Abstract

In the southern Gulf of Mexico, there is an important shrimp fishery industry with no recent works on the fish assemblage ecology coming from the trawling by catch. The objective of this work was to seasonally analyze the trophic spectrum and niche parameters of the most important fish coming from the shrimp by catch. During 1991 to 1994, 21 two hour trawls were done in the southem Gulf of Mexico off Veracruz, Mexico at a mean depth of 20m. The importance value of the food items, identified to the finest level possible, was used to calculate: the Levins niche breadth for each species; a cluster analysis, and the Rekonen index for niche overlap between species for three seasons. During the dry season, 26 fish species were analyzed which grouped into four clusters based on 24 food items. The highest Rekonen value (>53%) was for species feeding on benthic or zooplankton items. For the rainy season, 26 species were grouped into three clusters, of which the benthic feeders presented the highest niche overlap(>47%) and the least number of species. The northerly winds season was the richest in species (43), which were assembled in three groups according to their food items. One group was formed by two anchovies withahigh(> 80%) niche overlap. Thirty-six species formed a single group feeding on a variety of items (mainIy benthic) with a niche overlap > 50%. The high number of species feeding on similar items during the northerly winds season may be due to a higher productivity in the region produced by the river run off. In contrast to the other seasons, the amount of food items are restricted, thus diminishing the number of possible prey and increasing the niche overlap between trophic groups.

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