OdVs in the Maule, Biobío, and Toltén

Recently, I helped the team at the Centro de Cambio Global complete the aquatic ecology portion of the «Cuencas 2» project, funded by the Chilean Ministry of Energy. Our team was in charge of assessing a number of «Objetos de Valoración» (OdV) within the Maule, Biobío, and Toltén watersheds of Central and Southern Chile to assist with future sustainable hydropower development in Chile. In this framework, OdVs are – very broadly speaking – features or conditions in the watershed (either terrestrial or aquatic) that are determined to be of concern (environmentally, ecologically, socio-culturally, or economically) when considering the question of sustainable development.

 

Two major contributions I provided to the process were in the assessment of probable distributions of native and exotic fish species throughout these three watersheds as well as the creation of an additional OdV, «Watershed Accessibility,» which is an index that describes the proportion of the watershed accessible from any one river reach.

Probable Fish Distributions

The probable distributions of freshwater fishes were based on fundamental principles of ecohydrology at meso-spatial scales, and utilized many of the data derived for characterizing the physical characteristics of the watersheds that were done as another part of the Cuencas 2 project. The fish presence data were from the Chilean Ministry of Environment (MMA, native fishes) and the Chilean National Fisheries Service (Sernapesca, exotic fishes).

Three fish-species OdVs were generated for the watersheds: potential presence of endangered or vulnerable species, potential presence of native species, and general «intactness» of local fish communities. In general, rainbow and brown trout (exotic to Chile) were determined to be mostly in the mountainous uplands, while native fishes tended to be more predominant in the downstream, valley, portions of the watersheds. These general patterns comported with the general descriptions in the literature.

Watershed Accessibility

One major concern when thinking about hydropower development and fish ecology is the impact of dams on migration of fishes. One of the iconic examples of this is the impact of dams on salmon migration throughout coastal North America and Northern Europe. This type of migration (scientifically defined as anadromy) is not a feature of Chilean fishes, though. Two groups of Chilean fishes that do migrate to and from the ocean are freshwater eels (which are catadromous) and galaxids (which are amphidromous). However most of the rest do not migrate to the sea, but do utilize various portions of a watershed for different parts of their life histories. In other words, they are potadromous.

When considering the question of fish movement among Chilean fishes, therefore, the classical image of salmon returning to a natal stream is literally exotic to the Chilean condition. Instead, the most common image is that of a native species accessing various parts of a watershed during the year and throughout its life cycle, and never venturing out to the ocean. In such a case, therefore, the longitudinal accessibility – from the mountains to the river mouth and back again – is not as great a concern as topological accessibility – from one tributary system to another.

The «Watershed Accessibility» OdV is an attempt to create an index that determines the available amount of watershed that can be accessed from any one river segment, which is a potentially far more important measure of what is often termed «ecological connectivity» (which is an analogue of the terrestrial ecology concept of «fragmentation») than is described by various measurements of longitudinal connectivity. Its inclusion as one of the official OdVs to be considered by the Ministry of Environment is, I believe, a crucial step in defining an ecosystem metric which has the somewhat unique condition of Chilean fishes in mind.

Next Steps

The work done at the Centro de Cambio Global was on three of eleven watersheds that span the geographic area of Central Chile through to Patagonia. The other eight watersheds – and their OdVs – were characterized by teams from the University of Chile (watersheds in the Los Rios and Los Lagos Regions) and the University of Concepción (watersheds in Chilean Patagonia). We are currently working on a set of papers that will explain the modeling process and results of our combined work.

If you are interested in learning more about the project or its results, please feel free to contact me.