Eastern Taiwan Strait Research Articles

Anthropogenic footprints are invading global habitats of Indo-Pacific humpback dolphins

As ecologically fragile areas, coastal zones are affected by both anthropogenic activities and climate change. However, the impacts of these factors on large nearshore mammals, such as Indo-Pacific humpback dolphins (IPHDs, Sousa chinensis), are poorly understood. Here, modeling revealed that the suitable habitats of IPHDs are affected mainly by the sea surface temperature (SST), and the habitat suitability decreases as the distance to the nearest coastline increases. In addition, anthropogenic activities involving demersal fishing, contamination and shipping have narrowed IPHD habitats and reduced the habitat suitability. We found that climate change will further narrow suitable habitats located farther than 7 km from coastlines and trigger habitat losses in the eastern Taiwan Strait by 2090–2100 under the Representative Concentration Pathway (RCP) 8.5 scenario. The projected decreases in habitat suitability and area emphasize the urgency of establishing connected marine protected areas (MPAs) while considering climate change, intergovernmental cooperation, and public involvement.

Biophysical controls on spatial and summer/winter distributions of total and chromophoric dissolved organic matter in the Taiwan Strait

This study examined the physical and biogeochemical processes that determine the spatial and summer/winter distributions of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in the Taiwan Strait (TS). The hydrological conditions in the TS varied between early summer and winter because of differences in terrestrial input as well as input from the poleward South China Sea Water (SCSW) during the warm summer and the strong, nutrient-rich, equatorward China Coastal Water (CCW) in winter. Concentrations of dissolved organic carbon (DOC) ranged from 60 to 100 μM-C in early summer and from 70 to 144 μM-C in winter. The average stoichiometric ratio of DOC : DON:DOP was high (353:49:1) in the land-source impacted zones and low (168:21:1) in the SCSW-laden areas, both of which are higher than the Redfield ratio. The concentrations of DOC and nutrients were higher in the western TS (on the coast of China) than in the eastern TS (on the coast of Taiwan), and the highest concentrations were mostly found in the Minjiang River plume, reflecting the profound effects of freshwater input in early summer and CCW inflow in winter. The absorption and emission characteristics of the CDOM varied to a large extent with locations because of the mixing of the shelf water with different source waters. Although the absorption coefficient (aCDOM(325)) and fluorescence intensity of the terrestrial humic-like CDOM (Ft: Ex/Em= 260/400-460) were both strongly inversely correlated with salinity, as an optical tracer, Ft may be more effective than aCDOM(325) in examining the mixing among source waters, given that aCDOM(325) may be subject to various photobleaching effects in the TS. Ft was also significantly correlated with the concentrations of terrestrially derived nitrate and nitrite (N+N) and silicate. The results of factor analysis elucidated the complexity of the hydrological and biological processes that affect the distributions of DOM and CDOM in the TS.

Unstated impacts of the green energy industry on the habitat of a coastal delphinid: Turbid‐turbulent wakes induced by offshore wind turbine foundations

Abstract Offshore wind farms (OWFs) are a green energy solution to reducing CO2 emissions, but often encroach on major habitats of coastal delphinids. Clustered OWF construction in shallow waters may have cumulative negative impacts on coastal delphinids and marine ecosystems. Although the impacts of piling noise have been discussed extensively, the potential impacts of oceanographic alterations induced by wind turbine foundations are rarely discussed. Two OWFs were constructed near the core habitat of a critically endangered subspecies of humpback dolphin (Sousa chinensis taiwanensis) in the eastern Taiwan Strait. Turbid‐turbulent wakes induced by wind turbine foundations were inspected using Landsat images. Sighting rates of the humpback dolphin that were obtained from boat‐based line‐transect surveys near the northern OWF (OWFn) since the late 2000s were examined. Indicators of surface turbidity were used to highlight turbid‐turbulent wakes extending in the direction of the main current. Sighting rates of the humpback dolphins near the OWFn have been declining since the 2000s, but decreased significantly after the OWFn was constructed and began operating. The long‐term decline in sighting rates implies an alarming decline in the population size of humpback dolphins. Decreased sighting rates after the OWFn installation indicate the reduced utilization of a once‐important habitat. Offshore wind farm construction may influence prey abundance and composition and cause acute stress from piling noise; operational noise may mask the chorus of prey fish and turbid‐turbulent wakes may disturb the benthic ecosystem. Site selection committees for future OWFs should avoid the habitats of coastal delphinids and areas subject to strong ocean currents. Ecological impact assessments for OWF projects should examine the impacts of turbulent wakes on benthic ecosystems and of acoustic disturbance on marine mammals. Long‐term environmental monitoring programmes are recommended, which can be funded by wind energy companies as a compensatory measure.

Impact of Vessel Transit on Vocalizations of the Taiwanese Humpback Dolphin

Recent offshore windfarm development has led to increased vessel traffic in the Eastern Taiwan Strait, which is part of the habitat of the critically endangered Taiwanese humpback dolphin (Sousa chinensis taiwanensis). However, data on possible effects on the behavior of this endemic subspecies are lacking to date. In this study, we observed Taiwanese humpback dolphins’ acoustic behavior associated with shipping noise and analyzed their whistles and clicks before, during, and after vessel transit. Before vessel transit, the median rate of dolphin whistles and clicks was 100 and 1550 counts per minute, which significantly reduced to less than 8 and 170 counts per minute during and after vessel transit. Dolphins produced significantly shorter whistles during (0.07 s) and after (0.15 s) vessel transit. The vocalizing behavior of the Taiwanese humpback dolphin may be affected by vessel transit, which, if sustained, could possibly influence the individual communication and feeding success of the population. Implementing measures such as re-routing of the vessel lanes and regulating the speed of the vessel traffic in the habitat are proposed to overcome the influence of vessel noise on Taiwanese humpback dolphins.

The dynamical complexity of seasonal soundscapes is governed by fish chorusing

Passive acoustic monitoring technology can depict underwater soundscapes, yet phenological and seasonal patterns and shifts in soundscapes are still poorly understood. Here we analyse the seasonal soundscape in the Eastern Taiwan Strait in 2017 using nonlinear dynamical complexity modelling. We find an annual phenology of fish chorusing that begins in spring, and peaks in summer before beginning to subside in autumn and becoming silent in winter. During spring and summer, the soundscape exhibited significantly higher complexity and predictability than in autumn and winter, due to the presence of regular fish chorusing. Soundscape dynamics shifted from being nonlinear in spring and summer to being linear and stochastic in autumn and winter. Our findings suggest that soundscapes could be used to measure phenological patterns and seasonal shifts in marine species behaviour. We propose that monitoring soundscapes could help assess the long-term health of marine ecosystems under environmental and climatic change.

Modeling the Habitat Distribution of Acanthopagrus schlegelii in the Coastal Waters of the Eastern Taiwan Strait Using MAXENT with Fishery and Remote Sensing Data

Black sea bream, Acanthopagrus schlegelii, is among the most commercially valuable species in the coastal fishery industry and marine ecosystems. Catch data comprising capture locations for the gillnet fisheries, remotely sensed environmental data (i.e., sea surface temperature, chlorophyll-a concentration, and current velocity), and topography (bathymetry) from 2015 to 2018 were used to construct a spatial habitat distribution of black sea bream. This species is concentrated in coastal waters (<3 nm) from December to April (spawning season). The maximum entropy (MaxEnt) method and corresponding habitat suitability index among seasons were used to clarify the species’ spatial distribution and identify the seasonal variations in habitat selection. The patterns corresponded closely to the changes in oceanographic conditions, and the species exhibited synchronous trends with the marine environment’s seasonal dynamics. Chlorophyll-a concentration and bathymetry substantially influenced (80.1–92.9%) black sea bream’s habitat selection. By applying the MaxEnt model, the optimal habitats were identified with four variables including depth and satellite-derived temperature, current velocity and chlorophyll-a concentration, which provides a foundation for the scientific assessment and management of black sea bream in coastal waters of the Eastern Taiwan Strait.

Impact of pile‐driving and offshore windfarm operational noise on fish chorusing

AbstractOffshore windfarms have recently emerged as a renewable energy solution. The effects of pile‐driving and long‐term impacts of operational noises on fish chorusing still, however, remain largely unknown. In this study, we investigated the variations of fish chorusing intensity and duration during the construction (2016) and operational phases (2017–2018) of a windfarm at the Eastern Taiwan Strait (ETS). At the ETS, two types of fish choruses (Types 1 and 2) were found to repeat over a diurnal pattern. In the 2 days after the pile driving, Type 1 chorusing showed lower intensity and longer duration, while Type 2 chorusing exhibited higher intensity and no changes in its duration. During the operational phases in 2017 and 2018, both choruses were longer in duration (2–3 h for Type 1; 0.5–1 h for Type 2). The intensity of Type 1 chorus increased by 5–10 dB, but no significant variation was recorded for Type 2. Our findings document, for the first time, different behavioral responses of two chorusing types exposed to pile‐driving and windfarm noise pressure. Fish choruses have been associated with several behavioral functions. Deviation from a regular pattern might affect fish reproductive success, cause migration, augmented predation, or physiological alterations. Because offshore windfarms installations are growing in magnitude and capacity worldwide, this study provides essential insights for policymakers and constitutes an important reference for assessing the effects of noise from pile driving and windfarms on fishes.

Silent winters and rock-and-roll summers: The long-term effects of changing oceans on marine fish vocalization

The analysis of temporal trends and spatial patterns of marine sounds can provide crucial insights to assess the abundance, distribution, and behavior of fishes and of many other species. However, data on species-specific temporal and seasonal changes are still extremely limited. We report here the result of the longest recording ever conducted (five years, from 2014 to 2018) on fish vocalization. Findings from the Eastern Taiwan Strait (ETS) revealed a periodic fish chorusing pattern, with peaks in summer and almost complete silence, for ~2 months, during winter. Chorusing pattern was influenced by abiotic parameters, including temperature, tides and moon phase. We also report, for the first time, that extreme weather events (e.g., typhoons, storms with sediment resuspension) caused the cessation of the chorusing. The chorusing pattern explored in this long-term study provides important baseline data to understand the impact of climate change and of climate-driven extreme/episodic events on the phenology of fishes; this work also provides evidence that changes in the ambient conditions might significantly alter the phenology of vocalizing marine species.

Acoustic ecological investigation of estuary habitat on Indo-Pacific humpback dolphin (Sousa chinensis) in Yunlin, Taiwan

A sunspecies/population of Indo-Pacific humpback dolphins (IPHD, Sousa chinensis) lives in the shallow waters of Eastern Taiwan Strait. Their habitat is very close to the coast and suffering from the impact of human activities and marine pollution; the survival of this vulnerable group is at high risk. The long-term visual survey result shows that the Xinhuwei estuary has been an IPHD hot spot. Two Passive acoustic monitoring (PAM) stations with temperature sensors were deployed to detect IPHD sounds in the estuary habitat. During the past four seasons, underwater marine recorders and temperature-depth data loggers were deployed at two locations in the estuary of Xinhuwei creek, Yunlin, Taiwan. The total duration of valid data for each station is at least 19 consecutive days during each season. IPHD's click-trains and whistles were counted by a supervised detection method. The results show that the trend of click-trains (echolocation and foraging sounds) is positively correlated with sea temperature. The most active foraging behavior occurs during the daytime of summer. Whistles (social and communication sounds) are most common during spring. Except in winter, the number of click-trains and whistles are larger at the deeper measuring station (water depth of 11 m). This research was funded by Formosa Petrochemical Corporation.

Observation of continental shelf wave propagating along the eastern Taiwan Strait during Typhoon Meranti 2016

This study is the first to depict typhoon-induced continental shelf wave (CSW) propagation in the eastern Taiwan Strait (TWS) during the passage of Typhoon Meranti in 2016 using tidal gauge data and along-track satellite altimeter data. The strong amplitude response of sea level oscillations (within the range of 0.30–0.54 m) as a free, barotropic CSW after Meranti, which impacted the TWS, was clearly detected in time and frequency (in bands of 64–81 h) using wavelet and cross-wavelet analyses. The measured group and phase speeds were consistent with the dispersion curves for CSW with the first-mode derived from the cross-shelf sections of the eastern TWS, with the mean speeds reaching 3 and 5.6±0.7 m/s, respectively. Coincidentally, the typhoon-induced sea level anomaly (SLA) was also captured by the satellite altimeter before this CSW entered into the TWS. Using the theoretical cross-shore CSW modes to fit the SLA data, the results indicated that the first three wave modes can interpret this CSW event appeared in the southern TWS very well, with the first mode being the dominant one.

Geographic variation in pigmentation patterns of Indo-Pacific humpback dolphins (Sousa chinensis) in Chinese waters

The pigmentation patterns of Indo-Pacific humpback dolphins have not been well studied throughout most of the species' range. In the present study, both the subjective scoring method and a newly developed quantified scoring method were employed to evaluate the spotting intensity of 137 humpback dolphin individuals from the Xiamen and Beibu Gulf putative populations, including the Dafengjiang-Nanliujiang River Estuary (DRE) and Shatian-Caotan (SC) communities. Both scoring methods indicated that spotting intensity on the dorsal fin was lower than that on the body of humpback dolphins in all 3 groups. The SC and DRE humpback dolphins had significantly greater dorsal fin, body spotting intensity, and greater differences between spotting on the dorsal fin and body than Xiamen dolphins, while no differences were found between SC and DRE. The pigmentation variation is related to age class, young dolphins have more spotting density than adults, and young and adults showed similar geographical variation as above. The present paper, in combination with previous research, clarifies the general pattern of pigmentation for Chinese humpback dolphins. Eastern Taiwan Strait and Pearl River Estuary populations represent 2 extreme patterns of pigmentation, while the Xiamen population, SC community, and DRE community seem to be intermediate. The results suggest that these groups should be viewed as demographically distinct forms.

Noise impact assessment on Indo-Pacific Humpback Dolphin in the habitat of the East Taiwan Strait during the first two pile driving activities of demonstration offshore wind farm

Foundation piles of the first two wind turbines were driven off the coast of Miaoli, Taiwan in 2016. However, that area is also the habitat of the critically endangered Eastern Taiwan Strait (ETS) population of Indo-Pacific humpback dolphin (Sousa chinensis). To assess potential noise effects from pile driving on the humpback dolphins, we collected underwater noise data during the construction and found that the sound pressure level (Lrms) at 750m was less than 180dB re 1μPa and the peak sound pressure (Lpk, flat) was less than 190 dB re 1μPa. We also presented recommendations of noise and marine mammal monitoring for future pile driving activities. It includes an exclusion zone of radius 750m from the piling location and the peak sound pressure (Lpk, flat) not to exceed 190~220 dB re 1μPa at 750 m distance, and an observation zone extends to 1500m radius where both marine mammal observers and passive acoustic monitoring are posted. [This work was sponsored by Ministry of Science and Technology of Taiwan (105-3113-E-002 -002 -CC2), Taiwan Bureau of Energy and Industrial technology Research Institution (05HZT56002), and U.S. Marine Mammal Commission’s Research and Conservation Grant.]

Preliminary sex differentiation of Indo‐Pacific humpback dolphins (Sousa chinensis) in the Pearl River estuary and eastern Taiwan Strait using scarring of dorsal fins

Preliminary sex differentiation of Indo‐Pacific humpback dolphins (<i>Sousa chinensis)</i> in the Pearl River estuary and eastern Taiwan Strait using scarring of dorsal fins

Noise field characterization in the habitat of the East Taiwan Strait Indo-Pacific Humpback Dolphin during the pile driving activity of demonstration offshore wind farm

The Eastern Taiwan Strait (ETS) population of Indo-Pacific humpback dolphin (Sousa chinensis) is listed critically endangered in the Red List of Threatened Species by the International Union for Conservation of Nature due to its small population size and narrow distribution. The humpback dolphin habitats off the coast of Miaoli and Changhua are sites selected for future wind farms, therefore, the noise impact of pile driving on this critically endangered population is expected to be serious. This paper presents works done in (1) characterizing the sound field during the test pile driving and associated activities in the humpback dolphin habitat; (2) identifying dominant anthropogenic noise sources of the dolphin habitat during the construction of demonstration wind turbines and associated activities; and (3) examining the implications of the sound field from wind turbine construction and associated activities in relation to humpback dolphins’ hearing and communication. The results from the study can provide critical information and conservation recommendations for an environmental impact analysis for the full scale wind farm construction in 2017.

Conservation of the Eastern Taiwan Strait Chinese White Dolphin (Sousa chinensis): Fishers' Perspectives and Management Implications.

The abundance of the eastern Taiwan Strait (ETS) population of the Chinese white dolphin (Sousa chinensis) has been estimated to be less than 100 individuals. It is categorized as critically endangered in the IUCN Red List of Threatened Species. Thus, immediate measures of conservation should be taken to protect it from extinction. Currently, the Taiwanese government plans to designate its habitat as a Major Wildlife Habitat (MWH), a type of marine protected area (MPA) for conservation of wildlife species. Although the designation allows continuing the current exploitation, however, it may cause conflicts among multiple stakeholders with competing interests. The study is to explore the attitude and opinions among the stakeholders in order to better manage the MPA. This study employs a semi-structured interview and a questionnaire survey of local fishers. Results from interviews indicated that the subsistence of fishers remains a major problem. It was found that stakeholders have different perceptions of the fishers’ attitude towards conservation and also thought that the fishery-related law enforcement could be difficult. Quantitative survey showed that fishers are generally positive towards the conservation of the Chinese white dolphin but are less willing to participate in the planning process. Most fishers considered temporary fishing closure as feasible for conservation. The results of this study provide recommendations for future efforts towards the goal of better conservation for this endangered species.

Biology and Conservation of the Taiwanese Humpback Dolphin, Sousa chinensis taiwanensis.

The humpback dolphins of the eastern Taiwan Strait were first discovered scientifically in 2002 and since then have received much research attention. We reviewed all information published in peer-reviewed scientific journals on these dolphins and where appropriate and available, peer-reviewed scientific workshop reports and graduate theses were also examined. Recent evidence demonstrated that this population warranted recognition as a subspecies, Sousa chinensis taiwanensis. It is found in a highly restricted and linear strip of coastal waters along central western Taiwan. Numbering fewer than 80 individuals and declining, five main threats (fisheries interactions, habitat loss and degradation, loss of freshwater to estuaries within their habitat, air and water pollution, and noise) threaten the future existence of this subspecies. These dolphins have cultural and religious importance and boast the highest level of legal protection for wildlife in Taiwan. However, despite enormous efforts by local and international non-governmental groups urging immediate conservation actions, there have been no real government efforts to mitigate any existing threats; instead, some of these threats have worsened. Based on recent studies, we suggest the IUCN Red List status be revised to Critically Endangered CR 2a(ii); D for the subspecies.

Social structure in a critically endangered Indo‐Pacific humpback dolphin (Sousa chinensis) population

Abstract Social behaviour can be a vital aspect of population viability when it influences survivorship and reproductive fitness, which is often the case for especially social species, including cetaceans. Understanding this relationship is important in at‐risk populations, where knowledge of network structure can provide insight into how they may respond to human impacts. Association patterns in the critically endangered eastern Taiwan Strait (ETS) population of Indo‐Pacific humpback dolphins, Sousa chinensis, were investigated using the seasonally collected (2007–2010) photo‐identification data of 74 individuals. Social network structure was characterized by high strength and reach, features that are thought to be atypical for the species. Standardized lagged association rates were best fitted by a two‐level model: short‐term associations that dissipated in less than a day, and long‐term associations projected to persist nearly 10 years. These persisting relationships were primarily among calves and their inferred mothers. The short‐term associations, which were probably limiting the network's modularity, seemed to occur among more weakly associated individuals temporarily participating in large mother–calf groups. When associations were defined by proximity (within one body‐length), relationships involving calves were characterized by a significantly high clustering coefficient, and some calves had high associations with other calves and more than one adult, making maternal relationships ambiguous. This could be evidence for cooperative calf rearing, which may be important for calf survivorship and initiating dyadic relationships among calves. Given their apparent uniqueness among populations of this species, the association patterns observed among the ETS S. chinensis, calves and their inferred mothers in particular, could be a response to conditions (small population size, isolation, confined distribution, and anthropogenic stressors) that make long‐term cooperative behaviour advantageous. Thus, minimizing human impacts that disrupt social dynamics, such as interactions with fisheries and habitat fragmentation, should help to improve this population's long‐term viability. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Temporal and spatial patterns of marine soundscape in a coastal shallow water environment

Underwater acoustic recordings were made at two coastal shallow water locations, Yunlin (YL) and Waishanding (WS), off Taiwan between June and December 2012. The purpose of the study was to establish soundscape baselines and characterize the acoustic habitat of the critically endangered Eastern Taiwan Strait Chinese white dolphin by investigating: (1) major contributing sources that dominant the soundscape, (2) temporal, spatial, and spectral patterns of the soundscape, and (3) correlations of known sources and their potential effects on dolphins. Results show that choruses from croaker fish (family Sciaenidae) were dominant sound sources in the 1.2–2.4 kHz frequency band for both locations at night, and noises from container ships in the 150–300 Hz frequency band define the relative higher broadband sound levels at YL. In addition, extreme temporal variation in the 150–300 Hz frequency band were observed at WS, which was shows to be linked to the tidal cycle and current velocity. Furthermore, croaker choruses are found to be most intense around the time of high tide at night, but not so around the time of low tide. These results illustrate interrelationships among different biotic, abiotic, and anthropogenic environmental elements that shape the unique fine-scale soundscape in a coastal environment.

Viability of the Critically Endangered eastern Taiwan Strait population of Indo-Pacific humpback dolphins Sousa chinensis

The population of humpback dolphins Sousa chinensis that resides in the eastern Taiwan Strait (ETS) is geographically and genetically isolated from populations inhabiting the coastal waters of mainland China and appears to be facing unsustainable levels of human threats. Using VORTEX 9.99b, we modeled the viability of this Critically Endangered population under the present conditions as well as under realistic additional threat scenarios. We examined 6 differ- ent levels of bycatch mortality, 3 scenarios of habitat loss/degradation, and scenarios in which these threats were experienced together. Under the baseline (present) scenario, the population exhibited a decreasing growth rate and was predicted to be smaller than the initial population size in more than 76% of all model runs. In all scenarios with additional threats, the proportion of model runs in which population size was smaller than the initial size varied from 77.1 to 92.6%. Over the short term, fisheries-related mortality appears to have a more obvious impact on the pop- ulation's trajectory than habitat loss/degradation. Even minimal increases in mortality from the current baseline levels will increase the probability of extinction of this population. Due to the fragile situation of ETS humpback dolphins, mitigation actions to reduce the current threats to this population are needed immediately.

Hydroids (Cnidaria, Hydrozoa) from marine environments in Taiwan

AbstractBackgroundHydroids were identified from extensive surveys of benthos, and especially from worm tubes, in the Danshuei River estuary (DRE), in the northeast Taiwan Strait (NETS), and on a reef in Nanwan Bay (NWB), Taiwan.ResultsA total of 33 species (12 of them identified to generic and 1 to family rank only), referable to 22 genera, 12 families, and 2 orders, were distinguished. The majority of them were referable to order Leptothecata (84.8%) with the remainder being assigned to order Anthoathecata (15.2%). The only species found at NETS wasMonoserius pennarius(Linnaeus, 1758).Plumularia habereri(Stechow, 1909) was recorded at both DRE and NWB. The known range ofDynamena nanshaensis(Tang, 1991), recorded for the second time, is extended further north. Six species (Aglaophenia latecarinata,Plumularia floridana,Diphasia palmata,Dynamena brevis,Dynamena obliqua,Synthecium elegans) are recorded for the first time in waters adjacent to the Chinese mainland.ConclusionsSpecies composition and abundances varied considerably from one environment to another and especially between DRE and NWB. This study provides the first taxonomic account of the hydroid fauna inhabiting the eastern Taiwan Strait region.