Weddell seals show a clear diurnal haul-out pattern, while there have been few studies focusing on the influence of weather conditions. The present study investigates the relationship between the number of seals which haul-out on the fast ice and meteorological factors such as: air temperature, wind speed, humidity and irradiance in Syowa Station, East Antarctica. The number of seals was inversely related to wind speed (P  -8.3 °C), indicating that some other factors might influence the seal\u27s decision to stay in the water

Katsufumi Sato

Sakae  Kudoh

Yasuhiko Naito

Yasutaka Tsuchiya

National Institute of Polar Research Repository

Meteorological factors a#ecting the number of Weddellseals hauling-out on the ice during the molting seasonat Syowa Station, East AntarcticaKatsufumi Sato+, Yasutaka Tsuchiya,, Sakae Kudoh+and Yasuhiko Naito++National Institute of Polar Research, Kaga +-chome, Itabashi-ku, Tokyo +1-2/+/, Shimoda Marine Research Center, Tsukuba University, /+*+, Shimoda .+/**,/Abstract: Weddell seals show a clear diurnal haul-out pattern, while there havebeen few studies focusing on the inﬂuence of weather conditions. The present studyinvestigates the relationship between the number of seals which haul-out on the fast iceand meteorological factors such as: air temperature, wind speed, humidity and irradi-ance in Syowa Station, East Antarctica. The number of seals was inversely related towind speed (P*.**+), and positively related to air temperature (P*.*/), suggestingthat seals may enter the water to avoid excessive heat loss when the weather conditionwas severe. The number of seals varied greatly on calm days (wind speed/.-m/sand air temperature2.-C), indicating that some other factors might inﬂuence theseal’s decision to stay in the water.key words: haul-out, Weddell seal, Syowa Station, wind speed, air temperatureIntroductionThe Weddell seal (Leptonychotes weddellii) is normally found on fast ice areas ofthe Antarctic continent and adjacent islands (Stirling, +303; Kaufman et al., +31/).Mother Weddell seals arrive at tidal cracks in early austral spring and give birth to pupsfrom late September to early November (Smith, +30/; Kooyman, +302; Stirling, +303).During lactation from October to December, mothers and pups go into the waterprogressively more often as the pup grows (Thomas and DeMaster, +32-). Malesbegin to join the breeding colony approximately when the ﬁrst females haul out inSeptember, and compete for underwater territories beneath the tidal cracks (Kaufmanet al., +31/). Once the pups wean in December, mating takes place in water (Cline etal., +31+), and adult seals molt after mating (Thomas, ,**,).Weddell seals are able to rest, if not actually sleep, under the ice, surfacing only tobreathe (Stirling, +303). However, resting seals sometimes haul out on the ice and it isat this time they are most easily observed. Studies on the haul-out pattern of Weddellseals have shown that few Weddell seals haul out in the morning; most seals haul out inthe afternoon from +.-* to +1** during the molting season (Smith, +30/; Sini# et al.,+31+; Tedman and Bryden, +313; Thomas and DeMaster, +32-; Erickson et al., +323;Lake et al., +331). Several researchers have suggested that the number of seals thatE-mail address: ksato@nipr.ac.jp32Polar Biosci., +0, 32+*-, ,**- ,**- National Institute of Polar Researchhaul out ﬂuctuates depending on weather conditions, such as temperature, wind speed,solar radiation, cloud cover and snow (Matsuda, +30-; Smith, +30/; Sini# et al., +31+;Lake et al., +331). Yet, there have been very few studies focusing mainly on theinﬂuence of weather conditions on the haul-out pattern of Weddell seals. For example,Lake et al. (+331) reported that wind speed was negatively correlated with the numberof seals on the ice in January only. They suspected that females stay with their pups(born in October) even in strong wind during lactation. In the present study, observa-tions were conducted during the molting season (late February through April) toexclude the e#ects of reproductive activities and the presence of pups. The e#ects oftemperature, wind speed, humidity and irradiance on the haul-out number of Weddellseals were investigated.Materials and methodsDuring the austral summer, large numbers of Weddell seals can be seen in thevicinity of the Japanese Antarctic station, Syowa (03**S, -3-/E), which is coveredby fast ice from austral spring to autumn (Haga, +30+; Matsuda, +30-). Around EastOngul Island, on which Syowa Station is situated, there are small islands, groundedicebergs surrounded by tide and shear cracks and ﬂoating icebergs accompanied by shearcracks. Newly formed ice in the wake of the icebreaker Shirase’s departure provided afavorable structure for Weddell seals to haul out of the water in late summer fromMarch to April (Fig. +). Weddell seals began to appear on the ice in early spring(September), and their population reached a peak during the breeding season in OctoberFig. +. The observation site in the vicinity of Syowa Station, East Antarctica. Land is representedby the color gray and iceberg by the color black. The sea was covered in fast ice during thestudy period.Meteorological factors vs. hauling-out Weddell seals 99and November (Hoshiai, +32+; Naito and Hoshiai, +32-). They were rarely seen fromMay to August.We counted seals hauling out on the ice at a ﬁxed point (Fig. +) using binoculars(1/*, Carl Zeiss). Except for exceptionally low visibility days, the observations werecarried out +. times every day between +/** and +1** local time, when the most sealshauled out (Smith, +30/; Sini# et al., +31+; Tedman and Bryden, +313; Thomas andDeMaster, +32-; Erickson et al., +323; Lake et al., +331). The observation period wasfrom February ,0 to April ,2, +333, which coincided with the molting season of thisspecies at the study site.While crabeater seals (Lobodon carcinophagus) are occasionally found near SyowaStation in winter (Naito and Hoshiai, +32-), trips on the ice (-* times during the studyperiod of 0, days) revealed only Weddell seals. Crabeater seals have a circumpolarAntarctic distribution, spending the entire year in the pack ice zone (Bengtson, ,**,).Therefore, all seals counted at the study site, which was covered by fast-ice during thestudy period, were considered to be Weddell seals.Meteorological data were provided by weather stations at the altitude of +2..m,close to the study area (Fig. +). Katabatic winds ﬂow predominantly from east to westnear Syowa Station (the Bureau of Meteorology of Syowa Station, personal communi-cation +333). Therefore, Syowa Station is a good place to record the meteorologicalconditions at the study site (Fig. +). Air temperature (C), wind speed (m/s) at theheight of +*.+m from the ground, humidity () and irradiance (MJ/m,) were recordedevery hour. Data within+ hour of the seal count were used in analyses. Values areindicated as mean SD with the sample size in parentheses. We used StatView (ver/.*) for statistical tests and considered results statistically signiﬁcant if P*.*/. Thesigniﬁcance of the partial correlation coe$cients was determined using a t-test (Zar,+32.).Results and discussionThe number of seals hauled out on the ice varied from * to +* with the mean being,.*,.. (n/,). Mean air temperature was 2.-/.-C ranging from ,,.0 to +.1C.Mean wind speed was /.-..,m/s ranging from *.1 to +3.2m/s. Mean humidity andirradiance were 0..-+*.. and *.0*./MJ/m, ranging from .+.* to 2..* and from*.* to ,.*MJ/m,, respectively. Mean values are represented as vertical and horizontallines in Fig. ,. The seasonal decrease in number of seals on the ice might reﬂect theseasonal movement of seals associated with fast ice conditions (Kooyman, +302);however, the daily ﬂuctuation in the number of seals is believed to correlate with theproportion of seals hauled out. To exclude the seasonal trend and correlations amongall variables, partial correlation coe$cients were calculated among all variables toexamine the e#ect of weather conditions on the daily haul-out number of seals (Table+). Wind speed and air temperature signiﬁcantly a#ected the number of seals hauledout (Table +, partial correlation coe$cient*..3 and *.-., P*.**+ and P*.*/,n/,, respectively), though there were no signiﬁcant relationships between number ofseals and days from Feb. ,0, humidity or irradiance (Table +). The present studyindicates that the number of seals which hauled out was mostly a#ected by wind speed,K. Sato, Y. Tsuchiya, S. Kudoh and Y. Naito100Fig. ,. Number of seals as a function of days from Feb. ,0 (a), air temperature (b), wind speed (c),humidity (d) and irradiance (e) in the vicinity of Syowa Station, East Antarctica, +333.Mean values of variables are indicated as horizontal (no. of seals) and vertical (othervariables) lines.Meteorological factors vs. hauling-out Weddell seals 101as Smith (+30/) reported. The cooling e#ect would be ampliﬁed by wind. Thus, sealsmight experience discomfort in windy weather. Therefore, the haul-out pattern couldbe a behavioral attempt at thermoregulation to prevent heat loss.As shown in Fig. ,c, it is apparent that the number of seals hauled out was less onwindy days (wind speed/.-m/s), but it varied greatly on calm days (wind speed/.-m/s). The number of seals varied on warmer days (air temperature2.-C) (Fig.,b). These results indicate that hauling out onto the ice may be one of severalalternative responses to calm weather. The behavioral response is limited only duringthe stressful times of storm and cold days. There may be some other factors makingseals decide to stay in the water on calm days. During late lactation, adult females withpups conducted deep foraging dives, and a larger percentage of time was used forrepeated deep dives as the energy store was depleted (observed as a reduction in theindex of fatness) (Sato et al., ,**,). In the molting season, physiological conditionssuch as the degree of molting, which motivates them to haul out on the ice, or/and thedepletion in energy storage, which impels them to dive for foraging, may also a#ect theirbehavior. Studies focused on underwater behavior may also help to explain when theydecide to haul out onto the ice or stay in the water on calm days.AcknowledgmentsWe thank the Bureau of Meteorology for the weather records from Syowa Station.This study was conducted as a part of the monitoring study of the .*th JapaneseAntarctic Research Expedition (JARE-.*). The information on the iceberg wascollected by JARE-.+ and was provided by K. Watanabe. We also thank R. Andrews,M. Cameron and two anonymous reviewers for improvements to the manuscript.ReferencesBengtson, J.L. (,**,): Crabeater seal Lobodon carcinophaga. Encyclopedia of Marine Mammals, ed. by W.F.Perrin et al. San Diego, Academic Press, -*,-*..Cline, D.R., Sini#, D.B. and Erickson, A.W. (+31+): Underwater copulation of the Weddell seal. J. Mammal.,/,, ,+0,+2.Erickson, A.W., Bledsoe, L.J. and Hanson, M.B. (+323): Bootstrap correction for diurnal activity cycle incensus data for Antarctic seals. Mar. Mammal Sci., /, ,3/0.Table +. A matrix of partial correlation coe$cients betweem no. of seals and parameters. N/,.No. ofsealDays fromFeb. ,0AirtemperatureWindspeedHumidity IrradianceNo. of sealDays from Feb. ,0Air temperatureWind speedHumidity+*4*.+*4-. *4/0+ *4.3*4+0*4-/+ *4+-*4+0 *4*1 *4*1+*4*- *40- *4,3 *4+ *4,,The signiﬁcance of partial correlation coe$cients was examined using a t-test (Zar, +32.).P*4*/, P*4*+,  P*.**+.K. Sato, Y. Tsuchiya, S. Kudoh and Y. Naito102Haga, R. (+30+): Birds and seals around Japanese Syowa Base on Prince Harald Coast, Antarctica(preliminary). Nankyoku Shiryoˆ (Antarct. Rec.), ++, 200202.Hoshiai, T. (+32+): Aerial census of Weddell seal (Leptonychotes weddelli Lesson) in Lu¨tzow-Holm Bay,Antarctica. Nankyoku Shiryoˆ (Antarct. Rec.), 1+, +*3++,.Kaufman, G.W., Sini#, D.B. and Reichle R. (+31/): Colony behavior of Weddell seals, Leptonychotesweddelli, at Hutton cli#s, Antarctica. Rapp. P.-V. Re´un. Cons. Int. Explor. Mer, +03, ,,2,.0.Kooyman, G.L. (+302): An analysis of some behavioral and physiological characteristics related to diving inthe Weddell seal. Antarct. Res. Ser., ++, ,,1,0+.Lake, S.E., Burton, H.R. and Hindel, M.A. (+331): Inﬂuence of time of day and month on Weddell sealhaul-out patterns at the Vestfold Hills, Antarctica. Polar Biol., +2, -+3-,..Matsuda, T. (+30-): Some ecological observations on the Antarctic Weddell seal. Jap. J. Ecol., +-, +0++0- (inJapanese).Naito, Y. and Hoshiai, T. (+32-): A population study of the Weddell seal in Lu¨tzow-Holm bay and itsadjacent waters, Antarctica. Mem. Natl Inst. Polar Res., Spec. Issue, ,1, ,**,+*.Sato, K., Mitani, Y., Cameron, M. F., Sini#, D. B., Watanabe, Y. and Naito, Y. (,**,): Deep foraging divesin relation to the energy depletion of Weddell seal (Leptonychotes weddellii) mothers duringlactation. Polar Biol., ,/, 0301*,.Sini#, D.B., Tester, J.R. and Kuechle, V.B. (+31+): Some observations on the activity patterns of Weddellseals as recorded by telemetry. Antarct. Res. Ser., +2, +1-+2*.Smith, M.S.R. (+30/): Seasonal movements of the Weddell seal in McMurdo Sound, Antarctica. J. Wildl.Manage., ,3, .0..1*.Stirling, I. (+303): Ecology of the Weddell seal in McMurdo Sound, Antarctica. Ecology, /*, /1-/20.Tedman, R.A. and Bryden, M.M. (+313): Cow-pup behaviour of the Weddell seal, Leptonychtes weddelli(Pinnipedia), in McMurdo Sound, Antarctica. Aust. Wildl. Res., 0, +3-1.Thomas, J.A. (,**,): Weddell seal Leptonychotes weddelli. Encyclopedia of Marine Mammals, ed. by W. F.Perrin et al. San Diego, Academic Press, +-**+-*,.Thomas, J.A. and DeMaster, D.P. (+32-): Diel haul-out patterns of Weddell seal (Leptonychotes weddelli)females and their pups. Can. J. Zool., 0+, ,*2.,*20.Zar, J.H. (+32.): Biostatistical Analysis. Englewood Cli#s, Prentice-Hall, 1+2 p.(Received May -*, ,**,; Revised manuscript accepted September +1, ,**,)Meteorological factors vs. hauling-out Weddell seals 103

Meteorological factors affecting the number of Weddell seals hauling-out on the ice during the molting season at Syowa Station, East Antarctica

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Meteorological factors affecting the number of Weddell seals hauling-out on the ice during the molting season at Syowa Station, East Antarctica

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