Encounter frequencies and grouping patterns of narwhals in Koluktoo Bay, Baffin Island
- First Online:
- Cite this article as:
- Marcoux, M., Auger-Méthé, M. & Humphries, M.M. Polar Biol (2009) 32: 1705. doi:10.1007/s00300-009-0670-x
- 169 Views
The narwhal (Monodon monoceros) is a deep diving cetacean with a strictly Arctic distribution. The challenges associated with the remoteness of narwhals have resulted in a lack of knowledge of its social behaviour requiring direct, systematic observations. Bruce Head, a peninsula at the mouth of Koluktoo Bay (Nunavut), provides an exceptional site in Canada for nearshore observation of narwhals during the summer. In this study, we document the movement, timing and grouping patterns of narwhals observed from Bruce Head and how they relate to environmental factors such as the tide and the circadian cycle. Narwhals travelled in clusters of 1–25 individuals of mixed sex and age class. Narwhals entered the bay in bigger clusters than when they exited it. The clusters were part of herds that comprised up to 642 clusters. Narwhal movement patterns were not randomly distributed in time but did not consistently follow the tidal or circadian cycles across years. Bruce Head could host long-term behavioural studies of narwhals to unravel several unanswered aspects of narwhal biology.
KeywordsCircular statisticsBaffin IslandNon-invasive methods
Marine mammals, in general, and deep diving offshore cetaceans, in particular, are challenging research subjects because they spend most of their time underwater and far away from coastlines (Connor et al. 2000; Schipper et al. 2008). Overcoming these challenges to advance the understanding of a given species’ behaviour, ecology and conservation requires the use of remote monitoring technology (Kooyman 2004; Hooker et al. 2007) or capitalizing on brief windows of direct observation opportunity generated by the species’ behaviour and natural history (Baker and Herman 1981; Rugh et al. 2005).
Forms of remote monitoring technology frequently used in cetacean research include satellite telemetry (Mate et al. 1997; Laidre et al. 2004), time depth recorders (Laidre et al. 2002; Watkins et al. 2002), and acoustic monitoring (Stafford et al. 1998; Clark and Clapham 2004). Satellite telemetry and time depth recorders, in particular, have revolutionized marine mammal science because they provide detailed spatial and temporal data on behaviour and habitat use that cannot be obtained from direct observation (Laidre et al. 2003; Goldbogen et al. 2008). However, the expense of the technology, combined with the logistical challenges and invasiveness of attaching devices to free-ranging cetaceans, means that these approaches are most frequently employed by large, well-funded research programs and, yet, are usually limited to the monitoring of a small number of individuals (e.g., Johnson et al. 2004; Goldbogen et al. 2008).
Opportunities for direct observation generated by the species’ behaviour and natural history are, by their very nature, selective and, as a result, may not be broadly representative of the species’ behaviour and space use. However, they do permit detailed behavioural observation of many more individuals at much reduced cost, logistic complexity and levels of invasiveness. For example, much cetacean research has been conducted in near-shore areas from commercial whale watching vessels, including humpback whales (Megaptera novaengliae) in the Gulf of Maine (Clapham et al. 1993), resident killer whales (Orcinus orca) off the coast of British Columbia, Washington and Alaska (Baird 2000). More than 1,200 individually identified southern right whales (Eubalaena australis) have been observed from the cliffs of Peninsula Valdes, Argentina (Payne 1994). Extensive research has been conducted on bottlenose dolphins since 1970 in Sarasota, United-States (Irvine and Wells 1972) and since 1984 in Shark Bay, Australia (Connor and Smolker 1985). The deep near-shore waters off Kaikoura, New Zealand, has offered an ideal opportunity to study the behaviour and ecology of males sperm whales (Physetermacrocephalus) (Childerhouse et al. 1995) and other marine mammals (e.g., dusky dolphins, Lagenorhynchus obscurus, Au and Wursig 2004; southern right-whale dolphins, Lissodelphis peronii, Visser et al. 2004). These studies of cetaceans in near-shore areas have provided key insights about cetacean behaviour, which have contributed to major advances over the last several decades in the behavioural ecology of marine mammal foraging, parental care, and social organization (Connor et al. 1992; Ford et al. 1998; Mann and Smuts 1999).
Studying Arctic marine mammals is associated with additional research challenges due to remoteness, ice cover and the need for research approval by local community members. The narwhal (Monodon monoceros) is amongst the world’s most difficult whales to study, primarily because of its year-round, high latitude distribution including occurrence in consolidated pack ice with <3% open water (Laidre and Heide-Jørgensen 2005a) throughout the dark, Arctic winter. Most research conducted to date on narwhals has involved radio-tracking of habitat use (e.g., Laidre et al. 2003, 2004) and seasonal migration (e.g., Dietz et al. 2001; Heide-Jørgensen et al. 2003) as well as aerial surveys of population size and structure (e.g., Richard 1991; Heide-Jørgensen 2004). Narwhal samples from local harvests have been used to study diet (Finley and Gibb 1982; Laidre and Heide-Jørgensen 2005b), contaminant levels (Dietz et al. 2004, Wagemann and Kozlowska 2005) and genetic diversity (Palsbøll et al. 1997). In addition, acoustic devices have been used to record and study the underwater vocalisations of narwhals (e.g., Ford and Fisher 1978; Shapiro 2006). Despite these research efforts, narwhals have been identified as “special concern” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2004) and as “near threatened” by the International Union for Conservation of Nature (Jefferson et al. 2008), largely because of data deficiencies (COSEWIC 2004) and uncertainties about numbers and trends (Jefferson et al. 2008). The lack of direct observational studies of narwhal behaviour means that very basic aspects of their feeding behaviour (Thiemann et al. 2008), the function of seasonal migration (Laidre et al. 2004), sexual selection (Reeves and Mitchell 1981) and social structure remain unknown (Whitehead 1998).
In the current paper, we describe a unique opportunity for shore-based, direct observation of narwhals by providing the first, published documentation of narwhal visitation to a near-shore area off Bruce Head (N 72°04′, W 80°32′), Koluktoo Bay, northern Baffin Island. Bruce Head is a rocky, elevated point that juts out into Milne Inlet, creating a 5-km wide entry into Koluktoo Bay that causes narwhals to swim close to the shore on their way into or out of the bay. The tendency for narwhals to frequent Koluktoo Bay has long been known by local Inuit hunters (Mary-Roussilière 1984–1985), who continue to harvest narwhals there. We are aware of two companies that are currently offering kayak-based whale watching tours at the site. In addition, we know of at least three narwhal research projects that were conducted at Bruce Head. Of the six narwhals captured by Newman (1971) for a captive display at the Vancouver Aquarium, five animals were captured at Bruce Head. During three summers, Mansfield et al. (1975) collected samples from narwhals captured in nets at strategic points in Koluktoo Bay to investigate growth, reproductive traits and stomach contents. Ford and Fisher (1978) spent 5 days in Koluktoo Bay to record narwhal vocalizations. Additionally, narwhal predation by killer whales has been observed in the bay (Campbell et al. 1988). Here, we document the number and temporal pattern of narwhal observations made from Bruce Head during two recent field seasons. We describe how the timing of narwhal observations relative to tidal and circadian cycles varied over the 2 years, as well as the size and composition of observed groups, and relate these to hypotheses about the function of groupings in odontocetes.
To quantify the gregarious nature of narwhal travelling behaviour, we documented the number, size and composition of clusters composing herds that entered and exited the bay. A cluster was defined as a group of narwhals in which an individual was within 10 body widths of another. Body width measurements are more reliable than direct measurements across variable distances (Mann 2000). When there was a high density of clusters travelling in front of Bruce Head at the same time (the number of clusters could reach up to 25 clusters per minute), we would only note the presence of clusters. For most of the clusters, we noted their size and when possible, we also noted their composition. Smaller narwhals of grey colour were referred to as calves (up to 2 years of age; Hay and Mansfield 1989). Calves were differentiated from adults on the basis of being at least half the size of adults and usually close to a female in the “baby” or “echelon” position, and a more deliberate surfacing pattern (Mann and Smuts 1999). Larger narwhals with spotted patterns of black and white on their back were labelled as adults. We also labelled juvenile narwhals as adults. They were only slightly smaller than adults but did not show spotted patterns. When it was possible to observe the presence or absence of a tusk, we labelled adult narwhals with tusks as males and without tusks as females (Mansfield et al. 1975; Hay and Mansfield 1989). Females with tusks and males without tusks have been observed in harvested samples in low frequency (<5%: Hay 1984; Roberge and Dunn 1990). Since the presence and absence of the tusk was our only proxy for sex assignment, a few tusked females and tusk-less males could have been misclassified as males and females, respectively. However, given the low levels of occurrence of the two, we consider that they should not significantly alter our general results. A non-parametric Kolmogorov-Smirnov two-sample test was performed to examine the difference in the size of the clusters of narwhals entering and exiting the bay.
We defined a “herd” as an aggregation of clusters of narwhals that passed in front of the peninsula. We determined the end of a herd when we did not see narwhals for more than 30 min. We noted the timing of the herds and the number of clusters within each herd. We compared the duration as well as the size of the herds that entered and exited the bay with non-parametric Kolmogorov-Smirnov two-sample tests. To examine the distribution of different sex and age classes within herds, we divided the herds in four parts, each comprised of an equal number of clusters. We performed two sets of χ2-tests to assess whether clusters containing calves or males were distributed equally or unequally amongst the four parts of the herds.
Finally, we investigated the synchrony of the clusters within a herd. We looked at the independence in time of consecutive clusters by comparing the distribution of the periods between two clusters against a Poisson distribution using a Chi-square test. The Poisson distribution is regularly used to evaluate the statistical significance of spatial or temporal aggregations (e.g., Sibly et al. 1990).
Environmental correlates of narwhal observations
To evaluate whether movements were correlated with environmental variables, we compared the timing of entries and exits of clusters and herds observed during 2 weeks of 24-h observations (the two-first weeks of each season) to the tidal cycle as well as the circadian cycle. Data on the timing of tides were obtained from the Canadian Hydrographic Service (http://www.tides.gc.ca/) which uses measurements from a buoy located in Koluktoo Bay (N 72.31°, W 80.57°). The tides lasted from 11 h 23 min to 13 h 48 min.
We used circular statistics to analyse the behaviour of narwhals around the tidal and circadian cycles. We transformed observations into angles in order to perform circular statistics. For the tidal data, we calculated the time between the observation of narwhals and the last high tide and divided it by the interval of time between the two consecutive high tides. This value was multiplied by 360 to obtain degrees. Therefore, an observation made at high tide would get a value of 0°, and an observation at low tide, a value of 180°. Angular values for the observations in accordance to the circadian cycle were calculated similarly; for example, observations done at midnight received a value of 0° and at noon, a value of 180°. Since the herds varied in duration, we used the time with the highest density of clusters as the time value for each herd.
We used a Watson’s test for uniformity to evaluate the evenness of the movements around the tidal and the circadian cycle as well as a Watson’s test for the von Mises distribution (Watson 1961) to evaluate the normality of the dataset. The von Mises is a symmetric unimodal circular normal distribution that is the most often used for circular datasets (Jammalamadaka and SenGupta 2001). The concentration of observations around the mode in the von Mises distribution is evaluated with the κ value; values smaller than 2 indicate low concentration around the mode (Fisher 1993).
We performed a Watson’s U2 for two samples (Watson 1962) to test if the observations of clusters of narwhals entering and leaving the bay have the same distribution around the tidal cycle. We repeated similar tests for the circadian cycle. The statistical package “Circular” (Lund and Agostinelli 2007) written for R (R Development Core Team 2008) was used for the circular analysis.
We observed 215 herds that lasted from 30 min to 10 h 48 min. The herds of narwhals exiting the bay lasted longer than the herds entering the bay (3 h 49 min and 2 h 29 min, respectively, Kolmogorov-Smirnov two-sample test, P = 0.048). Herds comprised from 1 to 642 clusters (mean 22.4, Fig 4b). There was no difference between the number of clusters per herd between herds entering and exiting the bay (Kruskal-Wallis chi-squared = 0.036, df = 1, P value = 0.85). Clusters containing calves or males were distributed equally between the front, two central, and hind quarters of the herds (calves Pearson χ2 = 5.96, df = 3, P = 0.11; males Pearson χ2 = 4.41, df = 3, P = 0.22). For herds in which we were able to identify the sex of at least 10 individuals (n = 43 herds), 79% comprised a mix of male and female.
The clusters entering and exiting the bay where highly aggregated in time (Fig. 3) even within a herd (Chi-square against Poisson distribution test statistic = 10053.3, df = 8, lambda = 2.518, P < 0.001) with 44% having less than a minute between two clusters.
Environmental correlates of narwhal observations
The distribution of the herds around the tidal cycle did not differ significantly between years (Watson’s two-sample test of homogeneity = 0.026, P value > 0.1). Therefore, we pooled the data for the analysis. The herds were distributed uniformly around the tidal cycle (Watson’s test circular uniformity = 0.024, P value > 0.1, Fig. 6) and followed the von Mises distribution (Watson’s test for the von Mises distribution = 0.021, P value > 0.1, μ = 115.9, Fig. 6) but with a very low κ value (κ = 0.10). The tidal conditions associated with narwhal herds entering the bay did not differ from those exiting the bay (Watson’s two-sample test of homogeneity = 0.088, P value > 0.1, Fig. 6).
Statistical tests on the movements of clusters around the tidal and circadian cycles
Watson test uniformity
Watson test Von Mises
P < 0.01
P < 0.01
μ = 84.26°
κ = 0.84
P < 0.01
P < 0.01
μ = 348.96°
κ = 0.57
P < 0.01
P < 0.01
μ = 255.4°
κ = 0.39
Time of day
P < 0.01
P < 0.01
μ = 206.9°
κ = 0.17
Statistical tests on the movements of herds around the tidal and circadian cycles
Watson test uniformity
Watson test Von Mises
Watson two samples (in/out)
P > 0.10
P > 0.10
P > 0.10
μ = 115.9°
κ = 0.099
P > 0.10
P > 0.10
P > 0.10
μ = 292.8°
κ = 0.44
Additional Marine Mammal Observations
Other marine mammals observed from Bruce Head included 33 bowhead whale (Balaena mysticetus) sightings in groups of one or two individuals and nine beluga (Delphinapterus leucas) sightings including a mother and calf pair. Around 70% of the bowhead whales and belugas sighted were within a narwhal herd. We also observed a pod of a minimum of 12 killer whales that entered the bay on August 12 2008 at 16:20; about 5 h after a herd of approximately 135 narwhals went in the bay. At 19:45, we counted 61 narwhals exiting the bay. The killer whales exited the bay the following morning after staying around 14.5 h in Koluktoo Bay.
Bruce Head, at the entrance of Koluktoo Bay on northern Baffin Island, represents an exceptional locality for consistent observation of large numbers of narwhals from shore during the summer. Our estimated 8,750 narwhal sightings during 4 weeks in 2007 and 3,900 narwhal sightings during 3 weeks in 2008 likely under-represents the number of narwhals entering the bay, due to incomplete daily observation of narwhals (24 h per day for the two-first weeks, but only 16 h per day for the other 2 weeks) and incomplete observational coverage of the channel entering Koluktoo Bay (maximum observation distance was 450 m, representing only 8% of the 5.2 km wide channel). On the other hand, we are very likely to have counted many of the same individuals two or more times. Preliminary analysis of photo-identification photographs (Auger-Méthé 2008) indicates at least two individuals were resighted entering the bay on multiple days. We observed more narwhal clusters entering than exiting the bay. If narwhals tend to swim farther from shore or spend more time underwater when they are exiting than entering the bay, this could simply be a result of our observation bias towards narwhals swimming close to shore and surfacing frequently. Alternatively, if we were equally likely to observe narwhals entering and exiting, then the higher number of narwhals observed entering could reflect an accumulation of narwhals in Koluktoo Bay over the course of the summer. The most recent estimates of the narwhal population in the Eclipse Sound area are 13,000–27,500 individuals (Richard et al. 2009). Assessing the proportion of this estimated regional population that visits Koluktoo Bay one or more times in a given summer awaits more comprehensive photo-identification analysis of the narwhals passing by Bruce Head, which we are currently pursuing.
The narwhals we observed were in clusters comprising 1–25 individuals with an average of 3.5 individuals per cluster. The clusters formed herds of 1–642 clusters with an average of 22.4 clusters per herd (corresponding to herds of 4–2247 individuals with an average of 78 individuals, estimated by multiplying the number of clusters per herd by the average cluster size). These observations are similar to the group size estimates from aerial surveys in Lancaster Sound (Cosens and Dueck 1991) and shore-based surveys in Lancaster and Tremblay Sounds (Silverman 1979). The herds we observed were considerably larger than the 10 herds of 29–350 narwhals surveyed by Silverman (1979). In general, narwhal clusters and herds are bigger than the size reported for belugas (Michaud 2005), the species with the distribution and biology most similar to narwhals. Narwhals entered the bay in larger clusters than when they exited it. These larger clusters might be a by-product of the high densities of narwhals entering the bay in synchrony where two or more clusters could join and form a larger cluster to enter the bay. Thus, the size of the clusters of narwhals exiting the bay might be a better reflection of the typical size of stable groups of narwhals. For example, sperm whales form units that are stable for several years, but two or three units may join for a short period of time to form a larger group (Whitehead and Waters 1990).
There was an inverse relationship between cluster size and the degree of sexual segregation in narwhals as has been observed in other odontocetes. Small narwhal clusters were strongly sexually segregated, with 94% of clusters containing 2–9 narwhals composed exclusively of males or females with or without calves. However, the largest clusters and herds composed of many clusters almost always included a combination of males, females and calves. The occurrence of tusked females and tusk-less males might have altered our group composition observations and may result in an even greater degree of sexual segregation (if tusked narwhals in female groups were females and tusk-less narwhals in males groups were males). Observations of narwhals during spring migration also suggest a high degree of sexual segregation with males leading the migration (Greendale and Brousseau-Greendale 1976). Narwhal grouping behaviour resembles grouping in beluga, in which small groups are frequently sexually segregated but larger groups tend to mix (Michaud 2005). More generally, sexual segregation is common in odontocetes (e.g., Connor et al. 1992; Whitehead and Weilgart 2000). Hypotheses explaining social sexual segregation in odontocetes invoke communal care for calves (Béland et al. 1990), defence or avoidance of predators (Arnbom et al. 1987), or resource selection and competition (Whitehead and Weilgart 2000). On the other hand, other cetacean species form groups of mixed composition regardless of group size (e.g., Karczmarski et al. 2005) and, in some cases, both sexes can remain with their natal group (Bigg et al. 1990; Ottensmeyer and Whitehead 2003). Elucidating inter-specific variation in patterns of sexual segregation in odontocete remains a challenge and cannot be explained by a single factor (Michaud 2005). Species, such as narwhals, characterized by variable degrees of sexual segregation, offer excellent opportunities to test, at an intra-specific level, these alternative hypotheses for drivers of sexual segregation.
Environmental Correlates of Narwhal Observations
Narwhals passed Bruce Head in pulses of several individuals and might use environmental cues to synchronize their movements. Narwhal entries and exits into the bay were not randomly distributed in time but did not consistently follow the tidal or circadian cycles across years. In 2007, narwhal clusters generally tended to enter the bay shortly before ebb tide after midnight while in 2008, they preferred entering at the rising tide in the late morning. Although the tendency for movements to coincide with particular environmental conditions in a given year (e.g., before ebb tide in 2007) could suggest narwhals use these conditions as cues to synchronize movements, the lack of inter-annual consistency in these cues indicates that they do not represent constraints. This possibility is also supported by Vibe’s (1950) single year finding that narwhal entries at the head of Inglefied Bredning were associated with rising tide, which is similar to the tidal conditions we observed to be associated with movements in 2008. The reduced consistency and magnitude of circadian rhythmicity observed in this population of narwhals is similar to other mammals studied at high latitudes in summer (van Oort et al. 2005, Korslund 2006; but see Folk et al. 2006) and the general pattern of reduced daily periodicity in marine mammals relative to terrestrial mammals (Watkins et al. 2002; Baird et al. 2008).
The fidelity of narwhals to the same fjords and bays each summer is a key feature of this species’ behaviour, which allows us to observe large numbers of narwhals from Bruce Head; however, the reason why narwhals consistently visit the same fjords and bays is still under question. Feeding, escaping from predators and calving/rearing calves have been suggested to be drivers of site fidelity for other cetacean species (Rice et al. 1981; Simard and Lavoie 1999; Ford and Reeves 2008). Stomach content analyses clearly show that narwhals do not feed when they are in the bays and fjords during the summer (Finley and Gibb 1982, Laidre and Heide-Jørgensen 2005b). Narwhals tend to escape killer whale predation by moving into shallow waters close to shore (Steltner et al. 1984). Bays offer closer proximity to shoreline compared to the open water, which may allow the escape of narwhals to shallow waters. We observed narwhals swimming very close to the shore while exiting Kolutkoo Bay a few hours after a pod of killer whales entered the bay. The calving period of narwhals is from June to July (Mansfield et al. 1975; Hay and Mansfield 1989). The numerous mothers we observed with their calves were likely using the quiet waters of Koluktoo Bay to rear their calves. Knowledge of the context of aggregations of cetaceans in general is incomplete and understanding of the function of narwhal summer gatherings will contribute to further understand the habitat requirements of marine mammals.
There are two complementary approaches to the study of cetaceans in the wild. While remote technologies offer detailed spatial and temporal data that cannot be obtained from direct observations, non-invasive observational approaches allow research on larger numbers of undisturbed individuals. Bruce Head is a very promising site for applying non-invasive observational approaches as it provides the opportunity to frequently sight many individuals close to shore. The vertical contour of this peninsula facilitates the direct observation of narwhals, the deployment of underwater recording equipment, as well as the ability to take photographs of narwhals for photo-identification (e.g., Auger-Méthé 2008). In addition, Bruce Head provides an opportunity for counting narwhals and investigating population distribution and trends. However, limitations in the temporal and spatial extent of this study (i.e., partial observational coverage of narwhals entering one bay in the ice-free season) cannot be overlooked; like all wildlife research, results and applications must be interpreted in light of the study’s particular spatial, temporal and methodological context. It has been highlighted that research in the Arctic should “develop resident capacity and northern involvement in all stages of research in local, national and international issues” (Graham and Fortier 2005). While studies using remote sensing technologies frequently involve northern residents for the capture, handling and instrumentation of narwhals (e.g., Dietz et al. 2001; Heide-Jørgensen et al. 2003), the non-invasive observational techniques described in this paper may be more readily approved and adopted by local Inuit communities (George 2006). The narwhal is a key species for monitoring the impacts of environmental change in high Arctic ecosystems and communities (Laidre et al. 2008). In conjunction with information obtained from remote technologies, data from the non-invasive techniques described above can contribute to the development of effective monitoring and conservation strategies for narwhals.
We wish to thank the community of Mittimatalik for welcoming us to do research on their land, N. Inuarak, A. Kublu, L. Suqslak and K. Beardsley for assistance, as well as S. Ferguson and H. Whitehead for support. We are grateful to C. Agostinelli for assistance with the circular statistical analysis, as well as P.R. Richard and M. Castellini for helpful comments on the manuscript. This research would not be possible without the logistical support of Polar Sea Adventures. Funding for this study was provided by Arctinet, Canadian Wildlife Federation, Canadian Marine Environment Protection Society, Canadian Whale Institute, Department of Fisheries and Oceans, Natural Science and Engineering Research Council of Canada (NSERC) Northern Research Chair Program, Northern Scientific Training Program, and World Wildlife Fund Canada. M.M. was supported by the NSERC, the Eben Hopson Fellowship and the Lorraine Allison Scholarship and M.A.-M. by a NSERC scholarship.