Epidermal Lesions and Injuries of Coastal Dolphins as Indicators of Ecological Health

Broad-scale impacts of coastal mega-infrastructure project on obligatory inshore delphinids: A cautionary tale from Hong Kong

Inshore marine habitats experience considerable anthropogenic pressure, as this is where many adverse effects of human activities concentrate. In the rapidly-changing seascape of the Anthropocene, Hong Kong waters at the heart of world's fastest developing coastal region can serve as a preview-window into coastal seas of the future, with ever-growing anthropogenic footprint. Here, we quantify how large-scale coastal infrastructure projects can affect obligatory inshore cetaceans, bringing about population-level consequences that may compromise their long-term demographic viability. As a case in point, we look at the construction of world's longest sea crossing system and broad-scale demographic, social and spatial responses it has caused in a shallow-water delphinid, the Indo-Pacific humpback dolphin (Sousa chinensis). Soon after the infrastructure project began, dolphins markedly altered their home range near construction sites such that these waters no longer functioned as dolphin core areas despite the apparent presence of prey, indicating that anthropogenic impacts outweighed foraging benefits. The contraction of key habitats has in turn led individuals to interact over spatially more constricted area, reshaping their group dynamics and social network. Although there was no apparent decline in dolphin numbers that could be detected with mark-recapture estimates, adult survival rates decreased drastically from 0.960 to 0.904, the lowest estimate for these animals anywhere across the region to date, notably below the previously estimated demographic threshold of their long-term persistence (0.955). It is apparent that during an advanced stage of this coastal infrastructure project, dolphins were under a major anthropogenic pressure that, if sustained, could be detrimental to their long-term persistence as a viable demographic unit. As effective conservation of species and habitats depends on informed management decisions, this study offers a valuable lesson in environmental risk assessment, underscoring the implications of human-induced rapid environmental change on obligatory inshore delphinids-sentinels of coastal habitats that are increasingly degraded in fast-changing coastal seas.

Ranging pattern development of a declining delphinid population: A potential cascade effect of vessel activities

It is generally accepted that vessel activity causes various behavioral responses of cetaceans and undermines individual fitness. Whether or how it can lead to a demographic response of populations remains rarely examined. In the northern Beibu Gulf, China, vessel activities have sharply increased in the past two decades, while abnormal demographic dynamics was recently noted for the resident Indo-Pacific humpback dolphins. The present study first examined the humpback dolphins' utilization distribution (UD) from 2003 to 2019. Habitat suitability was then modeled with the sighting data collected before the most recent population reduction. Finally, we tried to disentangle the anthropogenic driver of dolphin demography by cross-referring the spatiotemporal development of dolphins' UD, vessel activities, and habitat suitability. Our results showed that the dolphins' UD shrank substantially during the port expansion in the early 2010s, and we suggest that the consequential increase in vessel activities might impose extra marine stressors on the resident humpback dolphins. To reduce the boat interaction, the dolphins steadily shifted their core area to a less suitable area in the east during 2015-2017, when unnaturally low survivals were recorded. Afterward, the dolphin core area partially shifted back to the more suitable area in the west, which corresponded to the improving dolphin survival in 2018. Our finding suggested that the vessel activity may be responsible for the dolphin displacement, while staying in the less suitable area may further lead to a more severe and acute demographic consequence on the population. The underlying and indirect impact of vessel activities as disclosed by the present study is particularly important for port management, marine planning, and conservation practice regarding coastal cetaceans, especially for those resident and endangered populations inhabiting the urbanized coastal areas.

Skin Marks in Critically Endangered Taiwanese Humpback Dolphins (Sousa chinensis taiwanensis)

As long-lived apex predators, Indo-Pacific humpback dolphins (Sousa chinensis) are key indicators of marine coastal environmental health. Skin marks can be observed on dorsal body surfaces that are visible during mark-recapture studies that rely on photo-identification (photo-ID) methods. Skin mark prevalence may be an indicator of environmental or anthropogenic stressors in the ecosystem, which may lead to individual and/or population-level health concerns. The prevalence of marks of anthropogenic origin was assessed in the Critically Endangered S. chinensis taiwanensis population along the coasts of central Taiwan. Fifty, twenty-eight, and thirty-four individuals were identified in 2018, 2019, and 2021, respectively. At least one category of injuries was observed in 47 of 57 distinctive individuals (82%), and adults showed a higher prevalence of deep injuries than the other coloration stages. At least one category of skin lesion was observed in 33 of 57 distinctive individuals (58%), and high prevalence of skin lesions was found in mature individuals. Given the difficulty in taking direct observations, skin mark prevalence is proposed as a proxy for estimating habitat health and anthropogenic stressors upon S. chinensis taiwanensis. The moderate-to-high prevalence of skin marks in this study was designated as a warning of risks. This study provides important updated information for the assessment of the health and survival of this population. More effective management measures are urgently needed to reverse the observed population decline.

Health conditions of Guiana dolphins facing cumulative anthropogenic impacts

Coastal areas are associated with anthropogenic activities and stressors that can expose the marine fauna to negative cumulative impacts. Apex predators, such as dolphins, can flag the quality of their environment through health parameters such as cutaneous and body conditions. We examined the potential relationship between environmental conditions and health parameters of Guiana dolphins around a port and a conservation unit within the Paranaguá Estuarine Complex, southern Brazil. During boat surveys between July 2018 and April 2019 covering both areas, we measured environmental parameters, photographed dolphins to infer their health condition and the frequency of use of the estuary. In total, 204 individual Guiana dolphins were photo-identified, 52 of which were seen in both years. In general, dolphins showed poor body condition (76% classified as emaciated or thin in 2018, and 79% in 2019), diverse cutaneous conditions (four types of lesions suggestive of an infectious aetiology, two conditions suggestive of traumatic events of anthropogenic origin, and two anomalous pigmentation) and a high prevalence of such cutaneous conditions (85% in 2018, 70% in 2019). Most individuals maintained their body and cutaneous conditions between the two years. There were no clear differences between the port and the conservation areas in terms of environmental conditions, frequency of use and health conditions of individual dolphins, suggesting that dolphins inhabiting this estuarine complex are exposed to potential cumulative impacts, such as pollutants, noise and habitat degradation. This study provides baseline information on some health parameters of Guiana dolphins in southern Brazil and highlights the need for systematic, long-term health assessment of Guiana dolphin populations to guide conservation actions to safeguard this vulnerable species.

Long-term increase in mortality of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary following anthropic activities: Evidence from the stranded dolphin mortality analysis from 2003 to 2017

With the dramatic increase in anthropogenic threats to the Pearl River Estuary (PRE), the population size of the Indo-Pacific humpback dolphins (Sousa chinensis) has significantly decreased over the past decade. To understand the impact and potential risks of intense human activities on these dolphins, factors related to the mortality of humpback dolphins in the PRE were investigated by a detailed examination of 343 dolphin specimens stranded during 2003-2017. There was a significant (p < 0.01) increasing trend for humpback dolphin stranding, reflecting the accelerating rate of the population decline. A large proportion of strandings (35.88%) were neonates. A low recruitment rate implies slow population growth, and hence, limited capacity to resist anthropogenic stress. The most commonly diagnosed causes of death were vessel collision and net entanglement. The concentrations of trace metals, polychlorinated biphenyl (PCB) congeners, dichlorodiphenyltrichloroethane, polycyclic aromatic hydrocarbons, and most of per- and polyfluoroalkyl substances (PFASs) in the dolphin samples were greater than those previously reported in cetaceans globally. Furthermore, Cu, PCB77, PCB169, PCB81, PCB37, and PFASs (excluding PFBA, PFPeA, PFHxA, PFHxDA, and PFODA) were the major pollutants accumulated in neonates. 67% of PCB, 78% of Cu, and 100% of perfluorooctane sulfonate concentrations in the neonates exceeded the threshold for toxicological effects in marine mammals, suggesting that these compounds could be important factors contributing to the low survival rate of calves in this area. This study revealed that vessel transportation, fishing activities, and pollutant bioaccumulation are the three major causes of humpback dolphin mortality in the PRE. These results highlight the need for more efforts to restrict anthropogenic activities, especially vessel traffic, the catching of these marine animals and fishing, and pollutant discharge, in order to prevent vulnerable species from continuous population decline and further extinction.

Visual Assessment of Contusion-Like Lesions Caused by Live Sharksucker (Echeneis naucrates) Attachment in an Indo-Pacific Humpback Dolphin (Sousa chinensis)

We observed contusion-like lesions caused by live sharksucker (Echeneis naucrates) attachment in an Indo-Pacific humpback dolphin (Sousa chinensis). Our report assists in differentiating epidermal lesions for visual health assessment in this vulnerable species and other cetaceans, and this adds new host and epibiont records for E. naucrates and S. chinensis, respectively.

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

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.

Ecological responses to flow variation inform river dolphin conservation

Many environmental flow (e-flow) studies and applications have predominantly used state—(i.e., at a single time point) and rate—(i.e., temporal change) based demographic characteristics of species representing lower trophic levels (e.g., fish communities) to build flow-ecology relationships, rather than using a process that incorporates population dynamics. Recent studies have revealed the importance of incorporating data on species traits when building flow-ecology relationships. The effects of flow on keystone megafauna species (i.e., body mass ≥ 30 kg) reverberate through entire food webs; however, the relationships between flow and these species are not well understood, limiting the scope of the relationships used in flow management. Here, we fill this gap by incorporating the habitat selection traits at different flows of a freshwater apex predator, Ganges River dolphin (GRD, Platanista gangetica gangetica), which plays a significant role in maintaining the structure, functions and integrity of the aquatic ecosystem. Using temporally and spatially measured GRD habitat selection traits, we quantified flow-ecology responses in the Karnali River of Nepal during the low-flow season when habitat was heavily reduced and water demand was highest. We define ecological responses as suitable habitat templates with enough usable surface area to support GRD fitness by improving reproduction and survival. We measured the available and occupied habitats to develop flow-ecology responses. Variation in flow resulted in substantial differences in the ecological response across time and space, suggesting that aquatic species adjusted in a variety of habitats to support their life histories and maintain viable populations. The limited availability of suitable habitats combined with uninformed water regulations by humans likely places GRDs under severe physiological stress during low-water seasons (i.e., January–April), suggesting that  reduced flows contribute to the process of endangering and extirpating highly sensitive endemic aquatic biodiversity. Our study reveals that ad hoc or experience-based flow management is no longer tenable to maintain the integrity and functionality of aquatic ecosystems. We stress that quantifying the flow-ecology relationships of foundational species, particularly megafauna, in response to flow variation is crucial for monitoring the effects of water alterations and determining the minimum flows needed for maintaining healthy and functional freshwater ecosystems in the Anthropocene.