SC / 61 / IA16(Not to be cited without author’s permission)

Influence of sea ice concentration on Antarctic minke whale abundance
estimation in the Ross Sea
KOJI MATSUOKA1), TAKASHI HAKAMADA1), KEISUKE KIMURA2) AND YOSIHIRO OKADA2)
1) The Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan
2) Tokai University Unified Graduate school of Earth and Environment Science, 3-20-1, Orido, Shimizu, Shizuoka,
424-0902, Japan
3) Nippon Kaiyo CO., LTD., Environmental Research and Marine Instrument Division, 9-2, Sakae-cho, Kita-ku,Tokyo, 114-0005, Japan
Contact e-mail:matsuoka@cetacean.jp
ABSTRACTThe relationship between the sea ice condition and the abundance estimates of Antarctic minke whales in the Ross
Sea was examined using the IDCR/SOWER and JARPA II survey data. For both IDCR/SOWER and JARPA II
surveys in the Ross Sea, abundance estimates were high when small ice extended in the survey area. In contrast, theabundance estimates were low when the sighting surveys were limited due to large sea ice extent. Sea ice
concentration anomalies in January from 1976 to 2008 were also examined. At the Ross Sea, the sea iceconcentration anomaly during CPII (1986) was almost lowest in the past 30 years, indicating that during CPII thesighting survey was able to cover the research area thoroughly. In contrast, the sea ice concentration anomaly washigh during CPIII (2004), indicating the sighting survey was unable to cover most, if not all, of the research area. Allof the information indicated that the survey coverage differed markly between CPII and CPIII. Estimates of recentJARPA II in 2006/07 and 2008/09 seasons suggested large fluctuation in abundance estimates between 2 seasons.
Magnitude of the fluctuation was four folds, possibly because of change in the sea ice extent, concentration andconfigurations in the Ross Sea. Recent sighting surveys conducted on the Japanese, German and Australian ice
breakers and aerial surveys reported the existence of Antarctic minke whales in the sea ice areas. These observations
suggest a relationship between abundance estimate and ice extent. Estimation of trend of abundance requiresconsideration of the effect of sea ice, particularly of year to year changes observed in sea ice extent; concentrationand configurations.
KEY WORDS: ANTARCTIC, SURVEY-VESSEL, ABUNDANCE ESTIMATE, SEA ICE, ANTARCTIC MINKEWHALE
INTRODUCTION
In recent years, SC/IA sub-committee recommended that the issue of sea ice condition in research areas thatappeared to influence abundance estimates of Antarctic minke whales should be examined using sea ice conditionindices such as sea ice concentration (“Changes in the location of the ice-edge and the proportion of animals southof the ice-edge”; IWC, 2003, 2005; Branch, 2007). The sub-committee also concerns about estimation of theAntarctic minke whales abundance inside of sea ice. Some preliminary studies for this including spatial analysis
have been presented (IWC, 2006, 2007, 2008).
It has been observed that Antarctic minke whales are concentrated along the ice edge. Similarly, Kasamatsu et al.
(2000) reported a significant negative correlation between Antarctic minke whale encounter rates and distance fromthe sea ice edge. In addition to that, recent sighting and aerial surveys conducted by the Japanese, German, and1

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Australian ice breakers and airplanes that covered the areas where SOWER vessels were not able to enter due to sea
ice reported existence of many Antarctic minke whales in such areas (Shimada and Murase, 2006, Shimada andKato, 2007, Scheidat, 2007, Kelly et al., 2008). Therefore, abundance of Antarctic minke whales estimated from thedata that was unable to cover these areas should be underestimated.
Last year, we hypothesized that, as the abundance estimates from CPII and CPIII from a given statistical area
were substantially different, the sea ice conditions should have been also quite different between the two. In fact,
this relationship was clearly seen in Area II (Weddell Sea) and Area V (Ross Sea) where the shape of ice field varies
substantially year by year due to changes in the sea ice and meteorological conditions. Abundance estimate was highat the year when the survey was able to cover the statistical area thoroughly, and was low when the survey was notable to do so due to the high ice concentration. Recent sighting survey conducted on the Japanese, German andAustralian ice breaker and aerial survey reported existence of Antarctic minke whales in such areas. Theseobservations strongly support this hypothesis and further qualitative analysis is required to accommodate thediscrepancy (Matsuoka et al., 2008).
This year, in this document, we focused the Ross Sea (south of 69oS) which Antarctic minke whale abundance
estimates were showed large fluctuation between CPII and CPIII. Further, we also using recent JARPA II estimates(two seasons), which were also showed large fluctuations between two seasons.
MATERIAL AND METHODSThe IDCR/SOWER sighting survey data (the ice edge lines, the searching effort and the primary sightings) were
provided by the IWC/ Database and Estimation Software System (DESS). To see the effect of change in sea ice
concentration on abundance estimation of Antarctic minke whales in the Ross Sea, January sea ice concentration
anomaly by each latitudinal sector from 69°S to the Antarctic continent from 1979 to 2008 was calculated using
satellite derived monthly sea ice data, Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I(Comiso, 1999). Resolution of original data was 25 * 25 km grid in polar stereographic projection and sea iceconcentration in each grid was available in the original data. Firstly mean sea ice concentration by each latitudinal
sector from 69°S to the Antarctic continent in each year was calculated using original data. Secondary, anomaly
from mean sea ice concentration values from 1979 to 2008 for respective latitudinal sector was calculated. The 2009
data was not available at this moment. The anomaly data were then plotted on time series contour plot. To clarify theeffect of sea ice of abundance estimation of Antarctic minke whale, past papers (Murase and Shimada, 2004;Shimada and Murase, 2006) were revisited in this paper.
The JARPA II dedicated sighting survey data (the same as above) were also used in this paper. Abundance
estimates of Antarctic minke whale in the Ross Sea in 2006/07 and 2008/09 seasons which assuming g(0)=1, wereprovided by one of the Authors (TH).
RESULTS AND DISCUSSIONS
The abundance estimates at Area V substantially differed between CPII and CPIII (Okamura and Kitakado, 2009).
At the Area, the abundance estimates were high during CPII and low during CPIII. This could indicate a decrease ofAntarctic minke whales over time or it could simply be due to operational difficulties on sea ice field. At this time,
we go for the latter explanation because it is known that concentration and configuration of sea ice usually varies
substantially year by year especially at the Ross Sea, resulting in changes in coverage area for the sighting survey
followed by subsequent underestimation of Antarctic minke whales abundance. Antarctic minke whale abundancemust be underestimated if sighting survey cannot cover all of the water in the research areas due to the higher seaice concentration that prevent the research vessels but not Antarctic minke whales. As same as last year (Matsuokaet al., 2008), we thus hypothesize that, if abundance estimates from CPII and CPIII from the same statistical area
were substantially different, the sea ice condition should have been also quite different between the two.

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Secondary, the sea ice condition during CPII to that during CPIII at the Ross Sea was carefully compared (Figures
1, 2 and 3). As a result, during CPIII, the ice edge was extended southwestward at the Ross Sea. There was anextensive sea ice area in the eastern part of the Ross Sea. The vessels could not survey this area and a narrower areaof coverage by the CPIII. This ice condition should have resulted in substantial reduction in coverage for sighting
survey followed by low abundance estimates during CPIII compared to CPII. In almost of this extensive sea ice area,
sea ice concentrations were between 12% (light blue colored) and 50 % (light orange colored), which prevent theresearch vessels but not Antarctic minke whales.
Then the level of sea ice concentration anomalies in January from 1976 to 2008 was compared between CPII andCPIII (Figure 4). At the Ross Sea, the sea ice concentration anomaly during CPII (1986) was the lowest in the past
30 years, indicating that during CPII the sighting survey were able to cover the research area thoroughly. In contrast,
the sea ice concentration anomaly was high during CPIII (2004), indicating the sighting survey was unable to covermost, if not all, of the research area. In fact, in 2002/03 season, SOWER vessels gave up the Ross Sea survey due toabnormal sea ice extent. All of the information indicated that at the Ross Sea, the areas covered by the sighting
survey quite differed between CPII and CPIII.
For the JARPA II estimates, the large fluctuation of abundance estimates of Antarctic minke whales was observedin the two seasons (2006/07 and 2008/09 seasons) in the Ross Sea. Comparison of these estimates which assumingg(0)=1, were 19,400 (CV=0.176) in 2006/07 season and 87,643 (CV=0.166) in 2008/09 season, respectively(Hakamada, per.com, in prep.). The estimate showed large fluctuation in the magnitude of four folds possibly during
2 years. Influence of the sea ice concentration was thus clearly seen on abundance estimates of Antarctic minke
whales during these seasons (Figures 5 and 6). As we hypothesized, at the Ross Sea, a negative relationship wasdetected as the abundance estimate was lower with higher sea ice concentration. Such phenomena were observed
possibly because Antarctica land shape and ice shape was variable in the Ross Sea.
Resent sighting survey conducted on the Japanese, German, and Australian ice breakers in fact reported existenceof many Antarctic minke whales within the ice edge areas (Shimada and Murase, 2006, Shimada and Kato, 2007,Scheidat, 2007). Spatial analysis also showed similar results (Murase et al., 2005; IWC, 2006). These observations
suggest a relationship between abundance estimate and ice extent. Further studies are necessary to investigate large
impact of sea ice conditions on Antarctic minke whale abundance estimation especially in Area V (Ross Sea) suchas case study of analysis by 10 degree longitudinal slices for small scale study area which already started in IA
e-mail sea ice working group (Shimada and Burt, 2007).
It is concluded that estimation of trend of abundance requires consideration of the effect of sea ice, particularly ofyear to year changes observed in sea ice extent; concentration and configurations. This trend should only beinterpreted as 2 abundance estimates at 2 different times under different sea ice extent, concentration andconfiguration.
ACKNOWLEDGEMENTS
We wish to express our gratitude to Hiroshi Hatanaka, Shigetoshi Nishiwaki, Hiroto Murase, Naohisa Kanda, Saeko
Kumagai and Hiroyuki Shimada for their constructive suggestions to improve a previous version of this paper. We
also thank Atsushi Wada and Tomoko Hasegawa for their help for this paper.
REFERENCES
Branch, T.A. 2007. Possible reasons for the appreciable decrease in abundance estimates for Antarctic minke whales
from the IDCR/SOWER surveys between the second and third circumpolar sets of cruises. Paper SC/58/IA4
presented to the 58th IWC Scientific Committee, June 2007 (unpublished). 8pp. [Paper available from the Office3

SC / 61 / IA16of this Journal].
Comiso, J. 1999, updated 2007. Bootstrap sea ice concentrations from Nimbus-7 SMMR and DMSP SSM/I. Boulder,CO, USA: National Snow and Ice Data Center. Digital media.
International Whaling Commission. 2003. Report of the Scientific Committee, Annex G. Appendix 10. Report of the
Sub-Committee on Other Southern Hemisphere Whale Stocks. J. Cetacean. Res. Manage. (Suppl.), 5:248-292.
International Whaling Commission. 2005. Report of the Scientific Committee, Annex G. Report of the
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Kasamatsu, F., Matsuoka, K and Hakamada, T. 2000. Interspecific relationships in density among the whale
community in the Antarctic. Polar Biol. 23: 466-473.
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Antarctica: report on 2007/08 test survey and future plans. Paper SC/60/IA4 presented to the 60th IWC ScientificCommittee, June 2008 (unpublished). 9pp. [Paper available from the Office of this Journal].
Matsuoka, K., Nishiwaki, S., Murase, H., Kanda, N., Kumagai, S. and Hatanaka, H., 2008. Influence of sea ice
concentration in the research area on IDCR-SOWER abundance estimation. Paper SC/60/IA12, presented to the60th IWC Scientific Committee, June 2008 (unpublished). 9pp. [Paper available from the Office of this Journal].
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whale abundance estimation in the Antarctic from 1978 to 2002. Paper SC/56/IA10, presented to the 56th IWC
Scientific Committee, June 2004 (unpublished). 15pp. [Paper available from the Office of this Journal].
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Area II in 1997/98 IWC/SOWER. Paper SC/57/IA6. 20pp.
Okamura, H. and Kitakado, T. 2009. Abundance estimates and some diagnosis of Antarctic minke whales from thehistorical IDCR/SOWER survey data using the revised OK method. Paper SC/61/IA6 (this meeting).
Scheidat, M., Kock, K-H., Friedlaender, A., Lehnert, L. and Williams, R. Using helicopters to survey Antarctic
minke whale abundance in the ice. 10pp.
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SC / 61 / IA16Figure 1. Ice edge anomaly between CPII and CPIII in the Ross Sea (south of 69°S between 165°E to 170°W(including west of 165°E and east of 170°W in the inner part of the Ross Sea). Grey color shows theAntarctica. Pink color shows extent sea ice north CPII than CPIII and blue color shows it extent north
CPIII than CPII (Shimada and Murase, 2006). There are large unsurveyed areas in the Ross Sea.

Figure. 2. Relationship between sea ice extent (without sea ice concentrations) and Antarctic minke whales in theRoss Sea using IDCR/SOWER CPII (left) and CPIII (right) data. Maps of sighting survey track lines,
boundary lines of strata, primary sighting positions of Antarctic minke whale (open circle), and observed sea
ice edge line by research vessels. Data were obtained from the IWC/DESS.

Figure 3. Sea ice concentration maps of CPII (left:1985/86) and CPIII (right: 2003/04).

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Figure 4. Sea ice concentration anomaly of the Ross Sea (south of 69oS) in January by longitude (from 1979 to 2008) with CPII (1986) and CPIII (2004) (colored squares).
Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I (Comiso, 1999). In 2003, SOWER vessels gave up the Ross Sea survey due toabnormal sea ice extent.

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Figure 5. Relationship between sea ice extent (without sea ice concentrations) and Antarctic minke whales (opencircle: primary sighting positions) in the Ross Sea using JARPA II 2006/07 (left) and 2008/09 (right) data.
Ice edge lines were estimated by the research vessels and satellite data.

Figure 6. Sea ice concentration maps of JARPAII seasons (left:2006/07, right: 2008/09).

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