NAMMCO/SC/16/MMFI/11

Prey preferences of common minke (Balaenoptera
acutorostrata), Bryde’s (B. edeni) and sei (B. borealis)
whales in offshore component of JARPNII from 2002 to
2007
HIROTO MURASE1, TSUTOMU TAMURA1, TATSUYA ISODA1, RYOSUKE OKAMOTO2, SHIROH YONEZAKI1, HIKARUWATANABE3, NAOKI TOJO4, RYUICHI MATSUKURA4, KAZUSHI MIYASHITA5, HIROSHI KIWADA1, KOJI MATSUOKA1,SHIGETHOSI NISHIWAKI1, DENZO INAGAKE6, MAKOTO OKAZAKI6, HIROSHI OKAMURA3 YOSHIHIRO FUJISE1 AND
SHIGEYUKI KAWAHARA7
1

The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, JapanTokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan
3
National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 2368648, Japan
4
Graduate School of Environmental Science, Hokkaido University, 3-1-1 Minato-cho, Hakodata, Hokkaido 0418611, Japan.
5
Field Science Center for the Northern Biosphere, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido,
041-8611, Japan
6
National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648,
Japan7
National Research Institute of Far Seas Fisheries, 5-7-1, Orido, Shimizu, Shizuoka, Shizuoka, 424-8633, Japan
2

ABSTRACTPrey preferences of common minke, Bryde’s and sei whales at meso scale were estimated using datafrom the cooperative surveys of cetacean sampling and prey of cetaceans. The surveys were conducted
as a part of the offshore component of JARPNII from 2002 to 2007. This was the first report of prey
preferences of minke, Bryde’s and sei whales in the offshore region of the western North Pacific. Prey
preferences of sei whales have not been reported in any part of world in the past. The preferences were
estimated as input parameters for a minimum realistic type ecosystem model. A prey preference index,
Manly’s α, was used in the analysis. The sum of Manly’s α for all prey species is 1 and prey species
with large values of Manly’s α indicates preference for it. For minke whales, Manly’s α of krill,
Japanese anchovy and Pacific saury were 0.05 (se=0.03), 0.36 (se=0.19) and 0.59 (se=0.17),
respectively. Minke whales showed preference toward pelagic fishes as previously reported. For
Bryde’s whales, Manly’s α of krill and anchovy were 0.05 (se=0.04) and 0.95 (se=0.04), respectively.
For sei whales, Manly’s α of copepods, krill, anchovy and saury were 0.41 (se=0.10), 0.13 (se=0.04),
0.25 (se=0.10) and 0.20 (se=0.08), respectively. Though preys of three baleen whale species overlapped,
Manly’s α suggested their trophic niches were different from each other. Minke and sei whales
coexisted in same survey blocks but their prey utilization patterns were different. For example,
distribution of minke and sei whales was overlapped in block A in 2003. In this block, minke whales
showed preference toward saury while sei whales showed preference toward copepods. Accumulationof prey preference data for long periods provides the basis for appropriate choice of functional response
form which is required by ecosystem models for fisheries management. Continuation of long term
research such as JARPN II is important to develop reliable ecosystem models.

INTRODUCTION
Study on the ecological niche theory is one of the most active fields of ecology (Hirzel et al.,2008). Estimation of prey preference is one of the study methods to define a trophic niche of a
species. Aside from such a pure scientific interest, prey preference plays important role inapplied science. It is one of the key parameters in the ecosystem model developed for a
purpose of fisheries management. The ecosystem approach to fisheries management is widely
accepted concept worldwide and many international organizations require its application(Morishita, 2008). The International Whaling Commission (IWC) unanimously decided tomake the study of interactions between whales and fish stocks matter of priority in 2001

1

NAMMCO/SC/16/MMFI/11(IWC, 2002). The IWC held the Modelling Workshop on Cetacean-Fishery Competition in2002 (IWC, 2004). The Scientific Committee of the IWC (IWC/SC) created working groupon Ecosystem Modelling with recognition of the importance of this matter. In response to therequests from the international community, scientists have developed a wide variety of
ecosystem models (Pláganyi, 2007 for review). Some ecosystem models such as
MULTISPEC (Bogstad et al., 1997) and GADGET (Begley, 2008) require prey preference of
predator as one of key parameters. A mathematical model for functional response of predator(relationship between consumption by predator and prey availability) is key function in otherecosystem models such as Ecopath with Ecosim (EwE) (Christensen et al., 2005). Functional
response required by such models can only be estimated using long term prey preference data.
Prey preference of predators can only be studied to compare species compositions of prey instomachs of predators with species compositions of prey in a field.
The second phase of the Japanese Whale Research Program under Special Permit in
the North Pacific (JARPN II) has been conducted since 2000. The research activity of JARPN
II is legal according to Japanese national regulation and the International Convention for the
Regulation of Whaling (ICRW). The overall goal of JARPN II is to contribute to theconservation and sustainable use of marine living resources including whales in the western
North Pacific, especially within Japan’s EEZ. One of the main objectives of JARPN II isestimation of prey preference of cetaceans. To estimates prey preference of cetaceans,concurrent cetacean sampling and prey surveys have been conducted as a part of JARPN II.
The surveys were conducted as feasibility studies in the first two years (2000 and 2001). Prey
preferences of common minke (Balaenoptera acutorostrata) and Bryde’s (B. edeni) whales
were estimated using data sets collected in the feasibility studies and results were reported to
IWC/SC (Government of Japan, 2002) and published in peer reviewed scientific journal(Murase et al., 2007). Based on the success of feasibility studies, JARPN II was expanded tofull scale in 2002. Sei whale (B. borealis) was added as a target cetacean species in addition
to minke and Bryde’s whales.
There are three spatiotemporal scale to link feeding ecology of cetaceans with
distribution pattern of them and the definitions are follows; at the macro scale, cetaceans
migrate seasonally between feeding and breeding grounds; at the meso scale, cetaceans moveover days and weeks in search of preferred local abundance of food; and at the micro scale,
whales dive and search for food within localised areas (IWC, 2003). In JARPN II, prey
preference of whales is considered as one of the input parameter of ecosystem models not at
individual level but at population level in the feeding area.
It was planned that the results of full scale JARPNII will be review every six years.
First six years period was 2002-2007. In the full scale survey, JARPNII has three components(three regional survey areas) namely off Sanriku, off Kushiro and offshore. In this paper,
results of estimation of prey preferences using data sets obtained by the offshore components
in first six years period were reported. Specifically, prey preferences of minke, Bryde’s andsei whales were estimated as a parameter for minimum realistic type ecosystem models
developed by Kawahara (2009). This was the first report of prey preference of sei whales
worldwide. Although prey preferences of common minke and Bryde’s whales in the western
North Pacific were estimated using data obtained feasibility studies of JARPN II (Murase etal., 2007), areal coverage was limited to the west of 150°E. Prey preferences of common
minke and Bryde’s whales to the east of 150°E were also studied in the full scale survey
where no results had been reported in the past. In this paper, preference is defined as theanimal choosing a resource irrespective of amount of resources.

2

NAMMCO/SC/16/MMFI/11

MATERIALS AND METHODS
Survey area, timing of survey and vessels
The survey area of the cetacean prey surveys in JARPN II offshore component was in thewestern North Pacific (Fig 1). Southern, northern, eastern and western boundaries of thesurvey area were 35°N, boundary of economic exclusive zone (EEZ) claimed by a foreigncountry, 170°E and eastern coast line of Japan, respectively. Continental shelf region of Japan(shallower than 200 m water depth) was not included. The survey area corresponds to Subareas 7, 8 and 9 which are set for the Implementation Simulation Trials of common minke
whale in the North Pacific (IWC, 1994). Although the most of survey area of offshore
component of JARPNII is out of EEZ of Japan, the area is migration corridors for many
pelagic fish such as Japanese anchovy (Engraulis japonicus), Japanese pilchard (Sardinops
melanostictus), Pacific saury (Cololabis saira) and chub mackerel (Scomber japonicus).
Because those pelagic fishes show seasonal migration between inside and outside of Japanese
EEZ, investigation of feeding impact of cetaceans on those species is important. Within thesurvey area, one to three small blocks were set for cooperative whale and prey surveys every
year. Locations and timing of surveys of these small blocks were shown in Table 1 and Fig. 1.
Both whale and prey surveys were conducted simultaneously in the survey blocks so that data
were collected at same spatiotemporal scale. Ideally, the cooperative survey should be
conducted in entire the survey area. However, because availability of fisheries research vessel
for prey survey was limited, small blocks were established within the survey area. Small
blocks were set considering potential influence from the oceanographic conditions, such as
positions of fronts and water masses as well as anticipated distribution pattern of the target
cetacean species so that the defined small blocks could be treated as representations of theentire survey area. The survey blocks were poststratified based on observed in-situ
oceanographic conditions and distribution patterns of target species. The cooperative whale
sampling and prey surveys were conducted from 2002 to 2007 (except 2006). Three sighting
and sampling vessels (SSVs) were engaged in the whale survey consisting of sighting andsampling of whales. Stomach contents of sampled minke, Bryde’s and sei whales were
initially examined on the research base ship, Nisshin-Maru. In addition to those whale survey
vessels, one trawler type fisheries research vessel was engaged in prey surveys every year.
Details of Survey area and timing of prey survey were summarized in Murase et al. (2009).
Concurrent surveys were conducted in daytime from 30 minutes after sunrise to 30 minutes
before sunset. Details of whale surveys were summarized in Tamura et al. (2009(b)).
Oceanographic observation
Oceanographic observation was conducted using CTD and XCTD to examine position ofoceanographic front in each block. Positions of the Subarctic Front (SAF, temperature front
defined by 4°C at 100 m), the boundary of warm side of the cold water (10°C isotherm at 100m (the boundary of cold side is 5°C at 100 m)) and the Kuroshio extension axis (14°C
isotherm at 200 m) were estimated by the ordinal Kriging method using observed data. Area
between the boundary of warm side of the cold water and the Kuroshio extension axis isdefined as the warm water.
Cetacean sighting survey
Distribution patterns of minke, Bryde’s and sei whales were examined by using cetaceansighting data recorded by SSVs. Zigzag tracklines were designed in survey blocks. SSVs
steamed on tracklines at a nominal speed of 10.5 knots. Sighting survey was terminated wheneither Beafout scale was higher than 4 or visibility was less than 2 n.miles. Primary observers
were allocated to the top barrel (3 observers) and the upper bridge. (2 observers). Once
3

NAMMCO/SC/16/MMFI/11

sightings were made, SSVs approached them to confirm species and number of individuals
within a school.
Stomach content analysis
Baleen whales have a four-chambered stomach system. Among them, the stomach contents
remain in the forestomach (1st. stomach) and fundus (2nd. stomach) were used in this study.
Details of stomach contents analysis was described in Tamura et al. (2009(a)).
Biomass estimation of prey species
Stomach contents analysis revealed main preys for minke, Bryde’s and sei whales (Tamura etal., 2009(a)). Minke whales mainly fed on Japanese anchovy and Pacific saury. Bryede’s
whales mainly fed on Japanese anchovy. Sei whales mainly fed on Japanese anchovy,
copepods and krill. Japanese anchovy and Pacific saury were abundant small pelagic fishes in
the Japanese water according to the recent stock assessment report by Government of Japan.
Based on these a priori information, four main prey species of three baleen whales, copepods,
krill, Japanese anchovy and Pacific saury, were considered in this analysis as well as in the
MRM developed by Kawahara (2009). In accordance with this, biomasses of these four
species were estimated in this study. We assumed that feeding of these three baleen whale
species took place upper 150 m water depth given known distribution patterns of preys. Thus,
biomasses of preys were estimated from 0 to 150 m water depth.
Biomass estimation using net data
Biomass of Pacific saury was estimated using a surface trawl developed by Ueno et al. (2004)
because it is distributed near sea surface and can not be detected by an echosounder. The
surface trawl was towed at 0-30 m water depth layer. The trawl was 86.3 m long with a mouth
opening of. 900 m2 and a 6.0 m cod end with a 17.5 x 17.5 mm mesh inner. Floats wereattached to the bridle so that the trawl could be towed at the surface. Towing duration waseither 30 or 60 minutes per haul. The surface trawl was towed at predetermined samplingstations. Surface trawl samples collected by Tohoku National Fisheries Research Institute(TNFRI) in special block A in 2002 and block A in 2003 were also used in the analysis.
TNFRI samples were collected almost same timing of the prey survey. Biomass of Pacificsaury was estimated based on a swept-area method (Mackett, 1973).
Biomass of copepods was estimated either using MOCNESS (Multiple Opening /Closing Net and Environmental Sampling System) or NORPAC (North Pacific standard net).
MOCNESS was used in 2003, 2004 and 2005 while NORPAC was used in the rest of years(2002 and 2007). Biomass of copepods in 0-150 m water depth layer was estimated. The
mouth opening size and mesh size of MOCNESS were 1 m2 and 0.33 mm2, respectively. At
the predetermined station, following depth layers were towed by MOCNESS; 0-20m, 20-40m,
40-60 m, 60-80 m, 80-100 m, 100-150 m, 150-200 m and 200-250 m. The mouth opening andmesh size of NORPAC are 45 cm and 0.35 mm, respectively. NORPAC was towed from150m to surface. Filtered water volumes were recorded by using flow meters except 2002.
Density of copepods was estimated 1 m2 divided by 0.159 m2 (area of mouth opening of
NORPAC). NORPAC samples collected by TNFRI in block A in 2002 were also used in theanalysis. TNFRI samples were collected almost same timing of the prey survey. Details ofsampling methods using trawl, NORPAC and MOCNESS were described in Murase et al.
(2009).

4

NAMMCO/SC/16/MMFI/11

Biomass estimation using echosounder data
Biomasses of Japanese anchovy and krill were estimated by using quantitative echosoudners.
Quantitative echosounders, either Simrad EK500 or EK60, equipped on a trawler type
fisheries research vessel were used to collect acoustic data. Acoustic data were recorded with
38 and 120 kHz transducers. Echosounders were calibrated every year based on the copper
sphere technique (Foote, 1982). Acoustic data were analyzed with the aid of Echoview(Myriax Software Pty. Ltd.) software at the laboratory. Nautical area scattering coefficient (sA,
m2/n.mile2) by species for every 1 km of survey transect over defined depth interval (10-150m) was calculated by following formula;s A = 4πr0218522 ∫rr2 sV dr (1

m2
n.mi 2)where r is depth from the sea surface, r0 = 1m representing the reference range forbackscattering strength. Average area biomass density ( ρ ) for each species was calculated asfollows;
ρ=

sA

σ

w.

W is wet weight of individual. The acoustic cross section (σ) was converted from target
strength (TS) as followed;
σ = 4π 100.1TS

The TS of krill at 38 and 120 kHz was estimated by using the Distorted Wave Born
Approximation (DWBA) model (Tojo et al. 2008):
TS 38kHz = 60.6 log10 (TL) − 177.2
TS120 kHz = 50.7 log10 (TL ) − 150.4

Backscattering from krill can be identified if the difference of mean volume backscatteringstrength between 120 and 38 kHz (ΔMBVS120-38) fells in a specific range (Miyashita et al.,
1997; Kang et al., 2002). ΔMBVS120-38 is equivalent to the difference of TS between 120 and
38 kHz (ΔTS120-38). Length frequency data of krill were sampled by the Isaacs-Kidd Midwater
Trawl (IKMT) in 2002. Ranges of ΔMBVS120-38 for krill in blocks A and B in 2002 were 15.4
– 17.5 and 14.5 – 17.0 dB, respectively. Mean TS120 of krill in blocks A and B in 2002 were 94.6 and 90.3 dB, respectively. Mean wet weights of individual krill correspond to mean TS
were 11.1 and 17.0 mg, respectively. The range of ΔMBVS120-38, mean TS and mean wet
weight in block A in 2002 were applied to block A in 2003, block “offshore” in 2004, Eastern
block in 2005 and blocks 1 and 2 in 2007. The range of ΔMBVS120-38, mean TS and mean wet
weight in block B in 2002 were applied to block B in 2003, western block in 2005 and block 3
in 2007.
Japanese anchovy, sardine and mackerels (including both Chub and Blue (Scomber
australasicus) mackerels) were only small pelagic fish species to form dense schools in thesurvey area. Pelagic fishes were distinguished from the other backscatterings based on the
shape and auxiliary acoustic characteristics though the species compositions in the schools
could not be identified. To add the species composition information to the acoustic data,
proportion of species composition by number of individuals was obtained using trawl data.
Both targeting and predetermined trawl hauls were used to calculate the proportion. The
proportion was calculated by SST in 1°C increments. Mean length of Japanese anchovy is
calculated by SST in 1°C increments in each block and then they are converted to TS using
following formula (Foote, 1987);
TS = 20 log TL − 71.9

5NAMMCO/SC/16/MMFI/11

Mean wet weights of Japanese anchovy corresponded to mean length were also calculated ineach block.
Following procedures were adopted from Jolly and Hampton (1990). Weighted ρ ofeach block was;
Nk

ρk =

∑ ρ ki (nk i )

i =1

Nk

∑ nk ii =1where ρ k = mean ρ in kth block, N k = number of transects in kth block, ρ ki = mean ρ on the
ith transect in kth block and nk i = number of 1 km averaging intervals on the ith transect in kth
block. In this formula, each transect was regarded as a single biomass density sample. Thenvariance of ρ k was calculated with the formula (Jolly and Hampton, 1990);
Nk2
2∑ ( ρ − ρ k ) nk i
N k i =1 k i
Var ( ρ k ) =2
N k −1 Nk ∑ nk i  i =1 Biomass was estimated as;
Bk = Ak ρ kwhere Bk is density biomass in kth block and Ak is area of kth blcok. Variance of Bk was
calculated with following formula;var(Bk ) = Ak 2 var(ρ k )Coefficient of variation of Bk was calculated as;var(Bk )CV ( Bk ) =Bk

Estimation of prey preference
The standardized form of Manly’s selection index called Manly’s α (Manly et al., 1972), also
known as Chesson’s index (Chesson, 1978), was used in the study as in the cases ofLindstrøm and Haug (2001) and Murase et al. (2007). Selection index is calculated as follows.
Sample proportion of number of individuals with dominant prey species i in their stomach (ni)in survey block j isIoi = nij / ∑ nij .
i =1

The results of stomach contents analysis indicated that 88.4 % of sampled minke whales in
JARPN II from 2000 to 2007 fed on single species (Tamura et al., 2008(a)). Likewise, 92.3
and 89.2 % of sampled Byrde’s and sei whales fed on single species. Based on theinformation, we assume that each individual consumes the average daily prey consumption
weight of dominant prey species i in the stomach. If more than two prey species is found in
the stomachs, we only considered dominant species (e.g. if 100 kg of anchovy and 10 kg of
krill are found in a stomach, the individual is treated as it consume only anchovy). Thus, oi isequal to sample proportion of prey species i by weight used by all animals. Sample proportionof available units (biomasses in survey block) in prey i in survey block j isI

π ij = mij / ∑ mij
i =1

6NAMMCO/SC/16/MMFI/11

where mij is an amount of available units in prey i in survey block j in a sample of available
resource units. Manly’s selection index is
wij = oij / π ij .

Standardized Manly’s selection index, Manly’s α is written as;
Bi =

wi
∑ wi
i

If B̂i is equal to 1/I (I is total number of prey species utilized by a predator species), species i
is randomly selected. If Bi greater than 1/I, species i is actively selected. If Bi is less than 1/I,
species i is avoided.
The log-likelihood function based on a multinomial distribution is given by
 Bi aij I J∑ ∑ nij log ∑ wk a kj 
i =1 j =1

where aij is the density of prey i in the survey block j. Our objective is to estimate the Bi
parameters by maximizing the above equation. Data from 2002 to 2007 were used to estimate
Bi as average values in the JARPN II offshore component survey area in summer from 2002
to 2007. Each density, aij, has its uncertainty in the form of CV. To account for the variationin estimation of selection indices, we used a Monte Carlo simulation technique with 1000
permutations. When aij* ~ LN(log(aij), CVij2), we calculate the Bi*s for each aij*. Then thevariance of Bi is given by var(Bi) = E(var(Bi*)) + var(E(Bi*)) where var(Bi*) is calculated bya Hessian matrix. Variance of Bi in each block in each year is also estimated using same
methods.
RESULTS
Poststratification of survey blocks
Predefined survey blocks were poststratified based on the position of the SAF (Figs. 2 - 11).
Poststratified blocks were set either around the SAF (about 2 latitudes from the SAF in northand south directions) or south of these blocks (mainly areas consisted of cold and warm
waters).
Distribution patterns and stomach contents of whales
Sighting positions and stomach contents of sampled common minke, Bryde’s and sei whalesin the poststratified blocks were shown in Figs. 2 - 11. As indicated in the figures, whales
were sampled randomly within the poststratified blocks. Summary of stomach contents in thepoststratified blocks were shown in Table 2. Prey species of minke, Bryde’s and sei whales
showed some overlap but their main preys were different. Sei whales fed on copepods, krill,
anchovy and Pacific saury. Bryde’s whales only fed on krill and anchovy. Minke whales fed
on krill anchovy and Pacific saury. Copepodite stage 5 (C5) of Neocalanus spp. was only
copepods identified to the species level in the stomach of sei whales sampled during
cooperative surveys. Several species of krill were identified in the stomachs of minke,
Bryde’s and sei whales. They were treated as krill in our analysis, because their species could
not be identified by echosounders.

7NAMMCO/SC/16/MMFI/11

Distribution patterns and biomasses of prey species.
Distribution patterns of preys of common minke, Bryde’s and sei whales in the poststratified
blocks were shown in Figs. 2 - 11. Biomasses of preys were summarized in Table 3. Because
Copepodite stage 5 (C5) of Neocalanus spp. was only copepods identified to the species levelin the stomach of sei whales, biomass of Neocalanus spp.(C5) was estimated in the analysis.
Prey preferences of minke, Bryde’s and sei whales
Prey preference of minke, Bryde’s and sei whales in each block in each year was summarizedin Table 4. Minke whales showed preference for fishes regardless of blocks and years (Table
4(a)). Bryde’s whales showed preference for anchovy except block B in 2003 (Table 4(b)).
Prey preferences of sei whales were variable among blocks (Table 4(c)).
Minke and sei whales co-exited in block A-N in 2002 (Fig. 2), block A-S in 2003 (Fig.
4) and block E-N in 2005 (Fig. 7) but they showed different prey preferences. Minke whales
showed preference for Pacific saury while sei whales showed preference for anchovy in block
A-N in 2002. Minke whales showed prey preference for Pacific saury and achovy while sei
whales showed preference for copepods in block A-S in 2003. Minke whales showed prey
preference for Pacific saury and anchovy while sei whales showed prey preference for krill
and Pacific saury in block E-N in 2005.
Table 5 showed the average Manly’s α of three baleen whale species in the JARPN II
offshore component survey area in summer from 2002 to 2007. Minke whales showed
preference for anchovy and suary while they avoided krill. Bryde’s whales showed preference
for anchovy while they avoided krill. Sei whales showed preference for copepods andanchovy while they avoided krill and Pacific saury.
DISCUSSION
This was the first report of prey preferences of minke, Bryde’s and sei whales in the offshore
region of the western North Pacific. Prey preference of sei whales have not been reported inany part of world in the past. During a period from 2002 to 2007, Manly’s α indicated that sei
whales preferred firstly copepods, secondary Japanese anchovy, thirdly Pacific saury andfourthly krill. Data collected during commercial whaling operation from 1952 to 1972
indicated that sei whales mainly fed on copepods in the north of 40°N while they fed on
pelagic fishes in the south of 40°N (Nemoto, 1957; 1959; Kawamura, 1973). Prey preferenceof sei whales in this study was mainly estimated from 35°N to 45°N. Our results generally
agreed with past findings. It was suggested that sei whale possibly switch its prey dependingon the abundance of preys as in the case of minke whales as reported by Kasamatsu andTanaka (1992). In the past studies, mackerels were mainly observed in the stomachs of sei
whales in 1970’s (Kawamura, 1973; 1982), but Japanese anchovy were majority of thestomach content in the this study. Catch statistics of pelagic fishes indicated that abundance ofmackerels was high in 1970’s, and Japanese anchovy became more abundant in 2000’s (Yatsu
et al., 2005 and updated by Takasuka et al. 2008). Though change in abundances of
Neocalanus spp. were reported from 1970’s to 1990’s (Chiba et al., 2006; Tadokoro et al.,2005), no data regarding these copepods was available for 2000’s at the time of the present
study. Presumably, proportion of copepods in stomachs of sei whales may change as change
in abundance of copepods in our survey area. No information was available on decadalchange in abundance of krill in the offshore region of the western North Pacific. Continuationof the cooperative surveys on cetacean sampling and prey of cetaceans is necessary to detect
how prey preference of sei whales changes in response to change in availability of preys.

8

NAMMCO/SC/16/MMFI/11

Murase et al. (2007) reported that minke whales showed preference for anchovy in thewater south of 42°N and west of 150°E from June to August in 2000 and 2001. The results ofthis study suggested minke whales showed preference for Pacific saury in addition to anchovy
in water south 46°N and around 157°E. The study by Murase et al. (2007) was conducted
June-August and no Pacific suary was observed in their survey area. Pacific saury migrates
from south to north in the offshore region in summer and then it returns to south along thecoast of Japan in autumn (Sugisaki and Kurita, 2004). Minke whales fed on northern migrantsof Pacific saury in the offshore region in summer (Tamura and Fujise, 2002). Present study
demonstrated that change in diet of minke whales reflected availability of preys as suggested
by Tamura et al. (1998) and Tamura and Fujise (2002). In the cases of studies in the
Norwegian water (Harbitz and Lindstrøm, 2001; Haug et al., 1996; Lindstrøm and Haug,
2001; Skaug et al., 1997, Windsland et al., 2007) and in the western North Pacific (Murase etal., 2007), minke whales showed preference for pelagic shoaling fishes while they avoided
krill in this study. Bryde’s whales showed preference for krill and anchovy depended onblocks but they showed preference for anchovy as indicated by average Manly’s α value in
the JARPN II offshore component survey area in summer from 2002 to 2007. Preference foranchovy could be general tendency of Bryde’s whales in the western North Pacific but it
seems that prey switching of Bryde’s from krill to anchovy (or vice versa) could occurred
irrespective of prey biomass. Further study is required to dismantle the mechanism.
Minke and sei whales are co-existed in some blocks but they showed different prey
preferences. The results suggested that prey species identification using stomach contents is
critically important to estimate prey preference when more than two species which potentiallyfeed on same preys are co-existed in same area. Several studies were conducted to examine
whale-prey relationships without using stomach contents. Piatt and Methven (1992)
investigated threshold foraging behavior of humpback (Megaptera novaeangliae), fin (B.
physalus) and minke whales on capelin in Witless Bay Newfoundland Canada. However,
because they did not confirm actual prey of baleen whales, it was obscure whether they fed on
capelin or not. Friedlaender et al. (2006) suggested that Antarctic minke whales showed
preference for larger individual krill and smaller aggregation area than humpback whales in
the Antarctic water. However, because they just investigated spatial relationships between
baleen whales based on a sighting survey and distribution of krill based on an echosoundersurvey, it was uncertain whether Antarctic minke whales actually fed on larger size krill than
humpback whales or not. Witteveen et al. (2008) attached acoustic tags to humpback whales
to investigate prey preference. They concluded that humpback whales showed preference forcapelin. However, because they just investigated relationships between swimming behaviourof humpback whales and distribution pattern of preys detected by an echosounder, there was
no evidence whether humpback whales actually fed on capelin or not. To study and quantify
estimate prey preference of baleen whales, prey species identification using stomach contests
is required.
Prey biomass estimations in selected survey blocks were used as an indicative of preyavailability to whales at meso scale. In JARPN II, prey preference of whales is considered as
one of the input parameter of ecosystem models not at micro scale (individual level) but at
meso scale (population level) in the feeding area. Thus our prey preference estimation
methods is satisfactory met the goal of the survey. Study on prey preference at micro scale
might help the interpretation of prey preference at meso scale. At the micro scale, prey
preference of whales can be related not only biomasses of prey but also to other factors suchas shapes and behaviour of schools of preys. Conventional quantitative echosounders such as
Simrad EK500 and EK60 can not collected such data fully. Newly developed fisheries
multibeam echosounder can record these detailed data (Trenkel et al., 2008). If the new9NAMMCO/SC/16/MMFI/11

technology is used along with conventional study methods, it will enhance our knowledge on
prey preference of whales.
As an initial attempt, constant prey preference was assumed in the MRM developed by
Kawahara (2009). Some ecosystem models such as EwE require functional response of
predator. Though functional response form is important in the EwE (e.g. Mori et al., 2009), it
has not been estimated for baleen whales using actual data because of lack of long term datacollection for it. Pláganyi (2007) strongly recommended that effort be focused on appropriate
data collection and/or experiments to assist in shedding light as to the most appropriate form
to represent feeding behaviour. Multispecies functional response of common minke whales inthe southern Barents Sea was estimated at micro scale (Smout and Lindstrøm, 2007). For
fisheries management purpose, ecosystem model at meso to macro scale is required.
Functional response at different scales could be different. Functional form required byecosystem model for fisheries model needs long term collection of prey preference data.
Continuation of JARPN II is important to develop appropriate functional response form forbaleen whales.
We estimated biomasses of preys from 0 to 150 m water depth based on known main
distribution depth of them: copepods (Neocalanus spp. (C5)) = 100 m (Murase unpublisheddata), anchovy = <100 m (Murase et al., 2007) and Pacific saury = <10 m (Ueno et al., 2004).
Main distribution depth of krill is deeper than 150 m (Murase et al., 2007). Because all whale
species considered in this study avoid krill, inclusion of biomass of krill deeper than 150 m
water depth would not reverse the results of our findings. Feeding depths of minke, Bryde’s
and sei whales in the western North Pacific have not been reported. It was reported thatmaximum dive depth of fin and blue whales were 470 m at least (Panigada, et al., 1999) and
204 m (Croll et al., 2001), respectively. Measurement of actual feeding depth of minke,
Bryde’s and sei whales using time depth recorder will be useful to define their feeding depth
ranges.
Biomass data of copepods and Pacific saury were spatially sparse because nets wereused. If their biomass can be estimated using echosounders, one will be able to study moredetailed prey preference of cetaceans in both spatial and temporal scales. Biomass ofcopepods can be estimated by using echosounders (Beardsley et al., 1996; Coyle, 1998; 2005)
if high frequency such as 200 and 420 kHz can be used in the survey. However, because ofsmall body size of copepods, estimation of target strength as well as development of
acoustical species identification methods are critically important. These points will be studies
in future JARPN II. Because Pacific saury is distributed mainly near ocean surface layer (e.g.
<10m), surface trawling technique developed by Ueno et al. (2004) is only way for estimationof biomass. Up looking echosounder mounted on Autonomous Underwater Vehicle (AUV)(Fernandes et al., 2003) can be used for alternation of trawling. However, development anddeployment of such new equipment will take time and they will not take place in immediate
future. To sample prey species, use of MOHT (Matsuda-Oozeki-Hu-Trawl) net in addition tonets used in JARPN II will enhance sampling efficiency as suggested by Oozeki et al. (2004).
Biomass estimation using echosounders in this study adopt up to date techniques used as
standard in worldwide. There are several sources of biases associated with biomass estimation
using echosounder. Demer (2004) pointed out that following potential sources of biases may
be appreciable components of measurement uncertainty: stemming from uncertainties in thetarget strength model, the length-weight model, the species classification methods, bubble
attenuation, signal thresholding and survey area definition. Though study of details of
acoustics is not main objective of this study, these technical points will be investigated asmuch as possible because biomass estimation of preys is very important for estimation of prey
preferences.

10NAMMCO/SC/16/MMFI/11

It is recognized that both climatic and biological regime shifts occurred in the North
Pacific Ocean and their effect on fisheries and ecosystem were actively investigated by North
Pacific Marine Science Organization (PICES). In the western North Pacific, commercial catch
histories of pelagic fishes have shown drastic fluctuation and quasi-decadal species alterations
so-called species replacement since the 1950’s (Yatsu et al. 2001). Species replacement is aform of a biological regime shift. Although there are many definition of regime shift, thestudy group of fisheries and ecosystem responses to recent regime shift under PICES defined
regime shift as “a relative rapid change from one decadal-scale period of a persistent state toanother decadal-scale period of persistent state” (King, 2005). Climate indices such as the
Pacific Decadal Oscillation (PDO) indicated that significant climatic regime shifts were
occurred around 1976, 1989 and 1998 in recent decades (Overland et al., 2008). Responses ofpelagic biological organisms to climatic regime shifts were reported including copepods(Tadokoro et al., 2005), Japanese anchovy, Japanese sardine, Pacific saury and mackerel(Takasuka et al., 2008; Tian et al., 2004; Yatsu et al., 2008). Some analysis provided simple
interpretation of interaction between climatic and biological regime shifts based on spawningtemperature optima theory (e.g. Takasuka et al., 2008) but the interpretation is difficult inother cases because of complexity of interactions (Yastu et al., 2008). In this study, Manly’s αsuggested that trophic niches of minke, sei and Bryde’s were different from each other.
However, a wide variety of prey species found in their stomachs (Tamura et al., 2009)
suggested that they could have capability to switch their prey in response to regime shifts.
Stomach contents collected by commercial harvesting indicated that common minke whales
switched their preys according to biological regime shift of prey abundances (Kasamatsu andTanaka, 1992). However, effects of both biological and climatic regime shifts on baleen
whales in the western North Pacific are still largely open to question because of lack of datacollected through systematic surveys. The ecosystem structure of the western North Pacific is“wasp-waist” (Bakun, 2006). In wasp-waist ecosystem, many species exist at the top and thebottom but a few dominant species (mostly small planktivorous fishes) occupied the middle(analogous to body shape wasp in terms of number of species in an ecosystem) (Bakun, 2006).
Pelagic fishes such as sardines and anchovies occupy the middle level of the ecosystem in the
North Pacific. Bakun (2006) suggested that feeding by predators could cause population
collapse (but not extinction) of prey at the middle level of ecosystem if the predation rate bypredator exceeds the production rate of the prey. Once climatic regime shift negatively affectthe production rate of the prey, predation by predators accelerate the rate of collapse of prey
population. Thus, predation by baleen whales could also affect regime shifts in otherorganisms especially small planktivorous fishes. So far, regime shift have not been reported
during JARPN II from 2002 to 2007. To detect effect of regime shifts on cetaceans as well as
effect of predation by cetaceans on biological regime shifts, long term cetacean prey survey
program is critically important.
ACKNOWLEDGEMENT
Authors expressed thanks to all the crews and researchers who engaged in the offshore
component of JARPNII. We expressed thank you to Ms. Tomoko Hasegawa for the data
management. We thank Dr. Kenji Konishi for his dedication to analyze stomach contents ofwhales. Trawl and NROPAC samples collected by TNFRI were kindly provided by Drs.
Yasuhiro Ueno and Kazuaki Tadokoro. This survey was supported by Fisheries Agency ofJapan, Fisheries Research Agency of Japan, and the Institute of Cetacean Research. We thankto these institutions for their support.

11

NAMMCO/SC/16/MMFI/11

REFERENCE
Bakun, A. 2006. Wasp-waist populations and marine ecosystem dynamics: navigating
the“predator pit”topographies. Prog. Oceanogr. 68: 271-288.
Beardsley, R. C., Epstein, A. W., Chen, C., Wishner, K. F., Macaulay, M. C. and Kenney, R.
D. 1996. Spatial variability in zooplankton abundance near feeding right whales in the GreatSouth Channel. Deep Sea Res. II 43: 1601-1625.
Begley, J. 2008. Gadget User Guide. Available from http://www.hafro.is/gadget/. 100pp.
Bogstad, B. Hauge, K H. Ulltang, O. 1997. MULTSPEC- A Multi-species model for fish andmarine mammals in the Barents sea. J.Northw.Atl.Fish.Sci. 22:317-341
Chesson, J. 1978. Measuring preference in selective predation. Ecol. .59:211-215.
Chiba, S., Tadokoro, K., Sugisaki, H. and Saino, T. 2006. Effects of decadal climate change
on zooplankton over the last 50 years in the western subarctic North Pacific. Glob. Change
Biol. 12: 907-920.
Christensen, V., Walters, C. J. and Pauly, D. 2005. Ecopath with Ecosim: a user's guide,
November 2005 Edition. Fisheries Centre, University of British Columbia, Vancouver,
Canada. 154pp.
Coyle, K. O. 1998. Neocalanus scattering layers near the western Aleutian Islands. J.
Plankton Res. 20:1189-1202.
Coyle, K. O. 2005. Zooplankton distribution, abundance and biomass relative to water masses
in eastern and central Aleutian Island passes. Fish. Oceanogr. 14(Suppl. 1): 77-92.
Croll, D A., Acevedo-Gutiérrez, A., Tershy, B R. and Urbán-Ramirez, J. 2001. The diving
behaviour of blue and fin whales:is dive duration shorter than expected based on oxygen
stores? Comp. Biochem. Physiol. A 129:797-809.
Demer, D. A. 2004. An estimate of error for the CCAMLR 2000 survey estimate of krill
biomass. Deep Sea Res. II 51: 1237-1251.
Fernandes, P. G., Stevenson, P., Brierley, A. S., Armstrong, F. and Simmonds, E. J. 2003.
Autonomous underwater vehicles: future platforms for fisheries acoustics. ICES J. Mar. Sci.
60: 684-691.
Foote, K. G. 1982. Optimizing copper spheres for precision calibration of hydroacoustic
equipment. J. Acoust. Soc. Am. 71:742-747.
Foote, K. G.. 1987. Fish target strengths for use in echo integrator surveys. J. Acoust. Soc. Am.
82:981-987.
Friedlaender, A. S., Lawson, G. L. and Halpin, P. N. 2006. Evidence of resource partitioning
and niche separation between humpback and minke whales in Antarctica: implications forinterspecific competition. Paper SC/58/E32 submitted to the 58th IWC Scientific Committee
Meeting, 37 pp. (unpublished)
Government of Japan. 2002. Report of 2000 and 2001 feasibility study of the the Japanese
Whale Research Program under Special Permit in the North Pacific – Phase II (JARPN II).
Paper SC/54/O17 submitted to the 52th IWC Scientific Committee Meeting. 202pp(unpublished)
Harbitz, A. and Lindstrøm, U. 2001. Stochastic spatial analysis of marine resources withapplication to minke whales (Balaenoptera acutorostrata) foraging: Asynoptic case study
from the southern Barents Sea. Sarsia 86:485-501.

12

NAMMCO/SC/16/MMFI/11

Haug, T., Lindstrøm, U., Nilssen, K. T., Rottingen, I. and Skaug, H. J. 1996. Diet and foodavailability for northeast Atlantic minke whales, Balaenoptera acutorostrata. Rep. Int. Whal.
Commn. 46: 371-382.
Hirzel, A. H. and Le Lay, G. 2008. Habitat suitability modelling and niche theory. J. Applied
Ecol. 45: 1372-1381.
International Whaling Commission. 1994. Report of the Working group on North Pacificminke whale management trials. Rep. Int. Whal. Commn. 44: 120-125.
International Whaling Commission.. 2002. Annual report of the International whaling
Commission 2002. Cambridge IWC. 159pp.
International Whaling Commission. 2003. Report of the Scientific Committee. J. Cetacean
Res. Manage. (Suppl.) 5:1-92.
International Whaling Commission. 2004. Report of the Modelling Workshop on CetaceanFishery Competition. J Cetacean Res. Manage. 6(suppl.):413-426.
Jolly, G.M. and Hampton, I. 1990. A stratified random transect design for acoustic sueveys offish stocks. Can. J. of Fish. Aquat. Sci. 47: 1282-1291.
Kang, M., Furusawa, M. and Miyashita, K. 2002. Effective and accurate use of difference inmean volume backscattering strength to identify fish and plankton. ICES J. Mar. Sci. 59:
794-804.
Kasamatsu, F. and Tanaka, S. 1992. Annual changes in prey species of minke whales taken
off Japan 1948-87. Nippon Suisan Gakkaishi. 58:637-51.
Kawahara, S. 2009. A minimum realistic model in the JARPNII offshore survey area. Paper
SC/J09/JR22 presented to the JARPN II review workshop, Tokyo, January 2009
(unpublished). XXpp.
Kawamura, A. 1973. Food and feeding of sei whale caught in the waters south of 40°N in the
North Pacific. Sci. Rep. Whales Res. Inst., Tokyo. 25:219-236.
Kawamura, A. 1982. Food habits and prey distributions of three rorqual species in the North
Pacific Ocean. Sci. Rep. Whales Res. Inst., Tokyo. 34:59-91.
King, J.R (Ed.). 2005. Report of the study group on fisheries and ecosystem responses torecent regime shifts. PICES Scientific Report 28, 162 pp.
Lindstrøm, U. and Haug, T. 2001. Feeding strategy and prey selectivity in common minke
whales (Balaenoptera acutorostrata) foraging in the southern Barents Sea during earlysummer. J. Cetacean Res. Manage. 3: 239-249.
Mackett, D. J. 1973. Manual of methods for fisheries resources survey and appraisal part 3.
Standard methods and techniques for demaersal fisheries resource surveys. FAO Fish. Tech.
Paper. No.124. 39p.
Manly, B. F. J., Miller, P. and Cook, L. M. 1972. Analysis of a selective predation experiment.
Am. Nat. 106:719-736.
Miyashita, K., Aoki, I., Seno, K., Taki, K. and Ogishima, T. 1997. Acoustic identification ofisada krill, Euphausia pacifica Hansen, off the Sanriku coast, north-eastern Japan. Fish.
Oceanogr. 6. 266-271.

13

NAMMCO/SC/16/MMFI/11

Mori, M., Watanabe, H., Hakamada, T., Tamura, T., Konishi, K., Murase, H. and Matsuoka,
K. 2009. Development of an ecosystem model of the western North Pacific. Paper
SC/J09/JR21 presented to the JARPN II review workshop, Tokyo, January 2009
(unpublished). XXpp.
Morishita, J. 2008. What is the ecosystem approach for fisheries management? Mar. Pol. 32:
19-26.
Murase, H., Tamura, T., Kiwada, H., Fujise, Y., Watanabe, H., Ohizumi, H., Yonezaki, S.,
Okamura, H. and Kawahara, S. 2007. Prey selection of common minke and Bryde’s whalesin the western North Pacific in 2000 and 2001. Fish. Oceanog. 16:186-201.
Murase, H., Watanabe, H., Yonezaki, S., Tamura, T., Matsuoka, K., Fujise, Y. and Kawahara,
S. 2009. Methodology and procedures of cetacean prey surveys in JARPN II –Offshore
Component-. Paper SC/J09/JR7 presented to the JARPN II review workshop, Tokyo,
January 2009 (unpublished). 11pp.
Nemoto, T. 1957. Foods of baleen whales in the northern Pacific. Sci. Rep. Whales Res. Inst.,
Tokyo. 12:33-89.
Nemoto, T. 1959 Food of baleen whales with reference to whale movements. Sci. Rep.
Whales Res. Inst., Tokyo. 14:149-290.
Overland, J., Rodionov, S., Minobe, S. and Bond, N. 2008. North Pacific regime shifts:
Definitions, issues and recent transitions. Prog. Oceanogr. 77: 92-102.
Panigada, S., Zanardelli, M., Canese, S. and Jahoda, M. 1999. How deep can baleen whales
dive? Mar. Ecol. Prog. Ser. 187: 309-311.
Piatt, J. F. and Methven, D. A. 1992. Threshold Foraging Behavior of Baleen Whales. Mar.
Ecol. Prog. Ser. 84: 205-210.
Pláganyi, E. 2007. Models for an ecosystem approach to fisheries. Rome: FAO, 108pp.
Skaug, H. J., Gjøsæter, H., Haug, T., Nilssen, K. T. and Lindstrøm, U. 1997. Do minke
whales (Balaenoptera acutorostrata) exhibit particular prey preferences? J. Northw. Atl.
Fish. Sci. 22:91-104.
Smout, S. and Lindstrøm, U. 2007. Multispecies functional response of the minke whale
Balaenoptera acutorostrata based on small-scale foraging studies. Mar. Ecol. Prog. Ser.
341: 277-291.
Sugisaki, H. and Kurita, Y. 2004. Daily rhythm and seasonal variation of feeding habit ofPacific saury (Cololabis saira) in relation to their migration and oceanographic conditions
off Japan. Fish Oceanogr. 13: 63-73.
Tadokoro, K., Chiba, S., Ono, T., Midorikawa, T. and Saino, T. 2005. Interannual variation in
Neocalanus biomass in the Oyashio waters of the western North Pacific. Fish Oceanogr. 14:
210-222.
Takasuka, A., Oozeki, Y. and Kubota, H. 2008. Multi-species regime shifts reflected inspawning temperature optima of small pelagic fish in the western North Pacific. Mar. Ecol.
Prog. Ser. 360: 211-217.
Tamura, T., Fujise, Y. and Shimazaki, K. 1998. Diet of minke whales Balaenoptera
acutorostrata in the northwestern part of the north Pacific in summer, 1994 and 1995. Fish.
Sci. 64: 71-76.

14

NAMMCO/SC/16/MMFI/11

Tamura, T. and Fujise, Y. 2002. Geographical and seasonal changes of the prey species ofminke whale in the Northwestern Pacific. ICES J. Mar. Sci. 59:516-528.
Tamura, T., Konishi, K., Isoda, T., Okamoto, R. and Bando, T.2009(a). Prey consumption andfeeding habits of common minke, sei and Bryde’s whales in the western North Pacific. Paper
SC/J09/JR16 presented to the JARPN II review workshop, Tokyo, January 2009
(unpublished). 36pp.
Tamura, T., Matsuoka, K. and Fujise, Y. 2009(b). Methodology and survey procedure under
the JARPN II - offshore component- with special emphasis on whale sampling procedures.
Paper SC/J09/JR4 presented to the JARPN II review workshop, Tokyo, January 2009
(unpublished). 16pp.
Tian, Y., Ueno, Y., Suda, M. and Akamine, T. 2004. Decadal variability in the abundance ofPacific saury and its response to climatic/oceanic regime shifts in the northwestern
subtropical Pacific during the last half century. J. Mar. Syst. 52: 235-257.
Tojo, N., Shimizu, D., Yasuma, H., Kawahara, S., Watanabe, H., Yonezaki, S., Murase, H.
and Miyashita, K. 2008. Quantitative analysis of isada krill (Euphausia pacifica) distribution
in the western North Pacific. Bull. Jpn. Soc. Fish. Oceanog. 72: 165-173. (in Japanese)
Trenkel, V. M., Mazauric, V. and Berger, L. 2008. The new fisheries multibeam echosounder
ME70: description and expected contribution to fisheries research. ICES J. Mar. Sci. 65:
645-655.
Ueno, Y., Suyama, S., Kurita, Y. and Kumazawa, T. 2004. Design and operation methods of a
mid-water trawl for quantitative sampling of a surface pelagic fish, Pacific saury (Cololabis
saira). Fish Res. 66: 3-17.
Windsland, K., Lindstrøm, U., Nilssen, K. T. and Haug, T. 2007. Relative abundance and size
composition of prey in the common minke whale diet in selected areas of the northeastern
Atlantic during 2000-04. J. Cetacean Res. Manage. 9: 167-178.
Witteveen, B. H., Foy, R. J., Wynne, K. M. and Tremblay, Y. 2008. Investigation of foraging
habits and prey selection by humpback whales (Megaptera novaeangliae) using acoustic
tags and concurrent fish surveys. Mar. Mamm. Sci. 24: 516-534.
Yatsu, A., H. Nishida, M. Ishida, A. Tomosada, T. Kinoshita and T. Wada. 2001. Trajectories
of catch and stock abundance of dominant small pelagic fishes and common squid with somerelated environmental indices around Japan. PICES Sci. Rep. 18: 175-178
Yatsu, A., Watanabe, T., Ishida, M., Sugisaki, H. and Jacobson, L. D. 2005. Environmental
effects on recruitment and productivity of Japanese sardine Sardinops melanostictus andchub mackerel Scomber japonicus with recommendations for management. Fish Oceanogr.
14: 263-278.
Yatsu, A., Aydin, K. Y., King, J. R., McFarlane, G. A., Chiba, S., Tadokoro, K., Kaeriyama,
M. and Watanabe, Y. 2008. Elucidating dynamic responses of North Pacific fish populations
to climatic forcing: Influence of life-history strategy. Prog. Oceanogr. 77: 252-268.

15

NAMMCO/SC/16/MMFI/11

Table 1. Timing of the cooprative whale and prey surveys from 2002 to 2007.
Year

2002

2003
2004
2005

2007

Prey Survey

Whale Survey

Block(Abbreviation)

Poststratified
blocks

VesselSpecial Block A

2002-A

2002-A-N

SYO

17-Jul

26-Jul18-Jul

1-AugSpecial Block B

2002-B

-

SYO

2-Aug

9-Aug

7-Aug

17-AugBlock A

2003-A

2003-A-S

SYO

15-Jun25-Jun10-Jun22-JunBlock B

2003-B

-

SYO

1-Jul

9-Jul

26-Jun29-JunOffshore

2004-O

2004-O-C

SYO

14-SepWestern Block2005-W-

SYO

Eastern Block2005-E

Block 1

Jan-07

2005-E-S
2005-E-N
2007-1-S
2007-1-N

Start

End

Start

End

1-Jul

7-Jul

19-Sep

5-Sep

8-Sep

12-Jul

25-Jul8-Jul

15-JulSYO

27-Jul11-Aug25-Jul

4-Aug

KK1

7-Jul

26-Jul9-Jul

22-JulBlock 2

Feb-07

2007-2-C

KK1

28-Jul21-Aug23-Jul

2-Aug

Block 3Mar-07

2007-3-C

KK1

24-Aug

4-Sep

11-Aug13-Aug

16

NAMMCO/SC/16/MMFI/11

Table 2. Summary of stomach contents of minke (a), Bryde’s (b) and sei (c) whales in thepoststratified blocks. Number of individuals with dominant prey species in their stomach wassummarized. If two prey species were found in the stomach, only a dominant species in wet
weight was counted.
(a) Minke whales
Year

Krill

Japanese
Anchovy

Pacific
saury# of ind.
6
0
1# of ind.
0
3
1# of ind.
11
10
7

Block

2002
2003
2005

A-N
A-S
E-N

(b)Bryde’s whales
Year

Block

2002
2003
2005
2007
2007

B
B
W
1-S
3-C

Krill

Japanese
Anchovy# of ind
0
13
9
0
0

# of ind
1
1
12
18
10

(c) Sei whales

Year

Block

2002
2003
2004
2005
2005
2007
2007
2007

A-N
A-S
O-C
E-S
E-N
1-S
1-N
2

Copepods

Krill

Japanese
Anchovy

Pacific
saury# of ind
1
8
4
2
1
0
5
10

# of ind
8
2
0
7
4
0
0
0

# of ind
1
1
1
0
0
5
0
0

# of ind
0
1
0
0
2
0
0
3

17

NAMMCO/SC/16/MMFI/11

Table 3. Biomasses of preys in the poststratified blocks.
Copepods
Year

Block
Biomass(million t)

2002
2003
2004
2005

2007

Japanese
Anchovy

Krill

A-N
B
A-S
B
O-C
E-S
E-N
W
1-S
1-N
2-C
3-C

0.48
0.38
0.01
0.000
0.42
0.00
0.85
0.47
-

CV

Biomass

0.12
0.70
0.38
0.7
0.21
0.28
0.19
0.17
-

0.978
0.231
0.843
0.459
0.048
0.44
0.31
0.11
0.45
0.51
0.13
0.12

(million t)

18

CV

Biomass

0.2
0.3
0.2
0.4
0.3
0.38
0.17
0.45
0.20
0.31
0.55
0.11

0.007
0.201
0.206
0.296
0.003
0.08
0.03
0.00
0.24
0.08
0.08
0.06

(million t)

Pacific
saury

CV

Biomass

0.2
0.5
0.9
0.5
1.0
0.47
0.50
0.44
0.68
0.42
0.59
0.88

0.32
0.34
0.00
0.00
0.14
0.00
0.02
0.10
-

(million t)

CV
0.15
0.17
0.27
0.50
0.38
0.00
0.44
0.47
-

NAMMCO/SC/16/MMFI/11

Table 4. Values of Manly’s α as a means of indications of prey preferences of minke (a),Bryde’s (b) and sei whales (c) in the poststratified blocks. Standard error (se) is also shown. If
Manly’s α is equal to 1/I, species i is randomly selected. If Manly’s α is greater than 1/I,
species i is actively selected. If Manly’s α is less than 1/I, species i is avoided.
(a) Minke whales
Japanese
Anchovy

Krill
Year

Block

Pacific
saury

Manly's αse

Manly's αse

Manly's α

se
0.07

2002

A-N

0.15

0.07

0.00

-

0.85

2003

A-S

0.00

-

0.33

0.23

0.67

0.23

0.55

0.27

2005

E-N

0.04

0.04

0.41

0.28

(b) Bryde’s whales
Year

Japanese
Anchovy

Krill

Block

Manly's αse

Manly's α

se

2002

B

0.00

-

1.00

-

2003

B

0.89

0.14

0.11

0.14

2005

W

0.02

0.02

0.98

0.02

2007

1-S

0.00

-

1.00

-

2007

3-C

0.00

-

1.00

-

(c) Sei whales
Year

Block

2002

A-N

Copepods

Japanese
Anchovy

Krill

Pacific
saury

Manly's αse

Manly's αse

Manly's αse

Manly's α

se

0.01

0.02

0.06

0.06

0.93

0.07

0.00

-

2003

A-S

0.67

0.23

0.16

0.22

0.10

0.11

O-C

0.44

0.32

0.08
-

0.07

2004

-

0.56

0.32

0.00

-

2005

E-S

1.00

-

0.00

-

0.00

-

0.00

-

2005

E-N

0.08

0.09

0.44

0.21

0.00

-

0.48

0.22

2007

1-S

0.00

-

0.00

-

1.00

-

0.00

-

2007

1-N

1.00

-

0.00

-

0.00

-

0.00

2007

2

0.42

0.19

0.00

-

0.00

-

0.58

0.19

19

NAMMCO/SC/16/MMFI/11

Table 5. Estimated average values of Manly’s α of minke, Bryde’s and sei whales α in the
JARPN II offshore component survey area in summer from 2002 to 2007 using the loglikelihood function based on a multinomial distribution.
Copepods

Species

Minke whale

Japaneseanchovy

Krill

Pacific
sauey

Manly's αse

Manly's αse

Manly's αse

Manly's α

se

-

-

0.05

0.03

0.36

0.19

0.59

0.17

Bryde's whale

-

-

0.05

0.04

0.95

0.04

-

-

Sei whale

0.41

0.10

0.13

0.04

0.25

0.10

0.20

0.08

20

NAMMCO/SC/16/MMFI/11

Fig. 1. Predefined survey blocks for the cooperative whale and prey surveys in JARPN II
offshore component from 2002 to 2007. Each colour represents boundary of surveyed blocks.
These blocks were poststratified based on observed oceanographic conditions. Zigzag line
within each block represent planned trackline of prey surveys.

21

NAMMCO/SC/16/MMFI/11

Fig.2. Maps in block A in 2002: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of common minke and sei whales (e). Sampled positions and stomach contents of minke (f) and sei (g)whales. Water temperature at 100 m (h) and at 200 m (i) water depth. Encircled area by red line is the poststratified area, A-N. Light blue line inmaps (a)-(f) represents 4°C isotherm at 100 m water depth.

22NAMMCO/SC/16/MMFI/11

Fig.3. Maps in block B in 2002: Distribution patterns of krill (a) and Japanese anchovy (b). Sighting effort and sighting positions of Bryde’s
whales (c). Sampled positions and stomach contents of Bryde’s whales (d). Water temperature at 100 m (e) and 200 m (f) water depth. Light blue
and orange lines in maps (a)-(d) represents 4°C and 10°C isotherm at 100 m water depth, respectively.
23

NAMMCO/SC/16/MMFI/11

43N

41N

39N

157E

(a)

(b)

(f)

(g)

(c)

(d)

(e)

159E

(h)

(i)

Fig.4. Maps in block A in 2003: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of common minke and sei whales (e). Sampled positions and stomach contents of minke (f) and sei (g)whales. Water temperature at 100 m (h) and 200 m (i) water depth. Encircled area by red line is the poststratified area, A-S. Light blue andorange lines in maps (a)-(g) represent 4°C and 10°C isotherm at 100 m water depth, respectively.

24

NAMMCO/SC/16/MMFI/11

Fig.5. Maps in block B in 2003: Distribution patterns of krill (a) and Japanese anchovy (b), Sighting effort and sighting positions of Bryde’s
whales (c). Sampled positions and stomach contents of Bryde’s whales (d). Water temperature at 100 m (e) and 200 m (f) water depth. Light blue
and orange lines in maps (a)-(d) represent 4°C and 10°C isotherm at 100 m water depth, respectively.

25

NAMMCO/SC/16/MMFI/11

Fig.6. Maps in block O in 2004: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of sei whales (e). Sampled positions and stomach contents of sei whales (f). Water temperature at 100
m (g) and 200 m (h) water depth. Encircled area by red line is the poststratified area, O-C. Light blue and line in maps (a)-(f) represents 4°C
isotherm at 100 m water depth.

26

NAMMCO/SC/16/MMFI/11

45N

47N

49N

157E

(a)

(b)

(c)

(d)

(f)

(g)

(h)

(i)

(e)

159E

Fig.7. Maps in block E in 2005: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of common minke and sei whales (e). Sampled positions and stomach contents of minke (f) and sei (g)whales. Water temperature at 100 m (h) and 200 m (i) water depth. Encircled areas by red and blue lines are the poststratified area, E-N and E-S,
respectively. Light blue line in maps (a)-(g) represents 4°C isotherm at 100 m water depth.
27

NAMMCO/SC/16/MMFI/11

Fig.8. Maps in block W in 2005: Distribution patterns of krill (a) and Japanese anchovy (b). Sighting effort and sighting positions of Bryde’s
whales (c). Sampled positions and stomach contents of Bryde’s whales (d). Water temperature at 100 m (e) and 200 m (f) water depth. Orange
lines in maps (a)-(d) represents 10°C isotherm at 100 m water depth.

28

NAMMCO/SC/16/MMFI/11

Fig.9. Maps in block 1 in 2007: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of common minke Bryde’s and sei whales (e). Sampled positions and stomach contents of minke (f)and sei (g) whales. Water temperature at 100 m (h) and 200 m (i) water depth. Encircled areas by red blue lines are the poststartifed area, E-N
and E-S, respectively. light blue and orange lines in maps (a)-(g) represent 4°C and 10°C isotherm at 100 m water depth, respectively.

29

NAMMCO/SC/16/MMFI/11

50N

45N

40N

35N
162E

165E

168E

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig.10. Maps in block 2 in 2007: Distribution patterns of krill (a), Japanese anchovy (b), copepods (Neocalanus spp. (C5)) (c) and Pacific suary(d). Sighting effort and sighting positions of Bryde’s and sei whales (e). Sampled positions and stomach contents of sei whales (f). Water
temperature at 100 m (g) and 200 m (h) water depth. Encircled area by red line is the poststratified area, 2-C. Light blue, orange and red lines inmaps (a)-(f) represent 4°C and 10°C isotherm at 100 m water depth, and 14 °C isotherm at 200 m water depth, respectively.

30

NAMMCO/SC/16/MMFI/11

40N

38N

36N

149E

(a)

(b)

(c)

(d)

(e)

(f)

151E

Fig.11. Maps in block 3 in 2007: Distribution patterns of krill (a) and Japanese anchovy (b). Sighting effort and sighting positions of Bryde’s
whales (c). Sampled positions and stomach contents of Bryde’s whales (d). Water temperature at 100 m (e) and 200 m (f) water depth. .Lightblue, orange and red lines in maps (a)-(d) repsentet 4°C and 10°C isotherm at 100 m water depth, and 14 °C isotherm at 200 m water depth,
respectively.

31