HAUL‐OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISK

Abstract

The potential for non‐aquatic predators to influence habitat use by harbor seals (Phoca vitulina) in a nearshore marine environment was studied by examining haul‐out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul‐out areas were quantified for each haul‐out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul‐out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul‐out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores.

DIVE BEHAVIOR OF A HARBOR SEAL (PHOCA VITULINA RICHARDII) IN THE PRESENCE OF TRANSIENT KILLER WHALES (ORCINUS ORCA) IN GLACIER BAY NATIONAL PARK, ALASKA

“…Thus, understanding how organisms respond to perceived predation risk or the actual presence of predators is central to understanding their foraging decisions, habitat use, reproductive effort, and other proximate behaviors ( e.g ., Sih 1982; Ydenberg and Dill 1986; Gillam and Fraser 1987; Heithaus and Frid 2003). For harbor seals ( Phoca vitulina richardii ), predation (or the risk of predation) is thought to be common enough to influence habitat utilization (Calambokidis et al 1987; Nordstrom 2002).…”

Terrestrial habitat preferences and segregation of four pinniped species on the islands off the western coast of the Baja California Peninsula, Mexico

“…Water depth was an important factor for pup and adult harbor seals during the breeding season, deep waters had a positive effect on pup and adult abundance. Nordstrom () found no relationship between bathymetry and overall abundance of harbor seals near Vancouver Island, Canada. In contrast, based on telemetry studies, pups are expected to use land sites near water depths of more than 25 m (Bjørge et al .…”

Evidence for long‐term spatial displacement of breeding and pupping harbour seals by shellfish aquaculture over three decades

“…A variety of factors may influence habitat availability for breeding, moulting, and resting pinnipeds, including coastal development (Seuront and Prinzivalli, 2005), human encroachment and disturbance (Yochem et al ., 1987; Gerrodette and Gilmartin, 1990; Suryan and Harvey, 1999; Thompson et al ., 2001), predation (Nordstrom, 2002), climate change (Freitas et al ., 2008), and natural variation in habitat suitability. Moreover, since longer lived, slowly reproducing K‐selected species maximize their long‐term survival, they tend to respond to human disturbances by increasing heart rates and energetic costs (Bisson et al ., 2009).…”