Fish sampling is carried out using double pots or butrones (according to FAO and European inter-calibration group terminology called "Twin Fykes"). The butrons consist of two conical structures formed by 7-9 plastic-coated metal rings and a white netting of 7 mm mesh size covering the structures. The entrance rings to the trap are semi-circular and are 50 cm in diameter for small pots and 80 cm in diameter for large pots. The conical structures are placed opposite each other, perpendicular to the flow of the current, and connected by an approximately 2 m long mesh that cuts off the fish and directs them to the trap entrance. The funnel-shaped design makes it easy for fish to enter and difficult for them to exit and become trapped in the net. The minimum number of gears set at each sampling point is four double pots, two large and two small. The booby traps are preferably set shortly before low tide or at the beginning of the incoming tide in the late afternoon, which determines the working period. It is not possible to set the traps on an ebb tide, as any fish that might enter would be exposed to fresh water or desiccation. The gears are placed more or less parallel to the shore, in such a way as to prevent them from drying out, as this would also result in the death of the trapped individuals. The double pots are fixed by means of metal bars. The buoons remain in place throughout the night, trying to cover a tidal cycle (low tide-tide-removal before low tide). In any case, the nets must be removed before low tide to avoid the problems of salinity or desiccation mentioned above. The captured fish are placed in white containers with clean water before being measured, renewing the water with some frequency if necessary to avoid heating and loss of dissolved oxygen. Subsequently, the species are identified, all specimens are measured and the abundance of each species (number of individuals) is quantified. The presence of conditions in the captured individuals is also noted. Individuals that cannot be identified in situ are preserved in 70% ethanol for identification in the laboratory, while the rest are returned to the environment to ensure their survival.
| Study Extent | The study of fish fauna was carried out in all the estuaries of the region. In each one, a sampling point has been established. |
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Method step description:
IHCantabria with the support of the Regional Government of Cantabria has been carried out since 2005 the monitoring of the coastal waters of Cantabria in accordance with the Water Framework Directive. Here is included the abundance and biomass of estuarine fishes obtained from field campaigns in all the estuaries of the region.