Application 124771 - Ministry of Fisheries

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MAY 2012 REPORT NO. 2167 | CAWTHRON INSTITUTE 2 Li 373 is currently farmed in two blocks of 11 x c.150 m floated backbone lines per block and is stocked with mussels of varying growth stages. No lines have been used for spat catching. Based on the assessment done on 14 December 2011, and the area of farm surface structures was mostly contained within the consented area. 1.2. Benthic assessment methods The benthic assessment was carried out using video transects and a grab sample within and adjacent to the proposed extension and currently farmed area (Figure 2). ± T5 Inshore west Li373 0 25 50 100 150 200 m South 361 north 396 Li396 T6 Li361 Li396 361 north Sediment Key Li361 South 361-396 Li373 current farm area Gravel Sand Silt & clay Li361 & 396 current farm areas Li373 farm extension Mussel extent Video transect Figure 2. Map of mussel farm Li 373 showing the location of the current farm (surface structures) and proposed farm extension, the estimated extent of mussel shell clumps beneath the farms, video transect locations and grain size at the sediment grab station. The current farm areas (surface structures) of the neighbouring mussel farms, Li 361 and Li 396, are shown in grey.
CAWTHRON INSTITUTE | REPORT NO. 2167 MAY 2012 Mussel shell drop-off is commonly used an indicator of the extent of benthic effects beneath mussel farms (Wong & O’Shea 2011), and video transects were used to determine the limits of mussel shell drop-off and/or mussel clumps on the seabed around the block of farms. Li 373 is situated adjacent to Li 396 and Li 361 and the extent of mussel shell drop-off was determined around the entire block of farms. An underwater video camera and light was attached to a sled and tethered via cables to a VCR and television on the boat. Six transects (Figure 2) were undertaken by lowering the sled and camera to the seabed and towing it in the required direction. GPS positions were recorded for each transect with observations of conspicuous epifauna and substratum type. A single grab sample was collected from t outside the southwest corner of the farm using a 0.01 m 2 van Veen grab sampler. A 63 mm diameter core sub-sample was photographed and the top 25 mm was collected for analyses of sediment grain size. Grain size was determined gravimetrically after separation of fractions by wet sieving and drying at 105°C, for gravel (≥ 2 mm), sand (≥ 63 μm - < 2 mm) and silt/clay (< 63 μm) size classes. Depth profiling was undertaken to assist in characterising the seabed. Continuous depth readings from a Garmin F100 depth sounder within and adjacent to the farm areas, and were sent to a PC via a RS232 serial output. The PC simultaneously collected separate RS232 serial output of latitude and longitude from a GPS, and both data streams were incorporated using communications software. Depths were standardised to chart datum and plotted as depth contours in ArcMap. 1.3. Benthic assessment results Video transects along the perimeter of the farm revealed mussel clumps, mussel shell drop-off and a fine covering of shell hash overlying mud (e.g. Appendix photographs 1 and 7). A patchy film of orange/brown benthic diatoms was present in some mud areas (Appendix photograph 2). Conspicuous epifauna included cushion stars (Patiriella sp.), ascidians (Styela clava), eleven-armed sea stars (Coscinasterias muricata), sea cucumbers and small feather hydroids. Two horse mussels (Atrina zelandica) were observed along the inshore transect. Burrows in the mud were common, suggesting that regular bioturbation occurs over the site. Other transects around this block of farms have shown a similar environment of mussel clumps and shell drop-off on mud (e.g. Appendix photographs 9 and 11); therefore, it is likely that this habitat is widespread beneath the farm. Mussel clumps and shell drop-off became less dense with distance from the farm. Beyond the mussel clump/shell drop-off areas (> 50-115 m north and south of the farm; > 20 m inshore of the farm) the substratum was mud, often covered with shell hash, with few epifauna present (Appendix photographs 2 and 6). 3
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Waikato Regional Council Private Ba
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REPORT NO. 2134 ASSESSMENT OF BENTH
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MAY 2012 REPORT NO. 2134 | CAWTHRON
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CAWTHRON INSTITUTE | REPORT NO. 213
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Application 124771 - Ministry of Fisheries

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