Right whales are the rarest of all large whale species. They grow to 45-55 feet and also may be among the rarest of marine mammals worldwide. However, historically more of these baleen whales have passed their lives in the Southern Hemisphere than scientists previously thought, says a new study.
That new historical awareness gives us a stronger timetable for how long Southern right whales might take to fully recover from near extinction. At this point, their recovery could be 50 to 100 years in the future, says the team from Oregon State University and several other institutions.
That international team looked at 19th century logbook catch records and used computer modeling to learn that perhaps 40,000 right whales once lived near New Zealand prior to whaling's heavy hit on their numbers. At the start of the 20th century, as few as 20 fully grown females might have been around to pass into the new time period.
"This is the first time we have been able to estimate the pre-whaling abundance for this population of right whales before they were nearly decimated," noted Scott Baker at Oregon State University and study co-author. "Only a handful of whales survived, and those were threatened again in the 1960s by illegal Soviet whaling."
Right whales have been highly diminished in population around New Zealand for nearly 200 years. Scientists generally know very little about the whales' ecological role before whaling occurred or how they may be active participants in ecosystems as they grow in number, said Baker.
The study took place over 10 years beginning in 1995, looking at the remnant right whale population in the New Zealand area, partly because this region has a richer historical record from catch documents and other sources. Southern right whales, like all right whales, got their name because they were easy to hunt. They lack speed and predictably go into sheltered bays to calve. This makes them easy targets.
"Once we had a good idea about the likely range of catches, we could do a full reconstruction using current estimates of abundance and population increase to measure the population's trajectory through time and how large it was," noted Jennifer Jackson, a study lead author who was a post-doctoral student at Oregon State while working on the study. She is now with the British Antarctic Survey.
Analysis found that before whaling took place, right whales around New Zealand numbered at about 28,000 to 33,000 individuals. The study calculated that if the majority of right whales harvested by whaling in the southwest part of the Pacific Ocean were from near New Zealand, the historical population rises to 47,000 whales.
"Put in context, the estimated size of the current New Zealand population is less than 12 percent of these numbers," said Jackson.
Results recently were published in the journal Royal Society Open Science.
Follow Catherine Arnold on Twitter at @TreesWhales.
