Complete List of Authors: Watt, Cortney; Freshwater Institute, narwhal… · 2017-01-12 · Draft 2...

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Spatial distribution of narwhal (Monodon monoceros L.)

diving for Canadian populations helps identify important seasonal foraging areas

Journal: Canadian Journal of Zoology

Manuscript ID cjz-2016-0178

Manuscript Type: Article

Date Submitted by the Author: 19-Jul-2016

Complete List of Authors: Watt, Cortney; Freshwater Institute,

Orr, Jack; Freshwater Institute Ferguson, Steven; Fisheries and Oceans Canada,

Keyword: narwhal, Monodon monoceros, satellite tags, dive behaviour, foraging range, seasonal diet

https://mc06.manuscriptcentral.com/cjz-pubs

Canadian Journal of Zoology

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Spatial distribution of narwhal (Monodon monoceros L.) diving for Canadian

populations helps identify important seasonal foraging areas

CA Watt1,2, JR Orr2, and SH Ferguson1,2

1Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2,

Canada

2Fisheries and Oceans Canada, 501 University Crescent, Winnipeg MB R3T 2N6,

Canada

Corresponding author: CA Watt2, [email protected], 204-983-5130

Email for other authors:

JR Orr: [email protected]

SH Ferguson: [email protected]

Running head: Narwhal foraging areas

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Spatial distribution of narwhal (Monodon monoceros L.) diving for Canadian

populations helps identify important seasonal foraging areas

CA Watt1,2, JR Orr2, and SH Ferguson1,2

Abstract

In Canada, narwhals (Monodon monoceros L., 1758) are divided into the Baffin Bay

(BB) and Northern Hudson Bay (NHB) populations. Satellite tracking of twenty-one

narwhals from BB and NHB provided information on their diving behaviour and was

used to identify foraging regions. Previous research from hunted narwhals indicated

that narwhals in both populations depend on benthic prey to meet their dietary

needs. To evaluate home ranges and define areas important for benthic foraging we

conducted kernel density analysis on narwhal locations and focused on areas where

deep diving occurs, as a proxy for foraging, in the winter, spring and migratory

periods. These analyses revealed important areas for foraging for BB narwhals on

the summer grounds in Eclipse Sound, and the winter grounds in Davis Strait, as

well as on the migratory pathway between regions. Similarly, important areas were

identified for the NHB narwhal population in northwestern Hudson Bay in summer,

in NHB and Hudson Strait on the migration, and to the east of the entrance to

Hudson Strait in the winter. This, along with an analysis of the absolute dive depths

provides information on seasons and regions important for foraging, which is

particularly relevant with increasing industrial activities in the Arctic.

Keywords: narwhal, Monodon monoceros, satellite tags, dive behaviour, foraging

range, seasonal diet

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Introduction

The Arctic is currently undergoing a reduction in total sea ice, changes in sea ice

extent, and a shift in the timing of ice freeze up and break up (Tivy et al. 2011).

These changes have facilitated increases in shipping traffic in the Arctic (Pizzolato et

al. 2014) and allowed access to enormous oil and gas reserves beneath the Arctic

Ocean (Reeves et al. 2014). Narwhals (Monodon monoceros L., 1758) are medium

sized (approximately 3-4m length for adults (Garde et al. 2015)) cetaceans endemic

to the Arctic and may be impacted by these increases in industrial activities. There

are two populations of narwhals, which are spatially and genetically distinct

(Petersen et al. 2011) that frequent Canadian waters. The Baffin Bay (BB)

population spends summer (approximately June – September) in the northeastern

fiords and inlets in Canada and the northwestern inlets of Greenland (Dietz et al.

2001, 2008; Heide-Jørgensen et al. 2003; Watt et al. 2012; Heide-Jørgensen et al.

2013a). They then begin their ~1,700 km migration to Davis Strait where they

overwinter, before beginning their migration in April back to the summering

grounds (Heide-Jørgensen et al. 2003; Watt et al. 2012; Fig. 1). Narwhals in this

population are divided into different management units, referred to as stocks, based

on their summering aggregations, and there are at least four defined stocks in

northern Canada (DFO 2012). The second Canadian population is the Northern

Hudson Bay (NHB) population. Whales in this population spend summer in northern

Hudson Bay, and then migrate ~1,250 km east to their wintering grounds in the

eastern Hudson Strait (Richard 1991; Fig. 1).

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The BB narwhal population is estimated to be approximately 140,000

individuals (Doniol-Valcroze et al. 2015) and the NHB population has approximately

12,500 individuals (Asselin et al. 2012). Narwhals are listed as special concern by

the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2004).

This was a change in status from their ‘not at risk’ listing in 1987, primarily because

of the uncertainty with the population size and levels of sustainable hunting, and

potential impacts of climate change (COSEWIC 2004). At the time of the listing,

industrial activities were of little concern, other than potential competition for

Greenland halibut (Reinhardtius hippoglossoides (Walbaum, 1792)) with the active

fishery that occurs in the summer in the region where narwhals overwinter.

However, since then, an iron ore mine has become operational on northern Baffin

Island and the port of Churchill is expanding (Reeves et al. 2014). There is no

information on how these industrial activities may impact narwhals, but having an

understanding of areas important for narwhal foraging may allow us to evaluate

how much overlap there will be in areas shared by narwhals and industry.

Currently our understanding of narwhal diet comes from satellite tag studies,

stomach contents, and stable isotope analysis (Laidre and Heide-Jørgensen 2005;

Watt et al. 2013, 2015). For the BB population, previous stomach content studies

have identified deep dwelling prey, such as Greenland halibut, which live at depths

of 400-1400 m (Peklova et al. 2012), as important to diet, particularly in the winter

months (Laidre and Heide-Jørgensen 2005). Based on stomach contents and dive

behaviour it has been suggested that narwhals forage intensively on Greenland

halibut in the winter months (Laidre et al. 2003; Laidre and Heide-Jørgensen 2005).

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Stable isotopes identified benthic prey, such as Greenland halibut and shrimp

(Pandalus borealis (Krøyer, 1838)), as contributing substantially to BB narwhal

summer diet (>50% of their diet; Watt et al. 2013). In addition, dive behaviour

indicated these whales spend a significant amount of time in, and make dives to 75-

100% of total bathymetric depth at all times of the year (Watt et al. 2015). Stomach

content studies have never been conducted on narwhals from NHB, but stable

isotopes confirmed that benthic prey makes up the majority of their summer diet

(up to 70% for males and 60% for females; Watt et al. 2013) and these results were

supported by dive behaviour which confirmed narwhals from this population make

a significant number of dives to 75-100% of total bathymetric depth (~26% of all

dives were to this portion of the water column; Watt et al. 2015). While benthic

foraging contributes substantially to the diet of narwhals in both populations (Watt

et al. 2013), no studies of where this foraging is occurring have been conducted for

either population. An understanding of areas critical for narwhal foraging is

important for determining how much regional overlap exists between industry and

narwhals, and for predicting anthropogenic impacts on narwhals.

Deep diving marine mammals are limited in their foraging time because of

their oxygen requirements at the surface. The time they need to spend at the surface

increases with dive length, and this must be traded off with the fact that longer dives

increase the chances of the animals finding and capturing prey (Kooyman and

Ponganis 1998). As a result, diving marine mammals need to offset the high costs of

diving by foraging on lipid rich and/or abundant prey in order to optimize their

energy budget (Bluhm and Gradinger 2008; Davis 2014). Due to this selectivity,

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animals may focus on specific areas of the water column and this can indicate where

foraging is focused (Laidre et al. 2003; Hauser et al. 2015). Narwhal are specially

adapted for deep diving (Laidre et al. 2003) and are known to forage heavily on

Greenland halibut (Laidre and Heide-Jørgensen 2005; Watt et al. 2013), which are

lipid rich benthic prey (Lawson et al. 1998). Since deep diving is so energetically

expensive it is often assumed that targeted deep dives indicate foraging (Laidre et

al. 2003; Robinson et al. 2012), and we assume narwhals would only make such

dives for foraging or some other unknown reason, but which also must be of great

importance. Therefore we used dives close to the bottom (75-100% of total bottom

depth) as a proxy for regions important for narwhal foraging or other life-history

traits. Home range analysis of satellite tag data has been conducted for both narwhal

populations, which has provided information on areas used by the animals (Heide-

Jørgensen et al. 2002; Westdal et al. 2010). However, a study on where dives close to

the bottom are occurring has never been conducted and may inform more

specifically on foraging regions, and identify areas to target for conservation efforts.

In this study we assessed the number of dives to different depth categories

for narwhals from BB and NHB and identified seasonal regions where targeted dives

close to the bottom are occurring as a proxy for foraging areas. This was an

extension of a study done in 2015 which had identified that dives close to the

benthos occurred in all seasons for both populations (Watt et al. 2015). In this study

we evaluated the number of dives narwhals made to 75-100% of total bottom depth

and found dives to this portion of the water column varied across seasons for the BB

narwhals but not for the NHB whales. From this work, we wanted to determine

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where these dives close to the bottom were occurring in all seasons to assess

important foraging areas, assuming that targeted dive depths can be an indication of

foraging (Laidre et al. 2003; Robinson et al. 2012; Hauser et al. 2015). Given that we

already had an understanding of where narwhals spend summer and winter and

how they migrate between the regions (Richard 1991; Dietz et al. 2001, 2008;

Heide-Jørgensen et al. 2003; Watt et al. 2012; Heide-Jørgensen et al. 2013a), we had

a good idea of where the whales would be located and assumed they would forage

on both the summer grounds (in northwestern Hudson Bay for NHB narwhals, and

Eclipse Sound for BB narwhals from the Eclipse Sound stock), and winter grounds

(just to the east of the entrance to Hudson Strait for NHB narwhals, and in the Davis

Strait for BB whales). However, this was somewhat exploratory in nature because it

has been thought that narwhal forage mostly in the winter with little foraging on the

summering grounds (Laidre and Heide-Jørgensen 2005), particularly by late

summer (Finley and Gibb 1985). We believed narwhal would forage, at least to some

extent, on the summering grounds since our previous study had found whales made

a significant number of dives and spent significant time close to the bottom (75-

100% of total depth) in summer, suggesting some foraging on benthic prey (Watt et

al. 2015). However, we also know that the summer area is used for calving (Koski

and Davis 1994), while mating occurs on the winter range (Best and Fisher 1974) or

during the migration (Heide-Jørgensen and Garde 2011). As a result, we

hypothesized that 1) narwhals would use only a subset of their winter and summer

range for foraging, rather than the entire home range, since a portion of these areas

may be used exclusively for other activities.

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Previous research has shown that winter is considered an important time for

narwhals gaining energy reserves and it has been suggested that this is the most

important season for foraging on benthic prey, such as Greenland halibut (Laidre et

al. 2003; Laidre and Heide-Jørgensen 2005). As a result we also hypothesized 2) that

the deepest dives would occur on the wintering grounds when narwhals are known

to inhabit deep regions and feed on Greenland halibut (Laidre and Heide-Jørgensen

2005), and 3) that the areas used for foraging in the winter would be larger than

those used in the summer, since feeding is thought to be more intensive in winter

(Laidre et al. 2003; Laidre and Heide-Jørgensen 2005). During the migratory phase,

narwhals typically migrate between the summer and winter areas quite quickly

(depending on ice break-up) and it was thought that migration was primarily

characterized by horizontal movements with little vertical movements (Heide-

Jørgensen et al. 2002); however, we did identify some dives close to the benthos at

this time for both populations suggesting a small amount of foraging may be

occurring (Watt et al. 2015). As a result, our final hypothesis was that 4) the

migration corridor between summer and winter ranges would not be used as much

for foraging, and we would expect only a small area of the entire range as a foraging

area. Determining how much of the seasonal home ranges are used for foraging and

how much overlap may existing with ongoing or proposed industrial activities in the

Arctic will help to better manage any potential interactions between narwhal and

industry.

Materials and methods

Study areas

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Narwhals were tagged near the communities of Pond Inlet, and Repulse Bay,

Nunavut, Canada. We only tagged one stock of narwhals from the Baffin Bay

population; whales from the Eclipse Sound stock were tagged near Pond Inlet in

Tremblay Sound (72º 21’ N, 81º 6’ W) in 2010 and 2011 (Fig. 1; Table 1). From the

NHB population narwhals were tagged near the community of Repulse Bay; five

narwhals were tagged in Lyon Inlet (66º 30’ N, 84º 00’ W) in August 2006, and four

narwhals were tagged in Repulse Bay (66º 31’ N, 86º 14’ W) in August 2007 (Fig. 1;

Table 1).

Capture and tagging

The whale capture and satellite tagging methods used in these study were

previously developed and used successfully by Orr et al. (2001), Dietz et al. (2001,

2008), and Heide-Jørgensen et al. (2003). Narwhals were caught in nets set

perpendicular to the shore. When a narwhal was detected in the net zodiac boats

would drive out and pull the narwhal(s) to the surface; a shore crew would then pull

the net into shore and position the whale with its tail in the shallowest water. A

looped rope with rubber coating was placed around the tail. For females, a hoop net

was placed over the head and for males the tusk was held by one or two people.

Once stabilized the satellite tag was attached with two or three 10 mm nylon pins

through the fat and blubber under the dorsal ridge. All work was conducted under a

DFO License to Fish, and prior approval was obtained from the Freshwater Institute

Animal Care Committee (NHB: FWI-ACC-2006-2007-009 and FWI-ACC-2007-2008-

037, and BB: FWI-ACC-2010-001, and FWI-ACC-2011-016). The entire tagging

process followed approved protocols and was monitored by a veterinarian.

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Narwhals were equipped with Wildlife Computers SPLASH tags and were

programmed to transmit daily from July 1 to September 31 and subsequently on a 3-

day duty cycle. Although daily transmissions provide more detailed movements of

narwhals, the duty cycle allows for a longer deployment period due to battery life

considerations. Data on location of all deployed tags were obtained from the ARGOS

system (CLS America). ARGOS data files were extracted using WC-DAP 3.0 Build 69

software (Wildlife Computers). Dive information was grouped into depth bins, and

represented the 6-hour time span directly prior to the transmission. The depth

reading to determine the start and end of a dive was set at 4 m. Due to the

differences in the ocean bathymetry for the different populations, tags were

programmed to collect data within different dive depth bins. For the BB population,

the number of dives to different depths were binned into 6, 8, 10, 12, 15, 20, 100,

200, 400, 800, 1000, 1400, 1800 and >1800 m bins, while dives from the NHB

population were binned in 6, 8, 10, 12, 15, 20, 25, 50, 100, 200, 300, 400, 500, and

>500 m depth bins.

Data Analysis

The number of dives to a particular depth bin was associated with a location

that occurred within the 6-hour binned time frame on that day. Location

information from the tags was categorized based on the accuracy of the

transmission, varying from poor to good: class A and B, and 0 to 3. Class A and B

provide no estimation of error, Class 0 includes an error range of >1500 m, class 1,

500-1500 m, class 2, 250-500 m and class 3, < 250 m (Lopez et al. 2014). Shape files

of ocean bathymetry were obtained from IBCAO (international bathymetric chart of

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the Arctic Ocean), which provide 500 m2 grid files (Jakobsson et al. 2012), and used

to estimate a depth for each narwhal location through extraction using ArcGIS. Only

class 2 and 3 locations were used in analysis (61% of all locations), as they are both

within the error range associated with the IBCAO depths. We only considered high

quality locations because we needed as accurate bottom bathymetry measures as

possible and did not want to add any extra error into the estimates. Generally, home

range estimates do not improve after approximately 50 observations (Seaman et al.

1999) and our study had >50 observations for each season for both populations;

however, because of the use of only high quality locations our home range estimates

should be considered minimum estimates. After bathymetry data for each location

was obtained, dives to a particular depth bin were converted into a percentage of

total depth. For the deep diving analysis we only included dives that were 75-100%

of the total depth (essentially dives close to the bottom; see Watt et al. 2015). Since

bottom bathymetries are not mapped well in this area we used a conservative

estimate for what constituted bottom diving to ensure we included all benthic dives.

When narwhals were making 25% or more of all their dives in the 6-hour binned

period to 75-100% of total bottom depth we considered them to be targeting this

region (Hauser et al. 2015) and likely a time when they would be foraging on

benthic prey. Bathymetric depths sometimes exceeded the tags' programmed depth

readings for the NHB population, where tags were only programmed to up to 500 m,

and then all dives >500 m fell into one bin together. Dives occurred in the >500 m

bin, but this bin was always included in the 75-100% depth category since narwhals

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from this population were never in waters deeper than 659 m according to the

IBCAO depths.

A repeated measures ANOVA with dive depth and season as fixed effects and

whale nested within depth as a random variable was used to evaluate absolute dive

depths for each population (Underwood 1997). When a significant interaction

between season and depth was found, a model with dive depth as a fixed effect, and

whale nested within depth as a random variable was conducted for each season;

Tukey’s HSD tests were used to determine where significant differences occurred

(Underwood 1997). Normality was assessed using normal probability plots. The

Mauchly criterion (Mauchly 1940) was used to assess sphericity and if sphericity

was violated, the adjusted Greenhouse-Geisser degrees of freedom were used

(Greenhouse and Geisser 1959).

All data was imported into ArcGIS 10.2 and all good quality locations (class 2

and 3) where dives were recorded, as well as only a subset of the locations where

the deepest dives occurred, were then analyzed using the Spatial Analyst toolbox

add-in for estimating the home range of an animal using a kernel density estimate in

an environment with barriers to movement (MacLeod 2013). This allowed us to

calculate a home range estimate for narwhals in the different seasons based on all

locations and then solely on locations where deep diving occurred; thus,

representing an estimate of foraging range. Percentage volume contours (PVC),

which represent the boundary of the area that contains a certain percentage (both

50% and 95% were calculated) of the volume of a probability density distribution,

were then calculated based on the home range estimates. The 50% percentage

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volume contour, which contains 50% of the location records for the population, is

often taken to represent the core range of the critical foraging of the population,

while the 95% PVC is representative of the entire range, excluding only extreme

outliers (MacLeod 2013). Both 50% and 95% were calculated for the wintering and

summering regions, as well as the migration pathway between the two regions.

Summering and wintering grounds were defined spatially based on previous

studies. Summer range for NHB narwhals encompassed Repulse Bay, Frozen Strait,

and north to Lyon Inlet, while the wintering region was just outside of Hudson Strait

(Richard 1991; Westdal et al. 2010). When whales moved out of these defined areas

they were considered to have left the summering or wintering regions, and were on

the migratory route. The definition of these areas resulted in dates of the seasons

varying between whales (Table 1). Migration encompassed both the fall and spring

movements since narwhals have to follow the same route through Hudson Strait for

both periods. However, as a result of the tag programming, and the duration of the

tags, the migratory season for NHB narwhals was dominated by the fall migration (n

= 83) with few locations from the spring migration (n = 9).

The summering range for narwhals from Eclipse Sound had been defined

previously as the Eclipse Sound region (DFO 2012). However, whether Admiralty

Inlet and Eclipse Sound are separate stocks or one stock has not been resolved

(Watt et al. 2012). Since satellite-tagged narwhals from Eclipse Sound travelled into

Admiralty Inlet in August, we included both regions in the summer home range. The

winter range was defined based on Heide-Jørgensen et al. (2002). This resulted in

seasonal dates varying for individual whales (Table 1). Spring and fall migrations

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were also combined for BB narwhals since the migratory routes are generally the

same for both seasons following ice formation and recession (Dietz et al. 2008;

Heide-Jørgensen et al. 2003); however, when all dives were considered there was

greater representation from the fall season (n = 279) compared to the spring (n =

167).

Results

NHB population

Sample sizes varied across the seasons for each population due to the programmed

duty cycle for the tags, the dates that were chosen to represent the seasons (based

on narwhal movements), and the quality of the locations (since only locations of

quality 2 or 3 were used in analysis). For the NHB population we had 240, 245, and

92 high quality locations with dive behaviour for the summer, winter, and migration

seasons respectively. Of these dives 128 (53%), 163 (67%), and 54 (59%) during

the summer, winter and migration respectively, represented locations where

narwhals were making at least 25% of their dives to 75-100% of total bottom depth.

For the NHB population we found a significant interaction between depth bin

and season (F9, 2284 = 52.24, P < 0.0001). Simple effects models found a significant

effect of depth bin in the summer (F4, 1008 = 32.88, P < 0.0001), winter (F4, 922 =

211.03, P < 0.0001), and migratory (F3, 286 = 34.82, P < 0.0001) seasons. Narwhals in

NHB made most dives to the 0-6 and 300-400 m depth bins and the least number of

dives to the >500 m depth bin during the summer and the migratory season (P <

0.05; Fig. 2). In winter, NHB narwhals made most dives to depths >500 m and the 0-

6 m depths, and the fewest dives to the 300-500 m depths (P < 0.05; Fig. 2).

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Kernel home range analysis for all locations where narwhals were diving in

NHB revealed a 50% PVC of 615 km2, 946 km2, and 143 km2 for the winter, summer

and migratory seasons, respectively (Fig. 3a, c, and e). The 95% contours

represented a total area of 1852 km2, 3954 km2, and 1394 km2 for the winter,

summer and migratory seasons, respectively (Fig. 3a, c, and e). Narwhals from NHB

made deep dives in their summering and wintering regions and on the migration

routes between the two areas (Fig. 3b, d, and f). In total, the area encompassed by

the 50% PVC for deep diving was 630 km2 in the summer, 469 km2 in the winter, and

228 km2 during the migratory phase for narwhals from NHB (Fig. 3b, d, and f). The

95% PVC for deep diving in the winter, summer, and the migratory phase was 2499

km2, 1896 km2, and 718 km2, respectively (Fig. 3b, d, and f).

BB population

For the BB population, we used 2101, 993, and 446 high quality locations for

the summer, winter, and migration seasons respectively. Of these dives, 837 (40%),

273 (27%), and 145 (33%) represented locations where narwhals were making at

least 25% of their dives to 75-100% of total bottom depth. For the BB population

absolute dive data was transformed to improve normality using a log+1

transformation, and adjusted Greenhouse-Geisser degrees of freedom were used to

meet the assumption of sphericity. An analysis of the absolute dive depths for

narwhals from the BB population found a significant interaction between dive depth

and season (F3, 5901 = 66.24, P < 0.0001). Simple effects models found a significant

effect of depth bin in the summer (F1, 17 = 123.86, P < 0.0001), winter (F2, 19 = 46.80, P

< 0.0001), and migratory (F2, 18 = 39.23, P < 0.0001) seasons. Narwhals in BB made

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most dives to the 0-6 m depth bin followed by the mid-depths in all seasons, and the

least number of dives to the deepest depths (≥ 1000 m) (P < 0.05; Fig. 4).

Kernel home range analysis for all locations where narwhals were diving in

BB revealed a 50% PVC of 1955 km2, 1608 km2, and 898 km2 for the winter, summer

and migratory seasons, respectively (Fig. 5a, c, and e). The 95% contours

represented a total area of 14244 km2, 6995 km2, and 6123 km2 for the winter,

summer and migratory seasons (Fig. 5a, c, and e). Narwhals from the Eclipse Sound

stock also made deep dives on the summering and wintering grounds and during

the migration. The 50% PVC for deep dives in the winter was 628 km2, 1051 km2 for

summer, and 227 km2 for the migration phase (Fig. 5b, d, and f), while the 95% PVC

for winter, summer, and migration were 3475 km2, 5203 km2, and 1691 km2,

respectively (Fig. 5b, d, and f).

Discussion

We were able to identify important foraging regions in all seasons (summer,

winter, and the migration period) for both populations using deep diving as a proxy

for foraging. Previous research has shown that narwhals gain a significant portion of

their prey from benthic sources (Laidre and Heide-Jørgensen 2005; Watt et al. 2013,

2015) and the present study demonstrates that narwhal carry out deep dives during

all seasons, suggesting some year-round foraging. This is not to say that shallower

dives within the pelagic zone could not indicate foraging; however, we are unable to

conduct such an analysis since we cannot determine where in the water column a

narwhal is foraging with the available data. Advances in tag technology have

permitted the use of stomach temperature pills in narwhals (Heide-Jørgensen et al.

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2014), which can pinpoint when a foraging event occurs; however, these pills are

short lived (maximum 2 weeks and most <48 hours), and are logistically difficult to

deploy in narwhals. As a result, we used dives close to the bottom to define a

minimum area used for foraging that may be important for narwhals. This is the first

study to evaluate foraging areas for each population and this is discussed below

with respect to shipping traffic (Pizzolato et al. 2014), seismic exploration (Reeves

et al. 2014), and expanding fisheries (Jørgensen and Arboe 2013) for each

population.

NHB population

Narwhals from NHB used in this study have been analyzed previously for

home range analysis in the month of August. This resulted in a summer home range

of 7900 km2 in 2006, and 4600 km2 in 2007 (Westdal et al. 2010). Our results, which

represent a smaller subset of total movements, but a much larger date span,

estimated a home range of ~4000 km2 for both years combined (sample sizes were

too small to investigate individual years). The discrepancy between the two studies

is in part due to the fact that Westdal et al. (2010) used all locations, even those with

lower quality, and only defined summer up until August 31st. Our estimate of

foraging range for this population represents a new analysis where deep diving is

occurring and indicates narwhals are using approximately 48 % of their total

summer home range for foraging and making most dives to the 200-400 m range

(400 m is the deepest bottom depth in their summer range). Generally, shipping and

oil and gas operations are very minimal in the NHB narwhal’s summer range (AMSA

2009; Reeves et al. 2014), and although there is potential for seismic exploitation,

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the large hydrocarbon reserves are primarily south of the critical foraging habitat

(Reeves et al. 2014); thus, we would expect little interaction between industry and

narwhals at this time.

No study has previously evaluated narwhal foraging during migration, most

focus on summer or winter diet (Finley and Gibb 1982; Laidre and Heide-Jørgensen

2005). However, whales in this population made many deep dives (>300 m) on the

migration route and we identified a small area in Hudson Strait used for foraging at

this time (~700 km2). When compared to the percent volume contour for all dives,

narwhals use ~52 % of the total migration range for foraging, and make more deep

dives (> 500 m) on the migration route compared to the summer season, which

suggests migration may be an important foraging time for NHB narwhals. At this

time of year narwhals may be interacting with shipping vessels since all shipping in

and out of Hudson Bay must travel through Hudson Strait (AMSA 2009) and there is

an operational well in the Strait (Reeves et al. 2014). This interaction may present a

threat of ship strikes or noise pollution that could impact narwhal communication;

however, currently there is no information on how this increase in shipping may

impact narwhals.

Our study found ~ 1850 km2 made up the winter home range for the tagged

narwhals from NHB; however, a greater area was actually used for deep diving

(~2500 km2). Despite the fact that fewer locations were used in the analysis, we

ended up with a smaller overall range when all dives were included. This suggests

that deep diving may have been excluded as the 5% outliers when all dives were

considered but were included when only a smaller subset was used. It could also

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have been impacted by the fact that for proper comparison, the same bandwidth

was used for both analyses. Regardless, this suggests deep diving is occurring

throughout the entire winter range, and this season is likely very important for

foraging. Narwhals also made most of their deep dives (>500 m) in the winter

season, confirming the importance of foraging at this time. The location of this

foraging range overlaps a demersal fish stock assemblage and current Greenland

halibut fishing region (DFO 2006); thus, increases in fishing pressure (Jørgensen

and Arboe 2013) could result in competition with narwhal for prey, which is part of

the reason they are listed as special concern by COSEWIC (COSEWIC 2004).

BB population

Previous home range analysis has been conducted on six narwhals tagged in Eclipse

Sound in 1999. They found the 95% summer home range was 3417 km2 and

included location information for August (Heide-Jørgensen et al. 2002). The summer

home range size for narwhals from BB in our study of whales tagged in 2010-2011

was almost double that found by Heide-Jørgensen et al. (2002). This may be due in

part to the greater date range, and larger sample of narwhals investigated in our

study (12 compared to 6). Dates were based on narwhal movements and we found

that most narwhals had not left the summering grounds until after August 31st,

which may reflect a change in the timing of migration for Eclipse Sound narwhals.

However, the biggest difference between the narwhals tagged in our study

compared to those in 1999 is that narwhals travelled out of the Eclipse Sound region

and into Admiralty Inlet. This movement between what have been defined as

independent summering regions (DFO 2008) had not been documented previously

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and may indicate a greater overall summer home range for the Eclipse Sound

population. Why they travelled into Admiralty Inlet is unknown, but prey

availability or presence of killer whales (Orcinus orca) in the area in 2010 (G. Freund

pers. comm.) may have contributed to their movements. It has been noted

previously that killer whales elicit behavioural changes in narwhals. Narwhals used

twice as much area when killer whales were present and shifted their distribution

away from the attack site during an encounter in Admiralty Inlet in 2005 (Laidre et

al. 2006). It is possible that narwhals may have moved out of Tremblay Sound and

into Admiralty Inlet because of killer whale presence. However, deep diving also

occurred in Admiralty Inlet suggesting foraging may have also been occurring since

narwhals are not known to dive to evade predators, rather they tend to make quiet

movements close to the shoreline at the surface (Laidre et al. 2006).

Overall, narwhals from Eclipse Sound used almost 75% of their total summer

home range for deep diving, suggesting there is some foraging occurring at this time,

and this would be counter to previous studies which have found many empty

stomachs in summer (Finley and Gibb 1982). Dietz et al. (2007) tagged narwhals

with Crittercams and DTAGS in Admiralty Inlet in 2003 and 2004 and found

narwhals spent only 12% of their time at the bottom, where they spent 80% of their

time upside down. This upside down behaviour is not unusual for narwhals, as

many observers have seen narwhals roll upside down in the water, and most of the

whales in this study rolled upside down after tag attachment and upon release.

However, why narwhals roll is unknown. Dietz et al. (2007) suggested the behaviour

may assist with foraging by orientating the tusk toward the benthos and stirring up

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prey that may be there, but no foraging was seen on the Crittercam footage (Dietz et

al. 2007). These tags were relatively short lasting (maximum ~15 hours) and the

maximum depths obtained were between 100-200 m (Dietz et al. 2007). Shortly

after narwhals were tagged they may not be inclined to forage. Whales tagged in our

study made most of their dives at 400-800 m depths, and thus may have been

foraging.

Narwhal may also dive for reasons unrelated to foraging. Evading predators

has been discussed and is unlikely based on behavioural observations of narwhals in

the presence of killer whales (Laidre et al. 2006). Molting is another possibility.

Narwhals may be diving to the bottom to rub off skin; much like has been seen in

beluga whales (Delphinapterus leucas) (St. Aubin et al. 1990). Another possible

explanation is that narwhals are diving to avoid hunters at the surface. It has been

noted that narwhals are very sensitive to sound and have dove right before rifle

shots (Gonzalez 2001), possibly because they can hear the rifle being loaded or

sense movement on the water or footsteps on the ice. Although this is possible, in

2010 and 2011 in Tremblay Sound hunting had ceased prior to tagging, so it is

unlikely this was the cause of such deep dives. Regardless of whether narwhals are

spending time diving to the depths because of foraging or some other reason, these

regions should still be considered important areas for narwhal since deep dives are

energetically expensive and no matter what is eliciting them, it must be of

importance.

In BB approximately 28% of the migration range was used for deep diving.

Most of the deep dives occurred along the shelf break and occasionally in fiords

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between Pond Inlet and Clyde River (Fig. 5d). In 2014 the National Energy Board

approved a proposal to conduct a five-year seismic testing survey off the coast of

Baffin Island (Speers-Roesch 2014). Community members from Clyde River have

since launched a legal fight to have the decision reversed, as they fear seismic

testing may deter marine mammals from the area. Previous research suggest

seismic testing may be responsible for entrapment events of narwhals (Heide-

Jørgensen et al. 2013b) and subsequent drilling can be clearly heard underwater at

distances up to 38 km (Kyhn et al. 2014). Both the narwhal’s summer and migratory

foraging grounds experience intermediate levels of shipping traffic (AMSA 2009;

Reeves et al. 2014) and oil and gas activity (Reeves et al. 2014), but it is unknown

how these activities may impact narwhal residence time or migration into and out of

the summering regions.

Previous 95% winter kernel home range estimates for one narwhal tagged in

Eclipse Sound in 1999, which included dates from November 10th–March 17th, was

12360 km2, while another whale’s winter home range was 13457 km2 (Heide-

Jørgensen et al. 2002). These values were comparable to what was found for the

winter home range for BB narwhals when all dives were investigated (~14000 km2).

Narwhals in BB used a much smaller proportion of their home range specifically for

foraging activities. For instance, in the winter, of the ~14000 km2 home range, only

~3500 km2 was used for deep diving (~24 %) and a greater total area was actually

used for deep diving in the summer (~5200 km2). This may suggest narwhals are

foraging more in the summer, or are foraging in a more condensed region in winter,

which makes sense given the limited open water available during the winter and the

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need for narwhals to recover at the surface after deep dives (Kooyman and Ponganis

1998). This small area may be very important for foraging and is also known as an

important region for Greenland halibut (DFO 2006). There has been an increase in

the landed catches of Greenland halibut in recent years (Jørgensen and Arboe 2013).

Competition between fisheries and narwhals in this region has been a concern in the

past and resulted in closing an area that overlaps the narwhal’s winter foraging

range (DFO 2007, 2014). However, we found that much of the narwhals diving is

spread out across the winter range, suggesting there may still be some competition

between the Greenland halibut fishery and narwhals outside of the closed fishing

zone (DFO 2014). How or if this overlap in fishing and narwhal foraging will impact

narwhals is unknown, but it may have little effect since the biomass and abundance

of Greenland halibut in the region is stable or increasing (Treble 2016).

Although the narwhal’s diet has been considered quite specialized in the past

(Laidre et al. 2008), recent research results suggests diet has shifted both inter and

intra annually suggesting some plasticity to altering food webs (Watt et al. 2013;

Watt and Ferguson 2015). Adaptability may be particularly important as narwhals

face increased shipping traffic, seismic testing, drilling operations, and enhanced

fisheries within their foraging range. Of particular importance for narwhal

populations are industrial activities on the migration route. We have shown that in

the migratory season, narwhals are not just making horizontal movements at the

surface but are diving 75-100% of the total water depth available to them. We

suggest this deep diving behaviour may indicate foraging, and thus interactions

between narwhal foraging and industry may occur at this time. Further research is

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needed to determine what affect this interaction could have on narwhal foraging

and movements. By determining important areas for narwhal foraging we are better

able to predict when and where industry may interact with narwhals, and build

partnerships with industry to better mitigate any potential impacts of increasing

anthropogenic disturbances in the Arctic.

Acknowledgements

We would like to thank the many dedicated people in the research field camps for

their assistance with capturing and handling the narwhals, particularly S. Black who

offered veterinarian assistance. We also thank P. Richard and K. Westdal for

assistance with tagging/data retrieval for NHB narwhals. Thanks to the Hunters and

Trappers Organizations in Repulse Bay and Pond Inlet, Nunavut, Canada, for all of

their support and the Polar Continental Shelf Program for logistic support. We thank

two external reviewers for comments on the paper, which improved the final

version. Fisheries and Oceans Canada, the Nunavut Wildlife Management Board,

Nunavut Implementation Fund, World Wildlife Fund Canada, ArcticNet, and the US

National Scientific Fund all provided research funding. NSERC, the Northern

Scientific Training Program, the E. Scherer Memorial scholarship, and the Garfield

Weston Foundation provided personal funding to C.A.W.

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Table 1. Tag number, deployment date, sex, the date of the final high quality location (Wildlife Computer class 2 or 3 1

locations) in each of the summer, winter, and fall and spring migration periods (combined for analyses), and the duration of 2

the tag (from tagging to final high quality location) for narwhals (Monodon monoceros) deployed with satellite-linked 3

transmitters in NHB and BB. 4

Population:

Tagging Location

Tag

Number

Deployment

Date

Sex

Final Date

in Summer

Region

Final Date on

Fall

Migration

Final Date in

Winter

Region

Final Date

on Spring

Migration

Tag

Duration

(days)

NHB: Lyon Inlet 57595 08/11/2006 M 10/31/2006 11/26/2006 5/12/2007 5/23/2007* 286

NHB: Lyon Inlet 57597 08/11/2006 M 10/28/2006 11/26/2006 12/7/2006* - 129

NHB: Lyon Inlet 57598 08/11/2006 M 10/24/2006 11/29/2006 4/18/2007* - 251

NHB: Lyon Inlet 57599 08/11/2006 F 10/28/2006 11/29/2006 3/26/2007* 228

NHB: Lyon Inlet 57596 08/11/2006 F 10/21/2006 11/26/2006 5/12/2007 6/1/2007* 295

NHB: Repulse Bay 36641 08/08/2007 F 10/28/2007 11/9/2007* - - 94

NHB: Repulse Bay 40152 08/09/2007 M 10/29/2007 11/21/2007* - - 103

NHB: Repulse Bay 37024 08/09/2007 M 10/28/2007 11/29/2007 12/15/2007* - 129

NHB: Repulse Bay 40622 08/10/2007 M 10/28/2007 11/17/2007* - - 100

BB 51871 08/21/2010 M 9/19/2010 10/6/2010 4/26/2011* - 248

BB 51872 08/21/2010 M 9/19/2010 10/8/2010 5/26/2011* - 278

BB 51873 08/22/2010 F 10/11/2010 9/30/2011†

11/2/2010 5/11/2011 6/18/2011 403

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BB 51874 08/22/2010 F 10/3/2010 2/9/2011* - - 170

BB 51875 08/24/2010 F 10/11/2010 11/6/2010 12/8/2010* - 105

BB 51876 08/16/2011 F 10/14/2011 10/31/2011 2/9/2012* - 177

BB 51878 08/16/2011 M 10/20/2011 11/5/2011 12/21/2011* - 128

BB 51879 08/16/2011 F 10/20/2011 11/6/2011 3/21/2012 6/25/2012* 314

BB 39314 08/18/2011 F 10/15/2011 11/5/2011 3/27/2012* - 222

BB 39270 08/18/2011 F 10/14/2011 10/31/2011 3/7/2012* - 202

BB 39315 08/19/2011 F 10/5/2011 11/2/2011 12/20/2011* - 124

BB 57590 08/19/2011 F 10/14/2011 10/29/2011 6/1/2012 6/15/2012* 301

* Indicates the final date for high quality locations within each of the seasons. †Indicates tags that went into another summer 5 season and date represents the first date for the following summer. 6

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Figure Captions 7

Figure 1. Tagging sites (circle), and closest communities (star) in Nunavut, Canada 8

where narwhals (Monodon monoceros) were tagged. Whales tagged in Tremblay 9

Sound in 2010-2011 represent whales from the BB population, while those tagged 10

in Lyon Inlet in 2006 and Repulse Bay in 2007 represent whales from the NHB 11

population. Repulse Bay is the closest community and was also the location for 12

tagging NHB narwhals in 2007. 13

Figure 2. Frequency of dives to different dive depth bins in summer (number of 14

high quality locations with dive information; (n) = 240), winter (n = 245), and 15

during the migration season (n = 92) for narwhals (Monodon monoceros) from NHB. 16

Figure 3. Kernel home ranges for all locations where dives occurred (panels a, c, 17

and e) and for locations where 25% or more of dives occurred at 75-100% of total 18

bottom depth (panels b, d, and f) for nine narwhals (Monodon monoceros) tagged 19

near Repulse Bay, Nunavut in 2006 and 2007. The 50% (light coloration) and 95% 20

(dark coloration) percentage volume contours are shown for the summer (a and b; 21

number of high quality locations with dive information (n) = 240, and 128 22

respectively), migration (c and d; n = 92, and 54), and winter (e and f; n = 245, and 23

163) seasons. 24

Figure 4. Frequency of dives to different dive depth bins in summer (number of 25

high quality locations with dive information (n) = 2101), winter (n = 446), and 26

during the migration season (n = 993) for narwhals (Monodon monoceros) from BB. 27

Figure 5. Kernel home ranges for all locations where dives occurred (panels a, c, 28

and e) and for locations where 25% or more of dives occurred at 75-100% of total 29

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Draft

36

bottom depth (panels b, d, and f) for twelve narwhals (Monodon monoceros) tagged 30

near Pond Inlet, Nunavut in 2010 and 2011. The 50% (light coloration) and 95% 31

(dark coloration) percentage volume contours are shown for the summer (a and b; 32

number of high quality locations with dive information (n) = 2101, and 837 33

respectively), migration (c and d; n = 446, and 145), and winter (e and f; n = 993, 34

and 273) seasons. 35

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Draft

110x64mm (300 x 300 DPI)

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Draft

Figure 2. Frequency of dives to different dive depth bins in summer (number of high quality locations with dive information (n) = 240), winter (n = 245), and during the migration season (n = 92) for narwhals from

NHB.

89x53mm (300 x 300 DPI)

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DraftMig

ratio

n W

inte

r Home range for all dives

Home range for dives 75%–100% of total depth

Sum

mer

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Draft

Figure 4. Frequency of dives to different dive depth bins in summer (number of high quality locations with dive information (n) = 2101), winter (n = 446), and during the migration season (n = 993) for narwhals

from BB.

89x53mm (300 x 300 DPI)

Page 40 of 41



DraftMig

ratio

n W

inte

r Home range for all dives

Home range for dives 75%–100% of total depth

Sum

mer

Page 41 of 41



Complete List of Authors: Watt, Cortney; Freshwater Institute, narwhal… · 2017-01-12 · Draft 2...

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