Table 1.
Data Summary.
Figure 1.
Tracking data from 209 female northern elephant seals from 2004-2010.
The map includes 195 tracks from the Año Nuevo, CA, USA colony (red point) and 14 tracks from the Islas San Benito, B.C., Mexico colony (yellow point).
Table 2.
Mean (± S.D.) foraging success parameters by year, season, and tagging location (ANNU - Año Nuevo, California and SABE - Islas San Benito, Mexico).
Figure 2.
Trip duration for female northern elephant seals observed with (n = 98) and without (n = 17) a pup after the post-molting migration from 2004-2010.
Most females that skipped breeding returned outside of the typical breeding season (January – February).
Figure 3.
Approximate location of dominant oceanographic features in the northeast Pacific Ocean.
The stippled region indicates the annual range of the Transition Zone Chlorophyll Front (TZCF). The location of the gyre-gyre boundary remains stable in contrast to the annual migration of the TZCF.
Figure 4.
Monthly kernel density distribution of female northern elephant seals from the Año Nuevo, CA colony from 2004-2010.
Tracking data were regularized to hourly positions prior to analysis and only complete trips were included (n = 195). The black line shows the monthly position of the gyre-gyre boundary, estimated from the 170 cm absolute dynamic topography climatology contour. White points indicate the position of the Transition Zone Chlorophyll Front, estimated from the 0.2 mg/m3 contour. Oceanographic climatologies include data from 2004 through 2008.
Table 3.
Mean (± S.D.) track parameters by year, season, and tagging location (ANNU - Año Nuevo, California and SABE - Islas San Benito, Mexico).
Table 4.
Mean (± S.D) diving parameters by year, season, and tagging location (ANNU - Año Nuevo, California and SABE - Islas San Benito, Mexico).
Figure 5.
Mean daytime dive depth for northern elephant seals from Año Nuevo, CA seals with a matched and complete diving and tracking record from 2004-2010 (n = 95).
Dives are shallower in the northern half of the sub-arctic gyre and coastal regions compared to the transition zone waters.
Figure 6.
Hotspot analysis (Getis-Ord Gi* statistic) across all years of the study (2004-2010) for female northern elephant seals using two foraging metrics: number of drift dives per day and daily transit rate.
Areas in red indicate statistically significant clustering of foraging activity, independent of the number of seals present. Grid cells informed by only one seal were removed to avoid high leverage.
Figure 7.
Temperature profile and female northern elephant seal density along a transect of the ∼163W meridian from 40N to 50N.
The temperature profile was created from TDR data between 28-July-2005 and 24-August-2005 (seal ID: 2005037; post-molting season). The 8°C isotherm, indicated with a black line, highlights the temperature inversion. The seal density was extracted from the inter-annual August kernel density (see fig. 5). The grey bar shows the position of the gyre-gyre boundary.