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Contemporary migration of fin whales through the Strait of Gibraltar

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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, use the area nowadays to travel between the Atlantic Ocean and the Mediterranean Sea. In this study we analyze 15 years 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, as well as their behavioral activity. Our main findings suggest a migration of a small community of fin whales through the Strait of Gibraltar, with remarkable seasonal directionality. All whales travelled towards the Atlantic Ocean in May-October and 69% towards the Mediterranean Sea in November-April. Observations of young whales exiting the Mediterranean Sea mainly in May-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 underwater 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 extension to the rest of the year of the existing recommendation of a seasonal vessel speed reduction to 13 knots.
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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Mar Ecol Prog Ser 588: 215–228, 2018
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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
... En los mares casi cerrados, como el Mediterráneo o el Golfo de California, existen poblaciones residentes que no realizan migraciones latitudinales, o éstas son mínimas (Panigada et al. 2017;Jiménez López et al. 2019). En el caso del mar Mediterráneo, algunos individuos salen al Océano Atlántico durante el invierno (Gauffier et al. 2018;, pero la mayoría se queda dentro y forman pequeños grupos de alimentación (Canese et al. 2006). Algunas poblaciones oceánicas también muestran patrones migratorios peculiares, como la población que habitaba en el Golfo de Cádiz. ...
... Se han identificado algunas zonas concretas donde hay rorcuales comunes durante el invierno, como las Islas Azores, la zona al suroeste de Portugal o el Purcopine Seabight, al oeste de Irlanda Romagosa et al. 2020). También se han observado ballenas cruzando el Estrecho de Gibraltar en ambos sentidos (Gauffier et al. 2018), lo que sugiere que algunas de las ballenas mediterráneas pasan el invierno en el Océano Atlántico ) y viceversa (Castellote et al. 2012;. Finalmente, también se ha detectado la presencia de rorcual común durante el invierno en las zonas de veraneo (Heide-Jørgensen et al. 2003). ...
... Por ejemplo, la población del estrecho de Gibraltar, una de las más intensamente explotadas a principios del siglo XX (Sanpera and Aguilar 1992), desapareció debido a la caza de ballenas y no se ha recuperado (Clapham et al. 2008). Este hecho es sorprendente dada la recuperación que han sufrido otras poblaciones del Atlántico Norte (Vikingsson et al. 2009) y al paso frecuente de ballenas por el lugar (Gauffier et al. 2018;. Se ha propuesto que, en el caso de que la localización de las zonas de veraneo se transmitiera culturalmente, esta información podría haberse perdido cuando se erradicó la población que habitaba el lugar (Clapham et al. 2008). ...
Thesis
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Fin whales (Balaenoptera physalus) is one of the most abundant mysticete species in the North Atlantic, and it is considered a species of high environmental importance by the Spanish legislation. However, large knowledge gaps exist in the biology of this species, especially in winter. The main goal of this thesis is to improve our understanding of the migrations of the fin whale analyzing chemical tracers in three different tissues. In the first chapter, alkenones were analyzed in blubber and the stomach content of the fin whales from Iceland and the NW of Spain. The alkenones are a group of organic molecules produced by some haptophyte species, and may be used to infer the water temperature where they were synthesized. The results show that these molecules can be transferred through the trophic web and detected both in the stomach content and the blubber of the whales. While the temperature estimated in the stomach content reflected the environmental SST 10 days before the sampling date, the alkenones in the blubber reflected the environmental temperature where the fin whales had roamed during winter. In the second chapter, the stable isotopes of amino acids were analyzed in baleen plate samples. The results showed that the trophic level of the individuals were higher and more variable during winter, which could indicate that they were including fish in their diet during the winter season. Furthermore, the baseline isotopic values suggested that the fin whales spent the winter season in zones of deep water emergence, which can support a higher primary production than the oligotrophic ocean. In the third chapter, the temporal consistency of the stable isotopes was measured in the earplugs of fin whales. The results showed that the fin whales are individual specialists, this is, they occupy a small portion of the population isotopic niche. Overall, the fin whale stocks studied in this thesis are more generalist during winter than during summer, however, the individuals tend to migrate and feed in specific zones every year, which are characterized by a high primary production.
... However, scientists have debated whether Mediterranean fin whales are currently moving into the NENA or not (Castellote et al., 2012;Gim enez et al., 2013;Castellote et al., 2014). Mediterranean fin whales have been assumed to be resident (Notarbartolo di Sciara et al., 2003), but the evidence showing that some individuals from the Mediterranean Sea travel toward the NENA is growing (Geijer et al., 2016;Gauffier et al., 2018). However, the frequency and the range of these excursions to the NENA are not clear (Notarbartolo di Sciara et al., 2003). ...
... II (Methods) were produced between September 2007 and April 2008, which matches the period of highest fin whale vocal activity described in the literature for the Northern Hemisphere (Watkins et al., 1987;Watkins et al., 2000;Stafford et al., 2007). It also matches the peak for the southwest Mediterranean Sea and Strait of Gibraltar, as described by Castellote et al. (2012), and the peak presence in the Strait of Gibraltar as described by Gauffier et al. (2018). Between May and August 2008, there were no days with high quality bouts, and automatic detections were reduced considerably. ...
... Cluster 1 was recorded during several months of the study-between September and December 2007 and between February and April 2008. Gauffier et al. (2018) performed an extensive study of the movements of fin whales between the Mediterranean Sea and NENA combining data from direct observations, vessel-, and land-based surveys with photo-identification over a period of 15 years. Between May and October, they found a directional movement toward the NENA of all of the whales observed during that period. ...
Article
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Fin whales were once abundant in the seas to the southwest of Portugal, but whaling activities decreased their numbers considerably. Acoustic data from ocean bottom seismometers provide an opportunity to detect fin whales from their notes, data that would otherwise be logistically challenging and expensive to obtain. Based on inter-note interval and frequency bandwidth, two acoustic patterns produced by fin whales were detected in the study area: pattern 1, described from fin whales in the Mediterranean Sea, and pattern 2, associated with fin whales from the northeast North Atlantic Ocean (NENA). NENA fin whales travel into the western Mediterranean Sea, but the Mediterranean population has not been documented to travel regularly into the NENA. In this study, 11 months of acoustic data recorded southwest of Portugal in the NENA were used to characterize 20-Hz fin whale notes into these patterns. Pattern 2 was the most common and occurred mostly in November–January. Pattern 1 occurred less frequently and mostly in September–December, February and April, which suggested a limited excursion of whales from the Mediterranean Sea. There were also occasions when the two patterns were recorded simultaneously. Results suggest that fin whales from the NENA and Mediterranean Sea might mix in the area during part of the year.
... However, a low male-mediated gene flow was also hypothesised because of the lack of divergence, highlighted by nuclear loci, between some North Atlantic areas and the Mediterranean Sea Palsbøll et al. 2004). The movement of fin whales through the Strait of Gibraltar was well documented and seems to occur seasonally (Gauffier et al. 2018). In addition, the isotopic analysis performed on baleen plates (Bentaleb et al. 2011) and the analysis of recorded fin whale songs (Castellote et al. 2012a) allowed the recognition of two distinct populations in the Mediterranean Sea. ...
... Sea, indicating that a North Atlantic origin is most likely for the individual ID531. North Atlantic fin whales would in fact pass through the Strait of Gibraltar to feed in the Mediterranean Sea during the winter months (Gauffier et al. 2018(Gauffier et al. , 2020. ...
Article
Full-text available
The fin whale Balaenoptera physalus is a large rorqual species occurring worldwide, mainly in temperate and subpolar zones. In contrast to many baleen whales, not all the fin whale populations show the same model of migration. In fact, migratory behaviours of this latter species range from long seasonal migration between high and low latitudes to a complete non-migratory behaviour. A resident fin whale population was described in the Mediterranean Sea, which is also frequented by North Atlantic individuals entering through the Strait of Gibraltar in winter to feed. Between 2020 and 2021 three individuals initially identified as fin whales died along the Tyrrhenian coasts (Mediterranean Sea, Italy). Their mitochon-drial DNA control region (mtDNA CR) was analysed and compared to fin whale haplotypes previously described in North Atlantic Ocean and Mediterranean Sea to identify their geographical origin. Our results show that two individuals most likely belong to the Mediterranean fin whale population, while an individual was recognised as a putative fin-blue whale hybrid (Balaenoptera physalus x Balaenoptera musculus) with a North Atlantic origin. The discovery of the first fin-blue whale hybrid in the Mediterranean Sea was confirmed by the analysis of a biparentally inherited marker, the α-lactalbumin (α-lac) nuclear gene, demonstrating that the morphological analysis alone does not allow to correctly identify hybrids, especially if intermediate characters of both parental species are not clearly distinguishable.
... Both populations cohabit annually in the Balearic Sea off southern Spain and along the Catalan coast (Castellote et al., 2008;Castellote et al., 2012a;Gauffier et al., 2020). The NENA population moves through the Strait of Gibraltar into the Mediterranean basin between November and April and leaves between May and October Gauffier et al., 2018;Gauffier et al., 2020). On the other hand, the Mediterranean subpopulation is found in the Ligurian Sea in summer from July to September and in the Eastern Mediterranean in winter, where they have been observed feeding around Lampedusa Island in February. ...
... This was especially noted when the whale dove quickly (Laist et al., 2001). The injuries were similar to those reported elsewhere in the Mediterranean and Strait of Gibraltar (de Stephanis and Urquiola, 2006;Panigada et al., 2006;Gauffier et al., 2018). The aforementioned two cases of severe vertebral column deformity and likely idiopathic scoliosis in 2018 and 2021, were determined as severe welfare cases. ...
Article
Full-text available
Ship strikes are a widespread conservation issue for many cetacean species globally. Population level impacts depend on the occurrence and severity of collisions, which may lead to life altering injuries or fatalities. Such impacts are a major concern for large, long-lived, and reproductively slow species like the fin whale. Since 2014, a seasonal feeding aggregation of fin whales has been monitored from February to June off the Catalan coast (Spain), in the northwest Mediterranean Sea. Oceanographical factors influence the occurrence and high density of krill within submarine canyons along the continental shelf, resulting in high whale abundance within a small spatial area. The study area extends 37 km offshore across a 1,944 km2 marine strip situated between the towns of Torredembarra and Castelldefels. This fin whale feeding ground is exposed to high density marine vessel traffic, given its location between the northern Mediterranean shipping lane, which links Barcelona and Tarragona Ports to the Atlantic Ocean and wider Mediterranean Basin. Ship strikes represent the greatest conservation threat for fin whales in the Mediterranean Sea. At least four fin whales have been found dead in Barcelona Port since 1986 due to ship strikes and seven live whales have been documented with injuries in the study area since 2018. Fin whale distribution was mapped with known high-risk marine vessels’ (cargo, tanker and passenger vessels) shipping lanes. Vessel density and shipping lanes characterised by speed were considered. Collision risk was estimated monthly based on the predicted fin whale occurrence and traffic density. Several shipping lanes crossed the fin whale feeding habitat every month with an average speed of 15 kn. Cargo vessels displayed the highest ship-strike risk during April, overlapping with the peak of fin whale sightings in the critical feeding area. Slower vessel speeds (8 kn) in waters <200 m depth or along the continental shelf should be implemented along the Catalan coast, during the whale season. These suggestions should be applied into the Barcelona Port transport separation scheme. Ship strike risk for this species will persist unless active management plans are adapted in the region to mitigate its risk.
... To these should be added the Mediterranean Sea subpopulation, which is considered a separate unit based on genetic, isotopic and contaminant differences (Aguilar et al., 2002;B� erub� e et al., 1998;Das et al., 2017;Gim� enez et al., 2013;Palsbøll et al., 2004). However, the connectivity of this last unit with the S sub-area has been under debate for decades Gauffier et al., 2018;Gim� enez et al., 2013;Notarbartolo di Sciara et al., 2016). Recent evidence has linked specimens from the Azores archipelago, currently included in the S feeding sub-area, to eastern Greenland and western Iceland summer feeding grounds (Silva et al., 2013). ...
... The fin whales occurring at the SoG have been at the center of the scientific debate for decades, as to whether the Strait represents a physical barrier that isolates individuals present in the Mediterranean Sea from those in the eastern North Atlantic. Most studies seem to point towards a distinctiveness of NW Mediterranean individuals (B� erub� e et al., 1998;Castellote et al., 2012;Das et al., 2017;Gim� enez et al., 2013;Ryan et al., 2013), but do not exclude some degree of connectivity through the SoG (Bentaleb et al., 2011;Gauffier et al., 2018;Gim� enez et al., 2014;Notarbartolo di Sciara et al., 2016;Palsbøll et al., 2004). In our study, SoG whales were sampled both during their western migration towards the Atlantic Ocean in May-October (peaking in June-July) and during their eastern migration entering the Mediterranean Sea in November-March . ...
Article
Highly migratory marine species pose a challenge for the identification of management units due to the absence of clear oceanographic barriers. The population structure of North Atlantic fin whales has been investigated since the start of whaling operations but is still the subject of an ongoing scientific debate. Here we measured stable isotopes of carbon, nitrogen and oxygen in skin samples collected from 151 individuals from western Iceland, Galicia (NW Spain), the Azores archipelago and the Strait of Gibraltar (SoG). We found spatiotemporal differences in stable isotope ratios suggesting that fin whales sampled in these four areas may share a common feeding ground within the Northeast Atlantic at different times during the year. Our results also suggest that SoG whales use this common feeding ground in summer but exploit Mediterranean resources during the winter months, further supporting the existence of a limited but current exchange of individuals between these two basins.
... This particular sighting was quite interesting as gray whales were last recorded in the North Atlantic in the 1700s and this was the first time that such an individual was sighted in the Mediterranean. Recent studies seem to indicate that some fin whales (Balaenoptera physalus), believed to belong to the north-east North Atlantic (NENA) stock, now use the Strait of Gibraltar to travel between the Atlantic Ocean and the Mediterranean Sea [16]. Apart from marine mammals and fish that migrate from the Atlantic to the Mediterranean, other species belonging to the crustacean subphylum have also been recorded as such. ...
Article
Full-text available
The Mediterranean monk seal (Monachus monachus) is classified as an endangered species by the IUCN, with a global population that does not exceed 800 individuals. There is limited understanding around the biology and health status of the species, rendering possible parasitic infections grave for its conservation efforts. The aim of the current study was the molecular identification of a parasitic nematode found in the digestive system of a sub-adult Mediterranean monk seal individual, that was found stranded in the area of Pagasitikos Gulf, Greece in 2019. Analysis of the stomach contents revealed the presence of two intact female nematode individuals. Standard protocols were followed as DNA extraction of the parasites was conducted and PCR amplification of the cytochrome oxidase subunit I (COI) mitochondrial gene was implemented. Sequencing analysis of a 585 bp-amplified product displayed a 96% similarity of the screened nematodes to the Pseudoterranova bulbosa species. Bayesian inference was implemented for the subsequent tree reconstruction. The phylogenetic tree revealed a clear genetic similarity between our parasitic nematode individuals named as Pseudoterranova spp. and Pseudoterranova bulbosa (bootstrap value: 82%), which is indicated for the first and only time as such, to be found in the waters of the Mediterranean Sea and also in the stomach of a Mediterranean monk seal.
... Recent studies have provided evidence of redistribution and/or a shift in diet composition of the North Pacific (Fleming et al., 2016), as observed in Southern humpback whales (Findlay et al., 2017) that were assumed to be a temporal response to a shift in prey availability and distribution due to climatic changes. Therefore, temporal variability observed in lifetime stable isotope profiles of the humpback whales EP022 and EP027 may provide evidence of large-scale decadal changes in habitat suitability and/or favorable prey abundance (Silva et al., 2019;Gauffier et al., 2018) and the resultant behavior of migratory marine mammals. ...
Article
Biological time series datasets provide an unparalleled opportunity to investigate regional and global changes in the marine environment. Baleen whales are long-lived sentinel species and an integral part of the marine ecosystem. Increasing anthropogenic terrestrial and marine activities alter ocean systems, and such alterations could change foraging and feeding behavior of baleen whales. In this study, we analyzed δ¹³C and δ¹⁵N of baleen whale earplugs from three different species (N = 6 earplugs, n = 337 laminae) to reconstruct the first continuous stable isotope profiles with a six-month resolution. Results of our study provide an unprecedented opportunity to assess behavioral as well as ecological changes. Abrupt shifts and temporal variability observed in δ¹³C and δ¹⁵N profiles could be indicative of behavior change such as shift in foraging location and/or trophic level in response to natural or anthropogenic disturbances. Additionally, five out of six individuals demonstrated long-term declining trends in δ¹³C profiles, which could suggest influence of emission of depleted ¹³CO2 from fossil fuel combustion referred to as the Suess effect. After adjusting the δ¹³C values of earplugs for the estimated Suess effect and re-evaluating δ¹³C profiles, significant decline in δ¹³C values as well as different rate of depletion suggest contribution of other sources that could impact δ¹³C values at the base of the food web.
... As the whales that know how to migrate die, so does the knowledge in the population. Direct observation and photographic evidence suggests that fin whales from the North East North Atlantic population migrate annually into the Mediterranean (Gauffier et al., 2018), yet genetic evidence suggests that the resident population does not mix with these itinerant whales, remaining genetically distinct (Bérubé et al., 1998;Panigada et al., 2017). It is possible that this population has been isolated long enough for the knowledge about migration possibilities and routes to have been lost. ...
Article
Full-text available
Climate change is expected to dramatically alter the distribution of many marine megafauna, impacting the people and economies that depend upon them. We build on the recent literature by developing a framework to describe the effects these changes will have on marine megafauna. With the goal to assist policymakers and grass roots organizers, we identify three illustrative pathways by which climate change drives these range shifts: (1) effects on habitat and shelter, (2) impacts on reproduction and disease, and (3) changing distribution of sources of food. We examine non-climate factors that may constrain or enable megafauna to adapt, creating winners and losers both for the species and the people dependent upon them. Finally, we comment on what management strategies exist at international and local scales that could help mitigate these impacts of climate change so that we, as a global community, can ensure that marine megafauna and people can best co-exist in a changing world.
... Remarks:Recent studies confirmed the hypothesis of genetic exchange between the Atlantic and Mediterranean populations, supported by observations in the Strait of Gibraltar(Gauffier et al., 2018). Records in Adriatic are reported by Notarbartolo di Sciara et al.(2016). ...
Article
Full-text available
The authors are grateful to the two anonymous reviewers for their extensive and detailed comments that greatly improved the clarity and readability of this article. They also like to thank the Museo Civico di Zoologia (Rome, Italy) for hosting the meeting on May 5 th , 2017 that set the basis for this essay. Abstract Checklists represent a basic tool for conservation and management of regional faunas. However, our knowledge on species composition in a territory changes over time due to species movements across borders, extinctions, introductions, as well as to new taxonomic evidence. We aimed to provide the most updated data on native and non-native species of mammals occurring, or that used to occur until recently, on the Italian political territory and seas. The checklist only includes species whose taxonomic status was explicitly agreed in the most recent peer-reviewed literature and based on the most updated taxonomic approaches. For each species, we provided the following information: scientific and common name, global and Italian range, relevant information for management and conservation (e.g. whether it is endemic, allochthonous, or listed in international regulations and red list assessments), as well as remarks on taxonomy and distribution. This new check list of Italian mammal fauna includes nine marine and 114 terrestrial species, belonging to seven orders (Erin-aceomorpha, Soricomorpha, Chiroptera, Carnivora, Cetartiodactyla, Rodentia, Lagomorpha), and 28 families. Vespertilionidae represents the richest family (n=27 species), followed by Cricetidae (n=12) and Soricidae (n=11). The list includes 15-16 allocthonous species. Considering the relative small size of the country, Italy is confirmed as a hotspot of mammal diversity in Europe, hosting the highest species richness in relation to the total area.
Article
The humpback whale is a cosmopolitan species, found in all oceans with distinct populations. This species is not common within the Mediterranean Sea and is therefore classified as a ‘visitor’ species. Occasionally, they enter through Gibraltar Strait, even if their occurrence pattern within the Mediterranean remains unknown. Herein, we document four exceptional sightings of a female and calf humpback whale within the Mediterranean Sea in 2020. A photograph of the female fluke has been compared with the North Atlantic Humpback Whale Catalog and with the Happywhale database. The whale was identified as NA05503, first and only photographed on the north of the Dominican Republic, on February 12th, 1986. Furthermore, we described changes in body condition of the female between the first and the fourth sighting, showing a progressive emaciated state. The photographic recapture after 79 days in the North of Western Mediterranean Sea may reflect a double attempt to “find the way to North Atlantic” feeding areas and an inability to “find the way back to the ocean”. Following published and unpublished records to date, this is the 45th reported sighting of humpback whales within the Mediterranean Sea and the first confirmed record of female and calf pair.
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