Some physical and chemical characteristics of bottom sediments in the South China Sea, Area I: Gulf of Thailand and east coast of Peninsular Malaysia

Investigations on horizontal and vertical distribution in levels of total organic matter contents (TOM), acid volatile sulfides contents (AVS), and water contents (WC) of bottom sediments from the eastern and western parts of the Gulf of Thailand and the eastern part of the Peninsular Malaysia have been carried out during 5-28 September 1995 and 24 April to 17 May 1996 by M.V. SEAFDEC. The overall results indicated comparatively low amount of organic matters and sulfides deposited in the sediments. Considering on the vertical profiles, coupled efforts of low rate of sedimentation of the organic matters and high rate of their decomposition should play an important role providing fast diagenesis of their organic substances. Nevertheless, the particulate matters which had settled onto the sea bed and formed the sediments can be remarkably observed to accumulate in two major zones in the Gulf of Thailand; one in the central part of the upper gulf (around Station 7) and another one in the western part of the gulf, near Samui Island (around Station 23). Such an accumulation pattern was considered to be directly controlled by the bottom topography and current effort. The accumulation of organic materials there also implied the mode of biological fishery resources. High abundant of organisms in the benthic community should be observed. Moreover, according to biogeochemical interaction between the sediment-water interface, phytoplankton production in the overlying water column should be enhanced and, consequently, a congregation of organisms in the upper trophic levels especially those of fish species were accordingly expected. Future assessment for development of the fishery resources in the Gulf of Thailand and the eastern part of Peninsular Malaysia has been discussed

Nutrient diagenesis in sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalam waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phosphate concentrations in pore water were in the ranges of 0.05 to 77.12 µg at NO3--N/L and 0.07 to 13.13 µg at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 µg at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah and Brunei Darussalam. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management

Biomass estimation by hydro-acoustic methods in the Gulf of Thailand and Peninsular Malaysia

The abundance of fisheries resources and their structure in the Gulf of Thailand and East coast of Peninsular Malaysia were investigated during the SEAFDEC Collaborative Research Survey. Hydro-acoustic surveying using a scientific echo sounder model FQ-70 was conducted to estimate the fish abundance and biomass. Two survey cruises were carried out by M.V.SEAFDEC during the pre and post-northeast monsoon seasons. The scientific echo-sounder was equipped with an echo-integrator and two quasi-ideal beam transducers with operating frequencies of 50 and 200 kHz. The volume back scattering strength (SV) of the fish schools were collected from the layer of water at a depth from 10 m to the bottom along the track of survey cruise. The estimated biomass measured by high frequency shows clearly that a high concentration is observed at the upper and middle part of the Gulf of Thailand and the border area between Thailand and Malaysia waters during the pre-northeast monsoon season. Whereas, high biomass concentration shows only in the middle part of the Gulf of Thailand during the post-northeast monsoon season

The Catalogue of Core Logging Sheets for Sediments of the Western Gulf of Thailand and Eastern Peninsular Malaysia in April 1996

Oceanographic survey on bottom sediment characteristics has been conducted in the sea areas in the western part of the Gulf of Thailand and the Eastern Peninsular Malaysia as one research program under the collaborative research project between SEAFDEC’s Training Department (TD) in Thailand and the Marine Fishery Resources Development and Management Department (MFRDMD) in Malaysia. This research program was carried out because of the interest in the nature of sea bottom in an area of which only few detail information exist. The information such as vertical distribution of different types of sediments, relationships among sediment physico-chemical process, biological processes in the water column and other fishery resources were of primary interest. The sediment samples surveyed in the Western Gulf of Thailand and Eastern Peninsular Malaysia during April 1996 were immediately recorded for their visible characteristics on board of M.V. SEAFDEC in core logging sheets by using general lithological symbols. The catalogue of core logging sheets here could thus be applicable to easily distinguish the vertical profiles of those bottom sediments. Such visible characteristics could also simply reflect both physic-chemical and biological compositions of bottom deposits in the designated areas

Nutrient Diagenesis in Sediments of the South China Sea, Area II: Sabah, Sarawak, and Brunei Darussalam Waters

Study on nutrient diagenesis and physico-chemical characteristics of bottom sediments of the Sabah, Sarawak and Brunei Darussalum waters had been carried out under the ongoing SEAFDEC Collaborative Research Project. The results indicated that organically enriched offshore sediments consisted high levels of pore water nitrate and phosphate concentrations. For the whole study area, the levels of nitrate and phopsphate concentrations in pore water were in the ranges of 0.05 to 77.12 ?g at NO3--N/L and 0.07 to 13.13 ?g at PO43--P/L, respectively. Upward diffusive fluxes of pore water nitrate widely changed in stations. At the nearshore area, the fluxes of pore water nitrate had an average of 26.5 mg at NO3--N/m2/d and were about one order of magnitude higher than those of phopsphate. However, phosphate upward fluxes were apparently high at deep areas off Sabah. Pore water ammonium concentrations were commonly very low but tended to be more accumulated at nearshore organically enriched areas. The ammonium concentrations for the whole study area ranged from non-detected level to 81.76 ?g at N/L. The nearshore stations showed very high upward fluxes of ammonium, which were nearly 10 times higher than those of nitrate and phosphate. Sedimentary organic levels were comparatively high in two distinct regions; (I) a shallow nearshore region of Sarawak, and (II) a deep offshore region of Sabah amd Brunei Darussalum. The sources of organic materials settled in Regions (I) and (II) were suggested to be derived from different origins. The Northeast monsoon can somewhat enhance organic accumulation in the nearshore region. Overall our results obtained from this study had been used to characterize the bottom sediments into three distinct regions and discussed for further fishery resource development and management

Biomass Estimation by Hydro-acoustic Methods in the Gulf of Thailand and Peninsular Malaysia

The abundance of fisheries resources and their structure in the Gulf of Thailand and East coast of Peninsular Malaysia were investigated during the SEAFDEC Collaborative Research Survey. Hydro-acoustic surveying using a scientific echo sounder model FQ-70 was conducted to estimate the fish abundance and biomass. Two survey cruises were carried out by M.V.SEAFDEC during the pre and post-northeast monsoon seasons. The scientific echo-sounder was equipped with an echointegrator and two quasi-ideal beam transducers with operating frequencies of 50 and 200 kHz. The volume back scattering strength (SV) of the fish schools were collected from the layer of water at a depth from 10 m to the bottom along the track of survey cruise. The estimated biomass measured by high frequency shows clearly that a high concentration is observed at the upper and middle part of the Gulf of Thailand and the boarder area between Thailand and Malaysia waters during the pre-northeast monsoon season. Whereas, high biomass concentration shows only in the middle part of the Gulf of Thailand during the post-northeast monsoon season

The Catalogue of Oceanographic Data of Northeast Indian Ocean

This catalogue contains some parts of the oceanographic data collected by MV.SEAFDEC during Cruise no. 17-10/1994, 18-11/1994, 19-1/1995, 20-2/1995, 21-2/1995, 28-10/1995, 29-1/1996, 30-2/1996, 37-9/1996, 39-2/1997 and 44-7/1997 between 1994-1997. These cruises were scheduled to carry out shipboard training for SEAFDEC trainees of various courses such as Fishing Technology, Marine Engineering, Hydroacoustic equipment use, Local fishermen, and Pelagic fishery courses and to conduct an oceanographic survey under the projects of Studies on fishing ground conditions along the cruise track of the training vessel. The survey areas were northeast Indian Ocean. The results reported in this catalogue are numerical sequences by catalogue number. The catalogue no. was created from the year, the month and the number of the station, the first numbers (two digits) being the year, the next two digits being the month and the last two represent the station number during that month: for example, Catalogue no. 941001 refers to the 1^st station during October in 1994