The North West Cape, Western Australia: A Potential 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 in Western Australian State waters, where the species remains unlisted. This lack of knowledge hinders the management and conservation of the species in a region of rapidly increasing coastal development. We conducted opportunistic boat-based surveys in April 2010 and present data on the location, size and composition of Humpback Dolphin groups encountered in the near-shore waters around the North West Cape, Western Australia. A total of 42 groups were encountered in a variety of habitats during 145 h on the water over ca. 80 km coastline. Group size ranged from 1 to 15, with a mean (± SE) of 5.3 (± 0.48) individuals. A total of 54 Humpback Dolphins were identified from photographs of the unique markings on their dorsal fins. The lack of a plateau in the cumulative discovery curve of identified individuals over the duration of the study suggests that only a subset of dolphins in the area was identified. This region is close to the south-western limit of the species’ Australian distribution and appears to represent an important location for Western Australian Humpback Dolphins. In light of increasing anthropogenic activity around the North West Cape and Exmouth Gulf, these preliminary findings from a limited survey effort indicate that further research into this population is required. Key words: cetacean, coastal development, cumulative discovery curve, occurrence, photographic identification, tropical delphinid.
T
INTRODUCTION
HE Indo-Pacific Humpback Dolphin Sousa chinensis (Humpback Dolphin hereafter) occurs in tropical and temperate inshore waters throughout the western Pacific and Indian Oceans (Parra and Ross 2009). They are known to occur along most of Australia’s tropical northern coast, with a lack of research effort in remote regions accounting for the few records between the Gulf of Carpentaria, Queensland, and Shark Bay, Western Australia (WA) (Parra et al. 2004). Their distribution in WA waters was documented as extending south-west to Ningaloo Reef, with sightings as far south as Shark Bay described as rare (Parra et al. 2004). Recent research confirmed that Humpback Dolphins occur in the waters off each coastal township across north-western WA (Coral Bay, Exmouth, Onslow, Dampier, Port Hedland and Broome) and suggested their known distribution be extended to 25°S in accord with increasingly frequent records from Shark Bay (Allen et al. 2012). Despite Humpback Dolphins being widely distributed in northern Australian waters, our understanding of their ecology and population status is limited to a few studies from eastern Queensland. These studies indicate that Humpback Dolphins live in small populations of approximately 50-100 individuals, between
which there are low levels of gene flow (Parra et al. 2006a; Cagnazzi 2011; Cagnazzi et al. 2011; Parra 2011). They have relatively small home ranges within near-shore habitats, with a preference for waters < 15 m deep (Parra et al. 2004; Parra 2006, 2006a,b; Cagnazzi 2011). To date, there are no abundance estimates available for any Humpback Dolphin population in WA waters. Based on data from Queensland and the extent of potentially suitable habitat, Bejder et al. (2012) estimated total numbers in WA to be in the low thousands of individuals (i.e., < 5 000). These relatively low numbers and the traits discussed above render Humpback Dolphin populations particularly vulnerable to environmental change, such as habitat degradation (Parra et al. 2006a; Jefferson et al. 2009, 2012; Bejder et al. 2012). All marine mammals in WA waters are afforded protection under the Wildlife Conservation Act 1950. Under this State legislation, species facing identified threats or impacts may then be listed as “Threatened” or “Specially Protected”. Such a listing for Humpback Dolphins is currently precluded by there being insufficient data upon which to base an assessment of their status. At a Commonwealth level, they are listed as “Migratory” under the Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and,
Murdoch University Cetacean Research Unit, Centre for Fish, Fisheries and Aquatic Ecosystems Research, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, Western Australia, 6150. Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, New South Wales 2480, Australia. 3 Cetacean Ecology, Behaviour and Evolution Lab, School of Biological Sciences, Flinders University, Bedford Park, South Australia 5042. 4 South Australian Research and Development Institute, West Beach, Adelaide, South Australia, 5606. *Corresponding author:
[email protected] 1
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PACIFIC CONSERVATION BIOLOGY Vol. 18: 240–246. Surrey Beatty & Sons, Sydney. 2012.
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internationally, “Near Threatened” on the IUCN Red List. Allen et al. (2012) and Bejder et al. (2012) highlighted the inconsistencies between international, Commonwealth and State conservation listings and the issues presented by the lack of data on tropical delphinids. In light of the scale of coastal development across northwestern Australia, they encouraged re-assessment of species listings as more information becomes available. Through the creation and expansion of industrial ports and coastal processing facilities to support the oil, gas and mining industries, many sections of the near-shore environment are undergoing or facing unprecedented, large-scale habitat modification (Bejder et al. 2012). The North West Cape is no exception, with several proposed port facility developments along the eastern coast, hydrocarbon exploration offshore and in the Exmouth Gulf, as well ongoing tourism activity associated with Ningaloo Marine Park (AMC Management 2011; CCG 2011). Here, we present preliminary information on the occurrence of Humpback Dolphins in the near-shore waters around the North West Cape, WA. We aim to: (1) provide preliminary baseline data on Humpback Dolphins around the North West Cape; (2) identify the implications this has for their effective management in habitats likely
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to undergo considerable change in the near future; and (3) make recommendations for future research efforts. METHODS Study site The North West Cape, situated at 21.8°S: 114.1°E, represents the north-western extremity of the Australian mainland (Fig. 1). Australia’s largest fringing coral reef, Ningaloo Reef, dominates its near-shore habitats, extending almost continuously from approximately 10 km north of Exmouth, around the north coast of the cape and down the west coast, creating a lagoon of up to several km in width. Much of the study site falls under the State and Commonwealth designation of the Ningaloo Marine Protected Area, which covers a total of 5 070 km2 of State and Commonwealth waters around the North West Cape. This area was awarded World Heritage status in 2011. The study area is a diverse environment, with habitats including subtidal and intertidal hard corals, bare reef, soft corals, sponge gardens, seagrass beds, sand flats, mud flats and mangroves (WA Department of Environment
Fig. 1. Study area, including vessel launch sites and Humpback Dolphin group locations and sizes observed around the North West Cape (excluding any Indo-Pacific Bottlenose Dolphins present).
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and Conservation 2011). While the waters of Exmouth Gulf are relatively shallow (predominantly < 20 m deep), depth increases west of the Ningaloo Reef to several hundred m within 10–15 km of the coast (WA Department of Environment and Conservation 2011). Data collection In April 2010, photo-identification surveys of Humpback Dolphins were conducted opportunistically around the top of the North West Cape (Fig. 1). These surveys were conducted as part of broader studies assessing the genetic connectivity of Indo-Pacific Bottlenose Tursiops aduncus, Australian Snubfin Orcaella heinshoni and Humpback Dolphins across north-western Australia. As biopsy sampling of the aforementioned species was a priority during fieldwork, limited effort was expended photographing evasive animals or those encountered during poor weather conditions (see Allen et al. 2012 for further details). Furthermore, the photo-identification effort was biased toward biopsied individuals, so some individuals were likely to have been missed. Data collection involved boat-based surveys of the near-shore waters along a ca. 80 km stretch of coastline. No pre-determined course was followed, with search patterns largely dictated by sea conditions (preference for Beaufort< 2 and swell < 0.5 m) and directed towards areas of potential Humpback Dolphin habitat (i.e., waters < 5 km from shore and 15 m depth). Three different boat launch sites (Exmouth Boat Harbour, Bundegi boat ramp and Tantabiddi boat ramp) were used (Fig. 1). The study area can be broadly defined as between 15 km south of Tantabiddi in the south-west and 15 km south of Exmouth in the south-east, and extending offshore to the 15 m depth contour. Search effort was greatest within 3 km of shore and concentrated around the top of the North West Cape between Bundegi and Tantabiddi. Time on the water was restricted to daylight hours (between ca. 0600 and 1800) and Beaufort sea states of < 3. The research platforms were small (5.5 m) aluminum boats, powered by 100 hp petrol outboard motors. Two teams used two vessels for the first six surveys, with just one team continuing thereafter. Three to four observers scanned the water surface for dolphins within 90 degrees of the vessel’s heading, using naked eye and, occasionally, hand-held binoculars. The vessel typically maintained a speed of 6-7 knots while searching for dolphins. When Humpback Dolphin groups were encountered, information was recorded on their location (latitude and longitude), group size,
group composition and water depth. As in Allen et al. (2012), a dolphin group was defined as one or more individuals within a 100 m radius of a central individual and engaged in similar behaviour. Photographic identification images were obtained for as many individuals as possible, using a single DSLR camera and a 100–400 mm telephoto zoom lens per vessel. Group size and the number of dependent calves (as defined by Parra et al. 2006a) were recorded at the onset of the sighting. Mixed-species groups of Humpback Dolphins and Indo-Pacific Bottlenose Dolphins were approached and recorded in the same manner, although information recorded on Indo-Pacific Bottlenose Dolphins within the group was restricted to the number of individuals present. Data presentation The locations of Humpback Dolphin groups and their distance from shore (minimum straight line distance from initial group location to high-water mark) were mapped using ESRI’s ArcGIS v9.3 software. A frequency histogram was produced to illustrate the distribution of group sizes encountered. We calculated summary statistics on group size and frequency of the presence of calves, water depth, and the distance from shore groups were observed. Results presented on group size and composition exclude any Indo-Pacific Bottlenose Dolphins present (unless stated otherwise). Photographs were examined for unique features (nicks, scars, pigmentation) on the dorsal fin and a catalogue of individual animals was developed (Würsig and Jefferson 1990). Dorsal fin features did not need to be deemed permanent due to the short duration of the study period. Only photographs of excellent and good quality (in terms of focus, contrast, and distance and angle to subject) were used for this purpose (e.g., Urian et al. 1999; Friday et al. 2000; Gowans and Whitehead 2001). A cumulative discovery curve was plotted to illustrate the rate at which new individuals were identified, and a histogram used to show the frequency with which individually identified dolphins were observed. RESULTS Total time on the water comprised 145 h over 18 days, or part thereof. One vessel contributed 45 h, while the other completed 100 h. This includes time searching for dolphins, time with dolphins and time motoring at speed. A total of 42 groups of Humpback Dolphins were encountered during the study period. The groups were encountered widely around the North West Cape (Fig. 1), with 23 groups sighted along the west and north-west coasts of the cape, 10 along a relatively short (ca. 5 km)
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stretch of coast with a north-east aspect at the tip of the cape and nine along the east coast. Groups were encountered at water depths between 1.2 and 20 m, with a mean (± SE) of 7.8 m (± 0.74). The majority of groups (95%) were encountered in waters < 15 m deep, where search effort was concentrated. The distance from shore at which groups were sighted ranged from 269 m to 4.5 km, with a mean (± SE) of 1 km (± 0.11). Group size ranged from one to 15 dolphins, with a mean (± SE) of 5.3 (± 0.48) individuals (Fig. 2). Approximately two thirds (n = 28) of the Humpback Dolphin groups encountered contained calves. A total of 54 individual Humpback Dolphins (excluding dependent calves) were photographically identified. The cumulative discovery curve indicated a relatively consistent increase in the number of individuals identified over the duration of the sampling period, with no indication of leveling off (Fig. 3). An examination of the sighting frequency of identified individuals indicated that 50% of individuals were observed only once, with a further 24% and 11% observed on two and three separate days, respectively. Four individuals (7%) were observed on four days, and another four individuals were sighted on five separate days.
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Cape. The water depths and distances from shore at which they were encountered were broadly similar to those reported from eastern Queensland (e.g., Parra 2006; Parra et al. 2006b; Cagnazzi 2011), although this may be biased by the greater time spent searching in near shore waters < 15 m deep. Mean group size reported here was slightly larger than that reported in Cleveland Bay (Parra et al. 2011) and along the Capricorn Coast (Cagnazzi 2011), although the range was very similar. Almost one quarter of all Humpback Dolphin groups encountered around the North West Cape also included Indo-Pacific Bottlenose Dolphins. Over eighteen days, 145 h on the water around the North West Cape yielded 54 identified individuals from 42 groups. The cumulative discovery curve indicated a relatively consistent increase in the number of individuals identified over the duration of the sampling period, with no plateau. This pattern, combined with the high proportion of animals which were only observed once during the study period, suggests that only a subset of the animals using the area were identified.
DISCUSSION
Certain comparisons can be drawn between the number of individual Humpback Dolphins identified here and those reported from studies in Queensland (Table 1). Using only the results from the first ca. 145 h of these dedicated photo-identification studies, the number of individuals 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). This indicates a larger number of initially identified individuals at the North West Cape than all but the Great Sandy Straits region, which, at approximately 1 000 km2, is four times larger than the ca. 250 km2 covered in this study.
Groups of Humpback Dolphins were encountered widely around the North West
At the 310 km2 study site of Cleveland Bay, Parra et al. (2006a) encountered 143 groups and
Fig. 2. Range of Humpback Dolphin group sizes documented around the North West Cape (excluding any Indo-Pacific Bottlenose Dolphins present).
Fig. 3. Cumulative discovery curve of adult and juvenile Humpback Dolphins identified over the study period.
Of the 42 Humpback Dolphin groups encountered, 10 (24%) also contained IndoPacific Bottlenose Dolphins. Mean (± SE) group size of mixed species groups was 9.5 (± 1.33) individuals, within which mean (± SE) numbers of Humpback and Indo-Pacific Bottlenose Dolphins were 5.5 (± 0.96) and 4.2 (±0.66), respectively.
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Table 1. Number of identified animals during initial ca. 150 h of effort and throughout entire study: comparison between the North West Cape and Queensland study sites. * time on water; ** search effort. Initially identified animals (effort)
Total identified animals (effort)
Population estimate
Size of study area (km2)
Reference
North West Cape, north-west WA Cleveland Bay, north-east QLD
54(145 h*)
na
na
250 (approx)
This study
16 (140 h*)
54 (630 h*)
310
Parra 2005; Parra et al. 2006a
Great Sandy Straits, east QLD Keppel Bay, east QLD Port Curtis, east QLD
71 (142 h**) 16 (150 h**) 46 (150 h**)
106 (1250 h**) 84 (775 h**) 63 (293 h**)
34 (95% Cl:24 -49) to 54 (95% Cl: 38-77) between 1999 and 2002 150 (95% Cl: 132.5-165.2) 107 (95% Cl: 97.5-116.5) 85 (95% Cl: 76.6-93.7)
1 000 650
Cagnazzi et al. 2011 Cagnazzi 2010
200
Cagnazzi 2010
Location
identified a total of 54 individual Humpback Dolphins in 630 h on the water over four seasons. A pattern of alternating small increases and plateaus in the cumulative discovery curve of identified individuals, combined with modelling of individuals’ lagged identification rate, suggested an open population with Humpback Dolphins moving in and out of their study area. Population estimates for Cleveland Bay ranged from 34–54 between 1999 and 2002 (Parra et al. 2006a). Over two wet and two dry seasons in the Great Sandy Straits, Cagnazzi et al. (2011) identified 106 adult Humpback Dolphin individuals from 263 groups. In contrast to the findings of Parra et al. (2006a), a cumulative discovery curve showed a distinct levelling off to an almost constant level, with 74% of the permanently marked individuals identified by the end of the first of four seasons. This was attributed to a geographically closed population, in which identified dolphins were primarily long-term residents in the study area. Abundance for two populations (northern and southern, with almost no spatial overlap) was estimated at approximately 75 individuals each (Cagnazzi et al. 2011). We acknowledge methodological differences in the photo-identification analyses, size and habitat characteristics of study areas, and the level of effort between this study and those reported in Parra et al. (2006a), Cagnazzi (2011) and Cagnazzi et al. (2011). However, our results suggest that longer-term, structured effort around the North West Cape would likely yield a higher density of Humpback Dolphins than those reported in Queensland. Allen et al. (2012) reported sightings of Humpback Dolphins off each coastal township across north-western WA in 2010; however, comparisons between the North West Cape and these other WA sites are hampered by methodological differences. Beyond the North West Cape, Humpback Dolphin encounters were only
recorded by Allen et al. (2012) when a biopsy sample was successfully obtained. Statistics for the number of samples obtained/hours on the water indicate that the North West Cape (24/ 145) was exceeded only by the Dampier Archipelago (20 /49), where the animals were qualitatively noted as being far more approachable than all other sites. All other sites yielded < 3 individuals sampled (Allen et al. 2012). It is important to consider the limitations of this study and the cautionary approach this should impose on the interpretation of our results. These data were collected opportunistically during research to acquire biopsy samples from all three tropical inshore delphinids occurring in north-western Australian waters (see Allen et al. 2012). Consequently, we did not engage in standardized survey protocols (e.g., structured distribution of effort) to estimate abundance or assess habitat preference. Additionally, a dedicated photo-identification study would have involved allocating more effort to obtaining identifiable photographs of all individuals. With dedicated effort on photoidentification during the same sampling period, it is likely that a greater number of individuals would have been identified, with consequential effects on the shape of the cumulative discovery curve. Furthermore, the study period reported here spans less than one month of the year; greater temporal coverage is required in order to fully assess the importance of this region to Humpback Dolphins. Despite these limitations, the preliminary data suggest that the North West Cape represents an important region comprising suitable habitats for Humpback Dolphins. In light of the paucity of information on Humpback Dolphins in WA waters, these data should serve as a platform for future research aimed at assessing population size and habitat requirements for this insufficiently known species around the North West Cape.
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The North West Cape remains relatively undeveloped to date. Those areas covered by the Marine Protected Area and World Heritage listings experience minimal commercial fishing activity, tightly regulated recreational fishing, and are not subject to major development pressures at present (DEWHA 2010). These conservation designations provide a strong legal basis for protection of the qualifying features and carefully managed development over a large proportion of the region. However, the inshore waters of the Exmouth Gulf south of Bundegi remain beyond these boundaries and are likely to experience considerable development in the future. The favourable proximity of the North West Cape to the expanding hydrocarbon facilities of the adjacent North West Shelf has attracted much interest as a hub for associated onshore facilities. AMC Management (2011) presented an examination of the feasibility and potential location of developing a common user facility (multiple user supply base / port infrastructure) on the north-west coast of Australia. They describe four different harbour-based developments in the Exmouth region which may serve as supply / logistics bases for offshore industry; one is currently under construction, while three are proposed / in planning (EPA 1997; AMC Management 2011; Learmonth Offshore Logistics Hub 2012). Additionally, interests have been expressed in the future utilization of the site and pier facilities (Harold E. Holt Communications Base) at the north-western tip of the North West Cape, also to support offshore industry (CCG 2011). At present, the majority of hydrocarbon exploration and production activity in the region takes place offshore, largely in excess of 20 km from the north coast of the North West Cape and with no associated pipelines coming ashore on the cape. Historically, activity closer to the coast has been limited, with only a small number of exploration wells in the Exmouth Gulf and patchy seismic survey effort around the North West Cape (WA Department of Mines and Petroleum 2012). However, interest in the potential resources of the Exmouth Gulf continues: several exploration permits within the western side of the Gulf remain active; an area of 2 813 km2 covering the rest of the Gulf was opened for tender in 2010 for exploration activities; and the majority of the Gulf is covered by active mineral (non-petroleum) exploration permits (Geological Survey of Western Australia 2010; WA Department of Mines and Petroleum 2012). With reference to protecting small cetaceans in the busy waters of Hong Kong, Jefferson et al. (2009) provided a summary of the main activities associated with coastal development that may impact Humpback Dolphins. Land
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reclamation, seabed construction (e.g., cable/ pipe laying), dredging and dumping of dredged material are major concerns; these cause modification or irreversible loss of inshore habitats and may influence water quality. Noise from increased vessel traffic and construction activities, such as pile-driving and underwater blasting, present further potential pathways for detrimental effects on sensitive marine species, as does noise associated with oil and gas exploration. The Hong Kong/Pearl River Estuary region is an extreme example of large-scale, long-term coastal development. Studies of the Humpback Dolphin population in this area have reported evidence of vessel strikes, entanglement, contaminant burdens, and high calf mortality (Jefferson et al. 2006, 2012). However, information on trends in abundance is lacking and the pathways between environmental stressors associated with coastal development and population-level impacts on Humpback Dolphins in the Hong Kong/Pearl River Estuary remain poorly understood. Adequate baseline data on marine megafauna, such as inshore delphinids, is an essential prerequisite to effectively assess the environmental impact of coastal developments and hydrocarbon exploration in north-western Australia. We have presented preliminary evidence that the inshore waters of the North West Cape are of importance for Humpback Dolphins, an insufficiently known species close to the south-western limit of its range. We recommend the development of a structured research program to assess the abundance and habitat use of Humpback Dolphins and other inshore delphinids around the North West Cape over a greater temporal range, in order to provide timely baseline information before extensive coastal development takes place. ACKNOWLEDGEMENTS This research was funded by Australian Marine Mammal Centre grants 2008-09/19 and 2009/19, and conducted under permits and approvals from the Department of Local Government Research and Development (U 6/ 2010-2011), the WA Department of Environment and Conservation (SF007596) and the Murdoch University Animal Ethics Committee (W2342/10). Michael Krützen provided the use of the second research vessel and vehicle and he, Dee McElligott, Frazer McGregor and Alice Soccadato assisted in the field. We are grateful to Tamara Organ for the fin-matching effort. We also extend thanks to Lyn Irvine for providing information on development projects in Exmouth Gulf and Aspen Parks for the provision of free accommodation for the research team. This manuscript was greatly improved by
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