First record of Norwegian killer whales attacking and feeding on a harbour porpoise

Abstract

Orcinus orca
is a cosmopolitan species and the most widely distributed marine mammal. Its diet includes over 140 species of fish, cephalopods, sea birds and marine mammals. However, many populations are specialised on certain specific prey items. Three genetically distinct populations have been described in the North Atlantic. Population A (that includes the Icelandic and Norwegian sub-populations) is believed to be piscivorous, as is population C, which includes fish-eating killer whales from the Strait of Gibraltar. In contrast, population B feeds on both fish and marine mammals. Norwegian killer whales follow the Norwegian spring spawning herring stock. The only description in the literature of Norwegian killer whales feeding on another cetacean species is a predation event on northern bottlenose whales in 1968. Daily land-based surveys targeting sperm whales were conducted from the Andenes lighthouse using BigEyes
®
binoculars (25×, 80 mm). The location of animals at sea was approximated through the use of an internal reticule system and a graduated wheel. On 24 June 2012 at 3:12 am, an opportunistic sighting of 11 killer whales was made off Andenes harbour. The whales hunted and fed on a harbour porpoise. Despite these species having overlapping distributions in Norwegian waters, this is the first predatory event reported in the literature.

Full text

First record of Norwegian killer whales
attacking and feeding on a harbour porpoise
a. mel cosentino
1,2
1
Institute of Biological and Environmental Sciences, University of Aberdeen, School of Biological Sciences, Tillydrone Avenue,
Aberdeen, AB24 2TZ, UK,
2
Hvalsafari A.S., Hamnegata 1B, 8480 Andenes, Norway
Orcinus orca is a cosmopolitan species and the most widely distributed marine mammal. Its diet includes over 140 species of
fish, cephalopods, sea birds and marine mammals. However, many populations are specialised on certain specific prey items.
Three genetically distinct populations have been described in the North Atlantic. Population A (that includes the Icelandic
and Norwegian sub-populations) is believed to be piscivorous, as is population C, which includes fish-eating killer whales
from the Strait of Gibraltar. In contrast, population B feeds on both fish and marine mammals. Norwegian killer whales
follow the Norwegian spring spawning herring stock. The only description in the literature of Norwegian killer
whales feeding on another cetacean species is a predation event on northern bottlenose whales in 1968. Daily land-based
surveys targeting sperm whales were conducted from the Andenes lighthouse using BigEyes
w
binoculars (25×, 80 mm).
The location of animals at sea was approximated through the use of an internal reticule system and a graduated wheel.
On 24 June 2012 at 3:12 am, an opportunistic sighting of 11 killer whales was made off Andenes harbour. The whales
hunted and fed on a harbour porpoise. Despite these species having overlapping distributions in Norwegian waters, this is
the first predatory event reported in the literature.
Keywords: killer whale, diet, behaviour, harbour porpoise
Submitted 8 April 2015; accepted 18 June 2015
INTRODUCTION
The killer whale (Orcinus orca, Linnaeus 1758) is a cosmopol-
itan species and the most widely distributed marine mammal.
It can be found in all of the world’s oceans, from the equator to
polar waters (Forney & Wade, 2007), and shows seasonal
movement patterns that are usually associated with increased
prey abundance (Lo
´pez & Lo
´pez, 1985; Simila
¨et al., 1996;
Ford et al., 1998;In
˜iguez, 2001; Esteban et al., 2013).
Worldwide, its diet includes over 140 species of fish, cephalo-
pods, sea birds, turtles and marine mammals. However, most
studied killer whale populations are specialized to feed on
certain specific prey items (Baird, 1994; Ford et al., 1998;
Pitman & Ensor, 2003; Herman et al., 2005; Pitman et al.,
2007; Esteban, 2008).
The best studied killer whale populations in the world are
found off the west coast of the US and Canada, where three
different ecotypes have been described: a ‘transient’ type
that specializes in feeding on marine mammals and sea
birds; a ‘resident’ type that feeds on fish in nearshore waters
and a piscivorous ‘offshore’ type (Bigg et al.,1990; Ford
et al., 1998; Herman et al., 2005). These ecotypes not only
differ in their diet, but also in their morphological traits,
acoustic behaviour and social structure. Transient and resi-
dent ecotypes killer whales have also been documented off
the Kamchatka peninsula and in the Sea of Okhotsk, in
Russian waters (Burdin et al., 2004).
Using microsatellites and mtDNA, three genetically distinct
populations have been identified in the North Atlantic (Foote
et al.,2011). A piscivorous population A specialized in feeding
on herring (Clupea harengus), the Norwegian, the Icelandic or
the North Sea herring stocks. In turn, this population is divided
into two sub-populations: the Icelandic and the Norwegian
(Foote et al., 2012). Individuals from population A were all
sampled at latitudes above 608N. Killer whales from popula-
tion B feed on both fish and marine mammals, and live in sym-
patry with population A in part of their range, as individuals
were sampled between latitudes 518N and 668N, and from
the North Sea to the West coast of Iceland (Foote et al.,
2011). Population C includes all individuals sampled in the
Strait of Gibraltar, which are specialized in feeding on
bluefin tuna (Thunnus thynnus) (Esteban, 2008), and indivi-
duals sampled in the Canary Islands (Foote et al., 2011),
whose feeding habits are unknown.
Although killer whales have been recorded along the entire
coast of Norway, as well as in offshore waters (Foote et al.,
2007), most of what is known about Norwegian killer whales
comes from research studies carried out in northern Norway,
especially during the winter time. These whales have been
intensively studied since 1983 in the Vestfjord–Tysfjord–
Ofotfjord area (Lofoten Archipelago), where they were
observed to return every year to feed on the over-wintering
Norwegian spring-spawning herring (NSSH) (Simila
¨et al.,
1996;Kuningaset al., 2007). Few killer whale observations
are made during the summer months, but they have been
recorded both off Andenes (Vestera
˚len Archipelago) and the
Lofoten Islands (Simila
¨et al., 1996; Simila
¨,1997; Ugarte,
2001; Stenersen & Simila
¨,2004). These whales show a
Corresponding author:
A. Mel Cosentino
Email: orcinus.orca.1758@gmail.com
1
Marine Biodiversity Records, page 1 of 5. #Marine Biological Association of the United Kingdom, 2015
doi:10.1017/S1755267215000895; Vol. 8; e108; 2015 Published online

preference for herring, and photo-identification and satellite
tags suggest that at least some groups follow the NSSH stock,
year round (Simila
¨et al., 1996;Stenersen&Simila
¨,2004;
Foote et al., 2011). In addition, they have also been observed
feeding on mackerel (Scomber scombrus), cod (Gadus
morhua, Linnaeus 1758), Atlantic salmon (Salmo salar,
Linnaeus 1758) and saithe (Pollachius virens, Linnaeus 1758),
as well as harbour seals (Phoca vitulina, Linnaeus 1758) and,
on rare occasions, sea birds (Simila
¨et al., 1996;Stenersen&
Simila
¨,2004;Vester&Hammerschmidt,2013).
Worldwide, there have been reports of killer whale preda-
tion on more than 20 other cetacean species, ranging from
small porpoises to great whales (e.g. Hoyt, 1990; Jefferson
et al., 1991). However, for the Norwegian population, there
is only a report on a single predation event on northern bottle-
nose whales (Hyperoodon ampullatus, Forster 1770)
(Jonsga
˚rd, 1968 in Simila
¨et al., 1996). Here I report and
describe the first case in which Norwegian killer whales have
been observed hunting and feeding on a harbour porpoise
(Phocoena phocoena, Linnaeus 1758).
MATERIALS AND METHODS
The event reported here occurred off Andenes harbour in
northern Norway, at approximately 69.3348N 16.1618E.
Since 2011, several land-based surveys were carried out in
the area on a daily basis (depending on weather conditions),
as part of a study focusing on sperm whales (Physeter macro-
cephalus, Linnaeus 1758). Such surveys were conducted from
the Andenes lighthouse using BigEyes
w
binoculars (25×mag-
nifications, 80 mm). The lighthouse is located at the northern-
most point of Andøy Island (69.32408N 16.11598E) and the
binoculars are assembled on the gallery deck at approximately
40 meters above sea level. For the above-mentioned sperm
whale surveys, the study area is divided into two contiguous
areas (each 1208wide): Bleik Canyon on the west side and
Andfjord on the east side of the island (Figure 1). Surveys
involve scanning one of the two areas for 2 out of every
5 min, for a period of 1 h (i.e. 12 scans per hour). Data are
collected using an Olympus Recorder WS-750M. Location
of animals at sea is approximated through the use of an intern-
al reticule system and a graduated wheel.
The 24 h of daylight during the summer months in the
study area makes it possible to conduct land-based surveys
at any time of day.
RESULTS
On 24 June 2012 at 03:10, an opportunistic sighting of a group
of 11 killer whales was made off Andenes in Andfjord waters
(69.284868N 16.187328E) (Figure 2). Based on body size, as
well as size and shape of the dorsal fin, it was determined
that the group was composed of four adult males, one calf,
one juvenile and five subadult individuals/adult females. The
whales were slowly travelling northwards in a loose formation,
less than two body lengths from each other (sensu
Barrett-Lennard et al.,1996). After 36 min, during a new
scan, the group was spotted again, still travelling northwards
and in a loose formation. At 03:55 they were seen less than
2000 m north-east off Andenes harbour, in a 20 m deep reef
area (69.329428N 16.176708E). The group was heading north-
east when, suddenly, the entire group turned southwards and
started porpoising at high speed towards the shore. It was then
decided to discontinue the sperm whale survey and perform a
focal follow on the killer whales instead. Within one minute, a
killer whale (a subadult or an adult female) rammed a harbour
porpoise from below forcing it out of the water and exposing
half of its own body at an approximately 758angle. The por-
poise was lifted into the air about 5 m above the killer whale.
High-speed chasing above the water is commonly observed
during killer whale predation on small- and medium-sized
cetaceans in other parts of the world (e.g. Baird, 1994;
Constantine et al., 1998; Visser et al., 2010; Coscarella et al.,
2015); however, this was not the case on this occasion, given
that the porpoise was first observed when rammed in the
air. The rest of the group continued porpoising for a few
seconds, gathering around the spot where both the killer
whale and the porpoise were last seen. After that, for
Fig. 1. Map of the study area in northern Norway.
2 a. mel cosentino

less than 1 min, the entire group remained underwater.
Suddenly a whale (again, a subadult or an adult female) rose
out the water as previously, but this time carrying the porpoise
in its mouth. Once more, the group gathered around the
attacking individual and started swimming erratically in the
area. Within the next few minutes, the porpoise was rammed
in the air once more, though not as high as the first time.
The porpoise was not seen again and the killer whales came
closer to each other, moving slowly, gathering around a
small area and facing towards where the porpoise was last
observed, suggesting prey consumption. Reuniting around
the prey during handling and after the kill suggests prey
sharing (e.g. Hoelzel, 1991; Baird, 1994). The event took
place in just over 6 min. The group remained in the area and
sea birds slowly gathered around, flying in circles above the
killer whales, occasionally plunging around the animals.
Whilst the adult males were not actively involved and
stayed to the side most of the time, the calf remained close
to the group throughout the whole predation event. This
has also been observed in North Pacific transients (Baird,
1994). After the kill, aerial behaviour was observed, including
several breaches and tail slapping, as well as other displays
such as rolling on their bodies and spyhopping, which are
indicative of socialization (Barrett-Lennard et al.,1996).
The whales started slowly moving to the north-east 10 min
after the kill, and divided into two smaller groups after
another 10 min: one male, the calf and three other individuals
remained together in that spot and the rest dispersed and
moved further northwards. Both groups were accompanied
by birds occasionally diving, suggesting the prey was shared
by both subgroups. At 04:45 all five remaining killer whales
started to disperse and also headed northwards. Observation
was then finished due to intense glare.
Harbour porpoises are known to be part of the diet of tran-
sient killer whales’ diets off the west coast of British Columbia,
Canada (Jefferson et al., 1991; Baird & Guenther, 1995).
Despite the fact that the species have overlapping distributions
in Norwegian waters (Bjørge & Øien, 1995; Foote et al.,2007),
no predatory interaction has been described previously in the
scientific literature. In April 2012 a photograph taken by a
tourist in Eikelandsfjorden in Hardanger, Southern Norway,
over 1500 km from our study area, was published in an
online local newspaper,
1
showing a killer whale (a subadult
or an adult female) ramming a harbour porpoise. However,
it is not known whether the porpoise was killed and consumed
by the whales.
It was, unfortunately, impossible to take photographs using
the binoculars from the land station for photo-identification.
However, the short distance to the event made it possible to
make reliable sketches of the dorsal fins of three individuals
that had distinctive nicks: an adult male, a juvenile and a
third individual, most likely to be an adult female. The
sketches and group composition strongly suggest that the
group was the same as one seen near Stø on 21 June 2012
(three days before), less than 30 km south-west of Andenes
(69.174998N 15.393008E). Photographs taken on that occa-
sion identified a total of 11 individuals, including one calf,
one juvenile, and four adult males. It was impossible to
attempt to photographically identify the whale in the photo-
graph published in the online newspaper due to the low
quality of the available image.
DISCUSSION
The above observations can be explained in one of three ways.
First, this may indicate an expansion in the range of
mammal-eating population B. Our current knowledge on
their distribution range is limited and while a range increase
in association with climate change (e.g. MacLeod, 2009)or
other factors should not be disregarded, this situation is prob-
ably unlikely given the distance between the study area and the
known range of population B. The other two possible explana-
tions are that members of population A may have learned to
take new prey animals only recently due to a changing envir-
onment, or that this behaviour has simply gone unnoticed to
date. Both are likely situations given the already reported
opportunistic foraging behaviour of this population, and
that most of what is known about the diet and feeding behav-
iour of Norwegian killer comes from studies carried out in the
wintering grounds of the NSSH stock (Simila
¨et al., 1996;
Simila
¨,1997; Ugarte, 2001; Stenersen & Simila
¨,2004;
Kuningas et al., 2007), despite the fact that several groups
have been observed in different seasons and study areas.
Recent studies suggest that the behavioural ecology of killer
whales off Scotland and Iceland is more consistent with special-
ization in foraging behaviour at the individual or group level
rather than population level (Beck et al., 2011). The possibility
that the Norwegian whales also show group or individual spe-
cialization in foraging behaviour cannot be disregarded. In fact,
Simila
¨et al.(1996) already noticed that at least some groups
had different prey preferences (e.g. young herring instead of
adults) associated with different seasonal occurrences. More
recently, killer whales have been regularly observed feeding
on harbour seals off Stø (northern tip of the island of
Langøya) during the summer months (C. Ilmoni, personal
communication) and on salmon in the Lofoten archipelago
(Vester & Hammerschmidt, 2013), although it is not yet
known if different groups are engaged in these activities.
In addition to the porpoise event, I recorded two observa-
tions of killer whales in what appeared to be foraging behav-
iour in search of seals on rocky islands in nearshore waters
(as described in Beck et al., 2011). The first sighting occurred
on 2 August 2012 off Stø, when a group of five killer whales,
initially observed feeding on fish (possibly mackerel), switched
to actively searching for seals around the rocky islands in the
Fig. 2. Map showing the locations where the killer whales were observed.
1
http://www.nrk.no/hordaland/fekk-blinkskot-av-spekkhoggar-1.8065404
killer whales feeding on harbour porpoise 3

area (Beck et al., 2011). On this occasion, at least one unsuc-
cessful attempt to catch a seal was made. Similar behaviour
was observed by a group of 20 to 25 whales on the 28
November 2012, off Andenes (on the west side of Andøy
Island), although no attempt to catch a seal was observed.
Interestingly, one subgroup in this second sighting caught
(and presumably ate) several sea birds (possibly King Eider
–Somateria spectabilis Linnaeus 1758). There are also
reports of killer whales harassing and probably feeding on
puffins (Fratercula arctica Linnaeus 1758) in the area (G.
Mann, personal communication). Together, these observa-
tions may indicate that the killer whales in northern
Norway prey upon an array of fish, sea bird and marine
mammal species, even though its presence in the area is
highly linked to the occurrence of the NSSH (Simila
¨et al.,
1996; Hvalsafari unpublished data). Furthermore, observa-
tions of killer whales harassing other cetacean species (e.g.
minke and sperm whales) off Andenes have been made
since 2011 (Hvalsafari, unpublished data). However, it is not
clear whether or not they were predatory interactions.
The ecological separation of the North Atlantic killer
whales is not as clearly defined as it is in the Eastern North
Pacific (de Bruyn et al., 2013). The NSSH has a complex life
cycle that requires suitable areas for each stage (i.e. spawning,
feeding, nursing and wintering). These areas and their migra-
tions routes vary somewhat unpredictably (Dickson &
Østerhus, 2007), which could explain the more generalist
behaviour observed for this killer whale population.
Baird & Dill (1996) estimated that the optimal group size
that maximizes energy intake for the North-east Pacific transi-
ents is three individuals, which coincides with the typical group
size (Baird, 1994). Other marine-mammal-eating killer whales
also have small group sizes: three individuals for the Punta
Norte (Patagonia) population (Hoelzel, 1991), and five for
killer whales in Scottish waters (Beck et al., 2011). Group size
for Norwegian killer whales, however, ranges from 6 to 30
animals, with a median of 15 (Simila
¨,1997). Foraging techni-
ques are transferred from one generation to the other
through social learning, as observed in Patagonia where killer
whales use an intentional stranding technique to catch seal
pups on the beach (Lo
´pez & Lo
´pez, 1985; Hoelzel, 1991).
As a population, Norwegian killer whales feedon various prey
species, ranging from fish, to birds to other marine mammals,
many requiring different complex hunting techniques that
require a high level of coordination for a successful attack. The
hunting behaviour described here greatly differs from the car-
rousel method used when feeding on herring (Simila
¨&
Ugarte, 1993) or that used for seal hunting (Beck et al., 2011).
Thus, this report increases our knowledge of killer whale diet
and foraging behaviour in the area and may suggest a wider sep-
aration from the Icelandic sub-population than previously
thought. Progress in the knowledge of this killer whale popula-
tion is slow due to the paucity of published reports. Increased
collaboration between research groups in the area will greatly
benefit the understanding of their feeding ecology at an individ-
ual and group level, as well as the ecology and social structure.
ACKNOWLEDGEMENTS
I would like to thank Arctic Whale Tours for providing the
killer whale photographs, and two anonymous reviewers for
their comments on early versions of this manuscript.
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Daly S., Hatwell T., Johnson T., Johnson W., Kay L., Maessen T.,
McKay V., Peters T., Turner N., Umuroa B. and Pace D.S. (2010)
First record of predation on false killer whales (Pseudorca crassidens)
by killer whales (Orcinus orca). Aquatic Mammals 36, 195– 204.
Correspondence should be addressed to:
A. Mel Cosentino
Wild Earth Foundation
Av de las Ballenas 9500
Puerto Pira
´mides, Peninsula Valdes
Chubut, Argentina
email: orcinus.orca.1758@gmail.com
killer whales feeding on harbour porpoise 5