Miscellany (pdf)

	CITES in Santiago
	Explorations of two underground water channels in Hong Kong!
	Ting Kok: a conservation issue
	The Virtual School of Biodiversity: an update
	Aeromonas and Vibrio spp. detected in Mai Po Nature Reserve and Inner Deep Bay
	Trawling experience and treasures in Hong Kong waters

Trawling experience and treasures in Hong Kong waters

by Benny Chan and Kenny Leung

During the summer of 2002, we received HKD1.3 million from CityU Professional Services Limited to carry out a consultancy study entitled "Provision of Services for Undertaking Laboratory and Field Programmes of Potential Biological Indicators for Monitoring Marine Pollution". The key purpose of this study was to validate the potential biological indicators or biomarkers for monitoring marine pollution :

We also quantified the levels of contaminants (PAHs and PCBs) in the tissues of fish and mussels. Owing to such a large-scale project, we were in collaboration with an overseas expert on EROD assay (Dr. Monique Gagnon, Curtin University of Technology, Australia) and other local companies. Additionally, there were two research assistants (RAs), Dr Alan Leung and Wolfy Lai, and eight student RAs involved in this project. One of the most exciting things was that we used shrimp-trawlers to sample fish (the flat head Platycephalus indicus, the sole Cynoglossus spp., the pony fish Leiognathus brevirostris and the rabbit fish Siganus oramin) from six locations (Deep Bay, Urmstron Road, Tolo harbor, Ninepin, Lamma and Tathong Channel) once in June and once in August 2002. At each location, we performed two 30 minutes tows. In this article, we would like to share some of our trawling experiences with Porcupine’s readers.

We spent three consecutive days carrying out the trawling survey at each of the six zones in June 2002 (Fig. 1). The first day of trawling began in Tolo Harbour. To all students, it was the first time that they had been onboard a shrimp-trawler. Most of us were unfamiliar with equipment and other things inside the trawler and the unpleasant smell of petrol. After we had arranged the equipment and ice-boxes in a systematic manner, the trawler arrived at the area outside Wu Kai Sha where the trawling commenced. After 30 minutes tow, we were very excited about the ‘catches’ from the trawl nets. After sorting the catch, we obtained the three target fish species except the Cynoglossus spp. The pony fish L. brevirostris was found to be the most abundant species at the location. The catch also consisted of a number of crab species, predominantly Portunus pelagicus, P. sanguinolentus, and Charybdis feriatus (Fig. 2). All these three crab species are commercially important. Furthermore, a large number of small crab species including Charybdis truncata and Dorippe granulata were also found (Fig. 2). The third and fourth legs of Dorippe are short and hooked; making the legs capable of placing a flat grey anemone (Carcinactis ichikawai) on the carapace for escape from predation (see illustration in Fig. 2; Morton and Morton, 1983). There were a large number of mantis shrimps, mainly Harpiosquilla harpax and Dictosquilla foveolata, found in the catch. Some of them were served as our lunch. Of course, they are very delicious! We also collected a considerable number of the bivalve Bassina calophylla. Bassina features with extensive lamellae on the shell surface to escape from predation by gastropod predators (Ansel and Morton, 1985). After collecting the target fish species, people started to get busy with dissecting the liver from fish and freezing it in liquid nitrogen. This was indeed one of the most difficult tasks because of the combined effects of both wave action and unpleasant petrol smell. The first day trip was finished in a half day.

On Day two, we went to Deep Bay and Urmstron Road, respectively. This time, we were on a new trawler (larger and cleaner) without any unpleasant smell of petrol. Unexpectedly, there was a very cute and friendly dog, cheering up all of us during the boating time. The catch in Deep Bay and Urmstron Road primarily consisted of P. indicus and L. brevirostris with only a small amount of Cynoglossus spp. The crab assemblages were mainly composed of Charybdis feriatus, C. anisodon, C. lucifera, Portunus gracilimanus, Dorippe granulata, Menippe spp. and the mangrove crab Scylla paramamosain (Fig. 2). Additionally, there was a species of sea pen Pteroeides sparmanni in which we observed a number of beautiful small porcelain crabs Porcellana picta indicating a commensal association between these two species (Fig. 2; Morton and Morton, 1983). In these western Hong Kong waters, bivalves were made up of a high abundance of Anadara spp., which has a thick shell with brown hairs. Furthermore, there were at least six species of mantis shrimps found in these areas including Clorida decorata, Dictyosquilla foveolata, Harpiosquilla harpax, Miyakea nepa, Oratosquilla oratoria, Oratosquillina interrupta and some of these species could not be observed in eastern Hong Kong Waters. Besides live organisms, the catch also consisted of a considerable number of large petrol drums and metal furniture frames, which were likely abandoned by fishermen. This waste material shows that the seabed in these areas has been heavily disturbed by human activities, apart from trawling. The mud in these areas was also black in colour with an unpleasant smell indicating high organic loads. This is likely attributable to pollution in the area.

The third day of the trawling trip was the hardest day, as we needed to survey three zones in one day. We started our trip at 7:30 a.m., travelling from Tuen Mun to the Ninepin. The waves around the Ninepin were so rough that the vessel rose and fell vigorously. Having sorted the target fish species, we needed to carry out the dissection of fish under extremely wavy conditions. During the dissection, many of us were seasick, feeling dizzy, with stomach upsets, vomiting and even losing the ability to carry on working. The remaining team members needed to work harder in this tough situation. Thank God! We finally finished the mission impossible – dissecting all the fish. Despite the seasickness, we saw a number of special and beautiful marine fauna. The ‘by catch’ in the Ninepin consisted of the box crab Calappa philargius, unidentified species of decorated crabs and some unidentified species of soft corals. After completion of the sampling at Ninepins, we headed towards Tathong Channel (i.e. Junk Bay) where the sea was far more ‘calm’. Like Urmston Road, there was a lot of rubbish on the seabed in Junk Bay. As a result, a considerable number of nets were broken during the trawling there. It was amazing that we found used toilet bowls, vehicle tires and furniture etc. inside the trawl nets. Because of the rough seabed, this is an unfavourable fishing location for fishermen. Because of this "artificial reef", it was not surprising that we found three groupers Epinephelus spp. (15-20 cm flock length). They were released back to the sea immediately.

Finally, we headed to South Lamma Island and arrived there in the late afternoon. At this site, we were able to obtain all four target fish species and we also got several large sized rays (Elasmobranchs). The rays were given to our fish expert Dr Yvonne Sadovy for her ongoing research on this group of fish species in Hong Kong. Crabs collected in Lamma channel mainly consisted of Charybdis feriatus and Dorippe granulata as well as some Eucrate spp.

The trawling survey left all of us with some unforgettable memories. It was a wonderful experience for the students who could see, touch and learn about the diversity of benthic organisms in Hong Kong, as well as see the operation of shrimp-trawlers. All these experiences will be useful for their third year course on ‘Fisheries and Mariculture’. In addition, the trawling survey has initiated some research interest for both of us. Although mantis shrimps are very common in Hong Kong waters, their ecology and population dynamics are largely unknown. If there is any funding available, Kenny would like to further study the species composition, spatial distribution, ecology and population dynamics of mantis shrimps in Hong Kong. During the trawling survey, Benny observed that the gills of the subtidal crabs, especially Portunus pelagicus, were colonized by a large number of stalked barnacles Octolasmis spp. which are considered to be parasites of crabs (woo.. Barnacles again!). Unlike other parasitic barnacles (e.g. Sacculina as reported Porcupine! 23, p.6) having a reduced larval stage and very patchy distribution, Octolasmis spp. shows a very wide distribution in Hong Kong and their larval stage is similar to that of other conventional barnacles. Therefore, Benny is currently working with Priscilla Leung to investigate the genetic differentiation of Octolasmis and Sacculina in Hong Kong to see whether or not the difference in larval dispersal will lead to different extents of gene flow in these parasitic barnacles.

Although Hong Kong waters are enriched with a huge variety of wonderful living organisms, such a great biodiversity is threatened by human activities such as sewage discharge, over fishing and illegal waste disposal. We therefore should work together in order to safeguard all these precious treasures. In the future, we will organise a few more trawling studies and you are welcome to join us to find out more about the treasures of Hong Kong Waters.

The authors are very grateful to undergraduates and postgraduates in DEB including K. H. Chu, Valerie Ho, O. S. Hung, George Kwok, H. L. Chan, Danny Lau, Kiwi Lee, Justine Tsui, and David Y.N. Poon for their assistance in this study.

Ansel, A. D. & Morton, B. (1985). Aspects of Naticid predation in Hong Kong with special references to the defensive adaptations of Bassina calophylla (Bivalvia). In Morton, B. & Dudgeon, D. (eds). Proceedings of the second international workshop in the malacofauna of Hong Kong. Hong Kong University Press, Hong Kong. pp. 635-660.

Morton, B. & Morton, J. (1983). Seashore ecology of Hong Kong. Hong Kong University Press.