Last Glacial Age Decimated Global Killer Whale Population
[ Watch the Video: Ice Age Decimated Killer Whales ]
Brett Smith for redOrbit.com – Your Universe Online
The study, which was published in the journal Molecular Biology and Evolution, is based on a genetic analysis of archival DNA that showed significant genetic diversity bottlenecks in orca populations the world over – and indication of a major population loss.
The study team did, however, find that killer whale populations around the coast of South Africa were an exception to this rule.
“Our data suggest that a severe reduction in population size during the coldest period of the last ice age could help explain this low diversity, and that it could have been an event affecting populations around the world,” said study author Rus Hoelzel, a biology professor at Durham University in the United Kingdom. “However, a global event is hard to explain, because regional modern-day killer whale populations seem quite isolated from each other.”
“What could have affected multiple populations from around the world all at the same time?” Hoelzel asked.
For the study, researchers used archive material from earlier studies or from museum specimens to assemble 2.23 gigabytes (GB) of Northern Hemisphere killer whale genomic data and mitochondrial DNA from 616 samples around the world.
The genetic analysis showed that the South African population of killer whales steered clear of the bottleneck faced by other populations, and the study team said one explanation could have been the Bengeula upwelling system – which drives nutrient rich cold water to the oceans off South Africa – being stable regardless of the last glacial period. Driven by oceanic winds, this upwelling of nutrient-rich water would have been capable of sustaining the fish and dolphins that killer whales near South Africa typically feed on.
The scientists added that other significant upwelling systems around the world — the California upwelling off North America; Humboldt upwelling off South America; and the Canary upwelling off the coast of North Africa — were either disturbed or faded away altogether during the previous glacial or Pleistocene periods, between 40,000 and 2.5 million years ago.
“The uniquely high levels of diversity we found for the population off South Africa suggest a possible explanation,” Hoelzel said. “These whales live in an environment that has been highly productive and stable for at least the last million years, while some data suggest that ocean productivity may have been reduced during the last glacial period elsewhere in the world.”
“If this is the case, then further research may suggest an impact on other ocean top predators during this time,” he continued. “It would also support concerns about the potential for climate disruptions to impact ocean ecosystems in future.”
The researchers said looking at the genetic diversity of sharks and other marine apex predators might suggest a negative impact on their numbers.
Conservationists have been voicing concern over the sustainability of today’s upwellings around the world. They argue that because these water are so productive, they attract large numbers of commercial fishermen and, as a result, are in danger of being disrupted.