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5.5.7 Parc Naturel Marin d'Iroise: Aims of scenario building process?

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Kelp management scenarios, tested in the VALMER project, are real-life scenarios agreed by harvesters, managers, scientists and state representatives, stakeholders and decision-makers upon a collaborative management process.

The scenarios aimed at comparing management options, in the context of various possible changes in the kelp socio-ecosystem. Some scientists and managers, who were part of the VALMER Parc Naturel Marin d'Iroise team, participated to the kelp management commission.

It was decided to rely initially on the discussions of the commission to capture the social perception of kelp ecosystem services and management needs. In addition to this, interviews with other stakeholders were carried out in a second step to further refine the operational characterization of some management rules and other factors of change.

Today, Laminaria hyperborea harvesting is managed through harvesting zones negotiated fifteen years ago with fishermen. Five large zones are subdivided into five sectors in which there is a rotation of harvesting and fallow periods. Each area is associated with a fishing quota fixed every year according to an assessment of the kelp standing biomass. When the production reaches 20% of the standing biomass, the fishery is closed for five years.

Whilst this management regime is a useful first step towards a sustainable exploitation of the kelp resource, the existing kelp harvesting management is relatively crude and damaging and should be reviewed in order to integrate the increasing demand of the sodium alginate market. It should also take into account many factors recently discussed between fishermen, managers and scientists, in particular:

  • Accessibility: total biomass of laminaria is different from the available biomass, which depends on the swell, the presence of rocks, etc. Today fishermen often operate in the same areas (accessible and benefiting from the proximity of natural reseeding sites). The harvesting of Laminaria hyperborea is not undertaken in winter due to weather conditions. At this time of year, species present in the kelp field (lobster, seabass, etc.) migrate to the Celtic Sea or the Bay of Biscay and then return in the spring. In winter, the algae are torn by the waves (about 300 000 tonnes), and fishermen often argue that they do not harvest as much as the quantity that reach the coast in winter due to storms.
  • The recent mapping of kelp: the total biomass appears to have been underestimated and fishermen may not have reached the maximum production potential of the kelp field yet.
  • The improvement of the knowledge on the kelp dynamics and ecological functionality: a new regime of kelp harvesting should better integrate the seasonality of the ecosystem services provision and identify the most damaging harvesting periods for the ecosystem balance.
  • Influence of environmental conditions: the harvesting pressure on the kelp ecosystem should also be compared to the impact of regular large strandings of kelp that are observed after winter storms (about 300 000 tons).

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