MARINE MAMMAL SCIENCE, 23(3): 688–693 (July 2007)C© 2007 by the Society for Marine MammalogyDOI: 10.1111/j.1748-7692.2007.02373.x

SPITSBERGEN BOWHEAD WHALES REVISITED

ØYSTEIN WIIG

LUTZ BACHMANN

Natural History Museum,University of Oslo, POB 1172

Blindern, N-0318 Oslo, NorwayE-mail: oystein.wiig@nhm.uio.no

VINCENT M. JANIK

Sea Mammal Research Unit, Gatty Marine Lab, School of Biology,University of St Andrews,

Fife KY16 8LB, United Kingdom

KIT M. KOVACS

CHRISTIAN LYDERSEN

Norwegian Polar Institute,N-9226 Tromsø, Norway

Bowhead whales (Balaena mysticetus) are endemic to arctic and subarctic regions ofthe Atlantic Ocean, and the Bering, Beaufort, Chukchi, and Okhotsk seas (Moore andReeves 1993) and often live in close association with the sea-ice edge. Five geographi-cally separated stocks are currently recognized: (1) the Bering/Chukchi/Beaufort Seasstock, (2) the Okhotsk Sea stock, (3) the Davis Strait stock, (4) the Hudson Baystock, and (5) the Spitsbergen stock distributed in the Greenland, Barents, and Karaseas. Exploitation over several centuries dramatically reduced the population sizeof this once abundant species (Woodby and Botkin 1993). Commercial hunting ofbowhead whales commenced in the early 1600s in the North Atlantic region aroundSvalbard and spread out into other regions when this stock became depleted. Thepre-exploitation population size of the Spitsbergen stock has been estimated to bebetween 25,000 and more than 100,000 individuals (Allen and Keay 2006). Aftercessation of the hunt, bowhead whales around Svalbard were considered to be extinct(JonsgA

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rd 1981). Today, the Spitsbergen stock of bowhead whales is believed to

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Figure 1. Survey track line and sightings of bowhead whales in the Fram Strait betweenSvalbard and Greenland. All tracks except the one going from Svalbard to the west at 80◦Nare along the ice edge. The ice was distributed west and north of the track line and changedduring the survey. Sightings of whales: (1) 17 April, 1 whale; (2) 18 April, 7+ whales; (3) 25April, 1 whale; (4) 26 April, 1 whale; (5) 26 April, 1 whale; (6) 26 April, 3 whales; (7) 28April, 1 whale; (8) 28 April, 3 whales.

number in the tens (Christensen et al. 1992) and is considered critically endangeredby the IUCN (Cetacean Specialist Group 2006). Systematic surveys for monitoringthe Spitsbergen stock have never been conducted. Here, we report results from a sur-vey for bowhead whales in the North Atlantic along the ice edge between Svalbardand Greenland in April 2006.

From 17 to 28 April 2006, we searched north and northwest of Svalbard forbowhead whales (Fig. 1) from the research vessel Lance (Norwegian Polar Institute).The survey started from Spitsbergen, Svalbard, and headed west along 80◦N towardthe edge of the drifting pack ice, which on 17 April 2006 was located at approximately0◦ longitude. We proceeded north along the ice to about 82◦N and then southeastto 80.12◦N, 11.27◦E north of Svalbard. On 25 April we went straight back throughopen waters toward the western ice edge at 80◦N where we continued our searcheffort. The total distance of the survey lines was approximately 2,000 km.

Throughout the survey, we continuously monitored the sea acoustically, and inaddition, at least two persons equipped with binoculars were actively searching forwhales from the bridge of the vessel (∼10 m above seal level) at all times. During 149h of the surveying time we towed two custom-made hydrophones 280 m and 380m, respectively, behind the vessel. The first hydrophone consisted of a PC5TUBE

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piezoelectric ceramic by Morgan Electro Ceramics (Stourport, UK) and a Magrec(Devon, UK) HP/02 amplifier enclosed in a Pirelli (Milano, Italy) Resin Kit. Thesecond hydrophone consisted of a Benthos (North Falmouth, MA, USA) AQ4 hy-drophone and a Magrec HP/01 amplifier suspended in a 1-in. diameter polyurethanetube filled with Isopar M hydrophone oil. The frequency response of both systemswas approximately 100 Hz to 15 kHz ± 3 dB. Both hydrophones were attached tothe same Kevlar-strengthened towing cable. At speed of 10 knt, this array tows atapproximately 5–6 m below the surface (Gillespie 1997).

If ice conditions did not permit towing of the acoustic gear, or when Lance wascruising at very low speeds, Dowty (London, UK) SSQ906 A(D) or Plessey (Cowes,UK) SSQ906 sonobuoys were deployed for acoustic monitoring (hydrophone depthset to 40 m). The sonobuoys were used for a total of 19 h of surveying and during4 h when small boats were engaged in attempting to biopsy the whales. Sonobuoyswere deployed from the ship and the signal was monitored while the ship cruisedaway from the buoy. While cruising we deployed one buoy every 30 min. Sonobuoysignals were received on a modified ICOM (Bellevue, WA, USA) VHF receiver thatreceived the full audio bandwidth of the signal.

All acoustic signals were high-pass filtered at 100 Hz using an F-J Electronics(Holte, Danmark) A/S AFF450 filter and then digitized at 50 kHz using an Avisoft(Berlin, Germany) Ultrasoundgate 416 digitizer connected to a Toshiba Tecra S1laptop computer. Monitoring was conducted by researchers listening continuouslyto the input on Sennheiser (Wedemark, Germany) HD280 Pro headphones andwatching real-time spectrograms (FFT length: 1024 points) produced by AvisoftRecorder software. The upper frequency limit of the spectrograms was set to 4 kHzon the screen to enlarge the relevant frequency band for this study.

We had eight observation events that included 17–20 bowhead whales (Table 1,Fig. 1). All whales were detected visually from the vessel’s bridge and all observationswere made in a relatively small area of the Fram Strait over the continental slope atdepths between 1,030 and 2,785 m. Age and sex of the animals were not determined,but those whales we got close to with small boats for biopsy darting were at least15-m long.

Habitat selection by bowhead whales is believed to change with season. Duringspring and summer, bowheads reside in continental-slope waters (Moore et al. 2000).This is consistent with our spring sightings, which were made on the continentalslopes of Svalbard. In this region, warm Atlantic water of the West SpitsbergenCurrent meets cold arctic water of the East Greenland Current (Schauer et al. 2004).When the annually formed winter sea ice melts in this region during the spring,phytoplankton begins to grow vigorously (Smith et al. 1987) making an abundantfood source for copepods (Hirche and Niehoff 1996). Bowhead whales feed mainlyon calanoid copepods and euphausiids (Lowry 1993, Lowry et al. 2004). We observeda dense layer that was consistent with a zooplankton signal at 80–100 m depth ona 120 kHz echo sounder (Simrad EK60) in those areas where whales were observed.Møller et al. (2006) found that the biomass of copepods in the upper 60 m of theGreenland Sea increased during spring to peak in June. We suggest that the whaleswe observed in the Fram Strait were feeding on copepods along the ice edge.

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We expected to hear singing or other calls from bowhead whales at this time ofthe year (Wursig and Clark 1993) but had no success in recording sound of any kindfrom the whales. Our recording system was tested with a variety of marine mammalsounds before this study. During our cruise we recorded our own ship engine, thatof another vessel, and songs of bearded seals. Because bearded seals use the samefrequency range as bowhead whales we are confident that the lack of vocal activitycannot be explained by problems with our recording equipment. It is, however,possible that bowhead sounds were masked by engine noise at large distances andthat the whales ceased vocalizing when the ship got close. We cannot rule out thatthe presence of our ship (and our three small satellite boats) may have influencedthe vocal behavior of the animals, although avoidance responses were not evidentprior to deployments of the small boats. R/V Lance is an ice-going vessel that uses avariable-pitch propeller. These propellers create considerably more noise than thosewith blades that are fixed in one position. Although we did not measure the sourcelevel of our engine, the noise it created could be recorded with sonobuoys at distancesof up to 10 km. Disturbance reactions of bowheads to loud noise have been welldocumented and include the temporary cessation of vocalizing (Richardson et al.1995). Further studies are needed to investigate the acoustic behavior of bowheadwhales in the North Atlantic.

The distribution of bowheads in the Fram Strait is well documented for the 17thand 18th century (Reeves 1980, Sanger 1991, Hacquebord 1999). There was a “bay”of ice-free water in the area between Svalbard and Greenland that was maintainedby the warm Atlantic water of the West Spitsbergen Current. The location of thenorthern extension of this bay varied considerably interannually but in some yearsreached up to 80◦N in late April. It was thought that the bowhead whales moved fromthe south into this ice bay in April. A huge number of whales were caught in this area,which whalers referred to as Whaler’s Bay or the Northern Whaling Ground. Thespring ice conditions in 2006 differed dramatically from those in historical whalingreports; there was open water as far north as 82◦N in April. For the surveyed area,we conclude that during April 2006 bowhead whales within the western range ofthe Spitsbergen stock were concentrated in the area 80◦–81◦N, 0◦–2◦E. Obviously,the occurrence of copepods that congregate to feed on the algal bloom along the iceedge, as well as the sea current systems that keeps this part of the Fram Strait more orless consistently open, make the area a favorable habitat for bowhead whales duringearly spring.

Records of bowhead whales have been sporadic but persistent for some time in theSvalbard area (Reeves 1980) and in the eastern part of the Barents Sea, particularly inthe Franz Josef Land area (Wiig 1991, Moore and Reeves 1993, de Korte and Belikov1994). In addition, reports of bowhead sightings have been received annually in thelast few years from Spitsbergen fjords during summer (Norwegian Polar Institute,unpublished data). There is also an apparent increase in the number of occasionalobservations of bowheads in Northeast Greenland during the last decades (Gilgand Born 2005). Preliminary results from aerial surveys conducted in the Canadianeastern Arctic from 2002 to 2004 suggest that the Davis Strait and Hudson Baystocks may be in the order of several thousand whales, rather than the few hundred

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that were estimated for this stock prior to this recent work (COSEWIC 2005).Currently, it is not known whether the observed bowhead whales in the Svalbardarea are stragglers from the Northwest Atlantic or survivors of the Spitsbergen stock.Planned comparative genetic analyses of West Greenland bowheads (Heide-Jørgensenet al. 2003) with biopsies obtained during our Svalbard survey will allow us to addressthis question.

ACKNOWLEDGMENTS

We are grateful to the crew of R/V Lance for help during the survey. We are also grateful toC. Freitas, R. Pike, G. Westereng, and J. R. Wiig for their participation in the survey team. C.Freitas also helped with making the figure. We acknowledge funding by the Norwegian PolarInstitute, the Research Council of Norway (grant no.: 153028/S40; 146515/420), and theStrategic University Program “National Centre for Biosystematics” (Project nr. 146515/420),co-funded by the Research Council of Norway and the NHM, University of Oslo. VMJ wassupported by a UK Royal Society University Research Fellowship.

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Received: 26 September 2006Accepted: 18 December 2006