las comunidades de peces del río guadiamar y el accidente minero ...

Las comunidades de peces del río Guadiamar
y el accidente minero de Aznalcóllar
Sampling protocol
The sampling period was divided into three campaigns: winter (2006) for the low flow
streams and spring and summer (2007) for the high flow courses that were not wadeable
during the rainy period (winter). In order to cover the whole perennial stream network
(except the marshland), 22 sampling sites were selected.
Using a geographic information system and high-resolution maps provided by the
Andalusian Government, the perennial stream network (291.94 km) was split into
hydrological fragments (part of a stream with similar hydrological features, located
between two tributaries or large disruptions). These hydrological fragments were
divided into approximately 10 km segments, and finally, every segment was divided
into high, mid-slope or lowland areas, and one sampling site was allocated to each of
these areas. The exact sampling site location was finally chosen in the field, whenever a
wadeable reach was found within the selected area. Fish abundance at each sampling
site was estimated by electrofishing (220 V, 2-5 A, C.C.). Backpacking (1300 W) was
the selected procedure for 1 m depth and 5 m width reaches. A more powerful engine
fixed to the riverbank (2400 W) was needed in order to maintain the same sampling
effort on larger reaches (Lobón-Cerviá, 1991). Caught fish were identified to species
and released into the stream again. Sampling effort was constant, collecting the
maximum number of individuals in one sweep.
Habitat data were collected at two different scales: catchment (considered as the
land surface covered by all permanent streams that drain onto a sampling site) and site
(the stream section where fishing takes place and field data are recorded). Throughout
the paper, both catchment and site will refer to scale, whereas basin, watershed, reach
and stretch are used to indicate specific areas. A total of 71 environmental variables
thought to be relevant for fish species richness and diversity were recorded at each
sampling site, by means of different methods (see Fernández-Delgado et al., 2010 for
further details) and at different sampling scales (Appendix 1). In several cases, variables
were summarized by means of PCAs (see Statistical analyses section and Appendix 1).
All catchment scale data and several site scale data were extracted from digital maps
provided by the Andalusian Government, using ArcGis ® software (see Fernández-
Delgado et al., 2010).
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