Content uploaded by Joan Giménez
Author content
All content in this area was uploaded by Joan Giménez on Feb 22, 2018
Content may be subject to copyright.
MARINE ECOLOGY PROGRESS SERIES
Mar Ecol Prog Ser
Vol. 588: 215–228, 2018
https://doi.org/10.3354/meps12449 Published February 8
INTRODUCTION
Animal migrations are of particular interest to both
scientists and the public as they occur in a wide
range of terrestrial and marine species including
birds, mammals, fishes, reptiles and arthropods (e.g.
Corkeron & Connor 1999, Witt et al. 2011, Sergio et
al. 2014). Over the last 2 centuries, these movements
have been severely disrupted by human activities
such as overhunting, anthropogenic barriers, habitat
loss and climate change (Bolger et al. 2008, Singh et
al. 2012). Regarding baleen whale migration, the
generally accepted model worldwide has been his-
torically described as seasonal movements between
feeding and breeding grounds in high and low lati-
tudes, respectively (e.g. Kellogg 1929), making them,
as well as most wide-ranging migratory marine spe-
cies, vulnerable to the effects of climate change and
human activities (Clapham et al. 2008, MacLeod
2009, Lascelles et al. 2014). However, a recent review
has shown that this model was too simplified to
describe the diversity of migration strategies of some
mysticete species, including the populations of fin
whales Balaenoptera physalus inhabiting the Medi-
terranean Sea. In the latter, resident whales (here-
after, MED) are believed to use nomadic and op por -
tunistic movement strategies within the north -
western and central Mediterranean Sea (Geijer et al.
© Inter-Research 2018 · www.int-res.com*Corresponding author: pauline@circe.info
Contemporary migration of fin whales through
the Strait of Gibraltar
Pauline Gauffier1,*, Philippe Verborgh1, Joan Giménez2, Ruth Esteban1,
Juan Manuel Salazar Sierra1, Renaud de Stephanis1
1CIRCE (Conservation, Information and Research on Cetaceans), Pelayo-Algeciras, 11390 Cadiz, Spain
2Estación Biológica de Doñana-CSIC, 41092 Sevilla, Spain
ABSTRACT: Fin whales Balaenoptera physalus used to be abundant in the Strait of Gibraltar and
nearby Atlantic areas until their rapid collapse due to intense whaling at the beginning of the 20th
century. Recent studies seem to indicate that some fin whales, believed to belong to the North East
North Atlantic (NENA) stock, now use the area to travel between the Atlantic Ocean and the
Mediterranean Sea. In this study, we analyzed 15 yr of direct observations combining vessel and
land-based surveys with photo-identification to characterize the migration of fin whales through
the Strait. These combined observations provide a temporal and spatial analysis of the whales’
movement patterns and behavioral activity. Our main findings suggest a migration of a small com-
munity of fin whales through the Strait of Gibraltar, with remarkable seasonal directionality. All
whales travelled towards the Atlantic Ocean between May and October, and 69% towards the
Mediterranean Sea between November and April. Observations of young whales exiting the
Mediterranean Sea mainly between May and July suggest that at least part of this community is
likely to calve in the basin. Due to the special sensitivity of the species to ship strikes and under-
water noise, and the intense maritime traffic in the Strait of Gibraltar, we urge Spain and Morocco
to cooperate through the International Maritime Organization (IMO) to ensure a safe crossing of
these whales by the effective implementation and year-round extension of the existing recom-
mendation of a seasonal vessel speed reduction to 13 knots.
KEY WORDS: Balaenoptera physalus · Migration · Respiratory rates · Swim speed · Ship strike ·
Strait of Gibraltar · Endangered species · Conservation
Resale or republication not permitted without written consent of the publisher
This authors' personal copy may not be publicly or systematically copied or distributed, or posted on the Open Web,
except with written permission of the copyright holder(s). It may be distributed to interested individuals on request.
Mar Ecol Prog Ser 588: 215–228, 2018
2016). The MED subpopulation was found to be gen -
eti cally distinct from those inhabiting the North
Atlantic Ocean, mainly through maternally inherited
mitochondrial DNA (Bérubé et al. 1998). Their dis-
tinctiveness was also evidenced by organochlorine
contaminants (Aguilar et al. 2002) and stable isotope
analysis (Giménez et al. 2013, Ryan et al. 2013, Das et
al. 2017), with a low recurrent gene flow between the
NW Spain and MED subpopulations (Palsbøll et al.
2004).
As the only connection between the Atlantic Ocean
and the Mediterranean Sea, the Strait of Gibraltar is
a mandatory pathway for whales migrating between
these 2 bodies of water. The first evidence of the
presence of fin whales in the area was unveiled by
bone remains found in excavations on both shores of
the Strait dated between 1350 and 2150 yr BP (Bernal
de Casasola & Monclova Bohórquez 2011). However,
the first quantitative information comes from Ameri-
can whaling vessels, which recorded 100 sightings of
fin whales between 1862 and 1889, mostly in the
adjacent Gulf of Cadiz (Aguilar & Borrell 2007). In
1910−1911, a Norwegian expedition reported a high
number of fin whales inside the Strait and the first
modern whaling company started exploitation in
April 1921 (Tønnessen & Johnsen 1982). Between
1921 and 1959, a minimum of 4535 individuals were
captured (Sanpera & Aguilar 1992), reflecting a re -
markable density of fin whales in the Strait of Gibral-
tar and the Gulf of Cadiz. In the early 1920s, catch
per unit of effort (CPUE) was very high, reaching the
second highest production of oil barrels per catcher
boat ever achieved for one season in 1923 (Tøn-
nessen & Johnsen 1982). In this first period, whalers
reported catching migrating whales entering the
Mediterranean within or nearby the Strait (Sanpera
& Aguilar 1992). However, by 1930 all companies
had ceased their activities due to the paucity of cap-
tures (Sanpera & Aguilar 1992, Clapham et al. 2008).
Hoping that the population would have recovered,
whaling activities resumed in 1948, but only 370 fin
whales were caught, and the fishery was definitely
abandoned in 1960 (Sanpera & Aguilar 1992).
Several authors have suggested an incursion of
North East North Atlantic (NENA) whales into the
Mediterranean Sea (e.g. Jonsgård 1966, Viale 1977,
Notarbartolo-di-Sciara et al. 2003, Castellote et al.
2012b), but the extent of this incursion and the limits
of the NENA and MED subpopulations within the
Mediterranean Sea have been a subject of on-going
debate during the last decade. Currently, some au-
thors believe that NENA whales could be dis tributed
from Gibraltar to the eastern Balearic Basin and MED
whales from the western Balearic Basin to the Ionian
Sea, with a temporal and spatial overlap of both sub-
populations within the Balearic Basin (Notarbartolo
di Sciara et al. 2016). However, Giménez et al. (2013,
2014) considered that the overlap may occur further
north, due to the presence of one individual with an
Atlantic isotopic signature in the northwestern Medi-
terranean Sea (NWMS) and a satellite-tagged indi-
vidual in the NWMS that moved to the Atlantic (Ben-
taleb et al. 2011). Although their interpretation of the
extent of overlapping area differs, all of these authors
suggest that whales currently crossing the Strait of
Gibraltar are NENA individuals.
Another point of debate is the seasonality in the
presence of these 2 subpopulations and of their pos-
sible migration through the Strait. In the 20th century,
fin whale catches were made throughout the year
with apparent no seasonality in CPUE, suggesting a
local, non-migratory subpopulation, but most of
these captures happened outside of the Strait, in the
Gulf of Cadiz (Sanpera & Aguilar 1992, Clapham et
al. 2008). Previously, Viale (1977) suggested that 2
populations from a North Atlantic migrating stock
cohabited in the Mediterranean Sea. A summer sub-
population was observed by whalers crossing Gibral-
tar to enter the Mediterranean Sea in May and June,
while a second population entered in winter to breed
in the NWMS and returned to the Atlantic during the
feeding season, as also suggested by Jonsgård
(1966). This would imply several periods of bi-direc-
tional movements through the Strait of Gibraltar.
Little information is currently available about fin
whales in the vicinity of the Strait of Gibraltar (Bayed
& Beaubrun 1987, Notarbartolo-di-Sciara et al. 2003).
The few reported observations may represent either
stragglers from the MED subpopulation or remnants
of the once-abundant Gibraltar subpopulation
(Clapham et al. 2008). De Stephanis et al. (2008) re -
ported only 3 (<1 %) observations of fin whales out of
606 cetacean sightings during summers from 2001 to
2004. Moreover, between 1989 and 2013 <4% (n =
19) of 511 cetacean strandings were identified as fin
whales on the Spanish and Moroccan shores of the
Strait, from Trafalgar Cape to Europa Point on the
northern shores, and from Cape Espartel to Almina
Point on the southern coast (Fernández-Maldonado
2015, Masski & De Stéphanis 2015). However, male
fin whale songs were detected continuously in the
Strait of Gibraltar between November and January,
suggesting a regular winter presence for the species
(Castellote et al. 2012b).
In this study, we investigated the current migration
of fin whales through the Strait of Gibraltar by com-
216
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
bining land- and vessel-based surveys with photo-
identification. We used the whales’ behavioral activ-
ity documented via respiratory rates, movement
direction and speed to characterize temporal and
spatial patterns of observations, and discussed what
could motivate these patterns.
MATERIALS AND METHODS
Data collection
Surveys were performed in the Strait of Gibraltar
(between 5.1 and 6.0°W; Fig. 1) from the 10 m re -
search boat ‘Elsa’ between 2001 and 2014 following
protocols described in de Stephanis et al. (2008).
Transects were conducted year-round without any
pre-defined track for each survey, but were designed
to provide even coverage. Two observers scanned
the 180° area in front of the boat with 7 × 50 binocu-
lars, when Douglas sea state was <4. The geographic
position of the ship was recorded every 1 min with a
Logger 2010 (IFAW). When fin whales were sighted,
they were approached and photo-identified when
possible. The number of animals from each age class
(calf, juvenile, adult) was estimated visually based on
body length, with juveniles measuring two-thirds,
and calves one-half the size of an adult. Behavior and
swimming direction were also recorded. In 1999 and
2000, the same data were collected opportunistically
from a whale-watching boat.
Additionally, a land-based platform was used bi -
annually from 2009 to 2013 to characterize fin whale
observations during 2 periods (May to July and
November to December), except in winter 2013. The
land station was located on the northern shore of the
Strait, 217 m above sea level and 900 m from shore
(see Fig. 2). At the station, 2 teams of 4 people oper-
ated in summer (09:00 to 15:00 h and
15:00 to 21:00 h local time) and 1 team of
5 people in winter (09:00 to 18:00 h),
approximately matching day light time.
Search effort was recorded hourly or
when a change occurred, and stopped
when Douglas sea state was >4 and/or
visibility decreased to less than one-
third of the study area due to fog or
rain. Two spotting observers scanned
the area of almost 180° using 7 × 50
binoculars with compass and reticules.
Once a whale was sighted by a spotter, a
theodolite operator located the ani -
mal using a surveyor’s theodolite (Leica
T1000) (Würsig & Würsig 1979). The
vertical and horizontal angles measured
by the theodolite were transmitted to a
laptop running the Cyclops Tracker
v.2.6 whale tracking software (un -
published software, E. Kniest, University
of Newcastle, NSW, Australia), which
automatically calculated the position of
the animal. When possible, the location
was also communicated to the vessel to
confirm group size and age classes, as
well as to perform photo-identification.
The theodolite operator aimed to record
the whale’s position at least once per
surfacing bout (i.e. when the whale is
blowing several times at the surface be-
tween longer dives; see ‘Respirations,
surface and dive time’ be low) to track its
movements through the Strait, until the
217
Fig. 1. Study area (SOG; Strait of Gibraltar) and places mentioned in the text.
BOB: Bay of Biscay; NWS: northwestern Spain; GOC: Gulf of Cadiz; AS: Alb-
oran Sea; BI: Balearic Islands; NWMS: northwestern Mediterranean Sea; IS:
Ionian Sea. Light grey shaded area shows Portuguese waters up to 60 nautical
miles while the dark grey shaded area shows the ‘Alborán Corridor Important
Marine Mammal Area’ (IMMA) (IUCN Marine Mammal Protected Areas
Task Force 2016). Open (North East North Atlantic [NENA] fin whale songs)
and closed circles (resident Mediterranean Sea [MED] fin whale songs)
indicate approximate hydrophone locations from Castellote et al. (2012b).
Diamond and cross indicate locations of Vilela et al. (2016) and Gutiérrez-
Expósito et al. (2012), respectively
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
animal was lost or too far away from the land station to
follow. When a group of whales (i.e. several whales
separated by <1000 m) was sighted, the theodolite
operator tried to take a position of the same whale
(e.g. the ‘leading’ whale). Although this was generally
feasible during one surfacing bout, it was not always
possible to ensure that the same whale was tracked in
subsequent surfacing bouts. However, group cohesion
was generally very high, so the error should be small.
The second spotter resumed scanning the area as
soon as possible. All fin whale tracks were plotted in
QGIS v.2.18 (QGIS Development Team 2016).
All calculations and comparisons were run in R
v.3.2.5 (R Core Team 2016), unless stated otherwise.
When applicable, normality was tested using a
Shapiro-Wilk test and homoscedasticity using a Lev-
ene test from the ‘car’ package (Fox & Weisberg
2011). Although the main target species was fin
whale, other cetacean species were recorded oppor-
tunistically when sighted from the land stations. Box-
plots of distances from the land station for each spe-
cies with more than one observation were compared
using a Wilcoxon rank sum test to provide a way of
assessing detection bias over the study area.
Using a Wilcoxon rank sum test, the total annual
number of observations and photo-identified animals
from the research vessel were compared for years
with or without land-based surveys. This provided an
assessment of the benefits of land-based assistance
to vessel activities, to determine if indeed land-based
assistance increased observations.
Swimming speed and linearity
Speed and linearity were calculated for each land-
based track by Cyclops Tracker v.2.6 using whales’
positions. Minimum swimming speed was calculated
as the distance between initial and final locations of a
track divided by total duration. Linearity was the
straight distance between initial and final locations
divided by the cumulative distance between all pairs
of consecutive positions. Only tracks with more than
3 positions in total were used for this analysis. Both
variables were compared for whales swimming west-
and eastwards, using a Wilcoxon rank sum test.
Encounter rates
Encounter rates (ERs) were calculated as the num-
ber of sightings per hour for the land-based observa-
tions for each survey; ERs were then compared annu-
ally between periods using a 2-proportion z-test. Sea
state conditions showed great spatial heterogeneity
but were similar for both seasons.
For boat-based observations, ER was calculated
monthly as number of sighting per 100 km searched
in the area, and Wilson’s confidence intervals were
calculated using the ‘binom’ package (Dorai-Raj 2014).
Respirations, surface and dive time
Respirations were recorded from land and vessels
for several purposes. One was to compare blow de -
tection from each platform as a way to further assess
the capacity of detection from the land station. Respi-
ration rates were also used to define a surfacing
period and to calculate blow intervals and diving
duration (see below), which can give an indication
about whale behavior. From the land station, all res-
pirations were called out by an assigned spotter and
recorded to the closest second; however, individuals
were not distinguishable except for pairs of adults
with calves. From the vessel surveys, respiration
rates were monitored beginning in 2009. Each respi-
ration was recorded to the closest second at the indi-
vidual level when the animals were distinguishable
without error due to natural markings (see ‘Photo-
identification’ below), or otherwise at the group level.
Blow intervals were calculated only from respira-
tions recorded by the vessel, for solitary animals or
groups of 2 animals with recognizable features, ex -
cluding calves. Respiratory intervals were divided
between intra-bout dives (i.e. short duration submer-
gences during surface activity clusters) and inter-
bout dives (i.e. longer terminal dives) (CeTAP 1982).
The breakpoint between surface bouts and dives was
estimated by a log survivorship analysis (Fagen &
Young 1978). Additionally, the duration of surfacing
time was calculated by adding intra-bout intervals
between 2 dives. Mean duration and standard devia-
tion of intra- and inter-bouts intervals as well as sur-
facing time were also calculated.
When fin whales were simultaneously tracked
from both platforms, the number of respirations re -
corded from each one was compared using a paired
t-test or Wilcoxon signed rank test with continuity
correction.
Photo-identification
Whenever possible, photographs of the whole fin
whale body were taken, as well as close-ups of the
218
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
rostrum, dorsal fin and peduncle, from both left and
right sides of the animal. These images were used to
create 2 catalogues. The main catalogue compiled
only individuals with recognizable features (avail-
able at www.cetidmed.com), including nicks on their
dorsal fins and severe scarring. Coloration patterns
on the head (or chevron) were not always visible due
to bad light or water covering the area and were
therefore only used as complimentary information. A
secondary catalogue was also created for each year
with the best photographs of each individual per
sighting regardless of their marking. While the main
catalogue was used to investigate possible resight-
ings over different years, the secondary catalogue
allowed the comparison of poorly marked individu-
als, mainly based on temporary scarring, within the
same year.
RESULTS
Sightings
A total of 254 fin whales were sighted in the Strait
of Gibraltar between 1999 and 2014, consisting of
155 observations (some observations contained more
than one individual) from the following platforms: 72
from the vessel only, 65 from land only and 18 from
both platforms (Table 1, Fig. 2). Overall, the direction
of migration was known for 93% (n = 239) of individ-
uals. All whales with known travelling direction
were headed towards the Atlantic Ocean be tween
May and October (n = 185), while 69% (n = 38) were
travelling towards the Mediterranean Sea during the
rest of the year. Eastbound whales were only
observed in the winter period, specifically in Novem-
ber and December (Table 1).
Animals with estimated age classes (n = 128) were
mostly adults (76%), although a lower proportion of
juveniles (12%) and calves (12%) were also ob -
served. Juveniles and calves were mainly observed
between May and July (Fig. 3). Age classes could not
be determined for most animals seen exclusively
from land, except a few obvious smaller animals trav-
elling with adults which were considered calves.
Whales travelled alone or in groups up to 5 individu-
als (mean ± SD = 1.6 ± 0.8). In general, only one sight-
ing was recorded during the same day from any plat-
form (82%), but a maximum of 5 sightings totaling 10
individuals were observed once.
Significantly more fin whales were observed (Wil -
coxan rank sum test, W= 54, p < 0.01) and photo-
identified (W= 50, p = 0.01) in years with combined
land and vessel effort, with a maximum of 29 sight-
219
Year Sightings Individuals Photo ID
May−October November−April Total May−October November−April Total
Boat Land Both Boat Land Both Direction Age class Direction Age class
W?A J CE W? AJC
1999a5571 71
2000a12 1 13 17 1 0 18 7
2001 1 133 33
2002 5 5831 85
2003b23521 111 5
2004 1 111 11
2005 4 462 64
2006 2 2 2 6312 2 11 62
2007 7 1 8839 11 1 12 7
2008 2 2112 1 21
2009c38 8 19 27 7 2 9 4 40 5
2010c434 8 19 20 12 3 9 1 1 29 18
2011c242 1173 29 21 8 21179310 1 50 12
2012c3108 1 2 24 35 19 4 2 2 38 19
2013d71 815 10 3 2 1 15 14
2014 6 614 8 2 14 14
Total 65 27 15 7 38 3 155 185 5 84 11 14 38 16 10 13 4 2 254 113
aData collected from whale-watching boats. bLand-based pilot project in winter 2003 and summer 2006. cBiannual dedicated
land-based surveys in May−July and November−December. dDedicated land-based survey only in summer
Table 1. Annual boat- and land-based fin whale sightings and individual counts from 1999 to 2014. For the period of November to April, the
given year applies to November. ‘Direction’ indicates the direction animals were swimming: west (W), east (E) or unknown (?); age classes
were estimated when possible as adult (A), juvenile (J) or calf (C). Photo ID is the number of individuals in each annual catalogue
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
ings of 50 individuals in 2011. From November to
April (2011), a maximum of 21 sightings of at least 29
whales were observed; 21 sightings of 35 whales
were observed between May and September (2012)
(Table 1).
The majority of fin whales observed in the summer
were travelling in the northern half of the Strait of
Gibraltar, especially those observed from land, which
occurred mostly in a 5 km strip from the Spanish
shore (Fig. 2C). Fin whale observations were more
widespread in the rest of the year (Fig. 2D).
Although fin whales were the target species ob -
served, all 7 cetacean species commonly inhabiting
the Strait of Gibraltar (de Stephanis et al. 2008) were
sighted at least once from the land
stations in both seasons, including
bottlenose dolphins Tursiops truncatus,
striped dolphins Stenella coeruleoalba,
common dolphins Delphinus delphis,
long-finned pilot whales Globicephala
melas and sperm whales Physeter
macro cephalus. A group of 4 killer
whales Orcinus orca was observed on 3
December 2011 and a humpback whale
Megaptera novaeangliae on 10 Ju ly
2013. Boxplots of distances from the
land station of fin, sperm and pilot
whales as well as grouped dolphin
species show that fin whales and dol-
phins were detected over a similarly
wide range of distances, while pilot and
sperm whales were sighted only at
greater distances (Fig. 4).
220
14
12
10
8
6
4
2
0
Number of individuals
Adults
January
February
March
April
May
June
July
August
September
October
November
December
Juveniles
Calves
Undetermined
Fig. 2. Fin whale tracks from (A,B) the land station (continuous lines) and (C,D) the vessel (dotted lines). Some tracks
correspond to the same sighting from both platforms
Fig. 3. Maximum monthly number of individual fin whales sighted by esti-
mated age class. Data include both land- and boat-based sightings
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
Encounter rates
Total effort from the land station from May to July
(798 h) was more than twice that during November
and December (307 h). Conversely, encounter rates
were overall 2 times lower in summer, with 0.05 fin
whale sightings h−1 compared to 0.12 sightings h−1 in
winter (z= 4.28, p < 0.001) (Fig. 5). However, a large
inter-annual variation was found within each period,
with ERs ranging from 0.01 to 0.07 and from 0.03 to
0.20, respectively.
Additionally, a total of ca. 46000 km was searched
between 1999 and 2014 over the study area with
85% of the effort concentrated between May and
October (Fig. 2A,B). Fin whale observations made
solely from the research vessel were recorded year-
round, except in April and November (Fig. 6). May,
and especially June and July were the months with
highest ER values, between 0.19 and 0.27 sightings
per 100 km. In comparison, August, September and
October had lower values (0.05 to 0.09) but still a rea-
sonable amount of effort. The other 6 months had
sporadic effort and ERs showed greater variability.
Swimming speed and linearity
Most whales showed a quasi-linear track west- or
eastwards (Fig. 2). Two whales observed on 28
November 2011 from both platforms presented a
convoluted swimming pattern which could indicate
foraging activity (Whooley et al. 2011). While swim-
ming eastward at the surface, they would then reap-
pear further to the west after each longer dive, but no
surface feeding events were observed
during the study period.
Speed and linearity were calculated
from 44 (53%) land-based sightings.
Average speed for the whales swim-
ming eastwards (6.0 ± 1.9 knots, n = 7)
was greater than for whales swimming
westwards (3.7 ± 0.2 knots; W= 221.5, p
< 0.01, n = 37), i.e. 2.3 ± 2.1 knots higher
for easterly whales. However, average
linearity was similar for both directions
(0.9 ± 0.02; W= 137, p = 0.8) and very
close to a completely linear trajectory.
Respirations, surface and dive time
Fin whale respirations relative to 16
vessel observations were recorded dur-
ing 23 h and 16 min, a total of 2563 res-
pirations. A total of 1224 blow intervals
(mean = 80 s) ranged from 4 to 829 s
(13.82 min), with a breakpoint of 22 s
between intra- and inter-bout intervals.
221
Fig. 4. Distance from the land station of each first observation
of fin whales and other cetaceans. Species with significantly
different distances are displayed with different colors
(Wilcoxon rank sum test, p < 0.05). The box spans the first to
third quartiles. The thick horizontal line represents the me-
dian. The whiskers show the minimum and maximum value
within 1.5 interquantile range, i.e. excluding outliers (circles)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0
0.35
100
200
300
400
500
600
700
800
2009 2010 2011 2012 2013 Total
Effort (h)
Encounter rate (sighting h–1)
Effort May-July
ER May-July
Effort Nov-Dec
ER Nov-Dec
Fig. 5. Annual effort in hours from the main land station (bars) and encounter
rate (ER) as sightings h−1 (dots). Vertical lines: 95% CI. No effort was made in
winter 2013. Periods within a year with significantly different ERs are dis-
played with open versus closed symbols (z-test, p < 0.001)
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
Consequently, 641 intra-bout intervals had a dura-
tion of 16 ± 4 s and 583 dives lasted 151 ± 170 s
(2.52 min). On 109 occasions, whales breathed only
once between 2 dives; therefore, no intra-bout inter-
val could be calculated. Mean surfacing time was
74 ± 46 s (1.23 min) with a maximum of 4.02 min.
Three extreme values (7.87, 14.67 and 27.77 min),
coming from the same solitary animal sighted on 19
August 2010, were discarded from this calculation.
A total of 6 simultaneous and independent observa-
tions were used to compare blow detectability from
land and vessels totaling 3 h and 53 min of tracking,
including one observation of a possible mother−calf
pair group. No difference was found between the
number of respirations recorded from each platform,
both with (Wilcoxon signed rank test with continuity
correction, U= 13, p = 0.17) and without the mother−
calf pair (paired t= 1.34, df = 5, p = 0.24). On 6 occa-
sions, although a blow was not spotted from land, a
body was seen on the surface and recorded as a ‘no
blow rise’ observation. All corresponded to
blows recorded from the vessel. A total of
64 blows were recor ded from the vessel for
the mother−calf observation, compared to
38 from land; most missed blows were from
the calf (n = 15). Additionally, information
was available at the individual level for 2
boat sighting of possible mother−calf pairs
(including the one described above) during
3 h and 40 min. In both cases, a greater
number of respirations were recorded for
the calf (55 to 59%) than for its suspected
mother (41 to 45%).
Photo-identification
Nearly 21000 photographs were
analyzed and 50 individuals were
included in the main catalogue. From
these animals, 5 individuals (10%)
were re sighted twice over the study
period from 9 mo to 3 yr apart
(Table 2). All 5 animals were sighted
between June and September swim-
ming towards the Atlantic Ocean, but
they were not spotted when entering
the Medi terranean Sea in between
these sightings. Two individuals were
travelling in groups during both
encounters, but their travelling part-
ners were different on each occasion.
Re garding the annual catalogues, up
to 19 individuals were photo-identi-
fied during a single year, and no
resighting happened within the same calendar year.
Two individuals (including the resighted BP_GIB_
007) showed heavy scarring on their peduncle that
could have been caused by a past ship strike (Fig. 7).
DISCUSSION
Our work supports evidence of a bi-directional
migration of a small community of fin whales through
the Strait of Gibraltar, with a main flow towards the
Atlantic Ocean between May and July and towards
the Mediterranean in November and December. This
temporal pattern corresponds to one of the early
hypotheses about Gibraltar whales (Jonsgård 1966,
Viale 1977). Moreover, while the summer peak was
clear from both platforms, the winter peak was only
detected by land observations. It is important to high-
light that higher ERs were detected in the winter
even if the effort in hours was much smaller in this
222
Individual 1st Group 2nd Group Difference
code sighting size sighting size Days Years
BP_GIB_003a25/07/2005 3 17/07/2008 6 1088 3.0
BP_GIB_007a22/09/2006 1 20/06/2007 2 271 0.7
BP_GIB_030 25/06/2008 1 20/07/2010 2 755 2.1
BP_GIB_048 20/06/2009 3 12/07/2012 2 1118 3.1
BP_GIB_065 19/08/2010 1 06/07/2012 2 687 1.9
aData reported in Gauffier et al. (2009)
Table 2. Individual fin whales resighted during the study period (dates
are dd/mm/yyyy)
0.0
0.2
0.4
0.6
0.8
1.0
Encounter rate (si
g
htin
g
per 100 km)
Effort (100 km)
Effort
Encounter rate
0
20
40
60
80
100
120
January
February
March
April
May
June
July
August
September
October
November
December
Fig. 6. Monthly effort in km searched by the research vessel from 1999 to 2014
(blue bars) and encounter rate as fin whale sightings per 100 km (red dots).
Red vertical dotted lines: 95% CI
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
season. Periods of 9 mo to 3 yr separated 2 observa-
tions of the same individuals on their migration to -
wards the Atlantic Ocean, showing that the animals
can spend as little as a few months in and out of the
Mediterranean Sea. Indeed, at least one animal
crossed the Strait of Gibraltar no less than 3 times
over 9 mo, as it was spotted 2 times exiting the Medi-
terranean and therefore must have entered at some
time in between. This suggests that some individuals
must exhibit at least a bi-annual migration through
the Strait, comparable to other marine species such
as bluefin tuna Thunnus thynnus (Block et al. 2005)
or Balearic shearwaters Puffinus mauretanicus (Guil-
ford et al. 2012).
The land station maximized the number of fin
whale encounters, which would otherwise have been
much fewer. When assisting boat activities, it was
especially important for photo-identification as it
greatly increased the possibility of finding resighted
animals. Additionally, observations of other ceta -
ceans at greater distances than fin whales provided
strong evidence for a good detectability of our target
species over the study area and are consistent with
the distribution of these species in the Strait of
Gibraltar (de Stephanis et al. 2008). Furthermore,
when tracked simultaneously from the land station
and the vessel, no difference was found in the num-
ber of blows detected from each platform, although
blows from calves accompanying an adult were
missed more often, as with humpback whales in east-
ern Australia (Godwin et al. 2016). In turn, the vessel
allowed for confirmation of group size, age classes
and photo-identifying animals; thus, surveys combin-
ing land and vessel platforms appear to be the best
way to study fin whales in the Strait of Gibraltar. Fin
whale swimming behavior was consistent with trav-
elling and/or migrating, presenting an
almost fully linear movement and short
diving times (Croll et al. 2001, Lafor-
tuna et al. 2003). Respiratory parame-
ters such as blow intervals, surface and
dive times were similar to other studies
on the species (Leatherwood et al.
1982, Stone et al. 1992, Kopelman &
Sadove 1995, Lafortuna et al. 2003).
Swimming speed was about 2 knots
higher for easterly than westerly
whales. This difference could be ex -
plained by the presence of a main east-
erly current in the upper water layer of
the Strait of Gibraltar (Lacombe &
Richez 1982). Fin whales have been
found to stay near the surface and
spend most of their time at <100 m depth, especially
when not foraging (Panigada et al. 1999, Croll et al.
2001, Stimpert et al. 2015). At this depth in the Strait,
longitudinal currents range from slightly positive to a
maximum of almost 3 knots, and even with the influ-
ence of tides, the overall average current flows east-
erly at about 1 knot (Lacombe & Richez 1982, Wang
1993, Sánchez Garrido et al. 2008), which corre-
sponds to the difference in fin whale swimming
speed.
In November and December, most animals were
travelling eastwards, consistent with a main migrato -
ry flow entering the Mediterranean Sea, but a small
proportion was swimming in the opposite direction.
This could suggest that some animals use both sides
of the Strait of Gibraltar as a wintering ground, as
proposed by Castellote et al. (2012b). Bentaleb et al.
(2011) also suggested that 2 individuals stranded on
the coast of Malaga (i.e. in the northern Alboran Sea)
were mainly feeding in the Mediterranean Sea with
short incursions in contiguous Atlantic waters due to
the longitudinal variations of their δ13C stable isotope
values along their baleen plates. However, regard-
less of their origin, a posterior analysis suggested
these animals had spent at least the last 2 yr of their
life foraging in the Mediterranean Sea (Giménez et
al. 2013). Although both matched the isotopic values
of Mediterranean whales, one animal showed values
close to the Atlantic data set (Giménez et al. 2013),
which could reflect intermediate prey values found
in the Gulf of Cadiz (Varela et al. 2013) or nearby
areas. Interestingly, an individual satellite-tagged in
the NWMS visited historic whaling grounds in the
Gulf of Cadiz and offshore Portugal in November and
December (Bentaleb et al. 2011). Indeed, some fin
whale populations also feed outside of the summer
223
Fig. 7. Two fin whale individuals, (a) BP_GIB_007 and (b) BP_GIB_068,
showing heavy scarring on their peduncle that could have been caused by a
past ship strike
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
(Aguilar et al. 2014, Geijer et al. 2016), and winter
feeding grounds have been identified in the Mediter-
ranean basin near Lampedusa Island in the Strait of
Sicily and in the Tunisian Plateau (Marini et al. 1996,
Panigada et al. 2017). Potential fin whale foraging
habitat in the Mediterranean Sea is more widespread
in winter (Druon et al. 2012), leading to the disper-
sion of whales after the summer (Notarbartolo-di-
Sciara et al. 2003, Panigada et al. 2017). Thus, the
mild meteorological and climatic conditions of the
Mediterranean Sea might have provided year-round
resident MED fin whales with an extended calendar
of feeding opportunities (Notarbartolo-di-Sciara et
al. 2003). NENA whales could also benefit from these
feeding opportunities if they use some of the same
winter grounds as MED whales. Nevertheless, the
location of the winter grounds of NENA whales
remains unclear but could include the Gulf of Cadiz,
the Alboran Sea and part of the NWMS (Sanpera &
Aguilar 1992, Castellote et al. 2012b, Giménez et al.
2013, Notarbartolo di Sciara et al. 2016).
In the present study, fin whales were observed
travelling towards the Atlantic Ocean with juveniles
and even small calves mainly between May and July.
This could indicate that these whales use the Medi-
terranean Sea for breeding and calving in the winter,
as proposed by Castellote et al. (2012b). If these are
the main reasons for NENA whales to enter the
Mediterranean Sea, then it would be crucial to assess
the degree of possible mixing of these animals with
the resident MED population. Indeed, there is some
evidence of spatial and temporal overlap between
these 2 subpopulations (Castellote et al. 2012b,
Gimé nez et al. 2013, 2014, Notarbartolo di Sciara et
al. 2016) that could explain the recurrent gene flow of
2 females per generation between northern Spain
and the NWMS (Palsbøll et al. 2004). Alternatively,
NENA whales could take advantage of the mild win-
ter conditions in the Mediterranean basin compared
to the North Atlantic Ocean while breeding sepa-
rately from the MED subpopulation, as suggested by
the different types of songs recorded in the basin
(Castellote et al. 2012b). Although newborn calves
have been observed in the Mediterranean Sea, pre-
cise calving locations have not been identified and
evidence suggests that breeding may be dispersed
throughout the basin (Notarbartolo-di-Sciara et al.
2003). As with other mysticete species, it is generally
assumed that young fin whales may learn migratory
routes from their mothers and at least some popula-
tions show maternally directed site fidelity (Clapham
& Seipt 1991, Mizroch et al. 2009, Kennedy et al.
2014). This remains to be investigated for the popula-
tions of fin whales inhabiting the Mediterranean Sea,
and especially for the animals crossing the Strait of
Gibraltar.
Fin whale counts in the Strait of Gibraltar were low,
even during peak season, and with a high resighting
rate which points to a small number of individuals
crossing the Strait of Gibraltar on a regular basis.
Based on passive acoustics and stable isotopes
(Castel lote et al. 2012b, Giménez et al. 2013), it was
suggested that these whales belonged to the north-
eastern North Atlantic Ocean, an estimated popula-
tion of about 20 000 fin whales, mainly distributed in
the offshore Bay of Biscay (Hammond et al. 2011). If
this is the case, only a small proportion of these ani-
mals was detected during the present study, even if
some whales could have crossed undetected at night.
More information is needed on the connectivity of
Gibraltar whales with neighboring areas and popula-
tions. Indeed, if Gibraltar whales exhibit a unique
migration pattern, they might not belong to the abun-
dant northeastern North Atlantic population, and
could therefore be a remnant from the historic non-
migrating population. In that case, the conservation
status of what would be a small subpopulation needs
to be urgently assessed.
Information about the current presence of fin
whales in the Gulf of Cadiz is scarce. Between 1986
and 2011, only 7 fin whales out of 303 (2%)
stranded cetaceans were recorded on a 60 km
Spanish beach of the Gulf of Cadiz at about 6.5°W
longitude (Gutiérrez-Expósito et al. 2012). Further
west, 30 nautical miles offshore south Portugal
(around 7.5 to 8°W), a spring survey found 0.5
encounters of the species per 100 km in waters from
about 200 to 750 m depth, mainly in April (Vilela et
al. 2016). Although 1035 fin whales were caught
between 1925 and 1951 off the west central Portugal
coast (Brito et al. 2009), recent distance sampling
surveys from cargo ships travelling from mainland
Portugal to Madeira Island between July and Octo-
ber only found a maximum encounter rate of 0.03
sighting per 100 km for un identified baleen whales
(which might include Balaenoptera physalus but
also B. acutorostrata; Correia et al. 2015). In coastal
Portuguese waters up to 60 nautical miles (see
Fig. 1), fin whales are quite rare (Brito et al. 2009,
Vingada et al. 2011, Santos et al. 2014, Goetz et al.
2015). Southward, low numbers of fin whale strand-
ings occur along the Moroccan Atlantic coast with
no apparent seasonality (Masski & De Stéphanis
2015), and few whales were confirmed to belong to
this species off Mauritania (Baines & Reichelt 2014).
This information seems to indicate that if fin whales
224
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
are regularly detected in the Gulf of Cadiz in winter
(Castellote et al. 2012), they must either leave the
area the rest of the year, or stay offshore where no
recent data are available, or in poorly studied
inshore locations. It further suggests that either the
proportion of NENA whales that undertake a migra-
tion back and forth to the Strait is small, or that the
route is located far offshore mainland Portugal and
the peak migration does not occur between July
and October. The latter temporally matches the
decrease in fin whale encounter rates from the end
of July to early November in the Strait of Gibraltar
reported in the present study. If Gibraltar whales do
migrate to the Atlantic Ocean in summer for feeding
purposes, it could be to take advantages of different
feeding grounds, including different prey items.
Indeed, while summer feeding grounds in the Medi-
terranean Sea seem to be restricted to the NWMS,
the Bay of Biscay and other areas of the North
Atlantic offer a larger prey biomass to support the
abundant NENA population (Hammond et al. 2013).
Moreover, while fin whales from the Medi terranean
and NW Spain seem to feed exclusively on krill
(Aguilar 1985, Notarbartolo-di-Sciara et al. 2003,
Canese et al. 2006, Borrell et al. 2012), individuals
from Irish and Icelandic waters also feed on small
schooling fishes such as sprat, herring capelin or
anchovies (Ryan et al. 2014, Vighi et al. 2016). In
NW Spain, fin whales used to be caught on a feed-
ing ground from July to October (Sanpera & Aguilar
1992) and recent population estimates for the Bay of
Biscay are higher in the summer (Laran et al. 2017).
However, foraging whales have been observed
around the Azores archipelago in spring (Visser et
al. 2011), then migrating to west Iceland and east
Greenland feeding grounds in the summer (Silva et
al. 2013), while some whales feed in Irish waters
from autumn to spring (Ryan et al. 2014, Baines et
al. 2017). Future research should focus on where
Gibraltar whales are going when they are not in the
Strait, either through direct evidence such as match-
ing photo-identification catalogues with other areas
and deploying satellite tags, or indirectly by com-
paring genetic and isotopic data with neighboring
populations.
This small community of fin whales regularly
travels through one of the most transited shipways
in the world (Abdulla & Linden 2008), and some
show signs of possible past collisions. In fact, the
species has been recognized as especially vulnera-
ble to ship strike and underwater noise (Laist et al.
2001, Panigada et al. 2006, Castellote et al. 2012a).
Therefore, special effort should be made to ensure
the safe crossing of these whales through the Strait
of Gibraltar, an area identified as a cetacean
critical habitat by the Agreement on the Conserva-
tion of Cetaceans of the Black Sea, Mediterranean
Sea and Contiguous Atlantic area (ACCOBAMS
2007) and an important marine mammal area by
the IUCN (IUCN Marine Mammal Protected Areas
Task Force 2016). Nevertheless, with nearly 110 000
ships navigating in the area in 2014 (Sociedad de
Salvamento y Seguridad Marítima 2014), automatic
information system (AIS) monitoring indicates that
mariners are not adhering to the 13 knot vessel
speed limit recommended by the International
Maritime Organization (IMO) since 2007 for the
Strait of Gibraltar traffic separation scheme (TSS)
(Silber et al. 2012, see Fig. 2). Migrating fin whales
use this seasonal vessel speed reduction area,
which was initially created for sperm whales from
April to August, in both summer and winter. There
is therefore an urgent need for an effective applica-
tion of this measure and its extension to the rest of
the year, which will require the international coop-
eration of Morocco and Spain through the IMO.
Indeed, restrictions of shipping activities through
this international organization are believed to be
most effective at reducing the risk of ship−whale
strikes (Geijer & Jones 2015). Moreover, slowing
maritime traffic would also reduce ship noise, as
shown in the eastern Mediterranean Sea, where
the noise level decreased by 50 to 65% when
steaming speed decreased from 15.6 to 13.8 knots
over 6 yr (Leaper et al. 2014). Finally, future analy-
ses should identify higher risk areas within the
Strait, while actions to mitigate anthropogenic dis-
turbances and to increase awareness of maritime
stake holders as well as the general public should
be implemented as soon as possible.
Acknowledgements. The authors thank CIRCE’s staff and
volunteers that took part in fieldwork and data entry, espe-
cially A. Blasi, as well as E. Kniest (University of Newcastle,
NSW, Australia) for providing Cyclops Tracker and for his
help with the software, C. Zimmerman for providing some
good quality photographs and A. Elbakyan for supplying
some references. We also thank IFAW (Logger 2010), as well
as the R Core Team and QGIS Team for providing free soft-
ware. This study is the result of a long-term monitoring pro-
gram and was partly funded by Fundación Biodiversidad,
Ministerio de Agricultura y Pesca, Alimentación y Medio
Ambiente, VOLCAM-Caja Mediterráneo, Consejería de
Medio Ambiente de la Junta de Andalucía and Autoridad
Portuaria de la Bahía de Algeciras. J.G. was supported by
the Severo Ochoa Programme for Centres of Excellence in
R+D+I[SEV-2012-0262]. We are grateful to Dr. C. Guinet, as
well as 3 anonymous reviewers, for insightful comments that
improved the manuscript.
225
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
LITERATURE CITED
Abdulla A, Linden O (2008) Maritime traffic effects on biodi-
versity in the Mediterranean Sea, Vol 1. Review of im -
pacts, priority areas and mitigation. IUCN Centre for
Mediterranean Cooperation, Malaga
ACCOBAMS (Agreement on the Conservation of Cetaceans
of the Black Sea, Mediterranean Sea and Contiguous
Atlantic) (2007) Resolution 3.22. Marine protected areas
for cetaceans. Third Meeting of the ACCOBAMS Con-
tracting Parties, Dubrovnik
Aguilar À (1985) Biología y dinámica poblacional del rorcual
común (Balaenoptera physalus) en aguas atlánticas
ibéricas [Biology and population dynamics of the fin
whale (Balaenoptera physalus) in the Iberian Atlantic
waters]. PhD thesis, Universitat de Barcelona
Aguilar A, Borrell A (2007) Open-boat whaling on the Straits
of Gibraltar ground and adjacent waters. Mar Mamm Sci
23: 322−342
Aguilar A, Borrell A, Reijnders P (2002) Geographical and
temporal variation in levels of organochlorine contami-
nants in marine mammals. Mar Environ Res 53: 425−452
Aguilar A, Giménez J, Gómez-Campos E, Cardona L, Bor-
rell A, Aguilar À (2014) δ15N value does not reflect fast-
ing in mysticetes. PLOS ONE 9: e92288
Baines ME, Reichelt M (2014) Upwellings, canyons and
whales: an important winter habitat for balaenopterid
whales off Mauritania, northwest Africa. J Cetacean Res
Manag 14: 57−67
Baines M, Reichelt M, Griffin D (2017) An autumn aggrega-
tion of fin (Balaenoptera physalus) and blue whales (B.
musculus) in the Porcupine Seabight, southwest of Ire-
land. Deep Sea Res II 141: 168−177
Bayed A, Beaubrun P (1987) Les mammiferes marins du
Maroc: inventaire preliminaire. Mammalia 51: 437−446
Bentaleb I, Martin C, Vrac M, Mate B and others (2011) For-
aging ecology of Mediterranean fin whales in a changing
environment elucidated by satellite tracking and baleen
plate stable isotopes. Mar Ecol Prog Ser 438: 285−302
Bernal de Casasola D, Monclova Bohórquez A (2011) Cap-
tura y aprovechamiento haliéutico de cetáceos en la
Antigüedad. De Iulia Traducta a Atenas. In: Bernal de
Casasola D (ed) Pescar con Arte. Fenicios y romanos en
el origen de los aparejos andaluces. Monografías del
proyecto Sagena 3. Servicio de Publicaciones de la Uni-
versidad de Cádiz, p 95−118
Bérubé M, Aguilar A, Dendanto D, Larsen F and others
(1998) Population genetic structure of North Atlantic,
Mediterranean Sea and Sea of Cortez fin whales, Bal-
aenoptera physalus (Linnaeus 1758): analysis of mito-
chondrial and nuclear loci. Mol Ecol 7: 585−599
Block BA, Teo SLH, Walli A, Boustany A and others (2005)
Electronic tagging and population structure of Atlantic
bluefin tuna. Nature 434: 1121−1127
Bolger DT, Newmark WD, Morrison TA, Doak DF (2008)
The need for integrative approaches to understand and
conserve migratory ungulates. Ecol Lett 11: 63−77
Borrell A, Abad-Oliva N, Gómez-Campos E, Giménez J,
Aguilar A (2012) Discrimination of stable isotopes in fin
whale tissues and application to diet assessment in
cetaceans. Rapid Commun Mass Spectrom 26: 1596−1602
Brito C, Vieira N, Sá E, Carvalho I (2009) Cetaceans’ occur-
rence off the west central Portugal coast: a compilation of
data from whaling, observations of opportunity and boat-
based surveys. J Mar Anim Ecol 2: 2−5
Canese S, Cardinali A, Fortuna CM, Giusti M, Lauriano G,
Salvati E, Greco S (2006) The first identified winter feed-
ing ground of fin whales (Balaenoptera physalus) in the
Mediterranean Sea. J Mar Biol Assoc UK 86: 903−907
Castellote M, Clark CW, Lammers MO (2012a) Acoustic and
behavioural changes by fin whales (Balaenoptera
physalus) in response to shipping and airgun noise. Biol
Conserv 147:115–122
Castellote M, Clark CW, Lammers MO (2012b) Fin whale
(Balaenoptera physalus) population identity in the west-
ern Mediterranean Sea. Mar Mamm Sci 28: 325−344
CeTAP (Cetacean and Turtle Assessment Program) (1982)
Characterization of marine mammals and sea turtles in
the Mid- and North Atlantic areas of the US outer conti-
nental shelf. Final Report of the Cetacean and Turtle
Assessment Program, NTIS PB83-2158555, Washington,
DC
Clapham PJ, Seipt IE (1991) Resightings of independent fin
whales, Balaenoptera physalus, on maternal summer
ranges. J Mammal 72: 788−790
Clapham PJ, Aguilar A, Hatch LT (2008) Determining spa-
tial and temporal scales for management: lessons from
whaling. Mar Mamm Sci 24: 183−201
Corkeron PJ, Connor RC (1999) Why do baleen whales
migrate? Mar Mamm Sci 15: 1228−1245
Correia AM, Tepsich P, Rosso M, Caldeira R, Sousa-Pinto I
(2015) Cetacean occurrence and spatial distribution:
habitat modelling for offshore waters in the Portuguese
EEZ (NE Atlantic). J Mar Syst 143: 73−85
Croll DA, Acevedo-Gutiérrez A, Tershy BR, Urbán-Ramírez
J (2001) The diving behavior of large whales: Is dive
duration shorter than predicted? Comp Biochem Physiol
A Mol Integr Physiol 129: 797−809
Das K, Holleville O, Ryan C, Berrow S, Gilles A, Ody D,
Michel LN (2017) Isotopic niches of fin whales from the
Mediterranean Sea and the Celtic Sea (North Atlantic).
Mar Environ Res 127: 75−83
de Stephanis R, Cornulier T, Verborgh P, Salazar Sierra J,
Pérez Gimeno N, Guinet C (2008) Summer spatial distri-
bution of cetaceans in the Strait of Gibraltar in relation to
the oceanographic context. Mar Ecol Prog Ser 353:
275−288
Dorai-Raj S (2014) Package binom: binomial confidence
intervals for several parameterizations. R package
version 1.1-1. https://cran.r-project.org/web/packages/
binom/ index. html
Druon JN, Panigada S, David L, Gannier A and others (2012)
Potential feeding habitat of fin whales in the western
Mediterranean Sea: an environmental niche model. Mar
Ecol Prog Ser 464: 289−306
Fagen RM, Young DY (1978) Temporal patterns of behav-
iour: durations, intervals, latencies and sequences. In:
Colgan FW (ed) Quantitative ethology. Wiley, New York,
NY, p 79−114
Fernández-Maldonado C (2015) Patología y causas de
muerte de cetáceos varados en Andalucía (2011-2014).
PhD thesis, Universidad de Las Palmas de Gran Canaria
Fox J, Weisberg S (2011) An R companion to applied regres-
sion, 2nd edn. Sage Publishing, Thousand Oaks, CA
Gauffier P, Verborgh P, Andréu E, Esteban R, Medina B,
Gallego P, de Stephanis R (2009) An update on fin whales
(Balaenoptera physalus) migration through intense mar-
itime traffic in the Strait of Gibraltar. Paper SC/61/BC6
presented to the Scientific Committee of the Interna-
tional Whaling Commission, May 2009, Funchal
226
Author copy
Gauffier et al.: Fin whale migration through Gibraltar
Geijer CKA, Notarbartolo di Sciara G, Panigada S (2016)
Mysticete migration revisited: Are Mediterranean fin
whales an anomaly? Mamm Rev 46: 284−296
Geijer CKA, Jones PJS (2015) A network approach to migra-
tory whale conservation: Are MPAs the way forward or
do all roads lead to the IMO? Mar Policy 51: 1−12
Giménez J, Gõmez-Campos E, Borrell AA, Cardona L and
others (2013) Isotopic evidence of limited exchange
between Mediterranean and eastern North Atlantic fin
whales. Rapid Commun Mass Spectrom 27: 1801−1806
Giménez J, Gõmez-Campos E, Borrell AA, Cardona L and
others (2014) The uncertain status of the Mediterranean
and northeastern North Atlantic fin whale subpopula-
tions: reply to Castellote et al. Rapid Commun. Mass
Spectrom. 2014, 28, 665–667. Rapid Commun Mass
Spectrom 28: 668−670
Godwin EM, Noad MJ, Kniest E, Dunlop RA (2016) Compar-
ing multiple sampling platforms for measuring the
behavior of humpback whales (Megaptera novaean-
gliae). Mar Mamm Sci 32: 268−286
Goetz S, Read FL, Ferreira M, Martínez Portela J and others
(2015) Cetacean occurrence, habitat preferences and
potential for cetacean-fishery interactions in Iberian At -
lantic waters: results from cooperative research involv-
ing local stakeholders. Aquat Conserv 25: 138−154
Guilford T, Wynn R, McMinn M, Rodríguez A and others
(2012) Geolocators reveal migration and pre-breeding
behaviour of the critically endangered Balearic shear -
water Puffinus mauretanicus. PLOS ONE 7: e33753
Gutiérrez-Expósito C, Rivilla JC, Alís S, Máñez M, Garrido
H, Jiménez FJ, Cobo MD (2012) Veinticinco años (1986–
2011) de monitorización de varamientos de mamíferos
marinos en el litoral de Doñana (Huelva, SO España).
Galemys 24: 1−5
Hammond PS, Macleod K, Burt L, Cañadas A and others
(2011) Abundance of baleen whales in the European
Atlantic. Paper SC/63/RMP24 presented to the 63rd Sci-
entific Committee of the International Whaling Commis-
sion, 30 May−11 June 2011, Tromsø
Hammond PS, Macleod K, Berggren P, Borchers DL and oth-
ers (2013) Cetacean abundance and distribution in Euro-
pean Atlantic shelf waters to inform conservation and
management. Biol Conserv 164: 107−122
IUCN Marine Mammal Protected Areas Task Force (2016)
Report of the workshop: First IMMA regional workshop
for the Mediterranean, Chania, 24−28 October 2016
Jonsgård Å (1966) The distribution of Balaenopteridae in
the North Atlantic Ocean. In: Norris KS (ed) Whales, dol-
phins and porpoises. University of California Press,
Berkeley, CA, p 114−124
Kellogg R (1929) What is known of the migrations of some of
the whalebone whales. Annual Reports of the Smithson-
ian Institute for 1928, Washington, DC, p 467−494
Kennedy AS, Zerbini AN, Vásquez OV, Gandilhon N, Clap -
ham PJ, Adam O (2014) Local and migratory movements
of humpback whales (Megaptera novaeangliae) satel-
lite-tracked in the North Atlantic Ocean. Can J Zool 92:
9−18
Kopelman AH, Sadove SS (1995) Ventilatory rate differ-
ences between surface-feeding fin whales (Balaenoptera
physalus) in the waters off eastern Long Island, New
York, USA, 1981–1987. Mar Mamm Sci 11: 200−208
Lacombe H, Richez C (1982) The regime of the Strait of
Gibraltar. Elsevier Oceanogr Ser 34: 13−73
Lafortuna CL, Jahoda M, Azzellino A, Saibene F, Colombini
A (2003) Locomotor behaviours and respiratory pattern
of the Mediterranean fin whale (Balaenoptera physalus).
Eur J Appl Physiol 90: 387−395
Laist DW, Knowlton AR, Mead JG, Collet AS, Podesta M
(2001) Collisions between ships and whales. Mar Mamm
Sci 17: 35−75
Laran S, Authier M, Blanck A, Dorémus G and others (2017)
Seasonal distribution and abundance of cetaceans within
French waters, Part 2. The Bay of Biscay and the English
Channel. Deep Sea Res II 141: 31−40
Lascelles B, Notarbartolo Di Sciara G, Agardy T, Cuttelod A
and others (2014) Migratory marine species: their status,
threats and conservation management needs. Aquat
Conserv 24: 111−127
Leaper R, Renilson M, Ryan C (2014) Reducing underwater
noise from large commercial ships: current status and
future directions. J Ocean Technol 9: 64−83
Leatherwood S, Goodrich K, Kinter AL, Truppo RM (1982)
Respiration patterns and ‘sightability’ of whales. Rep Int
Whaling Comm 32: 601−613
MacLeod CD (2009) Global climate change, range changes
and potential implications for the conservation of marine
cetaceans: a review and synthesis. Endang Species Res
7: 125−136
Marini L, Villetti G, Consiglio C (1996) Wintering areas of fin
whales (Balaenoptera physalus) in the Mediterranean
sea: a preliminary survey. In: Evans PGH, Nice H (eds)
European research on cetaceans, Vol 9. Proceedings of
the 9th annual conference of the European Cetacean
Society, 9−11 February 1995, Lugano, p 126−128
Masski H, De Stéphanis R (2015) Cetaceans of the Moroccan
coast: information from a reconstructed strandings data-
base. J Mar Biol Assoc UK 1: 1−9
Mizroch SA, Rice DW, Zwiefelhofer D, Waite J, Perryman
WL (2009) Distribution and movements of fin whales in
the North Pacific Ocean. Mammal Rev 39: 193−227
Notarbartolo-di-Sciara G, Zanardelli M, Jahoda M, Pani-
gada S, Airoldi S (2003) The fin whale Balaenoptera
physalus (L. 1758) in the Mediterranean Sea. Mammal
Rev 33: 105−150
Notarbartolo di Sciara G, Castellote M, Druon JN, Panigada
S (2016) Fin whales, Balaenoptera physalus: At home in
a changing Mediterranean Sea? Adv Mar Biol 75: 75−101
Palsbøll PJ, Bérubé M, Aguilar A, Notarbartolo-Di-Sciara G,
Nielsen R (2004) Discerning between recurrent gene
flow and recent divergence under a finite-site mutation
model applied to North Atlantic and Mediterranean Sea
fin whale (Balaenoptera physalus) populations. Evolu-
tion 58: 670−675
Panigada S, Zanardelli M, Canese S, Jahoda M (1999) How
deep can baleen whales dive? Mar Ecol Prog Ser 187:
309−311
Panigada S, Pesante G, Zanardelli M, Capoulade F, Gannier
A, Weinrich MT (2006) Mediterranean fin whales at risk
from fatal ship strikes. Mar Pollut Bull 52: 1287−1298
Panigada S, Donovan GP, Druon J, Lauriano G and others
(2017) Satellite tagging of Mediterranean fin whales:
working towards the identification of critical habitats and
the focussing of mitigation measures. Sci Rep 7: 3365
QGIS Development Team (2016) QGIS Geographic Informa-
tion system. Open Source Geospatial Foundation Project.
www.osgeo.org
R Core Team (2016) R: a language and environment for
statistical computing. R Foundation for Statistical Com-
puting, Vienna. www.R-project.org
227
Author copy
Mar Ecol Prog Ser 588: 215–228, 2018
Ryan C, McHugh B, Trueman CN, Sabin R and others (2013)
Stable isotope analysis of baleen reveals resource parti-
tioning among sympatric rorquals and population struc-
ture in fin whales. Mar Ecol Prog Ser 479: 251−261
Ryan C, Berrow SD, Mchugh B, O’Donnell C, Trueman CN,
O’Connor I (2014) Prey preferences of sympatric fin
(Balaenoptera physalus) and humpback (Megaptera
novaeangliae) whales revealed by stable isotope mixing
models. Mar Mamm Sci 30: 242−258
Sánchez Garrido JC, García Lafuente J, Criado Aldeanueva
F, Baquerizo A, Sannino G (2008) Time-spatial variability
observed in velocity of propagation of the internal bore
in the Strait of Gibraltar. J Geophys Res 113: C07034
Sanpera C, Aguilar A (1992) Modern whaling off the Iberian
Peninsula during the 20th Century. Rep Int Whaling
Comm 42: 723−730
Santos J, Costa R, Araújo H, Rodrigues P and others (2014)
Cetaceans and seabirds in the Portuguese Continental
Coast: What about their environmental status? Presented
at Research Day 2014, 3 June 2014, Universidade de
Aveiro
Sergio F, Tanferna A, De Stephanis R, Jiménez LL and
others (2014) Individual improvements and selective
mortality shape lifelong migratory performance. Nature
515: 410−413
Silber GK, Vanderlaan ASM, Tejedor Arceredillo A, John-
son L and others (2012) The role of the International Mar-
itime Organization in reducing vessel threat to whales:
process, options, action and effectiveness. Mar Policy 36:
1221−1233
Silva MA, Prieto R, Jonsen I, Baumgartner MF, Santos RS
(2013) North Atlantic blue and fin whales suspend their
spring migration to forage in middle latitudes: Building
up energy reserves for the journey? PLOS ONE 8: e76507
Singh NJ, Börger L, Dettki H, Bunnefeld N, Ericsson G
(2012) From migration to nomadism: movement varia -
bility in a northern ungulate across its latitudinal range.
Ecol Appl 22: 2007−2020
Sociedad de Salvamento y Seguridad Marítima (2014)
Informe anual. Spanish Maritime Safety Agency, Madrid
Stimpert AK, Deruiter SL, Falcone EA, Joseph J and others
(2015) Sound production and associated behavior of
tagged fin whales (Balaenoptera physalus) in the South-
ern California Bight. Anim Biotelem 3: 23
Stone GS, Katona SK, Mainwaring A, Allen JM, Corbett HD
(1992) Respiration and surfacing rates of fin whales (Bal-
aenoptera physalus) observed from a lighthouse tower.
Rep Int Whaling Comm 42: 739−745
Tønnessen JN, Johnsen AO (1982) The history of modern
whaling. University of California Press, Berkeley, CA
Varela JL, Rodríguez-Marín E, Medina A (2013) Estimating
diets of pre-spawning Atlantic bluefin tuna from stomach
content and stable isotope analyses. J Sea Res 76: 187−192
Viale D (1977) Contribution à l’étude des grands cétacés en
Méditerranée et sur la côte atlantique d’Espagne. Mam-
malia 41: 197−206
Vighi M, Borrell A, Aguilar A (2016) Stable isotope analysis
and fin whale subpopulation structure in the eastern
North Atlantic. Mar Mamm Sci 32: 535−551
Vilela R, Pena U, Esteban R, Koemans R (2016) Bayesian
spatial modeling of cetacean sightings during a seismic
acquisition survey. Mar Pollut Bull 109: 512−520 PubMed
Vingada J, Ferreira M, Santos J, Araújo H and others (2011)
SafeSea: Manual de Apoio para a Promoção de uma
Pesca Mais Sustentável e de um mar seguro para
cetáceos. Programa EEAGrants, EEA Financial Mecha-
nism 2004–2009 (Projecto 0039), Braga
Visser F, Hartman KL, Pierce GJ, Valavanis VD, Huisman J
(2011) Timing of migratory baleen whales at the Azores
in relation to the North Atlantic spring bloom. Mar Ecol
Prog Ser 440: 267−279
Wang DP (1993) The strait of Gibraltar model: internal tide,
diurnal inequality and fortnightly modulation. Deep Sea
Res I 40: 1187−1203
Whooley P, Berrow SD, Barnes C (2011) Photo-identification
of fin whales (Balaenoptera physalus L.) off the south
coast of Ireland. Mar Biodivers Rec 4: e8
Witt MJ, Augowet Bonguno E, Broderick AC, Coyne MS
and others (2011) Tracking leatherback turtles from the
world’s largest rookery: assessing threats across the
South Atlantic. Proc R Soc B 278: 2338−2347
Würsig B, Würsig M (1979) Behavior and ecology of the
bottle nose dolphin, Tursiops truncatus, in the South
Atlantic. Fish Bull 77: 399−412
228
Editorial responsibility: Scott Shaffer,
San Jose, California, USA
Submitted: February 13, 2017; Accepted: December 8, 2017
Proofs received from author(s): January 24, 2018
Author copy