Gs. Begg et al., ASSESSING THE VULNERABILITY OF SEABIRDS TO OIL POLLUTION - SENSITIVITY TO SPATIAL SCALE, Colonial waterbirds, 20(2), 1997, pp. 339-352
Area Vulnerability Scores (AVSs) are a measure of the potential impact
that oil pollution in an area of sea might have on seabird population
s. They are used in the United Kingdom and the Republic of Ireland as
a conservation tool, principally to inform the decision making process
es related to the licensing of oil exploration at sea and to responses
to oil pollution incidents. AVSs are currently calculated and mapped
at a scale of 15' latitude x 30' longitude grid squares. Patterns of s
eabird distribution are known to be scale dependent and the same is al
so true for oil pollution. This suggests that the physical interaction
s between oil pollution and seabirds may also be dependent on spatial
scale. We consider the sensitivity to spatial scale of the vulnerabili
ty that is determined by the interactions between oil pollution and se
abirds and examine the scale dependent variation in vulnerability, as
defined by AVS. The results demonstrate scale dependence in AVS and so
me features of its spatial distribution. These are decreasing heteroge
neity in AVS with increasing spatial scale, and the presence of some s
patial structure at a scale 20-30 km which could not be detected when
estimating AVS at larger scales. These patterns in vulnerability are a
consequence of scale dependence in the spatial distribution of seabir
d density In addition an increase in scale resulted in a tendency to o
verestimate AVS which also lead to an apparent expansion in size of th
e higher vulnerabilities such as those around the coast. These results
were an artifact of the calculation of AVS. The results of this study
have implications for the way in which we use AVS and other similar m
easures to assess vulnerability They suggest that calculation of AVS s
hould be done on a fine spatial scale, however, bird density data are
not available at the appropriate spatial resolution without combining
data over an extended temporal scale which runs the risk of distorting
the spatial patterns. These effects may be mitigated by calculating A
VS on a spatially stratified basis, at high resolution in the areas of
high density and coverage, and at low resolution in areas of low dens
ities and low coverage.