Figure 1.
Pliocene through Holocene eustatic sea-level changes, at two different scales.
Sea-level change [43] juxtaposed with A) the oldest known fossil belonging to the genus Eschrichtius, from the Pliocene of Japan (dashed line) [98]; and B) the relative temporal ranges from other historical gray whale data, with the oldest example belonging to the species occurrence (solid line), from the Palos Verdes Peninsula of California [101], [104]. Age for census estimates reflects an upper bound for reports from the written historical record [28], [29], [92], [93].
Figure 2.
Benthos availability, sea-level change and coastal configuration of continental margins in the North Pacific Ocean, at select intervals, during the last 120 ka.
A) Geographic plates at the top of the figure depict reconstructed coastal configurations and 20 m depth contours for (a) present day, (b) 15 ka, (c) 45 ka, (d) 70 ka, (e) 100 ka, and (f), 120 ka. See Table 1 for regional boundaries and summary data; depth data from ETOPO1 [115]. B) Left axis on the plot shows bar graphs with available benthos at 20 m increments at select time intervals (a–f). Right axis shows mean sea-level changes in past 130 ka, using data from Miller et al. [43]. Dashed lines indicate (left, in orange) current sea-level and (right, in blue) current benthos availability.
Table 1.
Regional definitions and current, minimum, and maximum benthos area available within 75 m of the surface during the last glacial cycle (120 ka), including the age and percent of current benthos of past minimum and maximum events.
Figure 3.
Estimated carrying capacity for North Pacific gray whales determined by benthos availability (<75 m) during the last 120 ka.
Dashed gray lines indicate current gray whale population size and red lines show harmonic means for carrying capacity estimates. A) Total and regional North Pacific unconstrained carrying capacities. Gray box indicates range of population size suggested by analysis of genetic diversity [15]. B) Total and regional North Pacific carrying capacities constrained to 22 k gray whales; see Table 2; C) Unconstrained, estimated carrying capacities of non-glaciated regions in the western and eastern Pacific; D) Estimated carry capacities of non-glaciated regions in the western and eastern Pacific constrained to 22 k gray whales; see Table 2.
Table 2.
Parameters and sources used to estimate carrying capacities for gray whales in the North Pacific Ocean during the last 120 ka.
Figure 4.
Gray whales amidst ice in the eastern North Pacific Ocean.
Taken as anecdotal evidence, this illustration, reproduced from [25], provides insight into gray whale behavioral plasticity, especially in the presence of sea and pack ice. Several observations (e.g., [59]) suggest that gray whales possess a latent ability to tolerate ice, which would be a beneficial trait during episodes of glacial maxima.
Figure 5.
Non-migratory gray whale feeding.
Photograph of a gray whale feeding on herring near Cape Scott, Vancouver Island, British Columbia, 17 April 2000. Photograph and observations by the late Donovan Girard, courtesy of K. Lihou and R. Graham.