![Overview of the systematic review selection process adapted from Moher et al.'s [68] PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) statement and Siddaway et al.'s [93] best practice guidelines. The number of papers obtained after each step of the selection process is shown (n = x).](https://www.researchgate.net/profile/Jared-Towers/publication/352541980/figure/fig1/AS:1039504529973249@1624848601720/Overview-of-the-systematic-review-selection-process-adapted-from-Moher-et-als-68_Q320.jpg)
Content uploaded by Jared R. Towers
Author content
All content in this area was uploaded by Jared R. Towers on Jun 28, 2021
Content may be subject to copyright.
Climate Change Ecology 1 (2021) 100009
Contents lists available at ScienceDirect
Climate Change Ecology
journal homepage: www.elsevier.com/locate/ecochg
Impacts of climate change on cetacean distribution, habitat and migration
Celine van Weelden
a
, Jared R. Towers
b
, Thijs Bosker
a , c , ∗
a
Leiden University College, Leiden University, P.O. Box 13228, 2501 EE, The Hague, the Netherlands
b
Bay Cetology, 257 Fir street, Alert Bay, BC, Canada
c
Institute of Environmental Sciences, Leiden University, P.O. Box 9518, 2300 RA Leiden, the Netherlands
Keywords:
Climate change
Cetacean
Distribution
Migration
Habitat
Sea surface temperature
Climatic changes have had signicant impacts on marine ecosystems, including apex predators such as cetaceans.
A more complete understanding of the potential impacts of climate change on cetaceans is necessary to ensure
their conservation. Here we present a review of the literature on the impacts of climate change on cetacean dis-
tribution, habitat and migrations and highlight research gaps. Our results indicate that due to rising sea surface
temperatures (SSTs) and/or reducing sea ice extent, a variety of impacts on the distribution, habitat and migra-
tion of cetaceans have been observed to date and several more are predicted to occur over the next century. Many
species have demonstrated a poleward shift, following their preferred SSTs to higher latitudes, and some have
altered the timing of their migrations, while others appear not to be aected. These changes may benet certain
species, while others will be placed under extreme pressure and may face increased risk of extinction. Broader
implications may include increased inter-specic competition, genetic alterations, ecosystem-level changes and
conservation challenges. Existing research on the topic is both extremely limited and unevenly distributed (geo-
graphically and phylogenetically). Further research is necessary to determine which species and populations are
most vulnerable and require the earliest conservation action.
1. Introduction
Anthropogenic activity has caused the Earth’s climate to change
at such a rate that the eects may be irreversible [21,42,99] . These
climatic changes have had severe impacts on marine ecosystems, in-
cluding uctuations in ocean temperature and chemical composition,
primary productivity and the distribution and abundance of species
[4 , 17 , 42 , 76] . The combination of changes in oceanic conditions and
prey distribution and abundance are likely to impact marine predators
at higher trophic levels, including cetaceans [4 , 89] . However, the exact
eects of climate change on marine megafauna, including cetaceans,
remain uncertain [26] .
Cetaceans play a key and irreplaceable role in marine ecosystems
and have been referred to as ‘ecosystem engineers’, crucial for oceanic
nutrient cycling [4,81,28] . For example, the faecal plumes they release
near the surface contain deep ocean nutrients which would otherwise
be unavailable to surface-dwelling species [54 , 82] . Their faeces are par-
ticularly high in iron and nitrogen, which are both required for phyto-
plankton blooms, the primary prey of Antarctic krill ( Euphausia superba )
[72 , 81] . Cetaceans are also known to be vital in controlling prey popula-
tions [20 , 97] and creating feeding opportunities for marine birds [27] .
These large marine mammals, which are still recovering from the severe
impacts of the whaling era and are already under extreme pressure from
∗ Corresponding author.
E-mail address: t.bosker@luc.leidenuniv.nl (T. Bosker).
various other anthropogenic stresses such as plastic [5,24,74] , chemical
[45 , 62] and noise pollution [47,71,108] , must also tolerate both small
and large-scale climatic changes [83] . Due to these stressors, multiple
cetacean populations may eventually collapse, which could result in per-
manent, long term consequences for marine ecosystem functioning and
services [4] . For these reasons, cetacean conservation should be a pri-
ority.
Cetaceans are dicult to study due to their high mobility, the
amount of time they spend under water, and the legal and political
constraints of researching protected species [11] . Nonetheless, some re-
search on the inuence of climate change has been conducted and a va-
riety of impacts on cetaceans have been observed to date. Documented
population level impacts include changes in distribution [53 , 100] , shifts
in the timing and duration of migrations [78 , 84] , habitat loss [29 , 37] ,
and reduced conception rate and reproductive success [19,26,66,90] .
Two examples of observed impacts at an individual level are increased
mortality due to algal blooms [10 , 36 , 57] and enhanced mercury bioac-
cumulation [12 , 58] .
To increase conservation success, a more complete understanding of
the potential impacts of climate change on cetaceans is necessary, and
insights into the potential climate-induced changes in their distribution
and movements are especially important for two reasons. Firstly, such
insights will help enable impacts of threats (e.g. shipping routes and pol-
https://doi.org/10.1016/j.ecochg.2021.100009
Received 28 November 2020; Received in revised form 19 April 2021; Accepted 13 May 2021
Available online 19 June 2021
2666-9005/© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
lution) associated with distributional changes to be predicted. Secondly,
they will facilitate improved conservation through the implementation
of new Marine Protected Areas (MPAs) and adaptation of both local
and global policies. Importantly, a thorough review of all existing lit-
erature on the topic has not been conducted since 2009 [55 , 59 , 94] . In
the past decade, there has been a signicant amount of research pub-
lished, which warrants an updated literature review. Therefore, the re-
search objectives of this qualitative systematic literature review are to
summarise the current literature on the impact of climate change on
cetacean distribution, habitat and migration and highlight the research
gaps. Based on the review we will provide suggestions for future re-
search as well as a basis from which well-informed conservation strate-
gies and policies can be devised and implemented.
2. Methodology
2.1. Methodological justification
This literature-based research was carried out according to the Sys-
tematic Literature Review (SLR) method described by Siddaway et al.
[93] . The Preferred Reporting Items for Systematic Reviews and Meta-
Analyses (PRISMA) checklist and ow diagram were also used [68] . This
established systematic literature review method was used to summarise
existing knowledge regarding the observed and predicted impacts of cli-
mate change on cetacean distribution, habitat and migration. By synthe-
sising existing knowledge on the topic, this review will highlight areas
which require the most urgent future research as well as act as a start-
ing point for developing policies and population management plans to
protect species that may already be at risk.
2.2. Search terms
A search string consisting of several search terms has been chosen
to cover the variation in terminology used in publications on this topic.
Subject keywords ‘cetacean’, ‘whale’, ‘dolphin’ or ‘porpoise’ were com-
bined with exposure keywords “climate change ”or “global warming ”.
The associated search string was run through the Web of Science and
PubMed with a cut-o date of July 22
nd
, 2020. Web of Science and
PubMed are two high-quality search engines and were employed to in-
crease chances of covering all relevant results [31 , 93 , 109] .
2.3. Screening and eligibility
All non-peer-reviewed articles as well as those not written in English
and any duplicates were excluded immediately ( Fig. 1 ). Subsequently,
papers were excluded if not deemed relevant following a screening of
the titles and abstracts. At this stage (screening), papers were excluded
if they met one or more of the following criteria:
I not focused on impacts on cetacean distribution, habitat or migra-
tion;
II not climate change related;
III review with no primary data;
IV had a study period of < 5 years or < 5 years of relevant data;
V focus on developing/testing a new methodology/concept;
VI focus on El Niño-Southern Oscillation (ENSO), Northern Atlantic Os-
cillation (NAO) or pacic decadal oscillation (PDO).
If the relevance of a paper remained uncertain based on its abstract,
it was included at this stage with the aim of maintaining the high sen-
sitivity recommended by Siddaway et al. [93] . If papers were excluded
based on lack of relevance, a brief explanation was also recorded. Papers
that were initially included were assigned keywords to facilitate further
research and write-up about specic topics. Examples of common key
words were range changes; migration changes; sea ice changes.
In the next step, the remaining papers were read in full and were ex-
cluded if they met one or more of the same exclusion criteria described
above. A table detailing borderline cases, the inclusion/exclusion de-
cision and reasoning can be found in the supplementary information
(Table S1). For the included papers, the species, location, method and
key ndings were recorded. Finally, the bibliographies of included pa-
pers, along with several review papers excluded during the screening
process, were scanned in search of other potential sources. Any papers
found through this method underwent the same selection criteria as the
rest of the papers. These additional papers were only included when
their content seemed essential for the narrative of the literature review.
This method of locating additional sources proved crucial in understand-
ing the impact of climate change on cetaceans, given the low level of
existing research on the topic.
2.4. Establishing geographical categories
All papers meeting the inclusion criteria were split into two sec-
tions: those that described observed impacts and those that predicted
future impacts. If an article included both observed and predicted im-
pacts, it was included in both sections. Next, papers were sorted based
on species, and papers focussing on multiple species were included in
the sub-sections of all relevant species. Finally, species were categorised
based on either their geographic range or the location of the studies
they were described in. For example, the narwhal, beluga and bowhead
whale were categorised as ‘Artic resident species’ because they remain
there year-round [37] . On the other hand, n and killer whales were
included in both the Subarctic category, as well as the ‘Other regions’
category, since included studies described impacts on these species in
both areas.
3. Results
3.1. Literature searches and screening
Searches in Web of Science and PubMed returned a total of 1,253
results, 273 of which were immediately excluded as they were either
duplicates (n = 204), not peer reviewed articles (n = 67) or not written in
English (n = 2; Fig. 1 ). Screening based on title and abstract left 178 ar-
ticles that were considered as potentially relevant. Following screening
based on full text, a further 122 articles were excluded. The main reason
for exclusion at this stage was a lack of focus on cetacean distribution,
habitat or migration (n = 49; Table S2). An additional two articles found
in the references of other articles were added which resulted in 58 arti-
cles being included in the nal review.
Of these 58 articles, 11 modelled future predictions for available
habitat over the next century, 46 reported results from studies and dis-
tance sampling surveys ranging from 1900-2018 and one investigated
both future predictions and past observations. The locations of the stud-
ies were unevenly distributed with many (n = 21) situated in the vicin-
ity of the continent of North America. All but four of the studies on
observed impacts took place in the northern hemisphere, between ap-
proximately 0 and 85°N ( Fig. 2 A). Five out of the 12 articles predicting
future impacts modelled scenarios for the Southern Ocean and Australa-
sia. Not all families in the cetacea order were equally represented in
the literature ( Fig. 2 B). In total, 29 species were discussed (see Table
S3). Balaenopteridae was by far the most researched family, with mem-
bers of this family being mentioned in 19 papers ( Fig. 2 B). No freshwa-
ter dolphins (Platanistidae, Iniidae and Pontoporidae) or pygmy/dwarf
species [Cetotheriidae, Kogiidae and pygmy killer whales ( Feresa atten-
uata )] were discussed in any of the included articles ( Fig. 2 B). Firstly,
the impacts observed to date will be described ( Fig. 3 , Table S4, S5),
followed by those predicted to occur over the next 100 years ( Fig. 4 ,
Table S6, S7).
2
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
n = 1253
results found using
search terms in Web
of Science
n = 204 duplicates
n = 1004
excluded during abstract
screening
n = 122
excluded during full text
screening
n = 2
articles from references
of other studies
NOITACIFITNEDIGN
I
N
E
ERCSYTILIBIG
I
LE
D
EDULCNI
n = 202
results found using
search terms in
PubMed
n = 2 not in English
n = 67 not peer reviewed
n = 1455
total results found
n = 1182
articles screened
based on abstract
n = 178
articles screened
based on full text
n = 56
eligible articles
n = 58
articles used in the
literature review
Fig. 1. Overview of the systematic review selection process
adapted from Moher et al.’s [68] PRISMA (Preferred Reporting
Items for Systematic reviews and Meta-Analyses) statement
and Siddaway et al.’s [93] best practice guidelines. The num-
ber of papers obtained after each step of the selection process
is shown (n = x).
3.2.1. Arctic
Of the 58 studies included, 12 focused on the impacts of climate
change on one or more of the three resident Arctic species, the bowhead
whale ( Balaena mysticetus; Fig. 3 , Table S4), the beluga ( Delpinapterus
leucas; Fig. 3 , Table S5), and the narwhal ( Monodon monoceros; Fig. 3 ,
Table S5), which are believed to be among the most vulnerable to cli-
matic changes [33 , 37 , 107] . Surprisingly, despite rising average SSTs,
several of the crucial (Canadian) wintering grounds of all three species
showed signicant declining trends in the fraction of open water during
winter between 1979-2001, and only a minority showed a slight increas-
ing trend [37] . Two important narwhal wintering grounds in Ban Bay
(Greenland) displayed high inter-annual variability in ice cover along-
side an overall decreasing trend [51] . Contrastingly, all large bowhead
wintering grounds and 12 of the 16 smaller ones displayed a weak pos-
itive trend in the fraction of open water between 1979 and 2002, with
extreme interannual variability [70] .
Shift in beluga sightings were observed in several studies ( Fig. 3 ,
Table S5). For example, an increase in sightings was found in the Sval-
bard Archipelago and northward shift in sightings in Disko Bay (Green-
land) which coincided with warming SSTs [38 , 100] . They expanded
their range to western Greenland when the sea ice contracted to the
east in 2006, but this was reversed when the sea ice increased again
in 2007-2008 [38] . A > 300% increase in sightings was observed in the
oshore Beaufort Sea from the 1980s (n = 305) to the 2000s (n = 1061),
which cannot be accounted for by population growth alone [34] . Beluga
also spent signicantly less time near tidal glacier fronts between 2013
and 2016 compared to 1995-2001 [33 , 107] .
Beluga migration also showed changes. For example, migration from
the Beaufort Sea to the Chukchi Sea was between 14 and 33 days later in
2007-2012 compared to 1993-2002, and the last day individuals left the
Beaufort Sea was delayed by 4.1 days each year between 2008 and 2013
[35] . Similarly, the beluga population resident to the Gulf of Alaska
entered the Cook Inlet earlier and extended their stay there in warmer
years [30] . In contrast, O’Corry-Crowe et al. [73] found no signicant
changes in the date that beluga returned to Kasegaluk Lagoon (Alaska)
between 1979 and 2013.
3.2.2. Subarctic
A signicant increase in the sightings of three subarctic baleen whale
species - humpback whales ( Megaptera novaeangliae ), n whales ( Bal-
aenoptera physalus ) and common minke whales ( Balaenoptera acutoros-
trata ) - in the Arctic over the past few decades has been observed
3
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
A B
Observed impacts Predicted impacts Both observed and predicted impacts 0 1-5 6-10 11-15 16-20
Delphinidae
Balaenopteridae
Eschrichidae
Monodondae
Physeteridae
Kogiidae
Ziphiidae
Cetotheriidae
Phocoenidae
Balaenidae
Platanisdae, Lipodae,
Iniidae & Pontoporiidae
MYSTICETES
ODONTECETES
Fig. 2. A) Locations of studies on cetaceans included in the literature review; B) Number of studies included in the literature review per family. Sources: Esri, GEBCO,
NOAA, National Geographic, DeLorme, HERE, Geonames.org.3.2 Observed Impacts
[14 , 100] . All three species displayed a northward shift between 2002
and 2014, with their annual maximum latitude increasing by 2°, 1°
and 1°, respectively [100] . The blue whale ( Balaenoptera musculus ) has
shown a 4° increase in annual maximum latitude [100] .
Humpback and n whale migrations to their summer feeding ground
in the Gulf of St. Lawrence, Canada, took place earlier in the year, with
each species’ mean rst arrival date shifting 1 + day(s) earlier each year
between 1987 and 2010 [78] . Fin whales extended their stay in the gulf
by an average of 16 days over the duration of the study period [78] .
Blue whales which feed o the west coast of California and those o the
south west coast of Columbia were arriving at their feeding grounds > 1
month earlier in 2018 and 2017 compared to 1988 and 2008, respec-
tively [9 , 102] . Their departure dates have remained relatively stable
over the same period resulting in signicantly increased occupancy and
feeding periods.
Grey whale ( Eschrichtius robustus ; another seasonal Arctic resident)
displayed a 1-week delay in the southbound migration, which passed
Yaquina Head (Oregon) around the 8
th
of January prior to 1980 com-
pared to the 15
th
of January after 1980 [84] . In addition, the increase in
grey whale calf sightings on the southbound migration along the west
coast of the US from 1952-2002 suggests a shift in calving grounds [91] .
Prior to 1976, no new-born calves were observed on this period of the
migration, but from 1976 onwards there was an increase in calf sightings
farther north.
At a local scale impacts were also observed. North Pacic Right
Whales ( Eubalaena japonica ) tagged in cold years (2008-2009) remained
in the middle of the Bering Shelf, travelled more slowly and covered a
smaller area than those tagged in the warm year (2004). A closely re-
lated species, the North Atlantic Right Whale ( Eubalaena glacialis ), has
exhibited a sudden shift from early to late occupancy in the Bay of Fundy
(Canada) in 2002 [25] , and calls have been increasingly detected out-
side the feeding season in Massachusetts Bay between 2007 and 2013
[111] .
Two species of subarctic toothed whale are also becoming more
prevalent in Arctic waters [40 , 100] . Sperm whales ( Physeter macro-
cephalus ) have demonstrated a northward shift in average maximum
latitude from 76°N in 2002 to 79°N in 2014 [100] . The number of killer
whales ( Orcinus orca ) sightings per decade in the Canadian Arctic has in-
creased rapidly from 5 in 1900, to 30 in 1990 and 140 in 2000 and both
the number of days and hours of detected calls have risen from 2009-
2015 [41,112] . Further evidence of increased killer whale presence is
the increase in percentage of bowhead whales in the same region with
scarring from killer whale rake marks, from ~2% (1986) to ~9% (2007-
2010) to ~15% (2011-2012) [79] . However, Ainley et al. [2] reported
a decrease in sightings and proportion of days seen in the Ross Sea.
3.2.3. Other regions
Both Bryde’s whales and n whales appear to have displayed distri-
butional shifts as a result of rising SSTs. Bryde’s whale ( Balaenoptera
edeni) calls were not recorded in the Southern Californian Bight be-
tween 2000 and 2001, but were recorded every year between 2003
and 2010 [49] . Fin whale sightings in the Tyrrhenian Sea (Italy) in-
creased by 300% from 0.08 sightings per hour of eort (ER) between
1990 and 1992 to 0.36 ER between 2007 and 2009 [7] . In contrast,
common bottlenose dolphin ( Tursiops truncates ), Cuvier’s beaked whale
( Ziphius cavirostris ) and striped dolphin ( Stenella coeruleoalba ) sightings
in the Tyrrhenian Sea did not dier between 1990-1992 and 2007-2009,
despite a marked rise in SST [7] .
Long-term stranding data sets have been used a proxy for pres-
ence in order to explore the impact of climate change on the distri-
bution of marine mammals. A study into seasonal and interannual pat-
terns of marine mammal strandings in the subtropical western south
Atlantic, recorded temperate/polar species strandings since the early
1980s while tropical/subtropical species strandings only occurred af-
ter 1993 [77] . These ndings suggest a poleward expansion of warm-
water species. Four cold-temperate water species, northern bottlenose
4
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
Observed Impacts
maximum latitude
habitat availability
migration dates
time spent in high latitude
visual/acoustic detections
strandings
other
Region
Species
Arcti c
Bowhead whale
Narwhal
Beluga
Subarctic
Humpback whale
Fin wha le
Common minke whale
Blue whale
Sperm whale
Killer whale
Grey whale
North Pacific right whale
North Atlantic right whale
Other
Bryde's whale
Humpback whale
Fin wha le
Blue whale
Antarctic minke whale
Killer whale
Northern bottlenose whale
Long-finned pilot whale
Short-finned pilot whale
Sowerby's beaked whale
White beaked dolphin
Fig. 3. Trends in observed impacts of climate change on cetacean distribution,
habitat and migration. Green with upward arrow signies an increase (earlier
regarding migration), red with downward arrow signies decrease (later regard-
ing migration), orange signies no change and light blue signies other changes
with no clear trend.
whales ( Hyperoodon ampullatus) , long-nned pilot whales ( Globicephala
melas ), Sowerby’s beaked whales ( Mesoplodon bidens ) and white-beaked
dolphins ( Lagenorhynchus albirostris ), all stranded in north-west Scot-
land signicantly less frequently between 1992 and 2003 than between
1948 and 1992 [60] . However, killer whales, which are considered to
withstand a wide range of SSTs, also stranded less frequently in 1992-
2003, highlighting that other factors might have inuenced this change
in standing patterns [60] . In contrast, harbour porpoise ( Phocoena pho-
coena ) and short-beaked common dolphin ( Delphinus delphis ) strandings
in the area showed an opposite trend [44 , 56 , 60] . This highlights a shift
in habitat in the region, favouring warm-water species over cold-water
species.
Harbour porpoise
Short beaked common dolphin
Common bottlenose dolphin
Cuvier’s beaked whale
Striped dolphin
Pacific white-sided dolphin
Northern right whale dolphin
Dall’s porpoise
Atlantic spotted dolphin
Tropical/subtropical species
Fig. 3. Continued
Predicted
Impacts
maximum latitude
habitat availability
occurrence
other
Region
Species
Arcti c
N/A
Subarctic
Humpback whale
Fin whale
Common minke whale
Blue whale
Sperm whale
Grey whale
North Pacific right whale
North Atlantic right whale
Other
Antarctic minke whale
Southern Right Whale
Harbour porpoise
Short beaked common dolphin
Cuvier’s beaked whale
Striped dolphin
Fig. 4. Trends in predicted impacts of climate change on cetacean distribution,
habitat and migration. Green with upward arrow signies an increase, red with
downward arrow signies decrease, orange signies no change and light blue
signies other changes with no clear trend. Occurrence refers to whichever re-
gion the article is discussing.
5
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
3.3. Predicted impacts
3.3.1. Southern ocean
Two studies have projected adverse impacts of climate change on
Antarctic minke whales ( Balaenoptera bonaerensis ), and predicted signif-
icant reductions in suitable habitat ( Fig. 4 , Table S6; [3 , 106] ). However,
Tulloch et al. [105] proposed that the predicted southward range shift
to 70-80°S will benet the species, as it will result in an increased access
to energy-rich prey. On the contrary, southern right whales ( Eubalaena
australis ) may experience a reduction in prey availability around 2100
following a southward range shift to 47-50°S [104 , 105] .
A study on the impacts of a 2°C rise in global air temperature
on cetaceans in the Southern Ocean found that humpback whales , n
whales , blue whales ( Fig. 4 , Table S6) and sperm whales ( Fig. 4 , Table
S7) are predicted to display a southward shift and contraction of forag-
ing habitat due to a similar shift of the Antarctic Circumpolar Current
(ACC) [106] . Finally, many humpback breeding grounds in Oceania are
predicted to become unsuitably warm by the end of the 21
st century
[26] .
3.3.2. Other regions
A study investigating current and future patterns of global marine
mammal biodiversity, including cetaceans, found that 54% of marine
mammal species are predicted to experience an increase in habitat by
2040-2049 based on the intermediate IPCC-A1B climate change sce-
nario, while 45% are predicted to experience a reduction and 1% are
predicted not to be aected [46] . Despite most of these changes being
< 10% per taxa, North Pacic right whales, North Atlantic right whales
and grey whales are predicted to benet from more substantial increases
in suitable habitat ( Fig. 4 , Table S6; 15%, 27% and 40% increase in habi-
tat, respectively). Projections of grey whale distribution in 2100 by Al-
ter et al. [6] also suggest an increase in suitable habitat around Canada,
Greenland and the Barents Sea alongside a northward shift in range and
Brüniche-Olsen et al. [15] predict an improvement of currently marginal
habitats in the Arctic ( Fig. 4 ; Table S6).
Lambert et al. [53] employed a bio-climatic envelope modelling tech-
nique to predict the impacts of three dierent future climate change
scenarios on several cetacean species in the Eastern North Atlantic. The
common minke whale is predicted to undergo a northward range con-
traction due to reduced availability of suitable habitat and summer feed-
ing grounds in UK and Irish waters ( Fig. 4 , Table S6; [53] ). The summer
occurrence of white-beaked dolphin in the area was also projected to
drop, while Cuvier’s beaked whale is likely to experience a northward
range contraction with signicant reductions in summer occurrence by
2090 [53] . In contrast, striped dolphins were predicted to undergo a
northward range expansion and an increase in summer occurrence [53] .
Sadykova et al. [85] demonstrated how incorporating dierent prey
species into predictive models can signicantly alter the predicted out-
comes of climate change. Within this model the impacts of climate
change were predicted based on the biology of the harbour porpoise
(single-species model), but also on the combined biology of harbour
porpoise and important prey species (herring or sandeel; joint-models).
The single-species harbour porpoise model and the joint herring-harbour
porpoise model predicted no large distribution shifts, however, the joint
sandeel-harbour porpoise model predicted a large distribution shift of
164km southwest [85] .
Finally, an article by Cañadas and Vázquez [18] created a model
to predict the impact of rising SST on short-beaked common dolphins
in the Alboran Sea over the next 100 years ( Fig. 4 ; Table S7) . The re-
sults showed no change in their distribution but suggested a decrease
in the amount of suitable habitat followed by a predicted reduction in
density from east to west. However, predictions of this species range in
the Northeast Atlantic display a signicant northwards range expansion
within the next few decades [52] .
4. Discussion
Due to rising SSTs and/or reducing sea ice extent, a variety of im-
pacts on the distribution, habitat and migration of cetaceans have been
observed to date and several more are predicted to occur over the
next century. A considerable number of studies have focused on the
observed impacts, highlighting that most species have demonstrated a
poleward shift, following their preferred SSTs to higher latitudes (e.g.
[38 , 53 , 100] ). The contrasting trends in reducing fractions of open water
in wintering grounds and decreasing Arctic Sea ice cover have resulted
in a reduction in the amount of suitable habitat for the three residential
Arctic cetaceans [37 , 51] . Subarctic species, such as humpback and n
whales, are showing increasing presence in the Arctic, which is likely
to continue with projected decreasing sea ice trends [14 , 100] . In ad-
dition, the migration timing of several species have also been delayed
or advanced [35 , 78 , 84] . In contrast, the distribution of certain popu-
lations of particular species, including bottlenose dolphins, striped dol-
phins and Cuvier’s beaked whales, does not appear to be impacted by
climatic changes/rising SST [7] .
Surprisingly, given the recent advances in climate and ecosystem
modelling, very few articles have attempted to predict future impacts
of climate change on cetacean distribution and habitat (n = 12). In most
of the studies that did, cetaceans are forecasted to shift their distribu-
tion to higher latitudes [53 , 104–106] . These shifts will result in a severe
reduction in suitable habitat by 2100 for eight out of the 14 species in-
vestigated. Northern Atlantic right whales, North Pacic white whales,
grey whales and striped dolphins are predicted to experience range ex-
pansions. It is understandable that striped dolphins would benet from
increased SSTs due to their preference for warmer water conditions, but
the three other species predicted expansions are due to melting sea ice
cover [53] .
Our results are in line with the latest two previous reviews on this
topic, which described similar ndings on the 29 species covered in
this review ( [55] and [59] ; Table 1 ). Many of the potential impacts of
climate change on species range outlined by Learmonth et al. [55] and
MacLeod [59] are already apparent in the observed impacts reported in
this review, despite only ten years having passed. For example, short-
beaked common dolphins have expanded their range northward in UK
waters [56,60] , while narwhal, beluga and bowhead whales have all
suered reductions in the amount of suitable wintering habitats [37 , 51] .
The increase in SST is an important determinant for species’ distri-
butions, and Arctic cetaceans are thought to be especially sensitive due
to a reduction of their preferred habitats (e.g., [33 , 37 , 107] ). Indeed,
the results of this review, as well as those by Learmonth et al. [55] and
MacLeod [59] , suggest that Arctic species have already undergone some
of the most severe reductions in range and suitable habitat due to rising
SSTs. Other species which prefer cooler waters are also suering (less
severe) reductions in suitable habitat, while those that prefer warm wa-
ter are beneting from the opposite. For example, the suitable habitat
of white-beaked dolphins (temperate-water species) in Scottish waters
decreased as the SST rose between 1948 and 2003, which resulted in re-
duced presence, whereas short-beaked common dolphins (warm-water
species) displayed an antagonistic trend in occupancy due to an expan-
sion of suitable range in the same area [60] .
On the other hand, the overall distribution of traditionally
widespread species that are comfortable in a range of SSTs, such as
humpback, n and sperm whales, has not been greatly impacted and
trends of reduced sea ice could allow them prolonged access to high nu-
trient waters of the polar regions [14 , 106] . As a result, species such as
humpback, n and blue whales (widespread) along with striped dol-
phins (warm water), appear signicantly less vulnerable to climatic
changes than narwhal, beluga, bowhead whales (Arctic) and white-
beaked dolphins (temperate-water). Interestingly, these are not the same
species that are considered most vulnerable by the IUCN ( Table 1 ). Since
the IUCN Red List is the most widely used system for identifying species
6
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
Table 1
Comparison of impact on species range/distribution reported by Learmonth et al. [55] , MacLeod [59] and this study’s review along with IUCN status (2020-2021)
Species IUCN Status Learmonth et al. [55] MacLeod et al. [59] Current review
Mysticetes
Bowhead whale ( Balaena
mysticetus )
LC contraction contraction (high risk for Sea of
Okhotsk population)
contraction
North Pacic right whale
( Eubalaena japonica )
EN unknown northward shift unknown
North Atlantic right whale
( Eubalaena glacialis )
CR contraction contraction unknown
Southern right whale ( Eubalaena
australis )
LC contraction (uncertain) southward shift/contraction
(high risk for population that
breeds in coastal waters of South
Africa)
predicted shift southwards
Humpback whale ( Megaptera
novaeangliae )
LC unknown unchanged Northward expansion (population in Southern
Ocean predicted to shift
southward)
Fin whale ( Balaenoptera physalus ) VU unknown unchanged Northward expansion (population in Southern
Ocean predicted to shift southward)
Blue whale ( Balaenoptera
musculus )
EN unknown unchanged unchanged (population in Southern Ocean
predicted to shift southward)
Common minke whale
( Balaenoptera acutorostrata )
LC unknown unchanged
(southward expansion of dwarf
sub-species)
unchanged with predicted contraction
Antarctic minke whale
( Balaenoptera bonaerensis )
NT unknown unchanged predicted contraction and shift southward
Bryde’s whale ( Balaenoptera
edeni )
LC unknown expansion expansion/shift northwards
Grey whale ( Eschrichtius robustus ) LC unknown expansion Unchanged/predicted expansion
Odontocetes
Narwhal ( Monodon monoceros ) LC contraction contraction (potentially high risk
if Arctic Sea disappears)
contraction
Beluga ( Delphinapterus leucas ) LC contraction contraction (potentially high risk
for some populations)
contraction
Species IUCN Status Learmonth et al. [55] MacLeod et al. 2009 Current review
Sperm whale ( Physeter
macrocephalus )
VU unknown Mostly unchanged with some
expansion
unchanged (population in Southern Ocean
predicted to shift southward)
Common bottlenose dolphin
( Tursiops truncatus )
LC expansion expansion unchanged/shift northward
Short-beaked common dolphin
( Delphinus delphis )
LC expansion (uncertain) expansion Northward expansion (predicted contraction
for population in the Alboran Sea)
White-beaked dolphin
( Lagenorhynchus albirostris )
LC unknown northward shift (high risk for
population around north-west
Europe)
contraction/shift northwards (predicted to
exacerbate)
Pacic white-sided dolphin
( Lagenorhynchus obliquidens )
LC contraction northward expansion northward contraction
Striped dolphin ( Stenella
coeruleoalba )
LC expansion (uncertain) expansion unchanged with predicted expansion
Atlantic spotted dolphin ( Stenella
frontalis )
LC expansion expansion unknown
Killer whale ( Orcinus orca ) DD unknown unchanged shift northwards
Northern right whale dolphin
( Lissodelphis borealis )
LC unknown northward expansion northward contraction
Long-nned pilot whale
( Globicephala melas )
LC unknown poleward expansion (high risk for
Mediterranean population)
shift northwards
Short-nned pilot whale
( Globicephala macrorhynchus
)
LC expansion expansion unknown
Sowerby’s beaked whale
( Mesoplodon bidens )
DD unknown poleward expansion shift northwards
Northern bottlenose whale
( Hyperoodon ampullatus )
DD contraction contraction shift northwards
Cuvier’s beaked whale ( Ziphius
cavirostris )
LC Unknown expansion unchanged
Harbour porpoise ( Phocoena
phocoena )
LC contraction (uncertain) northward expansion (high risk
for North-West European
populations)
expansion/shift northwards
Dall’s porpoise ( Phocoenoides
dalli )
LC Unknown expansion Northward contraction
N.B. LC = Least Concern; NT = Near Threatened; VU = Vulnerable; EN = Endangered; DD = Data Decient
∗
shift = no signicant change in total area of the species’ range
at risk of extinction, it has been suggested that its criteria should be
adapted to take into account sensitivity to current and future climatic
changes [4 , 22 , 98] . However, it should be noted that this review has only
considered the impacts of climate change on species distribution. A full
review of all other potential impacts, including pollution and sheries’
bycatch and competition, would be necessary in order to assess vulner-
ability more accurately.
Although most of our ndings are in line with Learmonth et al.
[55] and MacLeod [59] , we did nd several dierences ( Table 1 ).
MacLeod [59] stated that the impacts of climate change on the range of
Cuvier’s beaked whale would be favourable, whereas the current nd-
7
C. van Weelden, J.R. Towers and T. Bosker Climate Change Ecology 1 (2021) 100009
ings suggest that it has not yet been impacted [7] . Similarly, both Lear-
month et al. [55] and MacLeod [59] reported that common bottlenose
dolphins and striped dolphins had benetted from increased habitat due
to rising SSTs, while we did not nd evidence of such changes to date.
Nevertheless, striped dolphins were predicted to expand their distribu-
tion over the course of the next century [53] . Despite no positive changes
having been observed to date, both common bottlenose dolphins and
striped dolphins are commonly found in warmer waters and, therefore,
may be less sensitive to rising SSTs [53 , 59] . These dierences in ndings
are most likely due to a focus on distinct populations of each species.
Therefore, the impacts of climate change on multiple distinct popula-
tions of the same species should be investigated to prevent contradictory
understandings of the species’ overall vulnerability.
There are several potential explanation(s) for the observed and
predicted impacts described above. Cetaceans are endothermic, well-
insulated, and, for the most part, relatively large mammals, which makes
it unlikely that range changes are due to a direct relationship between
a species’ thermal limits and the water temperature ( [55 , 95] ; MacLeod
et al. [59] ). Rather, changes in physical barriers, such as the extent of
sea ice, may explain certain shifts in distribution and migration pat-
terns (Heide-Jørgensen et al. [37 , 39] ). For example, sea ice extent has
historically limited killer whale movement in the Arctic to the warmer
months, but this is changing as the ice-free period is extended due to ris-
ing SSTs [40 , 41 , 64] . Grey whales also appear to be beneting from the
reduced sea-ice cover as individuals have recently been documented in
the North and South Atlantic after presumably transiting through Arctic
waters from the Pacic Ocean [6] .
In addition, the habitat preferences of marine mammals are known to
be ecologically related to the distribution of preferred prey species. The
distributions of these prey species are, in turn, determined by the com-
plex combination of oceanographic conditions present, such as tempera-
ture, salinity, depth, slope, and nutrient concentration [95] . Therefore,
further research is required to better understand the predicted move-
ment of prey species, which would subsequently allow for the changes
in cetacean distribution and migrations to be modelled more accurately.
At a more localised scale, competition between two or more ecologi-
cally similar species can result in niche partitioning, which may impact
a species distribution in that area [59] . For instance, following a rise
in SST in Scottish waters, short-beaked common dolphins were found
in the same areas as white-beaked dolphins [61] . The common dolphin
outcompeted its white-beaked counterpart, which caused white-beaked
dolphins to stay in waters of less than 13°C, while common dolphins
were found in any waters above 14°C [61] . It is most probable that the
observed and predicted distributional changes are controlled by a com-
bination of physical barriers, prey movements and inter-specic compe-
tition.
Our results indicated four key implications of the observed and pre-
dicted changes on cetaceans. Firstly, distributional changes are likely
to result in the overlap of species’ ranges, which may lead to increased
inter-specic competition [14 , 32 , 100] . For example, the greater compe-
tition for euphausiids and copepods, by subarctic species such as hump-
back and n whales, may put additional pressure on the already vulnera-
ble Arctic residents [14 , 69] . Similarly, the prolonged presence of hump-
back and blue whales o the Antarctic Peninsula has been suggested to
have impacted body condition in Adelie ( Psygoscelis adeliae ) and Em-
peror penguins ( Aptendytes forsteri ), which also feed predominantly on
krill and small sh [1] . In the unique case of (mammal-eating) killer
whales, range expansion into Arctic waters may lead to rising predation
on cetacean species that are resident to the Arctic [13 , 40 , 73] . Addi-
tionally, the presence of killer whales appears to lead to behavioural
and distributional changes in all three Arctic cetacean species. Beluga
display increased evasive behaviour [73 , 110] and narwhal spend more
time near the coast in tight groups [13 , 50] . Similarly, bowhead whales
spend more time in shallow waters and dense sea ice [63 , 92] .
Secondly, cetacean range changes may also have impacts at a genetic
scale, both between populations of the same species and between species
[39 , 67] . At a population level, gene ow between previously genetically
isolated populations of the same species may increase variability within
the gene pool and thereby enhance the species’ ability to adapt to fu-
ture (climatic) changes [48 , 103] . Such ows may be possible because
of the opening of new migratory routes due to reduced sea ice con-
centrations. An example of this would be the opening of the northwest
passage linking bowhead whale populations in the Pacic and Atlantic
[39] . Contrarily, for some species, certain populations may be unable to
shift their distribution due to a combination of habitat preferences and
local bathymetry and will, therefore, become genetically isolated [95] .
This may result in reduced genetic diversity, as has been observed in
pygmy blue whales, which in turn reduced their adaptive capacity [8] .
Thirdly, due to their pivotal role as ‘ecosystem engineers’, shifts in
the distribution of various cetacean species is likely to have implications
on the wider marine ecosystem. At a large scale, the loss of rorqual
whales in some areas may result in reduced productivity and phyto-
plankton populations as was experienced in the Southern Ocean during
the peak of the whaling period [101] . Since marine predators are critical
for the management of prey populations, the disappearance of cetaceans
from certain regions could also lead to major alterations in community
structure and ecosystem function [20 , 97] . At a smaller scale, the absence
of various odontocetes may reduce the foraging opportunities of many
marine birds, which rely on toothed whales to drive sh towards the sur-
face while feeding [27] . These are just a few examples and, due to the
complexity of marine ecosystems, extensive research will be required
to understand and predict the potential changes in trophic interactions
following climate-induced shifts in cetacean distribution [85] .
Finally, continuous changes in the known distributions of species will
make it extremely important to generate legislation to alter existing pro-
tected areas to include new ranges [16] . Historically, MPAs were con-
sidered the most cost-eective and practical ocean conservation strategy
[80] . Yet thei