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Distribution and Abundance of Fish Larvae in the Gulf of Thailand
and South China Sea
BACKGROUND
In evaluating the factors contributing to the resilience of fisheries to the resource-related effects of high levels of fishing effort, and how spatial fisheries management tools could effectively contribute to building resilience in Southeast Asian fisheries, the Regional Working Group on Fisheries (RWG-F) has focused on the natural refugia concept in fisheries. Specifically, the group has considered the following “theoretical” natural refugia types and how they may relate to regional fisheries:
- Refugia related to depth stratification of the population or the selectivity of fishing gear causing parts of the population to have a very low probability of capture,
- Migrations to spawning area refugia located outside of the fishing grounds, and
- A refugia scenario where part of the population is located in the fishing ground, with another part of the population occupying areas that are not fished and providing a source of new recruits to the fished area.
Sixth Meeting of the Regional Working Group on Fisheries
During its Sixth Meeting in Sabah, Malaysia, 5th - 8th September, 2005, the RWG-F felt uncomfortable associating any of the above refugia scenarios with important fishes in the region, largely due to a lack of information about the biology and population dynamics of most species at that time. There was, however, consideration of the role of refugia in fisheries of other regions, with discussion of the example of high recruitment and catches of hake in the Mediterranean during the 1980s despite a complete lack of input/output controls and a high percentage of juvenile fish being caught by inshore trawlers. It was pointed out that it is believed this occurred due to larger spawning fish occupying deeper areas of the continental shelf in refugia created by the inefficiency of the fine inshore trawls for large fish, and making a major spawning contribution to the adjacent fishery.
Regardless of the lack of readily available regional examples of the role of natural refugia, the group agreed that the identification of such refugia should be the focus of efforts to establish management areas for regional fisheries as:
- It is “refugia” that most likely contribute to the resilience of fisheries to the effects of fishing,
- The concept is likely to be more easily understood by fishers and align closely with the traditional knowledge of fishers, and
- It may be easier to manage these areas with limited research and monitoring, control and surveillance resources than other technical-based measures.
Problems Identifying Natural Refugia in the Gulf of Thailand and South China Sea
Several members of the group have highlighted that they find it difficult to believe that many of the above-mentioned natural refugia remain in areas such as the Gulf of Thailand, especially considering the:
- Multi-gear/sector/jurisdiction nature of fisheries,
- The combined problems of over-exploitation and community dependence on fisheries,
- Reported ecosystem effects of fishing, and the
- Large scale fisheries habitat losses associated with the development of shrimp farming activities.
Accordingly, the RWG-F is of the opinion that it will be very difficult to base fisheries refugia on actual natural refugia, and is promoting the use of the RWG-F definition of refugia for the identification of fisheries refugia to “replace” those lost due to over-exploitation and the destruction of fisheries habitats. There is a common understanding that fisheries refugia relate to specific areas of significance to the life cycle of particular species, and that they should be defined in space and time, and serve to protect spawning aggregations, nursery grounds, and migratory routes.
Since it is not possible at this stage to describe any natural refugia for important species, the group believes that the action of establishing areas where management measures are applied to sustain important species during critical stages of their life cycle (e.g. nursery areas, spawning areas, migratory routes) is a reasonable starting point for a system of refugia and that the region should proceed on this basis. The group has indicated that they feel information needs will become apparent over time, enabling identification of future areas for research and the development of a better understanding of critical habitat-life cycle linkages.
Sixth Meeting of the Regional Scientific and Technical Committee
The Sixth Meeting of the Regional Scientific and Technical Committee in December 2005 recommended that the RWG-F focus part of its efforts on reviewing known spawning areas for pelagic and invertebrate species, with the aim of evaluating these sites as candidate spawning refugia. It was noted that by the RSTC that information regarding the spatial dynamics of pelagic fish and invertebrate populations, oceanographic features, fish behaviour, and fishing effort dynamics should be used to determine the optimum locations and sizes of spawning refugia in the Gulf of Thailand and South China Sea.
Joint South China Sea Project – SEAFDEC Meeting on Identification of Fish Spawning Areas
The development of a collaborative programme of technical consultations, working group meetings, and training workshops, aimed at strengthening efforts to establish a regional system of fisheries refugia, was discussed between the South China Sea Project and SEAFDEC during August 2006. In this connection it was agreed that it would be beneficial to convene a brief working meeting between representatives of the RWG-F and SEAFDEC’s Special Advisor and Research Scientist on the identification of fish spawning refugia. It was further agreed that the meeting would provide the RWG-F and SEAFDEC with an opportunity to develop a programme of work to (a) review past and ongoing fish early-life history research work, and (b) compile information on known spawning and nursery areas for significant fish species in the Gulf of Thailand and South China Sea.
This meeting was subsequently convened at the SEAFDEC Secretariat Office in Bangkok, Thailand on 25th September 2006. Dr. Yasuhisa Kato and Dr. Somboon Siriraksophon of SEAFDEC, and Christopher Paterson, the PCU Fisheries Expert, Khun Somsak Chullasorn, the Regional Fisheries Expert, and Khun Pirochana Saikliang, Fisheries Focal Point for Thailand participated in the meeting. The meeting discussed past research activities conducted in the 1970s and 1980s that had largely focused on the identification of spawning areas and migratory routes for Indo-Pacific Mackerel (Rastrelliger neglectus), round scads (Decapterus spp.), anchovy, and neritic tunas. It was noted and agreed that much of this information had been compiled in the Thai National Fisheries Report and is summarised in Annex 2 of document UNEP/GEF/SCS/RWG-F.8/5 “Information Collated by the Fisheries and Habitat Components of the South China Sea Project on Specific Locations Important to the Life-Cycles of Significant Fish Species”.
Recent Information Regarding the Distribution and Abundance of Fish Larvae in the Gulf of Thailand and South China Sea
Some limitations in the use of abovementioned research for the identification of spawning refugiawere noted during the course of the meeting, including reported ecosystem changes in the Gulf of Thailand over recent decades, and the fact that most data had been collected as part of short-term research activities. In this connection it was identified that data collected through ongoing research activities initiated by SEAFDEC in the late 1990s may provide a more recent and accurate information base for use in identify spawning and nursery areas.
SEAFDEC conducted a series of Marine Fisheries Resources Surveys from 1996-1999 in the Gulf of Thailand and South China Sea. These activities were part of the SEAFDEC Interdepartmental Collaborative Research Programme, and were implemented by the SEAFDEC Marine Fisheries Resources Development and Management Department, and the SEAFDEC Training Department, in cooperation with national fisheries departments and research institutes.
The main surveys of interest to the task of identifying fish spawning areas in the Gulf of Thailand and South China Sea were conducted using the SEAFDEC Research Vessel M.V. SEAFDEC in the following areas:
- Gulf of Thailand and East Coast of Penisular Malaysia (81 stations)
- West Coast of Sabah, Sarawak, and Brunei Darussalam (79 stations)
- West Coast of Luzon, Philippines (31 stations)
- Vietnamese Waters (58 stations)
The surveys focused on the collation of important fisheries-related information including the distribution and abundance of key resources, the fisheries biology of significant species, the primary production of coastal oceans (including distribution and abundance of phytoplankton), fisheries oceanographic information, and other environmental information. The information and data collected during the surveys was subsequently analysed and presented during a series of regional technical seminars convened from 1997-2000.
A total of 249 larval fish samplings were conducted using bongo nets in the period of the post-northeast monsoon (April-May) from 1996-1999. Information collected from fishing communities, processors, and past research suggests that many economically important species in the Gulf of Thailand and South China Sea spawn during the period from January to March each year. As such, it was agreed during the 25th September meeting that the results of past and ongoing larval fish surveys conducted by SEAFDEC during the post northeast monsoon may assist the RWG-F in developing a better understanding of spawning (sources) and nursery (sinks) locations for important species.
In this connection, Dr. Somboon of SEAFDEC delivered a presentation during the Eighth Meeting of the RWG-F on the distribution and abundance of larval fish in the South China Sea and Gulf of Thailand during the post northeast monsoon periods from 1996-1999. Species based maps of the distribution and abundance of the larvae of important pelagic and demersal fish species were developed and are presented below. The key conclusions from Dr. Somboon’s presentation included:
- There were four (4) main areas with high larval fish abundances (>6,000 individuals per m3). These were the upper Gulf of Thailand, Thailand (Lat 12.30N Long 100.25-100.75E), the east coast of Samui Island, Thailand (Lat 9.30N, Long 100.25E), the Miri Coastal Area of Sarawak, Malaysia (Lat 4.30N, Long 114.00E), and the Quang Tri Coastal Area of Viet Nam (Lat 15.00N, Long 107.00E).
- The larvae of four (4) groups of species were highly abundant in the upper Gulf of Thailand. These were the anchovies (Stolephorus spp.) (≈2,000 individuals per 1000m3), the jacks and trevallys (Caranx spp.) (≈1,000 individuals per 1000m3), the scads (Decapterusspp.) (≈500 per 1000m3), and the Yelllowstipe scad (Selaroides leptolepis) (≈500 per 1000m3).
- Nearly all Sardinella larvae (Sardinella spp.) were concentrated off the east coast of Thailand’s Samui Island and the transboundary area between Thailand’s Narathiwat Province and Kota Baru in Malaysia.
- The larvae of mackerels (Rastrelligerspp.) were observed to be most abundant adjacent to Samui Island. Larvae of this group were less observed in lower abundances in the southern Gulf of Tonkin in Viet Nam’s Quang Tri Province and at the Mekong River mouth in Viet Nam.
- The larvae of Spanish mackerel (Scomberomorus spp.) were shown to be most abundant at the lower end of the Gulf of Tonkin and adjacent to Con Dao Island in Viet Nam.
- The abundances of most tuna larvae were very low, except for Euthynnus affinis which were highly abundant in the Gulf of Tonkin, Viet Nam. The high abundance areas for E. affinis were located in the immediate vicinity of underwater sea mounts near the entrance to the Gulf of Tonkin.
- In terms of demersal species, the upper Gulf of Thailand appeared to be important for the larvae of most economically important species.
- There were three main sites utilised by fish larvae of important species: (1) Gulf of Tonkin, Viet Nam (Euthynnus affinis, Scomberomorus spp., Rastrelliger spp.), (2) Upper Gulf of Thailand (Stolophorus spp., Decapterus spp., and Caranx spp.), and (3) Samui Island (Rastrelliger spp., Sardinella spp., and Nemipterus spp.).
- Very few larvae of any important fish species were observed along the east coast of Peninsular Malaysia. The member participating in the meeting on behalf of the Malaysian Department of Fisheries has noted that larvae of very few economically important species are known to utilise this area. Similarly, the larvae observed in areas the Malaysian States of Sarawak and Sabah were of less important genera from the family Gobiidaeand Monacanthus spp. (Pipefish).
- The linking of an oceanographic circulation model for the South China Sea to the distribution and abundance of fish larvae would assist the Working Group in developing a better understanding of the sources and sinks of fish larvae for economically important species.
- Surveys conducted during the 1970s identified high relative abundances of scad (Decapterus spp.) larvae in the central Gulf of Thailand. The 1996-1999 surveys identified high relative abundances of scads in the upper Gulf of Thailand, whereas very few larvae of this group were observed in the central Gulf. Recent maps of the central Gulf of Thailand show that the areas utilised by the scads during the 1970s have been subjected to large-scale development in support of the oil and gas industry.
Maps of the Distribution and Abundance of Larval Fish in the Gulf of Thailand and South China Sea during the Post Northeast Monsoon Periods from 1996-1999
All Larval Fish Combined
Figure 1 The distribution and relative abundance of fish larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999) (all larvae combined).
Pelagic Fish Species
Figure 2 The distribution and relative abundance of fish larvae of jack and trevally (Caranxspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 3 The distribution and relative abundance of scad (Decapterusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 4 The distribution and relative abundance of kawakawa (Euthynnusaffinis) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 5 The distribution and relative abundance of skipjack tuna (Katsuwonus pelamis) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 6 The distribution and relative abundance of tuna (Thunnus spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 7 The distribution and relative abundance of mackerel (Rastrelliger spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 8 The distribution and relative abundance of sardinella (Sardinella spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 9 The distribution and relative abundance of Spanish mackerel (Sardinella spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 10 The distribution and relative abundance of yellowstripe scad (Sardinella spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 11 The distribution and relative abundance of baracuda (Sphyraenaspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 12 The distribution and relative abundance of anchovy (Stolephorusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Demersal Fish Species
Figure 13 The distribution and relative abundance of tropical snapper (Lutjanusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 14 The distribution and relative abundance of threadfin bream (Nemipterusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 15 The distribution and relative abundance of goatfish (Upeneusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 16 The distribution and relative abundance of big-eye cod (Bregmaceros rarisquamosus) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 17 The distribution and relative abundance of Callionymus spp. larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 18 The distribution and relative abundance of cardinalfish (Apogonspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 19 The distribution and relative abundance of toungesole (Cynoglossusspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 20 The distribution and relative abundance of flounder (Engyprosoponspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 21 The distribution and relative abundance of silver biddy (Gerresspp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 22 The distribution and relative abundance of Gobiidae larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 23 The distribution and relative abundance of ponyfish (Leiognathus spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 24 The distribution and relative abundance of filefish (Monocanthus spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 25 The distribution and relative abundance of bullseye (Priacanthus spp.) larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 26 The distribution and relative abundance of Sciaenidae spp. larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 27 The distribution and relative abundance of Serranidae larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 28 The distribution and relative abundance of Saurida spp. larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
Figure 29 The distribution and relative abundance of Tetraodon spp. larvae in the Gulf of Thailand and South China Sea during the post northeast monsoon period (1996-1999).
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