SC/J09/JR7

Methodology and procedures of cetacean prey surveys in
JARPN II -Offshore componentHIROTO MURASE1, HIKARU WATANABE2, SHIROH YONHEZAKI1 TSUTOMU TAMURA1, KOJI
MATSUOKA1, YOSHIHIRO FUJISE1 AND SHIGEYUKI KAWAHARA3
1

The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan
National Research Institute of Far Seas Fisheries, 2-12-4 Fukuura, Kanazawa, Yokohama,
Kanagawa 236-8648, Japan
3
National Research Institute of Far Seas Fisheries, 5-7-1, Orido, Shimizu, Shizuoka,
Shizuoka, 424-8633, Japan
2

ABSTRACT
Cetacean prey species surveys have been conducted every year since 2002 (except 2006) as a part of thefull scale surveys of offshore component of JARPN II. The main objective of the prey species surveys
were estimation of prey preference of cetaceans which is one of the most important parameters of
ecosystem models. Prey preference of cetaceans can only be studied by comparing species compositionsof prey in stomachs of cetaceans with species compositions of prey in sea. Prey of common minke, sei
and Bryde’s whales which are target sampling species of JARPN II were studied in the prey surveys.
Five vessels (a research base vessel, three sighting and sampling vessels and a prey survey vessel) were
engaged in the cooperative surveys of cetacean sampling and prey. In each year, one to three small
blocks (cooperative survey blocks) were established within the entire survey area of the offshore
component of JARPN II. Cetacean and prey surveys were conducted in the cooperative survey blocks inthe same spatiotemporal scale. A trawler type fisheries survey vessel conducted prey surveys including
net sampling and acoustic data recording by quantitative echosounders. Four types of nets (NORPAC,
IKMT, MOCNESS and midwater trawl) were used to sample various prey species from zooplankton tofish. A quantitative echo sounders, either EK500 or EK60 (Simrad, Norway) which is commonly usedin fisheries research worldwide, was used in the prey surveys. Oceanographic observations using CTD
and XCTD were also conducted in the prey surveys. At the same time of prey surveys, cetaceans were
sampled and their stomach contents were investigated. Using data acquired by the prey surveys,
distribution patterns and biomasses of copepods, krill, Japanese anchovy, and Pacific saury were studied.
Such a large scale multidisciplinary surveys in the marine ecosystem have not been conducted in theoffshore region of the North Pacific or other boreal regions of world. The data collected by the surveys
were used to estimates the prey preferences of cetaceans and results are presented to this workshop(Murase, et al., 2009). Climatic and biological regime shifts have been observed in the Pacific Ocean(Overland et al., 2008) though they have not been reported from 2000 to 2007. Regime shifts affectboth fisheries and the marine ecosystem substantially in negative and positive directions. Long term
cetacean prey survey program is critically important to detect how cetaceans and their prey respond to
regime shifts.

INTRODUCTION
The first phase of the Japanese Whale Research Program under Special Permit in the North
Pacific (JARPN) was conducted between 1994 and 1999. The main objective was to clarify
the stock structure of minke whales in the western North Pacific. As it proved that minke
whales feed on a good deal of fisheries resources such as Japanese anchovy and Pacific saury(Tamura et al., 1998; Tamura and Fujise, 2002), the feeding ecology was added in 1996 as afeasibility study. At the JARPN review meeting held by IWC/SC in February 2000, theworkshop agreed that the sampling regime must be designed to allow for a more quantitative
estimation of temporal and geographical variation in diet, and recommended that acoustic andtrawl surveys should be conducted concurrently with future whale surveys (IWC, 2001). The
government of Japan submitted the Research Plan for Cetacean Studies in the Western North1

SC/J09/JR7
Pacific under Special Permit (JARPN II) (Feasibility Study Plan for 2000 and 2001) to the52nd IWC/SC (Government of Japan, 2000). The overall goal is to contribute to theconservation and sustainable use of marine living resources including whales in the western
North Pacific, especially within Japan’s economic exclusive zone (EEZ). The priority in thissecond phase is on feeding ecology, involving the studies on prey consumption by cetaceans,
prey preference of cetaceans and ecosystem modelling. Prey preference of cetaceans isinevitable to most ecosystem models and estimated with the cooperative whale and preysurveys. As the cooperative whale and prey surveys had never been conducted in the western
North Pacific, a two-year feasibility study was conducted in 2000 and 2001. Prey distribution
and biomass data of common minke (Balaenoptera acutorostrata) and Bryde’s (B. edeni)
whales were collected by the cetacean prey survey in the feasibility study. The results of thefeasibility study in 2000 and 2001 were reviewed in the 54th IWC/SC (IWC, 2003). Some
results of feasibility study related to feeding ecology of cetacean were published in peer
reviewed scientific journal (Murase et al., 2007). Based on successful results of the feasibility
study, the study was expanded to full scale in 2002 (Government of Japan, 2002). Sei whales(B. borealis) was added as a target cetacean species in addition to minke and Bryde’s whales.
Although sperm whales (Physeter macrocephalus) have been a target species of the offshore
component of JARPN II since 2000, prey of sperm whales have not been studies in the preyspecies survey. 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. Thus, the main focus is to study
feeding ecology of cetaceans at meso scale in JARPN II. It was planned that the results of fullscale JARPN II will be review every six years. First six years period was 2002-2007. In thefull scale survey, JARPN II has three components (three regional survey areas) namely off
Sanriku, off Kushiro and offshore. In this paper, methodologies and procedures of cetacean
prey surveys in first six years of full scale JARPN II offshore component were reviewed.
SURVEY AREA
The survey area of the cetacean prey surveys was in the western North Pacific. Southern,
northern, eastern and western boundaries of the survey area were 35°N, boundary of EEZclaimed by a foreign country, 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 Sub-areas 7, 8 and 9 which are set for the Implementation Simulation Trials ofcommon minke whale in the North Pacific (IWC, 1994). Although the most of survey area ofoffshore component of JARPN II is out of EEZ of Japan, the area is migration corridors formany pelagic fish including 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 outsideof Japanese EEZ, investigation of feeding impact of cetaceans on those species is important.
Within the survey area, one to three small blocks were set for cooperative whale andprey surveys every year (Fig. 1). Ideally, cooperative survey should be conducted in the entire
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 the oceanographic conditions such as positions of fronts and water masses as well2

SC/J09/JR7
as anticipated distribution pattern of the target cetacean species so that small blocks could betreated as representative of the entire survey area.

Fig. 1. Survey blocks for cooprative whale and prey surveys in JARPN II offshore component
from 2002 to 2007. Each colour represents boundary of surveyed blocks. Zigzag line withineach block represent planned trackline.
For monitoring purpose, two regions were selected to set blocks: a region aroundboundary between Sub-areas 7 and 8 and a region around boundary between Sub-areas 8 and9. Surveys were also conducted in Sub-area 9. The region around boundary between Subareas 7 and 8 is under the influence of Kuroshio extension. Because positions and shapes ofKuroshio extension are highly variable both seasonally and yearly, positions of small blocks
were different from year to year according to the position and shape of Kuroshio extension.
Bryde’s whales were main target species in the region around boundary between Sub-area 7
and 8. Although there are seasonal as well as yearly changes in oceanographic conditions inmeridional (latitudinal) direction in a region around boundary between Sub-areas 8 and 9, thechange is relatively moderate in comparison with the region around Kuroshio extension.
Minke and sei whales are mainly distributed in the northern part of the region aroundboundary between Sub-area 8 and 9 while Bryde’s whales are mainly distributed in southernpart of it.
TIMING OF SURVEYS
Timing of cooprative whale and prey surveys from 2002 to 2007 was summarized in Table 1.
Both whale and prey surveys were conducted simultaneously in the survey blocks so that data
were collected at same spatiotemporal scale. As mentioned in Introduction section, scale of3

SC/J09/JR7
the interest of JARPN II is meso scale (cetaceans move over days and weeks in search ofpreferred local abundance of food). Each block was surveyed within one to three weeks.
Because no prey survey vessel was available, cooprative whale and prey survey was notconducted in 2006.
Table 1. Timing of cooprative whale and prey surveys from 2002 to 2007.
Year
2002

2003
2004
2005

2007

Prey Survey

Whale Survey

Block(Abbreviation)

Special Block A

2002-A

SYO

17-Jul

26-Jul18-Jul

1-AugSpecial Block B

2002-B

SYO

2-Aug

9-Aug

7-Aug

17-AugBlock A

2003-A

SYO

15-Jun25-JunVessel

Start

End

Start

End

10-Jun22-Jun26-Jun29-JunBlock B

2003-B

SYO

1-Jul

9-Jul

Offshore

2004-OSYO

14-Sep19-SepWestern Block2005-W

SYO

12-Jul

25-Jul8-Jul

15-JulEastern Block2005-E

SYO

27-Jul11-Aug25-Jul

4-Aug

Block 1

2007-1

KK1

7-Jul

26-Jul9-Jul

22-JulBlock 2

2007-2

KK1

28-Jul21-Aug23-Jul

2-Aug

Block 3

2007-3

KK1

24-Aug

4-Sep

11-Aug13-Aug

1-Jul

7-Jul

5-Sep

8-Sep

TRACKLINE DESIGN
Zigzag tracklines were constructed for prey survey in all cooprative survey blocks (Fig. 1).
The survey vessel steamed on planned zigzag tracklines. Spacing between waypoint were
decided based on avirable days of prey survey vessels.
RESEARCH VESSEL
Two trawler type fisheries research vessels(RVs), Shunyo-maru (Fisheries Research Agencyof Japan, 887 GT, SYO) and Kaiko-maru (Kaiko Senpaku, 860 GT, KK1), conducted preysurveys (Fig.2). SYO was used from 2002 to 2005 while KK1 was used in 2007. Net
sampling, acoustic data recording using quantitative echosoudners and oceanographic
observations were conducted by RVs.

(b)

(a)
Fig.2. Prey survey vessels. (a) Syunyo-maru (SYO) and (b) Kaiko-Maru (KK1)

Four vessels were engaged in whale surveys in cooperative survey blocks. Three vessels were
engaged in the whale survey consisting of sighting and sampling of whales. Those three4

SC/J09/JR7
vessels were termed as sighting and sampling vessels (SSVs). Sampling of whales is legal
according to Japanese national regulation and the International Convention for the Regulationof Whaling (ICRW). Stomach contents of sampled minke, Bryde’s and sei whales were
examined on the research base ship, Nisshin Maru (NM: 7,659GT). In 2002 and 2007
dedicated sighting vessels (SVs) conducted sighiting survey of cetaceans in cooperative
survey blocks. Details of whale surveys were described in Tamura et al. (2009).
NET SAMPLING
Four types of nets (NORPAC, IKMT, MOCNESS and midwater trawl) were used to sample
various prey species from zooplankton to fish (Fig.3).

(c)

(a)

(b)

(d)

Fig.3. Four types of nets used in the prey surveys: (a) midwater trawl (Fig.1 of Ueno et al.,2004), (b) MOCNESS, (c) IKMT and (d) NORPAC.
The midwater trawl (NST-99, Nichiomo, Japan) 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. Details of specification of the
midwater trawl are described in Ueno et al. (2004). The sampling depth and, the height andwidth of the mouth of the net were monitored with either by Scanmar net monitoring system(Scanmar, Norway) or PI32 Catch Monitoring System (Simrad, Norway). Towing speed of
the trawl net was 4-5 knots. Surface and midwater trawl was towed at predetermined andtargeted stations. Surface trawls were conducted using the midwater trawl net with the floats
attached to the bridle so that the trawl could be towed at the surface. Surface trawl was
designed for collecting Pacific saury which distributes near surface layer (Ueno et al., 2004).
Targeted trawls were conducted to identify the species and size compositions of biologicalbackscattering detected by the quantitative echosounder. The purpose of the predeterminedtrawls was to estimate the abundance and distribution patterns of cephalopods and neustnic

5organisms such as Pacific saury that are difficult to detect by the echosounder. Two different
depth layers were sampled at predetermined trawl stations; 0-30m (surface) and 0-100m(midwater). In general, midwater predetermined trawl was towed for 10 minutes at each depth
layer (0-30 m, 30-60 m, and 60-100 m) whereas surface predetermined trawl was towed for
30 minutes. All samples were identified to the species as much as possible and wet weight ofeach species was measured aboard the ship. For the major species, length of 100 individuals
was measured to examine their size composition.
MOCNESS (Multiple Opening / Closing Net and Environmental Sampling System)
was used to collect vertical distribution and biomass data of copepods. Because specialized
equipments were required to tow the MOCNESS, it was only used onboard SYO. MOCNESS
was used from 2003 to 2005. The mouth opening size and mesh size were 1 m2 and 0.33 mm
x 0.33 mm, respectively. At the predetermined station, following depth layers were towed; 020 m, 20-40 m, 40-60 m, 60-80 m, 80-100 m, 100-150 m, 150-200 m and 200-250 m. In somecases, target towing was also made to identify species and size compositions of biologicalbackscattering detected by the quantitative echo sounder. The samples were preserved in
10 % formalin for species identification at the laboratory.
IKMT (Isaacs-Kidd Midwater Trawl) was mainly used to sample krill. IKMT wasused in 2002 and 2007. IKMT with mouth opening of 1 m2 was used in 2002 while IKMTwith mouth opening of 9 m2 was used in 2007. IKMT was mainly used to investigate species
identification and size compositions of backscattering from krill detected by the quantitativeecho sounder. The samples were preserved in 10 % formalin for species identification at thelaboratory.
A small plankton net, NORPAC (North Pacific standard net), equipped with flow
meter was towed at most of trawl stations to estimate abundance of copepods in 2002 and2007. The mouth opening and mesh size of NORPAC are 45 cm and 0.35 mm, respectively.
NORPAC was towed from 150 m to surface but it was towed various depth range in somecases to identify species compositions of acoustical backscattering. The samples were
preserved in 10 % formalin for species identification at the laboratory.
Number of net hauls was summarized in Table 2.
Table 2. Number of net hauls in cooperative survey blocks form 2002 to 2007.
Block
2002-A
2002-B
2003-A
2003-B
2004-O
2005-W
2005-E
2007-1
2007-2
2007-3IKMTNORPAC

Predetermined

Midwater trawl
Targeted

Predetermined

MOCNESS
Targeted

Targeted

Predetermined

7
6
11
5
6
9
12
21
26
13

5
4
2
1
0
4
3
5
0
1

3
3
3
7
4
-

0
4
0
0
0
-

11
7
8
4
0

6
7
21
27
14

QUANTITATIVE ECHOSOUNDER

Quantitative echosounders were used in prey surveys to collect distribution pattern andbiomass data of prey species. EK60 (Simrad, Norway) was used onboard SYO while EK500(Simrad, Norway) was used onboard KK1 (Fig.4). Both EK60 and EK500 are commonly used6

for surveys on fisheries resources worldwide. Data recorded by 38 and 120kHz transceivers
were used for analysis. Only EK60 raw data were saved in 2002 and 2004 while data wererecorded with an aid of a software Echoview (Myriax, Australia) in other years. A calibration
was conducted within the survey area every year.

(a)

(b)

Fig.4. Quantitative echosounders; (a) EK60 and (b) EK500.
OCEANOGRAPHIC OBSERVATION

Water temperature and salinity profiles were recorded using Conductivity-Temperature-Depth
profiler (CTD, SBE-19, Seabird, USA) and expendable CTD (XCTD, Tsurumi Seiki Co.,
Japan) (Fig.5). CTD and XCTD casts were made most of net haul stations. Details of
oceanographic observations were described in Okazaki et al. (2009).

Fig.5. Oceanographic observation using CTD.
DISCUSSION
The cetacean prey surveys in offshore component of JARPN II took multidisciplinary
approach to collect oceanographic and prey species data. Such a large scale multidisciplinary
surveys in marine ecosystem have not been conducted in offshore region of the North Pacificor other boreal regions of world. The data collected by the surveys were used to estimates theprey preferences of cetaceans and results are presented to this workshop (Murase, et al., 2009).
Norway conducted several concurrent minke whale sampling and prey surveys in the polar
region of Norwegian waters (e.g. Haug et al., 1995; 1996; Lindstrøm et al., 2001). Prey
preferences of three baleen whale species, minke, Bryde’s and sei whales, were studied in
JARPN II. Minke, Bryde’s and sei whales feed on wide variety of preys. To collect these preyspecies data, wide variety of sampling gears were used in JARPN II. However, data of
copepods and Pacific saury were spatially sparse in comparison with other species because
nets were used. Species other than copepods and Pacific saury were studied using
echosounders. If their biomass can be estimated using echosouders, one will be able to study7more detailed prey preference of cetaceans in both spatial and temporal scales. Biomass ofcopepods can be estimated using echosounders. However, because of small body size ofcopepods, 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 estimation of biomass. Up
looking echousounder mounted on Autonomous Underwater Vehicle (AUV) can be used foralternation of trawling. However, development and deployment of such new equipment willtake time and they will not take place in immediate future. To sample prey species, use of
MOHT (Matsuda-Oozeki-Hu-Trawl) net in addition to nets used in JARPN II will enhancesampling efficiency as suggested by Oozeki et al. (2004). Small blocks of prey surveys weretreated as representatives of the entire survey area because availability of fisheries research
vessel for prey survey was not allowed to survey in entire area. Ideally, cooperative survey
should be conducted in entire the survey area. Entire survey area will be surveyed in future
JARPN II from time to time if conditions allow.
To estimate prey preference of cetaceans, examination of stomach contents data is
only way to identify species consumed by them specifically (e.g. Haug et al., 1995; 1996;
Lindstrøm et al., 2001; Murase et al., 2007., Tamura et al., 1998; Tamura and Fujise, 2002).
In addition, prey biomass should also be estimated concurrently with cetacean samplings.
There are several papers to study prey preference of cetaceans using distribution pattern dataof cetaceans and preys without using stomach contents of cetaceans (Friedlaender et al. 2006;
Piatt and Methven 1992; Witteveen et al., 2008). These studies only indicated effect of
distribution patterns of prey on distribution patterns of cetaceans but they could not tell any
prey preference of cetaceans because they could not identify actual prey species consumed bycetaceans. Feeding ecology of baleen whales can be studied using several methods other thanstomach contents. Barros and Clarke (2002) categorized those methods as follows; direct
observation of feeding (e.g Dunham and Duffus 2001; Hoelzel et al. 1989; Tershy 1992),
traditional methods (analysis of vomit, scat, stomach and intestine contents), fatty acids (e.g.
Møller et al. 2003), stable isotopes (e.g Gendron et al. 2001; Mitani et al., 2006; Todd et al.
1997), genetic identification of scat (e.g. Jarman et al., 2002) and video taping of feeding
behaviour. In addition, telemetries such as satelltite tag and time and depth recorder (TDR)(e.g. Croll et al. 2001; Fiedler et al. 1998) were also used for feeding ecology study in recent
years. Direct observation of feeding is limited to above the sea surface or short duration ofunderwater observation by scuba survey. Given diversities and vertical distribution patters of
prey species of minke, Bryde’s and sei whales direct observation method is not applicable tothose species. Haug and Lindstrøm (2003) compared the traditional methods with the rest of
new methods and concluded that those new methods have not proven to provide detailed
quantitative information on the diet of individual animals and must be supplemented withtraditional methods especially with identifying and measuring items in gastrointestinal
contents though the combinations of those methods can support their results each other.
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). Although there are many definition of regime
shift, the study 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 persistentstate to another 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 copepods8

(Tadokoro et al., 2005), Japanese anchovy, Japanese sradine, 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). Stomach contents
collected by commercial fisheries indicated that common minke whales switched their preys
according to biological regime shift of prey abundances (Kasamatsu and Tanaka, 1992).
However, effects of both biological and climatic regime shifts on baleen whales in thewestern North Pacific are still largely open to question because of lack of data collected
through systematic surveys. So far, regime shift have not been reported during JARPN II from2002 to 2007. To detect effect of regime shifts on cetaceans as well as effect of predation bycetaceans on biological regime shifts, long term cetacean prey survey program is criticallyimportant.
ACKNOWLEDGMENT
Authors expressed thanks to all the crews and researchers who engaged in the offshore
component of JARPNII. This survey was supported by Fisheries Agency of Japan, Fisheries
Research Agency of Japan and the Institute of Cetacean Research. We thank to these
institutions for their support.
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Okazaki, M., Inagake, D., Murase, H., Watanabe, H., Yonezaki, S., Nagashima H., Matsuoka,
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