| Resumo: | The Natural Protected Area Parque Nacional Bahia de Loreto, including five adjacent islands, was created in 1996. The park presents rocky and sandy shores, mangrove areas and small patches of reef corals, which have been used for fishing and ecotourism activities. The fishery of the brown sea cucumber Isostichopus fuscus is one of the most peculiar in the Gulf of California since early nineties and in the Park the fishery takes place since 2000 under special permits known as UMAS (units for wildlife management). However, little is known on the abundance of the resource in natural populations in México, crucial information to determine total allowable catch. The objective of this study was to assess the abundance of I. fuscus in the National Park Bahia de Loreto, Gulf of California, during the fishing season 2005-2006. Abundance was estimated through belt transects (25 x 2 m). A total of 29 sites or “banks” were visited, mostly sites where the fishery occurs. Data were analyzed to determine homoscedasticity and normality using the Levene and Kolmogorov-Smirnoff tests, respectively. To detect differences between the islands we used a one way ANOVA (model II; α=0.05) considering the islands as factors. We used linear regressions to detect geographic clines between population density and geographic location. The average abundance of I. fuscus in the PNBL was 1.41 + 0.02 individuals/transect, with an average density of 0.028 + 0.0004 ind/m2. Density was slightly higher in the southern banks. The lowest value was found at isla Montserrat, which is close to the coastline of the Baja California Peninsula, where most of the fishery occurs. No relationship was found between population density and latitudinal gradient, nor with the distance from the coastline. We concluded that even though density levels were low in PNBL, the situation of I. fuscus does not seem critical to populations.
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