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Vossgaetter L, Dudeck T, Crouch J, Cope M, Ivanova T, Siyan I, Niyaz A, Riyaz M, Araujo G. Non-invasive methods characterise the world's largest tiger shark aggregation in Fuvahmulah, Maldives. Sci Rep 2024; 14:21998. [PMID: 39313535 PMCID: PMC11420367 DOI: 10.1038/s41598-024-73079-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2024] [Accepted: 09/13/2024] [Indexed: 09/25/2024] Open
Abstract
Tiger sharks are apex predators with a circumglobal tropical and warm-temperate distribution, with a general lack of population data for the central Indian Ocean. In Fuvahmulah, Maldives, tiger sharks display frequent use of the harbour area, attracted by discarded fish waste. Here, we document the population structure, residency, and reproductive characteristics of the world's largest known tiger shark aggregation in a geographically-restricted area. Using non-invasive methods, photo identification and laser photogrammetry, we identified 239 individual tiger sharks over a 7-year study period. The aggregation was female-dominated (84.5%), with both large juveniles and adults present. Adult females were resighted over the entire study period displaying strong inter- and intra-annual site fidelity. Modelled residency using maximum likelihood methods suggests they spent 60.7 ± S.E. 7.5 days in Fuvahmulah, with a larger aggregation size, shorter residence periods and longer absence periods compared to juvenile females. Prolonged abdominal distensions of adult females indicate they likely stay near Fuvahmulah during gestation and reproduce biennially. Fuvahmulah seems to provide suitable conditions for gestation given the year-round provision of food and warm waters, exhibited by strong site fidelity and temporal residency. Our results show indications of a thriving population within the confines of protected waters.
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Affiliation(s)
- Lennart Vossgaetter
- Leibniz Centre for Tropical Marine Research, 28334, Bremen, Germany.
- University of Bremen, 28334, Bremen, Germany.
| | - Tim Dudeck
- Leibniz Centre for Tropical Marine Research, 28334, Bremen, Germany
- University of Bremen, 28334, Bremen, Germany
| | - Jamie Crouch
- Fuvahmulah Dive School, Fuvahmulah, 18011, Maldives
| | - Maiah Cope
- Fuvahmulah Dive School, Fuvahmulah, 18011, Maldives
| | | | | | | | | | - Gonzalo Araujo
- Marine Research and Conservation Foundation, Lydeard St Lawrence, Somerset, UK
- Environmental Science Program, Department of Biological and Environmental Sciences, College of Arts and Sciences, Qatar University, Doha, Qatar
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Serres A, Lin W, Liu B, Chen S, Li S. Skinny dolphins: Can poor body condition explain population decline in Indo-Pacific humpback dolphins (Sousa chinensis)? THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 917:170401. [PMID: 38280614 DOI: 10.1016/j.scitotenv.2024.170401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2023] [Revised: 01/22/2024] [Accepted: 01/22/2024] [Indexed: 01/29/2024]
Abstract
Indo-Pacific humpback dolphins (IPHDs) who form resident populations along the Chinese coastline are facing a wide range of anthropogenic disturbances including intense fishing and some populations have been shown to experience a severe decline. Body condition is thought to be a good indicator of health since it is linked to survival and reproductive success. In order to better understand population trends, we investigated whether the body condition of IPHDs is poorer in populations whose status is alarming than in other populations. UAV flights were conducted from 2022 to 2023 in four locations (i.e., Sanniang Bay, Leizhou Bay, Jiangmen, and Lingding Bay) in the northern South China Sea. Body ratios were calculated using the body length and widths of IPHDs and were used to analyze differences among seasons, locations, and demographic parameters. A PCA was then used to obtain a detailed picture of the body condition composition of dolphins at each location. Results showed that dolphins from Leizhou Bay and Jiangmen were in better body condition than those from Sanniang Bay and Lingding Bay. Since populations inhabiting Sanniang Bay and Lingding Bay have been shown to experience a sharp decline, it can be hypothesized that poor body condition may have played a role in such a trend. Further investigations of the factors impacting IPHDs' body condition are needed, including monitoring of prey density, contaminant concentration, stress levels, and impacts of human activities on dolphins' behavior. In addition, the creation of a robust scoring method would allow for regular monitoring of IPHDs' body condition to inform conservation measures.
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Affiliation(s)
- Agathe Serres
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China
| | - Wenzhi Lin
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China
| | - Binshuai Liu
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shenglan Chen
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Songhai Li
- Marine Mammal and Marine Bioacoustics Laboratory, Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China; The Key Laboratory of Aquatic Biodiversity and Conservation of the Chinese Academy of Sciences, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
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Pirotta E, Fernandez Ajó A, Bierlich KC, Bird CN, Buck CL, Haver SM, Haxel JH, Hildebrand L, Hunt KE, Lemos LS, New L, Torres LG. Assessing variation in faecal glucocorticoid concentrations in gray whales exposed to anthropogenic stressors. CONSERVATION PHYSIOLOGY 2023; 11:coad082. [PMID: 38026800 PMCID: PMC10660368 DOI: 10.1093/conphys/coad082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 10/05/2023] [Accepted: 10/10/2023] [Indexed: 12/01/2023]
Abstract
Understanding how individual animals respond to stressors behaviourally and physiologically is a critical step towards quantifying long-term population consequences and informing management efforts. Glucocorticoid (GC) metabolite accumulation in various matrices provides an integrated measure of adrenal activation in baleen whales and could thus be used to investigate physiological changes following exposure to stressors. In this study, we measured GC concentrations in faecal samples of Pacific Coast Feeding Group (PCFG) gray whales (Eschrichtius robustus) collected over seven consecutive years to assess the association between GC content and metrics of exposure to sound levels and vessel traffic at different temporal scales, while controlling for contextual variables such as sex, reproductive status, age, body condition, year, time of year and location. We develop a Bayesian Generalized Additive Modelling approach that accommodates the many complexities of these data, including non-linear variation in hormone concentrations, missing covariate values, repeated samples, sampling variability and some hormone concentrations below the limit of detection. Estimated relationships showed large variability, but emerging patterns indicate a strong context-dependency of physiological variation, depending on sex, body condition and proximity to a port. Our results highlight the need to control for baseline hormone variation related to context, which otherwise can obscure the functional relationship between faecal GCs and stressor exposure. Therefore, extensive data collection to determine sources of baseline variation in well-studied populations, such as PCFG gray whales, could shed light on cetacean stress physiology and be used to extend applicability to less-well-studied taxa. GC analyses may offer greatest utility when employed as part of a suite of markers that, in aggregate, provide a multivariate measure of physiological status, better informing estimates of individuals' health and ultimately the consequences of anthropogenic stressors on populations.
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Affiliation(s)
- Enrico Pirotta
- Centre for Research into Ecological and Environmental Modelling, University of St Andrews, The Observatory, Buchanan Gardens, St Andrews, Fife, Scotland KY16 9LZ, UK
| | - Alejandro Fernandez Ajó
- Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
| | - KC Bierlich
- Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
| | - Clara N Bird
- Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
| | - C Loren Buck
- Department of Biological Sciences, Northern Arizona University, 617 S. Beaver St., Flagstaff, AZ 86011, USA
| | - Samara M Haver
- Cooperative Institute for Marine Ecosystem and Resources Studies, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
- Department of Fisheries, Wildlife, and Conservation Sciences, Oregon State University, 104 Nash Hall, Corvallis, OR 97331, USA
| | - Joseph H Haxel
- Pacific Northwest National Laboratory, Coastal Sciences Division, 1529 W. Sequim Bay Rd., Sequim, WA 98362, USA
| | - Lisa Hildebrand
- Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
| | - Kathleen E Hunt
- Smithsonian-Mason School of Conservation & Department of Biology, George Mason University, 1500 Remount Rd, Front Royal, VA 22630, USA
| | - Leila S Lemos
- Institute of Environment, Florida International University, 3000 NE 151st St, North Miami, FL 33181, USA
| | - Leslie New
- Department of Mathematics, Computer Science and Statistics, Ursinus College, 601 E Main St, Collegeville, PA 19426, USA
| | - Leigh G Torres
- Geospatial Ecology of Marine Megafauna Lab, Marine Mammal Institute, Department of Fisheries, Wildlife and Conservation Sciences, Oregon State University, 2030 SE Marine Science Drive, Newport, OR 97365, USA
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