Long Distance Movements and Disjunct Spatial Use of Harbor Seals (Phoca vitulina) in the Inland Waters of the Pacific Northwest

Abstract

BackgroundWorldwide, adult harbor seals (Phoca vitulina) typically limit their movements and activity to <50 km from their primary haul-out site. As a result, the ecological impact of harbor seals is viewed as limited to relatively small spatial scales. Harbor seals in the Pacific Northwest are believed to remain <30 km from their primary haul-out site, one of several contributing factors to the current stock designation. However, movement patterns within the region are not well understood because previous studies have used radio-telemetry, which has range limitations. Our objective was to use satellite-telemetry to determine the regional spatial scale of movements.Methodology/Principal FindingsSatellite tags were deployed on 20 adult seals (n=16 males and 4 females) from two rocky reefs and a mudflat-bay during April–May 2007. Standard filtering algorithms were used to remove outliers, resulting in an average (± SD) of 693 (±377) locations per seal over 110 (±32) days. A particle filter was implemented to interpolate locations temporally and decrease erroneous locations on land. Minimum over-water distances were calculated between filtered locations and each seal's capture site to show movement of seals over time relative to their capture site, and we estimated utilization distributions from kernel density analysis to reflect spatial use. Eight males moved >100 km from their capture site at least once, two of which traveled round trip to and from the Pacific coast, a total distance >400 km. Disjunct spatial use patterns observed provide new insight into general harbor seal behavior.Conclusions/SignificanceLong-distance movements and disjunct spatial use of adult harbor seals have not been reported for the study region and are rare worldwide in such a large proportion of tagged individuals. Thus, the ecological influence of individual seals may reach farther than previously assumed.

Harbour seal Phoca vitulina movement patterns in the high-Arctic archipelago of Svalbard, Norway

“…Previous studies on harbour seals movement patterns indicate that this species is relatively sedentary through out the year, although seasonal shifts between favoured sites is common and in some areas the seals make offshore trips in the vicinity of the main haul-out sites to distances between 20 and 30 km (Thompson & Miller 1990, Thompson et al 1991, Thompson et al 1998b, Vincent et al 2010, Sharples et al 2012). However, longdistance movements have also been recorded in some areas, linked mainly to seasonal migrations to avoid ice or dispersal by immature animals (Lesage et al 2004, Peterson et al 2012, Sharples et al 2012 Table 5. Phoca vitulina.…”

“…Age, size and sex have also been shown to influence movement patterns of harbour seals (Thompson et al 1998b, Peterson et al 2012. Thompson et al (1998b) reported that sex and body size were correlated with trip duration in harbour seals in Moray Firth (Scotland) and that males had larger foraging ranges than females.…”

Source levels and call parameters of harbor seal breeding vocalizations near a terrestrial haulout site in Glacier Bay National Park and Preserve

“…Although harbor seals may range widely during the post-breeding season (Lowry et al, 2001;Peterson et al, 2012;Womble and Gende, 2013), they typically exhibit a high degree of fidelity to pupping areas during the breeding season (Blundell et al, 2011).…”

Predator-prey interactions between harbor seals and migrating steelhead trout smolts revealed by acoustic telemetry

“…Similar trends in harbor seal populations occurred in the Strait of Georgia during the same period (DFO 2010). Harbor seals feed predominantly on Clupeidae (herring) and Gadidae (cod and hake), but also feed opportunistically (Thomas et al 2011) from just a few to over 100 km from their (capture) haul-outs (Peterson et al 2012). Steelhead trout were not identified as prey in a fairly extensive year-round analysis of harbor seal diet around the San Juan Archipelago , Bromaghin et al 2013.…”