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Emma Lowe
Impacts of boat activity on Cardigan
Bay bottlenose dolphin (Tursiops
truncatus) behaviour and their
implications for the future
Emma Lowe
BSc (Hons) Marine Biology
Stage 4
Project Advisor: Dr Clare Embling
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Emma Lowe
Impacts of boat activity on Cardigan Bay bottlenose
dolphin (Tursiops truncatus) behaviour and their
implications for the future
Emma Lowe
Project Advisor: Dr Clare Embling
3
Emma Lowe
Abstract
Tursiops truncatus are a characteristic, social species that prefer coastal habitats,
consequently come into contact with human activity. Cardigan Bay is subject to high levels
of boat traffic during the summer months as tourism peaks, and there is increasing demand
for dolphin watching trips. New Quay Bay is a small bay located on the Southern end of
Cardigan Bay, and is a site often frequented by dolphins as feeding and nursing grounds. It is
therefore questioned whether this intense vessel activity in New Quay bay is impacting the
dolphins in terms of their behaviour. It was discovered that dolphins showed more staying
behaviours, involving long dives and irregular surfacing when boats were present compared
to when boats were absent (X2 = 17.1, d.f. = 6, p = 0.00876). These findings suggest that
boat occurrence significantly affects dolphin behaviour. Other studies have reported similar
results, with boat traffic causing short-term behavioural changes. The longer term
implications of these behaviours would merit further study; however may involve site
avoidance, reductions in biological fitness and lower breeding rates. Furthermore these
impacts may be detrimental to the population of T. truncatus in Cardigan Bay, which are
protected by the implementation of a Special Area of Conservation (SAC). This study
suggests that further work is carried out to estimate the extent of damage being done to
bottlenose dolphin populations via behavioural changes instigated by boat presence, and
that stricter regulations are implemented in the code of conduct of the SAC to ensure
effective protection of the species.
Keywords: Bottlenose dolphin, behaviour, human impacts, boat activity, ecology, Special
Area of Conservation
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Introduction
Human vessel activities in the marine environment and their wide-ranging impacts on marine life
have long been a cause for concern across the globe, notably influencing local megafauna and
disrupting delicate ecosystems (Torres et al. 2011). Simply vessel presence in an environment has
been observed to have significant effects on marine mammals, heavily influencing their behaviour
and disturbing their regular patterns and activities (Lusseau et al. 2009, Richter et al. 2006). Marine
mammals are impacted by boats on a large scale and in vastly different ways, from negative
interactions with fisheries involving bycatch (Read, 2008), to interference with underwater acoustics
(Erbe et al. 2002), and simply by disrupting natural behaviours (Blane & Jaakson 1994). This is
observed on a global scale, in a number of cetacean species. As the tourism industry develops the
demand for dolphin watching trips increases, putting more strain on marine mammals as they are
increasingly disturbed by boats invading their habitat (Bejder et al. 1999, Ribeiro et al. 2005).
The bottlenose dolphin (Tursiops truncatus) is widely distributed and well-studied species in regions
from Sarasota Bay in Florida to the Shannon Estuary in Ireland (Gregory & Rowden 2001). As a
coastal dwelling species bottlenose dolphins are often subject to the effects of human activity,
arguably the most of the odontocetes (Nowacek & Wells 2001). The semi-resident population found
in Cardigan Bay, along the West Wales coast (Wood 1998), is uniquely protected and has been
frequently observed in the area from the 1920’s (Bristow & Rees 2001). In common with other
coastal populations, the bottlenose dolphins of Cardigan Bay are specific to this site, identified as
their home range (Hudson 2005), making it vitally important to their survival and success that their
habitat is productive and remains undamaged (Ingram & Rogan 2002). Habitat protection via the use
of reserves has shown to be effective for the conservation of megafauna. Conversely megafauna are
useful indicators of ecosystem and trophic level health via both bottom-up, and top-down control,
and are increasingly used for the design of these reserves (Heithaus et al. 2008, Hooker & Gerber
2004).
The Cardigan Bay bottlenose dolphins are observed most in the area from April through to October
(Dunn et al. 2012, Gregory & Rowden 2001, Simon et al. 2010), however are not seen often during
the winter months and tend to move offshore into the Irish sea (Pierpoint et al. 2009). The number
of dolphins present in the area peaks during the summer season (Bristow 2004, Pierpoint et al.
2009), and although calves are born all year round calving numbers are at their highest during the
warmest months (Connor et al. 1996, Hudson 2005). Dolphins are regularly seen 15km from the
coast (Gregory & Rowden 2001) mainly between Cardigan and Borth in West Wales. This population
although semi-resident, has been described as fluid as the individuals in the population differ
annually, with some individuals disappearing for seasons at a time before returning (Bristow & Rees
2001). New Quay has been noted as one of the many favoured sites of the bottlenose dolphins
(Gregory & Rowden 2001), and it is used as a feeding and nursing ground (Simmonds et al. 2013).
Cardigan Bay and Pen Llŷn a’r Sarnau have protected status as a Special Area of Conservation (SAC)
by the EU Habitats directive, as part of the Natura 2000 (Fig. 1). The aim of this is to protect the
bottlenose dolphins in the area, as well as sand banks and cobble reefs which are important features
of the bay at risk from fishing activities; most notably scallop dredging for Pecten maximus (Hinz et
al. 2010, Simon et al. 2010). This protected habitat stretches across 1000km2, over Cardigan Bay, and
Pen Llŷn a’r Sarnau (Veneruso & Evans 2012). Despite the protection of Cardigan Bay concerns are
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high regarding damage done to the habitat by commercial fisheries, which may have knock-on
effects on the dolphins in the bay (Bear 2012, Pirotta et al. 2013, Smith 2012). Scallop dredging in
particular has been singled out, due to destruction of the seabed and changes to the habitat being
made (Robinson et al. 2001), which in turn causes disruption to the dolphins’ food chain.
Additionally, a fish factory is located on New Quay headland, which releases discards into the water
below, interfering with the local trophic levels, having potential implications for the dolphins
(Denton 2012).
Fig. 1: Cardigan Bay’s location in the United Kingdom, and the area designated as an
SAC where this study was based
Cardigan Bay is also subject to high levels of boat traffic, which peaks during the summer months
coinciding with the peak in dolphin presence (Pierpoint et al. 2009). High numbers of tourist wildlife
watching boats, fishing trips, commercial fishing vessels, recreational vessels such as canoes/kayaks,
sail boats, and privately owned motorboats operate in the bay throughout daylight hours. A
distinctive threat is posed to the dolphins here, in the form of disturbance, leading to behavioural
changes (Lusseau et al. 2006) and site avoidance (Bejder et al. 1999, Kruse 1991). Disturbance poses
potential impacts on the behaviour of these species, and as bottlenose dolphins are fairly long-lived,
and this population is semi-resident, certain individuals may be repeatedly exposed to human
activities. If these individuals feel threatened by boat activities they may become more sensitive to
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vessel presence and exhibit avoidance behaviours (Constantine et al. 2004, Williams et al. 2006).
This is particularly important for mother-calf pairs, as calves are born in the summer months, when
boat activities are at their peak, which may impact their behaviour and long-term health, especially if
it results in longer dives to avoid boats (Janik & Thompson 2006). An additional consideration is the
population function as a whole, as vital behaviours are disrupted as dolphins have to exert time and
energy avoiding these boats (Nowacek & Wells 2001). This may lead to less time for mothers to
nurse their calves (Stensland & Berggren 2007), a decrease in reproductive output as socializing time
is reduced (Lusseau 2004) and a decrease in biological fitness as energy budgets are interrupted by
the need to avoid disturbances by boats (Bejder et al. 1999, Gregory & Rowden 2001).
As bottlenose dolphins are protected in areas worldwide to encourage their conservation, it is vitally
important that we ensure that the measures being taken to protect this species are effective (Barros
& Wells 1998). It is crucial that the local protection is effective at ensuring their conservation and
protection as this is Britain’s largest breeding population of bottlenose dolphins. The findings of this
study will be used to evaluate the effectiveness of measures in place to protect the bottlenose
dolphins of Cardigan Bay, with a focus on investigating whether the local code of conduct effectively
protects the species from disturbance via vessel activities (Bejder et al. 2006b, Nowasek & Wells
2001). Additional stress being applied to these dolphins by boat presence and changes to behaviour
may have severe implications, potentially pushing them away from their habitat as they become
increasingly disturbed (New et al. 2013, Lusseau 2005, Williams et al. 2006). The long-term impacts
that may imprint on the dolphins are unknown, which makes it even more important to ensure that
they are receiving adequate protection by the SAC from further stress and interference (Sini et al.
2005).
What this study aims to do, firstly, is to determine the impacts this boating activity may have on
dolphin presence in the bay, which will contribute to the discovery of whether there is any shortterm site avoidance occurring. Secondly, it will investigate whether boat activity in the bay impacts
the behaviour of the dolphins; whether they exhibit some behaviour types more than others when
in the presence or absence of boats. Finally, it will determine whether certain types of boat produce
a behavioural response in the dolphins more than others. This will ascertain whether particular
boats have more stressful and potentially detrimental impacts on the dolphins. Furthermore, this
information could contribute to evidence supporting greater emphasis on the code of conduct.
Other factors, such as sea state are also considered to allow for the elimination of bias in the data
during particular environmental conditions. This study could support the view that there needs to be
a more authoritative and rigorous form of controlling the behaviour of local vessels than a voluntary
code of conduct. The work carried out aims to contribute to the work determining the best way
forward to ensure that the bottlenose dolphins of the Cardigan Bay SAC are receiving appropriate
and thorough protection.
The hypothesis this study is based on is that bottlenose dolphins will exhibit more reserved
behaviours, involving long dives and milling in the area, and less active and characteristic behaviours
such as leaping and lunging when boats are present compared to when they are absent.
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Methodology
Study site
Based on data between 2001 and 2007, the bottlenose dolphin population of Cardigan Bay is made
up of between 121 and 210 individuals (Pierpoint et al. 2008). New Quay Bay was the study site
used, which is a shallow bay, located in Cardigan Bay on the West coast of Wales, facing out to the
Irish Sea towards the West and bound by land on the other three sides (Fig. 2). Cardigan Bay is a
sheltered habitat with a depth on average around 40m (Evans, 1995). New Quay bay is comprised of
a heterogenous seabed, with sediment made up of primarily gravel and stones, with sand in the bay,
and behind the shelter of the harbour wall, and accumulated on the beach in front of the wall,
between the wall and the headland further down the coast (Barnes 2011, Fig. 2). In deeper waters
further out into there is sediment made up of stones and sand, showing primarily fine sediment,
however towards the cardinal marker 1km away from the wall into the bay, the benthos is
Fig 2: Line diagram of the study area, and location of data collection.
comprised of rock, sand and weed, which provides a more complex, three dimensional habitat for
the local ecosystem.
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Vessel activities in the area
Various kinds of vessels run in New Quay bay almost all year round – however the peak of vessel
activity is in the summer months, where visitor passenger boats (VPB) i.e. tourist and trip boats, are
able to utilise good weather conditions and high levels of tourists and run around the clock during
daylight hours, which were between 05:56 and 06:23 sunrise, and 20:36 and 20:02 sunset
throughout August. 13 VPB boats operate in the bay, along with 6 commercial fishing boats, and
there are 180 moorings for private boats in the bay. New Quay is a popular site in terms of fishing,
and there are distinct fishing seasons that lead to recreational and commercial fishermen travelling
to New Quay specifically to fish for species such as whelks (most notably Buccinum undatum),
scallops (Pecten maximus) and herring (Clupea harengus).
Data collection
Data for this study were collected by volunteers of Cardigan Bay Marine Wildlife Centre (CBMWC),
which enabled a more rigorous study of the bottlenose dolphins’ behaviour than already carried out
by the CBMWC. Watches were carried out by volunteers in 2 hour shifts, usually from 9am until 5pm
but occasionally starting at 7am and ending at 7pm. A watch in this context is the act of standing on
land at a specific location, and consistently scanning the bay for marine mammals and observing the
area attentively, both by eye and with the aid of binoculars. Watches were performed from New
Quay harbour wall, which extended out into New Quay Bay, Cardigan Bay, West Wales (Fig. 1),
where a volunteer would stand and watch for dolphin activity in New Quay harbour looking out at
Cardigan Bay, with the aid of a pair of Nikon Waterproof Binoculars Sporter EX 8x42.
Volunteers were fully trained in data collection for land-based surveys prior to the beginning of the
survey work, and all had backgrounds and experience in scientific data collection. Data was collected
daily from 1st of August – 4th of September 2015, with trial runs being held on the 30th and 31st of
July to test the effectiveness of the data collection sheets. August was chosen as the study period as
the annual peak of vessel activity in the bay is during this month (Hudson, 2014).
A separate land survey sheet (See Fig. 1, Appendix) was used to record environmental conditions
every 15 minutes, which were; Time, date, 15 minute period of the survey (designated letters A-H),
sea state (using the Beaufort scale 0-6+), general weather conditions (a key provided to match
weather conditions to a number), wind direction (a compass was used to determine from which
direction the wind was blowing), species sighted, sighting location with the use of maps of the
survey area, where the estimated location of the animal was plotted. Groups of dolphins studied
were defined as individuals within 100 meters of one another (Barnes 2011) and exhibiting similar
behaviours, showing social interaction between one another considerably more than with other
individuals in adjacent areas (Irvine et al. 1981).
The study area extended roughly 2km out to sea, a cardinal marker was used to measure 1km from
the harbour wall, and roughly a further kilometre was included in the survey area. Other landmarks
such as terrestrial features that lined up and buoys were used to estimate distance.
Behaviour of dolphin groups was collected every 5 minutes, where a sighted group of dolphins were
consistently observed and their behaviours noted down using the behaviour key (Fig. 2, Appendix).
The main behaviours observed involved staying behaviours, such as milling at the surface and
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carrying out dives, travelling behaviours where the dolphins were consistently heading in a direction,
and fast-moving behaviours, including leaping, chasing fish at the surface, tail slapping and lunging
(see Fig. 2 of Appendix for more details).
These behavioural codes were noted every 5 minutes on a separate data sheet (See Fig. 3,
Appendix), and it was also noted whether the group of dolphins were within 300m of a boat during
that 5 minute period, or not. Being within 300m of a boat was classed as a boat encounter. The total
number of boats in the survey area was also noted every 5 minutes. If a group of dolphins did
experience a boat encounter, additional data was required (Table 1) with use of the key provided
and a map of the area with sections numbered 1-8. If more than one group of dolphins experienced
a boat encounter, the first to have one was the group that was monitored closely and had additional
information noted about it; this allows identification of which group this additional information is in
reference to.
Table 1: Additional information collected when a group of dolphins experienced a boat
encounter, i.e. a boat came within 300m of the group.
Parameter measured
How many boats within 300m
Boat type
Obeyed code of conduct?
Group location
Immediate reaction by dolphins
Which dolphin group experienced encounter
How measured/example
Boat count of vessels within 300m
Motorboat/ Sail boat/ Visitor Passenger
Yes, slowed gradually and stopped
Which grid on the map they were located in
Tail slapping/ Deep dive/ leaping
G1/ G2 etc.
A maximum of 5 different groups of dolphins were recorded during the survey, as it would become
difficult to effectively monitor more groups than this at one time, and reliability of the results would
therefore be jeopardized. The number of dolphins in each group was also noted down.
Statistical analysis
Due to the data being count data, chi-square analyses were the most appropriate method for
statistical analysis.
Dolphin presence and absence versus boat presence and absence in the total survey area were
plotted, and a chi-squared analysis of the data was carried out, with the use of Microsoft Excel. The
raw data was put into proportion, along with the expected values, and plotted onto a bar chart for
visualisation (Fig. 3).
GLM analysis of dolphin presence absence, boat presence absence, and sea state in the total survey
area was carried out using Minitab 7 software.
A chi-square analysis was executed on the data involving dolphin behaviour, and boat presence and
absence. Each behaviour type was treated as a different category, and put against boat presence or
absence in a chi-square table.
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The same statistical test was then used to compare observed and expected values in terms of boat
type, and dolphin behaviour, which involved boats being within 300m of the dolphins. This raw data
was plotted on a bar chart showing the proportion of time dolphins spent exhibiting each behaviour
when experiencing a boat encounter with different boat types (Fig. 4, appendix). The code for each
boat type is also explained in the appendix (Fig. 5, appendix).
The additional data collected when dolphins experienced a boat encounter was not statistically
analysed for the purpose of keeping this study focussed on boat occurrence. However the detailed
nature of this additional information does provide scope for further study, and investigation into and
identification of precise parameters causing behavioural changes in bottlenose dolphins.
Results
A total of 2373 observations were made, where each observation was a 5 minute watch period,
collected from August 1st to September 4th 2015. Data was collected between the hours of 7am to
7pm, equating to 197.75 hours’ worth of effort, during all tidal states and weather conditions except
for in cases of extreme weather.
Dolphin and boat presence
There was a significant effect of boat presence on dolphin presence (X2=55.4, d.f.=3, p=<0.0001,
n=2373). There were significantly more dolphins present in the bay when boats were also present
than expected shown by Table 2. There were also fewer observations of dolphins when boats were
absent than expected. When boats were present in the bay there were fewer observation periods
without dolphins present than expected, so dolphins were present more in the bay alongside boats
than predicted by the expected values.
Table 2: Observed and expected data of dolphin presence/absence and boat presence/absence
Conditions
Observed
Expected
No dolphins, no boats
Dolphins, no boats
No dolphins, boats
Dolphins, boats
396
57
1349
571
332.7
120.3
1410.3
509.7
A general linear model showed that both boat presence and sea state significantly impact dolphin
presence/absence (Dolphin occurrence ~ Boat occurrence + Sea state, p= 0.005, <0.0001). Dolphin
presence was shown to be impacted by Beaufort sea states 1-4, however there was no significant
relationship between dolphin presence and sea state when at sea states 5 and 6. Sightings rates
were reduced as sea state increased, shown by Table 1, appendix. This however can be explained by
the difficulty to spot cetaceans at sea states of this magnitude (Barco et al. 1999, Forney 2000).
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Dolphin behaviour
Fig. 3 shows that long dives (S3) were carried out less than expected when boats were not present in
the bay. Fast circling, tail slapping and lunging behaviours (S6) were displayed less than expected
when boats were present, and in proportion this behaviour was displayed the least when boats were
present. S3 behaviours were observed more in the bay when boats were present than expected, in
proportion. There was little difference between observed and expected values for travelling
behaviours T1 and T2, however differences were seen in T3 rapid travelling, where without boats
present there were no observations of this behaviour at all, however this behaviour was observed
only very occasionally overall in the sheltered bay of a survey area. Table 4 shows the corresponding
codes and behaviours used in the experiment.
Fig. 3: The observed and expected proportion values of dolphin behaviour with and without boats
present.
Dolphin behaviour was shown to be significantly impacted by boat occurrence (X2 = 17.1, d.f. = 6, p =
0.00876). This showed that the observed amount dolphins carry out various behaviours with and
without boat present in the survey area are significantly different to what was expected (Table 3).
These results back up the pattern that is shown by the proportion data, where staying and long dive
behaviours (S3) are observed more than expected with boats present, and less than expected
without boats present in the bay. Additionally, S6 behaviours (see Table 4) are observed less than
expected with boats present, and almost twice as much as expected when boats are absent from the
survey area. Behaviours S3 and S6 are of greatest value in this study, as they represent a high
contrast in behaviour dependant on boat occurrence, and they achieve expected values over the
value of 5.The other values have limited value and trustworthiness due to their corresponding
expecting values being below 5.0.
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Table 3: Observed and expected dolphin behaviours with and without boats present
Behaviour
S2
S3
S4
S6
T1
T2
T3
With Boats
Observed
Expected
44
49.1
336
324.6
3
2.7
68
74.6
43
43.6
76
75.5
1
0.9
Without Boats
Observed
Expected
10
4.9
21
32.4
0
0.3
14
7.4
5
4.4
7
7.5
0
0.1
Table 4: Codes used in the study and the bottlenose dolphin behaviours they represent
Code
S2
S3
S4
S6
T1
T2
T3
Corresponding behaviour
Staying – slow circling, milling around (mingling) at the surface
Staying – long dives, potentially foraging at depth
Chasing prey at surface, fish seen
Staying – fast circling (mingling) at surface, leaps, tail slaps or lunges
Travel – regular surfacing, all animals keep same, consistent heading making determined
progress
Travel – long dives, surfacing at irregular intervals, thought to be searching for prey
while on the move
Travel – rapid progress with forward leaps or otherwise splashy surfacing
Additional data
A chi-squared test was also run on data on boat type and behaviour, however obtained a result that
showed boat type did not significantly impact dolphin behaviour (X2 = 28.353, d.f. = 30, p = 0.552).
Fig. 4, appendix, shows this raw data, in proportion.
Discussion
Dolphin occurrence, sea state and boat occurrence
The relationship between sea state and dolphin presence may be partially explained by the fact that
dolphin sightings are significantly reduced above sea states of 3 on the beaufort scale, due to
reduced ability to see dorsal fins in choppier conditions (Barco et al. 1999, see Table 1., appendix).
However the result that there are significantly fewer dolphins observed in the bay when there are
boats present is indicative that boats are having a negative impact on the dolphins; they are actively
avoiding the bay when there are boats present. This could eventually lead to long-term site
avoidance of New Quay Bay, if there is short-term avoidance of the area. Lusseau’s study from 2005
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looking at Tursiops truncatus in New Zealand demonstrates similar results; dolphins were shown to
avoid the site of heavy boat traffic when there is a particularly great amount of vessel activity
(Lusseau 2005).
Differences in behaviour with boats present and absent
Bottlenose dolphins were shown to carry out staying behaviours with long dives significantly more in
the presence of boats than without boats. This could mean that when boats are nearby, they are
spending their time primarily underwater, where they are less exposed, as they feel threatened. This
has been also observed in a number of other studies, where dolphins increase the length of their
dives and time spent underwater in the presence of boats, and breathing and surfacing rate is seen
to significantly decrease (Hastie et al. 2003). Hastie et al.’s work also showed that synchronous
breathing in individuals in a group of dolphins significantly increased in the presence of boats, this
could be indicative of some kind of defence mechanism against the anthropogenic disturbances the
dolphins are faced with. When exposed to boat traffic, Tursiops species have been shown to increase
their dive duration and this is widely treated as a behavioural trait associated with avoidance
(Seuront & Cribb 2011).
When boats were absent from the bay, bottlenose dolphins were shown to carry out splashy and
active behaviours, involving staying, fast circling, mingling at the surface, leaps, tail slaps or lunges,
more regularly than when boats were present. They also display more playful and outgoing
behaviours that may make them more vulnerable when there are not boats around compared to
when boats are in the area, showing that they’re more comfortable displaying these behaviours
when boat traffic is relatively quieter, and able to carry out usual behaviours that are disrupted in
the presence of vessels (Steckenreuter at al. 2012).
Other literature report that bottlenose dolphins exhibit widely ranging behavioural responses to
boat activities, from increasing swimming speed and directly avoiding boats (Bejder at al. 2006), to
being attracted to and interacting with vessels (Gregory & Rowden 2001). Attraction to boats was
also observed in New Zealand where Hector’s dolphins approached boats within the first 10-50
minutes of them entering the bay (Bejder et al. 1999). Some studies have even shown bottlenose
dolphin indifference to the presence of boats, where they have become acclimated to vessels being
nearby for so long that they no longer respond behaviourally to this disturbance (Acevedo 1991,
Hudson 2005). However the results of this study contradict reported positive reactions or
indifference to boat presence, as the dolphins behave in an elusive and reserved manner around the
boats in Cardigan Bay. Hastie et al.’s study from 2003 reinforces the notion that boats are a negative
disturbance to dolphins, and alludes to bottlenose dolphins seeing boats as a threat. Bottlenose
dolphins were shown to respond to boat presence by increasing their breathing synchrony and by
becoming a more tightly packed group (Hastie et al. 2003), a behaviour also observed by other
studies (Steckenreuter et al. 2012). This compact formation has been suggested as an antipredatory
behavioural response, as they are more prepared to respond to danger (Bejder et al. 2006a, Lusseau
2006). Bejder et al’s study (1999) supports this theory, where Hector’s dolphins form tighter groups
in the presence of boats, which has been associated with dolphins being threatened or in danger, so
that they provide enhanced protection on an individual scale (Bejder et al. 1999).
These various responses can cause significant short term implications for these marine mammals;
widely explored by a number of studies where the impacts of boat presence are distinctively
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impacting dolphin behaviour (Lusseau et al. 2006). However long-term implications of these of these
behavioural responses are poorly understood and difficult to predict in terms of the health of
populations of bottlenose dolphins and other cetaceans in the future (Lemon et al. 2006). An
example of this is an increase in the amount of time spent underwater and less regular surfacing
around boats, which could have physiological impacts on the population (Hastie et al. 2003). Mother
and calf pairs would be most vulnerable to these impacts due to the requirement of newborns and
calves to breathe more frequently than adult individuals (Hastie et al. 2003). Additional stress placed
on the calves of these slow growing and maturing species, along with their low fecundity rate may
have detrimental effects on the population as a whole (Currey at al. 2009, Seuront & Cribb 2011).
Avoidance of high volumes of vessel activities could also eventually cause some site avoidance, in
the short term and potentially long-term. A study on Killer Whales (Orcinus orca) in British Columbia
found that orcas made direct heading for open water when approached by boats, out of the narrow
Johnstone strait to less restrictive waters where they may potentially avoid vessels (Kruse 1991). The
Indo-Pacific dolphin Tursiops aduncus off the south coast of Zanzibar also displayed a negative
response to boat traffic; when boats were present female dolphins and their calves showed direct
avoidance behaviour by increasing travelling (Stensland & Berggren 2007). There is concern that
these behavioural responses eventually lead to site avoidance, and displacement of dolphins from
their local ranges (Bejder et al. 1999). Additionally, Lusseau’s report (2004) noted that boat presence
reduced the time dolphins spent socializing, which has previously been closely linked to the
fecundity of dolphin populations. This suggests that an increase in boat disturbance of dolphin
groups may decrease the overall reproductive output of the population, and decrease rates of
pregnancy as breeding success is reduced (Bejder et al. 1999, Lusseau 2004).
Some studies have alluded to consequences in terms of the wellbeing of mother and calf pairs, such
as a decrease in time available for mothers to nurse their calves as they are spending more of their
time avoiding boat traffic (Stensland & Berggren 2007). This reinforces the concern that mother and
calf pairs are most at risk to the costs of disturbance by heavy boat traffic. Bejder et al. (1999) also
suggested that there may be long-term costs in terms of biological fitness, where dolphins have to
exert a great amount of time avoiding boats, as their critical energy budgets become interrupted by
high use of avoidance strategies (Bejder et al. 1999).
Conversely, long diving and staying behaviours, with inconsistent surfacing patterns could be
associated with foraging, so it may be that the dolphins are simply feeding at that time, and
underwater for longer and surfacing less regularly as they are in pursuit of prey. However, the
shallow nature of the bay makes this unlikely, as it would be more likely to see the dolphins
splashing at the surface if they were feeding (Gregory & Rowden 2001). This additional theory
however is supported by the work of Engas et al. (1995), where dolphins could be responding to
boats by spending more time underwater and diving deeply due to prey aggregations as a result of
boat presence. Engas et al. (1995) found that cod (Gadus morhua), and herring (Clupea harengus),
both school together into dense and organised clusters, and swim towards the seabed in response to
boat engine noise. This may reflect the way dolphins appear more reserved around boats; they are
simply spending more time foraging. As these fish are able to hear and respond to boat engine noise
over vast distances, just having boats within the survey area may have instigated a response in the
behaviour of these fish, which would then have a knock-on impact on dolphin behaviour as they
respond opportunistically to this sudden influx of prey aggregations, and spend more time foraging
in response to this food source. Dolphins have a wide range of prey species (Pesante et al. 2008,
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Santos et al. 2001) hence it is widely believed that they feed opportunistically, which supports the
argument that they would exploit a temporary rich food source. The behaviours observed in
Cardigan Bay when boats were present however also involved a great amount of milling in the area
along with irregular surfacing, which has been noted by Steckenreuter at al. (2012) as behaviour
increased four times in the presence of boats compared to their absence (Steckenreuter at al. 2012).
The array of evidence supporting behavioural changes in bottlenose dolphins in response to boats as
a threat overwhelms the argument making it more plausible that they are negatively responding
directly to boat presence (Bejder et al. 2006a, Hastie et al. 2003, Ingram & Rogan 2003, Lusseau
2006, Lusseau et al. 2006). This reinforces the idea that boats are causing high levels of disturbance
to bottlenose dolphins, causing changes to natural, regular behaviours, with implications for
populations that we can only estimate (Constantine 2001, Ingram & Rogan 2003, Lusseau & Higham
2004).
Conclusions and recommendations for Cardigan Bay as a SAC
As boats have been shown to impact bottlenose dolphin, correct and appropriate protection for this
species is crucial. The protected status of Cardigan Bay as a SAC does allow boats to oprate in the
area, as long as they adhere to the Ceredigion Marine Code of Conduct. This dictates that boats may
not approach within 100m of dolphins or speed towards them, must slow down to a minimum speed
and make no sudden or erratic changes in course and not attempt to touch, feed or swim with
marine mammals in the area (Ceredigion County Council Department of Environmental Services and
Housing 2015). However it is questionable whether this is providing sufficient protection for the
dolphins. Concerns were raised by Nowacek & Wells where it was suggested that boat traffic causing
behavioural changes and associated implications such as changes in breathing, is technically a form
of harassment, as their usual behaviours are disrupted (Nowack & Wells 2001). The indisputable fact
that there is a distinct difference in the way Tursiops truncatus behaves when around boats
compared to when boats are not present illustrates that boats are having an impact on their
behaviour and therefore population health (Stensland & Berggren 2007). This suggests that heavy
boat traffic in Cardigan Bay could be unsustainable in the future, as the tourism industry grows in
New Quay levels of boat traffic are likely to increase to meet growing demands for dolphin watching
trips (Currey et al. 2009).
It is reflective of other studies that dolphins are responding to these vessels in the bay as a threat,
and will respond accordingly to what they precieve as a danger to them (Bejder et al. 2006a, Lusseau
2006). These responses however when exhibited too regularly, are in fact a threat to the wellbeing
of the dolphins, and so their being induced increasingly by the presence of boats may lead to
detrimental impacts on the population (Lemon et al. 2006). It is consequently recommended that
additional studies are carried out to consistently monitor dolphin behaviour in response to boat
traffic, to ensure a thorough understanding of the extent of the impacts of boat disturbance in New
Quay. Further work could investigate parameters recorded in this study however were not
examined, such as relationship between whether boats adhere to the code of conduct, and dolphin
behaviour. Findings such as these, along with more rigorous investigations into the impacts of boats
on dolphin behaviour, as well as monitoring over entire seasons, will allow an informed decision to
be made in terms of protecting this local population in the long term. However, a precautionary
approach should be adopted in terms of site management, and stricter measures implemented in
the code of conduct to ensure minimum impacts to the dolphins (Currey et al. 2009), as simply a
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Emma Lowe
voluntary code of conduct may not be enough to motivate boats operating in the area to adhere to
the rules in place. Correct operation of vessels around marine mammals is the very least that can be
done at the present time to ensure minimal disturbance; however this study and other work
highlights that there is an issue with boat traffic and its impact on bottlenose dolphins, which
requires further investigation and careful monitoring as the outcomes and long term implications
can not yet be predicted.
Acknowledgements
I would like to give a massive thank you to Sarah Perry of Cardigan Bay Marine Wildlife Centre for all
of her tremendous help throughout the making of this project. I am also very grateful to the CBMWC
volunteers who helped with the data collection throughout the month of August; including Rhian
Forrest, Masa Svent, James Clarke, Michael Naylor, Rhiannon Nichol, Laura Evans and Samantha
Patek, along with everyone else at CBMWC for all of their help. Additionally I am very grateful to Dr
Clare Embling for all of her help and guidance as my advisor for this project. Finally I would like to
thank my family, Sam and Matt for their unfailing support throughout all of my work.
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Appendix
Fig. 1: The data collection sheet used for collecting environmental data and general sightings information
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Fig. 2: Key to the codes of various behaviours and conditions potentially observed during a watch
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Fig. 3: Table used to collect data on dolphin behaviour whilst on watch
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Table 1: The number of observations (5 minutes watches) of each sea state achieved
Sea State (Beaufort scale)
0
1
2
3
4
5
6
Number of observations
0
882
783
264
294
144
6
Fig. 4: The various behaviours shown by dolphins when experiencing an encounter with
different boat types, in proportion
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Table 2: Codes used and their corresponding boat type
Code used
VPB
C
SAIL
MB
SB
CF
Boat Type
Visitor Passenger Boat
Canoe/Kayak
Any boat under sail
Motor boat
Speed boat/ RIB
Commercial Fishing vessel