Zoogeographic Determination of Soft Bottom Fishes in a Coastal Lagoon on the Pacific Coast of Baja California Sur, Mexico

The aim of this chapter was to determine the zoogeographic affinities of the fish species associated with soft bottoms recorded in laguna San Ignacio, B.C.S. Coastal lagoons and estuaries are physically unstable areas that typically show spatial and temporal variations of water temperature, salinity, dissolved oxygen and turbidity. This environmental complexity favours the ichthyofauna present there, which is usually characterized by juvenile organisms that use these coastal systems as feeding and breeding grounds. However, only a few species use these lagoons during their full life cycle, while many others use them during a specific part of their life cycle. San Ignacio lagoon is located on the west coast of Baja California Sur; this body of water has important bio-economic properties. It belongs to the temperate zone of the Californian province due to its geographic location. The fish fauna found in the lagoons of Baja California Sur has been the subject of numerous research, but the data gathered so far is insufficient to ensure the management and protection of this lagoon's fish population. The determination of the zoogeographic affinity of the species identified in the study area was based on the characterization of their distribution. Six samplings were conducted at 11 sites in the lagoon, from April 2013 to April 2014; an experimental trawl was used, and the physicochemical parameters were obtained at each sampling. A total of 2887 organisms from 26 families, 38 genera and 46 species of fishes were collected, the largest number of species were from the Haemulidae and Serranidae families. According to the analysis of presence/absence, different species were found each season. Although, there were more species with tropical affinity than species with temperate affinity. The zoogeographic affinities correspond to 28% Californian Province, 4% Cortez Province, 7% Mexican Province, 41% Panamic Province, 18% Eastern Pacific and 2% Circumtropical. The temperature of San Ignacio Lagoon has an impact on the zoogeographic affinity of fishes that prefer soft bottoms because it permits species with tropical and temperate affinities to coexist.