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The decline of common bottlenose dolphin (Tursiops truncatus) presence and group size in Montenegrin waters

Abstract and Figures

The Mediterranean subpopulation of common bottlenose dolphins (Tursiops truncatus) is classed as vulnerable with a decreasing population trend. Yet, research effort in the Mediterranean varies with relatively little being known of the Southern Adriatic Sea's bottlenose dolphins, which face increasing numbers of anthropogenic threats, mainly marine traffic, tourism, fishing and seismic activity. To investigate trends in bottlenose dolphin presence, group size and sub-adult presence in Montenegrin waters, 576 land and boat surveys were conducted from September 2016 to August 2020. Chi-squared tests showed a significant decline in bottlenose dolphin presence over the four years. Changes in group size over the four-year period were also assessed using Chi-squared tests, and results showed that in Year 1 (September 2016 to August 2017) significantly more medium (3-4 individuals) and large (over 5 individuals) groups were observed than expected. Whereas, in the following three years more small groups were observed (1-2 individuals). Neither bottlenose dolphin presence nor group size was found to be associated with season. Multinomial logistic regression was used to assess the relationship of sub-adult presence with year, season and group size. Sub-adults were most likely to be present in the summer (June, July and August) and when group size was large. Montenegrin waters are of significant importance to the wider Adriatic. Therefore, urgent action is required to identify the cause of the declining trends and to protect Montenegro's bottlenose dolphin population from anthropogenic pressures. A dedicated management strategy must be quickly and effectively implemented, while continuous study is required to monitor and assess trends moving forward.
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The decline of common bottlenose dolphin
(Tursiops truncatus) presence and group size in
Montenegrin waters.
Sian McGuinness
DMAD-Marine Mammals Research
Association
Antalya, Turkey
siankm@hotmail.com
Laura Rudd
DMAD-Marine Mammals Research
Association
Antalya, Turkey
laurarudd@dmad.org.tr
Evie White
DMAD-Marine Mammals Research
Association
Antalya, Turkey
eviewhitee@live.com
Selina Brouwer
DMAD-Marine Mammals Research
Association
Antalya, Turkey
selina@dmad.org.tr
Tim Awbery
DMAD-Marine Mammals Research
Association
Antalya, Turkey
tawbery@dmad.org.tr
Aylin Akkaya
DMAD-Marine Mammals Research
Association
Antalya, Turkey
aakkaya@dmad.org.tr
Abstract The Mediterranean subpopulation of common
bottlenose dolphins (Tursiops truncatus) is classed as vulnerable
with a decreasing population trend. Yet, research effort in the
Mediterranean varies with relatively little being known of the
Southern Adriatic Sea’s bottlenose dolphins, which face
increasing numbers of anthropogenic threats, mainly marine
traffic, tourism, fishing and seismic activity. To investigate
trends in bottlenose dolphin presence, group size and sub-adult
presence in Montenegrin waters, 576 land and boat surveys
were conducted from September 2016 to August 2020. Chi-
squared tests showed a significant decline in bottlenose dolphin
presence over the four years. Changes in group size over the
four-year period were also assessed using Chi-squared tests, and
results showed that in Year 1 (September 2016 to August 2017)
significantly more medium (3-4 individuals) and large (over 5
individuals) groups were observed than expected. Whereas, in
the following three years more small groups were observed (1-2
individuals). Neither bottlenose dolphin presence nor group size
was found to be associated with season. Multinomial logistic
regression was used to assess the relationship of sub-adult
presence with year, season and group size. Sub-adults were most
likely to be present in the summer (June, July and August) and
when group size was large. Montenegrin waters are of
significant importance to the wider Adriatic. Therefore, urgent
action is required to identify the cause of the declining trends
and to protect Montenegro’s bottlenose dolphin population
from anthropogenic pressures. A dedicated management
strategy must be quickly and effectively implemented, while
continuous study is required to monitor and assess trends
moving forward.
Keywords Southern Adriatic Sea, dolphins, conservation,
cetaceans, group size, population decline.
I. INTRODUCTION
The common bottlenose dolphin (Tursiops truncatus,
hereafter bottlenose dolphin) is a pan-oceanic species that
inhabits both coastal and offshore environments. As a key
indicator of ecosystem health, the bottlenose dolphin provides
a common metric for evaluating anthropogenic pressures [1].
Despite being the most frequent cetacean found over the
Mediterranean Sea continental shelf [2] the Mediterranean
subpopulation of bottlenose dolphins is listed as vulnerable on
the IUCN Red List of Threatened Species due to an
intensification of human activity in the region [3].
The Adriatic Sea comprises 5% of the Mediterranean Sea
and has a bottlenose dolphin population of around 5,700
individuals [4]–[6]. In the Northern Adriatic Sea, historical
data show that bottlenose dolphin abundance has been
decreasing for decades [7], with more recent studies
suggesting a continuation of this trend [8], [9]. A variety of
anthropogenic threats have been attributed to the decline,
including systematic culling campaigns which continued with
monetary rewards until 1960 [3], [7], overfishing, habitat
degradation, and the toxic effect of xenobiotic chemicals [5].
These combined pressures are believed to have caused the
short-beaked common dolphin (Delphinus delphis) to
disappear from the region [7], [10].
Contrastingly, in the Southern Adriatic bottlenose dolphin
peer-reviewed literature has only been published in the last
five years, and population trends have not been assessed [9],
[11]–[13]. Data suggests a constant presence of bottlenose
dolphins within the Bay of Kotor (Boka Kotorska), located in
the north of Montenegro. It is thought that the bay is a
temporary residence used for feeding and foraging [9], [11].
Overall, this four-year study of bottlenose dolphins in
Montenegro is the longest ongoing assessment in Southern
Adriatic waters.
In Montenegro, marine traffic, tourism, fishing practices
and seismic activity have been identified as the main
anthropogenic threats affecting bottlenose dolphins and the
marine environment [14], [15]. Negative impacts from
boating and shipping have been documented in the Adriatic
[8], [13], [16], while the rapid growth of Montenegro’s
tourism industry has resulted in coastal destruction, increased
numbers of luxury and speed boats, and higher levels of
pollution [14]. Although Montenegrin fish landings are
relatively low compared to surrounding Adriatic countries
[17], unsustainable practices of artisanal fishing and trawling
can alter habitats and have negative consequences on prey
availability [5], [18]. Finally, despite the Southern Adriatic
being acknowledged as an important cetacean habitat, two
seismic surveys took place in in late 2018 and early 2019 [19],
with further exploratory drilling occurring in spring 2021.
In the Adriatic Sea, marine protection is unevenly
distributed across political boundaries, with the majority
established in the waters of European Union countries. Until
this year, Montenegro had no formal protection regarding
bottlenose dolphins or its marine and coastal environment
[20]. However, in April 2021, the country established its first
Marine Protected Area (MPA), Platamuni, in its north western
coastal waters [21].
This project aims to fill the gap of unassessed bottlenose
dolphin presence trends in the Southern Adriatic Sea. The
objectives are to assess whether bottlenose dolphin presence
and group size has changed with year and season, and whether
sub-adult presence is associated with year, season and group
size. The data collected will provide baseline information for
future monitoring and help inform the implementation of
effective conservation and management plans.
II. MATERIALS AND METHODS
A. Data Collection
From September 2016 to August 2020, four surveys
(three land and one boat) were attempted each week. Survey
dates were divided into four years (Table I). Eight land survey
stations were pre-determined to optimise the field of view and
evenly distribute effort along Montenegro’s 293 km coastline
[22] (Fig. 1). Boat routes were established to ensure that both
coastal and offshore waters were surveyed, meaning depths
ranged from less than 1 metre to over 1000 metres and
included the semi-enclosed Bay of Kotor (Fig. 1). Surveys
took place in all seasons, but only in favourable conditions.
Seasons were defined as autumn (September, October and
November), winter (December, January and February), spring
(March, April and May) and summer (June, July and August).
Favourable conditions were fair weather, no precipitation,
good visibility and a Beaufort Sea State of three or less.
Surveys either began with sunrise or ended with sunset and
had a minimum duration of three hours.
Surveys were conducted by at least three researchers,
equipped with 7x50 binoculars to continuously scan the sea
surface. Bottlenose dolphins were classed as present during a
survey when at least one individual was sighted. Land surveys
utilised a Sokkia DT5A Electronic Theodolite to record
horizontal and vertical angles of dolphin groups relative to the
station. Pythagoras software (version 1.2) converted angles
into geographic coordinates. A variety of research vessels with
both inboard and outboard engines were used for boat surveys.
However, speed was kept relatively constant with an average
of four to five knots. Global Navigational Satellite System
(GNSS) tracking devices recorded the geographic position of
the research vessel every two minutes and Logger software
(version 2010) stored the data. Truer coordinates of sightings
Year Inclusive survey dates
1 15th September 2016 – 31st August 2017
2 1st September 2017 – 31st August 2018
3 1st September 2018 – 31st August 2019
4 1st September 2019 – 31st August 2020
TABLE I. DEFINITIONS OF THE CATEGORY YEAR.
Fig. 1. The eight survey stations located along Montenegro’s coastline and the effective survey area covered by land and boat surveys. Bathymetry
contours are shown in 100 metre depth intervals.
were determined using the nearest GNSS location and an
estimated distance and bearing of the dolphin group.
Sighted dolphin data were collected by instantaneous
focal group scan sampling in five-minute fixed time intervals.
Focal groups were defined as aggregations of dolphins in
clearly visible constellations less than 100 metres away from
the next individual [15]. Species, group size (minimum and
maximum estimates) and sub-adult presence were recorded.
Group size was determined by taking the largest minimum
group size observed across all data collected for the same focal
group. Group size was later categorised as small (1-2
individuals), medium (3-4 individuals), and large (5+
individuals). Sub-adults were identified as no more than two
thirds the body length of a nearby individual [23], and the
number was given as a best estimate. The next sighting was
classed as a new group once twenty minutes had passed
following the most recent sighting of a focal group. Research
vessels observed focal groups for no more than thirty minutes
to minimise stress, and kept speed relatively constant (< 5
knots).
B. Statistical Analysis
Chi-squared goodness of fit tests (χ2) were used to assess
the associations of bottlenose dolphin presence and group size
with year and season. Meanwhile, multinomial logistic
regression modelled the relationship of sub-adult presence
with year, season and group size. Rstudio (version 1.3.1073)
was used to conduct all analysis.
III. RESULTS
Over the four years, 576 surveys were conducted covering
c. 4,487 km² of Montenegro’s coastal and offshore waters. The
surveys had a mean duration of 3 hours and 29 minutes. The
number of surveys conducted each year and season varied due
to logistical and financial constraints. In Year 1, 175 surveys
were conducted, while there were 165 in Year 2, 142 in Year
3 and 94 in Year 4. Survey number was lower in Year 4 as
Montenegro implemented travel restrictions and went into
lockdown to combat the coronavirus pandemic. Overall, 151
surveys were held in the autumn, 116 in the winter, 139 in the
spring and 170 in the summer.
Sightings were recorded during 185 surveys (32%). Chi-
squared analysis found that bottlenose dolphin presence was
significantly associated with the year (χ2 = 13.6, df = 3, p <
0.05), but not season (χ2 = 0.944, df = 3, p > 0.05). Observed
bottlenose dolphin presence was higher than expected in Year
1 and 2 but lower than expected in Year 3 and 4 (Fig. 2).
During the study, 298 bottlenose dolphin groups were
sighted ranging in size from 1 to 16 individuals with a mean
and median of 3 and a mode of 2. Group size was significantly
associated with year (χ2 = 19.5, df = 6, p < 0.05) but not season
(χ2 = 5.99, df = 6, p > 0. 5). Year 1 had larger group sizes than
expected, while Year 2, 3 and 4 showed smaller group sizes
than expected (Fig. 3). The difference in the observed number
of small group sizes peaked in Year 4.
Fig. 3. The observed and expected values for small (S), medium (M) and large (L) dolphin group size for Year 1, Year 2, Year 3, and Year 4. Black
columns are observed values and white columns are expected values.
Fig. 2. The observed and expected values for bottlenose dolphin
presence per year and season. Black columns are observed values and
white columns are expected values.
Sub-adults were present in 109 of the groups sighted.
Multinomial logistic regression showed that sub-adult
presence was significantly affected by season and group size
but not year. Therefore, year was removed from the model.
Final analysis found that sub-adults were more likely to be
present in the summer followed by the autumn (p < 0.05), with
sub-adult presence in a group being 3.26 and 2.83 times more
likely in summer and autumn, respectively, than in winter (p
< 0.05). Spring did not significantly affect sub-adult presence
(p > 0.05). In addition, results showed that large groups had
the highest odds of sub-adult presence followed by medium
groups. Sub-adults were 18.54 times more likely to be present
in a large group than in a small group, and 5.64 times more
likely to be present in a medium group that a small group (p <
0.05) The logistic regression model classification prediction
accuracy was 77%.
IV. DISCUSSION
The presence of bottlenose dolphins significantly
decreased in the research area between September 2016 and
August 2020. The finding is similar to other areas of the
Adriatic, where increasing anthropogenic impacts, such as
nautical tourism and prey reduction, are thought to be
responsible [8], [24]. Anthropogenic pressures which may
have contributed to the decline in Montenegro include the
growing tourism industry, marine traffic, pollution, fishing
practices and oil and gas exploration [13], [14], [19]. It is
noteworthy that seismic surveys were conducted off the
Montenegrin coast in December 2018 and February 2019 to
explore natural gas potential [19]. As shown in Fig 2,
bottlenose dolphin sightings were significantly lower in Year
3 (September 2018 to August 2019) and Year 4 (September
2019 to August 2020) after the events took place. However,
causality has not been shown. Therefore, a threats assessment
of the research area is required to establish the contribution of
human presence to the decline of bottlenose dolphin presence
within the region. Natural variations in bottlenose dolphin
presence should also be considered [6], [24].
In Montenegro, bottlenose dolphin presence was not found
to be significantly associated with season, which contradicts
other studies in the Adriatic Sea where anthropogenic and
environmental factors are understood to cause seasonal
changes [16], [24], [25]. For instance, off the north-eastern
coast of Italy, bottlenose dolphin distribution varies with
seasonal forcing, likely due to hydrological changes shifting
prey distribution [25]. Whilst, in Kvarnerić, Croatia, sightings
have been linked to seasonal variations in marine traffic, with
the average monthly sighting rate reducing in the summer
when boat traffic and tourism intensify [16], [26]. Tourism is
a growing industry in Montenegro [14], and non-targeted
tourism vessels have been identified as a possible threat to
dolphin energy intake, with repeated exposure potentially
causing long-term negative effects [13]. Therefore,
monitoring bottlenose dolphin presence in Montenegrin
waters must continue to ensure that any future signs of
seasonal displacement are identified, and conservation
measures are appropriately implemented.
Mean bottlenose dolphin group size in Montenegro was
found to be smaller than in other Adriatic regions [23], [24],
[27], [28]. However, it should be taken into consideration that
group size calculation methodology can differ between studies
[28]. Group size has been linked to predation risk and
behavioural choices [17], [29], [30]. In the Adriatic, there is a
lack of evidence to suggest that bottlenose dolphins suffer
from shark predation [23], [24]. Whereas, analysis on
bottlenose dolphin behaviour in Montenegrin waters showed
that travelling is the most frequently displayed behaviour [12].
Groups have been found to be significantly smaller when
travelling than when socialising or feeding [31]. Therefore,
our results support the theory that Montenegrin waters are
used as a travel corridor connecting feeding sites elsewhere in
the Adriatic Sea [12].
In addition, bottlenose dolphin group size decreased over
the four-year study period. Bottlenose dolphins live in fusion-
fission societies, with individuals leaving or joining groups
depending on the costs and benefits associated with the social
structure and the surrounding environment [8], [32]. Smaller,
fragmented groups are at higher risk from stochastic processes
due to a reduction in genetic diversity potentially leading to
local and regional extinctions [7], [33].
Sub-adult presence was associated with season in
Montenegro. In line with other studies in the Adriatic, summer
had the highest likelihood of a sighting [8], [23], potentially
due to an increase in prey availability [25], [34]. However,
sub-adults were least likely to be observed in winter. Winter
is the season with the lowest sea surface temperatures [35].
Sub-adults thermoregulate, but have less blubber than adults,
which may result in water temperature acting as a thermal
barrier and limiting movement [36], [37]. Additionally, sub-
adults were most likely to be present in large groups. Again,
this finding is aligned with published literature from both the
Adriatic [23], [24] and worldwide [38], [39]. Larger groups
are thought to be beneficial due to alloparental care enabling
mothers to spend more time foraging, ensuring that energy
levels are kept high for lactation. Alloparental care also
enhances protection and knowledge transfer to sub-adults
[40].
V. CONCLUSION
The evaluation of presence, group size and sub-adult
presence gives valuable insight into the vulnerability and
viability of Montenegro’s bottlenose dolphin population [7],
[41]. The decreasing presence and group size of the Southern
Adriatic population must be continually monitored to assess
the effect of human impacts, ranging from unsustainable
tourism practices to marine pollution, habitat destruction and
recent oil and gas explorations. Furthermore, even though sub-
adult presence has not significantly changed since September
2016, a persistent decrease in group size may reduce the
alloparental care available and in turn negatively affect the
population status.
Montenegro’s waters are of significant importance to the
wider Adriatic bottlenose dolphin population [6]. Since
regions of the Adriatic have experienced declining population
trends for decades and life history characteristics result in slow
population recovery [42], the decrease in presence and group
size of Montenegro’s bottlenose dolphin population requires
urgent action. It is essential that the species does not become
regionally extinct in the Adriatic Sea, as in the case of the
common dolphin (Delphinus delphis). All factors impacting
bottlenose dolphins must be considered when creating
protective measures as specific causes are difficult to pinpoint
without extensive research. The MPA Platamuni must be
effectively managed and further sites established in
Montenegrin waters. Additionally, continuous study is
essential for monitoring the success of implemented
protective measures and the population trend moving forward.
ACKNOWLEDGMENT
Thanks go to the Environmental Protection Agency of
Montenegro and Montenegro’s Ministry of Tourism and
Environmental Protection for their constant support and for
granting the required study permits. The authors are incredibly
grateful to all the volunteers, interns and research assistants
who gave up their time to collect data for Montenegro Dolphin
Research. Finally, appreciation goes to Rufford Small Grant
Foundation for their financial support.
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The Adriatic Sea is home to five cetacean species, classified as at risk by the IUCN. Bottlenose dolphins (Tursiops truncates), striped dolphins (Stenella coeruleoalba), Risso’s dolphins (Grampus griseus), Cuvier’s beaked whales (Ziphius cavirostris) and fin whales (Balaenoptera physalus), are all identified as species in which the community has a vested interest and are under strict protection by the Montenegrin Government and by law. Since 2016, our studies, alongside existing data, have demonstrated the presence of resident bottlenose and striped dolphins in Montenegro, in addition to sightings of Cuvier's beaked whales and Risso's dolphins in its offshore waters. The regional status of species, assessments of threats and future conservation efforts can only be determined with dedicated and systematic surveys. Further, the Adriatic Pit, the deepest region of the entire Adriatic, holds the highest levels of biodiversity, whilst also being one of the most vulnerable regions to anthropogenic threats. The purpose of our survey effort is to expand upon the data we have already acquired within the coastal and offshore waters of Montenegro to cover data deficient species such as Cuvier's beaked whales and Risso's dolphins and to explore the possible presence of common dolphins that were thought to be regionally extinct until recent sightings in the summer of 2018 by the Blue World Institute. As a result of the necessity for economic growth, Montenegro is rapidly developing its tourism industry and more recently, the country has participated in oil and gas explorations. Yet any human activities that remain unregulated, are likely to form severe threats to marine species and their associated habitats. Therefore, our research and conservation outcomes form one of the most important steps towards effective conservation strategies, which promote not only the protection of nature, but also sustainable economic growth. For this reason, our project continues its dedicated survey effort in 2019, covering both the coastal and the offshore waters of Montenegro. Coupled with the recent addition of our sighting and stranding networks, we hope to aid the relevant authorities in the creation of regulation measures for the benefit of both nature and the economy. The dedicated survey effort of Montenegro Dolphin Research revealed the annual presence of bottlenose dolphins within coastal waters of Montenegro, with the Boka Kotorsko Bay hosting a high density of dolphin presence independent of season. Even though the sighting proportion for each season is around 36%, there is little significant variation between seasons. The northern region of Montenegro, (mainly the waters of Herceg Novi) is shown to be significantly more likely to have sightings compared to the central and southern waters of Montenegro. Furthermore, our photo identification study identified 72 individuals, with variations in their residency patterns. Additionally, the re-sighting rate of individuals and their site fidelities were very high, underlining the importance of Montenegrin waters for its bottlenose dolphin population. Striped dolphins were also documented sporadically in the offshore waters of Montenegro, which is likely to be the result of isolated survey efforts in offshore waters. The distribution and residency patterns of striped dolphins can only be fully understood with further dedicated survey effort towards offshore waters. 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Lastly, when marine traffic distribution and the presence of dolphins were mapped, the core bottlenose dolphin habitats overlapped with areas of dense marine traffic, resulting in the likelihood that several negative impacts ranging from ship strikes to noise pollution could occur. However, further studies are necessary in order to examine the effect of each threat on the populations. Striped dolphins appeared to have a lower occurrence of interaction with marine traffic. Despite this, their habitat is currently under the pressure of seismic activities related to oil and gas exploration, signifying the necessity for understanding both the short and long term effects of seismic practices in Montenegro. Montenegro Dolphin Research remains the first, and continues to be, the only annual cetacean monitoring project in Montenegro. By combining dedicated research effort with stakeholder engagement, not only will our understanding of cetacean populations in Montenegrin waters be considerably enhanced, but also our ability to turn this knowledge into a subsequent management plan. By establishing networks and producing influential documentation within the community, the conservation implications will be more effective and longer lasting.
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Full-text available
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Further, the Adriatic Pit, the deepest region of the entire Adriatic, holds the highest levels of biodiversity, whilst also being one of the most vulnerable regions to anthropogenic threats. The purpose of our survey effort is to expand upon the data we have already acquired within the coastal and offshore waters of Montenegro to cover data deficient species such as Cuvier's beaked whales and Risso's dolphins and to explore the possible presence of common dolphins that were thought to be regionally extinct until recent sightings in the summer of 2018 by the Blue World Institute. As a result of the necessity for economic growth, Montenegro is rapidly developing its tourism industry and more recently, the country has participated in oil and gas explorations. Yet any human activities that remain unregulated, are likely to form severe threats to marine species and their associated habitats. Therefore, our research and conservation outcomes form one of the most important steps towards effective conservation strategies, which promote not only the protection of nature, but also sustainable economic growth. For this reason, our project continues its dedicated survey effort in 2019, covering both the coastal and the offshore waters of Montenegro. Coupled with the recent addition of our sighting and stranding networks, we hope to aid the relevant authorities in the creation of regulation measures for the benefit of both nature and the economy. The dedicated survey effort of Montenegro Dolphin Research revealed the annual presence of bottlenose dolphins within coastal waters of Montenegro, with the Boka Kotorsko Bay hosting a high density of dolphin presence independent of season. Even though the sighting proportion for each season is around 36%, there is little significant variation between seasons. The northern region of Montenegro, (mainly the waters of Herceg Novi) is shown to be significantly more likely to have sightings compared to the central and southern waters of Montenegro. Furthermore, our photo identification study identified 72 individuals, with variations in their residency patterns. Additionally, the re-sighting rate of individuals and their site fidelities were very high, underlining the importance of Montenegrin waters for its bottlenose dolphin population. Striped dolphins were also documented sporadically in the offshore waters of Montenegro, which is likely to be the result of isolated survey efforts in offshore waters. The distribution and residency patterns of striped dolphins can only be fully understood with further dedicated survey effort towards offshore waters. The majority of the encountered groups, both for bottlenose dolphins and striped dolphins, were engaged in diving and travelling behaviours, which once again indicates that the area is likely to hold an important migration corridor between the neighbouring waters, as well as its importance as a foraging ground. Further, it is important to highlight that the majority of the sighted bottlenose dolphin groups hold several sub-adults, underlining the importance of Montenegrin and its adjacent waters containing possible nursing grounds. Socialising and resting behaviours were the least recorded within Montenegro for bottlenose dolphins. Nevertheless, socialising behaviours of striped dolphins were recorded in deep waters. Lastly, when marine traffic distribution and the presence of dolphins were mapped, the core bottlenose dolphin habitats overlapped with areas of dense marine traffic, resulting in the likelihood that several negative impacts ranging from ship strikes to noise pollution could occur. However, further studies are necessary in order to examine the effect of each threat on the populations. Striped dolphins appeared to have a lower occurrence of interaction with marine traffic. Despite this, their habitat is currently under the pressure of seismic activities related to oil and gas exploration, signifying the necessity for understanding both the short and long term effects of seismic practices in Montenegro. Montenegro Dolphin Research remains the first, and continues to be, the only annual cetacean monitoring project in Montenegro. By combining dedicated research effort with stakeholder engagement, not only will our understanding of cetacean populations in Montenegrin waters be considerably enhanced, but also our ability to turn this knowledge into a subsequent management plan. By establishing networks and producing influential documentation within the community, the conservation implications will be more effective and longer lasting.
Chapter
Seismic surveys have been identified as an important source of low-frequency ocean ambient noise. In 2018 and 2019, large-scale seismic surveys were conducted off Montenegro in the Adriatic Sea to explore the potential for natural gas extraction. A calibrated passive acoustic recorder was deployed at 1,000 m depth in the Southeastern Adriatic Sea at the northeastern edge of the South Adriatic Pit in October 2018. The seismic exploration surveys were conducted in December 2018 in depths between 70 and 800 m, and in February 2019 in depths between 50 and 100 m. The seismic surveys occurred at distances 70–125 km from the recording site. Time series of broadband sound levels, third octave bands centered at 65 and 125 Hz, and sound pressure levels (SPLrms) over the 15–200 Hz frequency band were calculated through February 2019. Also, power spectral densities from 15 to 900 Hz were calculated over the weeks before, during, and after the surveys. Overall low-frequency ambient sound levels at this deep site were relatively high. The highest SPLrms were recorded while the survey was conducted in deep waters. The South Adriatic has been recognized as an important area for cetaceans, which may be affected by increased sound levels.
Chapter
A boat-based, photo-identification survey of common bottlenose dolphins in Montenegrin territorial waters was carried out to create a baseline database and inform future studies on their abundance and distribution. A total of 21 sightings were recorded during 27 outings in the period from May to September 2013, resulting in a total of 73 identified individuals. A weighted mean encounter rate of 0.006 groups km⁻¹ was calculated using 5 × 5 km EEA grid cells with sufficient effort (>7.07 km per cell). Using the Chao Mth model, the abundance of the resident community of common bottlenose dolphins inhabiting Montenegrin waters was estimated to be 90 individuals (SE = 14.92, LCI = 71, UCI = 152). Preliminary data indicates that there is a subset of individuals regularly using the enclosed Boka Kotorska Bay and further research is needed to investigate specific habitat use patterns. A precautionary approach should be implemented in conservation plans dealing with this data deficient bottlenose dolphin community.
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The common bottlenose dolphin (Tursiops truncatus) population along the eastern Adriatic coast is believed to comprise discrete communities, yet many of them are unstudied. This study provides the first description of occurrence and demographic parameters for the community inhabiting waters of North Dalmatia. Dedicated boat‐based surveys conducted in summer months from 2013 to 2017 resulted in 13,896 km of research effort and 284 dolphin sightings from which 336 individuals were identified. Site‐fidelity analysis revealed that 52.1% of encountered marked adults occur in the area regularly or occasionally. No significant difference among years could be found for mean group sizes (5.73–7.46) and group encounter rates (1.159–1.942 groups/100 km). Pollock's Robust Design models estimated annually variable adult apparent survival (0.737–0.986) and constant temporary emigration rate of 0.172. The estimated abundance varied annually from 116 to 138 individuals and showed a negative slope, but a significant trend could not be confirmed. Age‐dependent models estimated first‐year calf survival at 0.875. These results provide a baseline for informed management of two Sites of Community Importance, and a benchmark for future monitoring in North Dalmatian waters, an area under significant anthropogenic pressure.
Article
We investigated the short-term effects of non-targeted tourism on the behaviour of bottlenose dolphins (Tursiops truncatus) off the coast of Montenegro, South Adriatic, by comparing dolphin group behaviour during impact (the presence of non-targeted tourism vessels) and control (absence of all marine vessels) scenarios. Tourism vessel and dolphin behavioural data were collected through systematic weekly land-based surveys. Using instantaneous focal ‘group’ scan sampling, the predominant behaviour of bottlenose dolphin groups were determined. To quantify the effect of vessel interactions on the behavioural budget of the dolphins, we followed a stepwise modelling approach. A first-order Markov chain was used to calculate the transition probabilities between behavioural states before a Monte Carlo simulation estimated the behavioural budgets of dolphins during impact and control situations. In the presence of non-targeted tourism, dolphins were found to be less likely to remain diving (during which dolphins were assumed to be feeding), whilst milling-socialising and surface feeding were completely absent from their behavioural repertoires. Nevertheless, the behavioural budgets demonstrated an increase in resting behaviour in the presence of non-targeted tourism vessels. No significant changes to travelling behaviour were observed. The decrease in foraging behaviour (both surface feeding and diving) could result in a reduction in energy intake for dolphins, which over time (assuming repeated disturbance) could end up negatively affecting body condition, and ultimately survival and reproduction. Regulations on non-targeted tourism should therefore be considered to minimise potential long-term negative effects on the dolphins within Montenegrin territorial waters.