Blue whales are the most massive animals to ever live on Earth, measuring some 100 feet long and weighing 190 tons. They also happen to be very, very endangered, hunted to near-extinction by human whalers. It appears that even the darkest clouds have silver linings, though, because researchers at the University of Washington have found that one species, the California blue whale, has rebounded to 97% of its historic population level.

“The recovery of California blue whales from whaling demonstrates the ability of blue whale populations to rebuild under careful management and conservation measures,” said Cole Monnahan, a UW doctoral student in quantitative ecology and resource management and lead author of the paper.

Due to their size and propensity to feed near commercial shipping lanes, California blue whales are likely being struck by passing ships more often than U.S. regulations allow. That hasn’t hurt their recovery to a significant degree, it seems.

Monitoring by research groups has their numbers at around 2,200, or 97% of the historical high-water mark determined by the model used by the UW team. That’s based on a recorded 3,400 caught between 1905 and 1971. For perspective on just how hard other blue whale species have been hit, it’s estimated that some 346,000 were caught near Antarctica during the same time – the California population has always been smaller.

Formerly classified Russian whaling archives – since made public – were the source of the previously unknown harvest data. New recordings of acoustic calls from different whale species were cross-referenced against the whaling data to come up with current population estimates.

An estimated 11 whales are struck each year by ships off the U.S. coast, but the number of ships could increase exponentially before causing a significant depletion in the California blue whale population.

“Even accepting our results that the current level of ship strikes is not going to cause overall population declines, there is still going to be ongoing concern that we don’t want these whales killed by ships,” said Trevor Branch, UW assistant professor of aquatic and fishery sciences and co-author.

The conversation efforts have been such a success that the team believes the only thing limiting the California blue whale population is nature itself.

“We think the California population has reached the capacity of what the system can take as far as blue whales,” Branch said.