Aquatic Mammals 2020, 46(1), 21-31, DOI 10.1578/AM.46.1.2020.21
Humpback Whales (Megaptera novaeangliae) in the
Cape Verde Islands: Migratory Patterns,
Resightings, and Abundance
Frederick W. Wenzel,1 Fredrik Broms,2 Pedro López-Suárez,3 Katia Lopes,3
Nadia Veiga,3 Kate Yeoman,4 Manuel Simão Delgado Rodrigues,4 Judy Allen,5
Thomas W. Fernald,5 Peter T. Stevick,5 Lindsey Jones,5 Beatrice Jann,6
Laurent Bouveret,7 Conor Ryan,8 Simon Berrow,9, 10 and Peter Corkeron1, 11
1NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center,
166 Water Street, Woods Hole, MA 02543, USA
2North Norwegian Humpback Whale Catalogue (NNHWC), Straumsvegen 238, N-9105 Kvaløya, Norway
3Bios, CV, Sal-Rei, Boa Vista, Republic of Cape Verde
4Naturalia, Sal Rei, Boa Vista, Republic of Cape Verde
5College of the Atlantic, 105 Eden Street, Bar Harbor, ME 04856, USA
6Swiss Whale Society, Via Inera, CH-6999 Astano, Switzerland
7Observatoire des Mammifères Marins de l’Archipel Guadeloupéen, Route Hégésippe Legitimus,
Beauport, 97117 Port-Louis, Guadeloupe, FWI
8Song of the Whale, Marine Conservation Research, 94 High Street, Kelvedon, Essex, CO5 9AA, UK
9Marine and Freshwater Research Centre, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland
10Irish Whale and Dolphin Group, Merchants Quay, Kilrush County Clare, Ireland
11Anderson Cabot Center for Ocean Life, New England Aquarium, Central Wharf, Boston, MA 02110, USA
resighted off Azores and the Canary Islands were
most often observed in May/June and were presum-
Effective conservation of the endangered North ably en route to their northern feeding grounds. The
Atlantic humpback whale (Megaptera novaean-largest number of recaptures from high-latitude feed-
gliae) which breeds in the eastern North Atlantic ing grounds were 44 individual humpbacks (44/267
around the Cape Verde Islands off West Africa = 16.4%) identified in both Cape Verdean and
requires information about their spatio-temporal Norwegian waters. Twelve humpbacks (12/267 =
distribution, population size, and migratory patterns. 4.5%) were identified in the Cape Verde Islands and
Understanding temporal distribution is particularly Iceland. Based on photo-identification of humpbacks
important as annually only a portion of this popu-in the Cape Verde Islands, we report a high inter-
lation migrates between high-latitude summer feed-annual resighting rate with 131 whales observed in
ing grounds and their breeding grounds. During the more than one year (131/267 = 49.1%). While this is
winter/spring months between 1990 and 2018, we partly due to high probability of detection in a small
conducted cetacean surveys targeting humpback population, these results nonetheless also suggest
whales. Survey periods varied from 30 to 90 days strong site fidelity to this breeding ground. The esti-
in duration. Collectively, we obtained fluke photo-mated total number of individual whales occurring
graphs from 267 individually recognizable hump-in this eastern North Atlantic breeding area between
back whales from this region. These fluke photo-2010 and 2018 was 272 (SE 10).
graphs have been compared and included in the
North Atlantic Humpback Whale Catalogue, which
Key Words: Cape Verde Islands, breeding
has nearly 11,000 individual flukes photographed
grounds, eastern North Atlantic, photo-identifica-
from throughout the North Atlantic. Photo-identified
tion, humpback whale, Megaptera novaeangliae
individuals from the Cape Verde Islands population
have been previously photographed/recaptured on
high-latitude feeding grounds in northern Norway
(including the Barents Sea and Svalbard archipel-
Humpback whales (Megaptera novaeangliae) in
ago), Iceland, Azores, Tenerife, Canary Islands, and
the North Atlantic Ocean constitute one of the best
Guadeloupe (southeast Caribbean). Those whales
studied populations of large whales in the world.
22 Wenzel et al.
Since the 1970s, extensive photo-identification
efforts have yielded substantial information on
the abundance and migratory movements of this
species (Katona et al., 1979; Katona & Whitehead,
1981; Katona & Beard, 1990; Clapham & Mead,
1999; Smith et al., 1999). Genetic tagging has also
been used to determine humpback whale migratory
destinations, stock identity, and fidelity to specific
regions of the North Atlantic (Palsbøll et al., 1995,
1997; Larsen et al., 1996; Valsecchi et al., 1997;
et al., 2004; Robbins et al., 2006).
North Atlantic humpback whales feed during the
summer in a number of relatively discrete regions,
including the Gulf of Maine, Newfoundland/
Labrador, the Gulf of St. Lawrence, Greenland,
Iceland, and Norway, including Svalbard. Fidelity
to these summer feeding areas is strong and is
apparently maternally directed, with genetic anal-
yses suggesting that the fidelity is maintained on
an evolutionary timescale (Larsen et al., 1996;
Palsbøll et al., 1997). Despite the low level of
movement between the feeding grounds, both
photo-identification and genotyping have demon-
strated that some individuals from all of the iden-
tified high-latitude areas migrate long distances
to the recognized major winter breeding grounds
on Silver Bank, Dominican Republic, where it is
assumed that this spatial overlap corresponds to
genetic mixing (Winn et al., 1975; Martin et al.,
1984; Clapham et al., 1992, 2005; Stevick et al.,
1998, 1999a, 1999b, 2003; Clapham & Mead,
1999; Smith et al., 1999). The only other known
breeding area for North Atlantic humpbacks is a
smaller humpback population utilizing the south-
eastern Caribbean in the waters near and around
the French island of Guadeloupe (Stevick et al.,
Photographic sighting history and migratory
patterns are reported in this article, and an updated
population estimate of identified humpbacks from
the Cape Verde Islands is provided. The popula-
tion of humpbacks breeding in the Cape Verde
Islands likely represent the remnants of a histori-
cally larger population breeding around the Cape
Verde Islands and off northwestern Africa (Reeves
et al., 2002). A recent review of the worldwide
status of humpback whales (Bettridge et al., 2015)
determined that this Cape Verde population com-
prises a “Distinct Population Segment” (DPS)
under the U.S. Endangered Species Act. The DPS
designation was based upon genetic evidence that
suggested a second breeding ground occupied by
humpback whales that feed primarily off Norway
and Iceland. Loss of this DPS unit would result
in a loss of this unique breeding population as
well as a significant number of whales that feed
in Iceland and Norway (Bettridge et al., 2015).
Our primary objective is to better understand
how the Cape Verde humpbacks are connected to
the other known North Atlantic breeding areas.
Recent research discoveries have identified some
exchange between both the Cape Verde Islands
and the Guadeloupe breeding grounds (Stevick
et al., 2016, 2018).
The Cape Verde Islands (CVI) are situated in the
eastern North Atlantic between 14° 48' to 17° 22' N
and 22° 44' to 25° 22' W, 460 to 830 km west of
Senegal, West Africa. The ten islands and several
islets are of volcanic origin, with steep shores aris-
ing from an ocean floor more than 3,000 m deep.
Only the islands of Maio, Boavista, and Sal have
a continental platform, while the northwestern
islands of São Vicente, Santa Luzia, Branco, and
Raso have limited shallow areas less than 100 m
deep surrounding them (Figure 1). Since 1990,
most cetacean research effort has been in the east-
ern sector of the archipelago, focused near the
islands of Maio, Boavista, and Sal.
The Cape Verdean waters are known to expe-
rience a harmattan season, which is a very dry,
dusty easterly or northeasterly wind from the West
African coast, occurring from December to mid/
late March. This often makes maritime navigation
around the islands difficult and hazardous as well
as produces less than ideal conditions for mariners
and whale researchers. These weather conditions
Figure 1. Map of the Cape Verde Islands (CVI) (Republic of
23Humpback Whales in the Cape Verde Islands
may help explain the low number of humpback
coverage is highly variable. Most photographs were
whale sightings and fluke photographs, and the
obtained from the western North Atlantic feed-
limited amount of cetacean information from this
ing grounds. Recently, there has been a significant
region (Reiner et al., 1996; Hazevoet & Wenzel,
increase in the collection of humpback fluke photos
2000; Jann et al., 2003; Wenzel et al., 2009;
from the eastern North Atlantic, including the
Berrow et al., 2015a, 2015b).
waters off Norway, Ireland, Azores, and Iceland,
and these are compared/merged in the NAHWC.
Data Collection Most photographic data came from two large-
Marine mammal surveys were conducted during
scale North Atlantic Ocean projects involving the
the winter/spring months (January to June) between
photo-identification of humpback whales: (1) the
1990 and 2018. Surveys varied from 30 to 90 days
Years Of the North Atlantic Humpback (YONAH)
in duration (see Reiner et al., 1996; Hazevoet &
project (1992 and 1993) and (2) the More North
Wenzel, 2000; Jann et al., 2003; Wenzel et al.,
Atlantic Humpbacks (MONAH) project (2004-
2009). Two simultaneous marine mammal surveys
2005). The YONAH project was an extensive study
occurred in the Cape Verde archipelago via sailing
of North Atlantic humpback whales in all known
vessels during 2003 and 2006. Ryan et al. (2013a,
major northern feeding grounds and the breed-
2014) conducted small (5 m) boat research, includ-
ing grounds of the Dominican Republic (Smith
ing biopsy and photo-identification efforts, during
et al., 1999). The YONAH project did not include
the 2011-2012 seasons. Since 2008, most data were
the waters of the CVI, Azores, or other parts of
collected from whale-watching vessels from early
the eastern North Atlantic. The MONAH project
March to late May. Additional research has been
focused on Silver Bank, Dominican Republic, and
conducted around the Cape Verde archipelago focus-
Gulf of Maine populations. All aforementioned
ing on Southern Hemisphere humpback whales that
North Atlantic humpback fluke collections have
may breed there during the austral breeding season
been merged under the NAHWC. The NAHWC
(Hazevoet et al., 2011; Berrow et al., 2015a, 2015b;
contains approximately 11,000 individual fluke
Ryan et al., 2019). However, in this article, we are
photographs from the entire North Atlantic. (The
only reporting on humpbacks found during the
NAHWC is maintained at Allied Whale, College
boreal breeding season (January to June).
of the Atlantic, 105 Eden Street, Bar Harbor, Maine
In recent years, more humpback sightings and 04609, USA; www.coa.edu/html/alliedwhale.htm).
fluke photographs were obtained due to increased Humpback whales are uniquely identifiable based
effort with larger vessels offering whale-watching primarily on the ventral side of their flukes (Katona
activities in Sal Rei and Boa Vista, as well as via & Whitehead, 1981). Identification can sometimes
citizen science from 2010 to 2018. Several research be augmented by other features such as dorsal fin
excursions were conducted in the western portion shape, scars, and genetic data (Smith et al., 1999).
of the Cape Verde archipelago, with very little The probability of capture/recapture frequently
success in locating humpbacks in that region. For varied due to differences in sampling effort and
each cetacean sighting, the time, GPS position, survey platforms as is the case in many studies of
group size and composition, and behavior were free-ranging cetaceans (Hammond, 1986, 1990;
noted. Fluke photographs—used to identify indi-Hammond et al., 1990). CVI humpback fluke pho-
vidual humpbacks from the unique pattern of pig-tographs have all been compared and catalogued
mentation and scars on the ventral surface—were within the NAHWC using methods described by
obtained with a 35-mm DSLR camera. Fluke pho-Katona & Whitehead (1981), Katona & Beard
tographs were graded for photo quality and indi-(1990), and Smith et al. (1999).
vidual distinctiveness (1 – Excellent, 2 – Good, 3 –
Fair, and 3- – Poor photo quality and no individual Abundance Estimation
distinctiveness). Only fluke photographs graded A Jolly-Seber open population model was fit to
better than 3- were used in this analysis (Friday the data from CVI using Rcapture, Version 1.4-2
et al., 2006, 2008). (Rivest & Baillargeon, 2014), using R, Version
3.5.3 (R Core Team, 2019), to estimate abundance
Photo Comparison from the photo-identification mark-recapture.
The North Atlantic Humpback Whale Catalogue
Prior to 2010, there was less effort, and fewer
(NAHWC) is the primary repository for humpback
whales were photo-identified annually (Tables 1
whale fluke photographs from throughout the North
& 2), so only the non-calf data collected during
Atlantic. Photographs date from 1976 to the pres-
2010 to 2018 were used to estimate the abundance
ent. The NAHWC is collaborative, and photographs
of non-calf humpback whales. Because there were
have been submitted by more than 700 international
too few individual whales that were identified to
contributors. Fluke photographs were most often
sex, the abundance analyses were conducted on
obtained opportunistically, so temporal and spatial
the pooled dataset. Note that not all parameters
24 Wenzel et al.
Table 1. From 1990 to 2018, the number of individual humpback whales (Megaptera novaeangliae) identified per year in
the Cape Verde Islands (CVI)
observations 1 year 2 years 3 years 4 years 5 years 6 years 7 years 8 years 9 years 10 years 11 years Total
individuals 136 52 27 22 12 6 4 5 2 0 1 267
Table 2. Inter-annual recapture history of individual CVI humpbacks (via fluke photographs)
Years 1991 1995 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Summary
2 1 21 0 1 15 19 15 2 16 0 9 10 33 41 45 63 57 59 58 60 69 596
0 0 0 0 0 0 7 3 1 7 0 4 3 16 22 25 32 40 35 46 48 40 329
2 1 21 0 1 15 12 12 1 9 0 5 7 17 19 20 31 17 24 12 12 29 267
for all years can be estimated using Joly-Seber by Friday et al. (2006, 2008). These records
modeling (Rivest & Baillargeon, 2014), so the identify 267 individual humpback whales (as of
estimated parameters for the first and final year of 1 January 2019) on this breeding ground. This
data have no estimates. includes 27 males whose sex determination was
Assumptions of the log-linear form of the based on one or more of the following methods:
Jolly-Seber open population model implemented whale identified as a singer, genetic verifica-
in Rcapture are those of the standard Jolly-Seber tion, photograph of genital area, and identified
model (Rivest & Baillargeon, 2014). The main as the primary escort of a female with newborn
assumptions (Williams et al., 2002) are as follow: calf. Thirty-two females were identified with the
determination based on one of more of the fol-
• Individuals retain their individual identifiers lowing methods: observation of a whale with a
through the sampling period; these are not over-newborn calf, genital photograph, and genetic
looked, and identifiers are recognized correctly. verification; and there were 208 individuals
whose sex is unknown (see Ryan et al., 2013a,
• Sampling periods are (relatively) instantaneous. 2013b, 2014). Of the 267, 131 (49%) were pho-
tographed in more than one year. A recent count
• Fates of all individuals with respect to cap-of the minimum number of whales identified for
ture and survival is independent of all other any one year on this breeding ground was 69
individuals. (2018; based on fluke photographs) and does not
include newborn calves.
• Every individual whale, whether it is identifi-
Calf flukes and ½ fluke photos were excluded
able or not, has the same probability of being
unless the calf was re-identified via another full
resighted and the same probability of survival
fluke photograph obtained one year or more after
between sampling periods.
its initial capture. There have been 12 calves iden-
tified via fluke photographs (of excellent photo
• Figures were produced using the ‘ggplot2’
quality) collected in the waters of the CVI since
package (Wickham, 2016).
2006. Three of these calves have returned to the
CVI waters more than a year after their initial (calf
year) photo capture and are included in the results.
Photo-Identifications Resightings of Individuals
There are 1,038 fluke photo-identified sighting
Male humpback NA04950 (aka NNHWC-200) has
records logged in the CVI database (based solely
been resighted in the Cape Verde archipelago 11
on fluke photographs) from 1990 to 2018 that
different years (from 2002 to 2018) and is always
were ranked as 3 or better in accordance with
sighted between 2 April and 20 May. It was resighted
the photo-quality guidelines and determinations
(photo recaptured) numerous times, with a residency
25Humpback Whales in the Cape Verde Islands
time exceeding 30 days in 2012 and 37 days in
2014 and 2016. This whale was also identified near
Tromsø, Norway, in 2012 and 2014 (F. Broms,
pers. comm.). The within-year frequency of Cape
Verdean humpback photo-identification recaptures
varied as most individuals were only captured once
per year/season. One humpback (sex unknown)
was resighted 15 days apart and nearly 100 km
away within the CVI archipelago. One male hump-
back (NA04750) was resighted numerous times
between 18 March and 12 May 2010, remaining
in the region for 61 days. Female humpbacks with-
out calves were most often sighted once within the
year. A few females, observed with a newborn calf,
maintained an extended residency of over a month.
Female humpback NA04906 was observed with
a newborn calf between 6 April and 12 May 2010
(36 d), and between 13 April and 4 May 2018 (21 d)
with another calf. Female humpback NA04968 was
resighted with a newborn calf numerous days from
10 March to 10 April 2017 (31 d).
There have been a few anecdotal observations of
humpbacks documented from shore in January and
as late as early June. Those humpbacks observed
between August and October are assumed to be
Southern Hemisphere humpbacks (Hazevoet et al.,
2011; Berrow et al., 2015a, 2015b; Ryan et al., 2019).
Humpbacks generally arrive in late February/early
March with consistency, and the last observations
are at the end of May. The frequency of sightings
and photographic identifications tend to peak in
mid- to late April, with the mean (across all years)
corresponding with 17 April (Table 3). Our earliest
photo-identification capture was 29 February 2016,
and the latest photo identification capture was on
26 May 2018.
The largest number of recaptures from eastern
North Atlantic high latitude feeding grounds was
44 individual humpbacks (44/267 = 16.5%) iden-
tified in both the Cape Verdean and Norwegian
waters, followed by 12 humpbacks (12/267 =
4.5%) identified in the CVI and Iceland. Fifteen
humpbacks were sighted in both the CVI and
Azores, with seven of these whales also having
Norwegian sightings. There has been one resight-
ing between Cape Verde and Tenerife, Canary
Islands, and there have been five resightings of
Cape Verde-identified humpbacks observed in
different years in the southeast Caribbean, around
the French West Indies island of Guadeloupe—
one of these whales has also been photographed
near Tromsø, Norway (Stevick et al., 2016).
Between 2010 and 2018 (inclusive), 228 indi-
viduals were identified. During this time period,
there were too few individual whales (29 females,
27 males, and 172 unknown) for which sex was
Table 3. All CVI fluke photo captures (1990-2018) by 2-wk
Dates Fluke captures
February 15-29 2
March 1-15 84
March 16-31 155
April 1-15 269
April 16-30 240
May 1-15 221
May 16-30 67
Note: On 29 February 2016, there were two fluke captures.
known to analyze the data separately by sex. The
discovery curve of identifications (Figure 2) did
not show an asymptote. A model with no “trap
effect” with an Akaike information criterion
(AIC) of 590.6 provided a better fit to the data
than one that included a trap effect (AIC 599.2).
This means that all identifiable individuals were
equally likely to be sampled throughout the study.
The fitted model included the probabilities of
capture and survival, both varying by sampling
period (i.e., annually). Annual capture probabili-
ties (Table 4) varied from 0.277 (Standard Error
[SE] 0.037) in 2015 to 0.4067 (SE 0.091) in 2011.
Estimates of the number of new arrivals between
years were highly variable, ranging from 0 to 31
(SE 25) (Figure 2). Estimates of annual abundances
ranged from 101 (SE 19) in 2011 to 213 (SE 16) in
2015 (Figure 3). The estimate of the total number
of individual whales that occurred in the study
area between 2010 and 2018 was 272 (SE 10). As
calves are not photo-identified (and as sightings of
calves are not independent from sightings of their
mothers, and so inappropriate for mark-recapture
analysis), these population estimates are for non-
Two spatially distinct tropical regions in the
North Atlantic are known to have been tradi-
tionally used by humpback whales (and whal-
ers) during the winter calving/breeding season:
(1) the southeastern Caribbean and (2) the Cape
Verde Islands (Reeves et al., 2001, 2002; Smith
& Reeves, 2003, 2010; Cabral & Hazevoet,
2011). Reeves et al. (2001) suggested a popula-
tion shift from the southeastern to the northern
West Indies based on the lack of historical records
26 Wenzel et al.
Figure 2. Cumulative tally of individual humpback whales (Megaptera novaeangliae) identified photographically, 2010 to
of 19th-century whaling from the Dominican
Republic. Kennedy & Clapham (2017) suggest it
may have been an inability of the whalers to obtain
the necessary licenses to hunt humpback whales in
the Dominican Republic rather than an absence of
whales in this region. Today, the largest concentra-
tions of North Atlantic breeding humpbacks are
observed on Silver, Navidad, and Mouchoir Banks
(north of Hispaniola, Dominican Republic), as
well as in Samaná Bay in the northeast Dominican
Republic (Winn et al., 1975; Smith et al., 1999).
The documentation of the inter-annual migra-
tory exchange between the southeast Caribbean
and the CVI sparks new interest in the relation-
ship between these two regions (Palsbøll et al.,
2017). Four thousand kilometers separate these
two breeding habitats, and five individuals have
been photo-documented in both regions (Stevick
et al., 2016, 2018).
There have been no photographic matches
between any of the Cape Verde humpback whales
and those on western North Atlantic feeding
grounds or to the West Indies/Dominican Republic
breeding ground despite the huge sample size that
exists from both of those regions (Jann et al., 2003;
Wenzel et al., 2009; Stevick et al., 2016, 2018).
This further supports the hypothesis that hump-
backs from the CVI constitute a Distinct (breed-
ing) Population Segment (DPS) that feeds exclu-
sively in northeastern Atlantic waters. This model
Table 4. Estimates of annual probability of capture of
individual humpback whales in the CVI study area, 2011
to 2017, derived from a Jolly-Seber open population model
fit to the data using Rcapture (Rivest & Baillargeon, 2014).
Where parameter estimates cannot be identified in the
model, the estimates are replaced with --.
Year Point estimate Standard error
2010 -- --
2011 0.4072 0.0907
2012 0.3338 0.0620
2013 0.3177 0.0458
2014 0.3409 0.0497
2015 0.2769 0.0373
2016 0.2890 0.0531
2017 0.3826 0.0753
2018 -- --
is supported by the existence of both nuclear and
mitochondrial DNA differences between hump-
backs from the eastern and western North Atlantic
(Palsbøll et al., 1995, 1997, 2017; Larsen et al.,
1996; Valsecchi et al., 1997). Further support may
be found in the disparity in the timing of migra-
tions and peak relative abundance on the breeding
27Humpback Whales in the Cape Verde Islands
Figure 3. Estimates of annual abundance of humpback whales in the CVI study area, 2011 to 2017, derived from a Jolly-
Seber open population model fit to the data using Rcapture (Rivest & Baillargeon, 2014). Bars show plus or minus one
grounds across the North Atlantic: earlier in the
female humpback whales migrate each year (e.g.,
west and later in the east (Stevick et al., 2016).
Brown et al., 1995), their likelihood of detection
We suspect that in animal populations with high (capture) each year is different from that of males.
resight and extended residency, as observed here, Indeed, Ryan et al. (2013b) determined a signifi-
site fidelity is similar to route ﬁdelity in that both cant genetically determined male:female bias in
refer to the repeated utilization of migratory desti-a very small sample of biopsied whales (n = 26)
nations (Horton et al., 2017). of 1.9:1. We cannot address this sex bias with the
Mark-recapture estimates of humpback whale data on hand and acknowledge this caveat in our
abundance in the CVI show that this population study. Furthermore, since individual whales have
has been, and remains, very small. Previous esti-discrete ranges within the Cape Verde archipel-
mates ranged from 99 (CV = 0.23) in 1999 to 2005 ago, their likelihood of detection in the study area
(Punt et al., 2006) to 170 to 260 (CV = 0.02) in may differ as data were collected from a small
2010 to 2013 (Ryan et al., 2014). In this study, we portion of the island group. However, running the
estimated that there were 272 (SE 10) individual, test for a trap effect (i.e., individual differences in
non-calf whales using the CVI between 2010 and likelihood of detection of whales) demonstrated
2018, with a maximum of 213 whales (SE 16) in that a model without a trap effect fitted the data
2015. Although Figure 3 shows annual abundance better than a model with a trap effect. That being
estimates for 2011 to 2017, the overall estimate of so, these biases, if they exist, are insufficient to
the number of humpback whales using the CVI is affect the acceptability of our modeling assump-
for all years’ data (i.e., 2010 to 2018). Because of tions and so do not detract from the primary mes-
the constraints of the Jolly-Seber model (Rivest sage of the mark-recapture analysis. The popula-
& Baillargeon, 2014), not all years’ annual abun-tion of humpback whales occurring in the CVI is
dances can be estimated. We recognize that our at very low abundance.
abundance estimate is likely biased, but our data-
The low abundance of humpback whales in this
set was too sparse to run more complex models to
breeding area probably indicates a slow recovery
address some of these biases. For example, there
(or even lack thereof) of this eastern North Atlantic
are too few individuals of known sex (29 females
humpback breeding population (Ingebrigtsen, 1929;
and 27 males) in the 2010 to 2018 dataset to derive
Kellogg, 1929; Reeves et al., 2001, 2002; Reeves
sex-segregated abundance estimates. As not all
& Smith, 2003; Smith & Reeves, 2003, 2010; Punt
28 Wenzel et al.
et al., 2006; Ryan et al., 2014). Analysis of 19th-
strong, local conservation measures for whales
century whaling logs indicates that the CVI histori-
and their habitat should be considered by the
cally hosted a much larger population of humpbacks
Republic of Cape Verde.
than it does today (Reeves et al., 2002; Reeves &
Importantly, this study provides further support
Smith, 2003). Although there are no recent mark-
for the idea that the Cape Verde humpback sub-
recapture estimates for the eastern North Atlantic
population is not reproductively isolated and that
feeding aggregations, there are, for example, over
additional genetic and photo-identification research
900 individual humpback whales photo-identified
is required. The large influx of animals estimated to
in the northern Norwegian humpback whale catalog
have occurred on three separate occasions indicates
(2011 to 2018; www.hvalid.no/catalogue/browse)
that immigration from elsewhere must be occurring.
as of 31 December 2018 (F. Broms, pers. comm.).
Photographic matches to the southeast Caribbean
There are sightings/resightings of humpbacks
indicate that one source of immigrants is from
migrating from the eastern North Atlantic (Norway
there, but we cannot rule out the possibility that
and Iceland) to the Dominican Republic and the
there is at least one other breeding area in the North
southeast Caribbean (Martin et al., 1984; Stevick
Atlantic that has yet to be discovered. Similarly,
et al., 1998, 2003, 2016, 2018); however, there are
there may be northern feeding areas that are not
too many whales in the high latitudes of the central
being adequately surveyed or photographically and
and eastern North Atlantic for the humpback whales
genetically sampled. Finally, this work adds to the
observed in the CVI to represent the only breeding
evidence (Stevick et al., 2018) that the West Indies
population from the eastern North Atlantic.
DPS recognized under the U.S. Endangered Species
The CVI population of humpback whales arrive
Act (Bettridge et al., 2015) comprises at least two
and depart 6 to 8 wks later in the winter breeding
reproductively distinct groups of whales.
season than do humpbacks found in the waters off
the Dominican Republic (Balcomb & Nichols, Acknowledgments
1982; Whitehead, 1982; Whitehead & Moore,
1982; Mattila et al., 1994). Stevick et al. (2018)
We wish to acknowledge the Captains and crews of
demonstrated that the southeast Caribbean hump-
the ships Iceni Queen, Holland, Corvette, and Sodade,
backs are on a similar reproductive schedule, arriv-
especially Luis and Carlos Albrecht, Captain Luis A.
ing and departing 6 to 8 wks later than those in the
Lopez, Captain Kees Roll, Captain Robert Mannink,
Dominican Republic, There is a marked cline from
Martin Wenger and the R/V Wanda, Joe Aston, Fiacc
west to east in the arrive/peak relative abundance/
O’Brolchain, and the volunteers who made this
departure time of whales. This may be attributed
research possible through their enthusiastic participa-
to the shorter distance traveled for humpbacks
tion—in particular, R. Clark, C. Carlson, G. Cascella,
migrating from the western North Atlantic feeding
D. Craig, Z. Evora, B. Gravanita, E. Magileviciute,
grounds (Gulf of Maine and eastern Canada) to the
A. Ramirez, A. Cecchetti, A. Ricard, S. Vieira, L.
Dominican Republic compared to the migration
Steiner, S. Hanquet, V. Chosson, A. Kennedy, K.
(distance traveled) from the eastern North Atlantic
Zbiden, M. Versluis, F. Hennicke, A. Hennicke, C.
feeding grounds of Iceland and northern Norway to
Rinaldi, R. Rinaldi, M. van der Linde, G. Karbus,
the CVI. Future studies should address how tempo-
C. Broechner Jespersen, G. Nicolas, R. Peres dos
ral, in addition to spatial, separation may maintain
Santos, L. Rudin, A. F. Aston, M. Aston, I. Enlander,
DPSs across the North Atlantic breeding areas.
L. Lysaght, J. O’Brien, M. O’Connell, D. Wall, T.
Whelan, J. Wilson, P. Whooley, D. B. Nuno, L.
Steiner, C. Schmidt, D. Vetsch, and W. Heckenthaler.
This study confirms previous findings (Punt et al.,
Partial funding support for research cruises and the
2006; Ryan et al., 2014) that the population of
photograph matching at the College of the Atlantic
humpback whales using the waters off the Cape
was through the Whale Dolphin Conservation
Verde Islands is extremely small and still numbers
Society (UK), S. Mackenzie and Cetacean Society
fewer than 300 individuals. Only the Arabian Sea
International (USA), Island Foundation (USA),
subpopulation of humpback whales, comprising
Heritage Council, Bord Iascaigh Mhara, Cape Verde
less than 100 individuals (Minton et al., 2011), is
Development (Ireland), and Karl Mayer Stiftung
smaller. Unlike several other populations (Thomas
(Liechtenstein). Special thanks to P. Clapham, P.
et al., 2016), the humpbacks found off the CVI
Palsbøll, M. Bérubé, R. Reeves, F. Larsen, J. Lien, E.
are not increasing rapidly. Effective monitoring
Wald, V. Brooks, M. A. Rasmussen, and A. R. Martin
efforts can provide insight into potential changes/
for numerous discussions over the years on this
trends within this whale population and are, there-
subject; to D. Palka and two anonymous reviewers
fore, a necessity. Put together, these findings gen-
for their helpful comments; and to S. Ratao and R.
erate concern for the conservation status of hump-
Moreno, Maio Biodiversity Foundation, S. Correia,
backs in the Cape Verdean waters, indicating that
Instituto Nacional de Desenvolvimento das Pescas
29Humpback Whales in the Cape Verde Islands
(INDP), Republic of Cape Verde, and the General
Friday, N., Smith, T. D., Stevick, P. T., Allen, J., & Fernald,
Directorate of Environment for research permits and
T. (2008). Balancing bias and precision in capture-
support of Sónia Araujo and Liza Lima within Cape
recapture estimates of abundance. Marine Mammal
Science, 24(2), 253-275. https://doi.org/10.1111/j.1748-
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