Cetacean Offshore Distribution and Abundance in the European Atlantic (CODA)

The aims of project CODA were to estimate the abundance and investigate the habitat use of cetacean species in European Atlantic waters beyond the continental shelf and to develop further a management framework (procedure) for determining safe bycatch limits and to provide indicative calculations for the common dolphin in European Atlantic waters. The results were intended to inform assessments of conservation status of all cetacean species, inform assessments of the impact of bycatch of common dolphin, and inform assessments of the impact of anthropogenic sound on deep-diving whales.

State-of-the-art visual survey methods were used on five survey ships to collect data for abundance estimation along 9,651 km of transects in a 968,000 km2 survey area off the continental shelves of Britain, Ireland, France and Spain in July 2007. Design-based and/or model-based estimation methods, appropriate to the data, were used to estimate abundance. Best estimates of abundance were: 116,709 (coefficient of variation = 0.34) common dolphins; 67,414 (0.38) striped dolphins; 19,295 (0.25) bottlenose dolphins; 25,101 (0.33) long-finned pilot whales; 2,077 (0.20) sperm whales; 6,765 (0.99) minke whales; 9,019 (0.11) fin whales; and 6,992 (0.25) beaked whales.

Passive acoustic data collected on all ships will be used in further research to distinguish vocalisations among odontocete species; this will aid in monitoring of some species. Sperm whale abundance was estimated from acoustic data for part of the survey area.

Habitat modelling revealed features of the environment that most influenced the distribution of the different species; sea surface temperature and depth were common predictors. Areas of higher density were predicted in the south of the survey area for common dolphins, striped dolphins and fin whales, in the north for pilot whales, and localised areas in the north and south for sperm and beaked whales.

To assess the status of common dolphins in the European Atlantic, an integrated population dynamics model was developed and fitted to data on abundance, life history and bycatch. The assessment was conducted for common dolphins assumed to be a single population in the SCANS-II and CODA survey areas 1990-2007. However, the assessment was unable to provide useful information about population growth rate; ways of improving it are discussed.

Bycatch management procedures first developed under project SCANS-II were further developed, tested for robustness, and used to calculate safe bycatch limits for common dolphins in the SCANS-II and CODA survey areas for three interpretations of the ASCOBANS interim conservation objective: to allow populations to recover to and/or maintain 80% of carrying capacity in the long term. These bycatch limits are indicative and cannot immediately be used for management purposes; a series of steps that must first be taken, initiated by agreeing conservation objective(s) at the policy level, is listed.

There is clear conservation benefit in having these new results on abundance, habitat use and capability to calculate safe bycatch limits to inform assessments of conservation status and the impact of bycatch and other human activities on cetacean species. They will contribute to national reporting under the EU Habitats Directive and to the work of international organisations (OSPAR, ICES, ASCOBANS, IWC) with a responsibility for and/or interest in the conservation of cetaceans.

Policy implications include anticipating the need for another SCANS/CODA-type survey to take place in 2015, and consideration of the steps necessary before the safe bycatch limits for common dolphin can be used for management purposes.