Distribution and Abundance of Fin whales and other baleen whales in the European Atlantic

Abstract

The abundance of fin whales (Balaenoptera physalus) and other baleen whales 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 the UK, 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 trialconfiguration method (BT-method) were used. Fin, sei (B. borealis) and minke whales (B. acutorostrata) were positively identified, with possible sightings of blue whales (B. musculus). Abundance was estimated for these species and for “large baleen whales” which included fin, sei, fin/sei and blue whales. Abundance for the larger species was estimated using the Mark- Recapture Line Transect design-based method and also model-based methods using density surface modelling. Sample size limitations dictated that conventional line transect sampling methods were used to estimate the abundance of minke whales. Estimates from the two methods were comparable but model-based methods improved the precision and were considered best estimates. The density of large baleen whale species 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 total abundance estimated for the entire survey area was 9,019 (CV=0.11) fin whales and 9,619 (CV= 0.11) large baleen whales. The uncertainty around these estimates due to duplicate classification and species identification were explored. The fin whale estimate is likely to be underestimated because it excludes unidentified large whales, of which a large proportion was likely to have been fin whales. Notwithstanding this, these large baleen whale abundance estimates are the first robust estimates (corrected for responsive movement and g(0)) for this area. The estimated abundance of minke whales was 6,765 (CV=0.99) and sightings were restricted to the northern blocks of the survey area. The minke whale estimate, although imprecise and likely underestimated, does provide a baseline figure for this area and, when considered with results from the SCANS-II continental shelf surveys of July 2005, gives a more comprehensive picture of this species in the European Atlantic. These abundance estimates are important contributions to the conservation and management of these species in the Northeast Atlantic.