Introduction
The Eurasian otter Lutra lutra has the widest distribution of all extant otter species, with a range stretching across Europe, Asia and North Africa (Hung & Law, Reference Hung and Law2016). Although the once-threatened European population is recovering (Ledger et al., Reference Ledger, Rutherford, Benham, Burfield, Deinet and Eaton2022), it is generally considered rare in Asia and the future of these eastern populations is not secure (Loy, Reference Loy, Duplaix and Savage2018; Yoxon & Yoxon, Reference Yoxon and Yoxon2019). Despite the species' threatened status in Asia, little research has been conducted on its ecology and threat processes in the region (Zhang et al., Reference Zhang, Wang, Yang, Li, Chan and Xiao2018; Basnet et al., Reference Basnet, Ghimire, Timilsina and Bist2020; Zhang & Fan, Reference Zhang and Fan2020). The Global Otter Conservation Strategy (Duplaix & Savage, Reference Duplaix and Savage2018) identified a number of goals and associated objectives and actions to protect otters, among which Actions 2.3 and 2.4 under Objective 2 (Locality-based implementation of conservation) and Actions 4.2 and 4.3 under Objective 4 (Strategic research) call for the identification and protection of critical otter habitats, and synthesis of otter records to determine historical and current distributions (Duplaix & Savage, Reference Duplaix and Savage2018).
Although the Eurasian otter is categorized as Near Threatened on the IUCN Red List (Loy et al., Reference Loy, Kranz, Oleynikov, Roos, Savage and Duplaix2022), the species has undergone substantial population and range reductions in East Asia (Sasaki, Reference Sasaki2016; Li et al., Reference Li, Zheng, Zhang, Yang and Chan2017; Li & Chan, Reference Li and Chan2018; Zhang et al., Reference Zhang, Wang, Yang, Li, Chan and Xiao2018; Chang et al., Reference Chang, Chang and Hsu2019; Han & Shi, Reference Han and Shi2019; Jang-Liaw et al., Reference Jang-Liaw, Tan, Chang, Juan, Hou and Chung2023), except in South Korea (Jo et al., Reference Jo, Lee, Park, Kim and Baccus2020). This general trend is echoed in the Hong Kong Special Administration Region, which is a metropolis with one of the highest human population densities and some of the busiest ports. Hong Kong was one of the first places in Asia to afford legal protection to the Eurasian otter; together with the Chinese pangolin Manis pentadactyla it was listed as a protected species in 1936. However, little published information is available on the local Eurasian otter, with only a few brief general accounts in early natural history publications (e.g. Herklots, Reference Herklots1951; Marshall, Reference Marshall1967a; Lance, Reference Lance and Loft1976; Hill & Phillips, Reference Hill and Phillips1981). Scientific studies of Hong Kong's terrestrial mammals only began in the 1990s and the status of the Eurasian otter remained obscure, with only occasional reports from the Mai Po Nature Reserve and the surrounding Deep Bay area (Goodyer, Reference Goodyer1992; Reels, Reference Reels1996; Shek, Reference Shek2003, Reference Shek2006; Suen, Reference Suen2003; Shek et al., Reference Shek, Chan and Wan2007). The first scientific research on Hong Kong otters was not completed until 2021, in which only seven individuals were genetically identified in a 2-year field study throughout its known local range, with Mai Po Nature Reserve and adjacent wetlands highlighted as the core habitat (McMillan et al., Reference McMillan, Wong, Tang, Yau, Gomersall and Wong2022). Despite being considered a species of high conservation priority (Fellowes et al., Reference Fellowes, Lau, Dudgeon, Reels, Ades and Carey2002; Shek, Reference Shek2003), there is no active conservation programme targeting this population (Agriculture, Fisheries and Conservation Department, 2014a; Kadoorie Farm and Botanic Garden, Reference Kadoorie and Botanic2018).
Historical data sources such as newspapers, archival documents, and traditional and local ecological knowledge have been increasingly used as an alternative approach for assessing species' population trends and ecosystem changes over time when conventional ecological data are lacking (Lotze & McClenachan, Reference Lotze, McClenachan, Bertness, Bruno, Silliman and Stachowicz2013; Thurstan et al., Reference Thurstan, McClenachan, Crowder, Drew, Kittinger and Levin2015). They can also be useful for identifying critical habitats of threatened species to inform conservation management (Hiddink et al., Reference Hiddink, Shepperson, Bater, Goonesekera and Dulvy2019; Moore & Hiddink, Reference Moore and Hiddink2022). McMillan et al. (Reference McMillan, Wong, Hau and Bonebrake2019) used local ecological knowledge to collect data on the past and current distribution of otters in Hong Kong but were unable to provide a long-term, Hong Kong-wide overview because of a lack of community memory pre-1950 and the limited geographical coverage of their interview study. Here we systematically review and collate all otter records in scientific publications, books, local newspapers and other popular publications from 1890 to 2020, and reconstruct a longitudinal pattern of temporal and spatial changes in otter abundance and distribution in Hong Kong. We also explore possible causes of the population collapse and recommend key conservation actions.
Study area
Hong Kong is a 1,100 km2 coastal city at the mouth of the busy Zhujiang (Pearl) River Delta in subtropical China. The topography is hilly, with flatlands limited to narrow coastal strips; most housing and other developments for the > 7 million residents are concentrated on 25% of the land. Hong Kong has a coastline of > 1,200 km and many sheltered bays have dense, although stunted, mangrove formations, especially along the western coastline, which receive discharge from the Zhujiang River, with salinity approaching that of fresh water in the rainy season. The only substantial alluvial landscape is the Yuen Long floodplain, drained by the Deep Bay Basin, supporting Hong Kong's largest wetland ecosystem and comprising rivers, marshes, reedbeds, aquaculture ponds, mangroves and mudflats. Hong Kong has been inhabited for at least 6,000 years and all ecosystems have been degraded, but 40% of the land area, mainly the hilly interior, is protected for nature conservation (Dudgeon & Corlett, Reference Dudgeon and Corlett1994). Although many forest-dependent and large mammals have been lost, the remaining fauna includes 14 medium- to large-sized non-volant wild mammal species, many of which have recovered from previous population crashes following the establishment of an extensive protected area system in the late 1970s (Shek et al., Reference Shek, Chan and Wan2007).
Methods
For otter-related newspaper articles, we reviewed Hong Kong newspapers on the WisersOne database and the Old Hong Kong Newspapers Collection in the Multimedia Information System of the Hong Kong Public Library using the search term ‘otter’ and the Chinese character for otters (獺). We also searched the archive of the South China Morning Post, a local English-language newspaper founded in 1903. We also searched Google Scholar (2022) and Google Books (2022) with the search terms ‘otter’, ‘lutra’ or ‘獺’, paired with ‘Hong Kong’ or the Chinese characters ‘香港’.
We also reviewed (1) annual reports of the Hong Kong government, (2) wildlife records in Porcupine!, a newsletter of the University of Hong Kong on local biodiversity, (3) literature about local natural history, natural environment and wildlife, and (4) documents submitted to the Hong Kong government's Environmental Protection Department under the Environmental Impact Assessment Ordinance. We also searched for place names containing ‘Otter’, ‘獺’ or ‘Chat’ (the Cantonese romanization of the character ‘獺’) using GeoInfo Map (2022).
For each record, the perceived local otter abundance was coded using a four-tier classification system modified from similar studies (Fortibuoni et al., Reference Fortibuoni, Libralato, Raicevich, Giovanardi and Solidoro2010; Al-Abdulrazzak et al., Reference Al-Abdulrazzak, Naidoo, Palomares and Pauly2012; Alleway & Connell, Reference Alleway and Connell2015; Al-Abdulrazzak & Pauly, Reference Al-Abdulrazzak and Pauly2017): common (commonly seen or no evidence of reduced abundance), present (present but with evidence of reduced abundance), rare (severely reduced abundance and already disappeared from some localities), and absent (no longer in existence). Not all occurrence accounts could be coded as some simply reported a sighting event, or only reported otter abundance in a specific location. We graphed the average otter abundance rank for each decade over the 131-year study period to produce a longitudinal trend of otter population change. Some researchers have suggested that the Asian small-clawed otter Aonyx cinereus may also occur in Hong Kong (Foster-Turley & Santiapillai, Reference Foster-Turley, Santiapillai, Foster-Turley, Macdonald and Mason1990; Wang & Xie, Reference Wang and Xie2009) but without any supporting evidence. Therefore, ‘otter’ refers here to the Eurasian otter. For locality names mentioned in the text, see Fig. 1.
Fig. 1 Eurasian otter Lutra lutra records in Hong Kong during 1890–2020. 1, Central; 2, Aberdeen; 3, Ping Shan; 4, Shing Mun; 5, Sha Tin*; 6, Shing Mun River*; 7, Lantau Island*; 8, Cheung Chau Island*; 9, Tsuen Wan Ka Loon Tsuen; 10, Castle Peak*; 11, Mai Po and Deep Bay; 12, Stonecutters Island*; 13, Stanley; 14, Repulse Bay; 15, Yuen Long*; 16, Lamma Island Picnic Bay; 17, Tin Shui Wai-Fung Lok Wai; 18, Nam Sang Wai; 19, Lok Ma Chau; 20, San Tin; 21, Hoo Hok Wai; 22, Mai Po San Tsuen-Tam Kon Chau; 23, Sandy Ridge; 24, Kam Tin; 25, Tai Sang Wai; 26, Ma Tso Lung; 27, Lo Wu; 28, Long Valley-Ho Sheung Heung; 29, Kwu Tung; 30, Tap Shek Kok; a, Chat Ling (獺嶺); b, Chat Ngam (獺岩); c, Chat Wan (獺灣). *Location point is approximate
Results
A total of 14,231 otter-related newspaper articles were examined. After removing false positives resulting from optical character recognition errors in the digital databases, irrelevant articles and dubious records, we retrieved 27 otter records for Hong Kong from 1890 to 2020. Eighty-one additional records were located from other sources; literature citing published information already collected was excluded. The year of publication was reported for those items that did not specify the year of record.
Seven of the 108 reports declared the otter extinct in Hong Kong. For those reporting its continued presence, a drastic reduction in range and abundance is evident. This can be divided into three phases: Phase I is pre-1933, during which the otter was reported to be relatively common until the first report of decline; Phase II is 1933–1962, when the otter population progressively declined and its range contracted; Phase III is post-1962, when the otter was on the brink of local extirpation, with a highly localized distribution. Figs 1 & 2 summarize all otter records in Hong Kong during the 131-year period; Supplementary Table 1 details the 108 records. Our extensive newspaper search revealed only three deliberate killings of local otters in 131 years. The species’ legal status was highlighted in 23 reports.
Fig. 2 Distribution of the Eurasian otter in Hong Kong (a) pre-1933, (b) 1933–1962 and (c) post-1962.
Historical otter distribution
The first otter report in our study period was one killed in Central, Hong Kong Island in 1898. Since then, the species has been reported from Kowloon, the New Territories and several offshore islands (Fig. 1). Although there are three records from hilly areas (Aberdeen, Shing Mun and Shing Mun River), otters were predominantly reported from lowland wetlands, including coastal waters, beaches, mangroves, marshes, mudflats, rivers, fishponds and intertidal shrimp ponds locally known as gei wai. Among the 70 records with specific locations, 56 (80%) were clustered in the Yuen Long floodplain, and the records span the 1900s to 2019, suggesting it is the critical otter habitat in Hong Kong. We found no unequivocal evidence of otters occurring in the eastern marine waters of Hong Kong dominated by oceanic waters from the South China Sea.
Of the seven otter-related place names located, Chat Ling (meaning Otter Ridge) is adjacent to Mai Po Nature Reserve in the Yuen Long floodplain, supporting the notion that place names can be a biogeographical indicator of the historical distribution of fauna (e.g. Cox et al., Reference Cox, Maehr and Larkin2002; Tattoni, Reference Tattoni2019), and four were likely to be named for the resemblance of a landscape feature to the otter's appearance or based on animal-related fung shui principles in Chinese culture or for other unrelated reasons (Iu, Reference Iu2012). We were unable to ascertain whether the remaining two locations (Chat Wan and Chat Ngam, meaning Otter Bay and Otter Rock) in eastern Hong Kong waters are associated with former otter occurrence.
Bunbury (Reference Bunbury1909) reported otters in ‘Ping Shan, New Territories’. However, in his revised edition, the location became ‘Ping Chau, New Territories’ (Bunbury, Reference Bunbury1913). Historically, there were two outlying islands named Ping Chau in Hong Kong; one is near Lantau and is now known as Peng Chau, the other is in the oceanic eastern waters and is now known as Tung Ping Chau (Fig. 1). The different localities given in the two editions have caused some confusion among local otter researchers regarding whether otters occurred in the eastern waters of Hong Kong (McMillan et al., Reference McMillan, Wong, Hau and Bonebrake2019, Reference McMillan, Wong, Tang, Yau, Gomersall and Wong2022). Although the possibility of otters occurring on these islands cannot be excluded, we think it likely that Ping Chau is a typographical error. Ping Shan was a popular location for early travellers and naturalists (e.g. Hurley, Reference Hurley1897; Heywood, Reference Heywood1938; Herklots, Reference Herklots1951), including Bunbury, and is within the Yuen Long floodplain.
The otter sightings on Stonecutters Island in 1948 are of special interest; the description of the animal, seen repeatedly, leaves no doubt that it was an otter. Together with the 1898 sighting from Central, this confirmed otters occurred in the busy Victoria Harbour until at least the late 1940s. Otter reports from Sha Tin, Shing Mun and Shing Mun River are also notable, as these are the only records from catchment basins emptying into the eastern waters of Hong Kong. Herklots (Reference Herklots1951) stated that otters used to occur on Hong Kong Island but could find no recent records. Ye (Reference Ye1958) noted that otters occurred in Stanley and Repulse Bay in the less developed parts of Hong Kong Island, but were rare. A newspaper article on an otter sighting at Repulse Bay in 1961 is the last otter report from Hong Kong Island. An otter was reported from neighbouring Lamma Island in the following year but it was found tied with a rope on a beach, and the possibility of it being caught elsewhere cannot be ruled out. This record suggests otters could have survived in the southern waters up to the early 1960s.
All otter records from Lantau, a rural area and the largest island of Hong Kong, with many mangrove-lined bays, were brief and no specific locations were given (Peplow, Reference Peplow1930; Peplow & Barker, Reference Peplow and Barker1931; The Government of Hong Kong, 1948; Herklots, Reference Herklots1951; Ye, Reference Ye1958; Webb, Reference Webb1961). Nonetheless, with contemporary records from adjacent Cheung Chau Island, Castle Peak and Tsuen Wan, we assume otters once occurred throughout Lantau in suitable habitats. Webb (Reference Webb1961) claimed local otters were mainly found on Lantau.
Change in otter abundance
According to local naturalist Geoffrey A. C. Herklots (1902–1986), the former Governor of Hong Kong, Sir Cecil Clementi (1875–1947), recalled seeing otters frequently when he was a cadet during 1899–1900 (Lethbridge, Reference Lethbridge1970). Kershaw (Reference Kershaw and Arnold1908) noted that otters occurred on Hong Kong Island and were common in the New Territories. Bunbury (Reference Bunbury1909, p. 17) also mentioned otters were seen ‘in great numbers on dark nights in the autumn’. The decline of local otters was first mentioned by Herklots in 1932, and progressive disappearance was reported in subsequent decades (Heywood, Reference Heywood1938; The Government of Hong Kong, 1948, 1950; Melville & Morton, Reference Melville and Morton1983). In a review of Hong Kong mammals, Vincent H.C. Jarrett (c.1895–1973) described that otters were ‘fairly common in certain localities … must be very rare now on Hong Kong (Island) itself, if still existent’ (Jarrett, Reference Jarrett1933, p. 1). The fact that the otter became legally protected in 1936 also indicates an early detectable decline. There were no otter records in the first 2 decades of Phase III, with most literature describing the otter as extremely rare and probably extinct. In the 1980s, some anecdotal reports from fishers of otter vocalizations in the western waters resurfaced, and the species' persistence was confirmed in 1986 in Mai Po Nature Reserve (Fig. 3a).
Fig. 3 Decadal changes in (a) the perceived abundance of the Eurasian otter during 1890–2020 (1, absent; 2, rare; 3, present; 4, common), and (b) the human population of Hong Kong during 1891–2021 (Census and Statistics Department, 1972, 1992, 2021). No data were available for perceived otter abundance in the 1910s and 1920s.
Discussion
Our study provides the first longitudinal overview of the distribution and abundance of the Eurasian otter in Hong Kong, revealing that the species was more widespread and common in historical times. Considering the presumed much lower observation effort and coverage in the first half of the 20th century, the species was most likely underreported. The local otter population started to decline around the 1930s, much earlier than previously estimated (McMillan et al., Reference McMillan, Wong, Hau and Bonebrake2019), and experienced progressive population and range reductions in subsequent decades. The otter population declined further from the 1960s, and only a remnant population now persists, in Mai Po Nature Reserve and the surrounding Deep Bay area.
Although our historical approach provides new insights into this threatened population, there are inherent limitations to our data: (1) not all newspapers published in the study period have been digitized and included in searchable databases, and there are missing issues and pages; our search was therefore not exhaustive, (2) although dubious records have been excluded, not all records are verifiable as detailed descriptions of many sightings are lacking, and (3) it is impossible to quantify differences in observation effort in space and time, which is likely to have resulted in some biases in the distribution pattern and perceived otter abundance. Nevertheless, we believe that our expansive review, spanning 131 years, reflects the longitudinal trend of the local otter population.
Our findings show that the local otters are strongly associated with coastal alluvial wetlands, which is unsurprising given that the hillside watersheds of Hong Kong are small and probably cannot sustain otter populations. The Yuen Long floodplain is probably the only wetland ecosystem in Hong Kong extensive enough to offer sufficient resources to support resident breeding otters, and is likely the local source population. Hong Kong's extensive protected area system mainly conserves headwaters and hillsides, and few alluvial and coastal habitats have statutory protection (Dudgeon & Corlett, Reference Dudgeon and Corlett1994; Yip et al., Reference Yip, Corlett and Dudgeon2004; Agriculture, Fisheries and Conservation Department, 2014a). Land-use change in rural lowlands has been a major conservation challenge for Hong Kong (Jim, Reference Jim1996; Agriculture, Fisheries and Conservation Department, 2014a), and apart from the 380 ha Mai Po Nature Reserve and the nearby 61 ha Hong Kong Wetland Park, the majority of otter habitats are unprotected and privately owned, and thus subject to heavy anthropogenic pressures.
Causes of otter decline
In the absence of archives on otter status, environmental issues and hunting records for Hong Kong, key drivers of the otter's local range reduction and population decline cannot be unequivocally established. We can, however, look at the major threats to otter survival from a global perspective based on the IUCN Red List, and assess the severity of these threats in the local context, offer some interpretation of the population collapse and make informed conservation recommendations.
Of the major threats to the Eurasian otter identified by Loy et al. (Reference Loy, Kranz, Oleynikov, Roos, Savage and Duplaix2022), habitat loss and degradation, hunting and pollution are possible contributing factors in Hong Kong. As elsewhere in South China, wildlife hunting and consumption used to be common in Hong Kong, resulting in defaunation of the local countryside (Marshall & Phillips, Reference Marshall and Phillips1965; Lance, Reference Lance and Loft1976; Lau et al., Reference Lau, Fellowes and Chan2010). Some researchers have attributed the decline of local otters to hunting (Marshall, Reference Marshall1967a,Reference Marshallb; Melville, Reference Melville1980; Foster-Turley & Santiapillai, Reference Foster-Turley, Santiapillai, Foster-Turley, Macdonald and Mason1990; McMillan et al., Reference McMillan, Wong, Hau and Bonebrake2019); however, we only found three reports of deliberate killings in 131 years. Local folklore and natural historian Kow Choy Iu, who worked in the conservation sector during 1955–1990, suggested that although local fish farmers might kill otters in retaliation for taking fish, otters were not commonly targeted by local game hunters (K.C. Iu, pers. comm., 2023). Many traditional game species, such as the northern red muntjac Muntiacus vaginalis, wild boar Sus scrofa, similar-sized carnivores such as the mainland leopard cat Prionailurus bengalensis and masked palm civet Paguma larvata were heavily hunted and threatened with local extinction (Marshall & Phillips, Reference Marshall and Phillips1965; Marshall, Reference Marshall1967a,Reference Marshallb; Lance, Reference Lance and Loft1976), but have benefited from better protection and are now widespread and common (Shek, Reference Shek2006; Shek et al., Reference Shek, Chan and Wan2007; Pei et al., Reference Pei, Lai, Corlett and Suen2010; Yang et al., Reference Yang, Li, Yeung, Au, Zheng, Giordano and Chan2022; authors unpubl. data). Even the Chinese pangolin and Chinese three-striped box turtle Cuora trifasciata, widely hunted in Hong Kong and elsewhere, remain relatively widespread in Hong Kong compared with the otter (Lau et al., Reference Lau, Chan, Crow, Ades, van Dijk, Stuart and Rhodin2000; Pei et al., Reference Pei, Lai, Corlett and Suen2010). Thus, we believe hunting was not a major driver of the otter's decline in Hong Kong.
The otter is a resilient species and can live in human-dominated landscapes provided that healthy riverine and/or coastal ecosystems are available (White et al., Reference White, O'neill, O'meara, Shores, O'reilly and Harrington2013; Jo et al., Reference Jo, Lee, Park, Kim and Baccus2020). Urbanization leads to the direct loss of otter habitat, and has been reported to be a major driver of local otter decline (McMillan et al., Reference McMillan, Wong, Hau and Bonebrake2019, Reference McMillan, Wong, Tang, Yau, Gomersall and Wong2022). Hong Kong was a modest trading port with a human population of 368,987 in 1901; the population swelled to > 1.6 million in 1941 and reached 3.1 million in 1961 (Census and Statistics Department, 1972; Fig. 3b). With high housing pressure, the government initiated a new town development programme in the early 1970s to relocate urban populations to rural districts, resulting in the reclamation of shallow bays at Tsuen Wan, Sha Tin, Castle Peak (renamed Tuen Mun in 1973), Tseung Kwan O and North Lantau (Tung Chung), and the urbanization of the alluvial lowlands of Tai Po, Fanling/Sheung Shui, Tin Shui Wai and Yuen Long. By the end of the 1990s, c. 3 million people were housed in nine new towns (Information Services Department, 2000), of which at least seven were once inhabited by otters.
To tackle recurring flooding, the Hong Kong government developed large-scale flood control schemes throughout the lowlands, including the Yuen Long floodplain (Wu, Reference Wu2003). Channelization projects in Hong Kong involve heavy engineering with concrete reinforcement, and these concrete-lined flood channels are impoverished wildlife habitats (Chan, Reference Chan2001; Chan & Dudgeon, Reference Chan and Dudgeon2001; Agriculture, Fisheries and Conservation Department, 2014b). The meandering 18 km Shenzhen River, the largest river basin in Hong Kong with prime otter habitats, was engineered and shortened to a 13.5 km drainage channel (Drainage Services Department, 2020). A Hong Kong-wide study of lowland freshwater fishes reported that > 44% of the surveyed river stretches had been channelized (Chan, Reference Chan2001). The potable and irrigation reservoirs throughout Hong Kong's hillsides impounded all sizeable river systems with auxiliary catchwaters to intercept neighbouring stream flows, which greatly affected the downstream flow regime and estuarine ecosystem (Dudgeon, Reference Dudgeon1996; Chan, Reference Chan2001). These extensive waterway engineering projects have resulted in a substantial loss of otter habitats in Hong Kong.
Water pollution has been identified as a major cause of otter decline in Europe and Asia (de Silva, Reference de Silva2011; Ledger et al., Reference Ledger, Rutherford, Benham, Burfield, Deinet and Eaton2022), and it has been suggested that contamination by polychlorinated biphenyl (PCB) affects otters in Hong Kong (Foster-Turley & Santiapillai, Reference Foster-Turley, Santiapillai, Foster-Turley, Macdonald and Mason1990; Liang et al., Reference Liang, Wong, Shutes and Revitt1999). Before 2001, municipal sewage from the burgeoning human population was discharged into Victoria Harbour with minimal pre-treatment (Watson & Watson, Reference Watson and Watson1971; Morton, Reference Morton1989; Drainage Services Department, 2009). Pollution was further aggravated by an industrial boom and the thriving livestock industry from the 1950–1960s, causing severe pollution in waterways and nearshore waters (Binnie and Partners, 1973, 1974; Tanner et al., Reference Tanner, Leong and Pan2000; Tang et al., Reference Tang, Ip, Zhang, Shin, Qian and Li2008). Approximately 40% of the waterways in the New Territories, including all major rivers in the Yuen Long floodplain, were classified as either polluted or badly polluted (Binnie & Partners, 1974). The timeline for the rising human population and worsening environmental problems appears to align with the widespread disappearance of the otter across Hong Kong.
Conservation recommendations
The insights from this study are crucial for improving the management of the small otter population and the aquatic ecosystems of Hong Kong. The sustained and severe anthropogenic impacts in the under-protected lowland wetlands have negatively affected otter survival and may also explain the failure of the otter population to increase despite the general trend of wildlife recovery.
If extinction of the Eurasian otter in Hong Kong is to be prevented, a multifaceted conservation project must be devised and implemented. Firstly, public and government support for otter conservation must be garnered and conservation action galvanized (Hong et al., Reference Hong, Do, Kim, Cowan and Joo2017; Khoo & Lee, Reference Khoo and Lee2020). This is particularly crucial with the looming Northern Metropolis development mega-plan recently released by the Hong Kong government (Information Services Department, 2021), which will drastically modify the rural landscape of the Yuen Long floodplain, home to a globally important Ramsar Site and the last local otters. This plan covers the whole Yuen Long floodplain and aims to develop housing, economic centres and related infrastructures for 2.5 million residents and create > 0.5 million jobs. A holistic nature-positive land-use plan must be developed to balance economic development and nature conservation, and ensure ecologically sensitive areas are preserved. Secondly, otters travel long distances in search of shelter, prey and/or mates (Erlinge, Reference Erlinge1967), and coastal alluvial wetlands are under-represented in Hong Kong's protected area system. Although the Hong Kong government has pledged to establish additional nature/wetland conservation parks in the Northern Metropolis, interconnecting eco-corridors must be built between these otter habitats. Thirdly, in the Yuen Long floodplain it is imperative to design and/or restore functional riverine ecosystems and re-establish connectivity with riparian wetlands to enhance these critical habitats for local otters. The restoration and maintenance of environmental flow for the extensive reservoir catchwater system should also be explored, so as to restore healthy estuarine ecosystems across a wider area. Fourthly, the Deep Bay Basin continues to be subject to domestic and industrial pollution, mainly from private properties; improving stakeholder engagement and law enforcement efficiency is essential to address the recurring pollution.
Acknowledgements
We thank Xi Zheng, Eric Au, Shirley Wong, Jianhuan Yang, Philip Lo and Fei Li for their assistance and helpful discussions, Abby Kwok, Meeco Leung, Gena Yip and South China Morning Post for their help with the literature review, and Kow Choy Iu, Chung Tong Shek and Wing Chi Tsui (Agriculture, Fisheries and Conservation Department) for sharing their views and for helpful discussions.
Author contributions
Both authors contributed equally.
Conflicts of interest
None.
Ethical standards
This research abided by the Oryx guidelines on ethical standards.
Data availability
The data supporting the findings of this study are available within the article and its supplementary material.
Open access
