Intra- and interannual resightings of bowhead whales

(Balaena mysticetus) in Disko Bay, West Greenland,

investigated by photo-identification

Louise Jensen (1,2); Mads Fage Christoffersen (2); Camilla Erika Ilmoni (3); Outi Maria Tervo (2); Andrew Foote (1); Reinhardt Møbjerg Kristensen (1) (1) Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, 2100 København, Denmark

(2) Arctic Station, University of Copenhagen, P.O. Box 504, 3953 Qeqertarsuaq, Greenland

(3) Arctic Whale Tours, 8438 Stø, Norway

Corresponding author: louise.nj@hotmail.com

Introduction From late February to early June bowhead whales aggregate in Disko Bay which is thought to be a mating and feeding

ground. Calves and juveniles have rarely been seen in Disko Bay and genetic investigations have shown that 78% of the

individuals are females, and individual occurrence in the area may be linked to a multiyear reproductive cycle (1, 2).

However, relatively little is known about the residence time of individual bowhead whales in Disko Bay.

The bowhead whale appears black except from white scars accumulated throughout life from contact with ice, collisions

with boats (Figure1A), killer whale attacks (Figure1B), and entanglement in nets and ropes. Previously, in other

geographical areas individual bowhead whales have primarily been identified from aerial photographs. The aim of this

study was to investigate the possibility of using non-invasive boat-based photo-identification to recognize individual

bowhead whales and to conduct capture-recapture investigations of bowhead whales in Disko Bay.

Methods All ID photographs were taken in Disko Bay in the vicinity of Qeqertarsuaq on Disko Island, West Greenland (Figure 2).

The field work was conducted on 18 different days from the 8 of March to the 18 of May 2010 and on 21 different days in

2011 between the 8 of March and the 4 of June. The photographs were taken from a small open boat with outboard

engine or from R/V Porsild, Arctic Station, using a NIKON D-200S camera with a 70-300 mm Nikkor lens. The ID photos

did not focus on a specific region of the whale so when possible, several photographs of the whales were taken to cover

as many angles and as much of the body as possible. Photographs were divided into encounters which were examined

for recaptures and individuals.

Encounter: Series of photographs of a whale not disappearing out of sight more than 5 minutes.

Recapture: Photos were compared within and between the seasons in order to find recaptures. Recaptures were

recognized by identical location and shape of either individual white scars or patterns of several scars. All inter-year

recaptures were confirmed by three different observers with experience of photo-identification analysis of other species.

Individual: Encounters could be classified as specific individuals if they were identified by distinctively different marking

on the same part of the body. Different encounters were described only as potentially different individuals when there was

no overlap in the photographed regions of the whales.

Molecular analysis of biopsies collected in connection with another study has revealed the sex of some of the

photographed whales.

Altogether 12 potentially different individuals were captured and recaptured at intervals between 2 and 56 days

within the same season (Figure 5). The remaining recaptures of potentially different individuals were captured and

recaptured within the same day and therefore excluded from figures 2 and 5.

Conclusions This study has shown that boat-based photo-identification is a usable method to conduct non-invasive capture-

recapture investigations of bowhead whales and demonstrates the applicability of ID-photos taken from boat for

recording residence time and inter-annual site fidelity of bowhead whales.

The recognition of the same individuals on different days within a season show that at least some individuals stay in

the Disko Bay area for at least 56 days.

In addition, three individuals have been photographically captured in both 2010 and 2011. Two of these individuals

were females. This demonstrated that at least some of the bowhead whales, including females, appear in Disko Bay

in successive years.

Figure 1. Bowhead whale with scars caused by a boat propeller (A) and from killer

whale attacks (B).

Figure 2. GPS – locations of bowhead whales recaptured in 2010 (circle) and 2011 (square). Each color

refers to different recaptures (see also figure 5). The recaptures consist of minimum 9 different individuals.

Figure 3. Number of captures of potentially different individuals

Figure 5. Diagram showing the dates of recaptures in 2010 (circles) and in 2011

(squares). Recaptures made during only a single day (n=16) have been

excluded. The interyear recaptures are highlighted with (grey). The recaptures

consist of minimum 9 different individuals.

Figure 4. Example of an individual (female) captured in both 2010 (left) and 2011 (right)

Bachelor project

Acknowledgement We want to thank A. Dahl, A. Brandt, J. Mølgaard, T. Mølgaard, A. Isaksen, J. Thormar, M.V. Jensen and M.P. Heide-Jørgensen for their help in the field. Arctic Station, University of Copenhagen, is thanked for providing excellent research

facilities. This study was funded by A.P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til almene Formaal (grant to RMK and OMT).

References 1) Heide-Jørgensen MP, Laidre KL, Wiig Ø, Postma L, Dueck LP, Bachmann L. (2010) Large scale sexual segregation of bowhead whales. Endangered Species Research. 13:73-78

2) Wiig, Ø., Heide-Jørgensen, M.P., Lindqvist, C., Laidre, K.L., Postma, L., Dueck, L.P., and Palsbøll, P.J., Bachmann, L. . (2011) Endangered Species Research 14: 235-242.

Results In 2010, a total of 123 encounters were made. From these 75 were identified only once. The remaining 48 encounters

included 17 potentially different individuals recognized between 2 and 5 times. At least 9 of these 17 individuals are

different as they have been identified from markings on the same part of the body (Figure 3).

The photographs from 2011 included 165 encounters and from these, 135 encounters were identified only once. The final

30 encounters make up 12 potentially different individuals recognized between 2 and 5 times (Figure 3).

Three individuals captured in 2010 were recaptured in 2011. It could be concluded that these are three different

individuals as they were all identified from different patterns of markings on the right side of their bodies (Figure 4).

Molecular analysis of biopsies collected in connection with another study showed that two of these recaptured individuals

were females. The sex of the third individual is unknown.

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