The Riches of the Sea, the Institute of Cetacean Research

Japan has been taking an active role in promoting scientific research on cetacean resources to contribute to an adequate management of whale stocks by the International Whaling Commission (IWC). To this end, it is essential to identify and classify the stock/sub-stocks within a species to implement a stock-by-stock management. Abundance estimation, monitoring of biological parameters such as age composition, types of feed organisms and nutritional conditions should be conducted on the basis of identified stocks.

Information other than stock size, should be examined fully from various aspects through whale samples by using the most up-to-date scientific methods and the random sampling of whales is necessary for this analysis. Such research should be continued for the advancement of cetacean science. The legality of cetacean research involving catch of whales is guaranteed under the International Convention for the Regulation of Whaling.

2. Why was the Japanese research catch of Northwestern Pacific minke whales started?

At its annual meeting in Kyoto, Japan in 1993, the IWC established a working group of experts for conducting the Revised Management Procedure (RMP) simulation trials of Northwestern Pacific minke whales. At that meeting, a few scientists argued that the Northwestern Pacific should be divided into 13 sub-areas based on the hypothesis that the minke whales in the Pacific coast of Japan to the Okhotsk Sea, then estimated to number more than 25,000, is not a single stock but rather is composed of (1) four putative sub-stocks having specific feeding grounds and (2) another putative stock migrating from the central Pacific area. This hypothesis contradicts the knowledge so far accumulated in the Scientific Committee and has a very thin scientific justification. In order to fully examine this hypothesis, Japan launched in 1994 a research catch program on the Northwestern Pacific minke whales, with the ultimate objective to achieve proper management of this whale resource based on the most updated scientific information on stock identity.

The IWC Scientific Committee noted that collection of information concerning the stock identity of the Northwestern Pacific minke whale will contribute to improving the present state of knowledge on the stock.

3. Research Methods

In 1994 and 1995, the offshore area of Japan close to the central part of the North Pacific (Sub-area 9) was surveyed with the aim to determine whether there exists another minke whale stock migrating from the central part of the North Pacific. The number of samples collected in the survey conducted in July-September 1994 was 2l minke whales and that in June-August 1995 was 100. Among other measurements, the body length and weight of the samples were measured and sex identification was made on board the research mothership. Samples of various parts of the body, stomach contents and parasites were also collected and laboratory analyses were carried out on these materials.

Why is lethal method necessary?

Although DNA and organochlorine analyses can be made using biopsies, they are by no means sufficient for the overall purpose of the study. In order to elucidate the stock/sub-stock structure of whales the following data/tissues are required, which can be obtained only through lethal take of the animals:

(1)

data on morphometric, sex, pollution, parasites and heavy metals, which strongly supplement other information in a comprehensive study on stock identity.

(2)

conception date data from fetus length needed for stock identification, differentiation and mixing.

(3)

skin, blubber and, internal organ tissues for the analysis of heavy metal accumulation.

(4)

samples of liver for isozyme analysis which is one of the best indicators for stock identification.

(5)

hard tissues, such as baleen, for stable isotope analysis.

4. Results

Main information obtained from the research and analyses to date can be summarized as follows:

(1)

Examination of allozymes in the whale tissues showed that the 121 samples of Sub-area 9 belonged to the same single breeding group (i.e. not the mixing of two or more stocks).

(2)

It was made clear from the following analyses that the 121 samples showed no substantial differences from the group caught under the past commercial small-type coastal whaling in the area off eastern Hokkaido and Sanriku and the area off Abashiri and Kitami in Hokkaido:

1.

isozyme analysis

2.

analysis of mitochondrial DNA D-loop-containing control region (See Fig. 1 and Fig.2 )

3.

analysis of the whole mitochondrial DNA genome

4.

comparative analysis of morphology and morphometry

5.

analysis of estimated breeding period

6.

analysis of the degree of accumulation of pollutants after body length correction

7.

identification of the types of parasites in the whale

(3)

The 121 samples, collected randomly, showed an unbalanced sex ratio (109 males versus 12 females). The knowledge on the Northwestern Pacific minke whale, accumulated to the present, indicates that the sex ratio in the population is almost even and that there exists a segregation according to sex and maturity stages within a stock. When the results obtained from the research is viewed in the light of this knowledge, it is suggested that the 121 samples collected in the research would most probably belong to a larger stock distributed in a wider region than the present research area.

(4)

According to the results of these analyses, the hypothesis that there exists another stock migrating from the central part of the North Pacific, does not seem plausible.

Future work

(1)

Examination of 4-sub-stocks hypothesis
The two-year research clarified that the minke whale from the Pacific coast of Japan and those from the offshore sub-area 9, belong to a single stock. In the years to come, efforts will be focused on examining the second hypothesis on the presence of four sub-stocks having specific feeding grounds. For this goal, research will be continued in sub-areas other than the Sub-area 9 covered in the past two researches.

(2)

Feeding ecology of whales
The researches revealed that the Pacific saury was common in the stomach of minke whales and larger-sized fishes such as salmon were also found. Detailed analysis will be undertaken on the feeding ecology of the minke whale to elucidate its role (through predation) in the ecosystem of the Northwestern Pacific. The information on feeding ecology is essential for interpretation of results on pollutants, parasites and stable isotopes.

Outline of the Research Catch of NorthWestern Pacific Minke Whale

Areas for research on Northwestern Pacific minke whales

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