Background on Gray Whales

Gray whales live in the waters along the west coast of North America (2). The southward migration of the whales along the North American coast from Alaska to Mexico happens during the fall (2). Northward migration happens after calves are born in the winter and lasts until May (2).

Alter et al. (2007) used estimates of genetic diversity to infer that North Pacific gray whales may have numbered ~96,000, including animals in both the western and eastern populations, 1,100-1,600 years ago (2). However, Jones et al. (1984) state that “most whaling historians and biologists believe the pre-exploitation stock size was between 15,000 and 24,000 animals." (29).

How is population size monitored?
Systematic counts of gray whales during their southward migration along the central California coast since 1967 (2).

The low population estimate in 1999-2000 is connected with a lack of food resources. More adult whales were found beached during that year, and in an emaciated condition. Whales were on average thinner, reared fewer calves, and there was a higher adult mortality rate (2).

Researchers are able to monitor gray whale mortality, and estimate how much of the strandings are due to anthropogenic factors versus natural causes. In the most recent years it has been found that humans are not a significant factor in the number of deaths seen in the whale populations (2).

What is the minimum population for these whales?
Minimum population estimate for this whale stock was 18,017 as of 2011 (2).

What is the current population trend?
Gray whales are increasing in number! The Gray whale population increased at an average of 3.3% per year between the years 1967-1988 (2).

Due to ambiguities regarding maximum growth rate during periods early in the history of whaling, researchers tend to model gray whale populations since 1930 or later, rather than from 1846-present (2).

PBR* (Potential Biological Removal) = 360 gray whales (2).

*The potential biological removal is the maximum number of animals, not including natural mortality  which can be removed while maintaining a sustainable population.

Other mortality?
One whale was illegally hunted at Neah Bay in 2007.
Gray whales are near shore migratory animals, which increases the potential for ship strikes. An estimated 1.2 whales per year are killed in this matter.
Two whales were found dead with harpoon injuries, presumably from the Russian aboriginal hunt (2).


Habitat Concerns Moving Forward:
Decrease in sea ice in some regions of the Arctic will impact the whales’ benthic food supply (25). Fortunately, gray whales feed both benthically (at the ocean floor) and pelagically (at the surface) which allows for flexibility in their diet depending on availability. Ocean acidification could also affect gray whale populations, due to the decrease in shell-forming organisms important in the diet of gray whales (2).

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