The ORHAGO 21 survey aims to complete a historical series of indicators of sole abundance and on the status of benthos ichthyic fish communities in the Bay of Biscay.

This fauna is widely exploited by large fishing fleets. The sole is indeed the first fishing resource in value of the Bay of Biscay. Its exploitation is managed by quotas that fishermen's representatives want as high as possible but also as stable as possible. The annual diagnoses carried out within ICES are thus an important economic and political stake and their quality is under attentive observation.

While commercial fishery data are of fluctuating quality, abundance indices from scientific surveys are a valuable aid for diagnoses of the state of the fishery resources. They make it possible to validate the trends observed in the fishing data and to separate, during the analysis of catches and CPUE, the evolutions due to the fluctuations of stocks from those caused by changes in fishing practices.

In addition, the scientific surveys are the only source of information for the age classes which are not yet exploited and on which the catch forecasts and the management advices are largely based. Indices of abundance therefore constitute a fundamental need for the quality of assessments of the state of the fishery resources. In the case of sole of the Bay of Biscay, no other campaign can be used (The GOV trawl of the EVHOE survey is poorly adapted to the capture of benthic species).

For this reason, ICES has recommended that ORHAGO surveys be set up for many years and their maintenance is essential for the quality of diagnostics and simulations for this stock. This importance made it possible to obtain co-financing of the survey by the European Union via the European Maritime and Fisheries Fund (EMFF), measure 77, up to 80% of the eligible costs.

The ORHAGO surveys are requested as part of the observation (program Fisheries Information System) and fishery resource assessment missions of the Department of Biological Resources and Environment of Ifremer. Since 2008, this survey has been integrated into the survey series coordinated by the ICES WGBEAM Working Group, which includes the main European surveys carried out with a beam trawl, which is the standard gear for flatfish abundance indicators. The protocol has been validated internationally and the data collected are made available to the international scientific community via their uploading in the ICES DATRAS database.

The ORHAGO surveys are carried out in November to maximize the catchability of all year-classes of sole. They implement a beam trawl whose mesh size in the cod-end is 40mm. Each haul lasts 30 minutes. The trawls are carried out on 48 fixed positions in order to guarantee the fidelity and the precision of the indicator of abundance of the sole.