Biological characterization of aggregates clogging fishing nets on the Basque coastal waters of France

Over the past fifteen years, gillnets used by fishermen of the Basque coast of France have been seasonally covered with aggregates. By making the nets more visible, this disrupts the coastal fishing activity and sometimes causes skin allergies. In 2010, we deployed for the first time a fine mesh device which was immersed permanently and attached to the bottom off the Bay of Saint-Jean-de-Luz in order to collect samples of these aggregates throughout the summer period.The first results reported in this work deal with the origin and biology of organisms forming these aggregates, excluding biochemical and bacteriological aspects. A remarkable feature is the wide variety of both planktonic and benthic components in the collected matter. More than 111 taxonomic units have been so far identified. In addition to these elements of marine origin, these aggregates deposited on fishing nets also contain exogenous matter of continental origin, mainly Grey Willow Salix atrocinerea silk's seeds, mammals' hairs and pollen. In this work, particular attention is also given to the potentially irritating and stinging organisms present in the aggregates. Finally, hypotheses are developed about the aggregation process of these living organisms and their pelagic sedimentation induced by the presence of fishnets in the water column.