Investigating the age composition of Indo-Pacific humpback dolphins in the Pearl River Estuary based on their pigmentation pattern

Guo, Lang; Lin, Wenzhi; Zeng, Chen; Luo, Dingyu; Wu, Yuping

doi:10.1007/s00227-020-3650-x

Cited by 27 publications

(38 citation statements)

References 52 publications

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“…As the age structure of humpback dolphin groups outside PRD remains unknown (Guo et al . 2020), we cannot distinguish between the influence of population‐specific discoloration rate and that of age composition. However, we compared the pattern of pigmentation of the most discolored dolphins, presumably the oldest individuals, and the most heavily speckled/darkest nursing females, presumably the youngest females reaching sexual maturity (Jefferson et al .…”

Section: Resultsmentioning

confidence: 99%

“…We suggest that the difference in the pigmentation pattern of the 4 putative populations examined in our study is due to different rates of discoloration, specific to each of these populations. As the age structure of humpback dolphin groups outside PRD remains unknown (Guo et al 2020), we cannot distinguish between the influence of population-specific discoloration rate and that of age composition. However, we compared the pattern of pigmentation of the most discolored dolphins, presumably the oldest individuals, and the most heavily speckled/ darkest nursing females, presumably the youngest females reaching sexual maturity (Jefferson et al 2012), among the 4 populations.…”

Section: Resultsmentioning

confidence: 99%

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Photo‐identification comparison of four Indo‐Pacific humpback dolphin populations off southeast China

Tang

Lin

Karczmarski³

et al. 2021

Integr. Zool.

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Indo-Pacific humpback dolphins (Sousa chinensis) inhabit shallow coastal waters of the Indo-Pacific region including southeast China, with at least 6 putative populations identified to date in Chinese waters. However, the connectivity among these populations has not yet been fully investigated. In the present study, we compared and crossmatched photographic catalogs of individual dolphins collected to date in the Pearl River Delta region, Leizhou Bay, Sanniang Bay, and waters southwest of Hainan Island, a total of 3158 individuals, and found no re-sighting of individual dolphins among the 4 study areas. Furthermore, there was a notable difference in the pigmentation pattern displayed by individuals from these 4 regions. We suggest that this may be a phenotypical expression of fine-scale regional differentiation among humpback dolphin groups, possibly distinct populations. Given the considerable conservation management implications it may carry (e.g. definition of management units), further research is much needed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Photo‐identification comparison of four Indo‐Pacific humpback dolphin populations off southeast China

Tang

Lin

Karczmarski³

et al. 2021

Integr. Zool.

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“…Recent and ongoing studies suggest limited movement and no apparent exchange between humpback dolphin groups seen in the LBD and those in western reaches of the PRD (Chan 2019; Guo et al . 2020). On the other hand, fishery surveys in the LDB (2014–2015), Modao Estuary (2013), and Yamen Estuary (2005–2007), all conducted with a standardized approach of a single trawl net and the catch per unit effort (CPUE) used to infer the spatial pattern of fish density (Sun 2008; South China Sea Fisheries Research Institute 2014; South China Sea Planning and Environmental Research Institute 2017), reported the fish abundance in western PRD (wPRD) to be 1.9 times higher than that in LDB (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…Regular photo-identification surveys were conducted across the PRD; initiated in Hong Kong waters in 2010 Chan & Karczmarski 2019) and later extended into the mainland China waters (Lin et al 2017(Lin et al , 2018Chan 2019;Guo et al 2020). Beginning with 2012, at each dolphin encounter, the presence/absence of fishing boat was noted, and when the dolphins were seen feeding in association with fishing vessels, the type of fishing gear was recorded.…”

Section: Field Observationsmentioning

confidence: 99%

“…Huang et al (2012) indicated that the PRD humpback dolphins, thought to be the world's largest population of this species (estimated at ∼2600 individuals in 2006; Chen et al 2010a;Jefferson & Smith 2016), are on a declining trajectory and may drop in numbers by ∼70% within 3 generations (∼60 years). More recent viability assessment which incorporated the population age structure suggests that this previous risk assessment may be overly conservative and the population may lose more than half its numbers in a lifespan of one generation (Lin et al 2017;Guo et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Prey decline leads to diet shift in the largest population of Indo‐Pacific humpback dolphins?

et al. 2021

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The Pearl River Delta (PRD) region on the southeast coast of China has long been known as a highly productive fishing ground. Since the late 1980s, fishing pressure in the PRD has been intense, which warrants concerns of potential fishery-related impacts on the food resources and foraging ecology of apex marine predators in this region, such as the Indo-Pacific humpback dolphin (Sousa chinensis). In this study, we examined 54 stomachs with food remains, collected from beached carcasses of humpback dolphins recovered during fifteen years between 2003 and 2017. The 6043 identified prey items represent 62 teleost taxa, primarily small estuarine fish, but also larger reef fish. The dolphins appear to be opportunistic foragers, hunting across the water-column, with preference for shoaling and meaty fishes (e.g. Collichthys lucidus IRI% = 38.6%, Johnius belangerii IRI% = 23.1%, Mugil cephalus IRI% = 14.0%). Our findings suggest a dietary shift in recent years, from primarily demersal (as previously reported) to greater intake of neritic and pelagic fish. Dolphin foraging group size has decreased in recent years, which corresponds with declining size and numbers of prey items retrieved from dolphin stomachs. We suggest that these are indicators of declining food resources. Faced with a shortage of preferred prey, humpback dolphins may have broadened their dietary spectrum to maintain their daily energy intake, while their foraging group size decreased in response to the altered tradeoff between the costs and benefits of group foraging.

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Population distribution, connectivity and differentiation of Indo‐Pacific humpback dolphins in Chinese waters: Key baselines for improving conservation management

Liu

Lin

2023

Aquatic Conservation

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1. Humpback dolphins (Sousa spp.), throughout their distribution ranges, are often designated as flagship species for coastal ecosystem conservation. Most of the early research on humpback dolphins was carried out in Chinese waters, and in the last two decades, numerous studies have provided abundant conservationvaluable findings.2. In this study, a systematic review was conducted to gain a comprehensive understanding of the distributional ecology of humpback dolphins in Chinese waters, to establish an updated national knowledge base about key conservation baselines on this flagship species. 3. Currently, there are at least eight main distribution areas of humpback dolphins along the coast of southern China, representing a clear picture of place-based conservation units. However, the overall biogeographical distribution pattern is discontinuous, and existing marine protected areas are far from sufficient to protect these key areas for the survival of humpback dolphins. 4. Based on the photo-identification technique, cross-matching of humpback dolphin individuals revealed extremely low inter-population connectivity among most of the known populations. Genetic studies suggested that several examined populations have low haplotype diversity levels, with limited inter-population gene flow. Morphological and behavioural evidence also supports population differentiation among geographical locations.5. These findings provide key baselines for the promotion of conservation management initiatives for humpback dolphins in Chinese waters. All recognizable geographical populations, together with each key habitat, should be considered as independent conservation units. With small distribution areas, low genetic diversity and unfavourable geographical isolation, several populations may be at a high risk of regional extinction. 6. A country-led scheme with cross-regional collaboration is required for sciencebased, action-focused and timely conservation efforts. Future conservation management initiatives should aim to increase or at least maintain key habitats, inter-population connectivity, population-level genetic diversity and effective population size.

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Investigating the age composition of Indo-Pacific humpback dolphins in the Pearl River Estuary based on their pigmentation pattern

Cited by 27 publications

References 52 publications

Photo‐identification comparison of four Indo‐Pacific humpback dolphin populations off southeast China

Photo‐identification comparison of four Indo‐Pacific humpback dolphin populations off southeast China

Prey decline leads to diet shift in the largest population of Indo‐Pacific humpback dolphins?

Population distribution, connectivity and differentiation of Indo‐Pacific humpback dolphins in Chinese waters: Key baselines for improving conservation management

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