(from "Research on Whales", ICR, 1995)

Kazuo Yamamura
Secretary General, ICR

Hunting of minke whales in the coastal waters of Japan was first conducted by both large whaling vessels and small vessels of about seven tons. Later, however, vessels of 10 to 20 tons were mostly used. Since 1949, the law has limited the vessel size to 49 tons or less. In addition to minke whales, these vessels were also used to hunt pilot whales and Baird's beaked whales.

The small size of the vessels limited hunting operations to those which could be completed within a day, which meant areas of hunting were restricted to waters close to the bases of operations. This type of whaling, therefore, came to be characterized as small-type whaling. Since 1949, small-type whaling has been under the control of the government as a category of fishery requiring the approval of the Ministry of Agricultural, Forestry and Fisheries.

Before it was suspended by the moratorium, minke whaling had been conducted by nine small whaling vessels operating in the waters off the coast of the Sanriku region, as well as in the waters off the coast of Hokkaido.

It was thought that the minke whales migrating through the coastal waters of Japan were divided into two stocks: one distributed in the Yellow Sea, the East China Sea, and the Sea of Japan; and the other distributed in the waters off the Sanriku coast and in the Sea of Okhotsk. The former stock is known to migrate, at least in the spring months, to the Sea of Okhotsk.

The sizes of the two stocks are estimated at an abundance of 7,000 and 25,000 animals, respectively. (Here, "stock" refers to a distinct group of whales which share the same breeding grounds and ordinarily do not mate with whales in other groups.)

In a meeting of the study team for the application of the revised management procedure (RMP) for North Pacific minke whales - immediately prior to the meeting of the Scientific Committee, 45th annual meeting of the International Whaling Commission (IWC), Kyoto, spring 1993 - it was pointed out that there existed a possibility that each of the two stocks mentioned above has a number of sub-stocks. Furthermore, an hypothesis was put forward suggesting the existence of a Pacific stock of minke whales whose breeding grounds are in the middle and low latitudes of the central North Pacific. It was further suggested that these whales are distributed in the waters west of 170 degrees east longitude - waters which had been regarded as the breeding grounds of the stock distributed in the waters off the Sanriku coast and in the Sea of Okhotsk.

The RMP is a formula which was developed over a period of several years by the IWC's Scientific Committee (IWC/SC) to calculate specific safe catch limits after the moratorium is lifted. This formula calls for rigorous subdivisions in marine management (especially when the information available is limited) and it emphasizes the safety aspects.

One factor that is common to all types of marine resources management is the fact that stock abundance is the most important determinant of safe catch limits. Monitoring of stock size on a unit marine area basis is a prerequisite to safe implementation of the RMP.

I stated earlier that the size of the whale stock in the waters off the Sanriku coast and in the Sea of Okhotsk is 25,000 whales. This figure represents the abundance of minke whales distributed in the Pacific to the west of 170 degrees east longitude and in the Sea of Okhotsk.

If indeed the hypothesis is correct that there exists a Pacific stock, and that this stock is distributed in the waters west of 170 degrees east longitude, we must first ascertain the ratio of mix between this stock and the Sanriku/Okhotsk stock in these waters. Otherwise, we will not be able to correctly estimate the abundance of the latter stock. Unless we can estimate the size of the Sanriku/Okhotsk stock, calculation of safe catch limits using the RMP also would be difficult. If the Sanriku/Okhotsk stock is further divided into sub-stocks, the confusion would be even greater.

The research which involved the scientific taking of North Pacific minke whales (beginning summer 1994) was designed to obtain basic data in order to calculate, using the RMP, safe catch limits of minke whales in Japan's coastal waters after the moratorium is lifted. The primary objective of this research is to accurately identify minke whale stocks; ascertain the extent of the distribution of the Sanriku/Okhotsk stock; and determine if sub-stocks exist. The explicit identification of minke stocks distributed in the Western Pacific is clearly an important task.

Such identification is accomplished by a combination of (1) direct methods, which mainly consist of analysing DNA and isozymes found in whale muscle and liver; estimation of the reproduction cycle by fetus growth; and morphological comparison requiring the measurement of body proportions; and (2) indirect methods of estimating the areas of distribution, which consist of analyzing parasites, such contaminants as PCBs, DDT, and heavy metals found in whale's bodies.

It was decided that in 1994, the first year of the study, a random sample of minke whales were taken between 157 degrees and 170 degrees east longitude, where presumably only the Pacific stock is distributed, to see if, among the captured whales, there are any which belong to stocks other than the Sanriku/Okhotsk stock.

Japan now has in storage specimens of muscles and livers from 1,000 whales caught in the coastal waters of Korea and Japan during the years of commercial whaling. We decided to extract DNA from these specimens, then identify the DNA types of the Sea of Japan, the East China Sea, and the Sanriku/Okhotsk stocks, and compare them with the DNA types found in the stored specimens. If the DNA type of all the minke whales caught during the present research cruises matches that of those which were caught off the coast of the Sanriku region, then we can conclude that the Sanriku/Okhotsk stock is distributed at least as far as 170 degrees east longitude, and the size of the stock is more than the 25,000 figure estimated from sighting surveys. After that, it will be necessary to ascertain how far to the east of 170 degrees east longitude the Sanriku/Okhotsk stock is distributed and whether sub-stocks exist within the region.

Conversely, if we conclude that all of the minke whales caught in the 1994 research do not belong to the Sanriku/Okhotsk stock, then we will have to make a downward revision from the estimated stock size of 25,000 whales. Even in that case, it will be necessary to conduct research in the waters west of 157 degrees east longitude to ascertain the limit of distribution of this stock and the existence of sub-stocks.

Furthermore, if we find one or more stocks other than the Sanriku/Okhotsk stock in the area we are currently studying, it will be necessary to expand the target area to determine exactly in what proportions different stocks are distributed. As the size of the stock in each area can be estimated by sighting surveys, by adjusting the distribution ratio, we can produce an accurate estimate of the abundance of the Sanriku/Okhotsk stock, which is the primary objective of our study.

These considerations will lead to the determination, based on results obtained in preceding years, of which area is to be studied in 1995 and thereafter. The primary objective of the present research is, as I have said, to ascertain how far east in the Pacific Ocean the stock of minke whales that migrate to the Pacific coast of Japan (the Sanriku/Okhotsk stock) is distributed and to obtain an accurate estimate of its stock size.

In addition, the research seeks to obtain such basic biological data as the age composition, sexual maturity, and growth status of the collected minke whales, as well as the type and quantities of their feed. Data also will be sought on the minke whales' environment: its structure, the status of contamination of the areas in which these whales are distributed, and the distribution of other species of whales.

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