SC/58/IA 17

The relationships between sea ice extension and trends in sighting parameters ofAntarctic minke whales based on IDCR-SOWER data from CPII to CPIII
KOJI MATSUOKA, HIROSHI KIWADA ANDTAKASHI HAKAMADAThe Institute of Cetacean Research, 4-5, Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan

Contact e-mail: matsuoka@cetacean.jp

ABSTRACTThe relationship between sea ice extensions and the trends in sighting parameters (Area size (A), effort (L),number of school sightings (ns), effective search half width (Ws), mean school size (E(s)), abundance estimates(P)) from CPII to CPIII, used in the estimations of abundance of Antarctic minke whale by Branch (2005), wasinvestigated. According to recent information, sea ice extensions were observed in most management Areas fromCPII to CPIII, except Area VI. Especially, large sea ice extensions were observed in Areas III and IV. On the otherhand, sea ice reduction was observed in Area VI. The present analysis was focused on Areas III-W, IV-E and
VI-W where survey area changed clearly due to the sea ice extension from CPII to CPIII. The sighting rate andmean school size decreased in the case of Areas III-W and IV-E, but they increased in the case of Area VI-W. It ispossible that sea ice extension has caused the under estimation of Antarctic minke whale abundance for CPIII in
Areas III and IV.
KEY WORDS: ANTARCTIC, SURVEY VESSEL, DISTRIBUTION, ABUNDANCE ESTIMATE, ANTARCTICMINKE WHALE

INTRODUCTION
It is clear that relationship between sea ice coverage and abundance estimates of Antarctic minke whales isrelevant, based on the following studies in recent SC meeting;1) Sea ice was more extensive in CPIII than CPII in Area I, II, III, IV and V based on the satellite data. It issuggested that estimates of Antarctic minke whales in these Areas were underestimated due to someunsurveyed area where vessels could not survey within the sea ice (Shimada and Murase, 2005).
2) According to the sea ice analysis in each Area between CPII and CPIII, an unusually extensive sea ice
free area, polynia, adjacent to the southeastern side of the Antarctic Peninsula was observed in the CPIIIin Area II. Such large polynia were not observed via satellite during the rest of the observation period(1979-2002). The vessels could not survey within the polynia because the sea ice prevented access to thepolynia (Murase et al, 2005).
3) By the ice breaker observations, it was confirmed that there were some Antarctic minke whales in the sea
ice area where the normal vessels could not enter the area (Shimada and Kato, 2005).
This paper reports relationship between sea ice extensions and the trends in sighting parameters of Antarctic
minke whales from CPII to CPIII, based on IDCR-SOWER abundance estimation.
MATERIAL AND METHODS
Sea ice dataFig. 1 show that January sea ice extent anomaly (million km^2) trend in each Area from 1979 to 2002.
Bootstrap sea ice concentrations are from Nimbus-7 SMMR and DMSP SSM/1. The triangles and circles
indicate survey years in CPII and CPIII, respectively. Sea ice extensions were observed in almost
management Areas from CPII to CPIII except Area VI (Shimada and Murase, 2005).
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Index of the sea ice extent and abundance estimates
Shimada and Murase (2006) investigated the Index of the estimated abundance and sea ice extent comparedto CPIII and CPII (Fig. 2).

Sea ice information and cruise track lines
We extracted these information from IWC/DESS. A database package called DESS 3.5 (Strindberg and Burt
2004) has been developed to automate the process of extracting survey data and to invoke the Distancesoftware program to provide estimates of abundance. Fig. 3a-3c compared the stratification and cruise tracklines from CPII and CPIII in Areas III, IV and V. Fig.5 compared the cruise track line and sighting positionsof the Antarctic minke whale in CP I, II and III.
Sighting parameters
We used the sighting parameters (Area size (A), effort (L), number of school sightings (ns), effective searchhalf width (Ws), mean school size (E(s)), abundance estimates (P)) between CPII and CPIII, based on
IDCR-SOWER abundance estimation (Table 4a- 4e, Branch, 2005).
RESULT AND DISCUSSION
Each Area was divided into two classes by Fig.2. Large abundance declines were observed in Areas III and IV.

On the other hand, sea ice reduction was observed in Area VI (Shimada and Murase, 2005). Fig. 3a-3c also
indicated the status of sea ice extensions and reduction. We found that west half of Area III, east half of Area
IV and west half of Area VI showed larger difference between CPII and CPIII. Therefore, we focus on Areas
III-W, IV-E and VI-W where survey area changed clearly due to the sea ice extension from CPII to CPIII.
However, we excluded Area II, because large polynia was not surveyed in CPIII and abundance estimate
could be underestimated greatly (Murase et al., 2005).
As a result, the sighting rate (ns/L) and mean school size (E(s)) were decreased in the case of larger
sea ice extension (Areas III-W and IV-E), but they increased in the case of sea ice reduction (Area VI-W)(Fig. 4a and 4b). Present results suggested that sea ice extension caused to decrease of the sighting rate(ns/L) and mean school size (E(s)) of Antarctic minke whales, and this caused the under bias of theabundance estimates in most Areas in CPIII.
Based on this conclusion, we should adopt the abundance estimates during normal sea ice condition
years, and would emphasize the necessity of appropriate corrections for estimates during sea ice extension
years in the CPIII. Present data support this conclusion.
ACKNOWLEDGEMENTS
We would like to thank Dr. Hiroshi Hatanaka, the Institute of Cetacean Research and Dr. Hidehiro Kato,
Tokyo University of Marine Science and Technology, for their valuable comments to improve earlier
manuscript. We also thank to Mr. Atsushi Wada for his construct of figures.
REFERENCES
Branch, T.A. Preliminary abundance estimates for Antarctic minke whales from three completed sets of IDCR/SOWER circumpolar
surveys, 1978/79 to 2003/04. , 2005. SC/57/IA16.
Murase, H., Kitakado, H. and Shimada, H., 2005. Alternative estimation of Antarctic minke whale abundance taking account ofpossible animals in the unsurveyed large polynia using GAM-based spatial analysis: A case study in Area II in 1997/98
IWC/SOWER. SC/57/IA6.
Shimada, H. and Murase, H. 2005. Relationship between sea ice and Antarctic minke whales. IWC/SC, ANNEX G, Appendix 3.
Shimada, H. and Kato, A. 2006. Preliminary report on a sighting survey of Antarctic minke whale within ice field conducted by theIce Breaker, Shirase in 2004/2005. SC/58/IA11.
Strindberg, S., and L. Burt. 2004. IWC Database-Estimation Software System (DESS) User Manual. University of St
Andrews, St Andrews. 450 pp.

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Fig.1. January sea ice extent anomaly (million km^2) trend in each Area from 1979 to 2002. Bootstrap sea ice
concentrations are from Nimbus-7 SMMR and DMSP SSM/1. The triangles and circles indicate survey years in
CPII and CPIII, respectively. sea ice extensions were observed in almost management Areas between CPII andCPIII except Area VI (Shimada and Murase, 2005）.

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Fig.2. Relationship between Index of estimated abundance and sea ice extent compare to CPIII and CPII (Shimada andMurase, 2006).

Fig. 3a.

Comparison of the stratification and cruise track between CPII and CPIII in Area III.
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Fig. 3b. Comparison of the stratification and cruise track between CPII and CPIII in Area IV.

Fig. 3c. Comparison of the stratification and cruise track between CPII and CPIII in Area VI. Survey area changed
clearly due to the sea ice coverage between CPII and CPIII.

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Fig. 4a. Trends in the sighting rates (number of whales / n.mile) of Antarctic minke whales in Closing mode (NSC)
between CPII and CPIII.

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Fig. 4b. . Trends in the mean school size of Antarctic minke whales in Closing mode (NSC) between CPII and CPIII.

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SC/58/IA 17Fig. 5. Comparison of the cruise track and sighting position of Antarctic minke whales in each Area (Upper: CPI,middle: CPII, Lower: CPIII).

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