Sunday 20 May 2012

Genetic diversity in Grey Whales.

Grey Whales (Eschrichtius robustus) in the Eastern Pacific were heavily hunted for commercial purposes in the nineteenth and twentieth centuries, something that is believed to have had a strong adverse effect on their population. However hard data on how much the populations declined during this time is hard to come by. Estimates for pre-whaling populations vary between about 15 000 and up to 116 000 individuals, compared to a current population of about 22 000 whales. Clearly it is important to have a good estimate of the original population in order to under stand how whaling affected the whales.

Grey Whale mother and calf in Monterey Bay, California. White patches are barnacles. Nancy Black/Monterey Bay Whale Watch.

In a paper published in the journal PLoS One on 9 May 2012, Elizabeth Alter and Stephen Palumbi of the  Department of Biological Sciences and Hopkins Marine Station, Stanford University, and Seth Newsome of the Department of Zoology and Physiology at the University of Wyoming detail the results of a study into the genetic diversity of pre-commercial whaling Whales, using DNA analysis of material from archaeological sites where Whales had been hunted by traditional techniques, not thought to have had a strong effect on Whale populations.

The trio used archaeological material from three sites on the Olympic Peninsula in Washington State, where material from Whales that had probably been caught in the Juan de Fuca Straight. These sites have well established established dates, ranging from 150-3500 years ago. In addition they used material from the Smithsonian Institution obtained from commercially caught Whales in the 1960s.

Map showing the sites where material for the study was collected. (1) Shell midden deposit
on Makah Tribal Reservation. (2) Ozette Site. (3) Shell midden deposit on Quilleute Tribal Reservation. Alter et al. (2012).

The study suggested that genetic diversity among Grey Whale remains on the Olympic Peninsula dropped abruptly during the period of commercial whaling, reflecting an estimated drop in population from about 96 000 individuals to around 10 000. The population is now recovering, with about 22 000 individuals, and a corresponding rise in genetic diversity.

Graph showing the abrupt drop in Grey Whale numbers during the period of commercial whaling. Alter et al. (2012).

They study cannot establish the cause of the drop in population, only indicate that it happened at the same time as the commercial whaling was taking place. However without any alternative explanation for the drop in Whale numbers it is reasonable to conclude that the two events were linked.

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