Gabriela Alvarez-Mieles’s research while affiliated with University of Guayaquil and other places

Wetlands are sensitive to hydrological conditions and human influence. The Abras de Mantequilla wetland (AdM) located at the centre of the Guayas River Basin (Western Ecuador), was declared a Ramsar site (2000) due to its important role in the conservation of bird fauna diversity. The wetland also supports significant populations of fish, including endemic species. The area exhibits two seasons: (i) a wet season (January–May); and (ii) a dry season (June–December). For the area of interest data is scarce, and a hydrodynamic model did not exist. In order to evaluate the interannual hydrodynamics and inundation patterns variability of this wetland system, a 2D hydrodynamic model was developed using the Delft3D software suite. Local knowledge was combined with field observations and expert elicitation to construct an appropriate model for the area. Results show that the Abras de Mantequilla is a river-wetland system that experiences extreme variations in hydrodynamic conditions from low water depths and almost stagnant conditions during the dry season, to a very dynamic behaviour during the rainy season. The inundation area ranges between 5 to 27 km², water depths vary from 0.4 to 9 m and flow velocities from 0.0 up to 0.9 m/s. The “Nuevo River” is the main inflow to the wetland, with an overall contribution of about 85–90%, with peak discharges during February and March. A numerical tracer analysis indicated that the wetland can be divided into three main areas (upper, middle and low), with higher residence times found in the middle area. Overall, based on numerical hydrodynamic simulations it was possible to obtain adequate indications of the relative importance of the different river inflow conditions, as well as spatial and temporal inundation patterns, velocities and residence times under hydrological conditions varying from dry to extremely wet years. Furthermore, the hydrodynamic model provides a basis for other studies such as water quality assessment and primary production dynamics, as well as for determining the habitat suitability for fish.

Freshwater fish communities in Ecuador exhibit some of the highest levels of diversity and endemism in the Neotropics. Unfortunately, aquatic ecosystems in the country are under serious threat and conditions are deteriorating. In 2018–19, the government of Ecuador sponsored a series of workshops to examine the conservation status of Ecuador's freshwater fishes. Concerns were identified for 35 species, most of which are native to the Amazon region, and overfishing of Amazonian pimelodid catfishes emerged as a major issue. However, much of the information needed to make decisions across fish groups and regions was not available, hindering the process and highlighting the need for a review of the conservation threats to Ecuador's freshwater fishes. Here, we review how the physical alteration of rivers, deforestation, wetland and floodplain degradation, agricultural and urban water pollution, mining, oil extraction, dams, overfishing, introduced species and climate change are affecting freshwater fishes in Ecuador. Although many of these factors affect fishes throughout the Neotropics, the lack of data on Ecuadorian fish communities is staggering and highlights the urgent need for more research. We also make recommendations, including the need for proper enforcement of existing environmental laws, restoration of degraded aquatic ecosystems, establishment of a national monitoring system for freshwater ecosystems, investment in research to fill gaps in knowledge, and encouragement of public engagement in citizen science and conservation efforts. Freshwater fishes are an important component of the cultural and biological legacy of the Ecuadorian people. Conserving them for future generations is critical.