Aquatic Mammals 2001, 27.2, 105–113 Behaviour patterns of bottlenose dolphins (Tursiops truncatus) relative to 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 Introduction Diurnal behaviour patterns of the bottlenose The bottlenose dolphin (Tursiops truncatus, dolphin (Tursiops truncatus) were investigated at Montagu) is a cosmopolitan species, found two sites in relation to tidal state, time-of-day, and throughout the world’s tropical and temperate seas boat traffic in Cardigan Bay, west Wales. The two and oceans (Shane, 1990). The wide distribution of sites chosen were New Quay and Ynys Lochtyn. this species has allowed detailed studies at a variety Between-site variability existed in the occurrence of of locations, such as Sarasota Bay, Florida, USA dolphins. However, no relationship was found (Irvine et al., 1981; Wells & Scott, 1997), Kino Bay, between the numbers of dolphins observed in rela- Gulf of California, Mexico (Ballance, 1990), the tion to the tidal cycle or time-of-day at either of the Moray Firth, Scotland (Wilson et al., 1997), and the two sites. Dolphin movement patterns were corre- Shannon Estuary, southwest (SW) Ireland (Berrow lated with tidal state at both sites, with the dolphins et al., 1996). Studies showed that the bottlenose moving with the tidal flow or during slack water. dolphin occupies a variety of marine habitats, from No relationship was found between movement deep oceans to shallow coastal regions, inshore patterns and time-of-day. Foraging behaviour was lagoons and estuaries (Leatherwood & Reeves, correlated with tidal state at both sites, with 1990). Populations can be either offshore-pelagic in dolphins foraging mainly between the flood and ebb their ranging patterns, or inshore-coastal resident tides of high water. Foraging in relation to group populations. Little is known about the ranging size was not significant at either site. No relation- patterns of pelagic bottlenose dolphins, but coastal ship was found between foraging behaviour and dolphins exhibit a full spectrum of movements, time-of-day. Statistically significant behavioural including seasonal migrations, year-round home responses were noted towards boat traffic. Dolphins ranges, periodic residency, and a combination of generally displayed a neutral response toward occasional long-range movements and repeated boats, i.e., the dolphins showed no apparent change residency (Wells & Scott, 1999). in directional movement, prior to and after the Resident populations have received most atten- arrival of the vessel. However, dolphins displayed a tion owing to their locally dispersed geographical negative response toward kayaks, and a positive ranges (Bräger, 1993; Lewis & Evans, 1993; Berrow response toward tourist boats. Dolphin’s reactions et al., 1996; Wilson et al., 1997). Most resident toward boats in relation to group size were not groups of bottlenose dolphins show systematic statistically significant. The study supported the patterns in their behaviour, such as foraging/ findings of previous studies on bottlenose dolphins feeding, socializing, and moving from area to area in other localities; however, the effect of kayaks in relation to environmental cues, such as the requires further investigation. Recommendations tides (Irvine et al., 1981; Leatherwood et al., 1983; are made for future avenues of research regarding Wilson et al., 1997), the time of day (Saayman et al., this species. 1973; Würsig & Würsig, 1979; Bräger, 1993), and depth (Wiley et al., 1994). Many potential threats exist to resident popula- Key words: bottlenose dolphin, Tursiops truncatus, tions, often via contact with human activities. These Cardigan Bay, diurnal behaviour patterns, tidal anthropogenic threats include entanglement in fish- state, time-of-day, boat traffic. ing gear (Vidal, 1993), exposure to environmental 2001 EAAM 106 P. R. Gregory and A. A. Rowden Figure 1. (a) Study sites in Cardigan Bay, West Wales, (b) New Quay, and (c) Ynys Lochtyn. ( —Observation points). pollutants (Morris et al., 1989; Borrell, 1993), and effect on the movement patterns of the bottlenose disturbances from boat traffic (Sorensen et al., dolphins. 1984; Janik & Thompson, 1996; Wells & Scott, 1997; Allen & Read, 2000). In inshore-coastal Materials and Methods waters the bottlenose dolphin is probably the second most common cetacean in the United Study area Kingdom (Evans et al., 1986; Evans, 1992). The Cardigan Bay is the largest bay in the British Isles, Cardigan Bay (West Wales) population is estimated bound on three sides by the Welsh coast and open to range from 130 to 230 individual dolphins to the Irish Sea on its western boundary (Fig. 1a). It (Grellier et al., 1995), with only a proportion of encompasses an area of approximately 5500 km2. the animals being resident throughout the year The water depth in the bay does not exceed 50 m (Arnold, 1993; Lewis & Evans, 1993). Bottlenose and becomes increasingly shallower from west to dolphins are frequently seen within 15 km of the east, with an average depth of approximately 40 m coast between Cardigan and Borth, from April (Evans, 1995a). The nature of the seabed in the bay to October. Headlands at Mwnt, Pen Peles, is extremely heterogeneous, ranging from fine sand Aberporth, Ynys Lochtyn, and New Quay are and broken shell, to gravel, shingle, and muddy particularly favoured feeding areas for bottlenose sand (Evans, 1995a). The tidal regime of the area, dolphins (Evans, 1996). results from the tide entering the Irish Sea through The principal aim of the present study was to St. George’s Channel in the south and travelling determine whether the tidal cycle or the time-of-day northward to meet the southward-moving tide from had an affect on the diurnal movement pattern of the north in the vicinity of the Isle of Man. The the bottlenose dolphin population, in two pre- resultant weak tidal currents run northward during determined geographical locations in Cardigan Bay. the flood and southward during the ebb (Evans, In addition, because the area is frequented by boats 1995b). The tides in the area are semi-diurnal and of various kinds, the study also aimed to assess the tidal range in Cardigan Bay is fairly uniform whether boat activity has a detrimental or benign (ca. 2 m at neaps and 4 m at springs). Behaviour patterns of the bottlenose dolphin 107 Boat traffic is prevalent in the area, especially by eye continuously for a full 6 h and 15 min, around Cardigan, Aberporth, New Quay, covering one half tidal cycle per day. Scans of the Aberaeron, and Aberystwyth, which are frequented horizon were conducted at 15-min intervals, with by tourists. During the tourist season (April to the aid of Opticron 8#24 lightweight water- October), boats operate out of New Quay and proof hand-held field binoculars and Nikon field Aberaeron, taking tourists on trips around the telescope. Time, position of dolphin(s) surfacing, bay to observe the dolphins and other wildlife. distance offshore, direction of travel, feeding Water sports and recreational boat activities behaviour, and sea state were recorded. Data were increase in the summer months, with many visitors only collected when the sea state (Beaufort Scale) launching powerboats, sailboats, and kayaks from was c3. With sea states >3, sightings become less the above ports. reliable (Barco et al., 1999). Dolphin counts were made once a dolphin(s) was sighted upon surfacing, and then observed for ca. 5 min or until the number Study sites of individuals counted became consistent, so as not A land-based observational study was adopted, to underestimate or overestimate dolphin numbers. rather than a boat-based one, to minimize the Dolphin positions were recorded every 10 min effects of observer presence on the dolphin’s natural once dolphin(s) were sighted, in addition to the behaviour. Two study sites where chosen in continuous observation of the study area. Cardigan Bay, locations being New Quay Headland Estimated distances offshore were obtained with (52 13 05 N, 04 21 84 W) and Ynys Lochtyn, a ) * ) * the aid of a 10-m motor vessel, which followed a northwesterly peninsula cliff-top (52 10 28 N, ) * transect offshore, stopping at distances of 500 m 04 27 98 W), (Fig. 1b and c). The observational ) * and 1 km. These distances were noted from shore areas were ca. 8km2 for both sites. New Quay and prior to and during the study (via VHF radio Ynys Lochtyn headlands were both chosen for their communication with the motor vessel) and used as high vantage positions over looking the bay (75 m visual references, with the additional aid of photo- and 40 m, respectively) and because dolphins were graphs. At the New Quay site, an additional refer- seen on a regular basis in the past at both sites. ence point (North marker buoy, 1 km offshore) was The New Quay site represents a shallow semi- used. The position and direction of travel of the enclosed bay with restricted tidal flow. The bottom dolphin(s) were recorded with the aid of a field- topography is smooth, with depths ranging from 1 sighting compass. Dolphin(s) positions and dis- to 12 m in a gradual sloping direction offshore. The tances offshore were plotted on a 1 km2 grid cell substrate at this site consists of coarse to fine sand. basis over time, using the appropriate scale on a The Ynys Lochtyn site comprises of a rocky head- map (New Quay; Ordnance Survey Map scale land which experiences relatively strong tide rips 1:10,000, SN 35 NE, SN 45 NW and SN 46 SW, and turbulence during the changes from each and Ynys Lochtyn; Ordnance Survey Map scale amplitudinal tide. The water depth is more constant 1:10,000, SN 35 SW and SN 35 NW).