Abstract
BackgroundA utilization distribution quantifies the temporal and spatial probability of space use for individuals or populations. These patterns in movement arise from individuals’ internal state and from their response to the external environment, and thus can provide insights for assessing factors associated with the management of threatened populations. The Western Distinct Population Segment of the Steller sea lion (Eumetopias jubatus) has declined to approximately 20% of levels encountered 40 years ago. At the height of the decline, juvenile survival appeared to be depressed and currently there is evidence that juvenile mortality due to predation may be constraining recovery in some regions. Therefore, our objectives were to identify what spaces are biologically important to juvenile Steller sea lions in the Kenai Fjords and Prince William Sound regions of the Gulf of Alaska.MethodsWe examined geospatial location data from juvenile sea lions tagged between 2000 and 2014 (n = 84) and derived individual and pooled-population utilization distributions (UDs) from their movements. Core areas were defined from the UDs using an individual-based approach; this quantitatively confirmed that all individuals in our sample exhibited concentrated use within their home range (95% UD). Finally, we explored if variation in UD characteristics were associated with sex, season, age, or region.ResultsWe found evidence that individual juvenile home ranges were region and sex-specific, with males having larger home ranges on average. Core space characteristics were also sex-specific, and exhibited seasonal patterns of reduced size, increased proximity to haulouts, and increased intensity of use in the summer, but only in the Kenai Fjords-Gulf of Alaska region.ConclusionsThis study highlights the areas of biological importance during this vulnerable life history stage, and the demographic, seasonal, and spatial factors associated with variation in movement patterns for a marine mesopredator. This can be useful information for promoting species recovery, and for future efforts to understand ecological patterns such as predator-prey interactions.
Highlights
A utilization distribution quantifies the temporal and spatial probability of space use for individuals or populations
Juvenile Steller sea lion (SSL) were tracked for an average of 77 days ±5.74, resulting in 72,816 pseudolocations generated across the 84 individuals (866.6 ± 68.45 per ID) [Additional file 1: Table S1]
This resulted in a core space area of 2799.4 km2, which accounted for 23.31% of the area of the home range
Summary
A utilization distribution quantifies the temporal and spatial probability of space use for individuals or populations. The characteristics of a utilization distribution may be influenced by an individual’s state (e.g. sex, age, body mass) and the external environment (e.g. conspecifics, Bishop et al Movement Ecology (2018) 6:6 habitat, prey density) dynamically interacting to influence an individual animals’ movement path [8]. As such, both home range and core spaces can vary in size, spatial pattern, or structure across temporal scales, regions, age-classes, or sexes [8, 11,12,13]. Beluga whales (Delphinapterus leucas) in the Eastern Beaufort and Eastern Chukchi Seas exhibited seasonal variation in the size and distribution of their home ranges [14] and male Eurasian lynx (Lynx lynx) had larger home ranges than females in all seasons [15]
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