Fig 1.
Northeast Pacific sampling zones.
Dots represent blue whale skin samples collected in the California Current System (CCS), Gulf of California (GC) and Costa Rica Dome (CRD). Dots with a cross represent blue whale baleen plates collected from dead stranded whales.
Fig 2.
Methods for blue whale skin and baleen plate preparation.
(A) Biopsy skin separation into strata: Stratum Basale (SB), Stratum Spinosum (SS) Stratum Externum (SE). The dermal papillae (DP) can be observed embedded in the skin. Dashed lines show were the cuts were made to separate the skin into stratums. (B) Blue whale baleen plate sampling: baleen powder was sub-sampled in 1 cm intervals along the outer edge of the plate starting from the proximal section of the plate nearest the gum.
Fig 3.
GAM analysis of the seasonal trend of skin strata δ15N values in two foraging zones.
The points represent the actual δ15N values of skin collected from whales within the Gulf of California (open circles) and the California Current System (open triangles). The colored lines represent the GAM model fit (predictions) and the fringe around the lines show the 95% confidence intervals. The gray shaded area represents the mean±SD of the trophic-corrected blue whale skin values for each foraging zone: Gulf of California (GC), the California Current System (CCS) and the Costa Rica Dome (CRS).
Table 1.
Trophic-corrected blue whale skin δ15N values for each foraging zone.
Table 2.
GAM results for the seasonal trends of δ15N and δ13C values in different skin strata sampled in the Gulf of California (GC) and California Current System CCS).
Table 3.
δ15N isotopic incorporation rates of blue whale skin strata in the Gulf of California and California Current System.
The number of days were estimated by extrapolating from the GAM predictions (model fit and the upper and lower 95% confidence limits) for skin δ15N values to change by 1.6‰ to isotopically equilibrate with local prey in each zone.
Fig 4.
δ15N values along the baleen plates from six whales, identified as A–F. Points represent actual values. The continuous line (blue: males; red: females) represents the GAM model fit and the narrow fringe around the lines represent the 95% confidence intervals. The gray shaded area represents the mean±SD of the trophic-corrected blue whale skin values for each foraging zone: Gulf of California (GC), the California Current System (CCS) and the Costa Rica Dome (CRS).
Table 4.
GAM results to assess the fluctuations of δ15N and δ13C in baleen plates.
Table 5.
Blue whale baleen growth rate: Estimated by using the distance between sequential δ15N minimums along the baleen plates from whales A to C.