutjanus analis and Calamuspenna. Lutjanus synagris, however, also of interest for the fishery, typlfies the upper slope assemblage. No temporal change was detected in the assemblage structure, at least for the samphng dates in this study, but many species in the assemblages were scarce and rare, Indicating high spatial and temporal patchiness. The assemblages found do not fully adjust to existing zonation schemes or assemblages defined in neighboring areas, probably due to the effect of the spatial scale of the studies and the width of the shelf in the Gulf of Salamanca.

Abstract. Hake (Merluccius gayi peruanus) predation plays an important role in the dynamics of the Humboldt Current ecosystem (HCE). Changes in the hake trophic habits associated with physical variability are expected to impact prey populations and to propagate through the food web. Time series (1995–2002) of (a) stomach contents of hake, (b) biomass estimations of fish prey species of hake, and (c) depth of the 15°C isotherm was analysed with the aim of exploring the impacts of El Niño 1997–1998 on the diet of hake. Biomass estimations of fish prey species were used to indicate resource availability, and depth of the 15°C isotherm to represent variability associated with the ENSO cycle in the physical environment of hake. The richness of prey species increased during the months when 15°C isotherm reached its deepest position, supporting the hypothesis of increased biodiversity (tropicalization) of the HCE during El Niño events. An increased variability in stomach fullness of hake was detected after 1999 which could indicate high heterogeneity in the food supply as a consequence of impacts of the warm event in the biotic community structure of the HCE, a physiological impairment of hake or an effect of the abrupt reduction in the mean total length of hake, postulated as a compensatory response to fishery pressure. Hake can be characterized as an opportunist predator according to the observed changes in its diet during 1995–2002. Overall, the diet of hake in the northern HCE exhibited transitory (e.g. increased richness of prey species in the stomach contents) and medium term (e.g. increased variability in feeding activity) responses associated with El Niño 1997–1998, which should be incorporated both in population dynamics and food web analyses.

Summary Growth parameters (K, L∞) and mortality rates (M, Z) were estimated for 20 fish populations (L∞ was estimated for six further species) of the Caribbean Sea. Samples were collected during 15 scientific cruises carried out between December 1995 and March 1998 in the Gulf of Salamanca, Colombia. Observed length frequency data were fitted to both standard and modified von Bertalanffy growth models to consider seasonal growth. For those species for which growth parameter sets were available in FishBase (http://www.fishbase.org) as of November 2003, comparisons in terms of the growth performance index (∅′) were conducted. Growth performances of most stocks of the Gulf of Salamanca do differ significantly from those of other stocks. Seasonal growth does not appear to be an adequate description of growth of the Gulf of Salamanca fish stocks, in spite of the presence of a seasonal upwelling phenomenon in the area.

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