SC/F16/JR17

Updated prey consumption by common minke whales andinteraction with fisheries in coastal areas of the Pacific side ofJapan
TSUTOMU TAMURA1, TOSHIYA KISHIRO2, HIDEYOSHI YOSHIDA2, KENJI KONISHI1, GENTA YASUNAGA1, TAKEHARUBANDO1, MITSUHIRO SAEKI3, KEIICHI ONODERA3, MASAKI MITSUHASHI4, YUUHO YAMASHITA5, TETSUICHIRO
FUNAMOTO5 AND HIDEHIRO KATO6
1

Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan.
National Research Institute of Far Seas Fisheries, 5-7-1, Shizuoka, 424-8633, Japan.
3
Miyagi Prefecture Fisheries Technology Institute, 97-6 Sodenohama Watanoha, Ishinomaki, Miyagi 986-2135, Japan
4
Kushiro Fisheries Research Institute, Fisheries Research Department, Hokkaido Research Organization, 2-6, Hamacho, Kushiro, Hokkaido 085-0024, Japan
5
Hokkaido National Fisheries Research Institute, 116 Katsurakoi, Kushiro, Hokkaido 085-0802, Japan
6
Tokyo University of Marine Science and Technology, Faculty of Marine Science, 4-5-7, Konan, Minato-ku, Tokyo,108-8477, Japan
Contact e-mail: tamura@cetacean.jp
2

ABSTRACTThe stomach contents of common minke whales (Balaenoptera acutorostrata), sampled off Sanriku from April to May and Kushiro region
from September to October by the Japanese Whale Research Program under Special Permit in the western North Pacific (JARPNII) werecollected and examined. The main purpose of this study was to estimate the amount of fish resources consumed by the common minke
whales, accounting for some uncertainties. Prey species of whales were identified by examining their stomach contents, and the amount of
prey consumed in the research area was estimated by using information on prey consumption per capita and the numbers of whales
distributed. In Sanriku region, the dominant prey species consisted of one krill (Euphausia pacifica) and two fishes (Japanese sandlance
and Japanese anchovy). Based on the results obtained by three equations combined and Monte Carlo simulations, the daily prey
consumptions per capita of common minke whales were 98kg and 106kg for immature male and female; and 166kg and 223kg for mature
male and female, respectively. The CVs was around 0.3. The seasonal consumption of total prey by common minke whales were 4,234
tons, 1,822 tons and 850 tons in 2005, 2006 and 2012 seasons, respectively. The CVs was around 0.2. The seasonal consumption ofJapanese sandlance were 3,709 tons, 1,522 tons and 656 tons in 2005, 2006 and 2012 seasons, respectively. It corresponded to 30-40% of
the fisheries catch on this fish resource in two years before the tsunami. In the Kushiro region, the daily prey consumptions per capita ofcommon minke whales were 82kg and 81kg for immature male and female; and 116kg and 155kg for mature male and female,respectively. The CVs was around 0.2. The seasonal consumptions of total preys by common minke whales were in the range 782-3,469
tons during the period 2002-2012. The CVs were in the range 0.2-0.3. The seasonal consumptions of Pacific saury and walleye pollock
were 0-843 tons and 85-1,546 tons, respectively. It corresponded to approximately 2-3% of the fisheries catch on these resources. Theseestimates on prey consumption will be useful as input data in ecosystem models.
KEYWORDS: COMMON MINKE WHALE; SANRIKU; KUSHIRO; 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 distributed mainly in the Sea of Japan - Yellow Sea - East China Sea (J stock)and the other 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 abroad variety of prey species with flexible feeding habits. According to previous reports, they consumed several preyspecies such as pelagic schooling fish and zooplankton (Kasamatsu and Hata, 1985; Kasamatsu and Tanaka, 1992;
Tamura et al., 1998, Tamura and Fujise, 2002a).
The results of the Japanese Whale Research Program under Special Permit in the Western North Pacific (JARPN) andJARPNII feasibility study showed that common minke whales fed on various prey species such as Pacific krill
Euphausia pacifica, Japanese anchovy Engraulis japonicus, Pacific saury Cololabis saira, walleye pollock Gadus
chalcogrammus, and Japanese common squid Todarodes pacificus, and the main prey species changed seasonally andgeographically. For example, they feed on Japanese anchovy in May/June and Pacific saury in July/August (Tamura
and Fujise, 2000a, 2002b). The estimated prey consumption by common minke whales was comparable to that of thecommercial fisheries (Tamura and Fujise, 2000b, 2002c), indicating the some extend interaction between common
minke whales and fisheries may occur in the coastal area from previous research results.

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In order to cover the geographical and seasonal gaps of JARPN and JARPNII feasibility study, sampling of common
minke whales in the coastal area using small type whaling catcher boats was planned in 2002 (Government of Japan,
2002).
The purpose of this study is to estimate the amount of fish resources consumed by the common minke whale off the
Pacific coast of Sanriku and Kushiro, accounting for some uncertainties, and to evaluate the feeding impact by common
minke whales on some fisheries resources. The study is based on JARPNII data and samples, and information fromcommercial fisheries.

MATERIALS AND METHODS
Research region, year, season and sample size
Sanriku region
The sampling area was within the 30 n.miles (maximum 50 n.miles) from the Ayukawa port (Figure 1). The researches
were conducted in April and May since 2003 excluding 2004 and 2011. The sample size for the minke whale in the
Sanriku component started with 50 animals in 2003. After 2005, the sample size changed to 60 animals to be taken in
every spring (April and May). These surveys were described in detail by Kishiro et al. (2009a, 2016 (SC/F16/JR3)).The
actual sampling number of whales between 2003 and 2013 is shown in Table 1.
Kushiro region
The study area was comprised north of 41°N and between longitude 143°E (Cape Erimo) and 146°E. The sampling area
was within the 30 n.miles (maximum 50 n.miles) from the Kushiro port (Figure 1). The researches were conducted in
September and October since 2002 excluding 2003. The sample size for the minke whale in the Kushiro component
started with 50 animals in 2002. After 2004, the sample size changed to 60 animals to be taken in every autumn(September and October). These surveys were described in detail by Kishiro et al. (2009a, 2016 (SC/F16/JR3)). The
actual sampling number of whales between 2002 and 2013 is shown in Table 1.

Sampling and treatment of stomach contents from minke whales
Baleen whales have four chambered stomach system (Hosokawa and Kamiya, 1971; Olsen et al., 1994). The stomach
contents remain in the forestomach (1st. stomach) and fundus (2nd. stomach).
The stomach contents were removed from each compartments and weighed to the nearest 0.1kg at the land station. Then,contents were weighed to the nearest 0.1kg. A sub-sample (1-5kg) of stomach contents was removed and frozen and/or
fixed with 10% formalin water for later analyses. The stomach contents were transferred to a system consisting of threesieves (20mm, 5mm and 1mm), which were applied in the Norwegian scientific research to filter off liquid from the restof the material (Haug et al., 1995). The sub-sample (3-4kg) included all undigested fish skulls, free otoliths and squid
beaks, which were kept frozen for later analyses in the laboratory.

Data analyses
Biological data
An estimate of the daily prey consumption requires the use of some additional biological and morphometric data. Body
length of the whales was measured to the nearest 1cm from the tip of the upper jaw to the deepest part of the fluke notch
in a straight line. Body weight was measured using large weighing machine to the nearest 50kg. Energy requirements
and feeding habit are different for sexual maturity classes; therefore, estimations of the daily prey consumption in thisstudy took into consideration information on sexual maturity. Sexual maturity of each whale was defined by testis
weight and ovaries observation.
Prey species identification and stomach contents weight
In the laboratory prey species in the sub-samples were identified to the lowest taxonomic level as possible. Undigested
preys were identified using morphological characteristic, based on different sources: copepods (Brodskii, 1950),
euphausiacea (Baker et al., 1990), squids (Kubodera and Furuhashi, 1987) and fish (Masuda et al., 1988; Chihara amd
Masuda, 1997). The otoliths and jaw plate were used to identify the fish with advanced stage of digestion (Morrow,
1979; Ohe, 1984; Kubodera and Furuhashi, 1987; Arai, 1993).
When undigested fish and squid were found, fork length, mantle length and the weights were measured to the nearest
1mm and 1g, respectively. This data were used for restoring their stomach contents with advanced stage of digestion.

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The total number of each fish and squid species in the sub-sample were calculated by adding to the number of
undigested fish or squid, undigested skulls and half the total number of free otoliths. The total weight of each preyspecies in the sub-sample was estimated by multiplying the average weight of fresh specimens by the number ofindividuals. The total number and weight of each prey species in the stomach contents were estimated by using thefigures obtained from the sub-sample and the total weight of stomach contents.
Prey composition (W %) in each region and year
In order to simplify the comparison of feeding indices, prey species were divided as follows: Pacific krill, sandlance(Ammodytes personatus), Japanese anchovy, Japanese sardine (Sardinops melanostictus), Pacific saury, walleye pollock(Gadus chalcogrammus, formerly Theragra chalcogramma), mackerels (Scomber japonicus, S. australasicus), Japanesecommon squid and other fishes (Japanese pomfret (Brama japonica), Salmonidae).
The relative prey composition (%) in weight of each prey species (RW) in each month was calculated as follows:
RW i = (Wi / Wall) × 100
W i = the weight of contents containing prey group i
Wall = the total weight of contents analyzed.

Estimation of daily and seasonal prey consumption in each whale species
Daily prey consumption
The amount of prey consumption consumed by common minke whales is estimated using theoretical energy
requirement calculations. The uncertainties associated to the relevant parameters were treated by Monte Carlosimulations.
The daily prey consumption (Dkg) in each sexual maturity class was estimated from the standard metabolic rate (SMRkJ)and energy deposit according to the following equations:
Dkg =(SMRkJ + EDkJ) / (EKJ * AE)(1)-1

Where Dkg is daily prey consumption (kg day ), SMRkJ is the standard metabolic rate (kJ day-1), EDKJ is Energy
deposition (kJ day-1), EkJ is the caloric value of prey species (kJ kg-1), and AE is Assimilation efficiency (%). The detailsof these items are described as follows:

SMR (STANDARD METABOLIC RATE, ALLOMETRIC RELATIONSHIPS)The uncertainty associated to several components involved in estimating the amounts and types of prey consumed bywhales was assisted by a review by Leaper and Lavigne (2007) and Tamura et al. (2009). They considered that theappropriate consumption estimates is between the high end of Equation 1 and the low end of Equation 2 (see below).
The estimate of consumption by Equation 3 was considered by the authors at the upper range of these reasonable values.
Furthermore, Equation 4 is used by PICES for estimating prey consumption of marine mammals (Hunt et al., 2000).
Equation 1: BMR = 0.42 M0.67 (Innes et al., 1986)
0.524

Equation 2: SMR = 2,529.2 M

0.783

Equation 3: SMR = 863.6M(2)(Boyd, 2002)(3)(Sigurjónsson and Víkingsson, 1997)

Equation 3-1: SMR = 690.36M0.783 (Sigurjónsson and Víkingsson, 1997)
0.75

Equation 4: SMR = 803.71M(Perez et al, 1990)

(4)
(5)
(6)

-1

SMR is the daily prey consumption (expressed by KJ day ) and M is body mass in kg. It should be noted here that theestimates from Equation 1 depend only on the body weight data (expressed in kg). The estimates from Equations 2, 3
and 4 require body weight data (expressed in kg) and energy content of prey (expressed in KJ kg-1). Equation 3.1
excluded an AE value of 80% from Equation 3. In this study, three equations (Equations 2, 3-1 and 4) were used in thesensitivity analysis with 10,000 Monte Carlo simulations using the electronic software package (Oracle ® Crystal Ball:
Release 11.1.2.3.). The details of these parameters are described as follows:
The mean caloric values of main prey species (krill, Japanese sandlance, Japanese anchovy, Japanese sardine, Pacificsaury, mackerels, walleye pollock and Japanese common squid) were measured using bomb caloric meter (Table 2).
These samples were obtained from the stomach contents of whales. The energy contents consumed by whales were
calculated based on their prey composition in each region. Prey composition (Weight of %) of whales sampled were
calculated in each region (Table 3). The energy contents consumed by whales were calculated based on their preycomposition and energy contents of prey species in each region (Table 3). The distribution assumed a triangular
distribution with minimum, maximum and average values.
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Although an Assimilation Efficiency (AE) of 0.8 (80%) is commonly assumed, this will clearly vary with prey condition,
size and species. The range of assimilation efficiency was assumed between 0.75 (75%) and 0.85 (85%), and used
randomly in the sensitivity analysis. The distribution assumed a uniform distribution between 0.75 and 0.85.
Many baleen whales are generally known to migrate between the feeding ground in high latitudinal waters in summer
and the breeding ground in low latitudinal waters in winter. There is some uncertainty in this parameter because theratio of high feeding season and low feeding season (r) and the proportion (P) of the energy intake per year during highfeeding season are assumed without actual data. For example, Lockyer (1981) indicated that around 83% of the annual
energy intake in Southern Hemisphere balaenopterid species is ingested during the summer season. If the number ofdays of high feeding season (HD) was 120 and the rest of the days were considered low feeding season (LD), r become
0.10. Leaper and Lavigne (2007) estimated the r to be from 0.34 (Antarctic minke whales) to 0.62 (North Atlantic
minke whales) based on other literatures.

The r was calculated as following:r = (365(1-P)) / (365-HD))/ (365P/HD)(7)

P is the proportion of amount during high feeding season per annual energy intake assumed.
The daily prey consumption of high feeding season was assumed to be the feeding index of high feeding season (Hindex). If the HD was 150days and the proportion of amount during high feeding season per annual energy intake
assumed 80% (0.8), H index was 1.95. HF is the feeding index as a multiplicative factor greater than one. The H index
was calculated as following:
H index = 365P / HD

(8)

The range of H index was assumed between 1.42 and 2.74 and used randomly in the sensitivity analysis (Table 4). The
distribution assumed a triangular distribution with minimum, maximum and average values (1.95).
Based on this assumption, the daily and seasonal prey consumption of high feeding season was calculated using
Equations 2, 3-1, 4 and H index.
SMR of high feeding season = H index * SMR(9)The body mass (M) of each sex and reproductive status of whales
The body mass data (M) were obtained directly by using the large electronic weighing system (track scale system) in
JARPNII. With regard to the measurement of body weight, little uncertainty is assumed. The average body mass isshown in Table 5.
The composition of maturity stages of whales sampled is also shown in Table 5. Males of minke whales were defined as
sexually mature by testis weight (larger side) of more than 290g (Bando et al., unpublished data). Female were defined
as sexually mature by the occurrence of at least one corpus luteum or albicans in their ovaries. These criteria arepractical ones and confirmed biologically (Bando et al, per com.).
The number of common minke whales distributed in Sanriku and Kushiro region
The number of whales distributed in each region and year was estimated by Hakamada et al. (2009) and Hakamada andMatsuoka (2016: SC/F16/JR11) (Table 6). The number of whales distributed in each sex, reproductive status in eachregion and year were calculated using Tables 5 and 6.
Prey species abundance and fisheries catch information
In Sanriku region, the prey survey was conducted since 2003 excluding 2004 and 2011. In Kushiro region, the preysurvey was conducted between 2004 and 2007. The details of the results were described in each cruise reports (Bando etal, 2008, 2011; Goto et al., 2007; Kishiro et al., 2003, 2005, 2006, 2008, 2010, 2012, 2014; Yasunaga et al., 2009, 2010,2012, 2013, 2014; Yoshida et al., 2004, 2006, 2007, 2009a, 2011, 2013, 2015).
The information on abundance and occurrence of prey species in Kushiro region is summarised in appendix 3, based on
the information from the Fisheries Research Agency of Japan (FRA), and Kushiro Fisheries Research Institute.
Fisheries catch information in Sanriku region is shown in Table 7 and Figure 2, and annual trend of the index ofJapanese sandlance abundance is summarised in Appendix 2. This information was based on the data from Miyagi
Prefecture Fisheries Technology Institute.
Fisheries catch information of Japanese sardine, mackerels, Pacific saury and walleye pollock in Kushiro are shown in
Table 7 and Figure 2, based on the data from the Marine Net Hokkaido constructed by the Hokkaido Research
Organization, Fisheries Research Department.

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RESULTS
Diversity of prey species
Sanriku region
A total of three main preys, including one species of euphausiids, two of fishes were identified in 486 stomachs ofminke whales (Table 8).
Kushiro region
A total of seven main preys, including one species of euphausiids, one of squid and five of fishes were identified in 589
stomachs of minke whales (Table 8).

Feeding habit of common minke whales
Sanriku region
Table 3 shows the prey composition (W %) of common minke whales sampled in each year. The dominant prey was
sandlance, it did not change since 2003 (Figure 3).
Kushiro region
Table 3 shows the prey composition (W %) of common minke whales sampled in each year. The dominant preychanged from Japanese anchovy in 2002-2011 to Japanese sardine in 2012-2013. In Kushiro region, long term
information for prey composition was obtained from the past commercial whaling, and reported by Kasamatsu andTanaka (1992). Figure 3 shows this information together with the results of JARPN and JARPNII surveys. Until 1976,
the dominant pelagic prey species of common minke whales was Chub mackerel. After that, the dominant prey species
were switched from Chub mackerel to Japanese sardine in 1977, from Japanese sardine to Pacific saury in 1996, andfrom Pacific saury to Japanese sardine and mackerels in 2012.

The size distribution of main prey species consumed by minke whales
Sanriku region
The size distributions of Japanese sandlance in the stomach of common minke whales, and in the environment, in eachsurvey year are shown in Figure 4. Common minke whale feed on both of juvenile and matured sandlance. The size
difference of sandlance consumed by the common minke whale in Sanriku region seems to depend on the size ofsandlance distributed in the area. It seems that the common minke whales have not prey size selectivity.
Kushiro region
The size distributions of walleye pollock found in immature whale stomachs and in the environment were similar,
showing a clear mode between 34 and 52cm in fork length (Figure 5). Sizes of Pacific saury in both stomachs of mature
whales and the environment mainly ranged from 28 to 31cm in knob length. However, immature whales fed mainly on
Pacific saury of from 25 to 28cm in knob length, which was smaller than the main size of Pacific saury found in thestomachs of mature whales and in the environment (Figure 5). Japanese anchovy mainly ranged in size from 11 to 14cm
in scale length in the stomachs of immature and mature whales, and in the environment (Figure 5).

The daily prey consumption estimates per capita of each sex and reproductive status in three equations combinedmodel
The daily prey consumption estimates per capita of each sex and reproductive status in three equations combined model
were shown in Table 9 and Appendix 1.
Sanriku region
The daily prey consumption per capita was 98kg and 106kg for immature males and females, respectively; and 166kg
and 223kg for mature males and females, respectively. The CVs was around 0.3.
Kushiro region
The daily prey consumption per capita was 82kg and 81kg for immature males and females, respectively; and 116kg
and 155kg for mature males and females, respectively. The CVs was around 0.2.

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The seasonal prey consumption by common minke whales in each region and season
The seasonal prey consumption estimates by common minke whales in each region and season were shown in Table 10
and Appendix 1.
Sanriku region
The seasonal prey consumptions in 2005, 2006 and 2012 were 4,234 tons, 1,822 tons and 850 tons, respectively. The
CVs was around 0.2 (Table 10).
Kushiro region
The seasonal prey consumptions during 2002 to 2012 were between 782 and 3,469 tons. The CVs were in the range 0.20.3 (Table 10).

DISCUSSION
Different in feeding habits between Sanriku and Kushiro
Sanriku region
The dominant prey species of common minke whales sampled off Sanriku region in April and May were Japanese
sandlance, followed by Japanese anchovy and Pacific krill. This result was similar to that of previous report (Kasamatsu
and Tanaka, 1992; Yoshida et al., 2009b). Kasamatsu and Tanaka (1992) examined the yearly change of prey species ofcommon minke whale off Sanriku during 1948 to 1987 based on commercial whaling data. 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, Japanese sandlance and iwashi (Japanese sardine and/or Japanese anchovy,
but main was Japanese sardine). They pointed out that the yearly change of Japanese sardine occupancy in stomach
contents were similar to the yearly trend of fisheries catch of Japanese sardine in this area.
Some sandlance 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 (< 50m depth) (Kobayashi et al., 1991). So,
Japanese sandlance as prey of common minke whale off Sanriku region is presumably available only from February toJune through a year.
Kushiro region
Kasamatsu and Tanaka (1992) examined the yearly change of prey species of common minke whale off Kushiro region
during 1948 to 1987 based on commercial whaling data. Commercial whaling was made from April to October withpeaks from July to September. After 1982, two peaks were observed in July and September. The dominant prey species
were krill, iwashi (Japanese sardine and/or Japanese anchovy, but main was Japanese sardine), chub mackerel, walleye
pollock, Pacific saury and Japanese common squid. They pointed out that the yearly change of Japanese sardine in thestomach contents were similar to the yearly trend of abundance of Japanese sardine in this area. The JARPNII revealed
that the variety of the prey species in recent 2000th was almost same as previous report, and the similar change in thedominant prey species was occurred again in recent years (Kishiro et al, 2009b, Tamura et al, 2016: SC/F16/JR24).
The similarity in the yearly trends of abundance and occurrence of prey species in the waters and density of the whales
migrated in the waters suggested that common minke whale was thought to be migrated into the Kushiro waters
according to the amount and availability of the pelagic preys resources, and such kind of migration was thought to be
triggered the direct conflict between the whales and local fisheries through the overlapping of local fishing grounds andwhale feeding grounds (see appendix 3).
Prey consumption of common minke whales in Sanriku and Kushiro
The daily prey consumption per capita and seasonal prey consumption by common minke whales in each region could
be estimated with appropriate level of statistical precision (CVs were in the range 0.2-0.3) at this stage. The uncertainty
derived from the use of different energetic models seems to be appropriately captured in the Monte Carlo simulation.
The feeding impact by common minke whales on fisheries resources
Sanriku region
Sandlance is targeted for commercially and it is important one in Sanriku region during spring. It is mainly caught bystick held dip net fisheries. The catches of sandlance in Sanriku region were several thousand tons since 2002. However,in 2011 and 2012, the fisheries efforts decreased by the effect of a tsunami in 2011 (Table 7).

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Based on results of the sand lance consumption by common minke whales and the degree of overlap between fisheries
ground of Japanese sandlance and sighting position of common minke whales, it is conceivable that the possibility withdirect interaction between common minke whale and Japanese sandlance fisheries occurs. The fisheries season ofJapanese sandlance is from February to May, and common minke whales also feed on Japanese sandlance in the latter
half of the season. Furthermore, sighting positions of common minke whales were overlapped with fisheries ground ofJapanese sandlance. With the decrease of the sandlance resources, the density of common minke whales showed adecreasing trend (Figure 6). Catch data of important commercial fish were provided from the Miyagi Prefecture
Fisheries Technology Institute. Some minke whales attack and feed on the school of sandlance when fishermen
attracted fishes around boat, causing dispersion of the schools of Japanese sandlance. The catch quota and season ofJapanese sandlance off the Sanriku region (around the Sendai Bay) is regulated by the fisheries conference in order toprotect the resources of Japanese sandlance and price control.
The consumptions of sandlance by common minke whales in 2005, 2006 and 2012 were estimated in 3,709 tons, 1,522
tons and 656 tons, respectively. It was equivalent to 48.7% and 5.4% of the 2005 and 2006 sandlance resources basedon echosounder data (Murase et al., 2009; Wada et al, 2016: SC/F16/JR19). It was also equivalent to 42.7% and 28.7%of the 2005 and 2006 fisheries catch (Tables 7 and 10).
Therefore, consumption by common minke whales should be taken into account for fishery management of Japanese
sandlance off Sanriku region. The ecosystem model (e.g. Okamura et al., 2009, Kitakado et al., 2016 (SC/F16/JR29))
will make clear the interaction between common minke whales and sand lance in next step.
Kushiro region
The change of prey species of common minke whales were corresponded with a change of the dominant species taken
by commercial fisheries in the same area (Figures 2 and 3). Annual trend of a total catch of fishes (Japanese sardine,anchovy, mackerels, Pacific saury, and walleye pollock in Table 7) by the fisheries, and the density of common minke
whales are shown in Figure 6. Catch trend was similar to those of whale’s density, and there were no negative
relationships such as increasing density with decreasing catch or vice versa.
As the case in Pacific saury, Tamura and Fujise (2002c) noted that most of the common minke whales sightings in subarea 7W occurred close to fishing grounds of Pacific saury in JARPN (Figure 7). The fisheries season of Pacific saury isfrom August to October, and common minke whales feed on Pacific saury in the same season. Some fishermen indicate
the fishing operation have interfered by common minke whales as same as the case in Japanese sandlance in Sanriku
region.
The prey consumptions of economically important Pacific saury and walleye pollock by common minke whales during
2002 to 2012 were calculated as 0–843 tons and 85–1,546 tons, respectively. It was equivalent to 0.0-1.75% and 0.132.83%, respectively (Tables 7 and 10). The biomass of prey species in this region could not be estimated, because oflogistical reasons. Though, it is difficult to evaluate the interaction between whales and fisheries, quantitatively at thisstage.
The fisheries catch is made by several kinds of fisheries in Kushiro region. For instance, Pacific saury is mainly caught
by stick held dip net fisheries, walleye pollock is mainly caught by otter trawl fisheries and Danish seine fisheries,
Japanese anchovy, Japanese sardine, and mackerels are caught by purse seine fisheries, and Japanese common squid iscaught by quid jigging fisheries (Appendix 3).
Modelling works
The ecosystem model is one of the useful methods to examine the effect of the consumption to the fish resources andthose fisheries. In Sanriku region, some modelling works could progress (Okamura et al., 2009, Kitakado et al., 2016
(SC/F16/JR29)). To improve the ecosystem model in Sanriku region will make clear the interaction between common
minke whales and sandlance in future. On the other hand, in Kushiro region, the actual and interesting circumstances of
the complexity could be revealed such as a lot of kinds of prey species, decadal change of the prey compositions, andmany type of fisheries engaged. These complexities preclude applying the simple model analyses. For fisheries
management in Kushiro region, model works will be considered the structure of ecosystem and application in the future.
It is needed the data of the number of common minke whales distributed and the biomass of prey species yearly basis,
especially for evaluating the interaction between whales and fisheries in detail.

ACKNOWLEDGEMENTS
We would like to thank all captains, crews and researchers, who were involved in coastal component of JARPNII
surveys. Our sincere thanks to Dr. Luis A. Pastene of the Institute of Cetacean Research (ICR) for the valuablesuggestions and useful comments on this paper. Catch data of sand lance ware provided from Dr. H. Nagashima of the
Miyagi Prefecture Fisheries Research and Dr. S. Izumi of the Development Centre and Fukushima Prefecture Fisheries
Research Centre. We would like to thanks them for their cooperation.

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SC/66a/SP7 submitted to the 66ath IWC Scientific Committee, 13pp.

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SC/F16/JR17
Table 1. Numbers of whales sampled in each region.
Sanriku

Kushiro

Year

Year

NumberNumber

2003

50

2002

50

2005

60

2004

59

2006

60

2005

60

2007

57

2006

35

2008

60

2007

50

2009

60

2008

50

2010

45

2009

59

2012

60

2010

60

2013

34

2011

60

486

2012

48

2013

58

Total

Total

589

Table 2. Results of caloric value of dominant prey species in Sanriku and Kushiro region.
SanrikuSpecies

Analyzed

Energy contents (KJ/kg)

NumberAvegage

S.D

Krill (Euphausia pacifica )

2

4,117

1,685

Sand lance

4

4,663

2,098

Japanese anchovy

2

6,942

942

KushiroSpecies

Analyzed

Energy contents (KJ/kg)

NumberAvegage

S.D

Krill (Euphausia pacifica )

2

3,449

325

Japanese anchovy

3

6,762

735

Japanese sardine

1

5,272

-

Pacific saury

212,343

1,124

Mackerels

1

13,836-

Walleye pollock

5

6,106

568

Japanese common squid

1

6,611

-

11

SC/F16/JR17

Table 3. Prey composition (%) of common minke whales and average energy values of stomach contents sampled off
Sanriku and Kushiro region
SanrikuYear

NumeberPrey composition (%)

(N)
2003

Krill

Sand lance

Anchovy

50
Immature male

12

72.6

Immature female

9

Mature male

20

Mature female

9

2005

27.4

0.0

64.3

35.7

0.0

0.0

100.0

0.0

56.4

43.6

0.0

77.1

19.0

60
Immature male

15

3.9

Immature female

23

0.0

94.4

5.6

Mature male

8

0.0

100.0

0.0

Mature female

14

17.9

82.1

0.0

2006

60
Immature male

14

0.0

52.9

47.1

Immature female

31

0.0

85.4

14.6

Mature male

12

0.0

94.2

5.8

Mature female

3

0.0

100.0

0.0

2007

57
Immature male

11

0.0

67.2

32.8

Immature female

29

0.0

52.9

47.1

Mature male

10

0.0

44.9

55.1

Mature female

7

0.0

82.0

18.0

2008

60
Immature male

19

0.0

100.0

0.0

Immature female

28

0.0

100.0

0.0

Mature male

4

0.0

100.0

0.0

Mature female

9

3.6

96.4

0.0

96.4

0.0

2009

60
Immature male

26

3.6

Immature female

32

7.4

88.6

4.0

Mature male

1

0.0

100.0

0.0

Mature female

1

0.0

100.0

0.0

0.8

2010

45
Immature male

12

33.0

66.2

Immature female

26

20.1

79.9

0.0

Mature male

6

0.0

45.2

54.8

Mature female

1

0.0

100.0

0.0

2012

60
Immature male

27

6.8

82.3

10.9

Immature female

28

24.4

75.1

0.5

Mature male

2

0.0

0.0

100.0

Mature female

3

0.0

100.0

0.0

0.0

2013

34
Immature male

15

0.0

100.0

Immature female

17

0.0

98.0

2.0

Mature male

2

0.0

0.0

100.0

Mature female

012Energy contents(KJ/kg)
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
100.0
0.0
100.0
100.0
100.0
0.0

SC/F16/JR17
Table 3. Continued.
KushiroYear
2002

Numeber

Average depth

(N)

(m)

Prey composition (%)
Krill

Anchovy

Sardine

Saury

Energy contents

Mackerel

Pollock

Squid(KJ/kg)50
Immature male

16

187

48.5

23.1

0.0

0.2

0.0

28.3

0.0

4,979

Immature female

11

197

7.1

35.0

0.0

0.0

0.0

57.8

0.0

6,147

Mature male

16

379

0.0

19.2

0.0

42.1

0.0

1.9

36.9

9,041

Mature female

7

159

0.0

4.3

0.0

0.0

0.0

19.5

76.2

6,519

2004

59
Immature male

15

832

10.1

65.0

0.0

19.1

0.0

5.8

0.0

7,457

Immature female

10

479

0.0

63.0

0.0

16.5

0.0

20.5

0.0

7,546

Mature male

32

934

0.0

49.7

0.0

50.3

0.0

0.0

0.0

9,570

Mature female

2

417

0.0

58.9

0.0

41.1

0.0

0.0

0.0

9,057

2005

59
Immature male

15

291

13.9

6.5

0.0

0.0

0.0

79.6

0.0

5,780

Immature female

14

329

69.6

9.6

0.0

0.0

0.0

20.8

0.0

4,319

Mature male

29

549

9.8

8.6

0.0

1.2

0.0

68.3

12.1

6,035

Mature female

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

Unidentified

1

503

0.0

0.0

0.0

0.0

0.0

100.0

0.0

6,106

2006

35
Immature male

12

409

2.4

88.6

0.0

0.0

0.0

9.0

0.0

6,624

Immature female

8

271

0.0

22.6

0.0

0.0

0.0

77.4

0.0

6,254

Mature male

11

579

0.0

50.0

0.0

28.2

0.0

0.0

21.8

8,302

Mature female

2

647

0.0

100.0

0.0

0.0

0.0

0.0

0.0

6,762

Unidentified

2

669

0.0

100.0

0.0

0.0

0.0

0.0

0.0

6,762

6,186

2007

50
Immature male

17

296

10.4

40.0

0.0

1.5

0.0

48.1

0.0

Immature female

17

243

1.4

56.2

0.0

0.0

0.0

42.5

0.0

6,439

Mature male

14

423

3.1

35.2

0.0

61.7

0.0

0.0

0.0

10,104

Mature female

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

Unidentified

2

231

0.0

3.5

0.0

0.0

0.0

0.0

96.5

6,616

2008

50
Immature male

32

374

8.2

37.0

0.0

0.0

0.0

54.8

0.0

6,131

Immature female

15

287

0.0

11.1

0.0

0.0

0.0

88.9

0.0

6,179

Mature male

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

Mature female

3

568

0.0

2.8

0.0

0.0

0.0

0.0

97.2

6,615

2009

59
Immature male

24

334

45.3

12.3

0.0

0.0

0.0

42.4

0.0

4,983

Immature female

23

273

18.9

15.8

0.0

0.0

0.0

65.3

0.0

5,708

Mature male

12

560

54.1

45.9

0.0

0.0

0.0

0.0

0.0

4,971

Mature female

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

2010

60
Immature male

32

211

0.0

13.9

0.0

0.0

0.0

86.1

0.0

6,197

Immature female

19

196

0.0

20.6

0.0

0.0

0.0

79.4

0.0

6,241

Mature male

9

374

0.0

62.3

0.0

0.0

0.0

37.7

0.0

6,515

Mature female

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

2011

60
Immature male

19

225

8.4

32.9

0.0

0.0

0.0

58.7

0.0

6,098

Immature female

22

173

0.0

31.5

0.0

0.0

0.0

68.5

0.0

6,313

Mature male

16

238

14.7

47.6

0.0

0.0

0.0

37.7

0.0

6,028

Mature female

3

90

0.0

100.0

0.0

0.0

0.0

0.0

0.0

6,762

2012

48
Immature male

21

479

0.0

0.0

27.2

0.0

1.6

71.2

0.0

6,000

Immature female

17

343

0.0

0.2

41.7

0.0

16.0

42.0

0.0

6,999

Mature male

6

712

52.3

0.0

6.8

0.0

1.8

27.7

11.3

4,859

Mature female

4

441

0.0

0.1

3.6

0.0

0.0

0.0

96.4

6,563

2013

58
Immature male

41

527

11.1

0.0

37.7

0.0

3.8

47.4

0.0

5,792

Immature female

10

405

0.0

0.0

14.7

0.0

6.1

79.2

0.0

6,458

Mature male

0

-

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

Mature female

7

432

0.0

0.0

45.0

0.0

0.0

17.5

37.5

5,920

13

SC/F16/JR17

Table 4. The values of the H index for the estimation of daily consumption.

H index

P (Percentage of annual prey consumption)(Residence days)

70

80

90

120

2.13

2.43

2.74

150

1.70

1.95

2.19

180

1.42

1.62

1.83

Table 5. The average of body mass (kg) and the sexual maturity composition (%) of whales sampled.
Sanriku
Average body mass (kg)Year

Sexual maturity composition (%)

IM

IF

MM

MF

2005

2,439

2,333

3,820

5,362

2003

50

26.0

40.0

16.0

18.0

2006

1,894

2,169

3,971

5,920

2005

60

25.0

38.3

13.3

23.3

2012

1,520

1,690

4,441

4,854

2006

60

25.4

50.8

18.6

5.1

2007

57

19.6

51.8

16.1

12.5

2008

60

32.2

49.2

6.8

11.9

2009

60

43.3

53.3

1.7

1.7

2010

45

26.7

57.8

13.3

2.2

2012

60

45.0

46.7

3.3

5.0

2013

34

44.1

50.0

5.9

0.0

Average

54

31.9

48.7

10.6

8.9

Year

Number

IM

IF

MM

MF

Kushiro
Average body mass (kg)Year

Sexual maturity composition (%)

IM

IF

MM

MF

2002

1,765

1,955

4,607

6,266

2002

50

32.0

22.0

32.0

14.0

2004

2,543

2,142

4,939

5,341

2004

59

25.4

16.9

54.2

3.4

2005

1,961

1,949

4,651

-

2005

60

25.4

25.4

49.2

0.0

2006

2,298

2,020

5,109

6,520

2006

35

34.3

22.9

37.1

5.7

2007

2,134

1,927

4,977

-

2007

50

36.0

34.0

30.0

0.0

2012

2,337

1,936

5,036

6,793

2008

50

44.0

30.0

20.0

6.0

2009

59

40.7

39.0

20.3

0.0

2010

60

26.7

36.7

31.7

5.0

2011

60

31.7

36.7

26.7

5.0

2012

48

43.8

35.4

12.5

8.3

2013

58

24.1

17.2

46.6

12.1

Average

54

33.1

28.7

32.8

5.4

Year

14

Number

IM

IF

MM

MF

SC/F16/JR17
Table 6. Estimated numbers of whales distributed in each region (Hakamada et al. (2009; 2016 (SC/F16/JR 11)).
SanrikuYear
2004

Estimates
260

CV

95% CI LL

95% CI UL

0.517

100

675

2005

401

0.300

226

713

2006

216

0.311

2012

124

0.371

119
61

392
251

2003-2013

252

0.385

121

521

KushiroYear
2002

Estimates
551

CV

95% CI LL

2003

888

0.406

2004

338

0.352

2005

290

0.350

2006

221

0.351

2007

130

2012

433

2002-2013

407

0.350

95% CI UL

283
413

1,073
1,909

173
149

660
565

0.553

113
47

431
358

0.542

160

1,171

0.415

187

889

15

SC/F16/JR17

Table 7. Fisheries catch data of major prey species off the Pacific coast of Sanriku and Kushiro (Iwashi* include
Japanese anchovy and Japanese sardine).
Sanriku
Year
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013

Kushiro(tons)
Krill
Sand lance
20,585.0
2,668.6
22,385.0
6,677.4
20,941.0
6,908.0
20,278.0
8,679.3
19,094.0
5,294.8
19,011.0
1,789.0
18,629.0
9,191.2
14,602.0
2,253.9
17,693.0
3,909.5
0.0
166.6
7,155.0
478.9
13,025.0
2,823.0

Year
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013

16

Iwashi* Mackerels
1.0
76,858.0
1,475.0
42,854.0
6.0
48,071.0
0.0
96,740.0
0.0 113,637.0
3.0 197,525.0
0.0 116,956.0
0.0 170,930.0
0.0 174,175.0
292.0 235,283.0
509.0 202,497.0
237,875.0
21,456.0
374,555.0
20,111.0
328,812.0
21,515.0
423,068.0
413.0
371,811.0
6.0
494,038.0
7.0
620,185.0
28.0
801,655.0
193.0
979,206.0
377.0
925,592.0
23.0
920,175.0
25.0
1,063,054.0
44.0
1,031,377.0
18.0
793,349.0
18.0
875,483.0
2.0
607,406.0
0.0
123,452.0
0.0
3,092.0
1,654.0
783.0
0.0
1.0
0.0
0.0
0.0
0.0
18.0
53,465.0
0.0
25,621.0
1.0
0.0
0.0
53.0
0.0
55,235.0
0.0
69,251.0
0.085,851.0
0.0
4,639.0
3,364.0
50,410.0
1,688.0
508.0
794.0
1,362.0
0.0
17,254.0
0.0
36,345.0
260.0
9,115.0
40.0
11,788.0
2,416.0
27,073.0
2,696.0

Saury
7,946.0
26,035.0
19,702.0
14,972.0
9,599.0
22,670.0
46,977.0
19,006.0
89,773.0
19,532.0
54,584.0
15,098.0
29,058.0
66,677.0
59,500.0
24,195.0
21,549.0
24,717.0
32,789.0
31,402.0
44,393.0
27,106.0
27,908.0
42,967.0
31,953.0
50,896.0
30,246.0
33,669.0
40,950.0
31,462.0
60,066.0
41,682.0
53,281.0
24,017.0
25,219.0
43,724.0
59,743.0
55,594.0
59,984.0
48,403.0
58,528.0
61,895.0
69,629.0
64,115.0
60,885.0
35,149.0
58,824.0
49,550.030,529.0(tons)
Pollock
62,817.0
85,826.0
109,013.0
205,407.0
301,145.0
272,363.0
310,803.0
380,384.0
557,645.0
577,889.0
488,950.0
498,019.0
387,189.0
199,281.0
163,657.0
167,430.0
220,112.0
191,952.0
181,116.0
195,467.0
177,238.0
194,290.0
384,597.0
387,709.0
251,348.0
146,888.0
181,205.0
123,562.0
138,201.0
165,937.0
113,671.0
103,400.0
99,860.0
116,140.0
103,305.0
118,729.0
61,720.0
52,524.0
75,041.0
65,186.0
54,628.0
56,582.0
51,088.0
65,086.0
56,718.0
64,710.070,700.0
59,061.0
66,317.0

SC/F16/JR17

Table 8. Prey species of common minke whales sampled off Sanriku and Kushiro region.
SanrikuSpecies
Main prey
Krill
PiscesEuphausia pacifica
Engraulis japonicus
Ammodytes personatus

Japanese anchovy
Sand lance

Theragra chalcogramma
Sardinops melanostictus

Walleye pollocke
Japanese sardine

Miner prey
PiscesKushiroSpecies
Main prey
Krill

Euphausia pacifica

PiscesEngraulis japonicus

Japanese anchovy

Sardinops melanostictus

Japanese sardine

Cololabis saira

Pacific saury

Scomber japonicus

Chub mackerel

Gadus chalcogrammus

Walleye pollocke(formerly Theragra chalcogramma )SquidsTodarodes pacificus

Japanese common squid

Paralepis atlantica

Duckbill barracudina

Brama japonica

Japanese pomfretOncorhynchus gorbuscha

Pink salmon

O. keta

Chum salmon

Miner prey
Pisces17

SC/F16/JR17

Table 9. Daily prey consumption estimates (kg) per capita of each sex and reproductive status.
Sanriku
Maturity stage

Consumption
98

CV
0.25

56

95% CI UL
149Immature female

106

0.26

60

162

Mature male

166

0.26

Mature female

223

0.30

91
112

249
356

Consumption
82

CV
0.19

Immature female

81

Mature male
Mature female

Immature male

95% CI LL

KushiroMaturity stage
Immature male

95% CI LL
53

95% CI UL
115

0.19

53

112

116

0.22

155

0.23

69
91

168
225

18

SC/F16/JR17
Table 10. Prey consumption by common minke whales sampled off Sanriku and Kushiro region.
SanrikuYear
2005

Numbers ofConsumption
whales(tons)
401
4,234

CV

95% CI LL

95% CI UL

0.16

3,066

5,767

2006

216

1,822

0.18

1,293

2,588

2012

124

850

0.20

599

1,325

Average

247

2,302

0.18

1,653

3,227

Year

Prey consumption (tons)
Krill

Sandlance Anchovy

2005

302

3,709

223

2006

-

1,522

300

2012

118

656

76

Average

210

1,962

199

19

SC/F16/JR17

Table 10. Continued.
KushiroYear

Numbers ofwhalesConsumption(tons)

CV

95% CI LL

95% CI UL

2002

551

3,469

0.17

2,747

5,436

2003

888

-

-

-

-

2004

338

2,182

0.23

1,436

3,446

2005

290

2,601

0.23

1,569

3,757

2006

221

1,596

0.19

1,128

2,370

2007

130

782

0.25

568

1,515

2012

433

3,264

0.22

2,408

5,838

Average

407

2,316

0.21

1,643

3,727

Prey consumption (tons)
Year
Krill

Anchovy Sardine

Saury

M ackerels

Pollock

Squid

2002

488

665

0

460

0

791

1,066

2003

-

-

-

-

-

-

-

2004

49

1,204

0

843

0

85

0

2005

627

220

0

18

0

1,546

190

2006

11

971

0

198

0

264

153

2007

41

338

0

170

0

233

0

2012

409

2

724

0

154

1,421

554

Average

271

567

121

282

26

723

327

20

SC/F16/JR17
Sanriku

KushiroFigure 1. Research area off Sanriku and Kushiro regions.

21

SC/F16/JR17(A) Sanriku(B) Kushiro

Figure 2. Catch information of fisheries off the Pacific coast of Sanriku (A) and Kushiro (B) (from Miyagi Prefecture
Fisheries Technology Institute, Hokkaido Research Organization, Fisheries Research Department, Marine Net
Hokkaido and Kishiro per com.)

22

SC/F16/JR17(A) Sanriku(B) Kushiro

Figure 3. Yearly change of dominant prey species of common minke whales sampled off Sanriku (A) and Kushiro (B)(from Kasamatsu and Tanaka, 1992; JARPN data set (1996); in this study (since 2000))23SC/F16/JR17

Sanriku(a) Sand lance
In environment

In whale stomach contents

2005 survey

2006 survey

2007 survey

Figure 4. The size distribution of sand lance in the stomach contents of common minke whales and in the environment
in Sanriku region

24SC/F16/JR17

In environment

In whale stomach contents

2008 survey

2009 survey

2010 survey

Figure 4. Continued.

25

SC/F16/JR17

In environment

In whale stomach contents

2012 survey

2013 survey

Figure 4. Continued.

26

SC/F16/JR17

KushiroFigure 5. The size distribution of walleye pollock, Pacific saury, Japanese anchovy in the stomach contents of common
minke whales and in the environment in Kushiro region.

27

SC/F16/JR17(A) Sanriku
Sand lance(B) Kushiro
Japanese anchovy, sardine, Pacific saury, mackerels, and walleye pollock

Figure 6. The relationship of minke whale’s D.I. (no. of ind. / 100n. miles searched) and (A) Sanriku, sand lance catch(tons) in Sanriku region (B) Kushiro, total catch (tons) of Japanese anchovy, Japanese sardine, Pacific saury, mackerels,
and walleye pollock in Kushiro region

28

SC/F16/JR17

Hokkaido
KushiroFigure 7. Relationship between minke whale sightings (dot) and the fishing ground (shaded portion) of Pacific saury inthe sub-area 7W during 22 July and 8 September 1996. The information of the fishing grounds was obtained from thetelex Nos. 27 - 33 on fishing grounds off the Pacific coast of eastern Hokkaido by the Fishing Information Service
Center in Japan (Redrawn from Fujise et al. 1997).

29

SC/F16/JR17

Appendix 1. The results of simulations
Daily prey consumption (kg) consumed by whales per capita

Sanriku

Immature male
Forecast: Sanriku-IM
Statistic

Forecast values

Trials

10,000Base Case

98

Mean

95

Median
Mode

92
'---

Standard Deviation 24
Variance576

Skewness

0.6592

Kurtosis

3.55

Coeff. of Variation
0.2532
Minimum

37

Maximum

212

Mean Std. Error

0

Immature female
Forecast: Sanriku-IF
Statistic

Forecast values

Trials

10,000Base Case

106

Mean

102

Median
Mode

99
'---

Standard Deviation 26
Variance684

Skewness

0.6612

Kurtosis

3.52

Coeff. of Variation
0.2565
Minimum

44

Maximum

228

Mean Std. Error0

Mature male
Forecast: Sanriku-MM
Statistic

Forecast values

Trials

10,000Base Case

166

Mean

159

Median
Mode

155
'---

Standard Deviation 41
Variance

1,661

Skewness

0.5418

Kurtosis

3.24

Coeff. of Variation
0.2571Minimum

59

Maximum

339

Mean Std. Error0

Mature female
Forecast: Sanriku-MF
Statistic

Forecast values

Trials

10,000Base Case

223

Mean

212

Median
Mode

203
'---

Standard Deviation 63
Variance

3,976

Skewness

0.7399

Kurtosis

3.64

Coeff. of Variation
0.2977
Minimum

70

Maximum

527

Mean Std. Error

30

1SC/F16/JR17

Kushiro

Immature male
Forecast: Kushiro-IM
Statistic

Forecast values

Trials

10,000Base Case

82

Mean

81

Median
Mode

80
'---

Standard Deviation 16
Variance

247

Skewness

0.3475

Kurtosis

2.9

Coeff. of Variation
0.1942
Minimum

41

Maximum

146

Mean Std. Error

0

Immature female
Forecast: Kushiro-IF
Statistic

Forecast values

Trials

10,000Base Case

81

Mean

80

Median
Mode

79
'---

Standard Deviation 15
Variance237

Skewness

0.3306

Kurtosis

2.86

Coeff. of Variation
0.1923
Minimum

37

Maximum

139

Mean Std. Error0

Mature male
Forecast: Kushiro-MM
Statistic

Forecast values

Trials

10,000Base Case

116

Mean

115

Median
Mode

113
'---

Standard Deviation 25
Variance645

Skewness

0.3276

Kurtosis

2.93

Coeff. of Variation
0.2216
Minimum

50

Maximum

207

Mean Std. Error0

Mature female
Forecast: Kushiro-MF
Statistic

Forecast values

Trials

10,000Base Case

155

Mean

152

Median
Mode

151
'---

Standard Deviation 35
Variance

1,196

Skewness0.3006

Kurtosis

2.84

Coeff. of Variation
0.2268Minimum

64

Maximum

281

Mean Std. Error

310SC/F16/JR17

Seasonal prey consumption by minke whales in Sanriku region (From April to May)
2005 season
Forecast: Prey consumption 2005
Statistic

Forecast values

Trials

10,000Base Case

4,234

Mean

4,308

Median
Mode

4,261
'---

Standard Deviation696
Variance

484,903

Skewness

0.3386

Kurtosis

3.11

Coeff. of Variation
0.1617
Minimum

2,132

Maximum

7,320

Mean Std. Error

72006 season
Forecast: Prey consumption 2006
Statistic

Forecast values

Trials

10,000Base Case

1,822

Mean

1,879

Median
Mode

1,854
'---

Standard Deviation331
Variance

109,479

Skewness

0.3865

Kurtosis

3.08

Coeff. of Variation
0.176
Minimum

911

Maximum

3,174

Mean Std. Error

32012 season
Forecast: Prey consumption 2012
Statistic

Forecast values

Trials

10,000Base Case

850

Mean

926

Median
Mode

911
'---

Standard Deviation189
Variance

35,798Skewness

0.4035

Kurtosis

3.11

Coeff. of Variation
0.2043
Minimum

383

Maximum

1,835

Mean Std. Error

32

2

SC/F16/JR17

Seasonal prey consumption by minke whales in Kushiro region (From September to October)2002 season
Forecast: Prey consumption 2002
Statistic

Forecast values

Trials

10,000Base Case

3,469

Mean

3,981

Median
Mode

3,941
'---

Standard Deviation688
Variance

473,510Skewness

0.3575

Kurtosis

3.15

Coeff. of Variation
0.1728Minimum

1,905

Maximum

7,170

Mean Std. Error

72004 season
Forecast: Prey consumption 2004
Statistic

Forecast values

Trials

10,000Base Case

2,182

Mean

2,293

Median
Mode

2,235
'---

Standard Deviation517
Variance

266,860

Skewness

0.5279

Kurtosis

3.15

Coeff. of Variation
0.2253
Minimum

993

Maximum

4,401

Mean Std. Error

52005 season
Forecast: Prey consumption 2005
Statistic

Forecast values

Trials

10,000Base Case

2,601

Mean

2,486

Median
Mode

2,426
'---

Standard Deviation559
Variance

312,968

Skewness

0.6307

Kurtosis

3.51

Coeff. of Variation
0.225
Minimum

928

Maximum

5,098

Mean Std. Error

33

6

SC/F16/JR17


2006 season
Forecast: Prey consumption 2006
Statistic

Forecast values

Trials

10,000Base Case

1,596

Mean

1,687

Median
Mode

1,660
'---

Standard Deviation322
Variance

103,933

Skewness

0.4082

Kurtosis

3.08

Coeff. of Variation
0.1911Minimum

814

Maximum

3,131

Mean Std. Error

32007 season
Forecast: Prey consumption 2007
Statistic

Forecast values

Trials

10,000Base Case

782

Mean

991

Median
Mode

973
'---

Standard Deviation244
Variance

59,488Skewness

0.3934

Kurtosis

2.99

Coeff. of Variation
0.2462
Minimum

339

Maximum

1,965

Mean Std. Error

22012 season
Forecast: Prey consumption 2012
Statistic

Forecast values

Trials

10,000Base Case

3,264

Mean

3,918

Median
Mode

3,847
'---

Standard Deviation880
Variance

774,894

Skewness

0.4672

Kurtosis

3.15

Coeff. of Variation
0.2247
Minimum

1,343

Maximum

7,505

Mean Std. Error

34

9SC/F16/JR17

Appendix 2.

Information of prey species in the coastal waters off Sanriku
MITSUHIRO SAEKI AND KEIICHI ONODERA
Miyagi Prefecture Fisheries Technology Institute, 97-6 Sodenohama, Watanoha, Ishinomaki, Miyagi 986-2135, Japan
Japanese sand lance
R/V Takuyo Maru (120GT), Miyagi Prefecture Fisheries Technology InstituteResearch period: every year in January
Research area: Sendai Bay
Methods: Bongo net by Takuyo Maru (120GT)
Index: CPUE (no. of individuals per m3)

Figure 1. Occurrence of sand lance (juvenile) in January around Sendai Bay (ind./m 3).

35

SC/F16/JR17

Year
Figure 2. Yearly change of Density Index (ind./m3) of sand lance in the estivation period around Sendai Bay.

36

SC/F16/JR17

Figure 3. Catch information of Sand lance (Juvenile (kounago) and adult (meroudo)) in Sendai Bay.

37

SC/F16/JR17

Appendix 3.

Information on distributed abundance of prey species taken
by common minke whales off Kushiro, with regard to themigration and feeding habit of the whales in the coastal waters
off Kushiro
TOSHIYA KISHIRO1, HIDEYOSHI YOSHIDA1, MASAKI MITSUHASHI2, YUUHO YAMASHITA3 AND TETSUICHIRO FUNAMOTO31

National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Yokohama, Kanagawa, 236-8648, Japan
Kushiro Fisheries Research Institute, Fisheries Research Department, Hokkaido Research Organization, 2-6, Hamacho, Kushiro, Hokkaido 085-0024, Japan
3
Hokkaido National Fisheries Research Institute, 116 Katsurakoi, Kushiro, Hokkaido 085-0802, Japan
2

ABSTRACTThis paper summarized the information on distributed abundance of five fish stocks (Japanese anchovy, Japanese sardine, Pacific saury,mackerels, and walleye pollock) and one squid stock (Japanese common squid) dominantly taken by common minke whales off Kushiro,
during the research periods of the JARPNII coastal component off Kushiro in 2002 and afterwards, and made some discussion about
migration, feeding habit, and feeding impact of common minke whales off Kushiro. The annual trends of the stock abundance andoccurrence of prey species in the Kushiro waters were apparently different among the species, i.e. during the survey periods, Japanese
anchovy and Pacific saury were decreased and Japanese sardine and mackerels were increased. In walleye pollock and Japanese common
squid, no apparent increasing and/or decreasing trends were observed. The yearly changes in the occurrence of common minke whales feedon pelagic prey species were similar to those in the abundance and occurrence of the corresponded species, and apparent change of thedominant prey species from Japanese anchovy to Japanese sardine with linked to the change of the availability in the environment for eachprey species were observed. These results and yearly change in the migration of the whales into the waters suggested that common minke
whales migrated into the Kushiro waters according to the amount and availability of the pelagic preys resources in the waters regardless of
the respective species (Japanese anchovy, sardine, Pacific saury and mackerels). This kind of migration manner of the whales was thought
to be triggered the direct conflict between the whales and local fisheries through the overlapping of local fishing grounds and whale
feeding grounds. The ratio of the estimated consumption by the whales migrated in the Kushiro waters to total abundance of the prey was
about 0.01 to 0.1%, but these values were only parts of the total consumption by the whale population to the prey resources. To examine
the final effects on the prey species populations from predation by the whales, including the information on the other areas and otherseason to cover the whole populations, and population dynamics studies through developing the ecosystem models will be needed.

INTRODUCTION
The first JARPNII coastal component off Kushiro was carried out in 2002, and the surveys have been conducted inevery year since 2004 (Kishiro et al., 2016: SC/F16/JR3). Main objective of this component is the JARPNII objective 1:
feeding ecology and ecosystem studies, and especially related to direct and/or indirect interaction between the whales
and local fisheries (and targeted fish resources). In this regards, the dedicated prey species surveys by echo soundertrawler survey vessels was conducted in the Kushiro waters from 2002 to 2007 (Watanabe et al., 2009a), and thoseresults were submitted to the the first Expert Workshop to review the JARPNII in 2009 (Watanabe et al., 2009b). But,
the survey was logistically restricted by the vessel availability, ability of the research equipment, and human resources,and difficult to continue in long term periods. Due to these problem, dedicated prey species surveys in the Kushiro
waters was suspended in 2008. However, in the coastal waters off Kushiro, fish resources have been independently anddiligently studied and surveyed by the dedicated fisheries research organizations outside of the JARPNII for theirtargeted fish resources and fisheries management. The information from these studies and surveys are valuable anduseful to grasp the prey species environment in the coastal waters off Kushiro.
In cooperation with those research institutes, this paper summarised information of stocks and migration index of fivefish and one squid species dominantly taken by common minke whales off Kushiro during the research periods of the
JARPNII coastal component off Kushiro in 2002 and afterwards, and made some discussion about migration, feeding
habit, and feeding impact of common minke whales off Kushiro.

MATERIALS AND METHODS
Prey species taken by common minke whales off Kushiro
Based on the stomach contents analyses of the coastal component off Kushiro, following species was identified as
dominant prey for common minke whales in the Kushiro waters (Tamura et al., 2016: SC/F16/JR17): krill (Euphausia
pacifica), Japanese anchovy (Engraulis japonicus), Japanese sardine (Sardinops melanostictus), Pacific saury(Cololabis saira), walleye pollock (Gadus chalcogrammus, formerly Theragra chalcogramma), chub mackerel
38

SC/F16/JR17(Scomber japonicus), and Japanese common squid (Todarodes pacificus). All of those species except for krill are
targeted by commercial fisheries off Kushiro, and studied by the dedicated research institutes. Thus, this paper
summarised information for above five fish and one squid resources.
Information of the stocks and abundance of prey species
Stocks structures and abundance of fish and squid resources around Japan have been well studied by the several
institutes of the Fisheries Research Agency of Japan (FRA) by cooperation with local fisheries research Institutes andFisheries Agency of Japan, and published for the stock assessment and coastal fisheries managements (Fisheries
Agency and Fisheries Research Agency of Japan, 2015). Basically, abundance of each stock was estimated by thecohort analyses with fisheries data and survey data. Among them, information of the stocks which was distributed andtargeted by the whales in the Kushiro waters were extracted and summarised.
Migration index of prey species into the Kushiro waters
To examine the annual trends of the prey species migration into the Kushiro waters, results of the several surveys in thesouth eastern coastal waters of Hokkaido (including Kushiro waters) conducted by the Kushiro Fisheries ResearchInstitute, Fisheries Research Department, Hokkaido Research Organization, and the Hokkaido National Fisheries
Research Institute, the Fisheries Research Agency of Japan were used. Basically, catch per unit efforts data (CPUE)
obtained from the dedicated surveys or commercial fisheries were used as an index of migration into the waters. Detailof each survey is described in each section below.
Information of common minke whales
Density index (Number of primary sightings per 100 nautical miles searched) obtained from the whale sampling
surveys in the coastal component off Kushiro was used to examine the annual trends of the whales into the waters.
Detail of the whale sampling surveys was described in Kishiro et al., 2016: SC/F16/JR3). Number of animals in thewaters estimated by dedicated sighting surveys (Hakamada et al., 2016: SC/F16/JR11) were also used as a reference
information. The occurrence of the prey species in the whale stomach was calculated annually as the ratio of the numberof the whales dominantly feed on corresponded species for the total number of the whales caught in corresponded years,
and the estimated amount of consumption by the whales was obtained from Tamura, et al. (2016: SC/F16/JR17).
RESULTS
Stocks and abundance of prey species targeted by common minke whales off Kushiro
Japanese anchovy: Pacific stock (Kamimura et al., 2015)
Individuals migrated to the coastal waters off Kushiro is classified as the Pacific stock, and distributed along the pacificside of Japan to the offshore waters in the western North Pacific. Main commercial fisheries taking this stock in thesouth eastern coastal waters of Hokkaido (including Kushiro waters) are purse seine fisheries. Estimated abundance of
this stock was quite high (around 1,400 thousand tons) in 2003 but gradually decreased, and about 600 thousand tons inrecent years.

Figure 1. Distribution and annual trend of the estimated abundance of Japanese anchovy, Pacific stock.
Japanese sardine: Pacific stock (Kawabata et al., 2015a)
Individuals migrated to the coastal waters off Kushiro is classified as the Pacific stock, and distributed along the pacificside of Japan to the offshore waters in the western North Pacific. As same as Japanese anchovy, main commercial

39

SC/F16/JR17

fisheries taking this stock are purse seine fisheries. Estimated abundance of this stock was low (below 200 thousandtons) but rapidly increased in 2010 and afterwards, and about 800 thousand tons in 2014.

Figure 2. Distribution and annual trend of the estimated abundance of Japanese sardine, Pacific stock.
Pacific saury: Northwest Pacific stock (Nakagami et al., 2015)
Individuals migrated to the coastal waters off Kushiro is classified as the Northwest Pacific stock, and widelydistributed around Japan, including East China Sea, Sea of Japan, Okhotsk Sea, and western North Pacific. Main
commercial fisheries taking this stock are stick held dip net fisheries. Estimated abundance of this stock was around
5,000 thousand tons in 2003, but gradually decreased, and below 3,000 thousand tons in recent years.

Figure 3. Distribution and annual trend of the estimated abundance of Pacific saury, Northwest Pacific stock.
Mackerels: Pacific stock (Kawabata et al., 2015b; 2015c)
Mackerels distributed around Japan includes two species; Scomber japonicus, and S. australasicus. Both species
migrated to the coastal waters off Kushiro are classified as the Pacific stock, and distributed along the pacific side ofJapan to the offshore waters in the western North Pacific. Main commercial fisheries taking these stocks are purse seine
fisheries. Estimated abundance of these stocks were low (around 500 thousand tons) in 2002 but gradually increased toover 2,500 thousand tons in 2014.

S. japonicas

S. australasicus

Figure 4. Distribution and annual trend of the estimated abundance of Mackerels, Pacific stock.

40

SC/F16/JR17

Walleye pollock: Japanese Pacific stock (Funamoto et al., 2015)
Individuals migrated to the coastal waters off Kushiro is classified as the Japanese Pacific stock. Distribution of thisstock is narrow and restricted in the coastal waters off the pacific side of northern Japan. Main commercial fisheries
taking this stock in the south eastern coastal waters of Hokkaido (including Kushiro waters) are offshore otter trawl
fisheries and Danish seine fisheries. Estimated abundance of this stock is around 1,100 thousand tons and relatively
stable compared with other fish stocks, though some fluctuations are observed.

Figure 5. Distribution and annual trend of the estimated abundance of walleye pollock, Japanese Pacific stock.
Japanese common squid: winter spawning stock (Yamashita et al., 2015)
Japanese common squids distributed around Japan are divided into two stocks; autumn spawning stock and winterspawning stock, and individuals migrated to the coastal waters off Kushiro is classified as the winter spawning stock,which spawns in the East China Sea in December to March, and migrated in around Japan. Main commercial fisheries
taking this stock are quid jigging fisheries. Estimated abundance of this stock is fluctuated from 600 to 1,200 thousand
tons, and no apparent increasing and/or decreasing trends are observed.

Figure 6. Distribution and annual trend of the estimated abundance of Japanese common squid: winter spawning stock.

Migration of common minke whales into the Kushiro waters
Figure 7 shows yearly change in density index (number of primary sightings per 100 nautical miles searched) ofcommon minke whales obtained from the whale sampling vessels in the coastal component off Kushiro (September to
October), and Figure 8 shows the number of common minke whales estimated by the dedicated whale sighting surveys
in the south eastern coastal waters of Hokkaido, including Kushiro waters (Hakamada et al., 2016: SC/F16/JR11) in thesame season. Research areas for sampling and sighting surveys is shown in Figure 9.

41

SC/F16/JR17

Figure 7. Yearly change in DI (no. of ind./100 n. miles searched)

Figure 8. Estimated abundance by sighting surveys by whale sampling surveys (Hakamada et al., 2016: SC/F16/JR11).

Figure 9. Research areas for whale sampling, and dedicated sighting surveys.

As shown in Figure 9, common minke whale sampling was made in the waters within a 30 nautical miles from theKushiro port, and the DI in Figure 7 indicates index of the migration into the narrow coastal areas off Kushiro.
Although the estimated number of animals in Figure 8 was obtained from wider areas than the whale sampling surveys,
both the DI and the estimated number of animals were high in 2002 to 2003, decreased through 2004 to 2006 or 2007,
and then increased in 2007 and afterwards. These results suggested that the migration of common minke whales into thecoastal waters off Kushiro in autumn season was frequently occurred in early 2000 th, decreased in mid-2000th, andincreased again in recent years.

Migration of prey species into the Kushiro waters, and occurrence of the prey in the whale stomach
The migration of common minke whales into the Kushiro waters might be affected by the environmental change in theprey in those waters. Thus, the annual trends of the prey species migration into the Kushiro waters in almost same
season were examined. These data were obtained from the independent dedicated fisheries surveys as follows:

42

SC/F16/JR17

Japanese anchovy, sardine, Pacific saury, and Mackerels
Information was obtained from the experimental Drifting Gill Nets surveys, conducted by the Kushiro Fisheries
Research Institute, Fisheries Research Department, Hokkaido Research Organization.
Research vessel: R/V Hokushin Maru (216GT)
Research period: every year in September (9 to 10 days)
Research area: 41°30’N-43°00’N, 143°00E-146°00’E
Methods: Experimental fishing by drifting gill nets
(5 to 8 research points)
Index: CPUE (no. of individuals per one research)
Japanese common squid
Information was obtained from the experimental Squid Jigging surveys, conducted by the Kushiro Fisheries ResearchInstitute, Fisheries Research Department, Hokkaido Research Organization.
Research vessel: R/V Hokushin Maru (216GT)
Research period: every year in late August (5 to 8 days)
Research area: along the coast line
Methods: Experimental fishing by squid fishing machine(8 to 10 research points)
Index: CPUE (no. of individuals per one hour)

Walleye pollock
Information was obtained from the trawl fisheries catch and effort data, analysed by the Fisheries Management Division,
Hokkaido National Fisheries Research Institute, Fisheries Research Agency.
Source: commercial otter trawl fisheries
Area: South eastern coastal waters of Hokkaido (Dohto area)
Statistics period: September and OctoberIndex: CPUE (catch (ton) per trawl cast)

The annual trends on the occurrence (CPUE) of Japanese anchovy and Japanese sardine in the Kushiro waters, with thefrequency of the whales dominantly feed on those species are shown in Figure 10. The same figures for Pacific saury
and Mackerels are shown in Figure 11. The yearly changes in the occurrence of these pelagic fish species in the Kushiro
waters were similar to those in the estimated abundance of each fish stock (see above section), and also similar to thosein the occurrence of the whales feed on corresponded prey species, though some time lags were observed. These results
suggested that common minke whales migrated into the Kushiro waters in autumn season utilized these pelagic fish
resources according to the availability and amount of the prey in the respective environment of the waters. These dataalso indicated apparent change of dominant prey species from Japanese anchovy to Japanese sardine, linked to thechange of the availability for each prey species.

43SC/F16/JR17

Figure 10. Annual trends on the CPUEs (upper) of Japanese anchovy and sardine, and the frequency of the common
minke whales dominantly feed on corresponded species (lower) in the Kushiro waters.

Figure 11. Annual trends on the CPUEs (upper) of Pacific saury and Mackerels, and the frequency of the common
minke whales dominantly feed on corresponded species (lower) in the Kushiro waters.

Figure 12 shows the annual trends on the occurrence (CPUE) of walleye pollock and Japanese common squid in theKushiro waters, with the frequency of the whales dominantly feed on those species. As well as the pelagic fish species,
the yearly changes in the occurrence of walleye pollock in environment were similar to those in the whales feed on thisspecies. This suggested that common minke whales also utilized mesopelagic species according to the availability in theenvironment. On the other hand, frequency of the whales feed on Japanese common squids were quite low, and noapparent relationship between the occurrence in environment with occurrence of the whales was observed.

44

SC/F16/JR17

Figure 12. Annual trends on the CPUEs (upper) of walleye pollock and Japanese common squid, and the frequency ofthe common minke whales dominantly feed on corresponded species (lower) in the Kushiro waters.

Feeding impact of common minke whales off Kushiro to abundance of the prey species stocks
Tamura et al. (2016: SC/F16/JR17) estimated consumption of each prey species by common minke whales distributedin the coastal waters off Kushiro in autumn season, based on the individual metabolic rate (energy requirement),
number of animals distributed, and prey species composition in the stomach. Among them, the number of animals was
based on the sighting surveys in the areas covered the south eastern coastal waters of Hokkaido as shown in Fig.9, andprey species composition was based on the results of whale sampling surveys in the waters within a 30 nautical miles
from the Kushiro port. Table 1 shows the respective values of the estimated amount of consumptions with a totalabundance of the corresponded prey species stock. The ratio of consumption to the abundance of stock was 0.0003 to
0.11% in Japanese anchovy, 0.11% in Japanese sardine, 0.0004 to 0.02% in Pacific saury, 0.01% in Mackerels, 0.01 to
0.14% in walleye pollock, and 0.02 to 0.14% in Japanese common squid. These results suggested that the feeding
impact of the whales distributed in the Kushiro waters in autumn season was about 0.01 to 0.1% of the total abundanceof the respective stock, and there was no distinct difference among the prey species.

45

SC/F16/JR17

Table 1. Estimated total abundance of the prey stocks and consumption by common minke whales in the Kushiro
waters.
Japanese anchovyYear

Abundance(tons)

Consumptionin Kushiro
waters (tons)

2002

1,226,000

665

2004

1,125,000

2005

Japanese sardine
Abundance(tons)

Consumptionin Kushiro
waters (tons)

0.05

157,000

0

1,204

0.11

109,000

974,000

220

0.02

2006

929,000

971

2007

815,000

2012

577,000

Abundance(tons)

Consumptionin Kushiro
waters (tons)

0.00

Not available

460

-

0

0.00

3,828,000

843

0.02

87,0000

0.00

4,073,000

180.00040.10

132,000

0

0.00

3,516,000

198

0.01

338

0.04

113,000

0

0.00

2,831,000

170

0.01

2

0.0003665,000724

0.11

1,920,000

00.00

Ratio (%)

Mackerels
Year

Pacific saury
Ratio (%)

Walleye pollock

Abundance(tons)

Consumptionin Kushiro
waters (tons)*

Abundance(tons)

Consumptionin Kushiro
waters (tons)*

2002

551,000

0

0.00

1,121,322

791

2004

1,378,000

00.00

887,771

2005

1,499,000

0

0.00

2006

1,335,000

02007

1,172,000

2012

1,777,000

Ratio (%)

Japanese common squid
Abundance(tons)

Consumptionin Kushiro
waters (tons)*

0.07

777,000

1,066

0.14

85

0.01

883,000

0

0.00

1,087,373

1,546

0.14

833,000

190

0.02

0.00

1,139,077

264

0.02

641,000

153

0.02

0

0.00

1,172,962

233

0.02

1,162,000

0

0.00

154

0.01

1,058,631

1,421

0.13

864,000

554

0.06

Ratio (%)

Ratio (%)

Ratio (%)*: Values of consumption was from Tamura et al. , 2016 (SC/F16/JR17)DISCUSSION
The annul trend of the abundance of prey species stock was apparently different among the species, i.e. Japanese
anchovy and Pacific saury were decreased and Japanese sardine and mackerels were increased. Similar trends wereobserved in the migration index of respective species in the Kushiro waters, and suggested that migration of these
species into the Kushiro waters was reflected by the current of those populations. The oceanographic conditions might
be influenced to the fluctuation of the population and local migration in these species. In a long term viewpoint, theoceanographic decadal oscillation observed in the Pacific Ocean (Okazaki et al., 2016a: SC/F16/JR5) may arouse theregime shift of climate and marine ecosystem change and/or the alternation of the fish species (Schwartzlose et al.,1999), as observed in this study. From a local point of view, yearly variations of the oceanographic conditions in theKushiro waters (Okazaki et al., 2016b: SC/F16/JR6) may affect the migration of prey species into the waters, and suchvariations is thought to be one of the reasons for the time lag of the trends observed between the stock abundance andthe local migration index.
The JARPNII coastal component of Kushiro in 2002 and afterwards revealed that the migration of common minke
whales into the Kushiro waters was also fluctuated, and suggested that the migration of the whales into these waters inautumn season was frequently occurred in early 2000th, decreased in mid-2000th, and increased again in recent years.
From the migration index of respective prey species, the relative abundance of the pelagic prey species in these waters
in the same season was thought to be also high in early 2000th (Japanese anchovy and Pacific saury), decreased in mid2000th, and increased again (Japanese sardine and mackerels) in recent years. These implied that the whales migrated
into the Kushiro waters according to the amount and availability of the pelagic preys regardless of the respective species(at least among Japanese anchovy, sardine, Pacific saury and mackerels) in the waters. In general, common minke
whales are thought to be opportunistic feeders with flexible feeding habit (Tamura et al., 2016: SC/F16/JR17), and thesimilarity on the trends between the occurrence of these pelagic fish species in the waters and the occurrence of thewhales feed on corresponded prey species observed in this study supported this point.
From the viewpoint of the interaction with fisheries, this kind of migration can be triggered the direct conflict between
the whales and local fisheries, because both the whales and fishermen flock around the place where their resources areabundantly distributed, and local feeding areas of the whales are overlapped with local fishing grounds. To resolve these46

SC/F16/JR17

problems, further information on the fisheries such as the methods and tactics of the fishing operations including fishinggears, time of operations, and detailed positions on the fishing grounds will be needed.
In context of the indirect interaction between the whales and fisheries, ratio of the estimated consumption by the whalesin the Kushiro waters to total abundance of the prey was about 0.01 to 0.1%, and feeding impact of the whales in theKushiro waters is not so large to the targeted fish populations. However, these values are only parts of the total
consumption by the whale stock to the prey resources. To examine the final effects on the prey species populations
through the mortality caused by predation, both the whales and prey species should be considered as a population level.
In this regards, including the information on the other areas and other season to cover the whole populations, gathering
the knowledge on distribution gap caused by the difference of seasonal migration between the populations, andpopulation dynamics studies through developing the ecosystem models will be needed.

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