Data from: Spatio-temporal modelling of auk abundance after the Erika oil spill and implications for conservation

Species distribution models are widely used in applied ecology and
conservation. While accounting for spatial dependences is now the rule,
temporal dependences have rarely been dealt with explicitly. In this
study, we analyse wintering auk distribution in the Bay of Biscay and
English Channel and estimate changes in abundance within and between years
while accounting for space–time dependencies. We then propose a
retrospective estimate of the impact of the Erika oil spill that occurred
in December 1999. Two series of extensive aerial surveys, repeated at
intervals of 1–2 months, were carried out at a 10-year interval off the
French Atlantic coast (2001–2002 and 2011–2012). Spatially and temporally
explicit Bayesian models were fitted to these data to provide
spatio-temporal predictions of auk abundance. These were then used to
compare abundances within the area affected by the Erika oil spill two and
twelve years after the catastrophe. The results showed that 1·55 million
auks wintered in the study area in 2011–2012. The main wintering area was
the English Channel (more than one million auks) but the Bay of Biscay
also became an important area in the middle of winter (470 000 auks) owing
to a strong southward shift in auk distribution. Two years after the
catastrophe (2001–2002), the area affected by the Erika oil spill hosted a
small proportion of auks of the Bay of Biscay – about 80 000 individuals.
This number increased by more than three times 10 years later and reached
270 000 individuals, whereas no significant change was detected elsewhere.
We suggest that it could result from a recovery after the extra-mortality
induced by the Erika oil spill. Policy implications. This study identified
major auk wintering areas, with abundances much higher than previously
realized. Oil spills have occurred regularly in these areas, with major
delayed impacts on auk breeding populations. The worst case scenario would
be if a major oil spill occurred in the English Channel in February, when
abundance reaches one million auks. Although such a disaster has not so
far occurred, stricter policies on the transport of hydrocarbons should be
implemented to prevent such a possibility.