Update: Threats to Taiwanese white dolphins from offshore windfarms

By Qingyi Zeng1 and Chiawen Kuo2
with input from John Y. Wang, Randall Reeves, Gianna Minton and Gill Braulik
1 Ph.D. student at University of Michigan, Ann Arbor
2 Researcher at Wild at Heart Legal Defense Association, Director of Matsu Fish Conservation Union

 

With the aim of reaching net-zero emissions by 2050, Taiwan has committed to achieving a total offshore wind power capacity of 5.6 GW by 2025 and 40–55 GW by 2050 (National Development Council, 2022). This energy policy has led to the rapid expansion of offshore windfarms along Taiwan’s west coast, all situated adjacent to or even within the habitat of critically endangered Taiwanese white dolphins (Sousa chinensis taiwanensis), thereby exacerbating the pre-existing threats to their survival from entanglement in gillnets, habitat loss, pollution etc.

Since 2003, this individual dolphin has been photographed almost annually (Photograph by: John Y. Wang / CetAsia Research Group Ltd.).

By the end of 2023, four windfarms, comprising 201 turbines, had been completed and were in operation. Six more offshore windfarms were under construction and another five were expected to be completed by 2027. While most of the windfarms are located more than 5 km away from shore, marine construction activities that include pile driving and cable laying, especially for the cables that must cross Taiwanese white dolphin habitat to reach the energy grid system on land, intrude into dolphin habitat.

In 2011 the Forestry and Nature Conservation Agency commissioned scientists to delineate Taiwanese white dolphin critical habitat, and an official announcement came into effect in September 2020. The designated critical habitat spans a total of 763 km2, from Miaoli County to Waisanding Zhou, Chiayi County.

Large offshore windfarm projects are under construction in and adjacent to the habitat of critically Endangered Taiwanese white dolphins (Photograph by: John Y. Wang / CetAsia Research Group Ltd.).

While the designation has helped to protect the dolphins’ habitat, the area does not encompass the entire known area used by the dolphins (see Figure below) nor does it extend to other areas of suitable dolphin habitat. These shortcomings were pointed out by teams of international scientists in 2014 and 2020, and the Ocean Affairs Council has been looking into the matter since then.

In addition to continuing habitat degradation and loss, large-scale offshore windfarm construction has resulted in a major surge in vessel traffic as well as increased construction activities, including sea-floor profiling and pile driving, which contribute substantially to underwater noise. Although pile-driving noise is typically low-frequency, research has shown that it can be broadband, with peak sound energy at frequencies of up to 10 kHz, meaning that the sound is well within the frequency range of humpback dolphins (Sousa spp.).

Figure 5 from Ross et al. (2010) showing “priority habitat” for the subspecies

Current regulations concerning offshore windfarm construction in Taiwan mandate that underwater noise within a 750 m radius of a pile-driving site should be kept below 160 dB re 1Pa for 95% of the monitoring time. However, this mitigation measure may be inadequate given that the onset of temporary hearing threshold shifts for certain high-frequency cetaceans can be lower than 160 dB re 1Pa. Also, the threshold for the onset of behavioral disturbance caused by continuous underwater noise, such as that from vibratory pile driving, can be as low as 120 dB re 1Pa.

Increasingly, offshore wind turbines are being installed in the dolphins’ habitat (Photograph by: John Y. Wang / CetAsia Research Group Ltd.).

Although the hearing thresholds of Sousa chinensis at low frequencies have not been tested empirically, there is considerable evidence to suggest that stricter regulation of anthropogenic underwater noise along the west coast of Taiwan is needed to provide a healthier soundscape for the critically endangered Taiwanese subspecies. Despite that evidence, for nearly the entire first 5.6 GW of wind power installation off western Taiwan, no effort was made to assess the impacts on dolphin behavior.

 

For relevant literature, see https://iucn-csg.org/csg-focal-taxa/eastern-taiwan-strait-humpback-dolphins/