SC/J09/JR28

Differences in cookie cutter shark-induced body scar marks between
J and O stocks of common minke whales in the western NorthPacific.
Goto, M., Kanda, N., Pastene, L.A., Bando, T. and Hatanaka, H.
The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan
Contact email:goto@cetacean.jp
ABSTRACTIn this study the status of cookie cutter shark scars on the skin of common minke whales was examined toevaluate whether or not it is possible to identify the stock of origin of the individual animals based on suchscars. The examination was made using samples of western North Pacific common minke whales collected byJARPNII. Assignments using the number of scars were not a full diagnostic for the minke whales of J and Ostocks. However, at least there is a strong likelihood that animals which have no scars on the body wereimmature J stock animals. There were significant differences between suspected J and O stocks animals in thenumber of scar on their body. Further significant differences were found between mature and immature
animals within both stocks in the number of scar as well.

KEY WORDS: COMMON MINKE WHALE, COOKIE CUTTER SHARK, SCAR, STOCKIDENTFICATION, JARPNII, NORTH PACIFICINTRODUCTION
Cookie cutter sharks (Isistius brasiliensis) live in the depths of all the oceans near the equator. As shown inFigure 1, this small shark is found in the western Atlantic Ocean from the Bahamas to the coast of southern
Brazil. In the eastern Atlantic Ocean, it is found from Cape Verde, Guinea to Sierra Leone, southern Angolaand South Africa including Ascension Island. The cookie cutter shark also lives in the waters of theIndo-Pacific from Mauritius to New Guinea, Lord Howe Island, New Zealand, Japan and the Hawaiian
Islands. It is found off Easter Island and the Galapagos in the eastern South Pacific Ocean. Records of cookie
cutter sharks off Australia include the waters off Queensland, New South Wales, Tasmania, and Western
Australia (Compagno, 1984). Around Japanese water, this shark has been observed in the southern Pacificside of Japanese archipelago (sub-area 2) but no record has been made in the East China sea and Sea of Japan(Nakano, H., pers. com.).
Compagno (1984) also reviewed the food habits of cookie cutter shark as follows. Forming a suction cup
with its mouth, the cookie cutter shark latches onto its prey. The top teeth are small, pointy and sharp to grasp
hold of the prey’s skin. Turning in a circle, this shark carves a round chunk of flesh out with its larger
razor-sharp, serrated or saw-like bottom teeth. In a flash, the cookie cutter scoops out the meal. Afterattacking, its prey is left with an almost perfectly round mark that looks like someone used a round cookie
cutter on its body. Cookie cutters bite chunks out of large billfish like marlins and tunas, large squid, seals,whales, dolphins, other sharks, and stingrays.
Most of the common minke whales taken by the JARPN/JARPNII survey in the Pacific side of Japan(known as O stock) have numerous white scars on the skin. However, a few of the sampled animals have noscar on the skin. Fujise et al (2001) examined relationship between genetically identified O or J stock animals
and occurrence of scars, based on samples of minke whales taken by JARPN. Their results showed highcorrelations between occurrence of scar and each stock determined by genetic data. In this study scar marks inthe body of common minke whale sampled by JARPN II (2002-2007) are examined to evaluate whether J andO stock common minke whales can be identified by taking into account the scar of the cookie cutter shark.

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MATERIALS AND METHOD
Samples
A total of 1,062 western North Pacific common minke whales collected in the offshore and coastal
components of JARPN II from 2002 to 2007 were examined. The scar types were categorized based on thenumber of scars as follows:
Type 1: No scar on the bodyType 2: 1-20 scars on a single side
Type 3: More than 20 scars on a single side
Number of scars was directly counted in Type 2 and Type 3 was not.
Kato (1992) estimated mean body length at the sexual maturity of the North Pacific minke whales to be 6.3
m for males and 7.1 m for females, so that we tentatively deal with animals less than 7m as immature andmore than 7m as mature in this study.
Assignment of JARPN II minke whales to J and O stocks
Microsatellites analysis and a Bayesian method were used to assign individuals minke whales to either J or Ostocks (see details in Kanda et al., 2009). The randomized chi-square Test of Independence (Roff and Bentzen,1989) was used to investigate the extent of differences among scar mark types (Types 1, 2 and 3), stocks (Jand O stocks) and sexual maturity of the animals by body length in each stock.
RESULTS
Table 1 shows the number of samples used in the present study by type of scar mark, stock (as assigned by thegenetic analysis), sub-area and the offshore and coastal components of JARPN II for the period 2002 to 2007.
Individuals with no scars on their body (Type 1) were not detected in sub-area 7E, 8W, 8E, 9W and 9E.
Table 2 shows the number of samples used for the statistical analysis by stocks, body length and type ofscar marks. In both stocks significant differences (P=<0.0001) were found between animals with more thanand less than 7m in body length. Further there were significant differences (P=<0.0001) between J and O
stocks animals with regard the number of scars as well.
It should be noted that most of J stock animals assigned by the genetic analysis were distributed within
sub-area 7W except for one individual in the sub-area 9W. Figure 3 shows the geographic distribution of Jstock animals within the sub-area 7W by type of scar mark. This figure shows no specific distribution by scar
mark types in coastal waters in the Pacific side of Japan. Figure 4 shows the distribution of O stock animals
by type of scar mark. There is no Type 1 animals assigned for O stock animals. Types 2 and 3 animals lessthan 7m in body length tend to distribute in coastal waters in the Japanese Pacific side. Although animals withmore than 7m in body length distribute uniformity in the research area, animals having a larger number ofscars tend to distribute in the northern part of the research area.
Figure 5 shows the frequency distributions of body length by types of scar marks and by J and O stocks as
assigned by the microsatellite analysis. Regarding the J stock, no scars were observed in animals with bodylength less than 7m. Regarding the O stock, there is no animal with Type 1 scar mark. Further the frequencyof Type 3 scar mark animals gradually increased with body length.
DISCUSSION
In this study scar marks on the body of common minke whale sampled by JARPN II (2002-2007) were
examined in order to evaluate whether J and O stock common minke whales in the western North Pacific canbe identified by using this non-genetic marker. The number of scars was not a full diagnostic character toassign individual minke whales to J and O stocks, because some J stock animals presented Types 2 & 3 scar
mark which was dominant in the O stock animals. However our findings were that at least there was a strong
likelihood that animals which have no scars on their body were J stock animals, and the number of scars in J
stock animals is apparently less than that in O stock animals. Further, number of scars in J and O stocks
animals is different by the body length, and smaller animals tend to have none or less number of scars. It is
important to note that there were significant differences between suspected J and O stocks animals in thenumber of scars on their body, and such differences were found in both animals with more than and less than2

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7m in body length as well.
Although it was predicted that most of the J stock animals would have no scars by the previous results (Fujiseet al., 2001), the present study showed that a large number of animals of the J stock have scars. One of thepossible examinations for this is that scars are not diagnostic characters to assign individual minke whales to Jand O stocks.
Other examination would be related to the migration pattern and distribution of J/O stock animals by its
body length and habitat of the cookie cutter sharks. Cookie cutter sharks lives in the depth in the ocean.
Around Japanese water, cookie cutter shark was detected in the southern Pacific side of Japanese archipelago(sub-area 2) and there is no record in the Sea of Japan and East China Sea (Nakano, H., pers. comm.).
Firstly, reason why many immature animals (tentatively less than 7m in this study) have no scar might bethat they preferred to distribute in the shallow waters close to the Japanese coastal line, then they have nochance to meet cookie cutter sharks that lives in the depth in the ocean even if they migrate through sub-area
2. Indeed, Kanda et al (2009) reported that most of bycaught individuals taken in sub-area 2 were J stock
animals and that average body length of the all animals bycaught on the set net fishery was 4.92 m, and all of
the set nets were settled within 3 n.miles from the Japanese coastal lines. Migration route of common minke
whale might be gradually shifted to the offshore area as they grown and this increased the chance to meet thecookie cutter sharks.
Secondly, regarding mature (tentatively more than 7m in this study) J stock minke whales, it was assumed
that animals with no scars observed in the Pacific side of Japan would migrate from East China Sea and Seaof Japan to the Pacific through the Tsugaru or Soya straits, and that animals having scars migrate to thePacific side through the sub-area 2. Under these assumptions, we will be able to estimate the migration patternof J stock animals by observing the scar on the body. In this study two animals with body length more than
7m were detected. One animal (7.12m) was taken by the offshore component at off Kushiro in 2006 and theother (7.23m) was taken by coastal component in Sendai Bay. These animals might be migrated from Sea ofJapan side to the Pacific through the northern straits and other animals through the sub-area 2 under theseassumptions.
Regarding the O stock animals, our results indicated that number of scar was different by the body length, andlarger animals tended to have larger number of scar. The observation that the number of the less than 7m(mostly immature) O stock individuals distributed in the Japanese coast of the North Pacific side was wellconsistent to that illustrated by Hatanaka and Miyashita (1997). If the number of scars was reflect the lengthof stay at suspected breeding area where cookie cutter sharks distribute in the low latitude in the North Pacific,
older animals would have more large number of scars. Figure 3 shows the animals have larger number of scarmigrate to more northern part of research area. This indicates that older animals migrate to more northern areafor feeding.
Fujise et al. (2001) examined the utility of three non-genetic markers (occurrence of scars, foetal length
reflecting the conception date and accumulations of some pollutants) for stock identification in the western
North Pacific minke whale. They found striking differences in these three markers between J and O stocks,
and genetics and non-genetics markers matched almost perfectly. This means that a combination of several
non-genetic markers would be useful for identification of these stocks. Therefore, we need to understand andrecognize both the advantages and disadvantages of each biological marker, and determine stock identity by
combining the information with genetic data. With this strategy it will be possible to identify stocks with moreaccuracy.
Regarding the number of scars unfortunately such information can not be obtained by observation of freeranging whales from sighting survey vessels because the distinction of scar on swimming whales is extremely
difficult (Miyashita, T., pers. com.).
REFERENCES
Compagno, L.J.V. 1984. FAO Species Catalogue - Sharks of the World part 1. Rome.
Fujise, Y., Zenitani, R. and Goto, M. 2001. Utility of non-genetic information for stock identification –Thecase of the western North Pacific minke whale-. Paper SC/53/SD5 presented to the IWC scientificcommittee. 9pp.
Hatanaka, H. and Miyashita, T. 1997. On the feeding migration of the Okhotsk Sea-West Pacific stock ofminke whales, estimates based on length composition data. Rep. int. Whal. Commn. 47: 557-564.

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Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. 2009. Individual identification andmixing of J and O stocks around Japanese waters examined by microsatellite analysis. PaperSC/J09/JR26 presented to the JARPN II Review Workshop, Tokyo, January 2009 (unpublished). 9pp.
Kato, H. 1992. Body length, reproduction and stock separation of minke whales off northern Japan. Rep. int.
Whal. Commn. 42:443-453.
Roff, D.A. and Bentzen, P. 1989 The statistical analysis of mtDNA polymorphisms: χ2 and the problem ofsmall samples. Mol. Biol. Evol., 6, 539-545

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Table 1. Number of samples used in the present study by type of scar, sub-area and stocks assigned by genetic
data. Samples collected by the offshore and coastal components from JARPN II during 2002 and 2007.

7W
Coastal7W
Offshore

7E
Offshore

8W
Offshore

8E
Offshore

9W
Offshore

9E
Offshore

Type of scar
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total
1 None2 1-20 scars
3 more than 21 scars
Total

Grand total

Microsatellite allocation
O?
J0435191039335
335354477901238413157
21219526
17000110700810000800236031600002020413061
500001930104
16112319100041080
4084
50856
10997

Table 2. Result of the statistical analysis of frequency of scar type by body length in each stocks.

Less than 7m
More than 7m
PType 135
2J stock
Type 233
17<0.001

Type 314Type 1005O stock
Type 255
47<0.001

Type 3246
485

P<0.001<0.001

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Fig.1. Geographical distribution of Cookie-cutter shark (after Compagno, 1984).

Fig. 2. The 18 sub-areas used for the Implementation
Simulation Trials for North Pacific minke whales.

645N

45N

35N
140E

35N

Fig.3 Distributions of J type animals by
Type of scar.
：None,; 1-20 scars
and; more than 21 scars.

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45N

45N

35N
140E

150E

35N
170E

160E

45N

45N

35N
140E

150E

35N
170E

160E

45N

45N

35N
140E

150E

35N
170E

160E

45N

45N

35N
140E

150E

35N
170E

160E

100%

100%

80%

80%

60%
Type3
Type2
Type140%

Number of animals

Number of animals

Fig.4. Distributions of O type animals by type of scar and body length. Upper left: Type 2 and less than 7m,upper right: Type 2 and more than 7m, lower left: Type 3 and less than 7m, lower right: Type 3 and more than
7m.

20%

60%
Type3
Type2
Type140%

20%

0%

0%

4

4.5

5

5.5

66.5
Body length (m)

7

7.5

8

8.5

4

4.5

5

5.5

6
6.5
Body length (m)

7

7.5

8

8.5

Fig.5. Frequency distributions of body length by types of scar and by J and O stock animals assigned by
microsatellite. The left figure correspond to J stock animals and the right figure to O stock animals.

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