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Symons J, Sprogis KR, Bejder L. Implications of survey effort on estimating demographic parameters of a long-lived marine top predator. Ecol Evol 2018; 8:10470-10481. [PMID: 30464819 PMCID: PMC6238146 DOI: 10.1002/ece3.4512] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 03/19/2018] [Accepted: 03/29/2018] [Indexed: 12/30/2022] Open
Abstract
Effective management of wildlife populations rely on knowledge of their abundance, survival, and reproductive rates. Maintaining long‐term studies capable of estimating demographic parameters for long‐lived, slow‐reproducing species is challenging. Insights into the effects of research intensity on the statistical power to estimate demographic parameters are limited. Here, we investigate implications of survey effort on estimating abundance, home range sizes, and reproductive output of Indo‐Pacific bottlenose dolphins (Tursiops aduncus), using a 3‐year subsample of a long‐term, capture–recapture study off Bunbury, Western Australia. Photo‐identification on individual dolphins was collected following Pollock's Robust Design, where seasons were defined as “primary periods”, each consisting of multiple “secondary periods.” The full dataset consisted of 12 primary periods and 72 secondary periods, resulting in the study area being surveyed 24 times/year. We simulated reduced survey effort by randomly removing one, two, or three secondary periods per primary period. Capture–recapture models were used to assess the effect of survey intensity on the power to detect trends in population abundance, while individual dolphin sighting histories were used to assess the ability to conduct home range analyses. We used sighting records of adult females and their calving histories to assess survey effort on quantifying reproductive output. A 50% reduction in survey effort resulted in (a) up to a 36% decline in population abundance at the time of detection; (b) a reduced ability to estimate home range sizes, by increasing the time for individuals to be sighted on ≥30 occasions (an often‐used metric for home range analyses) from 7.74 to 14.32 years; and (c) 33%, 24%, and 33% of annual calving events across three years going undocumented, respectively. Results clearly illustrate the importance of survey effort on the ability to assess demographic parameters with clear implications for population viability analyses, population forecasting, and conservation efforts to manage human–wildlife interactions.
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Affiliation(s)
- John Symons
- Cetacean Research Unit School of Veterinary and Life Sciences Murdoch University Murdoch Western Australia Australia
| | - Kate R Sprogis
- Cetacean Research Unit School of Veterinary and Life Sciences Murdoch University Murdoch Western Australia Australia.,Zoophysiology Department of Bioscience Aarhus University Aarhus Denmark
| | - Lars Bejder
- Cetacean Research Unit School of Veterinary and Life Sciences Murdoch University Murdoch Western Australia Australia.,Marine Mammal Research Program Hawaii Institute of Marine Biology University of Hawaii at Manoa Honolulu Hawaii
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2
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Maglietta R, Renò V, Cipriano G, Fanizza C, Milella A, Stella E, Carlucci R. DolFin: an innovative digital platform for studying Risso's dolphins in the Northern Ionian Sea (North-eastern Central Mediterranean). Sci Rep 2018; 8:17185. [PMID: 30464205 PMCID: PMC6249232 DOI: 10.1038/s41598-018-35492-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 11/06/2018] [Indexed: 11/09/2022] Open
Abstract
The Risso's dolphin is a widely distributed species, found in deep temperate and tropical waters. Estimates of its abundance are available in a few regions, details of its distribution are lacking, and its status in the Mediterranean Sea is ranked as Data Deficient by the IUCN Red List. In this paper, a synergy between bio-ecological analysis and innovative strategies has been applied to construct a digital platform, DolFin. It contains a collection of sighting data and geo-referred photos of Grampus griseus, acquired from 2013 to 2016 in the Gulf of Taranto (Northern Ionian Sea, North-eastern Central Mediterranean Sea), and the first automated tool for Smart Photo Identification of the Risso's dolphin (SPIR). This approach provides the capability to collect and analyse significant amounts of data acquired over wide areas and extended periods of time. This effort establishes the baseline for future large-scale studies, essential to providing further information on the distribution of G. griseus. Our data and analysis results corroborate the hypothesis of a resident Risso's dolphin population in the Gulf of Taranto, showing site fidelity in a relatively restricted area characterized by a steep slope to around 800 m in depth, north of the Taranto Valley canyon system.
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Affiliation(s)
- Rosalia Maglietta
- Institute of Intelligent Industrial Technologies and Systems for Advanced Manufacturing, National Research Council,Via Amendola 122/D-I, 70126, Bari, Italy.
| | - Vito Renò
- Institute of Intelligent Industrial Technologies and Systems for Advanced Manufacturing, National Research Council,Via Amendola 122/D-I, 70126, Bari, Italy
| | - Giulia Cipriano
- Department of Biology, University of Bari, Via Orabona 4, 70125, Bari, Italy
| | - Carmelo Fanizza
- Jonian Dolphin Conservation, Viale Virgilio 102, 74121, Taranto, Italy
| | - Annalisa Milella
- Institute of Intelligent Industrial Technologies and Systems for Advanced Manufacturing, National Research Council,Via Amendola 122/D-I, 70126, Bari, Italy
| | - Ettore Stella
- Institute of Intelligent Industrial Technologies and Systems for Advanced Manufacturing, National Research Council,Via Amendola 122/D-I, 70126, Bari, Italy
| | - Roberto Carlucci
- Department of Biology, University of Bari, Via Orabona 4, 70125, Bari, Italy
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Bradford AL, Baird RW, Mahaffy SD, Gorgone AM, McSweeney DJ, Cullins T, Webster DL, Zerbini AN. Abundance estimates for management of endangered false killer whales in the main Hawaiian Islands. ENDANGER SPECIES RES 2018. [DOI: 10.3354/esr00903] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Dulau V, Estrade V, Fayan J. Identifying key demographic parameters of a small island-associated population of Indo-Pacific bottlenose dolphins (Reunion, Indian Ocean). PLoS One 2017. [PMID: 28640918 PMCID: PMC5480988 DOI: 10.1371/journal.pone.0179780] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Photo-identification surveys of Indo-Pacific bottlenose dolphins were conducted from 2009 to 2014 off Reunion Island (55°E33’/21°S07’), in the Indian Ocean. Robust Design models were applied to produce the most reliable estimate of population abundance and survival rate, while accounting for temporary emigration from the survey area (west coast). The sampling scheme consisted of a five-month (June–October) sampling period in each year of the study. The overall population size at Reunion was estimated to be 72 individuals (SE = 6.17, 95%CI = 61–85), based on a random temporary emigration (γ”) of 0.096 and a proportion of 0.70 (SE = 0.03) distinct individuals. The annual survival rate was 0.93 (±0.018 SE, 95%CI = 0.886–0.958) and was constant over time and between sexes. Models considering gender groups indicated different movement patterns between males and females. Males showed null or quasi-null temporary emigration (γ” = γ’ < 0.01), while females showed a random temporary emigration (γ”) of 0.10, suggesting that a small proportion of females was outside the survey area during each primary sampling period. Sex-specific temporary migration patterns were consistent with movement and residency patterns observed in other areas. The Robust Design approach provided an appropriate sampling scheme for deriving island-associated population parameters, while allowing to restrict survey effort both spatially (i.e. west coast only) and temporally (five months per year). Although abundance and survival were stable over the six years, the small population size of fewer than 100 individuals suggested that this population is highly vulnerable. Priority should be given to reducing any potential impact of human activity on the population and its habitat.
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Affiliation(s)
- Violaine Dulau
- GLOBICE-Reunion, Grand Bois, Saint Pierre, Reunion Island, France
- * E-mail:
| | - Vanessa Estrade
- GLOBICE-Reunion, Grand Bois, Saint Pierre, Reunion Island, France
| | - Jacques Fayan
- BNOI-ONCFS, Parc de la Providence, Saint-Denis, Reunion Island, France
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5
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Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong: Modelling demographic parameters with mark-recapture techniques. PLoS One 2017; 12:e0174029. [PMID: 28355228 PMCID: PMC5371324 DOI: 10.1371/journal.pone.0174029] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 03/02/2017] [Indexed: 11/19/2022] Open
Abstract
Indo-Pacific humpback dolphins (Sousa chinensis) inhabiting Hong Kong waters are thought to be among the world's most anthropogenically impacted coastal delphinids. We have conducted a 5-year (2010–2014) photo-ID study and performed the first in this region comprehensive mark-recapture analysis applying a suite of open population models and robust design models. Cormack-Jolly-Seber (CJS) models suggested a significant transient effect and seasonal variation in apparent survival probabilities as result of a fluid movement beyond the study area. Given the spatial restrictions of our study, limited by an administrative border, if emigration was to be considered negligible the estimated survival rate of adults was 0.980. Super-population estimates indicated that at least 368 dolphins used Hong Kong waters as part of their range. Closed robust design models suggested an influx of dolphins from winter to summer and increased site fidelity in summer; and outflux, although less prominent, during summer-winter intervals. Abundance estimates in summer (N = 144–231) were higher than that in winter (N = 87–111), corresponding to the availability of prey resources which in Hong Kong waters peaks during summer months. We point out that the current population monitoring strategy used by the Hong Kong authorities is ill-suited for a timely detection of a population change and should be revised.
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Lin W, Karczmarski L, Xia J, Zhang X, Yu X, Wu Y. Increased human occupation and agricultural development accelerates the population contraction of an estuarine delphinid. Sci Rep 2016; 6:35713. [PMID: 27759106 PMCID: PMC5069629 DOI: 10.1038/srep35713] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/30/2016] [Indexed: 11/17/2022] Open
Abstract
Over the past few thousand years, human development and population expansion in southern China have led to local extirpation and population contraction of many terrestrial animals. At what extent this early human-induced environmental change has also affected coastal marine species remains poorly known. We investigated the demographic history of the Indo-Pacific humpback dolphin (Sousa chinensis) in the Pearl River Delta (PRD); an obligatory inshore species known for its susceptibility to anthropogenic impacts in one of China’s most developed coastal regions. Although the deltaic evolution of PRD has been influenced by climate since the Holocene, ~74% reduction of the dolphin’s effective population size occurred within the last 2000 years, consistent with ~61% habitat contraction during this period. This considerable and recent population contraction may have been due to land use practices and deforestation in the upper/middle Pearl River region, all leading to increasing sedimentation rate in the estuarine area. As anthropogenic impacts within the drainage of Pearl River affected a vast area, coastal dolphins and large terrestrial mammals in southern China may share a similar demographic history, whilst the demographic and biogeographic history of the PRD humpback dolphins may be symptomatic of similar processes that this species may have undergone elsewhere in the region.
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Affiliation(s)
- Wenzhi Lin
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center; Zhuhai Key Laboratory of Marine Bioresources and Environment, Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, PR China.,The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong
| | - Leszek Karczmarski
- The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Cape d'Aguilar, Shek O, Hong Kong
| | - Jia Xia
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center; Zhuhai Key Laboratory of Marine Bioresources and Environment, Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, PR China
| | - Xiyang Zhang
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center; Zhuhai Key Laboratory of Marine Bioresources and Environment, Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, PR China
| | - Xinjian Yu
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center; Zhuhai Key Laboratory of Marine Bioresources and Environment, Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, PR China
| | - Yuping Wu
- South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center; Zhuhai Key Laboratory of Marine Bioresources and Environment, Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, PR China
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Mikkelsen L, Rigét FF, Kyhn LA, Sveegaard S, Dietz R, Tougaard J, Carlström JAK, Carlén I, Koblitz JC, Teilmann J. Comparing Distribution of Harbour Porpoises (Phocoena phocoena) Derived from Satellite Telemetry and Passive Acoustic Monitoring. PLoS One 2016; 11:e0158788. [PMID: 27463509 PMCID: PMC4963116 DOI: 10.1371/journal.pone.0158788] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 06/22/2016] [Indexed: 11/18/2022] Open
Abstract
Cetacean monitoring is essential in determining the status of a population. Different monitoring methods should reflect the real trends in abundance and patterns in distribution, and results should therefore ideally be independent of the selected method. Here, we compare two independent methods of describing harbour porpoise (Phocoena phocoena) relative distribution pattern in the western Baltic Sea. Satellite locations from 13 tagged harbour porpoises were used to build a Maximum Entropy (MaxEnt) model of suitable habitats. The data set was subsampled to one location every second day, which were sufficient to make reliable models over the summer (Jun-Aug) and autumn (Sep-Nov) seasons. The modelled results were compared to harbour porpoise acoustic activity obtained from 36 static acoustic monitoring stations (C-PODs) covering the same area. The C-POD data was expressed as the percentage of porpoise positive days/hours (the number of days/hours per day with porpoise detections) by season. The MaxEnt model and C-POD data showed a significant linear relationship with a strong decline in porpoise occurrence from west to east. This study shows that two very different methods provide comparable information on relative distribution patterns of harbour porpoises even in a low density area.
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Affiliation(s)
- Lonnie Mikkelsen
- Department of Bioscience, Aarhus University, Roskilde, Denmark
- * E-mail:
| | - Frank F. Rigét
- Department of Bioscience, Aarhus University, Roskilde, Denmark
| | - Line A. Kyhn
- Department of Bioscience, Aarhus University, Roskilde, Denmark
| | - Signe Sveegaard
- Department of Bioscience, Aarhus University, Roskilde, Denmark
| | - Rune Dietz
- Department of Bioscience, Aarhus University, Roskilde, Denmark
| | - Jakob Tougaard
- Department of Bioscience, Aarhus University, Roskilde, Denmark
| | - Julia A. K. Carlström
- AquaBiota Water Research, Stockholm, Sweden
- Swedish Museum of Natural History, Stockholm, Sweden
| | - Ida Carlén
- AquaBiota Water Research, Stockholm, Sweden
- Coalition Clean Baltic, Uppsala, Sweden
| | - Jens C. Koblitz
- German Oceanographic Museum, Stralsund, Germany
- BioAcoustics Network, Stralsund, Germany
| | - Jonas Teilmann
- Department of Bioscience, Aarhus University, Roskilde, Denmark
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8
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Vermeulen E, Bräger S. Demographics of the disappearing bottlenose dolphin in Argentina: a common species on its way out? PLoS One 2015; 10:e0119182. [PMID: 25786234 PMCID: PMC4364992 DOI: 10.1371/journal.pone.0119182] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 01/25/2015] [Indexed: 11/19/2022] Open
Abstract
Populations of the once common bottlenose dolphin (Tursiops truncatus) in Argentina have precipitously declined throughout the country in the past decades. Unfortunately, local declines of common species are easily overlooked when establishing priorities for conservation. In this study, demographics of what may well be the last remaining resident population in the country were assessed using mark-recapture analysis (Pollock's Robust Design) of a photo-identification dataset collected during 2006-2011 in Bahía San Antonio (Patagonia, Argentina). Total abundance, corrected for unmarked individuals, ranged from 40 (95%CI: 16.1-98.8) to 83 (95%CI = 45.8-151.8) individuals and showed a decrease over the years. Adult survival rates varied between 0.97 (± 0.037 SE) and 0.99 (± 0.010 SE). Average calving interval equalled 3.5 ± 1.03 years, with 3.5 births/year in the entire population and a minimum annual birth rate of 4.2%. However, data suggest that calves may have been born and lost before being documented, underestimating birth rate, calf mortality, and possibly the number of reproductive females. Either way, the recruitment rate of calves appears to be insufficient to support the size of the population. This population is relatively small and declining. Considering the disappearance of populations north and south of the study area, an incessant decline will have severe consequences for the continuous existence of this species in Argentina, indicating an urgent need for serious conservation efforts. This study provides insight into how the failure to recognize local population declines can threaten the national (and eventually the international) status of a common species like the bottlenose dolphin.
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Affiliation(s)
- Els Vermeulen
- Laboratory of Oceanology, MARE Research Centre, University of Liège, Liège, Belgium
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Brown AM, Kopps AM, Allen SJ, Bejder L, Littleford-Colquhoun B, Parra GJ, Cagnazzi D, Thiele D, Palmer C, Frère CH. Population differentiation and hybridisation of Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins in north-western Australia. PLoS One 2014; 9:e101427. [PMID: 24988113 PMCID: PMC4079686 DOI: 10.1371/journal.pone.0101427] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Accepted: 06/06/2014] [Indexed: 12/02/2022] Open
Abstract
Little is known about the Australian snubfin (Orcaella heinsohni) and Indo-Pacific humpback (Sousa chinensis) dolphins (‘snubfin’ and ‘humpback dolphins’, hereafter) of north-western Australia. While both species are listed as ‘near threatened’ by the IUCN, data deficiencies are impeding rigorous assessment of their conservation status across Australia. Understanding the genetic structure of populations, including levels of gene flow among populations, is important for the assessment of conservation status and the effective management of a species. Using nuclear and mitochondrial DNA markers, we assessed population genetic diversity and differentiation between snubfin dolphins from Cygnet (n = 32) and Roebuck Bays (n = 25), and humpback dolphins from the Dampier Archipelago (n = 19) and the North West Cape (n = 18). All sampling locations were separated by geographic distances >200 km. For each species, we found significant genetic differentiation between sampling locations based on 12 (for snubfin dolphins) and 13 (for humpback dolphins) microsatellite loci (FST = 0.05–0.09; P<0.001) and a 422 bp sequence of the mitochondrial control region (FST = 0.50–0.70; P<0.001). The estimated proportion of migrants in a population ranged from 0.01 (95% CI 0.00–0.06) to 0.13 (0.03–0.24). These are the first estimates of genetic diversity and differentiation for snubfin and humpback dolphins in Western Australia, providing valuable information towards the assessment of their conservation status in this rapidly developing region. Our results suggest that north-western Australian snubfin and humpback dolphins may exist as metapopulations of small, largely isolated population fragments, and should be managed accordingly. Management plans should seek to maintain effective population size and gene flow. Additionally, while interactions of a socio-sexual nature between these two species have been observed previously, here we provide strong evidence for the first documented case of hybridisation between a female snubfin dolphin and a male humpback dolphin.
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Affiliation(s)
- Alexander M. Brown
- Murdoch University Cetacean Research Unit, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia
- * E-mail:
| | - Anna M. Kopps
- Centre for Ecology and Conservation, University of Exeter, Penryn, Cornwall, United Kingdom
- Marine Evolution and Conservation, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands
| | - Simon J. Allen
- Murdoch University Cetacean Research Unit, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia
| | - Lars Bejder
- Murdoch University Cetacean Research Unit, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia
| | | | - Guido J. Parra
- Cetacean Ecology, Behaviour and Evolution Lab, School of Biological Sciences, Flinders University, Adelaide, South Australia, Australia
- South Australian Research and Development Institute, Adelaide, South Australia, Australia
| | - Daniele Cagnazzi
- Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, New South Wales, Australia
| | - Deborah Thiele
- Fenner School of Environment & Society, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Carol Palmer
- Marine Ecosystems, Flora and Fauna Division, Department of Land Resource Management, Palmerston, Northern Territory, Australia
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia
| | - Celine H. Frère
- GeneCology Research Centre, University of the Sunshine Coast, Maroochydore DC, Queensland, Australia
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Palmer C, Brooks L, Parra GJ, Rogers T, Glasgow D, Woinarski JCZ. Estimates of abundance and apparent survival of coastal dolphins in Port Essington harbour, Northern Territory, Australia. WILDLIFE RESEARCH 2014. [DOI: 10.1071/wr14031] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context
Three dolphin species occur in coastal waters of monsoonal northern Australia: the Australian snubfin (Orcaella heinsohni), humpback (Sousa sp.) and the bottlenose (Tursiops sp.). Their overall population size and trends are poorly known, and their conservation status has been difficult to resolve, but can be expected to deteriorate with likely increased development pressures.
Aims
We sought to provide an estimate of abundance, and apparent survival, of the three dolphin species at the largely undeveloped harbour of Port Essington (325 km2), Northern Territory, with repeated sampling over a 2.9-year period. Given increasing obligations to undertake population assessments for impact studies at proposed development sites, we assess the strengths and limitations of a systematic sampling program.
Methods
We used photo-identification data collected during systematic boat-based transect surveys undertaken from 2008 to 2010 and Pollock’s robust capture–recapture design model.
Key results
Total abundance estimates for the three species were variable across different sampling periods. The estimated number of individuals in the sampled area varied per sampling episode from 136 (s.e. 62) to 222 (s.e. 48) for snubfin, from 48 (s.e. 7) to 207 (s.e. 14) for humpbacks and from 34 (s.e. 6) to 75 (s.e. 9) for bottlenose dolphins. Apparent survival was estimated for snubfin at 0.81 (s.e. 0.11), humpbacks at 0.59 (s.e. 0.12) and bottlenose at 0.51 (s.e. 0.17) per annum.
Key conclusions
(1) The values derived here provide some of the only estimates of local population size for these species across monsoonal northern Australia; (2) population-size estimates varied considerably among seasons or sampling episodes; (3) the low apparent survival probabilities indicated that many individuals may move at scales larger than the study area; (4) density of snubfin and humpback dolphins in the present study area exceeded the few other estimates available for these species elsewhere in Australia.
Implications
The present study provided the first baseline estimates of abundance and apparent survival for three coastal dolphin species in monsoonal northern Australia. Such information is becoming increasingly important as development pressures intensify in coastal areas. Sampling protocols for future monitoring and impact assessment need an enhanced consideration of seasonality and scale issues.
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