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

Authors:
  • Whalesafari AS / Aarhus University

Abstract and Figures

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.
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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 VestfjordTysfjord–
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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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
... The North Atlantic comprises of three killer whale populations. Population A eats predominantly fish, mainly herring (Clupea harengus), however has been often observed switching between fish and marine mammals-indicative of a more generalist predator [11][12][13][14]. Population B lives sympatrically with Population A and contains two subpopulations: a generalist feeding on fish and mammals and a specialist feeding on mammals [12,[15][16][17]. ...
... Population B lives sympatrically with Population A and contains two subpopulations: a generalist feeding on fish and mammals and a specialist feeding on mammals [12,[15][16][17]. Whereas Population C has been reported to eat fish, including bluefin tuna (Thunnus thynnus) [11,14,15,18,19]. ...
... After a successful predation, killer whales are often observed exhibiting active social behaviour at the surface, such as pectoral fin and fluke slapping, breaching, and spyhopping [11,49,50]. Similar surface active behaviour was observed at the completion of the predatory events in the Bremer Sub-Basin. ...
Article
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Observations of killer whales (Orcinus orca) feeding on the remains of beaked whales have been previously documented; however, to date, there has been no published account of killer whales actively preying upon beaked whales. This article describes the first field observations of killer whales interacting with, hunting and preying upon beaked whales (Mesoplodon spp.) on four separate occasions during 2014, 2015 and 2016 in the Bremer Sub-Basin, off the south coast of Western Australia. © 2016 Wellard et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
... x [40] x [41] x [49] Marine mammals Pilot whale (Globicephala melas) x x [40] Common minke whale (Balaenoptera acutorostrata) x x [50] x [51] Harbour porpoise (Phocoena phocoena) x x [40] x [51] x [52] White-beaked dolphin (Lagenorhynchus albirostris) x x [53,54] Bottlenose whales (Hyperoodon ampullatus) ...
... x [40] x [41] x [49] Marine mammals Pilot whale (Globicephala melas) x x [40] Common minke whale (Balaenoptera acutorostrata) x x [50] x [51] Harbour porpoise (Phocoena phocoena) x x [40] x [51] x [52] White-beaked dolphin (Lagenorhynchus albirostris) x x [53,54] Bottlenose whales (Hyperoodon ampullatus) ...
... x [51] Grey seal (Halychoerus grypus) x x [40] x [56] x [52] Harbour seal (Phoca vitulina) x x [56] x [46,52,57] Harp seal x [50] Hooded seal x [50] https://doi.org/10.1371/journal.pone.0207287.t002 ...
Article
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Killer whales have a cosmopolitan distribution and as a species are generalists, feeding on a variety of prey. However, local populations tend to specialise on specific prey types. In Ice-landic waters, killer whales are generally associated with herring and, thus, have been presumed to be herring specialists. However, recent studies suggest a more complex foraging ecology, possibly including a mosaic of strategies. With increased observational effort in recent years due to research and whale-watching activities, there have been several reports of interactions with different prey, including confirmed predation events. In this study we aimed to summarise the range of potential prey of killer whales observed in Icelandic waters. We report on 12 previously unpublished accounts and review 15 accounts published in the scientific literature or local newspapers, making a total of 27 events where killer whales were observed interacting with actual or potential prey. Thirteen different species, including birds (n = 1), cephalopods (n = 1), fish (n = 5) and marine mammals (n = 6), are reported, although herring is by far the species that killer whales are most often observed interacting with. This study provides the first summary of actual and suspected killer whale prey in Ice-landic waters, and contributes towards our understanding of this population's prey preferences. However, describing the diet of individuals/groups was not possible and this study points to a need for continued monitoring to understand the intricacies of killer whale foraging behaviour in this area.
... whales Globicephala melas and humpback whales Megaptera novaeangliae) seem to have increased in occurrence in the Norwegian Sea (Leonard & Øien, 2020b;Nøttestad, Krafft, et al., 2015), while other abundant baleen whales (e.g., common minke whales Balaenoptera acutorostrata acutorostrata and fin whales Balaenoptera physalus) may have switched from mainly feeding on planktonic prey to pelagic fish such as herring (see Nøttestad, Krafft, et al., 2015;Nøttestad, Sivle, Krafft, Langård, et al., 2014), implying possible variations in resource competition (see . Recent studies in seasons and locations not previously investigated have documented new prey types, that is, Atlantic salmon (Salmo salar; Vester & Hammerschmidt, 2013), Atlantic mackerel (Nøttestad, Sivle, Krafft, Langard, et al., 2014), harbor porpoise (Phocoena phocoena; Cosentino, 2015), lumpfish (Cyclopterus lumpus; Jourdain et al., 2019), and pinnipeds Vongraven & Bisther, 2014) for killer whales in Norway, including for individuals known as herring-eaters (see Jourdain et al., 2019Jourdain et al., , 2020. These new observations could be the result of enhanced research effort but could also reflect behavioral responses to a changing marine ecosystem. ...
Article
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This study investigates survival and abundance of killer whales (Orcinus orca) in Norway in 1988–2019 using capture–recapture models of photo-identification data. We merged two datasets collected in a restricted fjord system in 1988–2008 (Period 1) with a third, collected after their preferred herring prey shifted its wintering grounds to more exposed coastal waters in 2012–2019 (Period 2), and investigated any differences between these two periods. The resulting dataset, spanning 32 years, comprised 3284 captures of 1236 whales, including 148 individuals seen in both periods. The best-supported models of survival included the effects of sex and time period, and the presence of transients (whales seen only once). Period 2 had a much larger percentage of transients compared to Period 1 (mean = 30% vs. 5%) and the identification of two groups of whales with different residency patterns revealed heterogeneity in recapture probabilities. This caused estimates of survival rates to be biased downward (females: 0.955 ± 0.027 SE, males: 0.864 ± 0.038 SE) compared to Period 1 (females: 0.998 ± 0.002 SE, males: 0.985 ± 0.009 SE). Accounting for this heterogeneity resulted in estimates of apparent survival close to unity for regularly seen whales in Period 2. A robust design model for Period 2 further supported random temporary emigration at an estimated annual probability of 0.148 (± 0.095 SE). This same model estimated a peak in annual abundance in 2015 at 1061 individuals (95% CI 999–1127), compared to a maximum of 731 (95% CI 505–1059) previously estimated in Period 1, and dropped to 513 (95% CI 488–540) in 2018. Our results indicate variations in the proportion of killer whales present of an undefined population (or populations) in a larger geographical region. Killer whales have adjusted their distribution to shifts in key prey resources, indicating potential to adapt to rapidly changing marine ecosystems.
... In Norway, this includes predation on salmon (Salmo salar; Vester and Hammerschmidt, 2013). Furthermore, a small number of Norwegian killer whale groups appear to specialize in preying on seals (Similä et al., 1996;Stenersen and Similä, 2004;Jourdain et al., 2017;2020) and even harbour porpoises (Phocoena phocoena) (Cosentino, 2015). Also, summer fish surveys have revealed a strong relationship and spatial overlap between killer whales and mackerel distribution (Nøttestad et al., 2014;Nikolioudakis et al., 2019;Olafsdottir et al., 2019). ...
Article
Assessing the migratory behaviour of individual and groups of animals is key to understand the function of migration, its evolution, and how it is affected by environment and human activities. In the eastern North Atlantic, killer whales (Orcinus orca) presumably track herring stocks as they migrate between across the region. However, the detailed migratory and foraging behaviour of eastern North Atlantic killer whales is poorly understood. We report on the behaviour of 15 adult male killer whales equipped with Argos satellite transmitters during the winter of 2015-2016 along the coast of Troms, northern Norway. The animals were tracked for 8-104 days (mean: 41 days), during which they migrated 302-7608 Km (mean: 2646 Km). The observed movement of killer whales south to 64.2°N along the Norwegian coast following NSS-herring to their spawning grounds is in agreement with previous studies. However, our study is the first to also document northern migration of three of the Norwegian killer whales into the Barents Sea region towards Novaya Zemlya Island about 900 km from the Norwegian coast approaching 77.0°N. Importantly, using a Bayesian state-space model, we offer new insights on killer whale searching and transit movements, as well as diurnal patterns in swimming speed, preferred foraging habitat and feeding behaviour. The 15 tagged killer whales spend 75.0% of the time in an area restricted search (ARS) mode (range: 55.2-95.2%), 3.9% of the time in a transit mode (range: 0.0-16.1%) and 21.1% (range: 4.8-36.3%) in uncertain mode. The restricted search behaviour peaked at the end of January and beginning of February, after which the killer whales gradually performed transit behaviour as they followed the migrating herring out of the region, or shifted to other prey items.
... Seasonal movement pattern, site fidelity of identified individuals as well as complex coordinated feeding behaviors highlighted killer whales as herring specialists [27][28][29]. Sporadic predation observations also suggested additional types of prey including seals and harbor porpoise that support individuals feeding at higher trophic levels [24,30,31]. However, because these opportunistic observations often lack identification of individuals, the potential ecological specializations of marine mammal eating killer whales in Norwegian waters has remained largely undocumented. ...
Article
Full-text available
Killer whales (Orcinus orca) have been documented preying on either fish or marine mammals in several regions, suggesting that this odontocete species has the ability to specialize on different types of prey. Off Norway, killer whales have been shown to rely on the Atlantic herring (Clupea harengus) as a main prey resource. Infrequent observations have revealed seals as an additional component of their diet, yet the extent of predation on marine mammals has remained largely unknown. Here, we present the findings of 29 years of photographic and observational data on seal-feeding killer whale groups identified in Norwegian coastal waters. Four groups have been observed preying and feeding on seals over several years, taking both harbor (Phoca vitulina) and grey (Halichoerus grypus) seals. These stable groups are shown to adopt small group sizes, were typically observed in near-shore areas and were not encountered on herring wintering grounds. Behavioral and social traits adopted by these groups are similar to those of pinniped-feeding killer whales from other regions. The potential ecological reasons and the extent of such prey specializations are discussed.
Article
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Ecological diversity has been reported for killer whales (Orcinus orca) throughout the North Atlantic but patterns of prey specialization have remained poorly understood. We quantify interindividual dietary variations in killer whales (n = 38) sampled throughout the year in 2017–2018 in northern Norway using stable isotopic nitrogen (δ¹⁵N: ¹⁵N/¹⁴N) and carbon (δ¹³C: ¹³C/¹²C) ratios. A Gaussian mixture model assigned sampled individuals to three differentiated clusters, characterized by disparate nonoverlapping isotopic niches, that were consistent with predatory field observations: seal‐eaters, herring‐eaters, and lumpfish‐eaters. Seal‐eaters showed higher δ¹⁵N values (mean ± SD: 12.6 ± 0.3‰, range = 12.3–13.2‰, n = 10) compared to herring‐eaters (mean ± SD: 11.7 ± 0.2‰, range = 11.4–11.9‰, n = 19) and lumpfish‐eaters (mean ± SD: 11.6 ± 0.2‰, range = 11.3–11.9, n = 9). Elevated δ¹⁵N values for seal‐eaters, regardless of sampling season, confirmed feeding at high trophic levels throughout the year. However, a wide isotopic niche and low measured δ¹⁵N values in the seal‐eaters, compared to that of whales that would eat solely seals (δN‐measured = 12.6 vs. δN‐expected = 15.5), indicated a diverse diet that includes both fish and mammal prey. A narrow niche for killer whales sampled at herring and lumpfish seasonal grounds supported seasonal prey specialization reflective of local peaks in prey abundance for the two fish‐eating groups. Our results, thus, show differences in prey specialization within this killer whale population in Norway and that the episodic observations of killer whales feeding on prey other than fish are a consistent behavior, as reflected in different isotopic niches between seal and fish‐eating individuals.
Article
Killer whales (Orcinus orca) in Norwegian waters have long been known to rely on Atlantic herring (Clupea harengus) as a main prey resource. However, research almost exclusively conducted at seasonal herring grounds may have biased studies away from detecting other potentially significant prey species. Since 2013, dedicated research efforts have focused on monitoring killer whale occurrence and foraging ecology throughout the year in northern Norway. This study presents results on site‐fidelity of photographically identified individuals, predation records and behavioral patterns from five spring seasons (March–April) in 2014–2018 in Andfjord, northern Norway. A minimum number of 75 adult and subadult killer whales (out of a catalog of 971 individuals) returned seasonally to the study area for foraging and residency for up to six weeks. Lumpfish (or lumpsucker, Cyclopterus lumpus) was the only type of prey identified (based on molecular or visual identification) on 22 predation events from 2016 (n = 4), 2017 (n = 2) and 2018 (n = 16). Spatial group cohesion observed when foraging was a potential adaptation for efficiently hunting this prey species. These whales were also encountered at herring wintering grounds the same years, but with different group sizes. Such behavioral adaptations suggested intraannual switching between prey resources and foraging strategies.
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Two forms of killer whale (Orcinus orca), resident and transient, occur sympatrically in coastal waters of British Columbia, Washington State, and southeastern Alaska. The two forms do not mix, and differ in seasonal distribution, social structure, and behaviour. These distinctions have been attributed to apparent differences in diet, although no comprehensive comparative analysis of the diets of the two forms had been undertaken. Here we present such an analysis, based on field observations of predation and on the stomach contents of stranded killer whales collected over a 20-year period. In total, 22 species of fish and 1 species of squid were documented in the diet of resident-type killer whales; 12 of these are previously unrecorded as prey of O. orca. Despite the diversity of fish species taken, resident whales have a clear preference for salmon prey. In field observations of feeding, 96% of fish taken were salmonids. Six species of salmonids were identified from prey fragments, with chinook salmon (Oncorhynchus tshawytscha ) being the most common. The stomach contents of stranded residents also indicated a preference for chinook salmon. On rare occasions, resident whales were seen to harass marine mammals, but no kills were confirmed and no mammalian remains were found in the stomachs of stranded residents. Transient killer whales were observed to prey only on pinnipeds, cetaceans, and seabirds. Six mammal species were taken, with over half of observed attacks involving harbour seals (Phoca vitulina). Seabirds do not appear to represent a significant prey resource. This study thus reveals the existence of strikingly divergent prey preferences of resident and transient killer whales, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations. 1471
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In this study, all available records of stranded and incidentally caught harbour porpoise are reviewed. Eighty-one records of stranded animals, or of animals caught in fishing gear along the BC coast, from the period 1934-1991, are presented. Stranding records are concentrated where there are large areas of water ranging in depth from 10 to 100m, usually associated with human population centres. -from Authors
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A community comprises individuals that share a common range and associate with one another; a pod is a group of individuals within a community that travels together the majority of the time; a subpod is a group of individuals that temporarily fragments from its pod to travel separately; an intra-pod group consists of a cohesive group of individuals within a subpod that always travels in close proximity. Communities contain 3-16 (mean 9.5) pods; pods contain 1-3 (mean 1.7) subpods, subpods contain 1-11 (mean 1.9) intra-pod groups and intra-pod groups contain 2-9 (mean 3.6) individuals. Genealogical trees indicate that intra-pod groups are matrilines. A matrilineal group typically comprises of 2-3 generations (range 1-4; mean 2.3) and a generalized matrilineal group consists of a grandmother, her adult son, her adult daughter and the offspring of her daughter. Matrilineal groups are the basic unit of social organization. -from Authors
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The information available indicates a divided offshore distribution during summer for harbour porpoises in Norwegian waters, with a southern component in the North Sea area and a northern component from Lofoten and into the Barents Sea. The abundance estimates were about 82 600 porpoises (CV 0.24) for the southern component and about 11 000 porpoises (CV 0.44) for the northern component. -from Authors
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Killer whales (Orcinus orca) have been concentrating in northern Norwegian fjords during October-January for 20 years, where their main prey Norwegian spring spawning herring (Clupea harengus) has been overwintering. This has provided a unique possibility to study killer whale behavior and conduct long-term photo-identification work. We estimated the size and survival rates of identifiable animals in this population using photo-identification and mark-recapture techniques. Population size was estimated using simple two-sample estimators on pairs of years and using closed capture models in program MARK within years. In the latter analyses, the best models were selected using AIC; how well the models fit the data was explored using Goodness of Fit tests in programs RELEASE and MARK. The highest annual estimate of the number of identifiable animals was in 2003: 398 individuals (95% CI = 314-531). The proportion of identifiable individuals was estimated to be 0.556 (SE = 0.052) for 1992-1995 and 0.656 (SE = 0.041) for 2000-2003. Total population size for 2003 was estimated to be 606 individuals (95% CI = 460-800). Survival was estimated for stage/sex specific groups: adult males, adult females, sub-adults, juveniles and calves with Cormack-Jolly-Seber (CJS) open recapture models in program MARK. Adult male and adult female survival were estimated as 0.958 (SE = 0.0096, 95% CI = 0.935-0.973) and 0.959 (SE = 0.0142, 95% CI = 0.929-0.980), respectively. Lowest survival was estimated for calves, 0.816 (SE = 0.167, 95% CI = 0.335-0.975). Calving intervals were examined using photo-identification data of total 14 years (1989-2002). Calving intervals ranged from 3-14 years (mean = 5.93, SE = 3.087).
Article
Behavior of killer whales feeding on herring schools was recorded with a high frequency (455 kHz) sonar and recorded on a SVHS tape. Synchroniz-ation of surfacing behavior of killer whales was analyzed from 8 mm videotapes recorded between 1990–92. Two different feeding techniques, carousel feeding, where killer whales cooperatively herd herring schools into a tight ball towards the surface and feed on herring which have been stunned by tailslaps, and subsurface feeding were observed and compared. Subsurface feeding killer whales showed less coordination and spent less time around the herring schools than carousel feeding killer whales. Both feeding techniques were employed mainly in the upper 20 m of water but only carousel feeding killer whales brought the herring school to the surface. Subsurface feeding killer whales were observed approaching herring schools down to 98 m, but no feeding could be verified when the whales were deeper than 20 m. The possible causes for different techniques employed by killer whales feeding on herring are discussed as well as the apparent similarity of predator–antipredator behavior between schooling fish and their predators regardless of the species in question.
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Despite well-documented experimental evidence of echolocation in toothed whales, virtually nothing is known about the use and functional significance of cetacean sonar in the wild. Here, the patterns of echolocation sounds produced by killer whales, Orcinus area, off British Columbia and Alaska are described. Two sympatric populations with divergent food habits differed markedly in sonar sound production. Individuals belonging to the fish-eating 'resident' population produced trains of characteristic sonar clicks, on average, 4% of the time, 27 times more often than marine mammal-eating 'transient' killer whales. The click trains of residents averaged 7 s, more than twice as long as the trains of transients. Click repetition rates within resident's trains were constant or changed gradually; within transient's trains they often fluctuated abruptly. Transients produced isolated single or paired clicks at an average rate of 12/h, four times as often as residents. In general, the isolated clicks and infrequent, short and irregular trains of transients were less conspicuous against background noise than the sonar of residents. This difference in acoustic crypticity may reflect a flexible response to the probability of alerting prey, because marine mammals have more acute hearing than fish in the frequency range of sonar clicks. In both populations, echolocation use per individual decreased with increasing group size, suggesting the sharing of information between group members. No relationships were found between echolocation activity and water clarity for whales of either population. Transient whales often travelled or foraged without discernibly echolocating, suggesting that passive listening provides cues for prey detection and orientation.