VOL. 68, N O. 1 (MARCH 2 015) P. 54 – 61
First Records of Atlantic Mackerel (Scomber scombrus)
from the Svalbard Archipelago, Norway,
with Possible Explanations for the Extension of Its Distribution
Jørgen Berge,1,2,3 Kristin Heggland,1,2 Ole Jørgen Lønne,1 Finlo Cottier,4 Haakon Hop,5
Geir Wing Gabrielsen,1,5 Leif Nøttestad6 and Ole Arve Misund1,6
(Received 4 April 2014; accepted in revised form 19 June 2014)
ABSTRACT. Atlantic mackerel (Scomber scombrus) were recorded in Isfjorden, Svalbard (78˚15ʹ N, 15˚11ʹ E) in late
September 2013. This record is the northernmost known occurrence of mackerel in the Arctic and represents a possible
northward expansion (of ca. 5˚ latitude) of its distributional range. The examined specimens of mackerel were between 7
and 11 years old, with a mean size of 39 cm and a mean weight of 0.5 kg. Examination of stomach contents indicated that the
mackerel were feeding mainly on juvenile herring (Clupea harengus). The occur rence of mackerel in the Arctic is discussed
in relation to the recent increase in mackerel population size in the North Atlantic and the expansion of other North Atlantic
shes into the Svalbard region during the last decade. Using a decadal record of water temperature, we conclude that the
occurrence of Atlantic mackerel in Svalbard waters is a result of a continued warming of the ocean in the region and that it
follows a general trend of species’ extending their distributional ranges northward into the Arctic.
Key words: Arctic; Atlantic mackerel; Scomber scombrus; species distribution; oceanography
RÉSUMÉ. À la n de septembre 2013, la présence de grands maquereaux (Scomber scombrus) a été enregistrée à Isfjorden,
dans l’archipel du Svalbard (78˚15ʹ N, 15˚11ʹ E). Il s’agit de l’apparition de maquereaux la plus nordique à avoir été enregistrée
dans l’Arctique, ce qui pourrait représenter une extension vers le nord (d’environ 5 degrés de latitude) de la répartition de cette
espèce. Les individus qui ont été examinés étaient âgés de 7 à 11 ans, avaient une taille moyenne de 39 cm et un poids moyen
de 0,5 kg. L’analyse des contenus stomacaux a permis de déterminer que les maquereaux se nourrissaient essentiellement de
harengs juvéniles (Clupea harengus). La présence du maquereau dans l’Arctique est discutée à la lumière de l’augmentation
récente de la population dans l’Atlantique Nord et de l’afux d’autres poissons de l’Atlantique Nord dans la région du Svalbard
au cours de la dernière décennie. Grâce à l’enregistrement décennal de la température de l’eau, nous concluons que la présence
du grand maquereau dans les eaux du Svalbard résulte du réchauffement continu de l’océan dans la région et que cela suit la
tendance générale des espèces à étendre leur parcours vers le nord, dans l’Arctique.
Mots clés : Arctique; grand maquereau; Scomber scombrus; répartition des espèces; océanographie
Révisé pour la revue Arctic par Nicole Giguère.
РЕЗЮМЕ. В конце сентября 2013 года в Исфьорде, архипелаг Свальбард (78˚15ʹ с.ш., 15˚11ʹ в.д.), было зарегистрировано
самое северное появление атлантической скумбрии (Scomber scombrus). Эта находка представляет расширение
района встречаемости этого вида на примерно 5˚ широты в северном направлении. Возраст всех обнаруженных
экземпляров скумбрии составлял от 7 до 11 лет, средний размер 39 см и средний вес около 0,5 кг. Исследование
содержимого желудков пойманных экземпляров показало, что скумбрия питалась в основном молодью сельди
(Clupea harengus). Появление атлантической скумбрии в районе Свальбарда обсуждается в связи с увеличением
численности популяции этого вида в Северной Атлантике и расширением ареалов североатлантических видов рыб в
район Свальбарда в течение последнего десятилетия. На основе анализа декадных наблюдений за температурой воды
в исследованном районе сделан вывод о том, что появление атлантической скумбрии в водах Свальбарда является
результатом продолжающегося повышения температуры воды в регионе и отражает общую тенденцию смещения
границ ареалов видов умеренных широт в северном направлении.
Ключевые слова: Арктика; атлантическая скумбрия; Scomber scombrus; распределение видов; океанография
1 University Centre in Svalbard, 9171 Longyearbyen, Norway
2 Faculty of Biosciences, Fisheries and Economics, UiT The Arctic University of Norway, 9037 Tromsø, Norway
3 Corresponding author: firstname.lastname@example.org
4 Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll PA37 1QA, Scotland, United Kingdom
5 Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway
6 Institute of Marine Research, Box 1870, 5817 Bergen, Norway
© The Arctic Institute of North America
ATLANTIC MACKEREL IN SVALBARD • 55
In recent years, the Atlantic mackerel (Scomber scombrus
L.; hereafter, mackerel) in the North East Atlantic (NEA)
has extended its distribution and migration patterns (ICES,
2013a). Normally, after spawning west of the British Isles
during spring or early summer, the mackerel migrates
northward to feed in the Norwegian Sea, along the Nor-
wegian Coast, and partly in the North Sea before return-
ing to the spawning areas in late autumn (Iversen, 2004;
Fig. 1). In recent years, mackerel have been recorded and
shed commercially around the Faroe Islands and Iceland,
and have even been caught in the waters east of Greenland
(ICES, 2013b). This northward and westward expansion of
mackerel distribution appears to be related to increasing sea
surface temperatures in the NEA during summer, exempli-
ed by the warming of Atlantic water in two west Spitsber-
gen (Svalbard) fjords during the 1900s (Pavlov et al., 2013).
However, there are also signs of an increased abundance of
mackerel in general, with record high year-classes during
the last 10 years (ICES, 2013a, b).
The mackerel is a relatively long-lived species, reach-
ing a maximum age of around 20 years (Pethon, 2005).
For at least the last decade, the population of the Atlantic
mackerel has been quite stable, with a spawning stock of
about two to four million tonnes (Bakketeig et al., 2013),
but with indications of an increase of about 30% to nearly
six million tonnes during the last years (ICES, 2013a). A
remarkably stable recruitment and a good surplus produc-
tion in the stock have yielded catches of about 500 000 to
700 000 tonnes annually (ICES, 2013a) and around 900 000
tonnes annually during the last few years. The International
Council for the Exploration of the Sea (ICES) has recom-
mended catches of about 650 000 tonnes annually, but
possible overshing due to illegal, unreported, and unregu-
lated shing has been a controversial issue in the manage-
ment of the stock and was considered a problem until the
years 2000 – 05 (ICES, 2013b). In recent years, the expan-
sion in distribution has enabled Iceland and Greenland to
engage in shing of mackerel. Historically, these countries
did not have a quota according to the management agree-
ment between the coastal states that have been harvesting
the mackerel stock in the NEA. As a result the management
agreement was broken, and in the years 2010 – 13 there
was no international agreement on shing of mackerel.
The European Union, Faroe Islands, and Norway recently
agreed on a total allowable catch (TAC) with respective
allocations of mackerel in the NEA, but Iceland is still not
part of the new agreement (Anon., 2014).
In the autumn of 2013, a potential new chapter in the
evolving history of mackerel in the NEA began with the
rst record of the species in the Arctic waters of Svalbard
(Aaserud, 2013, and this study). We followed up this unex-
pected occurrence of mackerel in the Arctic with a small
survey near Longyearbyen, adding a description of related
oceanographic conditions of the sea in the area. Our aims
with this study were to evaluate the magnitude of the
mackerel inux into Isfjorden and to characterize basic bio-
logical traits of the individuals collected.
MATERIAL AND METHODS
Fish data for this study were collected from Isfjorden
(78˚15′ N, 15˚11′ E), a west-facing fjord in the Svalbard
archipelago (Fig. 1). Six mackerel were collected with hook
and line from the RV Viking Explorer on 22 – 23 September
2013. An additional four mackerel caught by local residents
during this period were included in the study. Scientic
bottom and pelagic trawling and hook-and-line shing in
the fjord from the RV Helmer Hanssen on 24 – 25 Septem-
ber 2013 caught no mackerel. During the collection period,
water temperature in the upper 40 m of the water column,
measured with a proling CTD rosette, ranged from 5.0˚C
Fish caught from RV Viking Explorer were identied
according to Pethon (2005) and frozen whole. After thaw-
ing in the lab, total length (cm) and total wet weight (g)
were measured. Otoliths were removed and ages estimated
from them by experts at the Institute of Marine Research in
Bergen, Norway, according to their standard procedures for
age determination of the species (Mjanger et al., 2013). Sex
FIG. 1. Distribution of Atlantic mackerel ( blue area). The red star indicates
the Isfjorden and Kongsfjorden areas of Svalbard. The black line shows the
previous northern distribution lim it, and orange indicates known spawning
56 • J. BERGE et al.
of individual specimens was determined through morpho-
logical examination of their gonads. The gonadal somatic
index (GSI) was determined from the gonadal weight as
a percentage of carcass weight (gonads and stomach con-
tents subtracted from total weight). Guts were removed and
stomach contents were weighed and recorded. Stomach
contents were identied to the lowest possible taxon under a
To investigate interannual variation in the local oceano-
graphic conditions, we used hydrographic data collected
since 2002 by oceanographic moorings in Kongsfjorden
(Fig. 1) since ocean dynamics and conditions in the adjacent
fjords of Kongsfjorden and Isfjorden are known to be simi-
lar (Nilsen et al., 2008; Pavlov et al., 2013). These moorings,
which have recorded the seasonal variability in ocean con-
ditions in this region (e.g., Cottier et al., 2005, 2007), were
placed in the entrance to Kongsfjorden, typically at water
depths of more than 200 m, with instrumentation span-
ning the water column from 20 m below the surface to 10 m
from the seabed. Most mooring deployments had at least 10
temperature sensors distributed throughout the depth range
(see Cottier et al., 2005 for typical mooring arrangement
and instrumentation). As winter conditions are considered
a precursor of subsequent summer intrusions of Atlantic
water into the west-facing Svalbard fjords (Nilsen at al.,
2008), we calculated the mean temperature integrated for
the water column during winter (Februa ry – April). A lso,
since winter temperatures might play an important role in
the survival of newly established populations, they are rel-
evant to our argument concerning the gradual increase of
boreal species entering the Arctic.
To test for signicant shifts in winter temperature, we
applied an algorithm to the resulting time-series of mean
winter temperatures. The algorithm detects shifts in the
data series by the sequential application of t-tests to deter-
mine whether each data point differs signicantly in its
properties from the preceding points (for details of the
computation, see Rodionov, 2004). Signicant changes are
conrmed or rejected by considering the subsequent data
points. In this way, there was no prior assignation of the
shift point; rather it emerges from the statistical treatment
of the data series. The cut-off length (l) is an important
criterion, which sets a minimum length of a period to be
considered a regime, as well as the signicance level p of
the t-test. In our analysis of winter temperatures, we used
l = 3 years because this length permitted better resolution
of regimes occurring in a relatively short data series. The
signicance level for the test was set to α = 0.1. Autocor-
relation of the data (deYoung et al., 2004) can introduce
red noise, which can be a problem in such time series; we
handled this by using a “prewhitening” technique [avail-
able at www.beringclimate.noaa.gov] that removes the red
noise component through subsampling and bias correction
We also document changes in the sh fauna of Kongs-
fjorden and Isfjorden on Svalbard over the last 15 years.
Data are derived mainly from our cruises with RV Helmer
Hanssen, from which the University Centre in Svalbard has
conducted regular surveys of the sh fauna every autumn
since the late 1990s. This information is supplemented by
observations from research cruises by UiT The Arctic Uni-
versity of Norway, the Norwegian Polar Institute, and pub-
In total, six mackerel were caught at 20 – 50 m depth dur-
ing six hours of shing on 22 – 23 September 2013 (Table 1).
Three additional sh were hooked, but lost at sea. In addi-
tion, four individuals collected at the same time in the
same area were made available to us by local inhabitants
of Longyearbyen. The 10 specimens had a mean weight of
510 ± 67.1 g, a mean length of 38.9 ± 1.6 cm, and a mean
age of 7+ years (Table 1). All sh were females, with GSI
ranging from 0.20% to 1.50%. Six taxa were present in
the stomachs of the mackerel (Table 2). Fish were the main
prey, present in 90% of the stomachs and constituting more
than 98% of the total prey dry weight. Two of the stomachs
contained only herring (Clupea harengus L.), and 41.7%
of the total consumed prey dry weight was unequivocally
identied as herring. However, the texture and color of the
remaining sh items (56.4% of prey dry weight) indicate
that all sh consumed were probably herring. Two of the
sh had eaten squid, but this group accounted for only 1.5%
of prey by weight. Crustacea (Calanus sp. and Thysanoessa
sp.) were present in two of the stomachs, although it is pos-
sible that some originated from the sh eaten by the mack-
erel. The consumed herring had large amounts of calanoid
copepods in their stomachs.
The time-series of winter mean temperatures indicated
that the temperatures were below zero (mean value = −1˚C)
from 2002 to 2005, whereas ve of eight winters had tem-
peratures above zero (mean value = 0.5˚C) from 2006
onwards (Fig. 2). Using the method outlined by Rodionov
(2004, 2006), we identied a statistically signicant shift in
winter temperatures in 2006 at p = 0.1. The occurrence of
a single shift in 2006 was insensitive to the use of l = 3, 4,
or 5 years, demonstrating that the result is quite robust to
selection of length.
The local newspaper, Svalbardposten, reported that
inhabitants of Longyearbyen had collected 72 specimens,
ranging between 35 and 40 cm long, one week earlier in
the same fjord (Aaserud, 2013). These individuals were not
available for examination and are therefore not included
in the present study. They do, nevertheless, underline the
fact that the occurrence of mackerel in Isfjorden involves
more than a few single individuals. The mackerel caught
by residents of Longyearbyen (Aaserud, 2013) and by the
RV Viking Explorer (this study) did conrm the occurrence
ATLANTIC MACKEREL IN SVALBARD • 57
of the species in Svalbard. However, the lack of mackerel
in the trawl catches from the same area by the RV Helmer
Hanssen over the next few days suggested that the numbers
of mackerel in the area were limited. The individuals caught
in Isfjorden were between 7 and 11 years old, paralleled by
the very strong year-classes in 2002, 2005, and 2006 (ICES,
2013b; Nøttestad, 2014). This age range also indicates that
it is the older individuals in the populations that make
such long migrations (see Nøttestad et al., 1999) beyond
the limits of their hitherto normal distribution ranges.
The mackerel were mature, but their low GSI (< 2%)
indicated that they were not in spawning but rather in post-
spawning condition. The NEA mackerel is a fast swimmer:
it can swim at a sustained speed of 1 m s-1 over extended
periods (He and Wardle, 1988). Therefore it is possible, if
the temperature range is within their tolerance limits, that
these mackerel are capable of covering the distance from
Tromsø, south of the previous northern edge of the species’
distribution, to Longyearbyen (973 km in a straight line)
within a two-week period (assuming a constant average
speed). Their optimum temperature is in the 7˚C – 13˚C
range, and their lower tolerance at around 4.5˚C (Iversen,
2004). An interesting observation in our study was that
mackerel were found to feed more or less exclusively
on juvenile herring, reinforcing the documentation that
mackerel can be effective predators on both larvae and
juvenile herring during their active feeding migration in the
Arctic (see Skaret et al., 2014, reporting from a study along
the Norwegian coast).
Large-scale Oceanographic Conditions and Ranges of
Most of the world’s oceans, including the North Atlan-
tic and Arctic Oceans, have experienced pronounced
variations in temperatures during the last 120 000 years
(Rahmstorf, 2002; Sarnthein et al., 2003). The warmer tem-
peratures of Atlantic water entering the Arctic Ocean in
the early 21st century have no precedent in the past 2000
years and are presumably linked to the Arctic amplication
TABLE 1. Total weight (TW, g), total length (TL, cm), dry weight of stomach contents (g), wet weight of gonads (g), gender, and age
(years) of 10 Atlantic mackerel collected in Isfjorden, Svalbard, on 22 – 23 September 2013. All individuals were mature, and the GSI was
below 2% for all examined individuals (data not shown).
ID TW(g) TL (cm) Dry weight stomach contents (g) Wet weight gonads (g) Sex Age (years)
1 486.6 41.2 2.0336 7.05 F 10
2 522.6 39.3 0.2234 6.02 F 10
3 465.9 38.0 0.1995 6.36 F –
4 509.4 38.5 1.1007 1.26 F 11
5 494.9 37.7 1.3267 0.97 F 7
6 421.3 37.4 1.4679 1.00 F 7
7 480.0 37.2 2.0513 1.05 F 7
8 677.5 42.0 11.8723 8.69 F 10
9 537.8 38.8 1.1498 6.05 F 7
10 503.8 39.3 0.8133 5.96 F 10
Mean 510.0 38.9 2.2224 4.44 – –
± SD 67.1 1.6 3.4487 3.01 – –
TABLE 2. Prey occur rence and prey weight from 10 mature
female Atlantic mackerel stomachs from Isfjorden, Svalbard.
%F = the number of stomachs containing a specic prey item
as percentage of all sampled stomachs. DW = the combined dry
weight (g) of each prey category consumed. %DW = dry weight as
a percentage of the total dr y weight of the total stomach contents.
Prey taxa %F DW %DW
Crustacea 20 0.07 0.3
Crust acea ind. 10 0.02 0.1
Calanus sp. 10 0.05 0.2
Thysanoessa sp. 10 < 0.01 < 0.1
Cephalopoda Theutoidea 20 0.34 1.5
Pisces 90 103.12 98.1
Unidentied sh 80 12.55 56.4
Clupea harengus 20 9.27 41.7
FIG. 2. New sh species in Svalbard waters in relation to ocean temperature.
Points on blue line represent mean water colum n temperatu res during winter
(February – April) in each year. Black line shows signicantly higher mean
winter temperatures since the 2006 warming event than before 2006 ( p = 0.1).
All new sh species were recorded during this warmer period. Red circles
below a year indicate rst records in Kongsfjorden for (A): Mallotus villosus,
(B): Melanogrammus aeglenus, (C): Entelurus aequoreus, (D): Gadus
morhua (juv.), (E): Melanogrammus aeglenus (juv.), (F): Clupea harengus,
and (G): Scomber scombrus.
58 • J. BERGE et al.
of global warming (Spielhagen et al., 2011). In the Barents
and Greenland Seas, these changes are manifested through
an increased volume transport of Atlantic water, which can
exchange with water found on the adjacent shelves and in
the fjords on the west coast of Svalbard (Cottier et al., 2005,
2007; Nilsen et al., 2008).
As the North Atlantic and Arctic Oceans and the Eur-
asian Arctic shelf seas are strongly linked through the
North Atlantic Current System (NACS), variations in this
current system are likely to have a direct and detectable
inuence on the marine ora and fauna in these regions
(Piechura and Walczowski, 2009; Narasyanaswamy et al.,
2010; Renaud et al., 2012). The main route for northward
migration of boreal and temperate species is the West Spits-
bergen Current (WSC). Recent work has shown that the
temperature change in the WSC has been approximately
0.01˚C per year for the last 15 years (Walczowski et al.,
2012) and that the maximum temperature in the adjacent
fjords has increased by around 0.02˚C per year over the last
century (Pavlov et al., 2013). This increase may be exempli-
ed by the past and current distributions of the blue mussel
(Mytilus edulis L.) in the Arctic (Berge et al., 2005) or the
change in hard-bottom benthos (Kortsch et al., 2012). The
presence or absence of blue mussels in Svalbard during the
last 11 000 years is probably linked to oscillations in ocean
climate that resulted from changes in the volume transport
of Atlantic water through the NACS (Berge et al., 2005,
2006). Accordingly, as the average temperature in the WSC
has not increased relative to that inside the fjords of Sval-
bard (Cottier et al., 2005, 2007; Walczowski et al., 2012;
Fig. 2), the appearance of boreal species is assumed to be
linked with processes that enable these species to enter the
fjord, rather than to those that allow them to reach this far
north. In the discussion below, we therefore treat the mack-
erel as having a more or less continuous distribution within
its known distributional range (see Fig. 1), although this
continuity is merely an assumption and the documented
distributional range is discontinuous. Nevertheless, the doc-
umented occurrence of mackerel in Svalbard fjords does
illustrate the interplay between large-scale oceanographic
conditions (mostly through the NACS) and more local
cross-shelf exchange processes at the mouth of the fjord,
both of which are essential for a temperate species to even-
tually enter the fjord.
Effect of Local Oceanographic Conditions on Boreal Fishes
Our oceanographic data from Kongsfjorden show a
measurable change in the winter oceanic conditions during
the last decade. While declaring a regime shift on the basis
of winter temperature alone should be done with caution,
the periods before and after 2006 are statistically different
(Fig. 2). Table 3 shows that except for Atlantic cod, all new
boreal sh species in Svalbard have been recorded since
2006. Previous work (Nilsen et al., 2008) has shown that
winter conditions, particularly those related to sea ice for-
mation, can modify the extent to which Atlantic water can
exchange effectively with the fjord in subsequent summers.
The shift in winter temperatures in Svalbard fjords
therefore has the potential to inuence the sh popula-
tion in two ways; directly through increased survival dur-
ing winter periods or more indirectly through an increased
inux of Atlantic water during summer and autumn sea-
sons. Advection of Atlantic zooplankton species into the
fjords has been demonstrated in Kongsfjorden (e.g., Willis
et al., 2006, 2008). Populations of such advected organisms
(those that are not active swimmers) are more likely to sur-
vive overwintering in the fjords when winter temperatures
are elevated (e.g., Berge et al., 2005). Long-term changes in
oceanic conditions, with enhanced winter survival through
increased inux of Atlantic waters, are likely important
regulating factors for new establishment of boreal spe-
cies in the fjords of Svalbard (e.g., Berge et al., 2009). The
occurrence of sh species in Svalbard waters seems to have
increased steeply since 2006. Mackerel, however, currently
appear to be present in Svalbard waters only as late summer
In accordance with these observations, mackerel may
be regarded as part of a sequence of marine temperate or
boreal organisms that move northward. Many boreal sh
species have recently shifted their distributions northward
in response to increasing ocean temperatures and decreas-
ing sea ice (Drinkwater, 2009; Wienerroither et al., 2011;
Renaud et al., 2012; Hop and Gjøsæter, 2013; Christiansen
et al., 2014; Table 3). The occurrence of mackerel reported
TABLE 3. Changes in the Pisces fauna in Kongsfjorden and Isfjorden (Svalbard) over the last 15 years.
Species Occur rence i n Svalbard
Atlantic cod (Gadus morhua) Caug ht since the mid-1990s. Adult cod have been caught regularly using a bottom trawl since the early
2000s. Juveniles (< 10 cm) have appeared in catches since 2008.
Capelin (Mallotus villosus) Adults have become increasingly common si nce 2006 ( Hop and Gjøsæter, 2013). The diet of kittiwakes
(Rissa tridactyla) shif ted from polar cod (Boreogadus saida) to capelin in 2007. Both adults and juveniles
have been sampled regularly since 2010.
Haddock (Melanogrammus aegle nus) First record in 2006. Juveniles (< 10 cm) have been recorded regularly since 20 08, and adults, since 2009.
Atlantic snake pipesh (Entelurus aequoreus) Recorded i n Svalbard waters from August 2006 (Fleischer et al., 2007), but is not regularly occurri ng.
Atlantic herri ng (Clupea harengus) Recorded in Kongsf jorden, with few individuals since 20 06 (Hop and Gjøsæter, 2013). In Isfjorden, Atlant ic
herring were rst recorded in April 2012 (adult specimens only), and juveniles have occurred regularly since
Atlantic mackerel (Scomber scombrus) First record i n September 2013. Adults only.
ATLANTIC MACKEREL IN SVALBARD • 59
here could also represent a unique observation of specimens
far outside their normal distributional area, rather than an
extension of mackerel distribution. However, occurrences
of several new sh species in the fjord that do not seem
to be related to a simple northward extension of isotherms
(see Walczowski et al., 2012) indicate that both large-scale
oceanographic alterations in volume transport through the
NACS and advection and physical cross-shelf exchange
processes are important factors for sh entry into the
fjords. One might also argue that the occurrence of mack-
erel in the Arctic is linked to the increasing population size
at lower latitudes (ICES, 2013b) and that its current north-
ward expansion is due mainly to the size and population
structure of the mackerel stock (Nøttestad, 2014). However,
other comparable changes in both benthic and pelagic fauna
have been detected (e.g., Beuchel et al., 2006; Greene et
al., 2008; Narayanaswamy et al., 2010; Berge et al., 2012;
Kwasniewski et al., 2012) and related to annual and decadal
oscillations in the transport and temperature of Atlantic
water (Polyakov et al., 2005; Pavlov et al., 2013). Although
the causes of such changes are not fully understood, their
consequences for the Arctic ora and fauna are likely sub-
stantial. The recent northward extension of the mackerel’s
distribution range should be interpreted in this context, not
as a unique and isolated incident, but as yet another part of
a domino sequence in which boreal species are established
at the northernmost extension of the North Atlantic cur-
rent system. It is therefore likely that even more new occur-
rences of boreal sh species will be observed in the Arctic.
Migrating species will likely change their distribution not
only in response to changes in temperature, which make it
possible for them to reach other food sources in the Arctic,
but also in relation to shifts in distribution of their preferred
prey species (Dalpadado et al., 2012).
The authors are grateful to an anonymous local resident in
Longyearbyen for delivering mackerel to us, two anonymous
reviewers who helped improve the quality of the manuscript, and
the captain and crew onboard the RV Helmer Hanssen and Viking
Explorer. A particular thanks to Colin Grifths for overseeing
the collection of mooring data in Kongsfjorden since 2002. We
thank Professor K. Kosobokova for helping with the Russian
abstract. The work is partly nanced by the Norwegian Research
Council through the Environmental Waste Management in the
Arctic Project 195160 and Circa Project 214271/F20. It is also
a contribution to the Natural Environment Research Council
program Oceans 2025.
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