Fine-Scale Variability in Harbor Seal Foraging Behavior

Abstract

Understanding the variability of foraging behavior within a population of predators is important for determining their role in the ecosystem and how they may respond to future ecosystem changes. However, such variability has seldom been studied in harbor seals on a fine spatial scale (<30 km). We used a combination of standard and Bayesian generalized linear mixed models to explore how environmental variables influenced the dive behavior of harbor seals. Time-depth recorders were deployed on harbor seals from two haul-out sites in the Salish Sea in 2007 (n = 18) and 2008 (n = 11). Three behavioral bout types were classified from six dive types within each bout; however, one of these bout types was related to haul-out activity and was excluded from analyses. Deep foraging bouts (Type I) were the predominant type used throughout the study; however, variation in the use of bout types was observed relative to haul-out site, season, sex, and light (day/night). The proportional use of Type I and Type II (shallow foraging/traveling) bouts differed dramatically between haul-out sites, seasons, sexes, and whether it was day or night; individual variability between seals also contributed to the observed differences. We hypothesize that this variation in dive behavior was related to habitat or prey specialization by seals from different haul-out sites, or individual variability between seals in the study area. The results highlight the potential influence of habitat and specialization on the foraging behavior of harbor seals, and may help explain the variability in diet that is observed between different haul-out site groups in this population.

Fractal analysis provides new insights into the complexity of marine mammal behavior: A review, two methods, their application to diving and surfacing patterns, and their relevance to marine mammal welfare assessment

“…Significant interindividual differences were found for diving and surfacing durations at both sites for harbor seals and at Phare de Walde for gray seals (Wilcoxon-Mann-Whitney U-test, p < 0.05). This result is consistent with the widely reported individual variability in behavior reported for those species, e.g., Van Parijs et al (2000), Wilson et al (2014), and Russell and McConnell (2014). In contrast, diving and surfacing durations did not significantly (Wilcoxon-Mann-Whitney U-test, p > 0.05) differ between sites for both harbor and gray seals (Table 1).…”

“…(), Wilson et al . (), and Russell and McConnell (). In this context, the results presented here should a priori be considered with caution due to the relatively limited number of distinct individuals used in our analyses (see Table ).…”

“…(), Wilson et al . (), and Russell and McConnell (). In contrast, diving and surfacing durations did not significantly (Wilcoxon‐Mann‐Whitney U ‐test, p > 0.05) differ between sites for both harbor and gray seals (Table ).…”

“…These differences can either be temporally or spatially consistent (Twiss and Franklin 2010), hence the concept of personality (see Bell 2007). Alternatively, individual variability in behavior can also be related to sites, seasons, time of day, and be sex-specific, e.g., Rogers and Cato (2002), Van Parijs et al (2000), Wilson et al (2014), and Russell and McConnell (2014). In this context, the results presented here should a priori be considered with caution due to the relatively limited number of distinct individuals used in our analyses (see Table 1).…”

Large‐scale molecular diet analysis in a generalist marine mammal reveals male preference for prey of conservation concern

“…As central place foragers, the movements of harbor seals are related to the distance of the haul‐out site and the distribution of their prey species (Jones, Sparling, McConnell, Morris, & Smout, ). In the Salish Sea, the dive behavior of harbor seals indicates that males consistently undertake more shallow dives whereas females perform deeper dives, indicative of benthic foraging (Wilson, Lance, Jeffries, & Acevedo‐Gutiérrez, ). Such behavioral pattern is consistent with our findings that female diet contained a greater fraction of demersal or ground living fish in addition to pelagic fish, whereas males tended to specialize on pelagic prey.…”