Research has shown these whales are not experiencing a population boom as argued by Japan.
"A female sperm whale may produce one calf every five years, after reaching sexual maturity at nine years. Males reach breeding age in their late twenties. It is not known how many calves a female may bear before reaching menopause or the rate of natural sperm whale mortality. A young whale may suckle from her mother for up to 15 years.
Scientists believe that it takes around 20 years on average for a female whale to replace itself with one mature female offspring. This does not account for the potential adverse impacts of new human-induced threats to whales such as bycatch, climate change, ozone depletion, marine pollution, ship strikes and underwater noise pollution."
"Economic aspects of renewable resource exploitation as applied to marine mammals(FAO Fish Ser., 5, Vol.3) indicated that the slow growth of marine mammals was in direct conflict with profits. Operational and capital costs were sufficiently high to make harvest rates that were biologically safe economically unsound."~ Colin W. Clark.
The following cetaceans have been killed in 2008 by Japanese whalers.