Also, while blue whales were not being hunted, many other species were being decimated. So, when the technology existed, a whole new species was available for exploitation. The pop. does not seem to be increasing in any noticeable way. Like any whale species, they produce one calf every two to three years. Attempts to understand blue whale migratory routes and reproduction patterns worldwide are underway in relatively small efforts due to logistics and money.
Conservation is through habitat protection.
Some populations were reduced to such low numbers that inbreeding, and just plain finding each other, may be a problem. Throw in natural calf mortality, and populations are slow to realize gains. Large whales represent tremendous biomass, and therefore harvest tremendous amounts of small prey items. They are and have been integral parts of the ecosystem. Effects on humans would include an emotional loss.