West Lantau Waters Biodiversity
By: Wwf Hk
Tags: Biodiversity, Fish, Hong Kong, Chinese White Dolphin, Conservation

by Thomas Gomersall

On the western fringes of Hong Kong, the Pearl River empties its sediment-laden waters into the Pearl River estuary, where the currents carry them south to western Lantau Island. The high sedimentation, poor visibility and variable salinity of these waters make them a challenging environment for marine animals to live in. In the last several decades, additional stresses have come in the form of habitat loss and degradation, overfishing, increased anthropogenic noise from boats and construction, and toxins like heavy metals and industrial waste washed down from the Pearl River.

Blasted and poisoned from all sides, it seems a wonder that anything can still survive here. But survive here they do in spite of the trials. Though with further development of the west Lantau waters imminent, and a frustrating lack of political will to establish effectively managed marine protected areas large or strategically placed enough, how much longer these species will be able to hold out remains in serious question.

Photo credit: Olivia To WWF-Hong Kong

Chinese White Dolphin (Sousa chinensis): If there’s one Hong Kong animal that grabs the public’s attention, it’s the Chinese white dolphin, more commonly known as the pink dolphin. Calves are initially born grey but turn a white to pale-pink colour as they mature. As specialists of estuarine habitats, these animals utilise estuarine areas throughout the Pearl River Estuary region, including in Hong Kong waters. Unfortunately, numerous ongoing offshore developments are threatening this vulnerable species, such as habitat loss and degradation, noise and water pollution, overfishing and boat traffic disturbance (WWF, Hong Kong; Barros et al, 2004).

Although some marine parks have been designated to protect them, the effectiveness of these spatial conservation plans is limited given that commercial fishing with a permit is still allowed in these parks and several other important dolphin habitats are not under official comprehensive protection. Moreover, ex-situ sources of human impact, such as untreated industrial waste and agricultural runoff, are not effectively regulated within protected areas (WWF, Hong Kong). Thus, through a combination of human impacts and inadequate protection, the estimated dolphin numbers in Hong Kong have dropped by over 70 per cent in the past 15 years (Agriculture, Fisheries and Conservation Department, 2020). To combat this, WWF-Hong Kong has published an emergency action plan calling for drastic conservation measures to be taken immediately in order to save the remaining dolphins.

Photo credit: YG Chan

Big Head Croaker (Collichthys lucidus): As its name suggests, the big head croaker (along with other members of the fish family Sciaenidae) communicates with others of its kind using a croaking sound, which it makes by vibrating special muscles against its swim bladder (Veerappan et al, 2009). It is an estuary specialist that sticks close to the seabed and is a favoured prey for the Chinese white dolphin (Barros et al, 2004).

Photo credit: Shutterstock

Yellow Croaker (Larimichthys crocea): Another prey for the Chinese white dolphin (Barros et al, 2004), the yellow croaker actually has a few things in common with its main natural predator. One being its familiarity to Hong Kongers, as it is a favoured food fish here. But another unfortunate similarity is that both species are affected by underwater noise as, like the dolphins, croakers are very sensitive to sound (Wang et al, 2017). In addition, they have also been intensively harvested by local fishermen in the past (Barros et al, 2004). While individuals sold in wet markets are unlikely to be wild-caught and are probably farmed in China, eating them is still not recommended as they are classified as unsustainable. The WWF Seafood Guide cites poor farm discharge regulation, unsustainably sourced fish-based feed and disease outbreaks in farms that could spread to wild fish as reasons for putting it in the red list.

Photo credit: Ranjith-chemmad

Yellowfin Seabream (Acanthopagrus latus): For some fish like the yellowfin seabream, sex changes are a normal part of life. Individuals are initially born male but upon reaching a certain size and life stage, some of them will change to females in a phenomenon known as protandry (Hong Kong Marine Fish Database; Vahabnezhad et al, 2016). One possible reason for this is because males have greater reproductive success when small but as they further mature, females have greater reproductive success. Thus, changing sex allows an individual to maintain maximum reproductive success throughout its life (Berglund, 1990). This fish lives mainly in the sea but has also been known to enter estuaries and river mouths (Lee et al, 2004, p. 183).

Photo credit: Shutterstock

Orange-spotted Grouper (Epinephelus coioides): The orange-spotted grouper was once a fairly abundant species in Hong Kong and a common sight in local fish markets. But as with other local grouper species, overfishing has drastically reduced its numbers and it is now uncommon in either the sea or the seafood markets here. Its preferred habitats are turbid coastal reefs or muddy and sandy areas, both close to the coastline and in deeper offshore areas, though juveniles have been known to travel into brackish waters (Sadovy & Cornish, 2000, p. 76, p.82–83).

References

· Agriculture, Fisheries and Conservation Department of Hong Kong SAR. 2020, ‘Monitoring of Marine Mammals in Hong Kong Waters (2019–2020): Final Report (1 April 2019 to 31 March 2020)’, https://www.afcd.gov.hk/english/conservation/con_mar/con_mar_chi/con_mar_chi_chi/files/Final_Report_2019_20.pdf (Accessed: 17 November 2020).

· Barros, N.B., Jefferson, T.A. and E.C.M. Parsons. 2004. Feeding habits of the Indo-Pacific Humpback Dolphins (Sousa chinensis) stranded in Hong Kong. Aquatic Mammals, vol. 30 (1): 179pp.–188pp.

· Berglund, A. 1990. Sequential hermaphroditism and the size-advantage hypothesis: an experimental test. Animal Behaviour, vol. 39 (3): 426pp.–433pp.

· Hong Kong Marine Fish Database, Acanthopagrus latus (Houttyun, 1782), [website], https://www.hk-fish.net/english/marine_fauna_database/fish_search_result_new_window.php?id=341 (Accessed: 25 July 2019).

· Lee, V.L.F., Lam, S.K.S., Ng, F.K.Y., Chan, T.K.T. and M.L.C. Young. 2004. Field Guide to the Freshwater Fish of Hong Kong, Friends of the Country Parks, Hong Kong, 183pp.

· Sadovy, Y., Cornish, A.S. 2000. Reef Fishes of Hong Kong. Hong Kong University Press, Hong Kong, 76pp., 82pp., 83pp.

· Vahabnezhad, A., Kaymaram, F., Taghavi Motlagh, S.A., Valinassab, T. and S.M.R. Fatemi. 2016. The reproductive biology and feeding habits of yellow fin seabream, Acanthopagrus latus (Houttyun, 1782), in the Northern Persian Gulf. Iranian Journal of Fisheries Sciences, vol. 15 (1): 16pp.–30pp.

· Veerappan, N., Pandi, V. and T. Balasubramanian. 2009. ‘Sound production behaviour in a marine croaker fish, Kathala axillaris (Cuvier)’. World Journal of Fish and Marine Sciences, vol. 1 (3): 206pp.–211pp.

· Viney, C., Phillipps, K. and C.Y. Lam. 2005. The Birds of Hong Kong and South China. Information Services Department, Hong Kong SAR Government, Hong Kong. 120pp.

· Wang, R., Xu, X., Zou, Z. and Y. Zhou, ‘Prediction of underwater blasting safe range for large yellow croaker (Pseudosciaena crocea)’, 2017 IEEE International Conference on Signal Processing, Communications and Computing (ICSPCC). Xiamen, China, IEEE, 2017.

· WWF Hong Kong, Chinese White Dolphins — Threats, [website], https://www.wwf.org.hk/en/reslib/species/chiwhitedolphin/threats/ (Accessed: 18 July 2019).