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Cetacean Assessment and Ecology

What’s the Catch? Using Soviet Whaling Data to Reveal Illegal Catches of Sperm Whales by Japan

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Summer 2015
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Figure 1. Locations of Soviet and Japanese sperm whale catches in the eastern North Pacific, 4-20 August 1969 (yellow box). Each point represents anywhere from one to many catches.


A new study (Ivashchenko and Clapham 2015) has used previously secret data on illegal whale catches made by the former U.S.S.R. to expose similar illegal whaling by Japan in the 1960s. Yulia Ivashchenko and myself (National Marine Mammal Laboratory) used information on the lengths of sperm whales killed by the U.S.S.R. in the North Pacific to assess the credibility of similar data reported by Japanese whaling fleets to the International Whaling Commission (IWC).

Starting in 1948, the Soviet Union conducted a 30-year global campaign of illegal whaling which killed almost 180,000 whales that were not reported to the IWC. IWC members were required to report accurate catch statistics, but Soviet whalers routinely falsified data to cover up the illegal whaling. However, the true data on the catches were carefully recorded in secret internal reports that were declassified only after Russia revealed the illegal whaling campaign in 1993, after the collapse of the U.S.S.R. Since then, biologists have worked with former Soviet whaling scientists to correct the IWC’s catch record with the true data. For the North Pacific, this process was completed by Ivashchenko only 2 years ago.

While analyzing the true data on catches of sperm whales in the North Pacific, Ivashchenko noticed that the Soviet length statistics were markedly different from those reported by Japan for similar catches of this species. Until 1972, whalers were prohibited from killing any sperm whale whose length was less than 11.6 m (38 ft), a restriction designed to protect immature animals, as well as younger females (in sperm whales, adult males are much larger than females). By comparing the actual lengths of sperm whales killed by the Soviets to lengths reported by Japan, it became clear that the latter were not credible.

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  Figure 2. Length-frequency distributions (percentage of total female catch) for Japanese and Soviet catches of female sperm whales in (a) 1968/1969 and (b) 1973/1974.

In 1968 and 1969, Japanese whaling fleets in the North Pacific killed 1,568 female sperm whales, of which 1,525 (97.3%) were reported as being at or above the minimum length. In contrast, Soviet fleets operating during this period killed 12,578 females, yet only 824 (6.6%) were of legal size. After adjusting for catch effort, we noted that the number of legal-sized females that Japanese whalers claimed to have killed was up to nine times that taken by the Soviets. The difference was even more dramatic during a period in August 1969 when both nations’ fleets were catching sperm whales in the same area (Fig. 1): during this time, Japan claimed to have killed more than 30 times the number of legal-sized females as one of the Soviet fleets. This is clearly impossible and indicates systematic falsification of the data to cover up extensive catches of under-sized whales.

The analysis also showed that after 1972, when international observers placed aboard factory ships made cheating much more difficult, the lengths of the killed whales became much more similar between the two countries (Fig. 2).

Japanese whalers were already known to have falsified catch data for sperm whales and other species killed by land-based whaling stations; but, while there were suspicions that the same practice was going on in the pelagic fleets, no one had previously been able to show this. We realized that the true Soviet data gave us a way to assess the credibility of the Japanese catches. Significantly, our study also quotes a Japanese scientist who said that biologists aboard the factory ships were not permitted to measure the whales that had been killed.

It is ironic that information from illegal whaling has proven to be the key to uncovering other violations of the whaling regulations.
Almost 315,000 sperm whales were killed in the North Pacific in the 20th century—far more than any other species—and the status of the population today is unclear. The existence of extensive false data in the catch record creates a major problem for the IWC, which requires accurate catch information to undertake current population assessments.

Our study was published in July 2015 in the journal Royal Society Open Science, and it has received considerable attention from the press.

By Phil Clapham



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