Composition, abundance and distribution of populations of commercially important gastropods in La Guajira, Colombian Caribbean. In the continental Colombian Caribbean the conch resource exploitation and the status of snails populations has been poorly studied, which are reflected in the lack of fisheries management. This study assesses composition, population density and distribution of the gastropods species that make conch resource in La Guajira region. Underwater visual censuses for snails were performed between September-November 2009 in 145 100x4m (400m 2) transects, spanning a total area of 56 920m 2 between Riohacha and Cabo de la Vela. The study was complemented with the evaluation of composition, abundance and size of gastropods conch found in the discarded-by-fishermen shell mounds in 13 beaches. In October 2010 another 40 transects were evaluated (16 000m 2) from the Southern of Riohacha to the Camarones village (La Guajira). We found a total of 9 911 snails belonging to 12 species, the most abundant being Strombus pugilis with 8 912 individuals and an average density of 1 538.4±3 662.6 ind./ha , followed by Vasum muricatum with 374 individuals and an average density of 51.8±91.2 ind./ha. Calculating the importance value index (IVI) for both living organisms as the empty shells on beaches, shows that Turbinella angulata is the most used species by artisanal fishermen in the region. Cassis madagascariensis and Cassis tuberosa are also important snail resources in the region (as suggested by the number of empty shells found in beaches), but its densities were low. Strombus gigas, with only three living organisms found in the area, presented the lowest abundance ever found in the Colombian Caribbean (0.52±3.6 ind./ha), showing that queen conch population in La Guajira cannot support commercial exploitation. The abundance of discarded S. gigas shells on beaches suggests resource exploitation in the recent past. Results remarks the urgency of implementing management plans for snail fisheries in the region.

The Environmental Sensitivity Index (ESI) mapping has been used globally for oil spill planning and response purposes in coastal areas since its development in the 1970s. However, application to riverine habitats has been very limited.  Following US National Oceanic and Atmospheric Administration (NOAA) formats and adapting them in working sessions held by a multidisciplinary team and in special sessions with experts and consultants in Colombia, this paper describes the development and application of the sensitivity index to develop maps for the conditions of the middle Magdalena River in Colombia.  The index developed (ESI-R) is useful for application on other major rivers in Colombia and areas with similar characteristics.  The use of the index to develop maps for smaller rivers and streams is likely to require further development.