Gray whales doing worse than we thought

Monday we heard that a group of rogue Makah Indians killed a gray whale without going through the red tape that they're supposed to (or bothering to land it). Tuesday comes a new study that shows the eastern Pacific gray whale population, from which the doomed creature was taken, isn't doing as well as we once thought. The first item is more sensational, but hardly ecologically significant, even with the new data on the whale's pre-whaling population size. But still, interesting timing...

The new study, by Elizabeth Alter, Eric Rynes, and Stephen R. Palumbi, measured genetic variation among 42 of the whales (nine introns and one mitochondrial DNA) and used the old genetic clock technique to calculate how large the population used to be. (DNA evidence for historic population size and past ecosystem impacts of gray whales, PNAS 104 (38): 15162-15167.)

(Watch Palumbi explain the study on this video.)

Palumbi has done this before, to some criticism, for humpback whales, and came up with a far larger number -- an order of magnitude -- than previous estimates, which were based on whaling records. This time the math produces a pre-whaling population three to five times bigger than today. Until now, the prevailing wisdom was the whales were pretty close to their historic carrying capacity. Instead of maxing out at 26,000 -- just three or four thousand more than currently estimated, the ancient population ranged between ˜76,000-118,000 individuals.

The consequence for the gray whales. According to Alter, Rynes and Palumbi,

These numbers suggest the eastern Pacific population, even if it historically accounted for only half of the entire Pacific population, should be considered depleted and should
regain higher management protection. Recently observed changes in the eastern Pacific gray whale population are unlikely to be the result of this population reaching its long-term carrying capacity; rather, these changes may have been transient or they
may represent first responses to altered ecological conditions and reduced carrying capacity in the Bering Sea and other habitats.

Philip Clapham of the Alaska Fisheries Science Center (a NOAA group) also thinks that this is worrisome.

"It's clear that future climate change will significantly impact the Arctic and sub-Arctic ecosystems on which gray whales and other species depend," he said. "But quite how that colossal unintentional experiment comes out is anyone's guess." (Nat Geo)

Now, genetic analysis isn't the final arbiter. Paleontologists are still arguing with the geneticists over which tools give us better phylogenies. But there does seem to be a trend here. Just about everywhere one looks, new evidence is showing that there used to be a lot more whales than we thought. And not just thanks to genetics.

The most endangered whales, for example, the bowheads of the Eastern Arctic, may have had a pre-whaling population size of 90,000, more than four times what most experts assumed. This number was produced in 1999 by a pair of Canadian economists, Robert C. Allen and Ian Keay, by giving a closer look at whaling records, the same kind of data that had been underestimating the gray whales (if Alter et al are correct).

Again, none of this means that the gray whales can't support the occasional loss of one whale. Even the Eastern Arctic bowhead, recently reevaluated to have a few thousand individuals, can lose one to hunters every couple of years without jeapordizing the entire population.

But it does make you wonder about just what ocean ecosystems were like back in the day. The gray whales were likely incredibly significant, in terms of producing nutrients for other species, as they churn up the benthos in order to strain crustaceans from the mud. Again, from the new study:

Assuming a population size then 16,000 individuals, a population of 96,000 gray whales would rework ˜ 7.2 x 108 m3 in a summer, ˜12 times larger than the sediment transport load of the largest river emptying into the Bering Sea, the Yukon River. Decreased sediment reworking could dramatically change nutrient recycling, and create shifts in benthic species dominance.

Similarly, feeding by gray whales provides nutrient subsidies from benthic marine communities to terrestrial ones, including food subsidies for at least four species of seabirds that feed on benthic crustaceans brought to the surface by gray whale feeding.

At the very least. the diminishing confidence in previous estimates of populations sizes for a variety of species suggests we should be even more conservative when setting maximum "harvest" numbers, and when declaring victory on recovery schemes.


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