SC/62/NPM4Levels of incidental catches of common minke whales in thewestern North Pacific
Hiroshi Hatanaka¹, Mutsuo Goto¹, Takashi Hakamada¹ and Yong-Rock An²¹Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan²Cetacean Research Institute, National Fisheries Research & Development Institute, 139-29, Maeamdong, Mam-gu, Ulsan, 680-050, Republic of Korea

Abstract
This paper provides information on incidental catches of common minke whales by Japan and Korea inthe western North Pacific. Some suggestions are made to get plausible estimations of future incidental
catches as well to reconstruct past series considered defective.

1. Incidental catch used in the Implementation Simulation Trials (IST) in 2003
1.1. The Republic of Korea
Option Ki : This is described in page 121 of JCRM 6 (Suppl) (IWC, 2004). Incidental catch in sub-area 6is assumed to be zero until 1988 after which it increases linearly to 78 in 1995. Reported catch of 45-148
are used from 1996 to 2001. Future catches are calculated by an equation in proportion to the population
size based on the average catch of 89 in 1996-2001.

Option Kii : This is described in page 121 of JCRM 6 (Suppl) (IWC, 2004). The historic catch until 2001
is the same as for Option Ki. Future catches are calculated by the fixed number of the equation, which ischanged from average (89) to maximum catch (148).

1.2. Japan
Option Ji: This is described in pages 121-122 of JCRM 6 (Suppl) (IWC, 2004). Catches from 1979-99 aretaken to be the reported catches in the Japanese progress reports. Catches before these years are set at 3.8
which is the average of these years. Future catches are taken in proportion to the population size using an1

equation with a fixed number of 25.

Option Jii : This is described in page 122 of JCRM 6 (Suppl) (IWC, 2004). An incidental catch of 100
animals is assumed in each year from 1900 to the present. Future catches are assumed by the same
equation but with a fixed number of 100 animals.

2. Record in recent years
2.1. The Republic of Korea
Incidental catches from 2002 to 2008 were reported in the Korean progress reports. Those are 61-107
animals.

2.2. JapanA new ministerial ordinance on the by-caught animals in Japan started in July 2001. This ordinanceallowed the sell of whale meat of by-caught animals with the condition of a registration of tissue sample
in the Japanese DNA register for large whales, and therefore it was believed that under-reporting wasdissolved in practical terms. By-catches are 109-156 after 2002, and an increasing trend is suggested(Hakamada and Ishikawa, 2009). Allocation of by-caught whales to stocks (J and O stocks) became
feasible by genetic analysis (Kanda et al., 2009).

3. Suggestions for establishing plausible time series of incidental catch
3.1. The Republic of Korea
Until 1995 records are not available, then until that year the same values with Ki and Kii are proposed
until reports become available. Future catches are proposed in proportion to the population size with afixed number corresponding to the average of the last five years. A maximum annual catch for the fixed
number causes overestimation.

3.2. Japan
The incidental catch series used in the 2003 IST contains arbitrary numbers, and the assumption of
100 animals during 100 years is a contradiction of the assessment that J-stock was depleted.

For

example, the assessment of J-stock in the 1987IWC SC meeting estimated a depletion of 18 – 43 % for an
initial population and RY of 0 – 175 (IWC, 1988). Consequently, the category of protection stock wasmaintained. On the other hand, the recent by-catch levels of Korea and Japan suggest that the 19872

assessment was too pessimistic.

More plausible time series of Japanese by-catch are suggested asfollows:i)

The incidental catch in 2001 is two times the reported catch (because new regulation startedin July this year) .

ii)

Incidental catches in 2002 to 2008 are as those reported under the new regulation.

iii)

Past incidental catches are estimated based on a BPUE analysis (Appendix 1). The estimatesfrom 1955 to 2000 were obtained (Table 5 of Appendix 1).

iv)

Incidental catches before 1955 are set as the average of those in 1955 to 1978.

v)

Future incidental catches will be taken in proportion to population size with a fixed number
corresponding to the average of the last five years.

Referenses
International Whaling Commission. 1988. Report of the Scientific Committee. Rep. Int. Whal.
Commn. 38, p47, 104.
International Whaling Commission. 2004. North Pacific minke whale Implementation Simulation
Trial specifications. JCRM. 6(Suppl), p121-2.
Hakamada, T. and Ishikawa, H. 2009. An examination of the trend in the number of common minke
whales caught incidentally in the CPUE of Japanese fishing set net in the context of the effect on
the J stock of future catches of the western North Pacific common minke whales. SC/J09/JR WP2.
(unpublished).
Kanda, N., Goto, M., Kishiro, T., Yoshida, H., Kato, H. and Pastene, L.A. 2009. Update of theanalyses on individual identification and mixing of J and O stocks of common minke whalearound Japanese waters examined by microsatellite analysis. SC/61/JR5.

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Appendix 1
A trial for estimation of the incidental catch of common minke whales in a period 1955 – 2000 byJapanese set net fishery in the coasts of Japan.

Takashi Hakamada and Hajime Ishikawa
Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo, 104-0055, Japan

ABSTRACTIn this paper we examined the reported incidental catches of common minke whales (Balaenopteraacutorostrata) in the Japanese coasts in relation to the number of set nets. We estimated a yearly trend ofby-catches per unit effort (BPUE). Using this BPUE trend, we estimated incidental catch for the period
from 1955 to 2000 which was believed to be under-reported. It is suggested that these estimates are moreplausible than assuming the constantly 100 animals in this period.

INTRODUCTION
The common minke whales have been incidentally taken by set net fisheries. During 1955 to 2000 thenumber of the incidental catch was reported (IWC, 2004) but it was believed to be under-reported(Tobayama et al., 1992). At the Implementation Simulation Trials (ISTs) of this species in 2003, the Jii)
option that assumes 100 animals incidentally taken every year from 1900 was adopted (IWC, 2004). A
new regulation which allows that meat of by-caught whales can be sold after genetic registration, wasstarted at 2001. It was assumed that this regulation will improve reporting substantially. Hakamada andIshikawa (2009) conducted BPUE analysis using a GLM. Their analysis can be used to estimate thenumber of the incidental catches in the period 1955 – 2000.

MATERIALS AND METHOD
Set net fisheries have been continued for a long time and are one of the traditional fisheries in Japan.
Although the method of set net fisheries has not changed through the time, the number of the set nets

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(both ‘large size’ and ‘salmon’ nets) has been decreasing gradually from 1994 to 2006 (Table 1). Table 2
shows the number of incidental catches of the common minke whales in the coasts of Japan from 1994 to2000 which were reported in the Japan Progress Report on cetacean research 1995-2001. These numbers
possibly include incidental catches by ‘small-type’ set net. However, these numbers were believed to beunder-reported (e. g. Tobayama et al., 1992). A new regulation on incidental catches was started in 2001.
Table 3 shows the number of the common minke whales incidentally caught by the ‘large-size’ and‘salmon’ set net from 2001 to 2006 (ICR, 2008). These data are applied to the model (1) described below.

The BPUE is defined by the annual number of incidental catches of the common minke whales divided by
the total number of ‘large-size’ and ‘salmon’ set nets. In previous analysis (Hakamada and Ishikawa,2009), the period 2001-2005 was selected to examine BPUE because the new regulation that started in2001 brought better reporting of incidental catch to local governments. In order to obtain data for longer
period to estimate the trend of the BPUE, we added the data for 1994 – 2000 to those for 2001-2006. To
estimate the trend of the BPUE from 1994 to 2006, we use the generalized linear model with Poisson
error distribution expressed by[]log E ( C y ) = log( E y ) + α y + P + β(1)where E(Cy) is the expected number of the incidental catches in year y, Ey is the number of the total
number of the ‘large’ and ‘salmon’ set nets (i.e. Effort) in year y, αestimated, βis the trend of the BPUE to beis the intercept and P is a categorical variable of the period during 1994-2000 comparing tothat during 2001-2006. The first term on the right-hand-side is offset.

RESULT AND DISCUSSION
Estimated parameters in the model (1) are shown in Table 4. The exponential increase in BPUE isestimated as 4.2% (SE=0.024, p-value=0.082). The estimated reporting ratio of the number of theincidental catch in the coasts of Japan during 1994-2000 to that during 2001-2006 was 0.265. By
multiplying this figure to the number of the incidental catches reported from 1955 to 2000, the corrected
number was obtained (Table5). It is suggested that these estimates are more plausible than assuming theconstantly 100 animals in this period.

REFERENCES
Hakamada, T. and Ishikawa, H. 2009. An examination of the trend in the number of common5

minke whales caught incidentally in the CPUE of Japanese fishing set net in the context ofthe effect on the J stock of future catches the western North Pacific common minke whales.
Paper SC/J09/JR WP2 presented to the JARPN II Review Workshop, Tokyo, January 2009(unpublished). 2pp.
Government of Japan. 1995-2001. Japan Progress report on cetacean research.
The Institute of Cetacean Research. 2008. Stranding Record 2008.
International Whaling Commission. 2004. Report of the Sub-Committee on the revised
anagement procedure. J. Cetacean Res. Manage. 6 (suppl.):75-184.
Statistics department, Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF). 2007.
Annual Statistics on Fishery and Aquaculture production in 2005. Association of agriculture
and forestry Statistics, Tokyo. (in Japanese).
Statistics department, Ministry of Agriculture, Forestry and Fisheries of Japan (MAFF). 2008.
nnual Statistics on Fishery and Aquaculture production in 2006. Association ofgriculture and forestry Statistics, Tokyo. (in Japanese).
Tobayama, T., Yanagisawa, F. and Kasuya, T. 1992. Incidental take of minke whales in Japanese
rap nets. Rep. Int. Whal. Commn. 42:433-6

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Table 1. The number of ‘large-size’ and ‘salmon’ set nets off Japan during 19942006 (Statistics Department, MAFF, 2007; 2008).
year
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006

'large-size'
814
790
799
787
787
786
781
775
781
781
757
729
703

'salmon'968
965
941
917
914
916
911
914
891
874
876
878
886

total
1782
1755
1740
1704
1701
1702
1692
1689
1672
1655
1633
1607
1589

Table2. The number of the common minke whales incidentally caught during 1994-2000 as reportedin Japan progress report. (Possibly including the incidental catches from the ‘O’ stock and/or by‘small-type’ set net.)
year
1994
1995
1996
1997
1998
1999
2000

bycatc h16
1927
27
24
19
28

Table 3. The number of the common minke whales incidentally caught by ‘large-size’ and ‘salmon’set nets during 2001-2006.
year
2001
2002
2003
2004
2005
2006

bycatch
104*
96
106
103
116
138

*: The figure is the double of the number of the incidental catches during thesecond half of 2001 because the new regulation was started on 1st July 2001.

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Table 4. Results of estimated parameters in the model (1).
Estimate
Intercept -87.680
year
0.042
Period
-1.328SE
48.8650.024
0.171

z value-1.794
1.738-7.783

Pr(>|z|)0.07280.0822
7.10E-15

Table 5. Corrected number of the incidental catches.

year
1955-78
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000

reported correc ted
3.8
1400
3
110000
830
415
2
8
13
49
415
830
830
2075
519
830
1453
16
60
2075
27
102
27
102
24
91
1972
28
106

*: The catches during 1955-78 are taken to equal the average of the number during
1979-87.

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