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Distribution and abundance of finless porpoises in Hong Kong and adjacent waters of China
Abstract
We studied the distribution and abundance of finless porpoises (Neophocaena phocaenoides) in Hong Kong and adjacent waters of China's Guangdong Province between September 1995 and November 2000. Vessel (50,194 km) and helicopter (2,696 km) surveys were used to assess distribution patterns, and estimates of abundance were calculated using line transect methods. Acoustic detection data from a towed porpoise click detector (POD) were used to make an estimate of the trackline detection probability [g(0)] for ship surveys, and surface and dive time data were used for correcting helicopter survey estimates. Porpoises occurred in Hong Kong and adjacent waters year-round, but showed evidence of seasonal movements, with porpoises largely vacating most of Hong Kong's southwestern waters in summer and autumn. Seasonal changes in overall abundance were also evident. The peak season within Hong Kong waters was spring, in which an estimated 152 porpoises inhabited territorial waters. The peak estimates for all areas combined (217 porpoises in spring and summer) can be viewed as a minimum estimate of the size of the local population. Examination of potential violations of line transect assumptions indicate that the techniques used were well-suited, with no evidence of serious biases. However, because the distribution clearly extends beyond the study area and the exact range limits are unknown, further work is needed to assess overall population size.
... Finless porpoises are small and difficult to study and estimates have only been made in a few areas in the region, such as Hong Kong and Sarawak, Malaysia (Jefferson et. al., 2002;Minton et al., 2013). Finless porpoise numbers were estimated to be 217 (Jefferson et al., 2002) in Hong Kong. ...
... al., 2002;Minton et al., 2013). Finless porpoise numbers were estimated to be 217 (Jefferson et al., 2002) in Hong Kong. ...
... Finless porpoises are classified as Vulnerable according to the IUCN Red list of Threatened Species and they are subject to various threats such as incidental entanglement in gill nets and large numbers continue to be killed in many parts of their range (Jefferson et. al., 2002;Wang & Reeves, 2017). In East Malaysia, finless porpoises are caught in "fish stakes" in Sabah (Jaaman et al., 2009) and one individual was found entangled in the line of a crab trap in Sarawak (Wang & Reeves, 2017). ...
The Indo-Pacific finless porpoise (Neophocaena phocaenoides) occurs in a narrow strip of shallow marine waters less than 50m deep. The finless porpoise although recorded in Malaysia has not been comprehensively studied. The documentation of the occurrence and distribution of finless porpoise in west and north-west Penang was carried out from 2011 to 2019.This included interview surveys every 3 months from December 2012 to December 2013, a collation of published literature and conducting preliminary boat surveys in 2019. A total of 240 structured, individual interviews were done with the local community. Based on the interview surveys, there were 6 sightings (n=6/240, 2.5%) of finless porpoises in 2013. Published data indicated that there were 19 sightings of finless porpoises in 2013 and 3 sightings in 2014. Twenty mortalities of finless porpoises have been recorded. Boat surveys recorded 14 sightings of finless porpoise with an encounter rate of 0.106 sightings per hour. Mean group size was 2.6 ± 0.4 SE. The finless porpoise appears to occur in Teluk Bahang, Pantai Kerachut, Sungai Pinang and Sungai Burung in west Penang. Overall, the data suggests that there is a consistent population where line transect surveys can be done to further elucidate the population status of finless porpoises in Penang.
... The only previous analysis of abundance and population status of finless porpoises in Hong Kong is from dedicated work conducted in the late 1990s through 2000 (Jefferson and Braulik, 1999;Jefferson, 2000;Jefferson et al., 2002). This work showed that finless porpoises occur year-round in Hong Kong, with seasonal influxes in cooler dry-season months, bringing the local numbers to a maximum of about 152 porpoises in spring (Jefferson et al., 2002). ...
... The only previous analysis of abundance and population status of finless porpoises in Hong Kong is from dedicated work conducted in the late 1990s through 2000 (Jefferson and Braulik, 1999;Jefferson, 2000;Jefferson et al., 2002). This work showed that finless porpoises occur year-round in Hong Kong, with seasonal influxes in cooler dry-season months, bringing the local numbers to a maximum of about 152 porpoises in spring (Jefferson et al., 2002). Porpoises also occur in adjacent mainland Chinese waters to the south and west of Hong Kong, and taking some of these areas into account, the overall population may have numbered at least 217 porpoises in 2000/2001. ...
... Porpoises also occur in adjacent mainland Chinese waters to the south and west of Hong Kong, and taking some of these areas into account, the overall population may have numbered at least 217 porpoises in 2000/2001. There is some evidence suggesting that the PRE contains a distinct population of finless porpoises (Jia et al., 2014), though little is known about individual movements into and out of Hong Kong waters (Jefferson et al., 2002). However, it is clear that Hong Kong itself does not contain a separate population of finless porpoises. ...
The Indo-Pacific finless porpoise (Neophocaena phocaenoides) occurs year-round in waters of southern and eastern Hong Kong. The population biology of the population was studied in the late 1990s and early 2000s, but has not been examined recently. There are several threats facing the animals, and there has been recent concern about this species’ status, due to an increase in the number of strandings in Hong Kong. Line-transect surveys using medium-size vessels have been conducted for small cetaceans in most of Hong Kong’s waters since 1996. We examined the density and abundance of finless porpoises in this area, using a Bayesian hierarchical framework, consisting of a Markov process model used to describe population dynamics and a distance-sampling observation model that links the line-transect data to the latent biological process. Time-series analyses for both dry- and wet-season data from 1996 to 2019 showed annual fluctuations in abundance indices, but no evidence of a significant long-term trend in finless porpoise abundance in Hong Kong. This indicates that the increase in strandings may be related to some factor other than changing population size of Hong Kong finless porpoises. In 2019, there were approximately 176 finless porpoises in Hong Kong’s waters in the dry season (winter/spring), the season of highest use. Highest densities (0.535 porpoises/km²) were recorded in South Lantau in the dry season. Based on the results of the current study, we recommend further survey work, improvements in data collection, possible tagging and molecular work to elucidate population structure, cumulative impact assessment, and the establishment of several marine parks for the conservation of finless porpoises in Hong Kong.
... Indo-Pacific finless porpoise (Neophocaena phocaenoides) is one of the two residential cetacean species in the Pearl River Estuary (PRE) (Jefferson et al., 2002a). The PRE is reported to be one of the most DDT-polluted areas in the world (Fu et al., 2003;Ying et al., 2009). ...
... Neophocaena phocaenoides is recently included in Appendix I of the Convention on International Trade in Endangered Species (CITES) (https://www.cites.org/eng/app/appendices.php) and is identified as "vulnerable" by IUCN (Wang and Reeves, 2017). The highest number of finless porpoises sighted per year in the PRE was 260 individuals during the period 2013-2014, which is consequently the minimum estimate for the size of this population (Jefferson et al., 2002a). However, there were on average approximately 30 cases of dead finless porpoise strandings that occurred in HK waters each year during the period 2004-2013, (http://www.afcd.gov.hk/english/conservation/con_mar/con_mar_fin/ ...
... The geometric mean concentration of DDTs in the adult male (AM) porpoises in this study was similar to the mean levels reported in the finless porpoises stranded in HK waters in 1996 (100 μg g −1 lipid) (Minh et al., 1999) and was one-fold lower than that found in the PRE AM humpback dolphins stranded on the coastline of the western bank of the PRE during 2007-2013 (175 μg g −1 lipid) (Gui et al., 2014). Compared to S. chinensis, which inhabits waters closer to the coasts that are heavily contaminated by pollutants from riverine input, N. phocaenoides in the PRE appears to avoid the brackish waters in the estuary (Jefferson et al., 2002a). Thus, the habitat of finless porpoises is less contaminated by DDTs, which explains marked lower levels of DDTs in finless porpoises as compared to the humpback dolphins. ...
A high prevalence of infectious diseases (mostly lungworms) is found in finless porpoises (genus Neophocaena) in the coastal waters of China, which is one of the most dichlorodiphenyltrichloroethane (DDT)-polluted areas worldwide, while its association with contaminant exposure remains undetermined. To address this gap, we investigated blubber levels of polychlorinated diphenyls (PCBs), organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons in Indo-Pacific finless porpoises (Neophocaena phocaenoides) stranded in the Pearl River Estuary (PRE) of China. In the post-mortem examinations, lungworms (Halocercus species) were found to be the most common parasites, with a high density observed in lungs and bronchi. Severe infections by nematode parasites were also found in the uterus (Cystidicola species), intestine (Anisakis typica) and muscle (A. typica). For all the pollutant compounds analyzed, only the concentrations of p,p’-DDT, p,p’-dichlorodiphenyldichloroethane (DDD) and o,p’-DDD were significantly higher in porpoises died of infectious diseases than in the “healthy” individuals (died from physical trauma). Contrasted accumulation pattern of DDTs and their metabolites was found between animals with different health status. The proportion of p,p’-DDT in ΣDDTs was higher than that of p,p’-dichlorodiphenyldichloroethylene (DDE) in diseased animals, whereas an opposite pattern was shown for “healthy” ones. Whilst this study is the first to describe a significant positive correlation between parasitic diseases and high levels of DDTs in cetaceans, the direction of causality cannot be determined in our data: either a parasitic infection affected the porpoises' ability to metabolize DDTs, resulting in high levels of p,p’-DDT in their blubber, or the pollutant burden rendered them more susceptible to parasitic infection.
... Thus, humpback dolphins prefer murky, brackish waters of the Pearl River Estuary, while finless porpoises typically are found in clear, more saline waters, often around reefs, less influenced by the freshwater input from the Pearl River (Jefferson, 2000;Parsons, 1997Parsons, , 1998b). The area north of Lantau Island has been identified as the most important habitat for Hong Kong humpback dolphins (Jefferson, 2000;Jefferson et al., 2002b; Parsons, 1998b). There is concern that pollution, loss of habitat, and interactions with fisheries may adversely impact the populations of resident cetaceans of Hong Kong (Jefferson, 2000;Jefferson, Curry, & Kinoshita, 2002a; Minh et al., 1999;Parsons, 1997Parsons, , 1998aParsons, , 1999aParsons, , 1999bParsons, , 2004aParsons & Chan, 1998;Smith & Jefferson, 2002). ...
... Dietary differences between the sexes and among seasons could not be addressed due to small sample sizes and large variability in these data. Seasonal shifts in dolphin distribution and abundance in North Lantau waters have been documented (Jefferson, 2000;Jefferson et al., 2002b;Parsons, 1998b). Li et al. (2000) observed seasonal variation in species composition of both pelagic and demersal fishes in waters of the Pearl River Estuary. ...
... Curiously enough, finless porpoises in Hong Kong waters have shown prey composition suggestive of feeding in association with trawlers ( Barros et al., 2002), in addition to the presence of undigested fish, squid, and shrimp in their stomachs. Because this behavior is far less documented for Hong Kong finless porpoises than for humpback dolphins (Jefferson & Braulik, 1999;Jefferson et al., 2002b;Parsons, 1997;Parsons & Wang, 1998;also see Torey, 2000, for anecdotal data collected through interviews with local fishermen), we suspect that porpoises may be more difficult to detect than dolphins when following pair trawlers ( Barros et al., 2002). ...
Dietary information derived from the examination of stomach contents of 29 Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong waters is presented in this study. Humpback dolphins in this area have a diet comprised nearly exclusively of fish. Prey spectrum from the 15 dolphins with contents includes a minimum of 24 species of fish, and one species of cephalopod. The croaker (Johnius sp.) was the most frequent and numerically most important prey, followed by the lionhead (Collichthys lucida) and ancho- vies (Thryssa spp.). The fish families Sciaenidae, Engraulidae, Trichiuridae, and Clupeidae accounted for over 93% of all prey consumed. Most of these prey are common in murky, brack- ish waters of estuaries and often occur in large shoals. There is some dietary overlap with fin- less porpoises (Neophocaena phocaenoides); the two species share some 13 fish species, but only anchovies figure among the top five prey for both species. In addition, finless porpoises rely more heavily on cephalopods (squids, cuttlefishes, and octopus) and may venture into deeper, clearer waters during foraging, whereas humpback dolphins seem to exploit demersal and shoaling fish of productive estuaries. The stocks of some fish species important in the diet of humpback dolphins may have been subjected to heavy exploitation by the fisheries in Hong Kong waters. Behavioral observations of dolphins feeding in association with pair trawlers suggest a somewhat different prey preference for some dolphins from the results of this study.
... These devices detect and log the occurrence and timing of cetacean echolocation clicks and have been used in studies of several cetacean species including bottlenose dolphins (Elliott et al., 2011;Philpott et al., 2007;Thompson et al., 2010) Jefferson et al., 2002), dusky dolphins (Pearson et al., 2012) and Hector's dolphins (Rayment et al., 2009a(Rayment et al., , 2009b. They have been used for studies of abundance (Jefferson et al., 2002), habitat use Simon et al., 2010;Verfuß et al., 2007) and behaviour (Koschinski et al., 2003;Leeney et al., 2007) of odontocetes, and in studies of effects of anthropogenic activities such as boat traffic (Lamb & Ugarte, 2005), military exercises (Lammers et al., 2017), wind-power generators (Carstensen et al., 2006;Koschinski et al., 2003;Scheidat et al., 2011), seismic surveys (Thompson et al., 2013), pile driving (Brandt et al., 2016;Leunissen et al., 2019), fisheries (Cox & Read, 2004) and aquaculture (Haarr et al., 2009). ...
... These devices detect and log the occurrence and timing of cetacean echolocation clicks and have been used in studies of several cetacean species including bottlenose dolphins (Elliott et al., 2011;Philpott et al., 2007;Thompson et al., 2010) Jefferson et al., 2002), dusky dolphins (Pearson et al., 2012) and Hector's dolphins (Rayment et al., 2009a(Rayment et al., , 2009b. They have been used for studies of abundance (Jefferson et al., 2002), habitat use Simon et al., 2010;Verfuß et al., 2007) and behaviour (Koschinski et al., 2003;Leeney et al., 2007) of odontocetes, and in studies of effects of anthropogenic activities such as boat traffic (Lamb & Ugarte, 2005), military exercises (Lammers et al., 2017), wind-power generators (Carstensen et al., 2006;Koschinski et al., 2003;Scheidat et al., 2011), seismic surveys (Thompson et al., 2013), pile driving (Brandt et al., 2016;Leunissen et al., 2019), fisheries (Cox & Read, 2004) and aquaculture (Haarr et al., 2009). ...
Aquaculture has maintained a sustained growth trend over the last 50 years, worldwide and in Aotearoa New Zealand.
This industry is known to have environmental consequences, such as impacts on benthos, water column and higher trophic levels. Some of these impacts have been thoroughly studied, while others, such as the effects on cetaceans, are not well understood.
This study used passive acoustic monitoring (PAM) to assess, for the first time, the overlap between kūtai—New Zealand greenlipped mussel ( Perna canaliculus )—farms and habitat use by endemic endangered Hector's dolphins ( Cephalorhynchus hectori hectori ) within the Banks Peninsula Marine Mammal Sanctuary.
T‐PODs were deployed in six bays, three with mussel farms and three without, between 2018 and 2019. Occurrence of dolphins, expressed as ‘dolphin positive minutes per day’ (DPM/day), was modelled using generalized linear mixed models.
Results showed a strong interaction between farm (presence/absence) and season (summer/winter), with fewer acoustic detections of dolphins in winter if farms were present. Furthermore, in bays with mussel farms, there were significantly more click train detections on the opposite side of the bay, compared to the side by the mussel farm.
Considering that results from this study suggest potential displacement of the dolphins due to the mussel farms, the recommendation is a precautionary approach. Further expansion of aquaculture in Hector's dolphin habitat should be done carefully, taking into account their habitat use, and conducting intensive monitoring including a robust ‘before and after’ design prior to the establishment of new farms.
... The decision to suspend survey effort when sea state conditions were greater than Beaufort 3 was made after considering the generally cryptic surfacing behaviour of Irrawaddy dolphins, the strong spatial heterogeneity of wind patterns in the Sound and the improbability of making a sufficient number of sightings in Beaufort 4 conditions or greater to allow stratification according to sea state. Simply deleting the survey effort conducted while sighting conditions were poor from the line-transect analysis, as done by Jefferson et al. (2002) for estimating the abundance of finless porpoises (a cetacean that exhibits somewhat similar inconspicuous surfacing behaviour), could have resulted in a severely biased abundance estimate. Spatial coverage would have been uneven (especially near Mt Capoas where convection winds often created poor survey conditions), while dolphin distribution within the Sound may have been clumped. ...
... Because the horizon was not visible in the Sound, this technique could not be used. Following the example of Jefferson and Leatherwood (1997) and Jefferson et al. (2002), a laser range finder (Bushnell Yardage Pro 1000) was used in training observers to more accurately estimate sighting distances by eye and to investigate potential distance estimation biases. Although a laser range finder cannot obtain a reading from a surfacing dolphin, training exercises were conducted using other objects on the water, such as fishing gear, boats and buoys. ...
A geographically isolated population of Irrawaddy dolphins was recently discovered in Malampaya Sound, Palawan, Philippines. Line-transect surveys conducted in April-November 2001 covered 884km of trackline in the entire Sound and resulted in a total population estimate of 77 individuals (CV = 27.4%), confined to the inner portion (133.7km2 ). For all Irrawaddy dolphin sightings, where ecological data were collected (n = 48), the mean temperature was 30.2°C, depth 6.5m, salinity 28.3ppt and turbidity 2.2NTUs. Significantly higher turbidity, lower salinity and shallower depth were recorded in the inner Sound compared to adjacent waters. Bottlenose dolphins Tursiops sp. (probably truncatus) were observed in waters just outside of where Irrawaddy dolphins were recorded. During the study, at least two Irrawaddy dolphins were accidentally killed in bottom-set nylon gillnets used to catch crabs, locally called matang quatro. Reports from local fishermen also indicated that as many as three additional animals may have been killed in these nets during the same period. These findings strongly suggest that the Irrawaddy dolphin population in Malampaya Sound is in immediate danger of extirpation due to low numbers, limited range and high mortality. This is the only known population of the species in the Philippines and the nearest known other population is in northern Borneo, some 550km to the south. Recommendations for conserving the population include that: (1) socioeconomic alternatives be developed to promote the conservation goal of reducing the incidence of dolphin entanglement in matang quatro gillnets; (2) gillnet free zones be established in core areas of dolphin distribution; (3) Irrawaddy dolphins be promoted as a flagship species of environmental health in the Sound; (4) a long-term programme be established to monitor the dolphin population; and (5) additional investigations be conducted to determine if Irrawaddy dolphins occur in other areas of the Philippines.
... angle difference between line bearing and bearing to sighting) and distance to sighting. Survey effort and all associated sightings at Beaufort >3 were excluded from the analysis (Jefferson et al., 2002). Line-transect data (i.e. ...
... Observers were rotated hourly to minimize fatigue, and only sightings in calm sea states were included in the analyses to minimize perception bias from missing animals in higher sea states, as suggested by Jefferson et al. (2002). It was not possible to determine if Irrawaddy dolphins and finless porpoises reacted to the observers before detection; if they did react by swimming away, this would result in underestimation of abundance. ...
• The paucity of baseline data on coastal cetaceans due to a lack of research in developing countries frequently precludes assessment of their status and informed management actions for conservation.
• This study provides the first abundance estimates of Indo-Pacific humpback dolphins, Irrawaddy dolphins, and Indo-Pacific finless porpoises in the coastal waters of Matang, Peninsular Malaysia.
• Boat-based surveys covering 1,152 km² of coastal waters with 4,108 km of survey effort were conducted between 2013 and 2016 to collect data for line transect analysis of Irrawaddy dolphins and finless porpoises. Photo-identification data of humpback dolphins were concurrently collected for mark–recapture analysis.
• Estimates of abundance from four sampling strata totalled 763 Irrawaddy dolphins (CV = 13%, 95% confidence interval (CI) [588, 990]) and 600 Indo-Pacific finless porpoises (CV = 27%, 95% CI [354, 1,016]).
• The annual abundance estimates of humpback dolphins ranged between 171 (95% CI [148, 208]) in 2014–2015 and 81 (95% CI [67, 98]) in 2015–2016, likely due to the presence of offshore individuals that moved in and out of the study area. The estuarine strata were inhabited by 68 (95% CI [63, 73]) inshore humpback dolphins in 2013–2014 to 87 (95% CI [78, 97]) dolphins in 2014–2015.
• As an International Union for Conservation of Nature important marine mammal area, the productive coastal waters of Matang are shown to support a high density of small coastal cetaceans, and the results serve as an important baseline for future studies to identify population trends for conservation management plans.
... The absence of natural individually discernible features, in combination with highly elusive behaviour, makes finless porpoises notoriously difficult to study in open marine areas with traditional field research techniques, such as transect surveys or individual photoidentification-but for a limited few examples, see Jefferson, Hung, Law, Torey, and Tregenza (2002) and Park et al. (2015). In the study presented here, samples of teeth and relevant biological data were collected from carcasses of the Indo-Pacific finless porpoise that stranded and were recovered in the Pearl River Delta (PRD) region, the largest estuarine system and one of the most important fishing grounds in southern China (Sun, 2007). ...
... The finless porpoise in the South China Sea appears to exhibit a calving peak between October and January according to Jefferson, Robertson et al. (2002), or from August to December according to Gao and Zhou (1993). During this time, the porpoise density appears to shift towards coastal waters (Jefferson, Hung, et al., 2002). In the present study, 79% of calves <1 year old were found between November and April (Figure 1), which represents the dry season . ...
1. The finless porpoise (genus Neophocaena) is susceptible to fishery‐caused mortality, and its numbers are thought to be in decline across its entire range. However, population demographics have rarely been quantified for this genus, with a few exceptions of the narrow‐ridged form (Neophocaena asiaeorientalis) in waters off Japan, Korea, and in the Yangtze River of China, all of which show a drastic decline in recent decades. Similar analyses have not been performed for the Indo‐Pacific (known also as the wide‐ridged) finless porpoise (Neophocaena phocaenoides) that inhabits (sub‐)tropical waters; thus, reliable risk assessments are lacking.
2. The demographic dynamics of the Indo‐Pacific finless porpoise in the Pearl River Delta (PRD) region were investigated by analysing 307 cases of beached carcasses that were recovered between 1996 and 2014. The mean instantaneous rate of increase r indicated a declining trend of 3.6% loss per annum during 1996–2005, and a subsequent recovering trend with 0.76% increase per annum during 2006–2014. The individual‐based Leslie matrix model constructed with the most up‐to‐date demographic parameters suggests that the conservation status of the finless porpoise in the PRD region corresponds to Near Threatened (NT) according to the International Union for the Conservation of Nature criterion A3.
3. This temporal demographic change may be due to changes in fishing effort, which has been declining locally since the late 1990s. Although more quantitative evidence is needed, it is shown that regulated management of coastal fisheries can serve as an effective tool in securing the long‐term persistence of Indo‐Pacific finless porpoise in the PRD region, which likely applies also elsewhere in the genus/species' range where coastal fisheries overlap with the porpoise habitat. Results provide baseline ecological indicators that can facilitate further monitoring of the population status and trend.
... Introduction 44 Preservation of top predators is considered a priority for ecosystem conservation, 6 / 23 131 The number of stranding events and stranded individuals were summarized for 132 different species, including baleen and toothed whales. ArcMap 10.1 was used to 133 show location information on these stranding records to reveal the spatial distribution 134 of stranded species [37]. ...
... natural and anthropogenic), as well as currents 207 and winds that affect whether carcasses reach the shore. In the present study, more (Fig. 3B), which might be potential habitats for this species in these 228 less-investigated waters [44]. ...
The South China Sea (SCS) is known to support diverse cetacean species, yet their stranding information has not been well documented. To fill this knowledge gap, available records on cetacean stranding around Hainan Island in the SCS from 1978 to 2016 were collected and overviewed. In total, 112 records were obtained. Among them, 19 records involved 19 baleen whales (5 mysticeti species) and 93 records involved 134 toothed whales (12 odontoceti species). More stranding events occurred in the waters along the east coast than in the waters along the west coast, which was especially true for toothed whales stranding events. This may reflect the distribution patterns of cetaceans around Hainan Island. The spatial distribution of stranding events might be driven by different oceanographic features between the east and west offshore waters of the Hainan Island. The number of stranding events increased gradually from 1978 to 2000 and more rapidly from 2000 to 2016, which is likely due to both increasing public attentions and increasing anthropogenic activities within the SCS in recent decades. Stranding events were recorded throughout the year but peaked in spring (p = 0.016). In sum, cetacean stranding events occurred rather frequently around Hainan Island. The establishment of a regional stranding network in the SCS is conducive for further research, conservation and management of cetaceans in this region. More scientific data about the survival status of cetaceans and threats to them in the SCS are also needed.
... When the construction of the present Hong Kong International Airport on Chek Lap Kok Island began in 1993, there were concerns that local humpback dolphin habitat would be degraded and destroyed, and that the dolphins would be seriously threatened (Leatherwood and Jefferson, 1997;Liu and Hills, 1997). To understand the potential impacts of this project on local marine mammals, the Hong Kong Special Administrative Region (SAR) Government funded several long-term studies on the status and biology of the two resident cetaceans, humpback dolphins and finless porpoises, within Hong Kong's territories (Parsons, 1997;Porter, 1998;Jefferson, 2000a;Jefferson, 2000b;Jefferson, 2007;Jefferson et al., 2002;Jefferson et al., 2006;Jefferson and Hung, 2004;Jefferson and Hung, 2007), and these studies are still ongoing (Hung, 2013). ...
... Recent abundance estimates from line-transect vessel survey data indicated there are approximately 2,500 animals (Chen et al., 2010) in the PRE, which includes the waters of Macau, Hong Kong and the People's Republic of China, with a resident group found in the waters around Lantau Island in Hong Kong . Long-term monitoring studies have shown that humpback dolphins mainly occur in the western waters of Hong Kong (near Lantau Island), and are only seen rarely in eastern waters where salinity is higher (Parsons, 1998;Jefferson, 2000a;Jefferson et al., 2002;Jefferson and Hung, 2004). The western waters around North and West Lantau Island represent the main distribution of humpback dolphins (Jefferson, 2000a;Jefferson and Hung, 2004;Hung, 2013). ...
Marine mammals with near-shore distributions are susceptible to human-related recreational and commercial disturbances, particularly near densely populated and industrialized coastal areas. A population of over 2,500 Chinese humpback dolphins (Sousa chinensis chinensis) occupies the Pearl River Estuary in southern China. A part of this population uses Hong Kong’s waters off of Lantau Island, where they are subjected to a number of anthropogenic threats, including vessel disturbance, fisheries interactions, and boat-based tourism. Previous research has shown that the abundance of this subspecies in Hong Kong’s waters has declined about 60% since 2003. Using a combination of acoustic recordings, dolphin distribution and abundance data, and vessel traffic information I found that: 1) Four types of vessels common to the waters on Hong Kong generate noise that is audible to Sousa chinensis chinensis; 2) The spatial distribution of underwater noise in Hong Kong’s waters does not significantly vary among the six sites sampled; 3) High-speed ferry traffic and passenger volume has increased dramatically during the study period; 4) There has been a significant decline in dolphin density in areas within and near vessel traffic; and 5) Dolphins are most at risk of vessel collisions and being exposed to vessel noise near Fan Lau and within the Urmston Road waterway just northeast of the Sha Chau and Lung Kwu Chau Marine Park . These results can inform future acoustic studies on this species and guide conservation and management efforts in Hong Kong.
... data). Even if the detection probability at zero distance g(0) is estimated to be 0.65 (an estimate from helicopter sighting surveys by Jefferson et al. 2002) instead of 1, the modified PBR would still only be 42 ind. Thus, bycatch estimates would still be > 5 times higher than the modified PBR. ...
... Bycatch during these sea- sons may be related to changes in density or behaviors. Seasonal changes in density of the genus Neophocaena have been described in various waters (Kasuya & Kureha 1979, Jefferson et al. 2002, Taguchi et al. 2007, Akamatsu et al. 2008, Kondo et al. 2010, Kimura et al. 2012. The peak of the calving season in the Ariake Sound/Tachibana Bay population has been determined to occur in fall and winter (M. ...
Bycatch of narrow-ridged finless porpoises Neophocaena asiaeorientalis in gillnets was estimated for the Ariake Sound/Tachibana Bay population in Japan using interview-based surveys. In 2007 and 2008, the minimum number (actual number reported by all interviewees) of bycatch was 31 to 35 individuals (ind.) yr-1. The number of interviewees was 131 to 136 in each year. The bycatch estimate was 238 (95% CI 123 to 353) to 270 (95% CI 148 to 391) ind. yr-1. The estimate exceeded the potential biological removal level of this population, 27 ind., which was calculated on the basis of a published abundance estimate. The bycatch estimate accounted for 8% of the abundance. The bycatch rate was 0.237 ind. gillnetter-1 yr-1 in 2007 and 0.257 ind. gillnetter-1 yr-1 in 2008. Additional analysis of information on bycatch in the bottom-set gillnet fisheries collected from 1987 to 1992 suggested an increase in bycatch during fall and winter seasons, the possible existence of a calving ground, and age-sex related habitat use patterns. Neonates were found in a restricted area, whereas nursing calves and possible calves were seen in a wide range of waters, implying outward movement of mother-calf pairs from a calving ground. Neither neonates nor nursing calves were captured in waters deeper than 30 m.
... The major exception has been in the surrounding area of Hong Kong. abundance estimates of N. phocaenoides using line-transect survey data in Hong Kong ranged from 55 porpoises in autumn to 152 porpoises in spring (Jefferson et al. 2002), indicating that substantial number of these animals were outside of Hong Kong waters in autumn months. Finless porpoises appear to avoid western waters of Hong Kong, which are heavily influenced by freshwater input from the Pearl river (Jefferson et al. 2002). ...
... abundance estimates of N. phocaenoides using line-transect survey data in Hong Kong ranged from 55 porpoises in autumn to 152 porpoises in spring (Jefferson et al. 2002), indicating that substantial number of these animals were outside of Hong Kong waters in autumn months. Finless porpoises appear to avoid western waters of Hong Kong, which are heavily influenced by freshwater input from the Pearl river (Jefferson et al. 2002). The group size of porpoises in Hong Kong tends to be small, ranging from 1 to 35 (rarely) animals per group. ...
Much of the knowledge about the wide-ranging finless porpoise species (Neophocaena phocaenoides) remains limited, as well as its phylogenetic relationship with another taxa (N. asiaeorientalis) in genus Neophocaena. Using 11 microsatellite loci, we first investigated population differentiation of N. phocaenoides within the Pearl River Estuary (PRE). We then used mtDNA control region (CR) and cytochrome b (cyt b) sequences from the PRE population (75) as well as those from other geographic populations to reveal the divergence level and phylogeny of the PRE N. phocaenoides. Pairwise F
ST analysis with mtDNA CR sequences determined that the PRE population was highly differentiated from other putative populations (with the closest population 400-km away in the Taiwan Strait) (F
ST = 0.388–0.764, p < 0.01). The level of genetic divergence between the PRE and its conspecific population was as high as comparisons between the two subspecies under N. asiaeorientalis (F
ST = 0.361, p < 0.01). Our results also revealed contrasting demographic histories between the PRE and the other geographic finless porpoise populations (the Taiwan Strait population, the southern and northern Yellow Sea population and the middle Yangtze River population), which suggested stability in the warmer waters of the Indo-Pacific and expansions in the colder waters of the North Pacific. Phylogenetic trees created using cyt b data indicated that some haplotypes exclusive to the PRE population were basal to the rest of the genus. Based on these results, we argue that the genus Neophocaena originated in tropical waters (because the PRE is the most southern location sampled, i.e., the closest location to tropical waters).
... Towed passive acoustic platforms have been developed as simultaneous or alternative methods to visual transects during vessel-based surveys (e.g., Thomas et al. 1986, Miller and Tyack 1998, Barlow and Taylor 2005. Acoustic systems often consist of cabled hydrophones, which are towed behind a ship or affixed to a mobile platform to detect echolocating dolphins and porpoises in a large area (e.g., Jefferson et al. 2002, Oswald et al. 2003, Thode 2004, Barlow and Taylor 2005, Rankin et al. 2007. Some studies reported that a combined approach of visual and acoustic observation is the best option (e.g., Jefferson et al. 2002) to remove biases of each method. ...
... Acoustic systems often consist of cabled hydrophones, which are towed behind a ship or affixed to a mobile platform to detect echolocating dolphins and porpoises in a large area (e.g., Jefferson et al. 2002, Oswald et al. 2003, Thode 2004, Barlow and Taylor 2005, Rankin et al. 2007. Some studies reported that a combined approach of visual and acoustic observation is the best option (e.g., Jefferson et al. 2002) to remove biases of each method. In joint visual-acoustic surveys for Yangtze finless porpoise, the probability of detection of porpoises by acoustic systems was about twice that of visual surveys, possibly due to less aerial activities of this species (Akamatsu et al. 2008), which was because of frequent sonar emission of the target animals, 5 s on average (Akamatsu et al. 2005a). ...
The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is an endangered freshwater porpoise subspecies unique to the Yangtze River basin. Seasonal variations in local distribution of the animal, as well as fish presence, sand dredging, ship navigation, and bridges were examined as potential factors affecting the occurrence of the animals. Passive acoustic surveys were performed regularly from May 2007 to August 2010, near the conjunction of the Yangtze River and Poyang Lake. The distribution of the porpoises was seasonally site‐specific. In May and August, the animals were detected more often at river junctions than in the lake, but vice versa from November to February. The rate of the porpoise detection was significantly higher in areas of fish presence than in areas of absence. The number of porpoises detected did not differ significantly between the sand dredging operation and the prohibition period (in 2008), although the number of vessels obviously declined in 2008. Ship traffic and bridges also did not appear to affect the presence of porpoises. These results showed the relative importance of the various environmental factors, which is important for conservation of not only Yangtze finless porpoise but also endangered isolated cetaceans.
... As shown in Figures 2 and 3, porpoise incidents were relatively higher during the spring and early summer than in other seasons. These seasonal variations in finless porpoise occurrences could be related to factors such as prey movements, freshwater discharge, or monsoon rains [42]. The porpoise's prey, such as the fishes Liza haematocheila, Sillago sihama, and Lateolabrax maculatus, prefer to gather near the shore and reproduce at this time of the year [24]. ...
Simple Summary
The East Asian finless porpoise is a common whale along Chinese coasts. The coast of the Shandong Peninsula is a substantial habitat for the species. However, there is relatively insufficient knowledge of and protection measures for the species population in this region. Based on public literature, media, and internet social websites, we collected and analyzed over two hundred reports on the stranding and accidental catching of finless porpoises along the coast of the Shandong Peninsula from 2000 to 2018. We found that bycatch and stranding incidents occurred widely across the peninsula throughout all seasons. The extensive use of fishing gear was the principal cause of porpoise mortalities and injuries along Shandong Peninsula. We recommend a comprehensive network consisting of an incident reporting system, fishing gear regulations, and scientific monitoring plans to protect the cetacean species in this region.
Abstract
The Shandong Peninsula is located on the western coast of the Pacific and is adjacent to the Bohai Sea (BS) and the Yellow Sea (YS) to the east. The East Asian finless porpoise Neophocaena asiaeorientalis sunameri, a subspecies of the narrow-ridged finless porpoise N. asiaeorientalis, is the dominant cetacean resident along the Shandong Peninsula. However, there is insufficient monitoring data to determine the status of the cetacean species in this region. Based on the publicly available literature, media, and internet social website, this study investigated the spatial–temporal distribution of porpoise stranding and bycatch along the coast of the Shandong Peninsula. Data on over five hundred porpoises from two hundred reports between 2000 and 2018 were compiled and analyzed. Results showed that the bycatch and stranding of porpoises occurred widely across the peninsula throughout all months and increased rapidly between 2010 and 2017. The incidents were more frequent in the area where the BS and YS converged during the spring and early summer than in other seasons. The mean body length of bycaught porpoises was smaller than that of those found stranded. Fishing activities could be the principal cause of local finless porpoise incidents. However, limited data hindered a quantitative evaluation of the living conditions of finless porpoises in this area. Establishing a comprehensive monitoring system, which includes standardized reporting, rescue operations, and scientific research, is essential to finless porpoise protection along the Shandong Peninsula.
... Finless porpoises were mostly seen in smaller group sizes and their behaviour was difficult to determine because of the brevity of sightings and the evasiveness of most animals observed. Thus, the group sizes for the finless porpoise may have been underestimated in the present study as a result of the brief sightings, lack of markings, and absence of a dorsal fin, which made it difficult to distinguish between successive surfacing of the same individuals(Jefferson, Hung, Law, Torey, & Tregenza, 2002). ...
• Coastal cetaceans in Southeast Asia are poorly studied and are particularly vulnerable to anthropogenic threats, especially in intensive fishing grounds.
• To investigate the distribution and habitat characteristics of cetaceans in the productive coastal waters of Matang, Perak, Malaysia, boat‐based line transect surveys were conducted between 2013 and 2016.
• The Irrawaddy dolphin (Orcaella brevirostris) was most frequently encountered at 3.87 sightings per 100 km, followed by the Indo‐Pacific finless porpoise (Neophocaena phocaenoides) at 1.72 sightings per 100 km, and the Indo‐Pacific humpback dolphin (Sousa chinensis) at 0.66 sightings per 100 km.
• The mean group size was largest for humpback dolphins (8.4 individuals), followed by Irrawaddy dolphins (6.4 individuals), and finless porpoises (2.8 individuals).
• Humpback dolphins exhibited a clustered distribution concentrated mainly in shallow estuarine waters (<10 m deep and <5 km from river mouths), whereas Irrawaddy dolphins were more widely distributed in farther coastal waters (<15 m deep and <15 km from river mouths), and finless porpoises were mostly found farthest from the shore in coastal waters (10–25 m deep and >15 km from river mouths).
• The spatial distribution of the three cetaceans overlapped minimally, and this is likely to reflect the distribution of preferred prey resources, species interactions, and their differential responses to anthropogenic activities and species dominance.
• The results from our study serve as baseline information for future research, conservation, and habitat management of these vulnerable and endangered coastal cetaceans. Conservation actions are recommended for the Matang area.
... Historical surveys indicate that no other dolphin species are found in the monitoring site and thus dolphin acoustic identification was not required (Jefferson et al., 2002;Wang et al., 2015b). The majority of humpback dolphin sounds (including whistles and clicks) were detected during periods of low ambient sound levels (Fig. 11A), which might reflect noise avoidance behaviors of this species of dolphin. ...
... The only other regularly occurring cetacean species in Hong Kong waters is the finless porpoise (Neophocaena phocaenoides), which occurs group members, the group was tracked by recordsouth of Lantau Island and produces acoustic sig-ing positions based on a central point within the nals above the recording frequency of the EARs group (Bejder, 2005). Tracking sessions continued (Goold & Jefferson, 2002;Jefferson et al., 2002). until animals were lost from view, either because Shore-based tracking effort was conducted they moved beyond visible range or due to enviduring daylight hours on approximately 6 d/mo. ...
Multiple concurrent approaches are often useful for investigating cetacean occurrence and behavioral patterns. For example, underwater passive acoustic monitoring (PAM) can document spatial and temporal patterns and variability in cetacean vocalizations, while visual observations at the sur-face can provide information on group size and composition, behavior, and surface movement patterns. Together, both types of data collection can elucidate the behavioral context of sound pro-duction, which is important to understand when using acoustic data to characterize habitat use, to inform abundance estimates, and to achieve other monitoring objectives. We compare the results of two observation modalities—(1) PAM using autonomous moored recorders and (2) shore-based theodolite tracking—both of which were conducted concurrently as part of a study of Indo-Pacific humpback dolphins (Sousa chinensis) north of Lantau Island, Hong Kong.
... In particular, the population abundance of this species is little known. One of the few studies on the abundance of N. phocaenoides showed that only about 217 (CV ¼ 21e150%) individuals have been observed in Hong Kong and its adjacent waters (Jefferson et al., 2002a). The Red List of Threatened Species from the International Union for the Conservation of Nature (IUCN) has identified N. phocaenoides as being a "vulnerable" species since 2008 (Wang and Reeves, 2012). ...
... Fishermen from Newlyn, Cornwall, put 'the bombs' on their nets in the Celtic Sea (Tregenza and Northridge, 2001), with results that surprised us and are covered later. Jefferson et al. (2002) surveyed the very busy waters of Hong Kong by deploying this first version of the POD several meters below a small surf board that was towed by a ferry. Finless porpoises (Neophocoena phocaenoides) are very hard to spot at sea, but the team found that nearly all the groups of animals they saw within 300 metres were also heard by the POD. ...
Monitoring echolocation using SAMs—static acoustic monitors—such as T-PODs or, more recently, C-PODs—has provided a wealth of information on the fine-scale distribution and activity of dolphins, porpoises and other toothed whales. Effects of marine construction noise on these animals have been identified at much longer ranges than expected. Strong diel, tidal and seasonal patterning of the animals’ habitat use has been found including coastal sites that are regularly used only at night. Arrays of SAMs are now being used for longer term monitoring to assess smaller population trends of lower density populations than could previously be assessed within the limits of economic feasibility. PODs have given insights into the significance of seabed ultrasonic noise from sediment in suspension and diel patterns of activity of benthic organisms, and have also revealed unknown sources of very fast trains of tonal clicks.
... Humpback dolphins also occur in more saline waters at the very edge of Pearl River Estuary influence off southwestern Lantau Island, especially near Fan Lau and the Soko Islands, with partial overlap there with the generally 68 Bernd Würsig et al. more easterly occurring finless porpoises (Figures 2 and 3). The two species are only rarely found close together, and the porpoises appear to avoid dolphin habitat during times of year that dolphins are more abundant there (Hung, 2008;Jefferson, 2000;Jefferson et al., 2002;Parsons, 1998a). Such habitat partitioning between the two coastal species was also observed in the western part of the Pearl River Estuary (S.K. Hung, Hong Kong Dolphin Conservation Society, personal communication). ...
Fewer than 200 Indo-Pacific humpback dolphins (Sousa chinensis) occur in Hong Kong waters (though these are part of a much larger population in the Pearl River Estuary), with a decrease in the past about 10 years. They have partially overlapping individual ranges (mean=100km2), and two partially overlapping communities. Seasonal occurrence is higher in June-November than December-May, approximate wet and dry monsoon seasons, respectively. Group sizes tend to average three dolphins, a decrease from the past decade. Feeding often occurs in abruptly changing water depths and off rocky natural shores. The area immediately north of Hong Kong International Airport is largely used for travelling between locations to the west, east and further north. The area around Lung Kwu Chau Island in northwest Hong Kong is a "hot spot" for foraging and socializing. The area off Fan Lau, southwest Lantau Island, is largely used for foraging. A former foraging "hot spot" was located around the Brothers Islands east of the airport, now reduced, possibly due to increases in high-speed ferries (HSFs) and other activities. Sound recordings of dolphins from bottom-mounted hydrophones suggest that northwestern Hong Kong waters are used more at night than in daytime. Sexual activity and calving occur throughout the year, with a peak in late spring to autumn (wet monsoon season). Humpback dolphins communicate acoustically with each other and probably passively listen to prey in murky waters, and anthropogenic noises may be masking communication and affecting prey location. Increasing sounds of shipping, HSFs and industrial activities are likely to alter dolphin habitat use patterns and overall behaviours beyond the present already affected status.
... Some surveys have managed to get helicopter time supplied by the military [e.g. Jefferson et al. (2002)]. As above, if the species of interest is found very close to shore, simultaneous boat survey/cliff-top observations could be used to quantify reactive movement. ...
This chapter discusses characteristics, taxonomy, distribution, abundance, and ecology of Cephalorhynchus Dolphins. The four dolphins of the genus Cephalorhynchus are small coastal species. They are blunt-headed, chunky dolphins with rounded, almost paddle-shaped flippers. The most characteristic feature of the genus is the dorsal fin, which is proportionately large, either with a shallowly sloping leading edge and a rounded, convex trailing edge [like a Mickey Mouse ear: Hector's (. C. hectori), Commerson's (. C. commersonii), and Chilean dolphins (. C. eutropia)] or upright and roughly triangular (Heaviside's dolphin, C. heavisidii). In color pattern, Chilean dolphins and Hector's dolphins are most similar. Cephalorhynchus dolphins are found only in Southern Hemisphere waters. Heaviside's dolphin occurs off the west coast of South Africa and Namibia. Hector's dolphin is found solely off New Zealand. The Chilean dolphin is found in the coastal waterways of Chile and along the exposed west coast. All four species feed on a wide variety of coastal prey, focusing on benthic and small pelagic schooling fish and squid.
... A previously published line transect survey indicated that a spatial and temporal segregation in the habitat usages existed in its sympatric Indo-Pacific finless porpoise (N. phocaenoides), which mainly occur in the southern and eastern water of Hongkong and does not appear to occur in most of Lingding bay of the Pearl River Estuary [42]. No other dolphin species was Table 3. Results of four-way ANOVA (diel * lunar * season * tidal) on the number of minutes with click trains per 10 minutes. ...
A growing demand for sustainable energy has led to an increase in construction of offshore windfarms. Guishan windmill farm will be constructed in the Pearl River Estuary, China, which sustains the world's largest known population of Indo-Pacific humpback dolphins (Sousa chinensis). Dolphin conservation is an urgent issue in this region. By using passive acoustic monitoring, a baseline distribution of data on this species in the Pearl River Estuary during pre-construction period had been collected. Dolphin biosonar detection and its diel, lunar, seasonal and tidal patterns were examined using a Generalized Linear Model. Significant higher echolocation detections at night than during the day, in winter-spring than in summer-autumn, at high tide than at flood tide were recognized. Significant higher echolocation detections during the new moon were recognized at night time. The diel, lunar and seasonal patterns for the echolocation encounter duration also significantly varied. These patterns could be due to the spatial-temporal variability of dolphin prey and illumination conditions. The baseline information will be useful for driving further effective action on the conservation of this species and in facilitating later assessments of the effects of the offshore windfarm on the dolphins by comparing the baseline to post construction and post mitigation efforts.
... The shared habitat exits between the Indo-Pacific bottlenose, the Indo-Pacific humpback, the Indo-Pacific finless porpoise and the Irrawaddy dolphin (Table 2). [22], Yellow Sea, (B) [23], Beigan and Nangan, Matsu Islands (C) [24], Bohai Sea region (D) [25]. Thickness of red line represents approximately 160km, indicating maximum distance that Neophocaena phocaenoides is likely to travel away from the coastline. ...
... Organochlorine concentrations in Hong Kong humpback dolphins are relatively high, and DDT and PCB levels are even higher than in the finless porpoise population that occurs in Hong Kong (Jefferson et al., 2002a;Ramu et al., 2005). This is not surprising, as the dolphins live in the estuary of the Pearl River, and are probably nearer the presumed source of the contaminants than are finless porpoises, which have a more southern and offshore distribution (see Jefferson et al., 2002b). There is also evidence that DDT use still continues in some parts of the Pearl River Estuary (Fu et al., 2003). ...
Factors related to mortality and disease in Indo-Pacific humpback dolphins (Sousa chinensis) from Hong Kong waters were investigated by detailed examination of dolphin specimens found stranded from 1995-2004. In total, 86 specimens were necropsied, but many of these were too badly decomposed to provide much information. Skin and blubber biopsies were also collected from six identified living individuals and concentrations of organochlorines (DDTs, PCBs and HCHs) were determined from blubber samples of stranded and biopsied dolphins. A large proportion of the strandings (53.2%) were young-of-the-year. The most commonly diagnosed causes of death were net entanglement and vessel collision. The pesticide DDT showed the highest concentrations and the ratio of DDT to its breakdown products (and other information) suggests that there may be a recent or nearby source of DDT into the dolphins’ ecosystem. Concentrations of both DDTs and PCBs showed a pattern of increasing with age in males. In females, they increased until sexual maturity, then decreased, and finally increased again in late life. This is consistent with a hypothesised transfer of pollutants from mother to offspring during gestation and lactation. Inter-laboratory differences and effects of decomposition of specimens are two potential biases that may significantly affect the quality of the present data. In order to resolve the potential problems associated with these issues, a long-term biopsy collection programme has recently been initiated.
... (Barros et al., 2002;Jefferson et al., 2002;Jefferson and Hung, 2004;Kasuya et al., 2002;Shirakihara et al., 1992;Shirakihara et al., 2007;Wang et al., 2008). 한편 ...
The seasonal appearance and distribution of finless porpoise (Neophocaena asiaeorientalis) was investigated with sighting survey method around Wido in West sea, Korea. Fishing survey with drag net was also conducted to investigate the species composition of inhabitants and the consignment quantity data of fisheries cooperation was collected to confirm the seasonal change of the composition and quantity of them. Finless porpoise didn`t emerged around Wido in winter season, but the number of appearance in summer season amounted to 1~15 indv. for 15 observing points and the appearance frequency became lower in open sea than in inshore. There was also significant relationship between the appearances of finless porpoise (Neophocaena asiaeorientalis) and that of inhabitants. we consequently concluded that finless porpoise typically distributes from April to september, and moves to another area for wintering and food consumption from October to March.
... The abundance estimate of 3093 in d. was calculated under the assumption that the detection probability on the track line in an aerial sighting survey, g (0), is equal to 1. If the abundance estimate is corrected by an available estimate of g(0) (= 0.65; Jefferson et al. 2002a), the estimate of M decreases to 5.3% (=250/[3093/0.65]). ...
The narrow-ridged finless porpoise Neophocaena asiaeorientalis is a coastal ceta cean that is threatened by various human activities. Bycatch mortality is a particular danger to the porpoise population in Ariake Sound and Tachibana Bay, Japan. To evaluate the impact of bycatch mortality on the viability of this population, we simulated changes in population size over the next 100 yr, using a Leslie matrix model. The simulation trials were repeated for 3 scenarios of possible bycatch mortality rates. If bycatch mortality remains at the reported level, the estimated annual rate of decrease is 0.671 to 3.87%, and the estimated population size reduction over 3 generations is 29.6 to 86.3%. A population size reduction of >= 30% was predicted in almost half the simulation trials, even in the most optimistic scenario. The reported bycatch mortalities would pose a serious threat to the viability of this porpoise population; therefore, the population should be classified at least as `Vulnerable' according to Criterion A4, as defined in the IUCN Red List. Our predictions were sensitive to annual bycatch mortality rate estimates. Hence, the collection of current abundance and bycatch data should be promoted in order to minimize uncertainty in risk assessments.
... Its predecessor, the T-POD, was designed to detect the echolocation clicks of harbor porpoises (Phocoena phocoena); Todd et al. (2009) provides a description of the T-POD and its data classification process. The T-POD is now an established tool used to monitor the occurrence of odontocetes and several studies have evaluated its performance for various species, including bottlenose dolphins, Tursiops truncatus (Philpott et al. 2007, Bailey et al. 2010, Elliott et al. 2012), Hector's dolphins, Cephalorhynchus hectori (Rayment et al. 2009), harbor porpoises (Thomsen et al. 2005;Kyhn et al. 2008Kyhn et al. , 2012, beluga whales, Delphinapterus leucas (Castellote et al. 2013), finless porpoise, Neophocaena phocaenoides (Jefferson et al. 2002), and in a multi-species context (Simon et al. 2010). Significant variation in sensitivity exists among individual T-POD units and between unit versions (D€ ahne et al. 2006). ...
We evaluated the performance of dolphin echolocation detectors (C-PODs) in the New River, North Carolina, by ground-truthing echolocation detections with digital acoustic recordings. We deployed C-PODs at three sites for a total of 204 monitoring hours. We also performed detection range trials at two sites where water depths ranged from 1.0 to 4.5 m. We used Detection Positive Minutes (DPMs), minutes of C-POD recordings that contained at least one echolocation click train, to indicate the presence of at least one dolphin. The C-PODs performed well in detecting dolphin click trains, although all units performed conservatively by failing to detect some echolocation events and therefore underestimated the true occurrence of dolphins. C-PODs reported only a small number of false detections, as indicated by low false positive rates ranging between 1% and 4% for individual units. Overall, C-PODs performed with a high accuracy (72%–91%) and detected echolocation at a distance of at least 933 m. We conclude that C-PODs hold considerable promise in future monitoring studies of this species, but recommend a careful study design especially in complex, coastal environments.
... In Hong Kong, humpback dolphins and finless porpoises may compete for food resources as they have a number of key prey species in common (Barros et al., 2002(Barros et al., , 2004Parsons, 1997). Barros et al. (2004) suggested that the need to reduce this competition may have led to the distributions of humpback dolphins and finless porpoises being largely separate, with the former occupying brackish estuarine waters and finless porpoises inhabiting cooler and more saline waters (Jefferson, 2000;Jefferson & Braulik, 1999;Jefferson et al., 2002;Parsons, 1998b), but when the distribution of humpback dolphins overlaps with porpoises, instead of spatially, their distribution is separated temporally (as seen in Parsons, 1998b). Barros et al. (2004) also suggested that competition might occur between humpback dolphins and other cetacean species, as shared prey species also have been documented with South China Sea bottlenose dolphins (Barros et al., 2000(Barros et al., , 2004. ...
... The relatively high proportions of unmetabolised DDT in the two coastal species suggest a closer proximity to the source of DDT-spatially, temporally, and trophically (Parsons & Chan, 2001). The slightly higher proportion of underived DDT in humpback dolphins versus finless porpoises suggests that humpback dolphins may be closer to the source of the DDT than the latter species, which makes sense because, in Hong Kong, humpback dolphins inhabit the estuarine waters of the Pearl River Estuary, whereas finless porpoises inhabit more oceanic waters (Jefferson et al., 2002;Parsons, 1998a;Parsons et al., 1995). Zhang et al. (1999) investigated organochlorine levels in sediment cores from Macau (which is situated on the opposite side of the Pearl River Estuary to Hong Kong) and noted that high DDT concentrations were found in sediments dating from 1976 to 1981, then concentrations dropped significantly between 1982 and 1991, but the highest concentrations were recorded between 1992 and 1994, after which levels dropped again. ...
Indo-Pacific humpback dolphins (Sousa chinen-sis) inhabit coastal and estuarine waters close to anthropogenic sources of pollution. Detailed studies of contaminant levels on Hong Kong's population of humpback dolphins showed high levels of organochlorines, in particular DDT, and mercury contamination. These contaminant levels are high enough to impact humpback dolphin health. It is likely that several other populations of humpback dolphins are contaminated to a similar degree, and urgent research is warranted. In addition to organo-chlorine and trace element pollution, the impacts of butyltin (BT), polyaromatic hydrocarbons (PAHs), tris(4-chlorophenyl)methane (TCPMe), tris(4-chlorophenyl)methanol (TCPMeOH), and sewage pollution on humpback dolphin populations should be investigated as a matter of urgency.
... Surveys in these eastern regions were mainly for Indo-Pacific finless porpoise (Neophocaena phocaenoides (G. Cuvier, 1829)) (Jefferson et al. 2002), another species monitored in Hong Kong. Survey tracks mostly ran north-south or east-west, roughly perpendicular to the shoreline, and were conducted from a 15 m inboard motor vessel with a maintained oneffort speed between 13 and 15 km/h (Hung 2008). ...
The way human activities impact animal populations can depend on social structure, which is important to understand in social species such as cetaceans. We investigated association patterns in Indo-Pacific humpback dolphins (Sousa chinensis (Osbeck, 1765)) inhabiting the Pearl River Estuary near Lantau Island, Hong Kong, using a 10-year data set for 88 individuals. Our analyses revealed two social communities. Each had its own region of core use, to the north and to the west of the island, but their overall ranges partially overlapped northwest of Lantau. The northern community had a fission–fusion structure characterized by short-term associations, while the western community had more long-term associations. Mixed-community groups included calves more often than exclusive groups, so between-community associations may arise from common habitat usage, by females especially, in the overlap area. Recent range extensions by the northern community into the west are likely a response to habitat destruction north of Lantau. This suggests ease of movement between the north and the west is necessary for northern-community dolphins to access suitable habitat, and gives new concern to construction projects planned for the region. We emphasize our study as an example of how sociobiological information can be important in understanding human impacts on animal populations.
Due to the accelerated development and transformation of coastal waters by humans, damage to marine mammals is a concern. To understand how coastal development may affect marine mammals, it is essential to determine their distribution characteristics. In this study, the appearance of finless porpoises was confirmed by passive acoustic monitoring around the Southwest offshore wind farm in July, 2020. Although there were no visual observation results of finless porpoises in the research area, the clicks measured in the offshore wind farm were verified by comparing with acoustic characteristics of the clicks measured in the area with a high detection rate. During the experimental period, clicks of finless porpoises were recorded for ten consecutive days, and Clicks per Porpoise Positive Minute (CPPM) was 40.7 clicks min-1, Porpoise Positive Minutes (PPM) was 9.7 %, Encounter duration and waiting time were 18.2 min and 94.9 min respectively. This study provides information on the appearance of them in the Southwest offshore wind farm and this result may help to monitor the impact of marine mammals from wind farm operation.
The Jinwan Offshore Wind Farm project in the Pearl River Estuary (PRE) is a new stressor for the resident marine mammals there, especially for the Indo-Pacific finless porpoise. A broadband recording system was deployed in the Jinwan Offshore Wind Farm, before and during the construction period, in order to determine how the finless porpoise responded to pile driving activity. The results showed that the wind farm area was an important habitat for the finless porpoise during the monitoring period. The finless porpoise also showed avoidance behavior of pile driving activity. There was a significant negative correlation between porpoise detection and pile driving detection, and the time between porpoise’s acoustic detections increased during pile driving compared to periods without pile driving. Our results indicated that acoustic protection measures are strongly recommended in future offshore wind farm developments in order to protect finless porpoises.
Habitat loss and degradation are currently the main anthropogenic causes of species extinctions. The root cause is human overpopulation. This unique volume provides, for the very first time, a comprehensive overview of all threatened and recently extinct mammals, birds, reptiles, amphibians, and fishes within the context of their locations and habitats. The approach takes a systematic examination of each biogeographic realm and region of the world, both terrestrial and marine, but with a particular emphasis on geographic features such as mountains, islands, and coral reefs. It reveals patterns useful in biodiversity conservation, helps to put it all into perspective, and ultimately serves as both a baseline from which to compare subsequent developments as well as a standardization of the way threatened species are studied.
The Pearl River estuary in Guangdong is home to the Indo‐Pacific humpback dolphin ( Sousa chinensis ) and the Indo‐Pacific finless porpoise ( Neophocaena phocaenoides ). However, limited data are available for the latter species.
Line‐transect passive acoustic monitoring surveys were conducted to investigate the distribution of the Indo‐Pacific finless porpoise in the Pearl River estuary in the period July to November 2019.
The south‐east region of the Pearl River estuary is an important habitat for the Indo‐Pacific finless porpoise, and more than half of the acoustic detections were within 2 km of islands, concentrated around the uninhabited islands of Soko, Sanmen and Aizhou.
The habitat extents of Indo‐Pacific finless porpoises in the survey areas were estimated as 209.04, 761.81 and 976.41 km ² using 50, 90 and 95% kernel densities, respectively. The 50% kernel density area was mainly around the aforementioned islands and is a priority candidate for protected area status.
This is the first report of the distribution and critical habitat of the finless porpoise in the study area. Given the increasing human development in the Pearl River estuary, the results provide important data to help inform the protection of the habitat of finless porpoise in the context of marine planning and development, and promote the establishment of marine protected areas and stronger fisheries management measures.
Accurate diet identification of top predators is crucial to fully understand their ecological roles. Compared to terrestrial animals, gathering dietary information from cetaceans is notoriously difficult. Here, we applied a multilocus metabarcoding approach to investigate the diet of vulnerable Indo‐Pacific humpback dolphins and Indo‐Pacific finless porpoises from the Pearl River Estuary (PRE), China. Our analyses identified 21 prey fish species from the 42 humpback dolphin stomachs, as well as 10 species of fish and one species of cephalopod from the 13 finless porpoise stomachs. All of the taxa were assigned to the species level, highlighting that the multimarker approach could facilitate species identification. Most of the prey species were small and medium‐sized fishes that primarily fed on zooplankton. The calculated similarity index revealed a moderated dietary overlap between the two cetaceans, presumably due to the feeding of the two predators in association with fishing vessels in the PRE. A more diverse diet was observed in humpback dolphins in the closed fishing season compared to the fishing season, implying the influence on the dolphin diet due to the availability of commercial fishery resources. However, according to the results of species rarefaction curves, our findings on the feeding habits of the two cetaceans are still limited by insufficient sample size and therefore should be interpreted with caution. This study represents a first attempt to apply the multilocus DNA metabarcoding technique in the diet analysis of small cetaceans, although more efforts are needed to improve this type of analysis. This article is protected by copyright. All rights reserved
We investigated the tissue distribution, trophic transfer, and ecological risk of 13 trace elements in 26 East Asian finless porpoises (Neophocaena asiaeorientalis sunameri), an endangered species found in the Liaodong Bay and the north Yellow Sea. All the investigated trace elements were detected in the tissue and food web of the East Asian finless porpoises. The concentrations of the potentially toxic elements were 2.37 × 10⁻⁵ – 754 mg kg⁻¹ dry weight (dw) in stranded porpoises and 0.01–159 mg kg⁻¹ dw in their food web. Tissue-specific distribution of the trace elements generally ranked as: liver > kidney > heart > lung > muscle. Zn was the dominant contaminant in the five investigated tissues. Significant positive correlations were found between body length or age and some trace elements, especially Cd. Adults (≥2 years old) presented higher concentrations of most of the trace elements than juveniles (<2 years old). Sex-dependent distribution of the trace elements was insignificant except for Mn, Ni, and Zn in muscle and renal tissue. As, Cu, Mn, Ni, Pb, and V biodiluted across the East Asian finless porpoise food web while Zn biomagnified. However, Hg, Cd, Co, Cr, Se, and Sn did not exhibit apparent trophic transfer trends. Overall, ecological risk assessment of trace elements in East Asian finless porpoises suggested that greater attention should be given to Hg, As, Cd, and Se.
As a part of the UNDP - GoI- GEF Sindhudurg Project, we carried out the Sindhudurg Cetacean Project to assess the biodiversity of marine mammals along the Sindhudurg coastline and estimate the population parameters of two coastal cetacean species, Sousa plumbea (Indian Ocean Humpback Dolphin) and Neophocaena phocaenoides (Indo-Pacific Finless porpoise). We recorded incidental mortalities and strandings of cetaceans throughout the Sindhudurg coast by setting up a community based monitoring network and examined carcasses to gain life history data. In addition, we assessed the dolphin- watching tourism industry and the role of dolphin watching on the socio-economic well being of local communities in Sindhudurg district, Maharashtra.
This is the final report of 'The Sindhudurg Cetacean Project', submitted by the Konkan Cetacean Research Team
Shifts in habitat use and distribution patterns in dolphins are often concerns that can result from habitat degradation. We investigated how potential changes to a habitat from human activity may alter dolphin distributions within Lingding Bay in the Pearl River Estuary, China, by studying the relationship between fish choruses, vessel presence and Indo-Pacific humpback dolphin (Sousa chinensis) detection rates. Analyses revealed temporal and spatial variation within fish choruses, vessel presence and dolphin detection rates. After accounting for any temporal autocorrelation, correlations between fish choruses and dolphin detection rates were also found; however, no relationship between fish choruses and vessel presence or dolphin detection rates and vessel presence were observed. Furthermore, fewer dolphins were detected at sites where fish activity was less intense. Thus fish activity, rather than vessels, may be a key factor influencing the distribution of the dolphins within the estuary. These findings emphasize the risk of potential shifts in habitat use for Indo-Pacific humpback dolphins due to detrimental changes to prey availability and dolphin feeding grounds from human activity, such as overfishing and coastal developments, within the estuary. This is a critical conservation issue for this dolphin population that is facing intense anthropogenic pressure.
Long-term passive acoustic monitoring (PAM) was conducted to study Indo-Pacific humpback dolphins, Sousa chinensis, as part of environmental impact assessments for several major coastal development projects in Hong Kong waters north of Lantau Island. Ecological acoustic recorders obtained 2711 days of recording at 13 sites from December 2012 to December 2014. Humpback dolphin sounds were manually detected on more than half of days with recordings at 12 sites, 8 of which were within proposed reclamation areas. Dolphin detection rates were greatest at Lung Kwu Chau, with other high-occurrence locations northeast of the Hong Kong International Airport and within the Lung Kwu Tan and Siu Ho Wan regions. Dolphin detection rates were greatest in summer and autumn (June–November) and were significantly reduced in spring (March–May) compared to other times of year. Click detection rates were significantly higher at night than during daylight hours. These findings suggest high use of many of the proposed reclamation/development areas by humpback dolphins, particularly at night, and demonstrate the value of long-term PAM for documenting spatial and temporal patterns in dolphin occurrence to help inform management decisions.
Both S. plumbea and N. phocaenoides are limited to shallow water, found in pockets almost all along the west coast of India. But little information is available on movement of local populations. These are the first population estimates from India for both species. Despite intense fisheries overlap, Sindhudurg supports a healthy S. plumbea population. N. phocaenoides being cryptic requires acoustics and Distance sampling for robust estimates, while S. plumbea with natural markings can be studied using Mark-recapture. Given the high mortality rates, this study shows the importance of a long-term population-monitoring program and developing standardised data-collection protocols from stranded animals
The marine mammal fauna of Southeast Asia consists of approximately 30 species, about 1/4 of the world's species, and includes several endemic species or subspecies. Examples of problems of conservation include bycatch in a tuna driftnet fishery, inshore habitat degradation, and depletion of humpback whales in the Philippines; possible disappearance of dolphins and porpoises From the Mekong Delta in Vietnam; and depletion of riverine dolphins and large bycatch in a shark fishery in Indonesia. Major causative factors include over-fishing, human overpopulation, development, vulnerability of marine mammals, and evolution of bycatch into directed dolphin fisheries. Needs are for inventory (stock identification and abundance estimation), bycatch monitoring, reduction of takes to sustainable levels, and regional international cooperation.
Researchers in China have studied marine mammals for over 80 years. In recognition of Acta Theriologica Sinica' s 30 year anniversary, we have reviewed the history of this research using an extensive published literature as well as our own research and experience, summarized its progress, and discuss future prospects. Marine mammals in this paper are divided into three groups : whales, pinnipeds, and other marine mammals. We have focused on research examining the ecology, rearing and breeding biology, conservation genetic, acoustics, and conservation biology for selected species. Two main points have been drawn from the review. First, Chinese research on marine mammals is at the forefront of some fields including research on rearing and breeding biology, conservation biology, and bio-acoustics of river dolphin or porpoise. The second point, unfortunately, is that there is a lack of systematics studies on marine mammals in Chinese coastal waters. Finally , we expect to see significant breakthroughs and real progress on the protection of endangered species in the near future.
Small boat surveys were conducted in the Kuching Bay area of Sarawak, East Malaysia, in order to determine the distribution and abundance of coastal cetaceans. Photographic data collected from Jul.2007 through Oct.2010 was used to generate mark-recapture abundance estimates of Irrawaddy dolphins in the study area, and provided insights into ranging patterns and site fidelity. Between Apr.2010 and Oct.2011, line transect surveys were conducted, and abundance estimates for Irrawaddy dolphins and Indo-Pacific finless porpoises were generated using distance sampling. The best mark-recapture estimate for Irrawaddy dolphins based on a weighted mean of estimates derived from photographs of left sides and right sides of dorsal fins was 233 (CV = 22.5%, 95% CI 151-360). Resighted individuals showed a high degree of site-fidelity, with less than 10 km between sighting locations over a period of four years for some individuals. A smaller proportion of re-sighted individuals ranged further-with a maximum straight-line distance of 26 km between sighting locations. The best line-transect estimate for Irrawaddy dolphins was 149 individuals (CV = 28%, 95% confidence interval 87-255). The line-transect estimate for finless porpoises was 135 individuals (CV = 31%, 95% confidence interval 74-246). Finless porpoise abundance varied seasonally, with higher densities observed between Mar. and May, coinciding with the occurrence of larger groups with very small calves. The line transect and mark-recapture derived estimates for Irrawaddy dolphins are compared, and viewed in the context of mapped relative densities that reveal key areas of habitat for the species. These abundance estimates provide a critical step toward the assessment of both species' local conservation status and can be used in the design of effective management strategies.
Fixed autonomous acoustic recording devices (autonomous recorders [ARs]) are defined as any electronic recording system that acquires and stores acoustic data internally (i.e., without a cable or radio link to transmit data to a receiving station), is deployed semi-permanently underwater (via a mooring, buoy, or attached to the sea floor), and must be retrieved to access the data. More than 30 ARs were reviewed. They varied greatly in capabilities and costs, from small, hand-deployable units for detecting dolphin and porpoise clicks in shallow water to larger units that can be deployed in deep water and can record at high-frequency bandwidths for over a year, but must be deployed from a large vessel. The capabilities and limitations of the systems reviewed herein are discussed in terms of their effectiveness in monitoring and studying marine mammals.
Fixed autonomous acoustic recording devices (autonomous recorders [ARs]) are defined as any electronic recording system that acquires and stores acoustic data internally (i.e., without a cable or radio link to transmit data to a receiving station), is deployed semi-permanently underwater (via a mooring, buoy, or attached to the sea floor), and must be retrieved to access the data. More than 30 ARs were reviewed. They varied greatly in capabilities and costs, from small, hand-deployable units for detecting dolphin and porpoise clicks in shallow water to larger units that can be deployed in deep water and can record at high-frequency bandwidths for over a year, but must be deployed from a large vessel. The capabilities and limitations of the systems reviewed herein are discussed in terms of their effectiveness in monitoring and studying marine mammals.
Visual line-transect surveys for the finless porpoise (Neophocaena phocaenoides) were conducted in the offshore of the west coast of Korea (WCOK) from 18 April to 17 May 2001 (34^{\circ}18`\;to\;37^{\circ}18`N,\;123^{\circ}00`\;to\;126^{\circ}00`E), and in the inshore of the west coast of Korea (WCIK) from 29 July to 2 August 2003 (35^{\circ}17`\;to\;36^{\circ}17`N,\;126^{\circ}00`\;to\;126^{\circ}25`E). A total of transect survey efforts were 810.27 n.m. in 2001 and 216.09 n.m. in 2003, which cover a survey areas of 23,012\;n.m^2\;and\;1,550\;n.m^2, respectively. There were 76 and 24 sightings for the finless porpoise during the surveys in the WCOK (2001) and the WCIK (2003), respectively. More than 80\% of the finless porpoise occurred near the coast within 15 n.m. from the land. Porpoise were observed mainly in a depth range from 20 to 50 m (78\%). Few porpoise were observed in a depth shallower than 10 m or deeper than 60 m. The hazard-rate model, truncated at the largest 5\% distance, showed the best fitting from the frequency distribution of perpendicular distance of the finless porpoise sighted from the trackline in the WCOK (2001), while the uniform model showed the best fitting from in the WCIK (2003). Abundance of finless porpoises were estimated to be 58,650 individuals (95\% CI
To confirm the distributon of finless porpoise, Neophocaena phocaenoides, in the South Sea of Korea, data on bycatch, stranding, and drifting of finless porpoises from 1999 to 2009 were used and a sighting survey was conducted from the R/V Tamgu No. 9 and 10 in June and November, 2009 and March, 2010. The total number of bycaught, stranded, and drifting finless porpoises was 607, with position being known for 186 of these. At the center of Yeosu, there were few position data on bycaught, stranded, and drifting finless porpoises, and data could not confirm the distribution of finless porpoises. Thus, there were limits on the usefulness of bycaught, stranded, and drifting data for confirming the distribution of finless porpoises. In the three sighting surveys, the sighting rate was highest at 0.231 ind./n.m. in the western South Sea in June, 2009. Sighting rate was less than 0.1 ind./n.m. in November, 2009 and March, 2010. This is likely to be due to seasonal migration in western South Sea. All sighting rates in the eastern South Sea were over 0.13 ind./n.m.. According to the results of the sighting survey, finless porpoises are distributed around the islands and inner bay along the path of the research vessel in the South Sea. There were numerous finless porpoises in the offshore areas of Mokpo, Yeosu, Tongyeong, Dadaepo, and Gaduk-do. This study will be utilized as part of a future abundance assessment of finless porpoise in the South Sea of Korea.
Small boat surveys were conducted in the Kuching Bay area of Sarawak, East Malaysia, in order to determine the distribution and abundance of coastal cetaceans. Photographic data collected from Jul.2007 through Oct.2010 was used to generate mark-recapture abundance estimates of Irrawaddy dolphins in the study area, and provided insights into ranging patterns and site fi delity. Between Apr.2010 and Oct.2011, line transect surveys were conducted, and abundance estimates for Irrawaddy dolphins and Indo-Pacifi c fi nless porpoises were generated using distance sampling. The best mark-recapture estimate for Irrawaddy dolphins based on a weighted mean of estimates derived from photographs of left sides and right sides of dorsal fi ns was 233 (CV = 22.5%, 95% CI 151–360). Re-sighted individuals showed a high degree of site-fi delity, with less than 10 km between sighting locations over a period of four years for some individuals. A smaller proportion of re-sighted individuals ranged further—with a maximum straight-line distance of 26 km between sighting locations. The best line-transect estimate for Irrawaddy dolphins was 149 individuals (CV = 28%, 95% confi dence interval 87–255). The line-transect estimate for fi nless porpoises was 135 individuals (CV = 31%, 95% confi dence interval 74–246). Finless porpoise abundance varied seasonally, with higher densities observed between Mar. and May, coinciding with the occurrence of larger groups with very small calves. The line transect and mark-recapture derived estimates for Irrawaddy dolphins are compared, and viewed in the context of mapped relative densities that reveal key areas of habitat for the species. These abundance estimates provide a critical step toward the assessment of both species' local conservation status and can be used in the design of effective management strategies.
The importance of floods as an incentive for river regulation is apparent from the fact that 10% of China's area, inhabited by 65% of the population and responsible for 70% of the agricultural and industrial output, is below the flood level of major rivers. This review considers the ecological implications of planned or existing schemes for the regulation of southern Chinese rives. Particular attention is paid to the Chang Jiang and Zhujiang (Pearl River) which, by volume of discharge, are the two largest rivers in China. -from Author
We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect
methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to
these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring
Sumo Nada (5) and Yatsushiro Sound (4). In Ariake Sound, 225 porpoise groups (369 animals) were detected during all flights
totalling 1,694.4 km. In Tachibana Bay, a total of 997.8 km was surveyed and 55 groups (290 animals) were sighted. However,
no sightings were recorded in Sumo Nada (distance searched = 148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few
sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of
less than 50 m depth. The population size was estimated as 1,983 animals in Ariake Sound (95% CI = 1,382-2,847), 1,110 in
Tachibana Bay (95% CI = 642-1,920), and 3,093 in the 2 waters (1.3 individuals/km2, 95% CI = 2,278-4,201).
We studied the surface and dive times of finless porpoises (Neophocaena phocaenoides) in Hong Kong from three land-based survey sites in winter/spring 2000, to allow the estimation of the trackline detection probability [g(0)] for helicopter line transect surveys in Hong Kong. We determined that groups of finless porpoises in Hong Kong spend on average about 60% of their time at or near the surface, and 40% of their time on a long dive (30 sec. or greater). Surface times apparently increase in larger groups. We conclude that finless porpoises in Hong Kong, while being challenging targets for sighting surveys, are apparently available at the surface to be seen for a higher proportion of time than are harbour porpoises in some deeper water habitats.
We used aerial surveys and line-transect methods to estimate the abundance of the finless porpoise (Neophocaena phocaenoides) in Omura Bay, Japan. We conducted 4 surveys once each season from August 1993 to May 1994. We surveyed 621.5 km and sighted 54 porpoise groups (87 animals). In the spring survey, we detected porpoises offshore as well as inshore, whereas porpoises were mostly inshore in all other seasons. The abundance of porpoises was estimated to be 187 animals (0.6 , CV = 20%).
Harbor porpoise (Phocoena phocoena), and most other cetaceans, spend a significant proportion of time submerged, and are undetectable from the air. Abundance estimates based on line transect sampling may be severely biased by assuming that all porpoise near the line are detected [g(0) = 1]. By tracking groups of harbor porpoise from land, we estimated the proportion of time harbor porpoise spent at the surface and the probability that aerial observers detected groups within 200 m of the transect line. Two teams on land, equipped with electronic theodolites, tracked harbor porpoise while surveys were conducted from an aircraft equipped with side-bubble windows and a belly window. During 7 days, 33 hours of observation were made in a high-density area for harbor porpoise near Orcas Island, Washington. We monitored 7 different harbor porpoise groups from 15 to 66 minutes each. The average proportion of time at or near the surface was 0.231 (SE = 0.032). From a selected sample of 164 land-based sightings of harbor porpoise groups, 50 (30.5%) were observed from the aircraft. For our aerial line transect surveys of harbor porpoise conducted by experienced observers, (g) over cap(0) = 0.292 (SE = 0.107). However, for the inexperienced observers, (g) over cap(0) was 0.079 (SE = 0.046), which demonstrates the importance of experience and training.
Mutation can critically affect the viability of small populations by causing inbreeding depression, by maintaining potentially adaptive genetic variation in quantitative characters, and through the erosion of fitness by accumulation of mildly detrimental mutations. I review and integrate recent empirical and theoretical work on spontaneous mutation and its role in population viability and conservation planning. I analyze both the maintenance of potentially adaptive genetic variation in quantitative characters and the role of detrimental mutations in increasing the extinction risk of small populations. Recent experiments indicate that the rate of production of quasineutral, potentially adaptive genetic variance in quantitative characters is an order of magnitude smaller than the total mutational variance because mutations with large phenotypic effects tend to be strongly detrimental. This implies that, to maintain normal adaptive potential in quantitative characters under a balance between mutation and random genetic drift (or among mutation, drift, and stabilizing natural selection), the effective population size should be about 5000 rather than 500 (the Franklin-Soulé number). Recent theoretical results suggest that the risk of extinction due to the fixation of mildly detrimental mutations may be comparable in importance to environmental stochasticity and could substantially decrease the long-term viability of populations with effective sizes as large as a few thousand. These findings suggest that current recovery goals for many threatened and endangered species are inadequate to ensure long-term population viability.