We investigated the impact of the “Erika” oil spill in the
Bay of Biscay (France) on seabird populations. Relative abundance and
spatial distribution at sea between 1980-1999 and 2000-2002 periods were compared.
This study took place in a standardized monitoring at sea carried out with Coast Guard
vessels following the line transect method. This work rests on 107 551
standardized counts of one minute before “Erika” and 23 449 after the oil spill.
There was not a simple correlation between the number of individuals found
oiled and the numerical variation of the populations at sea during the two
years following the accident. The guillemot Uria aalge, the most frequently
collected species in the north of the Bay of Biscay, showed no decrease in at sea
abundance during the two years following the pollution. Conversely, some
species found in small numbers on the coast (e.g. divers Gavia sp., razorbill
Alca torda, common scoter Melanitta nigra) decreased significantly
at sea (20 to 80%). Overall, marine bird populations declined significantly in the
northern sector of the Bay of Biscay (48°32' to 46°58' north) and increased
in the southern sector (45°13' to 43°15' north), whereas decreases and increases
occurred in the central sector (46°57' to 45°14' north). Changes in
the spatial distribution of the species after the “Erika” oil spill occurred
through disappearance or retraction (Bay of Vilaine, Houat-Hoedic
archipelago), or through displacement and reinforcement (Gouf of Capbreton).
Overall, this suggests a redistribution of the populations within the Bay of
Biscay, depending on the level of injuries to the ecosystems caused by the
pollution.