Spatiotemporal analysis of fish diversity and biotic integrity in two western Mexico watersheds.

Authors: Brenda Mendoza, Norman Mercado-Silva, Einar Beath, Luis Rivera

Year: 2025

Abstract

Water reserves were legally established for several river basins in Mexico in the late 2010s. Since then, the National Network for Water Reserve Monitoring (RedMora) has implemented numerous studies to calculate and implement environmental flows in five hydrologic regions of the country. These include social-economical and eco-hydrologic approaches that have provided a wealth of information to be used in implementing environmental water flows. The Cuitzmala and Purificación Rivers (SW Jalisco) have water reserves but are experiencing population growth, water extraction and increased agricultural and livestock activities. Their fish communities, which include endemic species (e.g., Poecilia chica and Poeciliopsis turneri) and others considered priority species by IUCN (e.g., Xenotaenia resolanae and Gobiesox fluviatilis), have experienced changes as areas of these basins have been affected by human activity. We used field data from 10 sites taken over two periods (2013 and 2022-2023) to analyze differences in species richness and abundance for each site and collection event. We also performed analyses of true diversity, beta diversity, and their turnover and nesting components. Additionally, we calculated fish-based Index of Biotic Integrity (IBI) scores for each collection event; these were contrasted spatially and temporally. In the Cuitzmala River, Sicydium multipunctatum was the most abundant species in 2013 while Poeciliopsis baenschi was the most abundant species in 2022–2023. In the Purificación River, P. baenschi was the most abundant species in both periods. In both rivers, true diversity was greater in the middle and lower reaches than in the headwaters. Species turnover (βSIM) was the predominant component of beta diversity. Beta diversity was higher in the Purificación than in the Cuitzmala. Relatively low IBI values were obtained in the middle reaches of both rivers, and these were lower in 2023 than in 2013.