Aquatic Mammals 2001, 27.2, 105–113

Behaviour patterns of bottlenose dolphins (Tursiops truncatus) relativeto tidal state, time-of-day, and boat traffic in Cardigan Bay, West

Wales

Paul R. Gregory and Ashley A. Rowden

Department of Biological Sciences, University of Plymouth, Drake Circus, Plymouth,Devon PL4 8AA, UK

Abstract

Diurnal behaviour patterns of the bottlenosedolphin (Tursiops truncatus) were investigated attwo sites in relation to tidal state, time-of-day, andboat traffic in Cardigan Bay, west Wales. The twosites chosen were New Quay and Ynys Lochtyn.Between-site variability existed in the occurrence ofdolphins. However, no relationship was foundbetween the numbers of dolphins observed in rela-tion to the tidal cycle or time-of-day at either of thetwo sites. Dolphin movement patterns were corre-lated with tidal state at both sites, with the dolphinsmoving with the tidal flow or during slack water.No relationship was found between movementpatterns and time-of-day. Foraging behaviour wascorrelated with tidal state at both sites, withdolphins foraging mainly between the flood and ebbtides of high water. Foraging in relation to groupsize was not significant at either site. No relation-ship was found between foraging behaviour andtime-of-day. Statistically significant behaviouralresponses were noted towards boat traffic. Dolphinsgenerally displayed a neutral response towardboats, i.e., the dolphins showed no apparent changein directional movement, prior to and after thearrival of the vessel. However, dolphins displayed anegative response toward kayaks, and a positiveresponse toward tourist boats. Dolphin’s reactionstoward boats in relation to group size were notstatistically significant. The study supported thefindings of previous studies on bottlenose dolphinsin other localities; however, the effect of kayaksrequires further investigation. Recommendationsare made for future avenues of research regardingthis species.

Key words: bottlenose dolphin, Tursiops truncatus,Cardigan Bay, diurnal behaviour patterns, tidalstate, time-of-day, boat traffic.

Introduction

The bottlenose dolphin (Tursiops truncatus,Montagu) is a cosmopolitan species, foundthroughout the world’s tropical and temperate seasand oceans (Shane, 1990). The wide distribution ofthis species has allowed detailed studies at a varietyof locations, such as Sarasota Bay, Florida, USA(Irvine et al., 1981; Wells & Scott, 1997), Kino Bay,Gulf of California, Mexico (Ballance, 1990), theMoray Firth, Scotland (Wilson et al., 1997), and theShannon Estuary, southwest (SW) Ireland (Berrowet al., 1996). Studies showed that the bottlenosedolphin occupies a variety of marine habitats, fromdeep oceans to shallow coastal regions, inshorelagoons and estuaries (Leatherwood & Reeves,1990). Populations can be either offshore-pelagic intheir ranging patterns, or inshore-coastal residentpopulations. Little is known about the rangingpatterns of pelagic bottlenose dolphins, but coastaldolphins exhibit a full spectrum of movements,including seasonal migrations, year-round homeranges, periodic residency, and a combination ofoccasional long-range movements and repeatedresidency (Wells & Scott, 1999).

Resident populations have received most atten-tion owing to their locally dispersed geographicalranges (Bräger, 1993; Lewis & Evans, 1993; Berrowet al., 1996; Wilson et al., 1997). Most residentgroups of bottlenose dolphins show systematicpatterns in their behaviour, such as foraging/feeding, socializing, and moving from area to areain relation to environmental cues, such as thetides (Irvine et al., 1981; Leatherwood et al., 1983;Wilson et al., 1997), the time of day (Saayman et al.,1973; Würsig & Würsig, 1979; Bräger, 1993), anddepth (Wiley et al., 1994).

Many potential threats exist to resident popula-tions, often via contact with human activities. Theseanthropogenic threats include entanglement in fish-ing gear (Vidal, 1993), exposure to environmental

? 2001 EAAM

pollutants (Morris et al., 1989; Borrell, 1993), anddisturbances from boat traffic (Sorensen et al.,1984; Janik & Thompson, 1996; Wells & Scott,1997; Allen & Read, 2000). In inshore-coastalwaters the bottlenose dolphin is probably thesecond most common cetacean in the UnitedKingdom (Evans et al., 1986; Evans, 1992). TheCardigan Bay (West Wales) population is estimatedto range from 130 to 230 individual dolphins(Grellier et al., 1995), with only a proportion ofthe animals being resident throughout the year(Arnold, 1993; Lewis & Evans, 1993). Bottlenosedolphins are frequently seen within 15 km of thecoast between Cardigan and Borth, from Aprilto October. Headlands at Mwnt, Pen Peles,Aberporth, Ynys Lochtyn, and New Quay areparticularly favoured feeding areas for bottlenosedolphins (Evans, 1996).

The principal aim of the present study was todetermine whether the tidal cycle or the time-of-dayhad an affect on the diurnal movement pattern ofthe bottlenose dolphin population, in two pre-determined geographical locations in Cardigan Bay.In addition, because the area is frequented by boatsof various kinds, the study also aimed to assesswhether boat activity has a detrimental or benign

effect on the movement patterns of the bottlenosedolphins.

Materials and Methods

Study areaCardigan Bay is the largest bay in the British Isles,bound on three sides by the Welsh coast and opento the Irish Sea on its western boundary (Fig. 1a). Itencompasses an area of approximately 5500 km2.The water depth in the bay does not exceed 50 mand becomes increasingly shallower from west toeast, with an average depth of approximately 40 m(Evans, 1995a). The nature of the seabed in the bayis extremely heterogeneous, ranging from fine sandand broken shell, to gravel, shingle, and muddysand (Evans, 1995a). The tidal regime of the area,results from the tide entering the Irish Sea throughSt. George’s Channel in the south and travellingnorthward to meet the southward-moving tide fromthe north in the vicinity of the Isle of Man. Theresultant weak tidal currents run northward duringthe flood and southward during the ebb (Evans,1995b). The tides in the area are semi-diurnal andthe tidal range in Cardigan Bay is fairly uniform(ca. 2 m at neaps and 4 m at springs).

Figure 1. (a) Study sites in Cardigan Bay, West Wales, (b) New Quay, and (c) Ynys Lochtyn. (-—Observation points).

106 P. R. Gregory and A. A. Rowden

Boat traffic is prevalent in the area, especiallyaround Cardigan, Aberporth, New Quay,Aberaeron, and Aberystwyth, which are frequentedby tourists. During the tourist season (April toOctober), boats operate out of New Quay andAberaeron, taking tourists on trips around thebay to observe the dolphins and other wildlife.Water sports and recreational boat activitiesincrease in the summer months, with many visitorslaunching powerboats, sailboats, and kayaks fromthe above ports.

Study sitesA land-based observational study was adopted,rather than a boat-based one, to minimize theeffects of observer presence on the dolphin’s naturalbehaviour. Two study sites where chosen inCardigan Bay, locations being New Quay Headland(52)13*05+N, 04)21*84+W) and Ynys Lochtyn, anorthwesterly peninsula cliff-top (52)10*28+N,04)27*98+W), (Fig. 1b and c). The observationalareas were ca. 8 km2 for both sites. New Quay andYnys Lochtyn headlands were both chosen for theirhigh vantage positions over looking the bay (75 mand 40 m, respectively) and because dolphins wereseen on a regular basis in the past at both sites.

The New Quay site represents a shallow semi-enclosed bay with restricted tidal flow. The bottomtopography is smooth, with depths ranging from 1to 12 m in a gradual sloping direction offshore. Thesubstrate at this site consists of coarse to fine sand.The Ynys Lochtyn site comprises of a rocky head-land which experiences relatively strong tide ripsand turbulence during the changes from eachamplitudinal tide. The water depth is more constantand ranges from 12 to 18 m, while the substrateconsists of mainly gravel to shingle and coarse sand(Evans, 1995a).

Field methodologyThe study was conducted during the entire monthof August 1999, a period when dolphin sightings aremost numerous (Evans, 1996). The 121

2 hour tidalperiod was divided into four observational periods:high water to 1

2 ebb, 12 ebb to low water, low water to

12 flood, and 1

2 flood to high water. One 12 tidal cycle

was covered each day, either high water—low wateror low water—high water; this was dependent onthe available daylight hours. Observational periodsin relation to the time-of-day were divided intothree time classes: 06:00–10:30, 10:30–15:00, and15:00–19:30 hrs. The time-of-day that the studycommenced each day varied, due to the variation ofthe tidal cycle.

Observations were alternated between the twosites every one or two days, so as not to confoundthe study temporally. Observations were conducted

by eye continuously for a full 6 h and 15 min,covering one half tidal cycle per day. Scans of thehorizon were conducted at 15-min intervals, withthe aid of Opticron 8#24 lightweight water-proof hand-held field binoculars and Nikon fieldtelescope. Time, position of dolphin(s) surfacing,distance offshore, direction of travel, feedingbehaviour, and sea state were recorded. Data wereonly collected when the sea state (Beaufort Scale)was ¦3. With sea states >3, sightings become lessreliable (Barco et al., 1999). Dolphin counts weremade once a dolphin(s) was sighted upon surfacing,and then observed for ca. 5 min or until the numberof individuals counted became consistent, so as notto underestimate or overestimate dolphin numbers.Dolphin positions were recorded every 10 minonce dolphin(s) were sighted, in addition to thecontinuous observation of the study area.

Estimated distances offshore were obtained withthe aid of a 10-m motor vessel, which followed atransect offshore, stopping at distances of 500 mand 1 km. These distances were noted from shoreprior to and during the study (via VHF radiocommunication with the motor vessel) and used asvisual references, with the additional aid of photo-graphs. At the New Quay site, an additional refer-ence point (North marker buoy, 1 km offshore) wasused. The position and direction of travel of thedolphin(s) were recorded with the aid of a field-sighting compass. Dolphin(s) positions and dis-tances offshore were plotted on a 1 km2 grid cellbasis over time, using the appropriate scale on amap (New Quay; Ordnance Survey Map scale1:10,000, SN 35 NE, SN 45 NW and SN 46 SW,and Ynys Lochtyn; Ordnance Survey Map scale1:10,000, SN 35 SW and SN 35 NW). The referencepoints used for mapping were St. Ina’s Church,Llanina for the New Quay site and Bird’s Rock forYnys Lochtyn (110) and 54) from the respectiveobservation points). Each day’s observations of thedolphin(s) and direction(s) were plotted indi-vidually for each determined observational period(6 hr and 15 min), to establish movement and direc-tion in relation to tidal state at each site. A largegrid cell size of 1 km2 was chosen to overcome theproblems of accurately assigning the dolphin’s pos-ition to a particular location. The use of a theodo-lite was used initially for position fixing; however,this was found to be unsuitable when more than onedolphin group was in the area, due to the possibilityof overlooking individual dolphin movements.

The direction of travel was classified as travellinginshore, offshore, or neutral (no observable direc-tion). Offshore and inshore directional movementswere recorded in association with observations ofthe local tidal flow (i.e., changes in tideline, foam-line of tidal fronts around headlands). Positiveforaging behaviour was classified as repeated back

107Behaviour patterns of the bottlenose dolphin

and forth movements in a small discrete area, withfish occasionally chased out of the water. Behav-iours, such as leaps, splashes, tail slaps, and physi-cal contact occasionally were observed while thedolphins foraged; however, these observations werenot used due to them occurring on only two oc-casions, and only when fish were chased out ofthe water. Dolphins when not engaged in positiveforaging behaviour were classed as travelling(continuously moving from one area to another).

A group was defined as a collection of individualswithin which no dolphin was separated by greaterthan 50 m. For this study, this definition pertainedstrictly to a spatial conformity, because individualswithin such associations were observed frequentlyto behave independently. Group sizes were classi-fied as: 1–2, 3–6, or >6 dolphins. Subject identifi-cation numbers were given to the dolphins ordolphin groups for each 1

2 tidal cycle, if dolphin(s)merged together the subsequent subject identifica-tion numbers were collated throughout the remain-der of the observation. If however, the originalsighting of dolphins(s) split off into different direc-tions, these individual observations kept the samesubject identification number but with revised num-bers of individuals. This was conducted to avoidcounting the same individual or group twice.

Dolphin/boat interactions were recorded when aboat was no further than 250 m from any dol-phin(s), with each interaction lasting no longer thanca. 5 min. Data were later pooled for both sites, dueto low sample sizes and the fact that the majority ofboats were observed at both sites. Time, boat type,boat position, distance offshore, direction of travel,dolphin(s) subject identification number, reactionof dolphin(s) towards boat, and distance of boatfrom dolphin(s) were recorded. Boat type wasclassified as: speedboat/dinghy, fishing boat/motorsailboat, tourist boat, or kayak. Boat position wasplotted along with the dolphin(s) position on a gridmap, to determine the dolphin(s) response towardsthe boat over time on a daily basis. Identificationnumbers were given to each dolphin/boat inter-action so as to identify which boat was associatedwith which dolphin or dolphin group. Dolphinbehaviour toward the boats was classified as nega-tive if the dolphin(s) moved away from the vessel,positive if the dolphin(s) moved towards the vessel,or neutral if the dolphin(s) showed no apparentchange in directional movement, prior to and afterthe arrival of the vessel. Dolphin(s) behaviourrelative to group size was recorded once alldolphin(s) showed the same behavioural responsetowards the vessel. If behavioural variationsoccurred within a group (i.e., a group size of four,two dolphins moved towards the vessel, while twodolphins showed no directional movement), theseobservations were ignored.

Data analysisTo identify between-site variability in the numberof dolphins observed in relation to the tidal stateand the time-of-day, a 2-way analysis of variance(ANOVA) was performed separately for eachfactor (STATGRAPHICS plus for Windows 3.0).Dolphin movements and foraging behaviour inrelation to the tidal state and the time-of-day,foraging behaviour in relation to group size,dolphin reactions to boat type and in relation togroup size, were all subjected to a ÷2 (goodness-of-fit test, Microsoft Excel for Windows 97).

Results

During the study period, 142 hrs of observationswere conducted. Total number of sightings ob-served during the course of study was 70, with 221counted dolphins. Thirty-nine sightings were atNew Quay, representing 153 counted dolphins, and31 sightings representing 68 counted dolphins wereat Ynys Lochtyn. Dolphins could only be observedeffectively up to 2 km offshore at both sites,although visibility on most days was up to 5 km.

Occurrence in relation to tidal state andtime-of-dayThere was a significant difference in the number ofdolphins between the two sites, with respect to tidalstate (F=4.81, P <0.05) and time-of-day (F=13.80,P <0.001). The mean number of dolphins observedin relation to the tidal state at New Quay washighest (11.0) between low water and 1

2 flood andlowest (4.2) between 1

2 flood and high water. Themean number of dolphins observed at YnysLochtyn in relation to the tidal state was highest(5.0) between high water and 1

2 ebb and also betweenlow water and 1

2 flood (4.8) and lowest (2.4) between12 flood and high water.

The mean number of dolphins observed in re-lation to the time-of-day at New Quay was highest(5.5) in the morning (06:00–10:30 hr), with numbersbeing relatively uniform for the rest of the day (3.3and 3.0). The mean number of dolphins observed inrelation to the time-of-day at Ynys Lochtyn wasuniformly low throughout the day (2.2), means inthe morning (06:00 to 10:30 hr) being 2.3 and forthe rest of the day 1.8.

Movement in relation to tidal state and time-of-dayThe examination of dolphin movement patternsand the tidal state at New Quay (Fig. 2a) revealedthat the highest number of dolphins moved offshorebetween 1

2 ebb and low water (32 individuals) andbetween low water and 1

2 flood (42 individuals). Thehighest number moving inshore was between 1

2 floodand high water (12 individuals), while 27 indi-viduals showed neutral movements between high

108 P. R. Gregory and A. A. Rowden

water and 12 ebb. The relationship between direction

of movement and tidal state at New Quay wasstatistically significant (÷2=94.55, df=6, P<0.001).Dolphins did not show statistically significantmovement patterns in relation to the time-of-day atNew Quay (÷2=6.32, df=4, P>0.1).

At Ynys Lochtyn (Fig. 2b), the highest number ofdolphins moved offshore between low water and 1

2

flood (17 individuals), while 13 individuals movedoffshore between high water and 1

2 ebb and 11individuals between 1

2 ebb and low water. Thehighest number (12 individuals) observed showingneutral movements was between high water and 1

2

ebb. There were no movements inshore at this site.The relationship between direction of movementand tidal state at Ynys Lochtyn also was statisti-cally significant (÷2=16.44, df=3, P<0.001).Dolphins did not show statistically significant

movement patterns in relation to the time-of-day atYnys Lochtyn (÷2=1.97, df=2, P>0.3).

Foraging behaviour in relation to tidal state andtime-of-dayMost dolphin foraging (Fig. 3a) took place betweenhigh water and 1

2 ebb (27 individuals) at New Quay.Traveling behaviour (offshore or inshore) domi-nated the remaining tidal states, particularlybetween low water and 1

2 flood (51 individuals). Therelationship of foraging behaviour with respect totidal state at New Quay was statistically significant(÷2=66.35, df=3, P<0.001). At Ynys Lochtyn (Fig.3b), dolphin foraging behaviour was concentratedbetween high water and 1

2 ebb (12 individuals) andbetween 1

2 flood and high water (8 individuals).Traveling behaviour was observed most often inbetween 1

2 flood and high water, with most dolphins

Figure 2. (a) Bottlenose dolphin directional movements relative to tidal state at New Quay(HW=high water, LW=low water), (b) directional movements relative to tidal state at YnysLochtyn (HW=high water, LW=low water).

109Behaviour patterns of the bottlenose dolphin

(17 individuals) traveling (offshore direction)between low water and 1

2 flood. The relationship offoraging behaviour with respect to the tidal stateat Ynys Lochtyn was statistically significant(÷2=23.94, df=3, P<0.001).

No relationship was found between dolphinforaging behaviour and the time-of-day at NewQuay (÷2=4.35, df=2, P>0.001). However, therewas a statistically significant relationship found atYnys Lochtyn (÷2=15.52, df=2, P<0.001), withmost foraging taking place in the morning. Four-teen individuals were observed foraging between06:00–10:30 hrs, while 24 individuals also wereobserved travelling offshore during this period.Relatively few dolphins were observed undertakingeither activity in the evening period (Fig. 4).

No relationship between dolphin foraging behav-iour in relation to group size was found at NewQuay (÷2=0.44, df=2, P>0.8) and Ynys Lochtyn

(÷2=0.39, df=1, P>0.5). However, at YnysLochtyn no group sizes above 4–6 individuals wereobserved.

Dolphin behaviour in relation to boat trafficDolphin response(s) to boats showed that 62% ofobservations were neutral i.e., the dolphins showedno apparent change in directional movement, priorto and after the arrival of the vessel. Twenty-twopercent of observations showed a negative response(moving away from the vessel), while 16% showed apositive response (moving towards the vessel).These differences in responses in relation to boattraffic were statistically significant (÷2=14.32, df=6,P<0.02). Dolphins showed a positive response (23%of observations) towards tourist boats, while thedolphins showed a negative response (57% ofobservations) towards kayaks. However, thereactions towards kayaks were from the same group

Figure 3. (a) Dolphin foraging behaviour relative to tidal state at New Quay (HW=high water,LW=low water), (b) Dolphin foraging behaviour relative to tidal state at Ynys Lochtyn (HW=highwater, LW=low water).

110 P. R. Gregory and A. A. Rowden

of 4–8 dolphins. Positive response(s) were not notedtowards kayaks or speedboats, while negativeresponse(s) were not noted for fishing boat/motorsailboats (Fig. 5). The relationship between groupsize and the response to boat traffic was notstatistically significant (÷2=4.36, df=4, P>0.4).

Discussion

During August, the bottlenose dolphin populationof Cardigan Bay showed a significant degree of sitepreference, with observations more frequent andconsisting of larger groups at New Quay than atYnys Lochtyn. A possible explanation could be thatdolphins are feeding on different prey items. Inthe shallower more sheltered areas of New Quay,dolphins possibly feed on benthic fish (i.e., dab,

Limanda limanda), which are characteristic speciesof soft sandy, gravely substrates. Feeding in such anenvironment could require more dolphins to searcha given area for inconspicuous prey. In the deepermore open waters around Ynys Lochtyn dolphinscould possibly feed on more conspicuous pelagicspecies (i.e., mackerel, Scomber scombrus), whichbottlenose dolphins seem to show a consistentpreference for (Mead & Potter, 1990). These speciesof fish could be detected more easily in the openwater, resulting in fewer dolphins required to searchan area.

Our observations suggested that the dolphinsused the tides and traveling with the tidal flow, ortraveling when the tidal flow is at its least strongestaround slack water. By adopting such a strategydolphins could reduce the energetic costs of

Figure 4. Number of bottlenose dolphins involved in foraging behaviour in relation to the time-of-day at Ynys Lochtyn.

Figure 5. Bottlenose dolphin reaction(s) to boat type at New Quay and Ynys Lochtyn(Negative=move away from vessel, Positive=move towards vessel, Neutral=no apparent responseto vessel).

111Behaviour patterns of the bottlenose dolphin

moving. Dolphins appeared to be strongly influ-enced by the tides in the studies carried-out in theShannon Estuary, SW Ireland, in which dolphinswere frequently recorded during mid-ebb tide,when the tidal current was strongest (Berrow et al.,1996). Irvine et al. (1981) also reported bottlenosedolphins in Sarasota Bay, Florida mainlyswimming with the tidal currents.

Alternatively, dolphins could be responding tofood availability due to the tidal variations byactively following their prey, since many fish speciesshow a tendency to follow the tides in searchof food (Harden Jones, 1968; Gibson, 1978;Wirjoatmodjo & Pither, 1984). Foraging behaviourwas correlated with the tidal state at both studysites. Observations were greatest between highwater and 1

2 ebb at New Quay and Ynys Lochtyn,and also between 1

2 flood and high water at YnysLochtyn. The foraging behaviour suggested that thedolphins could be responding to the tidal variationsdue to food availability, which is consistent withfindings from studies conducted in the Golfo SanJosé, Argentina (Würsig & Würsig, 1979), the coastof southern California (Hansen, 1990), and in theShannon Estuary, S.W. Ireland (Berrow et al.,1996).

Dolphin numbers generally were uniformly dis-tributed throughout each time class, with no rela-tionship found between dolphin movement patternsand the time-of-day at either of the two sites. Therewas no relationship between foraging activities andthe time-of-day at New Quay, but a relationshipwas found at Ynys Lochtyn. This may have beenbecause only dolphin(s) traveling offshore wererecorded at this site and no inshore movementswere observed. However, Saayman et al. (1973)found that foraging and feeding activity werestrongly correlated with the time-of-day inPlettenberg Bay, South Africa, and considered thatthis may have been related to the availability anddiurnal activity cycles of food-fish.

Foraging at New Quay and Ynys Lochtynmainly consisted of solitary individuals. Würsig &Würsig (1979) suggested that nearshore searchingfor food usually involves solitary individuals, whiledeeper water prey searches relies on a large groupthat often use combined sensory and echolocationabilities to locate and capture prey. Shane (1990)reported that ‘habitat structure and activitypatterns’ have the most influence on bottlenosedolphin group size and that ‘group size tends toincrease with water depth or openness of thehabitat.’ However, the correlation between habitatstructure and activity patterns relative to group sizewas not tested in the present study.

Behavioural responses of bottlenose dolphinstoward boats mainly were neutral, i.e., the dolphinsshowed no apparent change in directional move-

ment, prior to and after the arrival of the vessel.This neutral response could be due to habituationby the dolphins toward the boats, since most boattraffic in the area consists of tourist boats, whichconduct daily transects of the bay. Allen & Read(2000) found that vessel densities were not sufficientto evoke a measurable response in the bottlenosedolphins in Clearwater, Florida, and suggested thatthe dolphins are habituated to the level of vesseltraffic encountered.

A positive response towards tourist boats wasobserved, with dolphins usually swimming towardsthese vessels to bow-ride, which has been observedin studies involving bottlenose dolphins (Lockyer,1978; Würsig & Würsig, 1979) and other smallcetacean species, such as Hector’s dolphins (Stoneet al., 1995). Dolphins generally showed a negativeresponse towards kayaks, with 57% of observationsshowing dolphins moving away from this type ofvessel. The negative reactions towards kayaks werefrom the same group of 4–8 individuals, and wererepeatedly observed actively moving away to avoidthese types of vessel, often traveling up to distancesof 200 m away. This reaction could be due to a’startle response’ elicited in the dolphin(s) by thistype of vessel, due to their relatively silent approachcompared with a motor vessel. Kayaks are able tocome within a few metres of the dolphins when theyare foraging before dolphins react. Negativeresponses of bottlenose dolphins toward boat pres-ence have been reported in previous studies(Sorensen et al., 1984; Janik and Thompson, 1996),but these were related mainly to motor-vessels (andassociated noise disturbance). It has been suggestedthat disturbance may influence dolphin foragingactivity, which has a potential affect on populationstructure, i.e., reduction in food consumption couldresult in subtle changes in growth rate, reproductiverates, or unknown physiological effects of stressfrom remaining in an area with high disturbance,short-term or permanent movements to less favour-able areas, and ultimately survival (Grellier et al.,1995).

The current study suggests that the bottlenosedolphin population of Cardigan Bay displaydiurnal movement patterns relative to tidal state,either moving with the tides or moving when thereis least tidal resistance. It is most likely that thesemovement patterns are associated with distributionor movement of potential prey. Conversely, thetime-of-day does not seem to be involved in thedolphin’s occurrence or behaviour patterns. Localhabitat preference is possibly responsible for thedolphin population’s distribution between NewQuay and Ynys Lochtyn. In order to better under-stand the ecology of the bottlenose dolphin inCardigan Bay, detailed information on prey distri-bution and movement, preference for individual

112 P. R. Gregory and A. A. Rowden

prey items and prey migration in relation to thetides would be most useful. In addition, insightwould be further enhanced by extending futurestudies temporally. The present study raises interestin the effect of kayaks in Cardigan Bay, previouslybelieved to be benign, on the behaviour of thebottlenose dolphin population. Future studies onthe effects of boat disturbance would benefit from aconsideration of kayaks as having a potential influ-ence on the natural behaviour patterns of dolphins.However, in the present study certain parameterssuch as, change in surfacing duration, swimmingspeed, and changes in diving behaviour, whichcould indicate a reaction toward boats were un-recorded. The inclusion of such behaviours towardboats as an indication of boat disturbance wouldalso be of benefit to future studies.

Acknowledgments

The authors thank Drs. Peter Evans and JimHeimlich-Boran for their invaluable informationand advice. Thanks must also go to Drs. JulianStander and Peter Cotton at the University ofPlymouth, Liz Allan, Alison Gill, Holly Arnold,Steve Hartley and two reviewers for commentson this manuscript. P. R. Gregory thanksAmanda Brown for her inexhaustible tolerance andassistance throughout the entirety of this work.

Literature Cited

Allen, M. C. & Read A. J. (2000) Habitat selection offoraging bottlenose dolphins in relation to boat densitynear Clearwater, Florida. Marine Mammal Science 16,815–824.

Arnold, H. (1993) Distribution, abundance, and habitatuse of bottle-nosed dolphins in Cardigan Bay, Wales.European Research on Cetaceans 7, 63–66.

Ballance, L. T. (1990) Residence patterns, group organ-ization and surfacing associations of bottlenosedolphins in Kino Bay, Gulf of California, Mexico.Pages 267–284. In: S. Leatherwood and R. R. Reeves(eds.). The Bottlenose Dolphin. Academic Press,London.

Barco, S. G., Swingle, W. M., McLellan, W. A., Harris,R. N. & Pabst, D. A. (1999) Local abundance anddistribution of bottlenose dolphins (Tursiops truncatus)in the nearshore waters of Virginia Beach, Virginia.Marine Mammal Science 15, 394–408.

Berrow, S., Holmes, B. & Kiely, O. R. (1996) Distributionand abundance of bottle-nosed dolphins Tursiopstruncatus (Montagu) in the Shannon Estuary. Biologyand Environment: Proceedings of the Royal IrishAcademy 96B, 1–9.

Borrell, A. (1993) PCB and DDTs in blubber of cetaceansfrom the Northeastern North Atlantic. MarinePollution Bulletin 26, 146–151.

Bräger, S. (1993) Diurnal and seasonal behavior patternsof bottlenose dolphins (Tursiops Truncatus). MarineMammal Science 9, 434–438.

Evans, C. D. R. (1995a) Offshore Environment, chapter2.2. In: J. H. Barne, C. F. Robson, S. S. Kaznowskaand J. P. Doody (eds.). Coasts and Seas of the UnitedKingdom. Region 12 Wales: Margam to Little Orme.Joint Nature Conservation Committee, Peterborough.239 pp.

Evans, C. D. R. (1995b) Wind and Water, chapter 2.3. In:J. H. Barne, C. F. Robson, S. S. Kaznowska and J. P.Doody (eds.). Coasts and Seas of the United Kingdom.Region 12 Wales: Margam to Little Orme. Joint NatureConservation Committee, Peterborough. 239 pp.

Evans, P. G. H., S. Harding, G. Tyler & S. Hall.(1986) Analysis of Cetacean Sightings in the BritishIsles, 1958–1985. Nature Conservancy Council,Peterborough, 71 pp.

Evans, P. G. H. (1992) Status review of cetaceansin British and Irish waters. UK Mammal SocietyCetacean Group. Report to the UK Department ofEnvironment, London, 98 pp.

Evans, P. G. H. (1996) CCW Regional CoastalDirectory—Evans, P. G. H. (1995) Whales dolphinsand porpoises. Pages 137–140. In: J. H. Barne, C. F.Robson, S. S. Kaznowska and J. P. Doody (eds.).Coasts and Seas of the United Kingdom. Region 12Wales: Margam to Little Orme. Joint NatureConservation Committee, Peterborough. 239 pp.

Gibson, R. N. (1978) Lunar and tidal rhythms in fish.Pages 201–213. In: J. E. Thorpe (eds.). RhythmicActivity in Fishes. Academic Press, London.

Grellier, K., Arnold, H., Thompson, P., Wilson, B. &Curran, S. (1995) Management recommendations forthe Cardigan Bay bottlenose dolphin population. CCWContract Science Report 134.

Hansen, L. J. (1990) California coastal bottlenosedolphins. Pages 403–420. In: S. Leatherwood and R. R.Reeves (eds.). The Bottlenose Dolphin. Academic Press,London.

Harden Jones, F. R. H. (1968) Fish Migration, EdwardArnold, London.

Irvine, A. B., Scott, M. D., Wells, R. S. & Kaufman, J. H.(1981) Movements and activities of the Atlantic bottle-nose dolphin, Tursiops truncatus, near Sarasota,Florida. Fishery Bulletin 79, 671–688.

Janik, V. M. & Thompson, P. M. (1996) Changes insurfacing patterns of bottlenose dolphins in response toboat traffic. Marine Mammal Science 12, 597–602.

Leatherwood, S., Foster, L. & Reeves, R. R. (1983) TheSierra Club Handbook of Whales and Dolphins. SierraClub Books, San Francisco, CA.

Leatherwood, S. & Reeves, R. R. (1990) The BottlenoseDolphin. Academic Press, London.

Lewis, E. J. & Evans, P. G. H. (1993) Comparativeecology of bottle-nosed dolphins Tursiops truncatus inCardigan Bay and the Moray Firth. European Researchon Cetaceans 7, 57–62.

Lockyer, C. (1978) The history and behaviour of a solitarywild, but sociable, bottlenose dolphin (Tursiopstruncatus) on the west coast of England and Wales.Journal of Natural History 12, 513–528.

Mead, J. G. & Potter, C. W. (1990) Natural history ofbottlenose dolphins along the central Atlantic coast ofthe United States. Pages 165–195. In: S. Leatherwoodand R. R. Reeves (eds.). The Bottlenose Dolphin.Academic Press, London.

113Behaviour patterns of the bottlenose dolphin

Morris, R. J., Law, R. J., Allchin, C. R., Kelly, C. A. &Fileman, C. F. (1989) Metals and organochlorines indolphins and porpoises of Cardigan Bay, West Wales.Marine Pollution Bulletin 20, 512–523.

Saayman, G. S., Tayler, C. K. & Bower, C. (1973) Diurnalactivity cycles in captive and free-ranging Indian Oceanbottlenose dolphins (Tursiops aduncus Ehrenberg).Behaviour 44, 212–233.

Shane, S. H. (1990) Comparison of bottlenose dolphinbehavior in Texas and Florida, with a critique ofmethods for studying dolphin behavior. Pages 541–558In: S. Leatherwood and R. R. Reeves (eds.). TheBottlenose Dolphin. Academic Press, London.

Sorensen, P. W., Medved, R. J., Hyman, M. A. M. &Winn, H. E. (1984) Distribution and abundance ofcetaceans in the vicinity of human activities along thecontinental shelf of the northwestern Atlantic. MarineEnvironmental Research 12, 69–81.

Stone, G., Brown, J. & Yoshinaga, A. (1995) Diurnalpatterns of Hector’s Dolphin as observed fromclifftops. Marine Mammal Science 11, 395–402.

Vidal, O. (1993) Aquatic mammal conservation in LatinAmerica: problems and perspectives. ConservationBiology 7, 788–795.

Wells, R. S. & Scott, M. D. (1997) Seasonal incidence ofboat strikes on bottlenose dolphins near Sarasota,Florida. Marine Mammal Science 13, 475–480.

Wells, R. S. & Scott, M. D. (1999) Bottlenose dolphinTursiops truncatus (Montagu, 1821). Pages 137–182 In:S. H. Ridgway and R. Harrison (eds.). Handbook ofMarine Mammals. Volume 6. The second book ofdolphins and the porpoises. Academic Press, London.

Wiley, D. N., Wenzel, F. W. & Young, S. B. (1994)Extralimital residency of bottlenose dolphins in theWestern North Atlantic. Marine Mammal Science 10,223–226.

Wilson, B., Thompson, P. M. & Hammond, P. S. (1997)Habitat use by bottlenose dolphins: seasonal distribu-tion and stratified movement patterns in the MorayFirth, Scotland. Journal of Applied Ecology 34,1365–1374.

Wirjoatmodjo, S. & Pither, T. J. (1984) Flounders followthe tides to feed. Estuarine Coastal & Shelf Science 19,231–241.

Würsig, B. & Würsig, M. (1979) Behavior and ecology ofthe bottlenose dolphin, Tursiops truncatus, in the SouthAtlantic. Fishery Bulletin, US 77, 399–412.

114 P. R. Gregory and A. A. Rowden