SC/56/O17

Preliminary analyses of interaction between common minke
whales and sand lance fisheries off Sanriku region
TSUTOMU TAMURA1), KENJI KONISHI1), TOMIO MIYASHITA2), HIDEYOSHI YOSHIDA2), HIDEHIRO KATO 2) AND SHIGEYUKI
KAWAHARA2)
1) The Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan,
2) National Research Institute of Far Seas Fisheries, 5-7-1, Shizuoka, 424-8633, Japan.
Contact e-mail: tamura@cetacean.jp
ABSTRACTThe stomach contents of fifty common minke whales Balaenoptera acutorostrata sampled off Sanriku region from
April to May as part of the 2003 JARPN II were analyzed. The prey species consisted of one krill (Euphausia pacifica)
and two fish (Japanese sand lance Ammodytes personatus and Japanese anchovy Engraulis japonicus). All these preyspecies are target by local fisheries. Japanese sand lance and krill were dominant prey species, and their compositions inwet weight were 70.7 % and 29.3 %, respectively. The total prey consumption of Japanese sand lance and krill bycommon minke whales in one year was estimated as 3,900 tons and 1,600 tons, respectively. The sizes of Japanese sandlances fed by common minke whales were ranged from 120 to 130 mm, which composed to adult individuals.
Distribution of common minke whale in Sendai Bay overlapped Japanese sand lance fisheries ground. Japanese sandlance is one of the important coastal fishery species, and their population has kept low level since late 1980’s. There is apossibility that direct competition between common minke whale and Japanese sand lance fisheries in this region. To
evaluate this competition more precisely, more information of accurate abundance and resident period of common
minke whales around the Sendai Bay are needed.
KEYWORDS: COMMON MINKE WHALE; NORTH PACIFIC; FISHERIES INTERACTION, SCIENTIFICPERMIT
INTRODUCTION
The common minke whale Balaenoptera acutorostrata is widely distributed in the world. In the western North Pacific,
two stocks have been recognized: one in the Sea of Japan - Yellow Sea - East China Sea (J stock) and the another in the
Sea of Okhotsk – West Pacific (O stock) (IWC, 1983). The abundance of common minke whales was estimated to be
19,209 animals with 95 % confidence interval (10,069 – 36,645) in the Sea of Okhotsk and 5,841 animals with 95 %confidence interval (2,835 – 12,032) in the Northwest Pacific during August and September in 1989 and 1990 (IWC,1992). In the western North Pacific, common minke whales are opportunistic feeders consuming a broad of prey withflexible feeding habits. According to previous reports, they consume several prey species such as pelagic schooling fishand zooplankton (Kasamatsu and Hata, 1985; Kasamatsu and Tanaka, 1992; Tamura et al., 1998).
The results of the Japanese Whale Research Program under Special Permit in the Western North Pacific (JARPN) andJARPN II feasibility study showed that common minke whales fed on various prey species such as Japanese anchovy
Engraulis japonicus, Pacific saury Cololabis saira, walleye pollock Theragra chalcogramma and Japanese common
squid Todarodes pacificus, and the main prey species changed seasonally and geographically. For example, they feedon Japanese anchovy in May/June and Pacific saury in July/August (Tamura and Fujise, 2000a, 2002a). The estimatedprey consumption by common minke whales was comparable to that of the commercial fisheries (Tamura and Fujise,
2000b, 2002b), indicating the competition between common minke whales and fisheries may occur in the coastal area.
However, our interests of coastal matter, the Nisshin-Maru and large sighting/sampling vessels can not be operated in
the near shore area because of various restrictions and obstacles. Furthermore, these vessels can not join survey fromlate autumn to early spring for operational reason.
In order to cover the geographical and seasonal gaps of JARPN and JARPN II feasibility study, sampling of common
minke whales in the coastal area using small type whaling catcher boats was planed in 2002 (Government of Japan,
2002. These coastal surveys were conducted off Kushiro in 2002 and off Sanriku in 2003. The details of these surveys
were reported in Kishiro et al. (2003) and Yoshida et al. (2004).
Off Sanriku region, the coastal component of JARPN II was conducted in April and May in 2003. The research area
covers within the 30 n.miles (maximum 50 n.miles) from the Ayukawa port (fig.1). In previous report, common minke
whales fed mainly on krill and Japanese sand lance Ammodytes personatus during spring off Sanriku region (Kasamatsu
and Tanaka, 1992). Yoshida et al (2004) reported that the dominant prey species of common minke whales sampled off
Sanriku region were Japanese sand lance and krill Euphausia pacifica.
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In this document, the abundance of common minke whales and the consumption of targeted fisheries species consumed
by common minke whales were calculated using some assumption off Sanriku region. Then, the prey consumption bycommon minke whales and fisheries catches were compared. In Japanese sand lance fisheries, small larvae and adults
were exploited separately, since common minke whales feed mainly on large (>10cm) fish. So, only adult Japanesesand lance is covered in this document.
MATERIALS AND METHODS
The abundance of common minke whales off Sanriku region
The area was 17,403.9 nml2, and the density of minke whales was assumed 0.033ind. / km2 (data form Syunyo Marusighting cruise in 1991 and 1992). The abundance of common minke whales within 50 n.miles from the Ayukawa port
estimated 574 individuals (95% confidence interval was from 191 to 1,653ind.).
Sighting and sampling of common minke whales
Sighting and sampling methods of common minke whales were described by Yoshida et al (2003). Four small-typewhaling catcher boat, Taisho Maru No. 28, Sumitomo Maru No. 31, Katsu Maru No.7 and Koei Maru No.75 were used.
All common minke whales sighted excluding the cow-calf pair were targeted for sampling. When a school size wasmore than one animal, sampling target was selected randomly from the school. After the target was sampled by harpoon,she moved to the Ayukawa port as soon as possible, to land research station.
Sampling of the stomach contents
Biological research such as measurement of body proportion was conducted for all common minke whales sampled.
After the stomach contents were removed, the contents from each stomach were weighed to the nearest 0.1 kg, and subsample were removed from all individuals and frozen for later examination. The contents were first classified to major
prey groups, such as euphausiids, copepods, fish and others. The freshness of stomach contents was categorized into
four classes (1 = fresh, 2 = lightly digested, 3 = moderately digested, 4 = heavily digested).
The sub-samples were identified to the lowest taxonomic level as much as possible. When undigested fishes were found,standard lengths and weight were measured to the nearest 1 mm and 1 g, respectively. When fishes occurred in the subsamples, the total number of each prey species was estimated by adding the number of undigested specimens and thenumber of intact skulls. The total weight of each prey species was estimated by using the average weight of fresh
specimens. The total number and weight of each prey species were estimated by using the results from the sub-samples.
Then, the relative prey importance by weight of each prey species (RW) was calculated as follows:
RW = (Wi / Wall) *100
Wi = the weight of contents containing prey group i
Wall = the total weight of contents analyzed.
The consumption by common minke whales
The sample size of common minke whales, which were used for stomach contents analyses, was listed in Table 1. The
diet composition (RW) of common minke whales was shown in Table 2. The maturity composition of common minke
whales was listed in Table 3.
The daily prey consumptions by both immature and mature common minke whales were calculated with theassumptions below.
a. Mean body weight (Tamura and Fujise, 2002b) :Immature male:

2,500 kg

Immature female: 2,600 kg
Mature male:

4,800 kg

Mature female:

5,900 kg

These weights were obtained from JARPN and JARPNII survey data.
b. The residence time of the common minke whale off Sanriku region: 60 days (April and May)
Off Sanriku region, common minke whales mainly distribute from April and May (Hatanaka and Miyashita, 1997).
And past commercial whaling season off Sanriku region was from April and May. Therefore, residence time of thecommon minke whale off Sanriku region was assumed to be 60 days.
c. Field metabolism Immature male or female: 1.58*80*body weight (kg) KJ / day (Markussen et al., 1992)
Mature male or female:

1.25*80*body weight (kg) KJ / day (Nordoy et al, 1995)

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The average field metabolism used in these calculations was obtained from Blix and Folkow (1995). The value of
80 kJ/kg per day is based on indirect determination of oxygen consumption from studies of the respiratory rates.
d. Average caloric value of prey species: 6,000 KJ / kg
Stomach content analyses show much variation in the diet of common minke whales in the western North Pacific(Kasamatsu and Tanaka, 1992; Tamura et al., 1998, Tamura and Fujise, 2000a, 2002a). In the North Atlantic, theenergy contents of the prey species varies from 3,720 kJ/kg when feeding on Parathemisto spp. to as high as
12,500 kJ / kg when feeding on herring (Markussen et al., 1992). In this study, the mean caloric value of krill,
Japanese anchovy, Pacific saury, walleye pollock and Japanese common squid Todarodes pacificus were
calculated using bomb caloric meter. The mean caloric value of krill, Japanese anchovy, Pacific saury, walleye
pollock and Japanese common squid were calculated to be 3,600 kJ/kg, 6,400 kJ/kg, 13,000 kJ/kg, 6,200 kJ/kg and
6,600 kJ/kg, respectively (Tamura and Fujise, 2002b). Total prey species were assumed to be 6,000 kJ/kg by
average of above values.
e. Assimilation efficiency:80%

The assimilation efficiency of the common minke whales is assumed to be 80 %. (Markussen et al., 1992).
f. Reproduction cost:

20kg / day

The total reproductive cost for the female common minke whale was re-calculated to be 1.9*107 kJ (Lockyer,1981), assuming a length at birth fetus of 280 kg (Christensen, 1981). The pregnancy rate is 95 % for mature. Allenergy related to reproduction costs as obtained during the residence (feeding) time in the western North Pacific(180 days) were assumed.
The each calculated prey consumption by common minke whales from April to May is shown in Table 5.
The fisheries catches of Japanese sand lance (>10cm) and Euphausia pacifica around the Sendai Bay fromFebruary to May
Catch data ware provided from the Miyagi Prefecture Fisheries Research and the Development Centre and Fukushima
Prefecture Fisheries Research Centre. The fisheries catch of sand lance (>10cm) and E. pacifica were listed in Table 6.
The catches of Japanese sand lance and E. pacifica around the Sendai Bay from February to May were 6,000 tons and
30,000 tons, respectively.
Interaction index between common minke whales and fisheries catch
The interaction was evaluated by means of comparison between the prey consumption by common minke whales andfisheries catches as follows:
I index = Call / F *100
I index = Interaction index between common minke whales and fisheries
Call = Consumption by common minke whales (tons)
F = Fisheries catch (tons)

RESULTS
Three prey species consisting of 1 krill and 2 fish (Japanese sand lance and Japanese anchovy) were identified instomachs of common minke whales caught off Sanriku region as part of 2003 JARPNII. Japanese sand lance and krill
were dominant prey species and composed 70.7 % and 29.3 % in wet weight (%), respectively (Table 2).
The estimated daily prey consumption weights during feeding period off Sanriku region were 120 kg and 125 kg for
immature male and female, and 183 kg and 244 kg for mature male and female, respectively.
The prey consumption by common minke whales off Sanriku region from April to May was estimated to beapproximately 5,500 tons. The total prey consumption of Japanese sand lance and E. pacifica by common minke whales
were estimated as 3,900 tons and 1,600 tons, respectively.
The body length of Japanese sand lance ingested ranged from 120 to 130 mm (Fig. 2). These sizes were equivalent toadult size of Japanese sand lance.
The I index were 63 in Japanese sand lance (>10cm) and 5 in E. pacifica, respectively. Sighting positions of mink
whales were overlapped fisheries ground of Japanese sand lance off Sanriku where rough sand bottom are dominant.
(>10cm) (Fig. 3).

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DISCUSSION
The present study indicates that there is large impact of predation by common minke whale on sand lances in Sendai
Bay. To figure out how and how much impacts common minke whales to off Sanriku region ecosystem, Japanese sandlance is one of the most important key prey species off Sanriku region.
Some sand lance species in the world have specific habit, summer aestivation. (Robards et al, 1999). They hidethemselves in near shore substrates every summer, when water temperature is high. In Sendai Bay, they hide during
August and December, at mainly rough sand sediment in shallow water (< 50 m depth) (Kobayashi et al. 1991). So,
Japanese sand lances as prey of common minke whale off Sanriku region are presumably available only from February
to June through a year.
In 2003 coastal component of JARPN II, the dominant prey species of common minke whales sampled off Sanriku
region in April and May were Japanese sand lance and krill Euphausia pacifica. This result was similar to that ofprevious report (Kasamatsu and Tanaka, 1992). They analysed the yearly change of prey species of common minke
whale off Sanriku during 1948 to 1987. Commercial whaling had been made from January to September with peaks
from April to June. After 1980, the peak of catch was observed in April. The dominant prey species were krill, Japanesesand lance and iwashi (Japanese sardine and/or Japanese anchovy). They pointed out that the yearly change of Japanesesardine in stomach contents were similar to the annual trend of abundance of Japanese sardine in this area.
The maximum stomach contents weight was 102.6 kg (2.0 % of body weight). Our daily estimated prey consumption
was from 120 kg to 244 kg (from 3.8 % to 4.8 % of body weight). Common minke whale should take on prey at several
times due to meet a demand for their energy requirement in a day. Based on diurnal change in feeding activity ofcommon minke whale in the western North Pacific, Tamura and Fujise (2000c) pointed out that common minke whales
feed on prey at several time throughout the day at the surface. Our results supported their consideration.
The seasonal consumption of 574 common minke whales distributed off Sanriku during April and May (60 days) was
5,500 tons. The total consumption of Japanese sand lance estimated 3,900 tons, equivalent to 63% of current
commercial fisheries catch of Japanese sand lance.
Based on results of the sand lance consumption by common minke whales and the degree of overlap between fisheries
ground of Japanese sand lance and sighting position of common minke whales, it is conceivable that the possibility withdirect competition between common minke whale and Japanese sand lance fisheries occurs. The fisheries season ofJapanese sand lance is from February to May, and common minke whales also feed on Japanese sand lance in the later
half of the season. Furthermore, sighting positions of common minke whales were overlapped fisheries ground ofJapanese sand lance (>10cm). The catch quota and season of Japanese sand lance off the Sanriku region (around the
Sendai Bay) is regulated by the fisheries conference in order to protect the resources of Japanese sand lance and pricecontrol, however common minke whales feed on Japanese sand lance more than half of catch. Therefore, consumption
by common minke whales should be taken into account for fishery management of Japanese sand lance off Sanriku
region.
Furthermore, some fishermen indicate the fishing operation have interfered by common minke whales. Some minke
whales attack and feed on the school of sand lance when fishermen attracted fishes around boat, causing dispersion of
the schools of Japanese sand lance.
This preliminary analysis was based on the result of only once research in 2003. To evaluate the competition between
common minke whale and Japanese sand lance fisheries, more information of accurate abundance in prey species andcommon minke whales, and the accurate resident period of common minke whale around the Sendai Bay are needed. It
needs the long-term monitoring research in this area in future.
ACKNOWLEDGEMENTS
We would like to thank all captains, crews and researchers, who were involved in coastal compornent of JARPNII
surveys in 2003. Our sincere thank to Dr. H. Hatanaka and Dr. Luis A. Pastene of the Institute of Cetacean Research(ICR) for their valuable suggestions and useful comments on this paper. Catch data of sand lance ware provided fromDr. H. Nagashima of the Miyagi Prefecture Fisheries Research and Dr. S. Izumi of the Development Centre andFukushima Prefecture Fisheries Research Centre. We would like to thanks them for their cooperation.
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Christensen, I. 1981. Age, determination of minke whale, Balaenoptera acutorostrata, from laminated structures in the
tympanic bullae. Rep. int. Whal. Commn. 31:245-53.
Government of Japan, 2002. Research Plan for Cetacean Studies in the Western North Pacific under Special Permit(JARPN II). Paper SC/54/O2 presented to the IWC Scientific Committee, May 2002 (unpublished). 115pp.

4

Hatanaka, H. and Miyashita, T. 1997. On the feeding migration of the Okhotsk Sea – West Pacific stock of minke
whales, estimates based on length composition data. Rep. Int. Whal. Commn 47: 557-67.
International Whaling Commission. 1983. Report of the Sub-Committee on minke whales. Rep. int. Whal. Commn.
33:91-122.
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Commn. 42:156-77.
Kasamatsu, F and Hata, T. 1985. Notes on minke whales in the Okhotsk Sea -West Pacific area. Rep. int. Whal. Commn.
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Kasamatsu, F. and Tanaka, S. 1992. Annual changes in prey species of minke whales taken off Japan 1948-87. Nippon
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Kishiro, T, Kato, H., Ohizumi, H., Yoshida, H., Saito, T., Isoda, T., Tabata, S., Sakakibara, M., Saino, S., Hara, T.,
Hayashi, T., Miyashita, T., Fukudome, K., Kiwada, H. and Kawahara, S. 2003. Report of the 2002 JARPN II survey inthe western North Pacific. Part II: Coastal component – Coastal survey off Kushiro, northeast Japan. Paper SC/55/O8
submitted to the 55th IWC Scientific Committee Meeting, 26pp.
Kobayashi, T., Nagashima, H., Kodama, J., Kikuchi, Y., Kobayashi, I. And Sato, K. 1991. The ecology and resources ofsand lance off Tohoku region. Paper presented to the report of the resource study meeting of sand lance, December
1991 (unpublished). 92pp. (in Japanese).
Lockyer, C. 1981. Estimation of the energy costs of growth, maintenance and reproduction in the female minke whale,(Balaenoptera acutorostrata), from the southern hemisphere. Rep. int. Whal. Commn 31:337-43.
Markussen, N.H., Ryg, M. and Lydersen, C. 1992. Food consumption of the NE Atlantic minke whale (Balaenoptera
acutorostrata) population estimated with a simulation model. ICES J. mar. Sci. 49:317-23.
Nordøy, E.S., Folkow, L.P., Mårtensson, P.E. and Blix, A.S. 1995. Food requirements of Northeast Atlantic minke
whales. pp. 307-17. In: A.S. Blix, L.Walløe and Ø. Ulltang (eds.) Whales, seals, fish and man. Elsevier.
[Developments in Marine Biology] 4:720pp.
Roberds, M.D., Willson, M.F., Armstrong, R.H. and Piatt, J.F. 1999. Sand lance: A review of biology and predatoy
relations and annotated bibliography. USDA. [Research Paper PNW-RP 521]:157pp.
Tamura, T., Fujise, Y. and Shimazaki, K. 1998. Diet of minke whales Balaenoptera acutorostrata in the Northwesternpart of the North Pacific in summer, 1994 and 1995. Fisheries Science 64(1): 71-6.
Tamura, T. and Fujise, Y. 2000a. Geographical and seasonal changes of prey species in the western North pacific minke
whale. Paper SC/F2K/J22 presented to the JARPN review meeting, February 2000 (unpublished). 26pp.
Tamura, T. and Fujise, Y. 2000b. Daily and seasonal food consumption by the western North Pacific minke whale
Paper SC/F2KJ24 presented to the JARPN review meeting, February 2000 (unpublished). 18pp.
Tamura, T. and Fujise, Y. 2000c. Diurnal change in feeding activity in the western North Pacific minke whale. Paper
SC/F2KJ23 presented to the JARPN review meeting, February 2000 (unpublished). 16pp.
Tamura, T. and Fujise, Y. 2002a. Food habit of common minke whales based on JARPN II. Apendix 4, pp 47-63. In:
Government of Japan (Fujise, Y., Kawahara, S., Pastene, L.A. and Hatanaka, H. Eds.) Report of 2000 and 2001
feasibility study of the Japanese Whale Research Program under Special Permit in the western North Pacific-Phase II(JARPN II). Paper SC/54/O17 submitted to the 54th IWC Scientific Committee Meeting (Available from the IWC
Secretariat).
Tamura, T and Fujise, Y. 2002b. Daily and seasonal prey consumption by common minke whale and Bryde’s whale in
the western North Pacific. Appendix 4. pp 85-96. In: Government of Japan (Fujise, Y., Kawahara, S., Pastene, L.A.
and Hatanaka, H. eds.), Report of 2000 and 2001 feasibility study of the Japanese Whale Research Program underSpecial Permit in the western North Pacific-Phase II (JARPN II). Paper SC/54/O17 submitted to the 54th IWC
Scientific Committee Meeting (Available from the IWC Secretariat).
Yoshida, H., Kato, H., Kishiro, T. Iwasaki, T., Miyashita, T., Ryono, T., Tabata, S., Sakakibara, M., Saino, S., Hara, T.,
Hayashi, T., Tomizawa, Y., Tamai, K., Okamoto, R., Fukuoka, M., Watanabe, H., Tsunekawa, M. and Kawahara, S.
2004. Report of the coastal survey on common minke whales off Sanriku coast, northeast Japan: the Japanese Whale
Rsearch Program under Special Permit in the western North Pacific-Phase II (JARPN II) in 2003 (Part II) – Coastal
component. Paper SC/56/O14 submitted to the 56th IWC Scientific Committee Meeting, 31pp.

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Table 1. Sample size of common minke whale off Sanriku region.
Year

Month Number

2003

April
May

Empty

Broken

0
0

2
1

49
1

Table 2. Diet composition (RW: %) in the stomach contents of common minke whales off Sanriku region.
Month
April

Year
2003

N
47

Sand lance
70.7

Krill
29.3

Anchovy<0.1

Table 3. Sex and maturity composition of common minke whales off Sanriku region.
N

%

13

26.0

Immature female

20

40.0

Mature male
Mature female

8
9

16.0
18.0

Month

Sex and maturity

April-May Immature maleTable 4. Estimated field metabolism and daily consumption during feeding period of common minke whales.

Sex and maturity

Body

Field

Daily

weightmetabolism

consumption(kg)(KJ/day)(Feeding period: kg)

Immature male

2,500

395,000

120.1

Immature female

2,600

410,800

125.0

Mature male

4,800

600,000

182.5

Mature female

5,900

737,500

244.3

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Table 5. Seasonal consumption by common minke whales off Sanriku region from April to May.
A. Japanese sand lance (>10cm)
Abundance of common minke whale

Consumption(Individuals)(tons)

574

Abundance estimate

3,885

191

Lower level of 95%CI

1,293

1,653

Upper level of 95%CI

11,187

B. KrillAbundance of common minke whale

Consumption(Individuals)(tons)

574

Abundance estimate

1,610

191

Lower level of 95%CI

536

1,653

Upper level of 95%CI

4,636

Table 6. Fish catches of the Japanese sand lance (>10cm) and Euphausia pacifica in Sendai Bay from February to May.
A. Japanese sand lance (>10cm)

B. Euphausia pacifica

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200m

1,000m

50n.miles
500m

Fig1. Research area off the Sanriku, northeast Japan.

Fig. 2. Length distribution (S.L.) of Japanese sand lance in the stomachs of common minke whales.

8Fig.3: Sighting positions and stomach contents of common minke whales sampled in JARPNII 2003 (Fishing ground ofJapanese sand lance (>10cm) shows). Area of rough sand sediment redraws using the data from Kobayashi
et al. 1991 ()

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