MARINE MAMMAL SCIENCE, 23(3): 688–693 (July 2007)
C 2007 by the Society for Marine Mammalogy
DOI: 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, Norway
E-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 of
the Atlantic Ocean, and the Bering, Beaufort, Chukchi, and Okhotsk seas (Moore and
Reeves 1993) and often live in close association with the sea-ice edge. Five geographically separated stocks are currently recognized: (1) the Bering/Chukchi/Beaufort Seas
stock, (2) the Okhotsk Sea stock, (3) the Davis Strait stock, (4) the Hudson Bay
stock, and (5) the Spitsbergen stock distributed in the Greenland, Barents, and Kara
seas. Exploitation over several centuries dramatically reduced the population size
of this once abundant species (Woodby and Botkin 1993). Commercial hunting of
bowhead whales commenced in the early 1600s in the North Atlantic region around
Svalbard and spread out into other regions when this stock became depleted. The
pre-exploitation population size of the Spitsbergen stock has been estimated to be
between 25,000 and more than 100,000 individuals (Allen and Keay 2006). After
cessation
of the hunt, bowhead whales around Svalbard were considered to be extinct
a
(JonsgArd 1981). Today, the Spitsbergen stock of bowhead whales is believed to
688
NOTES
689
Figure 1. Survey track line and sightings of bowhead whales in the Fram Strait between
Svalbard and Greenland. All tracks except the one going from Svalbard to the west at 80◦ N
are along the ice edge. The ice was distributed west and north of the track line and changed
during the survey. Sightings of whales: (1) 17 April, 1 whale; (2) 18 April, 7+ whales; (3) 25
April, 1 whale; (4) 26 April, 1 whale; (5) 26 April, 1 whale; (6) 26 April, 3 whales; (7) 28
April, 1 whale; (8) 28 April, 3 whales.
number in the tens (Christensen et al. 1992) and is considered critically endangered
by the IUCN (Cetacean Specialist Group 2006). Systematic surveys for monitoring
the Spitsbergen stock have never been conducted. Here, we report results from a survey for bowhead whales in the North Atlantic along the ice edge between Svalbard
and Greenland in April 2006.
From 17 to 28 April 2006, we searched north and northwest of Svalbard for
bowhead whales (Fig. 1) from the research vessel Lance (Norwegian Polar Institute).
The survey started from Spitsbergen, Svalbard, and headed west along 80◦ N toward
the edge of the drifting pack ice, which on 17 April 2006 was located at approximately
0◦ longitude. We proceeded north along the ice to about 82◦ N and then southeast
to 80.12◦ N, 11.27◦ E north of Svalbard. On 25 April we went straight back through
open waters toward the western ice edge at 80◦ N where we continued our search
effort. The total distance of the survey lines was approximately 2,000 km.
Throughout the survey, we continuously monitored the sea acoustically, and in
addition, at least two persons equipped with binoculars were actively searching for
whales from the bridge of the vessel (∼10 m above seal level) at all times. During 149
h of the surveying time we towed two custom-made hydrophones 280 m and 380
m, respectively, behind the vessel. The first hydrophone consisted of a PC5TUBE
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MARINE MAMMAL SCIENCE, VOL. 23, NO. 3, 2007
piezoelectric ceramic by Morgan Electro Ceramics (Stourport, UK) and a Magrec
(Devon, UK) HP/02 amplifier enclosed in a Pirelli (Milano, Italy) Resin Kit. The
second hydrophone consisted of a Benthos (North Falmouth, MA, USA) AQ4 hydrophone and a Magrec HP/01 amplifier suspended in a 1-in. diameter polyurethane
tube filled with Isopar M hydrophone oil. The frequency response of both systems
was approximately 100 Hz to 15 kHz ± 3 dB. Both hydrophones were attached to
the same Kevlar-strengthened towing cable. At speed of 10 knt, this array tows at
approximately 5–6 m below the surface (Gillespie 1997).
If ice conditions did not permit towing of the acoustic gear, or when Lance was
cruising at very low speeds, Dowty (London, UK) SSQ906 A(D) or Plessey (Cowes,
UK) SSQ906 sonobuoys were deployed for acoustic monitoring (hydrophone depth
set to 40 m). The sonobuoys were used for a total of 19 h of surveying and during
4 h when small boats were engaged in attempting to biopsy the whales. Sonobuoys
were deployed from the ship and the signal was monitored while the ship cruised
away from the buoy. While cruising we deployed one buoy every 30 min. Sonobuoy
signals were received on a modified ICOM (Bellevue, WA, USA) VHF receiver that
received 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 S1
laptop computer. Monitoring was conducted by researchers listening continuously
to the input on Sennheiser (Wedemark, Germany) HD280 Pro headphones and
watching real-time spectrograms (FFT length: 1024 points) produced by Avisoft
Recorder software. The upper frequency limit of the spectrograms was set to 4 kHz
on 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 observations
were made in a relatively small area of the Fram Strait over the continental slope at
depths 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 least
15-m long.
Habitat selection by bowhead whales is believed to change with season. During
spring and summer, bowheads reside in continental-slope waters (Moore et al. 2000).
This is consistent with our spring sightings, which were made on the continental
slopes of Svalbard. In this region, warm Atlantic water of the West Spitsbergen
Current 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 abundant
food source for copepods (Hirche and Niehoff 1996). Bowhead whales feed mainly
on calanoid copepods and euphausiids (Lowry 1993, Lowry et al. 2004). We observed
a dense layer that was consistent with a zooplankton signal at 80–100 m depth on
a 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 the
Greenland Sea increased during spring to peak in June. We suggest that the whales
we observed in the Fram Strait were feeding on copepods along the ice edge.
NOTES
691
We expected to hear singing or other calls from bowhead whales at this time of
the year (Würsig and Clark 1993) but had no success in recording sound of any kind
from the whales. Our recording system was tested with a variety of marine mammal
sounds before this study. During our cruise we recorded our own ship engine, that
of another vessel, and songs of bearded seals. Because bearded seals use the same
frequency range as bowhead whales we are confident that the lack of vocal activity
cannot be explained by problems with our recording equipment. It is, however,
possible that bowhead sounds were masked by engine noise at large distances and
that the whales ceased vocalizing when the ship got close. We cannot rule out that
the presence of our ship (and our three small satellite boats) may have influenced
the vocal behavior of the animals, although avoidance responses were not evident
prior to deployments of the small boats. R/V Lance is an ice-going vessel that uses a
variable-pitch propeller. These propellers create considerably more noise than those
with blades that are fixed in one position. Although we did not measure the source
level of our engine, the noise it created could be recorded with sonobuoys at distances
of up to 10 km. Disturbance reactions of bowheads to loud noise have been well
documented and include the temporary cessation of vocalizing (Richardson et al.
1995). Further studies are needed to investigate the acoustic behavior of bowhead
whales in the North Atlantic.
The distribution of bowheads in the Fram Strait is well documented for the 17th
and 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 maintained
by the warm Atlantic water of the West Spitsbergen Current. The location of the
northern extension of this bay varied considerably interannually but in some years
reached up to 80◦ N in late April. It was thought that the bowhead whales moved from
the 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. The
spring ice conditions in 2006 differed dramatically from those in historical whaling
reports; 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 of
the 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 ice
edge, as well as the sea current systems that keeps this part of the Fram Strait more or
less consistently open, make the area a favorable habitat for bowhead whales during
early spring.
Records of bowhead whales have been sporadic but persistent for some time in the
Svalbard area (Reeves 1980) and in the eastern part of the Barents Sea, particularly in
the Franz Josef Land area (Wiig 1991, Moore and Reeves 1993, de Korte and Belikov
1994). In addition, reports of bowhead sightings have been received annually in the
last few years from Spitsbergen fjords during summer (Norwegian Polar Institute,
unpublished data). There is also an apparent increase in the number of occasional
observations of bowheads in Northeast Greenland during the last decades (Gilg
and Born 2005). Preliminary results from aerial surveys conducted in the Canadian
eastern Arctic from 2002 to 2004 suggest that the Davis Strait and Hudson Bay
stocks 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 Svalbard
area are stragglers from the Northwest Atlantic or survivors of the Spitsbergen stock.
Planned comparative genetic analyses of West Greenland bowheads (Heide-Jørgensen
et al. 2003) with biopsies obtained during our Svalbard survey will allow us to address
this question.
ACKNOWLEDGMENTS
We are grateful to the crew of R/V Lance for help during the survey. We are also grateful to
C. 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 Polar
Institute, the Research Council of Norway (grant no.: 153028/S40; 146515/420), and the
Strategic 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 was
supported by a UK Royal Society University Research Fellowship.
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Received: 26 September 2006
Accepted: 18 December 2006