Case study: Basque estuaries. 2.1.1. Fieldwork data collection Fieldwork research was carried out in 12 estuaries (i.e. Barbadun, Nerbioi, Butroe, Oka, Lea, Artibai, Deba, Urola, Oria, Urumea, Oiartzun and Bidasoa) located at the coast of the Basque Country, in the South-Eastern part of the Bay of Biscay (Figure 1). Surveys, which started in April 2008 and lasted until September 2010, were always carried out during periods of high or rising tide periods. 2º W ORIA UROLA 20 10 Escala (km) BILBO 3º W 43º 20’N XXXXXXX XXXX XXXXXX STIA DEBA NERBIOI BARBADUN XXX XXX MAR CANTÁBRICO BUTROE N Figure 1: Basque coast graphic representation including the location of the 12 estuaries included in this study. Green: intertidal Atlantic estuary, where fresh water dominates marine water, Yellow: intertidal Atlantic estuary, where marine water dominates fresh water, and Red: subtidal Atlantic estuary. Hydromorphological and biological benthic surveys were carried out in the inner, middle and outer sections of each estuary. For the Oiartzun and Bidasoa estuaries, two different inner areas were identified, and consequently surveyed. For each estuary section, a transect path was defined and hauled three times in order to obtain replicates.. To collect the samples, a Narwhal zodiac with a towed 1.5 m wide beam trawl, which had a tickler chain and internal and external nets of 8 mm and 40 mm mesh respectively, was used. The beam trawl was dragged along the defined transect path for 10 min at a constant speed of
