Stimulating investment in pearl farming in ... - World Fish Center

Abundance, Size Structure and Quality of Silver-lip Pearl Oysters in the Solomon Islands Final, June 2008The relative position of each location is shown in Figure 1. Malaita and Marau weresurveyed in April 2007, as were some transects at Mboli Passage (Narula Passage). SandflyPassage, Mbili Passage and Telina were surveyed in May 2007 and Kia and Waghina weresurveyed in October 2007. The sites selected for investigation within each location wereplaces that the interviewees reported as historically and/or currently most favourable forsilver-lip pearl oysters. A local fisher or fisheries officer accompanied the survey boat toassist with specific local knowledge and finding the recommended sites.2.2 Underwater Visual CensusAt each location, three sites were surveyed by pairs of divers towed very slowly beneath asmall outboard boat and supplied with air via hoses from a compressor in the boat(“hookah” system). Pearl oysters were collected by the divers from four randomlypositioned4 m wide transects. The latitude and longitude at the beginning and end of eachtransect, time and duration of the dive, maximum bottom depth and the type of substratafound along each transect were recorded (Appendix 1). Position and depth were taken froma Hummingbird 737 combination GPS/Echo sounder. Transects varied in length from 69 to725 m and in maximum depth from 12.4 to 40.5 m, with the average being 305 m long and27.3 m deep. It should be noted that these lengths are derived from straight lineinterpolations between transect start and finish points. As far as was possible divers weretowed in a straight line and we have assumed that each diver adhered to a 2 m widetransect.Oysters found by the divers were placed in mesh bags and returned to the boat. On thesurface, the length and width of each pearl oyster shell was measured to the nearestmillimetre using callipers and recorded. The quality of the shell exterior was assessedvisually as being either high grade, of suspect quality or unwanted. The criteria used in thisassessment were related to the Australian standard of B FAQ and C respectively (Hart andFriedman 2004). At each site up to ten, haphazardly selected shell were sacrificed to allowthe colour of the margin and centre of the nacreous layer to be assessed. Ten pearl oystersfrom three locations were taken at (Kia, Waghina and Mboli) but only five were collected atMarau, while only a single shell was available from Malaita. All of these shells werephotographed and have been archived at the Nusa Tupe Research Station of the WorldFishCenter.2.3 Remote Video CensusRemote video censuses were undertaken at Malaita (Kau), Marau, Sandfly Passage, Kia andWaghina. The system comprised a Deep Blue Pro II colour video camera mounted onto analuminium sled and connected to a Sony VRD-VC30 DVD recorder and a 45M068X LCDscreen. Two water-proof laser pointers were attached to the camera and aligned in parallel,160 mm apart. These spots were readily viewable under all lighting conditions and alloweddimensional calibration of the images. Tows were initially planned for 30 minutes, but atMalaita and Marau this was found to be optimistic. In practice a series of 10 minute towswas found to be most effective in allowing straight line navigation, minimum disruptionfrom encounters with irregular bottoms and ensuring data security. After Marau, weattempted to obtain three ten minute tows from each of three locations. Where possible wetargeted a depth range deeper than the dive tows, typically 40-50 m. At those locationswhere video treansects were made, the GPS co-ordinates (latitude and longitude), durationof tow, bottom time, depth range surveyed and length of each transect were noted(Appendix 2).The Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 6