Long‐term changes in the fish assemblage of the Laja River, Guanajuato, central Mexico

Abstract

ABSTRACT1. The structure and composition of fish communities in rivers of central Mexico have been altered as a result of water over-exploitation, habitat fragmentation, introduction of exotic species, and pollution. However, the specific pattern and degree of change are poorly documented.2. Long-term information from the Laja River (Guanajuato, Mexico) in the Lerma River basin was used to explore trends in fish species richness and community composition (species origin, trophic niche, tolerance, and preferred habitat) from the 1960s to the present in both river and reservoir sites.3. Declines in native, sensitive, benthic native and carnivore species ranging from 11% to 30% per decade, and increases in the number of tolerant and exotic species by 9-20% per decade, are documented. Repeated measures ANOVA and sign tests revealed significant declines in the number of benthic, native, carnivore and sensitive species. Species richness, number of exotics, tolerant species and omnivore species did not change statistically, though statistical power was low. Some important changes occurred in these variables, such as the expansion and establishment of exotics such as Xiphophorus variatus and Micropterus salmoides, which pose a serious potential threat to native species.4. The changes in fish community composition for the Laja portray how the fish communities in other rivers in central Mexico, for which long-term data do not exist, have changed or could change if environmental deterioration continues.

Long term changes in the fish fauna of Lago de Patzcuaro in Central Mexico

“…Historical research on changes in ecosystem elements and processes help understand the effects of anthropogenic threats and provide specific information that can be used to reduce further ecosystem degradation (Karr, 1981;Mercado-Silva et al, 2006). Data about long-term changes can aid in developing monitoring strategies and future conservation efforts (Olden & Poff, 2005;Mercado-Silva et al, 2006). Although anthropic effects on the watershed and the water quality of Lago de Pátzcuaro are relatively well documented, this study represents the first effort to understand the long-term changes of the fish assemblages in this lake.…”

“…For most records no information on sampling effort or gear type was available, and we had to assume that sampling efforts adequately sampled the entire fish community. Because of this limitation, only presence/absence data were considered for analysis following Mercado-Silva et al (2006).…”

“…Further information on the nature of the impacts can be obtained from the ecological attributes of individual species (Karr, 1981;Lyons et al, 1995). Ecological studies on fish assemblages can integrate and evaluate a variety of impacts (water quality, habitat structure, species interactions) on biotic systems (Hobbie et al, 2003;Mercado-Silva et al, 2006). Species origin, feeding preferences and species tolerance to environmental degradation are fish attributes to consider when analysing community change and understanding cumulative anthropic impacts (Lyons & Mercado-Silva, 1999;MercadoSilva et al, 2006).…”

Habitat associations of a semi-arid fish community in a karst spring-fed stream

“…Such pumping has become increasingly prevalent due to human populations growth in areas adjacent to karst aquifers. Currently, the Devils River is without extensive anthropogenic alterations, but increasing pressure for groundwater extraction from the Edwards Aquifer might threaten the future of the Devils River fish assemblage, similar to other streams altered by groundwater extraction (Mercado-Silva et al, 2006). This study demonstrated spring flows serve as refugia for spring-associated species during winter and summer months and maintain environmentally variable areas downstream for riverine species, which collectively support a diverse fish assemblage.…”

Long-term change in the biotic integrity of a shallow tropical lake: A decadal analysis of the Lake Chapala fish community

“…Similar patterns of human impact are occurring in lakes and rivers elsewhere in Mexico and in other tropical countries, and highlight the urgent need to implement habitat protection and enhancement in nearshore areas and to prevent exotic species introductions (Bence et al 2002, Bronte et al 2003, Mills et al 2003, Mercado-Silva et al 2006. The IBI provides a tool to quantify the effectiveness of such conservation measures.…”