Integrating disparate datasets to model the functional response of a
marine predator: a case study of harbour porpoises in the southern North
Sea
Abstract
1. Quantifying consumption and prey choice for marine predator species
is key to understanding their interaction with prey species, fisheries,
and the ecosystem as a whole. However, parameterising a functional
response for large predators can be challenging because of the
difficulty in obtaining the required datasets on predator diet and the
availability of multiple prey species. 2. This study modelled a
Multi-Species Functional Response (MSFR) to describe the relationship
between consumption by harbour porpoises (Phocoena phocoena) and the
availability of multiple prey species in the southern North Sea.
Bayesian methodology was employed to estimate MSFR parameters and to
incorporate uncertainties in diet and prey availability estimates. Prey
consumption was estimated from stomach contents data of stranded harbour
porpoises. Prey availability to harbour porpoises was estimated based on
the spatial overlap between prey distributions, estimated from fish
survey data, and porpoise foraging range in the days prior to stranding
predicted from telemetry data. 3. Results indicated a strong preference
for sandeel in the study area. Prey switching behaviour (change in
preference dependent on prey abundance) was confirmed by the favoured
Type III functional response model. Variation in the size of the
foraging range (estimated area where harbour porpoises could have
foraged prior to stranding) did not alter the overall pattern of the
results or conclusions. 4. Integrating datasets on prey consumption from
strandings, predator foraging distribution using telemetry and prey
availability from fish surveys into the modelling approach provides a
methodological framework that may be appropriate for fitting MSFRs for
other predators.