Japanese whaling fleets have been accused of systematically falsifying data on the number and size of sperm whales they killed in the late 1960s, calling into question our understanding of current whale populations.



A study has compared official Japanese whaling data submitted to the International Whaling Commission (IWC) with formerly secret internal Soviet whaling industry reports. The findings suggest the Japanese caught large amounts of small illegal-sized whales, but reported these as lower numbers of larger whales – for example, counting two smaller whales as one legal-sized animal.



Our understanding of how whales recover from being hunted is dependent on determining a ‘baseline’ whale population, from before widespread whaling.

Since this is based on historical catch data, the Japanese misreporting could have a significant impact on our knowledge of how whale numbers react to whaling, suggests Andrew Brierley, a marine ecologist at the Scottish Oceans Institute, University of St Andrews.



“If there’s been unreported catches, then we don’t know how many whales have been taken from the population,” he said. “This could mean our understanding of how the population is responding to fishing could be wrong.”



760,000 sperm whales were killed in the 20th century, with some 315,000 caught in the North Pacific alone. The vast majority of these were hunted by Japanese and Soviet fleets.



It is well known that Soviet whaling fleets lied to the IWC in official reports in the 1960s and ‘70s. However, industry documentation, declassified in the 1990s, has provided accurate data on Soviet catch statistics.



Researchers at the National Marine Mammal Laboratory in Alaska compared this accurate Soviet data with the official data the Japanese submitted to the IWC in 1968-69. In particular, they compared the number of legal-sized female sperm whales – those over 11.6m in length – reported by both countries.



The findings, published in the journal Royal Society Open Science on Wednesday, showed the Japanese reported catching 15 times more legal-sized female sperm whales than the Russians, despite fishing the same seas at the same time, and the Soviets having a larger fleet. Japanese figures reported that 97.3% of the females they caught were of a legal size, compared to just 6.6% of the females the Soviets caught.



The authors conclude that such disparity is just not possible, and indicates extensive and intentional misreporting of the killing of sperm whales by Japanese fleets at the time.



The apparent deception was made possible as whaling was not subject to independent inspection until the introduction of an International Observer Scheme, set up by the IWC in 1972. After this, falsifying catch data became more difficult, although there are still reports of international observers failing to report infractions, either through distraction or direct collusion.



Given the ease and temptation to misreport catch data, the scientists suggest any future whaling activities should be monitored by a comprehensive and transparent independent observer scheme, a finding supported by Brierley.



“We have to have faith that the numbers reported today are those that are caught,” he said. “But unless you have an independent observer on the boat, it’s very hard to know.”