| Summary: | The abundance of fin whales (Balaenoptera physalus) was generated from data collected during shipboard sightings surveys as part of the Cetacean Offshore Distribution and Abundance in the European Atlantic project (CODA). The survey area covered offshore waters beyond the continental shelf of Britain, Ireland, France and Spain. The area was stratified into four blocks and was surveyed by five ships during July 2007. Double platform methods employing the trial-configuration method (BT-method) were used. Abundance was estimated using the Mark-Recapture Line Transect design-based method and also model-based methods using density surface modelling. Estimates from the two methods were comparable but model-based methods improved the precision and were considered best estimates. The total abundance estimated for the entire survey area was 9,019 (CV=0.11) fin whales. This is likely to be underestimated because it excludes unidentified large whales, of which a large proportion were likely to have been fin whales. The uncertainty around these estimates due to duplicate classification and species identification were explored. The density of fin whales was greatest in the southern end of the survey area and water depth, temperature and distance to the 2000m contour were important predictors of their distribution. The North Atlantic Sightings Surveys have periodically covered parts of the CODA region since the 1980s but interpretation of the results is complicated by inconsistencies in survey and analytical methodologies. Only the most recent estimates from the 2007 TNASS project correct abundance estimates of fin whales for g(0). The CODA abundance estimates are the first robust estimates (corrected for responsive movement and g(0)) for this area. They are important contributions to the conservation and management of this species in the Northeast Atlantic
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