SC/J09/JR5
Methodology and procedures of surveys of prey of common minke whales
JARPN II - Coastal component of Sanriku SHIROH YONEZAKI1, HIROSHI NAGASHIMA2, HIROTO MURASE1, HIDEYOSHI YOSHIDA3, TAKEHARU BANDO1,
MUTSUO GOTO1, SHIGEYUKI KAWAHARA4, AND HIDEHIRO KATO5
1

Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan

2

Miyagi Prefecture Fisheries Technology Institute, 97-6 Sodenohama, Watanoha, Ishinomaki, Miyagi 986-2135, Japan

3

National Research Institute of Far Seas Fisheries, Oceanic Resources Division, 2-12-4 Fukuura, Kanazawa-ku, Yokohama,

Kanagawa, 236-8648 Japan
4

National Research Institute of Far Seas Fisheries, Project Management Division, 5-7-1 Orido, Shimizu-ku, Shizuoka, Shizuoka,

424-8633 Japan
5

Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan

ABSTRACT
Methodology and procedures of survey of prey of common minke whales in the coastal component of JARPN II in the Sanriku
region during 2003 – 2007 (except 2004) are described. The main objective of the prey species surveys was the estimation of prey
preference of common minke whales. Prey preference was one of the most important parameters of ecosystem models. This
could only be studied by comparing species compositions of prey in stomachs of common minke whales with species compositionsof prey in area. Both the whale sampling and prey surveys were conducted in the same season though the prey survey period was
shorter than that of the whale sampling survey. While the whale sampling surveys were conducted in the coastal waters within amaximum of 50 nautical miles from Ayukawa, Miyagi prefecture, the prey species surveys were conducted in the wider area of theSanriku region. In each year, two to nine small blocks were established within in the Sanriku region of coastal component of
JARPN II. Trawler type fisheries survey vessels conducted prey surveys including net sampling and acoustic data recording by
quantitative echosounders. Four types of nets (IKMT, Bongo, Sabiki, and midwater trawl) were used to sample various preyspecies from zooplankton to fishes. Quantitative echo sounders, EK 500 and EK 60 (Simrad, Norway) commonly used for fisheries
research worldwide, were used in the prey surveys. Oceanographic observations using CTD and EPCS were also conducted aspart of the prey surveys.

INTRODUCTION
The first phase of the Japanese Whale Research Program under Special Permit in the western North
Pacific (JARPN) was to obtain data necessary to address questions related to stock identity, and this implied that asampling regime was not optimal for the ecological studies. The workshop of IWC recommended that future surveys
should consider a sampling design specifically for the research objective on feeding ecology. In particular, there wasa need to design surveys in coastal areas to evaluate the interactions between common minke whale (Balaenoptera
acutorostrata) and some fisheries (IWC, 2001).
The full-scale surveys of the second phase of the Japanese Whale Research Program under Special
Permit in the western North Pacific (JARPN II) started in 2002 (Government of Japan, 2002). The main focus of the
JARPN II was the study of the possible competition between whales and fisheries, and to elucidate the role of thecetaceans in the western North Pacific marine ecosystem. The relation between whales and fisheries will be
examined by developing ecosystem simulation models. Information important for the construction of these models is
obtained through quantitative research on the cetacean prey species, prey consumption and prey preferences of eachwhale species. Although prey preference of cetacean is not easy to know, it will be estimated based on stomach
contents of cetaceans and prey species biomass in their habitat. The purpose of this prey species surveys is toestimate the prey abundance for investigating prey preference of common minke whales that is an importantparameter for ecosystem modelings in the Sanriku region. Details of analysis of prey preference of common minke

whales were described in Murase et al. (2009).
The outlines of the investigation in the each year were shown by IWC / SC documents (Kawahara et al.,
2004; Yonezaki et al., 2006, 2007, 2008).

SURVEY AREA
In the full-scale survey, JARPN II has three components namely off Sanriku, off Kushiro, and offshore. The
Sanriku region is northeastern part of the Japanese Main Island that was known to be major grounds of the pastcommercial whaling of common minke whales in spring season (Hatanaka and Miyashita, 1997). This region is oneof the most productive waters in the world ocean due to the mixing of Kuroshio and Oyashio currents. Generally, theOyashio water dominates in the survey area in the investigation period (Hanawa and Mitsudera, 1987). Therefore,
this region was an important fishing ground for commercial species such as Japanese sand lance (Ammodytes
personatus) (Nagashima, 2000), Japanese anchovy (Engraulis japonicus) (Nagashima, 2007), and Pacific krill(Euphausia pacifica) (Taki et al., 1993; Taki, 2002). The possible competition between the whales and the fisheries inthis area was suggested by the JARPN and the JARPN II feasibility study (Tamura and Fujise, 2000).
Prey species surveys were conducted in the coastal region off Sanriku, independently from the coastal
sampling surveys for common minke whale during 2003 – 2007 (except 2004) as a part of JARPN II. The sampling
surveys of common minke whale were conducted in the coastal waters within the 30 nautical miles (maximum of 50
nautical miles) from Ayukawa, Miyagi prefecture. The survey area of the prey species surveys was wider than that ofwhale survey and embraced it. In 2003, the survey was conducted in a wider area off the Pacific coast of thenorthern Japanese Main Island, to cover the distribution of main prey species (Fig. 1). To avoid the conflict with nets
in the coastal waters, the waters within 10 miles from the coast were excluded in principle. The survey area divided
into two parts (Block I and II). A zigzag track lines were set to cover two blocks.
The surveys during 2005 – 2007 were conducted in a wider area at depths between 20 m and 200 m from 37° – 00´ N
to 38° – 40´ N off Sanriku (Fig. 2). To avoid the conflict with set nets in the coastal waters, the waters within 10 miles
from the coast were excluded in principle. The survey area was divided into nine blocks (A, B, C, D, E, F, G, HI, andJ) at depths of 40 m / 100 m and 37° – 40´ N / 37° – 54´ N / 38° – 15´ N. A zigzag track lines were set to cover eachblock. The survey of Block HI and J was carried out in 2006 only.

Block I

Block II
Figure 1. The survey area and two blocks of preyspecies surveys of Sanriku region in 2003.

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Ayukawa

100 m
200 m

MIYAGIA

B
E

FUKUSHIMA

C
F

HI

D
G

J

40 m

Figure 2. The survey area and nine blocks of prey species surveys of Sanriku region from 2005 to 2007. Block HI
and J were investigated in 2006 only.

TIMING OF SURVEYS AND RESEARCH VESSELTiming of whale sampling and prey surveys from 2003 to 2007 was summarized in Table 1. Both whale
sampling and prey surveys were conducted in the same season though the prey surveys period was shorter than thatof whale sampling surveys. The surveys were conducted during daytime from an hour after sunrise to an hour
before sunset. Zigzag track lines were constructed for prey surveys in all survey blocks (Fig. 1 and 2). The surveys
vessels steamed on planned zigzag track lines.
The research vessels (RVs) used were Kaiyo-maru No.7 (Nippon Kaiyo Co., Ltd, 499 GT, KY7),
Takuyo-maru (Miyagi Prefecture Fisheries Technology Institute, 120 GT, TKY), and Shunyo-maru (National ResearchInstitute of Far Seas Fisheries, 887 GT, SYO) that were trawler type fisheries research vessels (Fig. 3). Net sampling,
acoustic data recording using quantitative echosounders and oceanographic observations were conducted by RVs.
Details of whale sampling surveys were described in Kishiro et al. (2009).
Table 1. Timing of whale samplings, prey surveys, survey blocks, and research vessels from 2003 to 2007.

Year

Prey Survey

Survey Block

Research Vessel

Start

End

2003

9 – April

28 – April

I, II

2005

11 – April

27 – April

2006

11 – April

2007

9 – April

Whale Sampling Survey
Start

End

KY7

8 – April

2 – May

A, B, C, D, E, F, G

TKY

11 – April

21 – May

27 – April

A, B, C, D, E, F, G, HI, J

TKY, SYO

12 – April

24 – May

27 – April

A, B, C, D, E, F, G

TKY

16 – April

31 – May

3

(a)

(b)

(c)

Figure 3. Prey surveys vessels. (a) Kaiyo-maru No.7 (KY7), (b) Takuyo-maru (TKY), (c) Shunyo-maru (SYO)NET SAMPLING
Three types of nets (IKMT, Bongo, and midwater trawl) and Sabiki fishing gear were used tosample various prey species from zooplankton to fishes.
The trawl nets of KY7 and SYO were both mouth opening of 30 m width / 30 m height and a 17.5mm liner cod end. The trawl net of TKY was a mouth opening of 7 m width / 3.5 m height and a 3 mm liner
cod end. The sampling depths and height of the net mouth were monitored by Scanmar net monitoring
system (Scanmar, Norway). Towing speed of the trawl nets was 2 – 5 knots.
IKMT (Isaacs-Kidd Midwater Trawl) and Bongo net were mainly used to sample Pacific krill andjuvenile Japanese sand lance. These nets were used in 2003 and 2006. The mouth opening of IKMT
was about 3.7 m width / 3.1 m height. Sabiki fishing was the sampling using the fishing rod with artificial
bait, and it was mainly used for the fishes.
All samples were identified to the species as much as possible and weighted aboard the vessels.
For the major species (ex. Japanese anchovy, Japanese sand lance, Pacific krill), a sample of 100 animals
was taken, and lengths and weights were measured. Scaled and standard lengths were used to Japanese
anchovy and adult / juvenile Japanese sand lances, respectively. Total length from the tip of the rostrum tothe end of the teleson was used for Pacific krill. Trawl frozen samples were taken for further laboratory
analysis. IKMT and Bongo net samples were preserved in 10 % formalin for further investigation at thelaboratory. These data were used to identify the species and size compositions of biological backscattering
detected by the quantitative echosounder.
Number of net hauls was summarized in Table2.

Table 2. Number of net sampling from 2003 to 2007.

Year

Midwater trawl

Bongo net

Sabiki

IKMT

2003

22

4

–

17

2005

14

–

–

–

2006

11

1

2

–

2007

10

–

–

–

QUANTITATIVE ECHOSOUNDER
Quantitative echosounders were used in prey surveys to collect distribution pattern and biomass
data of prey species. EK 60 and EK 500 (Simrad, Norway) were used onboard KY7 and TKY, respectively.
These are commonly used for surveys on fisheries resources worldwide. Acoustic data collected by 38
and 120 kHz transceivers steaming at about 9 – 10 knots along the track lines. Those raw data wereanalyzed using software Echoview (Myriax, Australia). Calibration was carried out at a depth around 30 m
in the survey area using the copper sphere technique described in EK 500 manual.

OCEANOGRAPHIC OBSERVATION
Water temperature and salinity profiles were recorded using Conductivity Temperature Depth
profiler (CTD, Seabird, USA). CTD casts were made most net stations. Details of oceanographic
observations were described in Okazaki et al (2009).

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