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Short-term reactions of sperm whales ( Physeter macrocephalus) to whale-watching vessels in the Azores

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There is a great lack of information on the ffects of boat operations on sperm whales (Physeter macrocephalus), which is the target species of the recent whale-watching industry in the Archipelago of the Azores. During the 1998 Azorean whale-watching season, between 4 June and 23 September, observa- tions were carried-out from land-based lookouts and at sea from whale-watching boats to quantify short-term reactions of sperm whales to the pres- ence and manoeuvres of boats. Results from land-based observations did not indicate changes in the behaviour of sperm whales, either due to the presence of boats or when exposed to inappropriate boat manoeuvres (as designated by proposed Azorean legislation). From boat-based observations, change in the whale's speed and the presence of aerial displays were significantly more frequent when facing inappropriate boat manoeuvres. The presence of swimmers also led to a higher frequency of aerial displays by whales. In the presence of boats, mature females and immature individuals significantly increased their individual mean blow interval when accompanied by calves. Although some indications of disturbance were detected, we found no clear pattern of short-term reactions of sperm whales to whale-watching boats. It is strongly recommended that the activity is continuously monitored to assess its long-term effects, which generally remain unclear.
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Aquatic Mammals 2002, 28.3, 267–274
Short-term reactions of sperm whales ( Physeter macrocephalus)to
whale-watching vessels in the Azores
Sara Magalhães
1
,Rui Prieto
1
,Mónica A. Silva
1,2
,João Gonçalves
1
,
Manuel Afonso-Dias
3
,Ricardo S. Santos
1
1
Departamento de Oceanografia ePescas, Universidade dos Açores, Horta, PT9901-862, Portugal
2
Instituto de Conservação da Natureza, Rua Ferreira Lapa 29, 1150 Lisboa, Portugal
3
Faculdade de Ciências do Mar edoAmbiente, Universidade do Algarve, 8000 Faro, Portugal
Abstract
There is agreat lack of information on the e ects of
boat operations on sperm whales ( Physeter macro-
cephalus), which is the target species of the recent
whale-watching industry in the Archipelago of the
Azores. During the 1998 Azorean whale-watching
season, between 4June and 23 September, observa-
tions were carried-out from land-based lookouts
and at sea from whale-watching boats to quantify
short-term reactions of sperm whales to the pres-
ence and manoeuvres of boats. Results from land-
based observations did not indicate changes in the
behaviour of sperm whales, either due to the pres-
ence of boats or when exposed to inappropriate
boat manoeuvres (as designated by proposed
Azorean legislation). From boat-based observa-
tions, change in the whale’s speed and the presence
of aerial displays were significantly more frequent
when facing inappropriate boat manoeuvres. The
presence of swimmers also led to ahigher frequency
of aerial displays by whales. In the presence of
boats, mature females and immature individuals
significantly increased their individual mean blow
interval when accompanied by calves. Although
some indications of disturbance were detected, we
found no clear pattern of short-term reactions of
sperm whales to whale-watching boats. It is
strongly recommended that the activity is continu-
ously monitored to assess its long-term e ects,
which generally remain unclear.
Key words: boat-based observations, land-based
observations, Physeter macrocephalus,behaviour,
whale-watching, short-term reactions, Azores,
sperm whale.
Introduction
Cetaceans always have aroused human emotions
and scientific interest. With the current increase
in environmental awareness the whale-watching
tourism industry is growing worldwide. This ac-
tivity was recognized by the International Whaling
Commission as ‘. .. contributing largely to the
economy, education and to the furthering of scien-
tific knowledge of anumber of countries ...’(IWC,
1993). It is necessary that this activity is monitored,
to guarantee asustainable use of cetaceans as a
resource.
In the Azores Archipelago, whale-watching has
been occupying an increasingly important role at a
socio-economical level. The activity is growing
rapidly, having registered 100 clients in 1992, the
first year of operation, to approximately 7000
in 1998. In the waters around the Azorean archi-
pelago, located in the Northeast Atlantic (see
Fig. 1), 22 confirmed cetacean species have been
recorded (Reiner, 1990; Reiner et al., 1993; Steiner,
1995). The archipelago has avolcanic origin, which
results in the lack of acontinental shelf. These
reasons make the Azores aprivileged place for
watching oceanic cetacean species close to the shore
(Santos et al., 1995).
The sperm whale ( Physeter macrocephalus)isthe
main target species of the Azorean whale-watching
activity. The area south of Pico Island is one of the
most important places for this activity, in the same
way that formerly it was one of the most prosperous
Azorean sperm whaling grounds. The whale-
watching season starts in late April and lasts until
September, when appropriate climatic conditions
can be found. The whale-watching fleets operate
mainly with small inflatable boats powered with
out-board engines and depend on directions given,
by VHF radio, from land-based observers, who
locate the animals.
The sperm whale is the largest of the odontocete
cetaceans, displaying ahigh degree of sexual dimor-
phism. It spends about 75% of its time foraging, in
which it performs aseries of long and deep dives
(sometimes for about 40 min reaching 1000 m)
"2002 EAAM
searching for prey (mostly cephalopods). These
dives are interspersed with recovery periods of
about 10 min at the surface (Best, 1979; Clarke
et al., 1980; Papastavrou et al., 1989). When social-
izing or resting, the whales stay at or near the
surface for longer periods, almost immobile or
interacting with each other. Mature females typi-
cally form groups with calves and immature indi-
viduals and inhabit temperate to tropical waters.
Mature males are solitary and frequent colder
waters, occasionally visiting females in warmer
waters to breed (Best, 1979; Whitehead et al., 1991).
The Azores Archipelago is frequented by female
groups more often than by mature males (Gordon
&Steiner, 1992).
There is agreat lack of information on the e ects
of boat operations on sperm whales. We found
three studies on this topic, all conducted onboard;
two have been carried-out by McGibbon (1991) and
Gordon et al. (1992) in New Zealand, and another
by Eberhardt (1993) in Norway. All had as targets
male sperm whale populations. However, all are
still only available as unpublished reports. The
Gordon et al. (1992) study, which dierentiates
between resident and transient whales in the area,
described high variability in behaviour among indi-
viduals. Obvious reactions were noticed when the
whales were exposed to careless boat handling. The
study was carried-out onboard and therefore, could
not rule-out the e ects of the observation vessel on
the behaviour of the whales. No references were
found on land-based remote observations of sperm
whales.
The tourism activity is at an initial phase of
development in the Azorean Archipelago and there
is an increased need for scientific knowledge on the
interactions between whale-watching and cetacean
communities. This study was carried-out during the
formulation of the first regional management plans,
which included acode of conduct for the whale-
watchers in the vicinity of cetaceans. By then, the
operators were aware of this ethical code of con-
duct, which in part had been suggested by them.
This code of conduct was integrated in the Azorean
legislation that came into force in March 1999. The
aim of this study is to present apreliminary descrip-
tion of short-term (immediate) reactions of sperm
whales due to the presence of whale-watching
boats, in the light of the codes of conduct proposed
for legislation. It also discusses the two methods of
observation used (direct and remote) and their
utility for this topic.
Materials and Methods
Data collection
Land-based observations were carried-out from
two old whaling lookouts, one located in the south
of the Island of Pico (‘Vigia da Queimada’, at a
75 mheight) and the other southwest of the Island
of Faial (‘Vigia dos Capelinhos’, at a110 mheight)
from 4June to 23 September 1998, whenever
Figure 1. Map with three of the nine islands of the Azores Archipelago showing the location of the two land-based
lookouts.
268 S. Magalhães et al.
visibility and sea conditions allowed, between 07:30
and 21:00h (Fig. 1). Searching and tracking of
whales was made using 15x80 Steiner binoculars
with acompass mounted on tripods, performed by
two observers simultaneously. One of the observers
was an experienced lookout that worked in awhal-
ing company searching for sperm whales for 36
years. Whenever awhale or group was sighted,
information was annotated on data sheets and the
search proceeded. Only sperm whale sightings made
up to 10 nmi o shore were investigated (maximum
range for reliable observations).
Opportunistic boat-based observations were
carried-out between 3July and 15 September 1998.
One researcher joined whale-watching trips when-
ever possible and registered data on atape recorder.
For both methods, if agroup was seen to split, or
joined-up with another group during atrack, only
one of them was considered for details and regis-
tered as anew sighting (Best et al., 1995). If no boat
was in the vicinity of the whales, the new group to
be followed was randomly chosen. If aboat was
present, the group closer to the boat was followed.
For all sightings (from lookouts) and encounters
(at sea), information on group size, individual rela-
tive sizes, and group type was registered. One
observer registered the observations continuously.
Behavioural variables recorded for whales were
heading, speed, spatial arrangement (from look-
outs), swimming pattern (recorded as constant or
erratic, from at sea observations), diving pattern
(fluke-up or not), aerial displays (e.g., spy hop,
breaching, lob-tailing), and activity (behavioural
state, such as feeding or socializing/resting; see
IFAW, 1996).
Subsequently, behavioural analysis was based on
the presence/absence of changes in behavioural
variables (Martin &Bateson, 1993). Changes in
sperm whales behaviour were considered to occur
whenever one of the following was observed:
change in heading exceeded 30$ ,abrupt change in
swim speed, altered spatial arrangement in any way,
erratic swimming pattern, or adeep dive not pre-
ceded by afluke-up (adapted from IFAW, 1996).
For land-based observations, groups, were con-
sidered as aunit for statistical treatment (i.e., if a
change was detected in one individual it was con-
sidered to occur in the group). For boat-based
observations, the observer would do acontinuous
scan-sample of all individuals in agroup. Individ-
uals were treated as statistical units, either when
isolated or belonging to asame group.
Whale size was categorized in three classes: small
(ca.<6m), medium ( ca.7 to 12 m), and large
(ca.>13 m), with the first corresponding to calves,
the second to mature females and immature indi-
viduals, and the third to mature males (Best, 1968,
1969). In this study, three group types were desig-
nated according to their known social structure:
small and medium-sized whales formed mixed
groups, the large-sized whales constituted male
groups (usually lone individuals), and all sizes to-
gether formed mixed groups with visiting males.
For each observation, the presence or absence of
boats was noted. Boats were considered to be
‘present’ when the distance to the closest whale was
ca.<500 m. Number of boats, boat type, boat
manoeuvres (such as distance, speed, and angle),
and the number of swimmers (if present) were
registered. Two periods were distinguished during
boat-based data collection: approach to cetaceans
and manoeuvres during the period of encounter.
These were classified as ‘correct’ or ‘inappropriate’
in the light of the codes of conduct described in the
first Azorean legislation proposal. The proposed
policy stated that: the approach should be within an
angle of 60$from behind with aconstant speed at a
maximum of 4kts. During the encounter, the boat
should be positioned in an angle of 60$from
behind, keeping aminimum distance of 100 mfrom
the nearest whale (if feeding or socializing). The
swim speed of the whales should never be exceeded.
The encounters should not exceed 30 min and only
two boats were allowed within adistance of 400 m.
No swimming with whales should be allowed.
Ventilation patterns
Ventilations were recorded with achronometer to
measure the interval (in sec) between consecutive
blows. This only happened whenever the observer
could guarantee that only one individual was being
measured. Individual mean blow intervals (MBI)
and standard errors (SE) were calculated by
averaging the measured intervals. Only the last 20
blow intervals before fluking-up were considered
for statistical procedures. Blow intervals >50swere
excluded from the analysis; these typically represent
shallow dives during asurface sequence (Gordon &
Steiner, 1992). The ventilation pattern of small
whales was not analysed, due to the low sample
size, since priority was given to medium-sized
whales. Dierences between ventilation data col-
lected from both methods of observation were
investigated.
Statistical procedures
Because the hypothesis of normality and homogen-
eity of variance of the behavioural data collected
was rejected, non-parametric statistics were used for
analysis. Moreover, independence of events could
not be assured. The Fisher Exact Test was used in
the analysis of discrete data (presence or absence of
changes in behaviour) in small samples and when
dealing with boat manoeuvres (correct or inappro-
priate) (Martin &Bateson, 1993).
269Short-term reactions of sperm whales to whale-watching vessels
For land-based observations, presence of changes
in behaviour and the ventilation patterns were
compared in the presence and absence of boats. For
both methods of observation, and when boats
were present, changes in behaviour were compared
between correct and inappropriate boat ma-
noeuvres. Although the hypothesis of normality
(Kolmogorov-Smirnov Test) was accepted for ven-
tilation data, there was no homogeneity of variance
in the sample (Levene’s Test). Moreover, the non-
assurance of independence of events and asmall
sample size in some cases makes the use of non-
parametric statistics more appropriate. Mann-
Whitney UTest was used to investigate dierences
in ventilation patterns.
The level of significance used in this study for
rejection of all null hypotheses was P " 0.05. Stat-
istical procedures followed Zar (1996) and data
were analysed using the software Statistica for
Windows
"
version 5.5 (StatSoft, Inc., 1999).
Results
Land-based observations
An overall observation e ort of 187.5 hwas con-
ducted on 39 dierent days, of which 84.5% was
south of Pico Island. Atotal of 216 sightings were
recorded, comprehending nine dierent cetacean
species. Sperm whales were sighted 69 times, of
which 64 were up to 10 nmi o shore and are
considered here for statistical procedures. Atotal of
49 sperm whale sightings comprehended isolated
individuals and the remaining 15 comprised groups.
The groups averaged 3.1 (#0.3 SE) whales per
group, with amaximum of five. Of the group types
observed, 34 (53%) were mixed groups, 16 (25%)
were males, and 14 (22%) remained undetermined.
No mixed groups with visiting males were recorded.
Calves were registered on 14 occasions, always
included in mixed groups. For 43 (67%) of the
sightings, sperm whales were reported in feeding
activities and for 3(5%) in socializing/resting. In the
remaining 18 (28%) occasions, activity type was not
possible to determine.
Whale-watching boats were present in 39 (61%)
of the 64 sperm whale sightings. No change in
apparent activity, such as feeding and socializing/
resting was ever registered, despite the presence of
whale-watching boats. Change of heading, spatial
arrangement, diving pattern, and frequency of
aerial displays was greater in the presence of boats.
Changes in swim speed occurred more often in the
absence of boats. However, none of these dier-
ences were statistically significant (Fisher Exact
Test, n=64; heading: P=0.489, speed: P=0.161,
spatial arrangement: P=0.489, swimming pattern:
P=0.311, aerial displays: P=0.664, Fig. 2).
Boats entirely respected the regulations proposed
in 18 (46%) of the encounters. Approach was in-
appropriate on 10 (26%) occasions, and ma-
noeuvres during encounters were inappropriate
on 18 (46%) occasions. The angle was the most
violated rule observed during approaches (9%,
n=6). Violating angle and distance simultaneously
were the most frequently observed inappropriate
manoeuvres during encounters (12.5%, n=8). There
were no significant e ects of inappropriate boat
handling manoeuvres on any of the behavioural
patterns analysed (Table 1).
Boat-based observations
In 25 days of fieldwork, 106.8 hwas spent at sea. A
total of 107 encounters involved nine dierent
cetacean species; 40 were sperm whales and investi-
gated herein. During these encounters, atotal of 80
individuals was observed, 18 of which were isolated.
Mean group size of the 22 groups observed was 3.1
(#0.3 SE), with amaximum of seven individuals.
Figure 2. Frequency of changes of the behavioral patterns of sperm whales in the presence and absence of boats
(total n=64). Results from land-based observations.
270 S. Magalhães et al.
On four occasions, all size categories were observed
together, with mature males visiting mixed groups.
The remaining three records of large whales com-
prised lone individuals. The presence of calves was
registered on 12 occasions. Feeding was the main
activity observed (55%, n=22), while socializing/
resting was reported in 6(15%) of the observations,
and on 12 (30%) occasions the activity was not
classified.
Only asingle whale-watching boat (with the
observer onboard) was present on 75% of occasions
(n=40), with amean of 1.6 (#0.1 SE) boats per
encounter, and amaximum of six. In 16 (40%) of
the encounters, boats entirely respected the regula-
tions proposed. The angle was the most commonly
disrespected rule of approach (6 of 9, 67%). Simul-
taneously, inappropriate manoeuvres were the
mostly observed during encounters (5 of 17, 29%).
When swimmers were put into the water the boat
would position ahead of the whale and drop the
swimmers in their path. In the nine occasions
observed, swimmers were equipped with snorkeling
gear. Of these, five were with asingle swimmer and
amaximum of four swimmers was seen once.
No change in feeding or socializing/resting was
ever observed. The behaviour of the 80 individuals
observed was analysed. For each test performed,
when n<80the behaviour was undetermined in the
remaining occasions. It was verified that changes in
swim speed and the presence of aerial displays were
significantly more frequent when exposed to in-
appropriate boat manoeuvres (changes in speed:
correct manoeuvres n=3,inappropriate ma-
noeuvres n=19) (Fisher Exact Test: n=74, P=0.00)
(presence of aerial displays: correct manoeuvres
n=2,inappropriate manoeuvres n=20) (Fisher
Exact Test: n=74, P=0.00). The frequency of aerial
displays was significantly higher when swimmers
were in the water (frequency of aerial displays:
absence of swimmers n=9,presence of swimmers
n=13) (Fisher Exact Test: n=80, P=0.00). No
statistically significant changes were detected in any
of the other parameters analysed, such as heading,
swimming pattern, or diving pattern due to the
eect of boat manoeuvring or the presence of
swimmers (see Table 1).
Ventilation patterns
Atotal of 34 sperm whales ventilation cycles was
considered here. No dierences were found in the
medium-sized whale’s MBI without calves and in
the presence of boats between land-based
(MBI=13.6 s, #0.7 SE, n=7)and boat-based ob-
servations (MBI=14.0 s, #1.3 SE, n=7). Subse-
quently, ventilation data were pooled from both
methods when boats were present and compared
with the ‘control’ sample when boats were absent
(observed from the lookouts only).
No statistically significant dierences were found
in MBI between medium-sized whales (13.9 s,
#2.8 SE, n=28) and large whales (18.7 s,
#3.3 SE, n=6).
The presence of calves did not cause asignificant
eect on the MBI of medium-sized whales (ac-
companied by calves: MBI=15.9 s, #1.6 SE, n=4;
not accompanied by calves: MBI=13.5 s, #0.5 SE,
n=24). No significant dierences were found be-
tween the MBI of medium-sized whales when boats
were present (MBI=14.4 s, #0.7 SE, n=17) or
absent (MBI=13.0 s, #0.8 SE, n=11). However,
when boats were present, medium-sized whales
showed asignificantly higher MBI when ac-
companied by calves (with calves MBI=17.3 s,
Table 1. Fisher Exact Tests statistical significance of the e ect of boat manoeuvring (during approach and encounter) and
of the presence of swimmers on several sperm whales behavioural parameters analysed. Results from land-based and
sea-based observations.
Method Behaviour
Approach Encounter Swimmers
nPn PnP
Land Heading 37 0.376 38 0.541 ——
Speed 37 0.730 38 0.526 ——
Spatial arrangement 60.500 50.700 ——
Diving pattern 33 0.257 36 0.470 ——
Aerial displays 37 0.780 38 0.730 ——
Sea Heading 69 0.546 63 0.185 69 0.150
Speed 80 0.187 74 0.000* 80 0.066
Swimming pattern 76 0.596 48 0.610 76 0.174
Diving pattern 51 0.114 48 0.519 51 0.530
Aerial displays 80 0.187 74 0.000* 80 0.000*
*Significant dierence at P "0.05.
271Short-term reactions of sperm whales to whale-watching vessels
#1.2 SE, n=14; without calves MBI=13.8 s,
#0.7 SE, n=3)(U
14,3
=5.000, P<0.05).
No statistically significant dierences were found
between the MBI of large-sized individuals when
boats were present (MBI=20.5 sec, #4.9 SE, n=4)
or absent (MBI=15.1 sec, #0.8 SE, n=2).
Discussion
Methods
Much of the behaviour of sperm whales is veiled to
observers above the water surface, especially when
whales are foraging. In addition, the long range of
most land-based observations means that, it is most
likely that individuals are not seen when they are
just below the surface. Moreover, the number of
calves can be underestimated (Whitehead, 1996).
Despite this, land-based observations give abetter
understanding of group behaviour than boat-based
observations. The most striking advantage of land-
based observations, which has not been reported
before for sperm whales, is that it allows the
collection of information on the undisturbed behav-
iour of whales. It also makes possible the collection
of information before, during, and after boat en-
counters. In addition, it does not introduce new
potential sources of disturbance to the whales.
Conversely, the proximity of boat-based observa-
tions allows the collection of more detailed in-
formation on individuals, particularly calves. Fur-
thermore, it provides the chance of making photo-
identification and acoustic studies. Opportunistic
observations onboard whale-watching vessels that
are near whales anyway should be made. The
disadvantages of this method are that it provides
information on the behaviour of potentially dis-
turbed whales and it is dicult to evaluate the level
of disturbance imposed by the presence of the boat
itself.
For the purposes outlined here, we suggest that
the use of remote observations is most valuable,
since it allows the comparison of the natural behav-
iour of an animal with behaviour under dierent
sources of possible disturbance. The use of athe-
odolite allied with innovative geomatic techniques,
would allow the improvement of the accuracy in the
geographic positioning and distance assessment.
Behaviour
Feeding was the most common activity observed in
sperm whales, as verified by Gordon &Steiner
(1992), in this area. In fact, the mean group size
observed in this study (3.1 individuals) was within
the values reported by Whitehead &Arnbom (1987)
for foraging sperm whales, seen at the surface in
small sets of one to four individuals. The predomi-
nance of feeding over other activities, and the
frequency of observed calves, suggests that this area
is an important feeding ground for female sperm
whales and their o spring. Mutual caring for calves
by females against predators and cooperation in the
location and capturing of food are the two main
factors for the evolution of gregariousness of the
species (Best, 1979).
Changes in the activity apparently performed by
sperm whales, such as feeding or socializing/resting,
due to the presence of boats were not detected in
this study.
From the analysis of land-based observations, we
found no significant evidence of disruption in sperm
whales behavioural patterns due to the simple
presence of boats, although there seemed to be a
tendency towards disturbance (Fig. 2). Aland-
based study of killer whales ( Orcinus orca)ident-
ified an increase in swim speed (but not change in
course) as acommon response to the presence of
boats (Kruse, 1991). Regarding boat manoeuvring,
results from land-based observations did not point
towards significant dierences in behavioural
changes when exposed to correct and inappropriate
boat manoeuvres, despite the high rate of inappro-
priate boat handling observed. However, from
boat-based observations we detected significantly
higher changes in speed and in the frequency of
aerial displays of individuals when exposed to in-
appropriate boat manoeuvres. Gordon et al.(1992),
in aboat-based study in New Zealand, found that
in 10% of boat encounters, sperm whales were
disturbed when facing careless boat handlers that
did not respect the local guidelines about minimum
distance and approach. Whale reactions included
no fluking-up before diving, abrupt heading
changes, and higher frequency of aerial displays. In
our study, the percentage of inappropriate boat
manoeuvring verified by both methods of obser-
vation used was similar. Dierences in the results
found between the two methods could be due to a
higher sensitivity of in situ observations, through
the detection of smaller changes in behaviour, but
at the cost of introducing apossibly new source of
disturbance.
The presence of swimmers in the water led to a
significant increase in the aerial displays performed
by sperm whales, but it did not a ect any of the
other behavioural parameters analysed. However,
these observations were based on asmall sample
size (n=13). In astudy in New Zealand, Bejder
et al.(1999) did not detect significant changes in the
behaviour of Hector dolphins ( Cephalorhynchus
hectori)due to the presence of swimmers. These
authors suggested that this evidence could be an-
swered by the easy avoidance of swimmers by
dolphins and concluded that dolphins avoided more
pronouncedly the presence of boats than the swim-
mers themselves, which does not apply in the case
of sperm whales. It is also possible that swimmers
272 S. Magalhães et al.
were not seen as athreat by sperm whales. Alarger
sample size of observations would allow clearer
conclusions.
The fact that in this study immediate distur-
bances were not clearly detected does not imply a
lack of responses. Further research to increase
sample size and observation time is advisable, to
assess the e ects of whale-watching activities at the
population level.
Ventilation patterns
The ventilation results in this study cannot be
directly compared to others of the same species (or
dierent species) since they employ adi erent stat-
istical treatment. Herein, the individual MBI is the
unit compared among individuals, instead of aset
of blows per individual classes. Individual MBI
prevents the statistical error known by pseudo-
replication, which happens when treatments are not
replicated (though samples may be) or replicates are
not statistically independent (Hulbert, 1984). More-
over, known studies of sperm whale ventilation
were conducted onboard vessels that could not
discard the e ect of their own presence in the
blowing behaviour of the whales.
Blow intervals change significantly with order
during asurfacing sequence, the last blows being
higher and more likely to be seen than the first ones,
which occur immediately after surfacing (Gordon &
Steiner, 1992). For this reason, only the last twenty
blows of aset before fluke-up per individual were
investigated.
The fact that no statistically significant dier-
ences between the MBI of medium-sized and large
whales were found, could be due to the very low
sample size of large males (n=6). Gordon &Steiner
(1992) studied ventilation and dive patterns of
sperm whales and found ahigher MBI for mature
males (15.9 s) (after excluding blow intervals >50s,
which accounted for much of the variance) than for
females (12.4 s).
Some authors suggested that blow rates could be
useful in characterizing dierent behavioural states
and, therefore, to assess the eects of disturbance
on whales (Würsig et al., 1986). However, others
( e.g., Watkins, 1986; Watkins et al., 1984) argued
that the use of these parameters as afeasible
indicator of whales’ reactions is questionable due to
the natural and frequent changes in cetacean behav-
iour and blow frequency. The results presented here
point toward longer blow intervals as aresponse of
both mature females and immature individuals in
the presence of calves and boats, although these
were not significant. Moreover, it also indicated
that this class of individuals, when boats were in the
vicinity, showed asignificantly higher MBI if ac-
companied by calves. Previous studies showed that
females seem to show alloparental care, by reducing
their dive synchrony when calves are present, and
thus likely increase calf protection while permitting
greater foraging freedom for mothers (Whitehead,
1996). It is then possible that the occurrence of
calves by itself already interferes in adults diving
physiology. In addition, the presence of whale-
watching boats could amplify existing disturbances
with biological significance. Conversely, boats did
not seem to a ect the ventilation pattern of mature
males, although the small sample size did not allow
clear conclusions.
Because no clear evidence of disturbance to the
sperm whale population occurred due to the expo-
sure to whale-watching boats, it did not seem
necessary to suggest modifications to the actual
Azorean legislation, which was enforced later in
March 1999, or to prevent the growth of the
whale-watching industry in the region. However,
reinforcement is highly recommended facing the
percentage of inappropriate boat handling ob-
served. It is necessary to keep in mind that this
work is apreliminary approach to this issue and to
take in account that short-term studies might not
detect long-term factors that could lead to signifi-
cant biological and ecological consequences. Some
of them include population distribution and nega-
tive e ects on reproductive rate. In the Azores, the
sperm whale possibly uses the area to mate and bear
calves (Evans, 1987) and the potential disturbance
to sperm whale reproduction (mating and/or calve
survival) is of further concern, given the currently
accepted population parameters for the species. The
IWC (1982) suggested amaximum potential rate of
increase of less than 1% per year for sperm whales.
Future studies should focus on the carrying capac-
ity of cetacean populations in this area and on the
validation of rules proposed by legislation. The
activity should be continuously monitored to assure
constant revision of management plans and there-
fore, guarantee asustainable use of cetaceans in the
area.
Acknowledgments
We acknowledge the enterprises Espaço Talassa,
Norberto Diver and Aquaçores for their support in
the field. Mr. João ‘Vigia’ Gonçalves and Mr.
Sidónio Gonçalves (from Espaço Talassa) gave
invaluable support in the lookouts. We are very
grateful for the valuable input of Pedro Afonso in
behavioural issues. This work was partly funded by
the Azorean Regional Tourism Directorate and by
the EU LIFE Project ‘Integrated Management of
Coastal and Marine Areas in the Azores’ (B4–3200/
98/509). We thank Carlos Guerra, President of the
Institute for Nature Conservation (Portugal) for
allowing Mónica A. Silva to participate in this
study. Arevision by Mark Bolton, Peter Wirtz and
273Short-term reactions of sperm whales to whale-watching vessels
two anonymous reviewers greatly improved this
manuscript.
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Social organization in sperm whales, Physeter macrocephalus Behaviour of Marine Mammals
  • P B Best
Best, P. B. (1979) Social organization in sperm whales, Physeter macrocephalus. In: H. E. Winn &B.L.O lla (eds.) Behaviour of Marine Mammals. Volume 3, pp. 227–289. Plenum Press, New York.
The sperm whale ( Physeter catodon) o ff the west coast of South Africa—2. Reproduction in the female. South African Department of Industries
  • P B Best
Best, P. B. (1968) The sperm whale ( Physeter catodon) o ff the west coast of South Africa—2. Reproduction in the female. South African Department of Industries, Division of Sea Fisheries Investigational Report 66, 32 pp.
Records of marine mammals of the Azorean islands
  • F Reiner
Reiner, F. (1990) Records of marine mammals of the Azorean islands. Garcia da Orta, Séries Zoológicas 15, 21–36.
Pregnancy rates of sperm whales in the Southeast Pacific between 1959 and 1962 and ac omparison with those from Paita, Peru, between
  • R Clarke
  • L A Aguayo
Clarke, R., Aguayo, L. A. &P aliza, O. (1980) Pregnancy rates of sperm whales in the Southeast Pacific between 1959 and 1962 and ac omparison with those from Paita, Peru, between 1975 and 1977. Report of the International Whaling Commission (Special Issue) 2, 151–158.
Behaviour of gray whales summering near St
  • B Würsig
  • R S Wells
Würsig, B., Wells, R. S. &C roll, D. A. (1986) Behaviour of gray whales summering near St. Lawrence Island, Bering Sea. Canadian Journal of Zoology 64, 611–21.
Report of the international workshop on special aspects of watching sperm whales
IFAW (1996) Report of the international workshop on special aspects of watching sperm whales, Roseau, Commonwealth of Dominica. IFAW, Crowborough, UK.