Fish community composition of The Santiago River Basin, Mexico, during its hydraulic development

Abstract

The Santiago River basin located in northwest Mexico is one region with important fish diversity in North America. The objective of this paper is to identify temporal and spatial changes in the fish community over three stages of the river hydraulic development, when certain degrees of connectivity existed, from its origin to its sea mouth. 1032 fish records from national and international databases belonging to132 localities in five sub-basins were analyzed. In total, 44 species were recognized, 13 endemic of the Lerma-Chapala-Santiago region, 22 natives to Mexico, 7 introduced and 2 translocated. In the first stage up to 1970, 33 species were gathered, mainly in the upper part of the basin. In the second stage from 1971 to 2000, 32 species were registered, and in the last stage (2001 to 2006), only 25 taxa. According to their relative abundance six species represented 71% of the total collection and 22 had distributional amplitude between 5% and 36%. Even though differences in periods of time for each development stage, catching methods and localities, due to their temporal absence and habitat reduction in their distributional range, eight species are apparently extirpated and 17 species are at risk in the Santiago River. Overall environmental degradation and fragmentation have reduced native and endemic species and an increase in the introduced ones have been observed mainly in the Santiago and Verde rivers. Based on their conservation degree and potential presence of isolated fish populations, a follow-up monitoring program is proposed in the Huaynamota and Bolaños rivers to preserve representative areas of the fish community in the basin.