Daytime trawl sampling was conducted by a local trawler equipped with a Global Positioning System (GPS) to ensure accurate positioning of each trawl. A trawl with five nets was used for the biota harvesting. The diameter of the net mouth was at least 2.5 m, with a net mesh size of 40 mm at the mouth and 24 mm at the cod end.

A minimum of two replicate 10 minute trawls were undertaken at each station, along one or more transects, using a towing speed considered appropriate for the station conditions and dependent on the capabilities of the vessel. Catches from all nets in the first trawl were combined, washed and sorted to identify the three most common species (in terms of biomass). (The first trawl thus served as the "preliminary run" referred to in Section 6.4.1 (x) of the Study Brief.) These species represented the Target Species used for tissue analysis for each particular station surveyed. Target Species were retained for processing in the analytical laboratory. Ideally, the same three target species would have been used for all stations and surveys for data comparison purposes. Species that are commercially marketed for human consumption were also given priority. During the course of this baseline Study, however, it was not always possible to obtain enough tissues from the biota to provide adequate biomass for contaminant chemical analyses (as discussed in Section 3.1).

For the second and remaining trawls, catches from all nets were combined, washed and sorted to provide the three selected target organisms. Where sufficient biomass was not captured in the two replicate trawls, additional 10 minute trawl replicates were conducted. The field contractor continued

conducting 10 minute replicate trawls until one or more of the following conditions was satisfied:

• sufficient tissue samples were obtained (ie up to five replicate samples per target organism per station per survey); or

• the total area swept by all nets for all replicate trawls at the given station was greater than or equal to 12,000 m2; or

• an entire survey day had been expended at the given station.

Target organisms were stored in sterilised (hexane-rinsed) glass jars, chilled to 4°C and transported to the laboratory for sorting and chemical analysis. In the analytical laboratory each individual was identified and measured to the nearest 1 mm and the mass recorded to the nearest 0.1 g. Target Species were dissected with a sterilised (with hexane) titanium knife. Tissues from at least three (usually five when available) individuals of the same target organism of similar size were combined to form composite tissue samples(18)) of the required quantity for analysis. A minimum of 30 g of tissue was required for Total PAH, Total PCB and Total DDT analyses and 20 g of tissue was required for the TBT analysis. Frozen composite samples were shipped to the testing laboratory for analysis.

The tissue samples were collected four times during the baseline SUSDEV 21 studies. Sampling was conducted twice in both the wet and dry seasons to allow for any changes over time (temporal) because differences in contaminant levels are known to occur due to events such as spawning or different rates of contaminant deposition in sediment that are utilised by benthic species. Trawl sampling was conducted during the following periods:

• 7-8 December 1998 (dry season);

• 21-22 January 1999 (dry season);

• 6-9 August 1999 (wet season); and,

• 2-3, 8 September 1999 (wet season).

The first wet season trawl sampling was originally scheduled for 24-26 June 1999, however, owing to a fishing ban imposed in PRC waters during this period, and hence problems identifying a trawl contractor, the June trawling was re-scheduled for August 1999. Trawling frequency criteria provided coverage of both wet and dry seasons and also allowed replication of data within each season. Data replication is required in order to provide a statistically robust analyses of toxic organic contaminants present in the biota and thus improve the overall SUSDEV 21 baseline results.

When ample tissue was available, five replicate samples were collected for the tissue sampling programme in order to provide an indication of the natural variance in the data. Sample replication formed an important part of the tissue sampling programme in view of the paucity of existing data on organic toxics in tissues of local marine species. A list of the Target Species stations trawled and number of replicates analysed for Total PAHs, Total PCBs, Total DDT and TBT are provided in Table 3.3a to Table 3.3d. The trawling station coordinates are presented in Annex B.

Table 3.3a List of Target Species Collected During December 1998

Note
(1): MB - Mirs Bay; PS - Port Shelter; SW - Lamma; DB - Deep Bay.
(2): Charybdis affinis was incorrectly termed Charybdis japonica, Inegocia japonica was incorrectly termed Onigocia macrolepis in Annex A.
(3): n - Number of replicates.

Note
(1): MB - Mirs Bay; PS - Port Shelter; SW - Lamma; DB - Deep Bay.
(2): In Annex A, Bursa rana was incorrectly termed Bursa granularis, Clausinella isabellina was incorrectly termed Clausinella tiara, Scapharca subcrenata was incorrectly termed Scapharca labiosa , Charybdis affinis was incorrectly termed Charybdis japonica, Evynnis cardinalIs was incorrectly termed Paragyrops edita.
(3): n - Number of replicates.

Note
(1): MB - Mirs Bay; PS - Port Shelter; SW - Lamma; DB - Deep Bay.
(2): Charybdis affinis was incorrectly termed Charbdis japonica in Annex A.
(3): n - Number of replicates.

Tissue preparation was conducted under the supervision of an ERM representative. A total of 60 biota samples (4 stations x 3 species x 5 replicates) were collected during each trawl for analysis of Total PAHs, Total PCBs, Total DDT and TBT. Sufficient tissue for five replicates of the target species was obtained for three of the four surveys. There was, however, insufficient tissue to provide five replicate samples for a number of the target species during the January 1999 survey and only 37 replicates were analysed. The number of replicates for each target species at each station is shown in Tables 3.3a to 3.3d. Representative photographs of all Target Species are shown in Figures 3.3a to Figure 3.3f.