Gray whales (Eschrichtius robustus) return from Arctic
feeding grounds to lagoons in Mexico each winter to
give birth. New genetic results indicate that in the past,
the number of whales returning to these lagoons may
have been much larger.
Photo location: Laguna San Ignacio, Mexico.
Credit: Geoff Shester
With large numbers of gray whales swimming south from the Arctic in terrible condition, here’s another development that suggests something fundamental has shifted in the marine food chain of the Far North ocean.
Gray whales may have once numbered more than 96,000 in the North Pacific Ocean — churning up muck and plumes that fed millions of seabirds and replenished the Bering and Chukchi seas with nutrients, according to new research published this week in the Proceedings of the National Academy of Sciences.
This genetic analysis suggests the whales were once three to five times more numerous and, as a result, have not yet come close to recovering from decimation by commercial whaling.
The findings raise stunning implications about how little people really know about the marine world. We do not, even now, fully appreciate how much the ocean has changed from pre-historic times.
Gray whales were heralded as one of the world’s great conservation success stories and pulled from the Endangered Species list. When whales began showing up very skinny, with bones protruding, possibly near starvation, some biologists speculated that the population had expanded beyond its historic limits.
Now it appears that the grays haven’t actually rebounded. The population hasn’t broken historic limits. And their pending starvation may be a harbinger: Something has gone wrong in the North Pacific.
“Despite our best efforts,” said Stanford University marine biologist Steve Palumbi, in a story posted online, “these genetic results suggest gray whales have not fully recovered from whaling. They might be telling us that whales now face a new threat — from changes to the oceans that are limiting their recovery.”
The study adds to a growing ecological insight: that the oceans were once far more diverse and productive than people realize. Palumbi was one of 13 authors that worked with biologist Boris Worm in an alarming study about the crisis in marine ecology, published in 2006 in Science.
A release says:
The study reveals that every species lost causes a faster unraveling of the overall ecosystem. Conversely every species recovered adds significantly to overall productivity and stability of the ecosystem and its ability to withstand stresses.
“Whether we looked at tide pools or studies over the entire world’s ocean, we saw the same picture emerging,” Worm said. “In losing species we lose the productivity and stability of entire ecosystems. I was shocked and disturbed by how consistent these trends are — beyond anything we suspected.”
Here’s more detail about the gray whale study:
Today’s population of more than 22,000 gray whales has successfully been brought back from the threat of extinction and is now the most abundant whale on the North American west coast.
Credit: Geoff ShesterBut the new findings from researchers at Stanford University and the University of Washington suggest that the current population is actually far below the original number — estimated by genetic methods at 96,000 animals — that once roved the Pacific Ocean.
The report also weighs in about why large numbers of gray whales have recently been discovered suffering from starvation. Previously it was assumed that the thin and starving animals are a consequence of the gray whale population exceeding its historical ecological limits.
But if the Pacific normally housed 96,000 gray whales, then starving whales may be suffering reduced food supply from changing climate conditions in their Arctic feeding grounds.
This possibility parallels reports last year of major climate shifts in the Arctic ecosystems in which gray whales feed. The study also suggests that lowered numbers of gray whales no longer play their normal role in ocean ecology. Gray whales were hunted extensively in the late 19th century.
“The lagoons of Baja California were the primary killing fields for gray whales,” recounted lead author S. Elizabeth Alter, a Stanford researcher. “But we don’t know exactly how many there were before whaling took its toll.”
The new research measures the amount of genetic variation in current gray whales across ten different sections of their genome, and back calculates the long-term population size based on new measurement of the mutation rate of these gene segments.
Steve Palumbi, the Harold A. Miller Professor in Marine Sciences at Stanford’s Hopkins Marine Station, explained, “Our survey uncovers too much variation for a population of 22,000. The overabundance of genetic variation suggests a much larger population in past centuries.”
The study uses computer-based genetic simulations to show that the level of genetic variation is instead more likely to be from a past population of 76,000 to 118,000 animals (with an average of 96,000).
A gray whale calf breaches in Bahia Magdalena.
Credit: Sergio Nigenda.Such a vastly reduced population of gray whales has likely exerted large changes in Pacific ocean ecosystems. Unique among whales, the gray bulldozes the oceans, digging troughs through the sea floor for food. In the process, they resuspend ocean sediments bring food to the surface.
“A population of 96,000 gray whales would have resuspended 12 times more sediment each year than the biggest river in the Arctic, the Yukon,” said Alter, “and would have played a critical role in the ecology of the Bering Sea.”
Other species may have felt the loss of whales as well.
“The feeding plumes of gray whales are foraging grounds for Arctic seabirds,” Palumbi said. “96,000 gray whales would have helped feed over a million seabirds a year.”
The research also raises questions about how many whales the current oceans can now support — and whether the future of whales, even if whaling is limited, may be reduced by new problems in the guise of oceanic overfishing and global climate change.
“Decades ago, whales were the first creatures to tell us that we were overfishing the oceans,” Palumbi concluded. “Maybe now they trying to tell us the oceans are in deeper trouble.”
