Linking movement and dive data to prey distribution models: new insights in foraging behaviour and potential pitfalls of movement analyses

Abstract

Background: Animal movement data are regularly used to infer foraging behaviour and relationships to environmental characteristics, often to help identify critical habitat. To characterize foraging, movement models make a set of assumptions rooted in theory, for example, time spent foraging in an area increases with higher prey density. Methods: We assessed the validity of these assumptions by associating horizontal movement and diving of satellite-telemetered ringed seals (Pusa hispida) - an opportunistic predator - in Hudson Bay, Canada, to modelled prey data and environmental proxies. Results: Modelled prey biomass data performed better than their environmental proxies (e.g., sea surface temperature) for explaining seal movement, however movement was not related to foraging effort. Counter to theory, seals appeared to forage more in areas with relatively lower prey diversity and biomass, potentially due to reduced foraging efficiency in those areas. Conclusions: Our study highlights the need to validate movement analyses with prey data to effectively estimate the relationship between prey availability and foraging behaviour.

The dynamic interaction between predator and prey drives mesopredator movement and foraging ecology

“…3A, B, and see (35)). This simpler model not only performed worse than the models that included polar bear use, but also overlooked the complex relationship between ringed seals, prey diversity, and polar bear use, which could lead to misleading inference (35). Once polar bear use was included as a covariate, the model revealed a possible predator-mediated relationship between ringed seals and their prey, demonstrating the importance of including top-down pressures when studying the ecological response of species to their prey and environment.…”

“…Our movement models and activity budgets suggest that low move-persistent behaviors conclude or are avoided when risk is high. Low move-persistence may reflect area-restricted search and is often associated with foraging; however, it may also represent a composite of resident movement patterns including resting, sleeping, intraspecific interactions, or predator avoidance (e.g., (33)(34)(35)). Regardless of the specific behavior, low move-persistence is associated with residency, and our results show it to be explained by polar bear use.…”

“…For example, if polar bear use was not included as an interacting term with prey diversity in our habitat selection or dive duration models against prey diversity, prey diversity would not be interpreted as an important variable (grey dashed line in Fig. 3A, B, and see (35)). This simpler model not only performed worse than the models that included polar bear use, but also overlooked the complex relationship between ringed seals, prey diversity, and polar bear use, which could lead to misleading inference (35).…”

“…Additionally, our prey and polar bear use data were modeled predictions and thus inherently represent a theoretical distribution of these species that may differ from empirical distributions. However, both approaches have performed well in validation exercises (29,35,57)(see SI Appendix). We acknowledge that our polar bear use variable was calculated using sea ice concentration and bathymetry as covariates, and that our models also included these covariates.…”

“…Prey base (fish) predictions. We used modeled ringed seal prey biomass data for three prey species that were shown to explain the movement ecology of Hudson Bay ringed seals (29,35): Arctic cod (Boreogadius saida), capelin (Mallotus villosus), and northern sand lance (Ammodytes dubius). In addition, as ringed seal movement behavior was shown to be associated with prey diversity (35) we used a Simpson's Diversity Index (D, herein "prey diversity") which included the eight most common ringed seal fish prey species: Arctic cod, capelin, northern sand lance, Pacific sand lance (Ammodytes hexaoterus), Arctic staghorn sculpin (Gymnocanthus tricuspis), shorthorn sculpin (Myoxocephalus Scorpius), mustache sculpin (Triglops murrayi), and rainbow smelt (Osmerus mordax).…”