Taiwanese white dolphins

In 2002, the first dedicated surveys for cetaceans in the shallow, nearshore waters of central western Taiwan confirmed the presence of humpback dolphins (Sousa chinensis) (Wang et al. 2004a). This finding extended the species’ range to include the eastern Taiwan Strait (ETS), which still represents the easternmost limit of the species’ known distribution.

The ETS humpback dolphins were eventually shown to merit recognition as a separate subspecies, the Taiwanese humpback (or white) dolphin S. chinensis taiwanensis (Wang et al. 2007a; Wang et al. 2015).  Multiple lines of evidence (morphological differences, geographical isolation, general biology of the genus, etc.) strongly support the view that there is no contemporary exchange of humpback dolphins across the Taiwan Strait (Wang et al. 2015; Wang et al. 2016b).

Distribution and Habitat

The Taiwanese subspecies is restricted to the shallow coastal waters of central western Taiwan year-round  with no obvious seasonal movements (Wang & Yang 2011). Its total distribution covers roughly 750 km2, but the core distribution comprises only about 330 km2 in a narrow strip of habitat about 110 km long, stretching from Tongshiao, Miaoli County, to Taixi, Yunlin County (Wang et al. 2016a), but see Wang et al. (2017) for correction of core distribution). The majority of sightings have been made in waters less than 20 m deep and within 3 km of shore, but individuals have been known to cross deep (>30 m) shipping channels in inshore waters that have been dredged (Dares et al. 2014).

Abundance

A long-term individual photo-identification (photo-ID) monitoring programme began in 2007 and continues to the present. Mark–recapture analyses of the photo-ID data collected from 2007 to 2010 resulted in annual total abundance estimates that varied from 54 (in 2009) to 74 (in 2010) with CVs ranging between 4% and 13% (Wang et al. 2012). The highest point estimate of 74 was very precise (CV=4%) and the upper 95% confidence limit was 80 individuals.

Threats

Several persistent and compounding human activities continue to seriously threaten the Taiwanese subspecies. Five major categories of anthropogenic threat were identified by a panel of experts including (1) fisheries interactions, (2) habitat degradation and loss, (3) air and water pollution, (4) reduction of freshwater outflow into estuaries, and (5) noise disturbance.

Fisheries are considered to pose the most direct and immediate threat to these dolphins.  Gillnets and trammel nets pose the greatest risk while other gears such as trawl nets, longlines and other hook-and-line methods are considered less likely to kill dolphins (Slooten et al. 2013).  Photographic evidence indicated that 49 of 93 photo-documented individuals (52.7%) had injuries consistent with harm by human activity of some kind. It was possible to confirm that 29 of the 93 individuals (31.2%) had likely been injured as a result of interactions with fisheries, and this proportion is probably an underestimate (Slooten et al. 2013).  A larger study showed that 57.7% of the known individuals exhibited major injuries (Wang et al. 2017) and some have experienced severe mutilation and likely extreme and intense suffering (Wang & Araújo-Wang 2017).

Over the years, photographic evidence has also indicated the presence of emaciation in Taiwanese white dolphins (Slooten et al. 2013). Overfishing in Taiwan may be at least partially responsible for the poor body condition of some individuals (Slooten et al. 2013) as they could be nutritionally stressed from insufficient quality or quantity of prey.

The very high human population density and the rapid industrial development of the west coast of Taiwan over the past century have had a number of negative effects on the environment. The natural coastline in humpback dolphin habitat declined by 20% between 1995 and 2007 due to measures taken to combat erosion and control flooding and the expansion of fishing ports, power plants and other public facilities (Wang et al. 2004b; Wang et al. 2007b). Multi-purpose industrial parks have been constructed on “reclaimed” land as a way of reducing the impacts of industrial expansion on local agricultural and residential properties (Wang et al. 2004b; Wang et al. 2007b). As of 2007, 59 large-scale industrial projects were either underway or completed, another 20 are under development, and at least 80 are awaiting approval (Wang et al. 2007b).

The coastline and adjacent regions of western Taiwan that border Taiwanese white dolphin habitat are dominated by industrial infrastructure (industrial “parks”), including petroleum storage facilities, petrochemical plants, industrial harbours, fuelling stations, high-tech electronics facilities and power plants (Wang et al. 2007b). Pollutants produced by such facilities are released into the local air and water and thus affect the quality of dolphin habitat and prey resources. A study predicted that 68% of Taiwanese humpback dolphins have tissue levels of PCBs above the level shown to have negative effects on the immune function of captive harbour seals (Phoca vitulina)  (Ross et al. 1996; Riehl 2012). Furthermore, mature male dolphins and neonates, especially the offspring of primiparous females, were the most heavily burdened individuals and hence the most likely to be at risk of immunotoxicity (Riehl 2012). There is already some evidence suggestive of immune dysfunction as, in one study, 37% of photographed individuals appeared to have epidermal conditions that have been linked in bottlenose dolphins (Tursiops truncatus) to water salinity and/or temperature as well as exposure to contaminants (Yang et al. 2013). Spinal anomalies (Weir and Wang 2016) may also be suggestive of some congenital issues or exposure to pollutants.

More recent moves to “greener” sources of energy has the government in Taiwan planning massive offshore wind farms (with up to 1000 turbines) to be installed within and adjacent to the known habitat of the Taiwanese white dolphins. As proposed, this project will not only further reduce the already restricted dolphin habitat but will likely add harmful levels of noise and disturbance to their habitat

Conservation

Taiwanese white dolphins were assessed as a Critically Endangered subpopulation in the IUCN Red List of Threatened Species in 2008. This risk level will remain for the subspecies when the Red List is updated in December 2017.

A great deal of energy and time has been invested by nongovernmental organizations (NGOs) as well as individual scientists, activists and residents of Taiwan in trying to conserve Taiwanese white dolphins. Although some progress has been made in halting emerging threats (e.g., the cancellation of the proposed 4,000 ha land “reclamation” project for the petrochemical facilities of the Kuokuang Petrochemical Company), it is important to emphasize that actions have yet to be taken by the local government to reduce any of the five existing, major threats. Without a reduction of these recognized threats, the subspecies will probably become extinct in the near future (Wang et al. 2004b; Wang et al. 2007b; Slooten et al. 2013; Araújo et al. 2014).

The Forestry Bureau of Taiwan preannounced a proposal to designate “Major Wildlife Habitat” for the dolphins in 2014, several years after recommendations for the legal protection needs of Taiwanese humpback dolphins were published (Ross et al. 2010). Although this proposal can be viewed positively as an official recognition of the urgency to protect the dolphins’ habitat, the proposed area fell short of the area recommended and have not progressed beyond the preannouncement.  An international workshop, focused on the most effective strategies to reduce fisheries related threats to Taiwanese white dolphins, recommended that Taiwan ban all gillnet and trammel net fishing within all identified confirmed and suitable dolphin habitat, enforce the pre-existing ban on trawling within 3 nm (or about 5.5 km) of shore, compensate the affected fishers and support fishers in transitioning to more dolphin-friendly fisheries (i.e. hook and line) (Ross et al. 2015). The Taiwanese government recently announced that it will increase enforcement of the existing trawl ban but little has been done to deal with the more serious issue of fishing with gillnets or trammel nets.

Although the Taiwanese white dolphins are considered in environmental impact assessments for new development projects, a failure to consider all data and sources of information has limited the value of mitigation techniques in new proposals

Eastern Taiwan Strait Sousa Technical Advisory Working Group (ETSSTAWG)

The ETSSTAWG was established in early 2008, following on the recommendations of a 2007 workshop (Wang et al. 2007b) and is comprised of 17 international and Taiwanese marine mammal and marine science experts. The ETSSTAWG was established to provide expertise and guidance on scientific research and conservation issues related to the Taiwanese humpback dolphin. At the request of local conservation groups, the ETSSTAWG has also convened four other international scientific workshops on the Taiwanese humpback dolphin (in 2009, 2011, 2014, and 2017).  The ETSSTAWG has also met with various Taiwanese government agencies and officials and reported on the state of the Taiwanese white dolphins to other organizations and international meetings.

Recent News Updates
June 2017 News Update

References

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