This article at HowStuffWorks mentions that the blue whale population, once believed to be as high as 200,000, is now at around 10,000, and is not expected to recover. They don’t explain why. I’m assuming they mean even if no more blue whales are hunted, but still, given enough time, why wouldn’t the population recover?
Hmmm…Well numbers are hard to estimate for whales, especially semi-elusive species like the Blues. I’ve seen estimates of anywhere from 5,000 to 15,000 ( so 10,000 may not be a bad guess ). Here is one table, with some estimates:
http://www.hsi.org.au/estimates.html
There seems to be some signs of recovery, at least in the East Pacific. But see below for comments on a possible "redistribution ( as well as some idle speculation on the lagging recovery ):
http://www.personal.psu.edu/users/k/e/kem171/blue.htm
In addition to the comments on the page above, I might add that this is a critter that can take ten years to reach sexual maturity and is found in somewhat fragmented populations. Recovery under these conditions is going to be very slow indeed. In fact part of the problem may be that some of these population fragments may have declined in size to the point where losses exceed additions, year by year. As a result what we may see is a slow ( very slow ) recovery in larger populations, like off of CA, and the slow decline and disappearance of smaller non-viable populations elsewhere. Pollution et al aside, even if you removed every human on the planet, recovery to historic levels could conceivably take many decades, if not centuries.
- Tamerlane
At least part of the problem is that the Bue Whale is not strictly a separate species. Hybridisation betweeen blue whales and humpback and fin whales is fairly common (in excess of a couple of births a year, which for a population of 10,000 animals with a long reproductive cycle is pretty high). According to DNA results this was were occuring long before human hunting became significant. With the decimation of Blue populations the incidence of hybridisation has aparently risen.
There is concern in some quarters that the blue whale as a species/subspecies may still vanish as their genoype is swamped by the smaller whales. As more hybrids are produced the chances of the offspring back-crossing with blues becomes even higher because they are more similar to blues than their non-blue parent. Exactly why the smaller whales are believed to have a higher reproductive success I don’t know.
I would think that inbreeding would become a factor at low population levels. Maybe 10k is high enough to prevent this but maybe it isn’t.