A matter of scale: Identifying the best spatial and temporal scale of
environmental variables to model the distribution of a small cetacean
Abstract
The importance of scale when investigating ecological patterns and
processes is recognised across many species. In marine ecosystems, the
processes that drive species distribution have a hierarchical structure
over multiple nested spatial and temporal scales. Hence, multi-scale
approaches should be considered when developing accurate distribution
models to identify key habitats, particularly for populations of
conservation concern. Here, we propose a modelling procedure to identify
the best spatial and temporal scale for each modelled and remotely
sensed oceanographic variable to model harbour porpoise (Phocoena
phocoena) distribution. Harbour porpoise sightings were recorded during
dedicated line-transect aerial surveys conducted in the summer of 2016,
2021 and 2022 in the northeast Atlantic. Binary generalised additive
models were used to assess the relationships between porpoise presence
and oceanographic variables at different spatial (5, 20 and 40 km) and
temporal (daily, monthly and across survey period) scales. Selected
variables included sea surface temperature, thermal fronts,
chlorophyll-a, sea surface height, mixed layer depth and salinity. A
total of 30,514 km was covered on-effort with 216 harbour porpoise
sightings recorded. Overall, the best spatial scale corresponded to the
coarsest resolution considered in this study (40 km), while porpoise
presence showed stronger association with oceanographic variables
summarised at a longer temporal scale (monthly and averaged over survey
period). Habitat models including covariates at coarse spatial and
temporal scales may better reflect the processes driving availability
and abundance of prey resources at the large scales covered during the
surveys. These findings support the hypothesis that a multi-scale
approach should be applied when investigating species distribution.
Identifying suitable spatial and temporal scale would improve the
functional interpretation of the underlying relationships, particularly
when studying how a small marine predator interacts with its environment
and responds to climate and ecosystem changes.