1Murdoch University Cetacean Research Unit, Centre for Fish, Fisheries and Aquatic Ecosystems Research, School of Biological Sciences and Biotechnology, MurdochUniversity, Murdoch, Western Australia, 6150.2Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, New South Wales 2480, Australia.3Cetacean Ecology, Behaviour and Evolution Lab, School of Biological Sciences, Flinders University, Bedford Park, South Australia 5042.4South Australian Research and Development Institute, West Beach, Adelaide, South Australia, 5606.*Corresponding author: alex.brown@murdoch.edu.au

PACIFIC CONSERVATION BIOLOGY Vol. 18: 240–246. Surrey Beatty & Sons, Sydney. 2012.

The North West Cape, Western Australia: APotential Hotspot for Indo-Pacific Humpback

Dolphins Sousa chinensis?

ALEX BROWN1*, LARS BEJDER1, DANIELE CAGNAZZI2, GUIDO J. PARRA3,4 and SIMON J.ALLEN1

Indo-Pacific Humpback Dolphins Sousa chinensis (Humpback Dolphins hereafter) are listed as ‘near threatened’on an international level and ‘migratory’ in Australian waters. There is limited information on Humpback Dolphins inWestern Australian State waters, where the species remains unlisted. This lack of knowledge hinders the managementand conservation of the species in a region of rapidly increasing coastal development. We conducted opportunisticboat-based surveys in April 2010 and present data on the location, size and composition of Humpback Dolphin groupsencountered in the near-shore waters around the North West Cape, Western Australia. A total of 42 groups wereencountered in a variety of habitats during 145 h on the water over ca. 80 km coastline. Group size ranged from 1 to15, with a mean (± SE) of 5.3 (± 0.48) individuals. A total of 54 Humpback Dolphins were identified from photographsof the unique markings on their dorsal fins. The lack of a plateau in the cumulative discovery curve of identifiedindividuals over the duration of the study suggests that only a subset of dolphins in the area was identified. Thisregion is close to the south-western limit of the species’ Australian distribution and appears to represent an importantlocation for Western Australian Humpback Dolphins. In light of increasing anthropogenic activity around the NorthWest Cape and Exmouth Gulf, these preliminary findings from a limited survey effort indicate that further researchinto this population is required.

Key words: cetacean, coastal development, cumulative discovery curve, occurrence, photographic identification, tropicaldelphinid.

INTRODUCTION

THE Indo-Pacific Humpback Dolphin Sousachinensis (Humpback Dolphin hereafter) occursin tropical and temperate inshore watersthroughout the western Pacific and IndianOceans (Parra and Ross 2009). They are knownto occur along most of Australia’s tropicalnorthern coast, with a lack of research effort inremote regions accounting for the few recordsbetween the Gulf of Carpentaria, Queensland,and Shark Bay, Western Australia (WA) (Parra etal. 2004). Their distribution in WA waters wasdocumented as extending south-west toNingaloo Reef, with sightings as far south asShark Bay described as rare (Parra et al. 2004).Recent research confirmed that HumpbackDolphins occur in the waters off each coastaltownship across north-western WA (Coral Bay,Exmouth, Onslow, Dampier, Port Hedland andBroome) and suggested their known distributionbe extended to 25°S in accord with increasinglyfrequent records from Shark Bay (Allen et al.2012).

Despite Humpback Dolphins being widelydistributed in northern Australian waters, ourunderstanding of their ecology and populationstatus is limited to a few studies from easternQueensland. These studies indicate that Hump-back Dolphins live in small populations ofapproximately 50-100 individuals, between

which there are low levels of gene flow (Parraet al. 2006a; Cagnazzi 2011; Cagnazzi et al.2011; Parra 2011). They have relatively smallhome ranges within near-shore habitats, with apreference for waters < 15 m deep (Parra et al.2004; Parra 2006, 2006a,b; Cagnazzi 2011).

To date, there are no abundance estimatesavailable for any Humpback Dolphin populationin WA waters. Based on data from Queenslandand the extent of potentially suitable habitat,Bejder et al. (2012) estimated total numbers inWA to be in the low thousands of individuals(i.e., < 5 000). These relatively low numbersand the traits discussed above render HumpbackDolphin populations particularly vulnerable toenvironmental change, such as habitat degrada-tion (Parra et al. 2006a; Jefferson et al. 2009,2012; Bejder et al. 2012).

All marine mammals in WA waters areafforded protection under the WildlifeConservation Act 1950. Under this Statelegislation, species facing identified threats orimpacts may then be listed as “Threatened” or“Specially Protected”. Such a listing forHumpback Dolphins is currently precluded bythere being insufficient data upon which to basean assessment of their status. At aCommonwealth level, they are listed as“Migratory” under the Environment Protection andBiodiversity Conservation (EPBC) Act 1999 and,

BROWN ET AL.: NORTH WEST CAPE, W.A.: POTENTIAL HOTSPOT FOR HUMPBACK DOLPHINS 241

internationally, “Near Threatened” on the IUCNRed List. Allen et al. (2012) and Bejder et al.(2012) highlighted the inconsistencies betweeninternational, Commonwealth and Stateconservation listings and the issues presented bythe lack of data on tropical delphinids. In lightof the scale of coastal development across north-western Australia, they encouraged re-assessmentof species listings as more information becomesavailable. Through the creation and expansionof industrial ports and coastal processingfacilities to support the oil, gas and miningindustries, many sections of the near-shoreenvironment are undergoing or facingunprecedented, large-scale habitat modification(Bejder et al. 2012). The North West Cape is noexception, with several proposed port facilitydevelopments along the eastern coast,hydrocarbon exploration offshore and in theExmouth Gulf, as well ongoing tourism activityassociated with Ningaloo Marine Park (AMCManagement 2011; CCG 2011).

Here, we present preliminary information onthe occurrence of Humpback Dolphins in thenear-shore waters around the North West Cape,WA. We aim to: (1) provide preliminary baselinedata on Humpback Dolphins around the NorthWest Cape; (2) identify the implications this hasfor their effective management in habitats likely

to undergo considerable change in the nearfuture; and (3) make recommendations forfuture research efforts.

METHODS

Study site

The North West Cape, situated at 21.8°S:114.1°E, represents the north-western extremityof the Australian mainland (Fig. 1). Australia’slargest fringing coral reef, Ningaloo Reef,dominates its near-shore habitats, extendingalmost continuously from approximately 10 kmnorth of Exmouth, around the north coast ofthe cape and down the west coast, creating alagoon of up to several km in width. Much ofthe study site falls under the State andCommonwealth designation of the NingalooMarine Protected Area, which covers a total of5 070 km2 of State and Commonwealth watersaround the North West Cape. This area wasawarded World Heritage status in 2011.

The study area is a diverse environment, withhabitats including subtidal and intertidal hardcorals, bare reef, soft corals, sponge gardens,seagrass beds, sand flats, mud flats andmangroves (WA Department of Environment

Fig. 1. Study area, including vessel launch sites and Humpback Dolphin group locations and sizes observed around the NorthWest Cape (excluding any Indo-Pacific Bottlenose Dolphins present).

242 PACIFIC CONSERVATION BIOLOGY

and Conservation 2011). While the waters ofExmouth Gulf are relatively shallow(predominantly < 20 m deep), depth increaseswest of the Ningaloo Reef to several hundred mwithin 10–15 km of the coast (WA Departmentof Environment and Conservation 2011).

Data collection

In April 2010, photo-identification surveysof Humpback Dolphins were conductedopportunistically around the top of the NorthWest Cape (Fig. 1). These surveys wereconducted as part of broader studies assessingthe genetic connectivity of Indo-PacificBottlenose Tursiops aduncus, Australian SnubfinOrcaella heinshoni and Humpback Dolphinsacross north-western Australia. As biopsysampling of the aforementioned species was apriority during fieldwork, limited effort wasexpended photographing evasive animals orthose encountered during poor weatherconditions (see Allen et al. 2012 for furtherdetails). Furthermore, the photo-identificationeffort was biased toward biopsied individuals, sosome individuals were likely to have beenmissed.

Data collection involved boat-based surveys ofthe near-shore waters along a ca. 80 km stretchof coastline. No pre-determined course wasfollowed, with search patterns largely dictated bysea conditions (preference for Beaufort 2 andswell 0.5 m) and directed towards areas ofpotential Humpback Dolphin habitat (i.e., waters< 5 km from shore and 15 m depth). Threedifferent boat launch sites (Exmouth BoatHarbour, Bundegi boat ramp and Tantabiddiboat ramp) were used (Fig. 1). The study areacan be broadly defined as between 15 km southof Tantabiddi in the south-west and 15 kmsouth of Exmouth in the south-east, andextending offshore to the 15 m depth contour.Search effort was greatest within 3 km of shoreand concentrated around the top of the NorthWest Cape between Bundegi and Tantabiddi.Time on the water was restricted to daylighthours (between ca. 0600 and 1800) andBeaufort sea states of 3.

The research platforms were small (5.5 m)aluminum boats, powered by 100 hp petroloutboard motors. Two teams used two vessels forthe first six surveys, with just one teamcontinuing thereafter. Three to four observersscanned the water surface for dolphins within90 degrees of the vessel’s heading, using nakedeye and, occasionally, hand-held binoculars. Thevessel typically maintained a speed of 6-7 knotswhile searching for dolphins.

When Humpback Dolphin groups wereencountered, information was recorded on theirlocation (latitude and longitude), group size,

group composition and water depth. As in Allenet al. (2012), a dolphin group was defined as oneor more individuals within a 100 m radius of acentral individual and engaged in similarbehaviour. Photographic identification imageswere obtained for as many individuals aspossible, using a single DSLR camera and a100–400 mm telephoto zoom lens per vessel.Group size and the number of dependent calves(as defined by Parra et al. 2006a) were recordedat the onset of the sighting. Mixed-speciesgroups of Humpback Dolphins and Indo-PacificBottlenose Dolphins were approached andrecorded in the same manner, althoughinformation recorded on Indo-Pacific BottlenoseDolphins within the group was restricted to thenumber of individuals present.

Data presentation

The locations of Humpback Dolphin groupsand their distance from shore (minimumstraight line distance from initial group locationto high-water mark) were mapped using ESRI’sArcGIS v9.3 software. A frequency histogram wasproduced to illustrate the distribution of groupsizes encountered. We calculated summarystatistics on group size and frequency of thepresence of calves, water depth, and the distancefrom shore groups were observed. Resultspresented on group size and compositionexclude any Indo-Pacific Bottlenose Dolphinspresent (unless stated otherwise). Photographswere examined for unique features (nicks, scars,pigmentation) on the dorsal fin and a catalogueof individual animals was developed (Würsigand Jefferson 1990). Dorsal fin features did notneed to be deemed permanent due to the shortduration of the study period. Only photographsof excellent and good quality (in terms of focus,contrast, and distance and angle to subject) wereused for this purpose (e.g., Urian et al. 1999;Friday et al. 2000; Gowans and Whitehead2001). A cumulative discovery curve was plottedto illustrate the rate at which new individualswere identified, and a histogram used to showthe frequency with which individually identifieddolphins were observed.

RESULTS

Total time on the water comprised 145 h over18 days, or part thereof. One vessel contributed45 h, while the other completed 100 h. Thisincludes time searching for dolphins, time withdolphins and time motoring at speed. A totalof 42 groups of Humpback Dolphins wereencountered during the study period. Thegroups were encountered widely around theNorth West Cape (Fig. 1), with 23 groupssighted along the west and north-west coasts ofthe cape, 10 along a relatively short (ca. 5 km)

<<

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BROWN ET AL.: NORTH WEST CAPE, W.A.: POTENTIAL HOTSPOT FOR HUMPBACK DOLPHINS 243

stretch of coast with a north-east aspect at thetip of the cape and nine along the east coast.

Groups were encountered at water depthsbetween 1.2 and 20 m, with a mean (± SE) of7.8 m (± 0.74). The majority of groups (95%)were encountered in waters < 15 m deep, wheresearch effort was concentrated. The distancefrom shore at which groups were sighted rangedfrom 269 m to 4.5 km, with a mean (± SE) of1 km (± 0.11). Group size ranged from one to15 dolphins, with a mean (± SE) of 5.3 (± 0.48)individuals (Fig. 2). Approximately two thirds (n= 28) of the Humpback Dolphin groupsencountered contained calves.

A total of 54 individual Humpback Dolphins(excluding dependent calves) werephotographically identified. The cumulativediscovery curve indicated a relatively consistentincrease in the number of individuals identifiedover the duration of the sampling period, withno indication of leveling off (Fig. 3). Anexamination of the sighting frequency ofidentified individuals indicated that 50% ofindividuals were observed only once, with afurther 24% and 11% observed on two andthree separate days, respectively. Fourindividuals (7%) were observed on four days,and another four individuals were sighted onfive separate days.

Of the 42 Humpback Dolphin groupsencountered, 10 (24%) also contained Indo-Pacific Bottlenose Dolphins. Mean (± SE) groupsize of mixed species groups was 9.5 (± 1.33)individuals, within which mean (± SE) numbersof Humpback and Indo-Pacific BottlenoseDolphins were 5.5 (± 0.96) and 4.2 (±0.66),respectively.

DISCUSSION

Groups of Humpback Dolphins wereencountered widely around the North West

Cape. The water depths and distances fromshore at which they were encountered werebroadly similar to those reported from easternQueensland (e.g., Parra 2006; Parra et al. 2006b;Cagnazzi 2011), although this may be biased bythe greater time spent searching in near shorewaters < 15 m deep. Mean group size reportedhere was slightly larger than that reported inCleveland Bay (Parra et al. 2011) and along theCapricorn Coast (Cagnazzi 2011), although therange was very similar. Almost one quarter of allHumpback Dolphin groups encountered aroundthe North West Cape also included Indo-PacificBottlenose Dolphins.

Over eighteen days, 145 h on the wateraround the North West Cape yielded 54identified individuals from 42 groups. Thecumulative discovery curve indicated a relativelyconsistent increase in the number of individualsidentified over the duration of the samplingperiod, with no plateau. This pattern, combinedwith the high proportion of animals which wereonly observed once during the study period,suggests that only a subset of the animals usingthe area were identified.

Certain comparisons can be drawn betweenthe number of individual Humpback Dolphinsidentified here and those reported from studiesin Queensland (Table 1). Using only the resultsfrom the first ca. 145 h of these dedicatedphoto-identification studies, the number ofindividuals identified was 16 (Cleveland Bay), 71(Great Sandy Straits), 16 (Keppel Bay) and 46(Port Curtis) (Cagnazzi 2011; Cagnazzi et al.2011; Parra 2005; Parra et al. 2006a). Thisindicates a larger number of initially identifiedindividuals at the North West Cape than all butthe Great Sandy Straits region, which, atapproximately 1 000 km2, is four times largerthan the ca. 250 km2 covered in this study.

At the 310 km2 study site of Cleveland Bay,Parra et al. (2006a) encountered 143 groups and

Fig. 2. Range of Humpback Dolphin group sizesdocumented around the North West Cape (excludingany Indo-Pacific Bottlenose Dolphins present).

Fig. 3. Cumulative discovery curve of adult and juvenileHumpback Dolphins identified over the study period.

244 PACIFIC CONSERVATION BIOLOGY

identified a total of 54 individual HumpbackDolphins in 630 h on the water over fourseasons. A pattern of alternating small increasesand plateaus in the cumulative discovery curveof identified individuals, combined withmodelling of individuals’ lagged identificationrate, suggested an open population withHumpback Dolphins moving in and out of theirstudy area. Population estimates for ClevelandBay ranged from 34–54 between 1999 and 2002(Parra et al. 2006a).

Over two wet and two dry seasons in the GreatSandy Straits, Cagnazzi et al. (2011) identified106 adult Humpback Dolphin individuals from263 groups. In contrast to the findings of Parraet al. (2006a), a cumulative discovery curveshowed a distinct levelling off to an almostconstant level, with 74% of the permanentlymarked individuals identified by the end of thefirst of four seasons. This was attributed to ageographically closed population, in whichidentified dolphins were primarily long-termresidents in the study area. Abundance for twopopulations (northern and southern, with almostno spatial overlap) was estimated at approxi-mately 75 individuals each (Cagnazzi et al. 2011).

We acknowledge methodological differences inthe photo-identification analyses, size andhabitat characteristics of study areas, and thelevel of effort between this study and thosereported in Parra et al. (2006a), Cagnazzi (2011)and Cagnazzi et al. (2011). However, our resultssuggest that longer-term, structured effortaround the North West Cape would likely yielda higher density of Humpback Dolphins thanthose reported in Queensland.

Allen et al. (2012) reported sightings ofHumpback Dolphins off each coastal townshipacross north-western WA in 2010; however,comparisons between the North West Cape andthese other WA sites are hampered by methodo-logical differences. Beyond the North WestCape, Humpback Dolphin encounters were only

Initially Totalidentified identifiedanimals animals Population Size of study

Location (effort) (effort) estimate area (km2) Reference

North West Cape, 54(145 h*) na na 250 (approx) This studynorth-west WACleveland Bay, north-east QLD 16 54 34 (95% Cl:24 310 Parra 2005;

(140 h*) (630 h*) -49) to 54 (95% Parra et al.Cl: 38-77) between 2006a1999 and 2002

Great Sandy 71 106 150 (95% Cl: 1 000 Cagnazzi et al.Straits, east QLD (142 h**) (1250 h**) 132.5-165.2) 2011Keppel Bay, 16 84 107 (95% Cl: 650 Cagnazzi 2010east QLD (150 h**) (775 h**) 97.5-116.5)Port Curtis, 46 63 85 (95% Cl: 200 Cagnazzi 2010east QLD (150 h**) (293 h**) 76.6-93.7)

Table 1. Number of identified animals during initial ca. 150 h of effort and throughout entire study: comparison betweenthe North West Cape and Queensland study sites. * time on water; ** search effort.

recorded by Allen et al. (2012) when a biopsysample was successfully obtained. Statistics forthe number of samples obtained/hours on thewater indicate that the North West Cape (24/145) was exceeded only by the DampierArchipelago (20 /49), where the animals werequalitatively noted as being far moreapproachable than all other sites. All other sitesyielded 3 individuals sampled (Allen et al.2012).

It is important to consider the limitations ofthis study and the cautionary approach thisshould impose on the interpretation of ourresults. These data were collected oppor-tunistically during research to acquire biopsysamples from all three tropical inshoredelphinids occurring in north-western Australianwaters (see Allen et al. 2012). Consequently, wedid not engage in standardized survey protocols(e.g., structured distribution of effort) toestimate abundance or assess habitat preference.Additionally, a dedicated photo-identificationstudy would have involved allocating more effortto obtaining identifiable photographs of allindividuals. With dedicated effort on photo-identification during the same sampling period,it is likely that a greater number of individualswould have been identified, with consequentialeffects on the shape of the cumulative discoverycurve. Furthermore, the study period reportedhere spans less than one month of the year;greater temporal coverage is required in orderto fully assess the importance of this region toHumpback Dolphins.

Despite these limitations, the preliminary datasuggest that the North West Cape represents animportant region comprising suitable habitatsfor Humpback Dolphins. In light of the paucityof information on Humpback Dolphins in WAwaters, these data should serve as a platform forfuture research aimed at assessing populationsize and habitat requirements for thisinsufficiently known species around the NorthWest Cape.

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BROWN ET AL.: NORTH WEST CAPE, W.A.: POTENTIAL HOTSPOT FOR HUMPBACK DOLPHINS 245

The North West Cape remains relativelyundeveloped to date. Those areas covered bythe Marine Protected Area and World Heritagelistings experience minimal commercial fishingactivity, tightly regulated recreational fishing,and are not subject to major developmentpressures at present (DEWHA 2010). Theseconservation designations provide a strong legalbasis for protection of the qualifying featuresand carefully managed development over a largeproportion of the region. However, the inshorewaters of the Exmouth Gulf south of Bundegiremain beyond these boundaries and are likelyto experience considerable development in thefuture.

The favourable proximity of the North WestCape to the expanding hydrocarbon facilities ofthe adjacent North West Shelf has attractedmuch interest as a hub for associated onshorefacilities. AMC Management (2011) presentedan examination of the feasibility and potentiallocation of developing a common user facility(multiple user supply base / port infrastructure)on the north-west coast of Australia. Theydescribe four different harbour-based develop-ments in the Exmouth region which may serveas supply / logistics bases for offshore industry;one is currently under construction, while threeare proposed / in planning (EPA 1997; AMCManagement 2011; Learmonth Offshore LogisticsHub 2012). Additionally, interests have beenexpressed in the future utilization of the site andpier facilities (Harold E. Holt CommunicationsBase) at the north-western tip of the North WestCape, also to support offshore industry (CCG2011).

At present, the majority of hydrocarbonexploration and production activity in theregion takes place offshore, largely in excess of20 km from the north coast of the North WestCape and with no associated pipelines comingashore on the cape. Historically, activity closerto the coast has been limited, with only a smallnumber of exploration wells in the ExmouthGulf and patchy seismic survey effort around theNorth West Cape (WA Department of Mines andPetroleum 2012). However, interest in thepotential resources of the Exmouth Gulfcontinues: several exploration permits within thewestern side of the Gulf remain active; an areaof 2 813 km2 covering the rest of the Gulf wasopened for tender in 2010 for explorationactivities; and the majority of the Gulf is coveredby active mineral (non-petroleum) explorationpermits (Geological Survey of Western Australia2010; WA Department of Mines and Petroleum2012).

With reference to protecting small cetaceans inthe busy waters of Hong Kong, Jefferson et al.(2009) provided a summary of the mainactivities associated with coastal developmentthat may impact Humpback Dolphins. Land

reclamation, seabed construction (e.g., cable/pipe laying), dredging and dumping of dredgedmaterial are major concerns; these causemodification or irreversible loss of inshorehabitats and may influence water quality. Noisefrom increased vessel traffic and constructionactivities, such as pile-driving and underwaterblasting, present further potential pathways fordetrimental effects on sensitive marine species,as does noise associated with oil and gasexploration. The Hong Kong/Pearl River Estuaryregion is an extreme example of large-scale,long-term coastal development. Studies of theHumpback Dolphin population in this area havereported evidence of vessel strikes, entangle-ment, contaminant burdens, and high calfmortality (Jefferson et al. 2006, 2012). However,information on trends in abundance is lackingand the pathways between environmentalstressors associated with coastal developmentand population-level impacts on HumpbackDolphins in the Hong Kong/Pearl River Estuaryremain poorly understood.

Adequate baseline data on marine megafauna,such as inshore delphinids, is an essentialprerequisite to effectively assess theenvironmental impact of coastal developmentsand hydrocarbon exploration in north-westernAustralia. We have presented preliminaryevidence that the inshore waters of the NorthWest Cape are of importance for HumpbackDolphins, an insufficiently known species closeto the south-western limit of its range. Werecommend the development of a structuredresearch program to assess the abundance andhabitat use of Humpback Dolphins and otherinshore delphinids around the North West Capeover a greater temporal range, in order toprovide timely baseline information beforeextensive coastal development takes place.

ACKNOWLEDGEMENTS

This research was funded by AustralianMarine Mammal Centre grants 2008-09/19 and2009/19, and conducted under permits andapprovals from the Department of LocalGovernment Research and Development (U 6/2010-2011), the WA Department ofEnvironment and Conservation (SF007596) andthe Murdoch University Animal EthicsCommittee (W2342/10). Michael Krützenprovided the use of the second research vesseland vehicle and he, Dee McElligott, FrazerMcGregor and Alice Soccadato assisted in thefield. We are grateful to Tamara Organ for thefin-matching effort. We also extend thanks toLyn Irvine for providing information ondevelopment projects in Exmouth Gulf andAspen Parks for the provision of freeaccommodation for the research team. Thismanuscript was greatly improved by

246 PACIFIC CONSERVATION BIOLOGY

incorporating the recommendations of twoanonymous reviewers.

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