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249
E. Wolanski (ed), The Environment in Asia Pacific Harbours, 249–259.
CHAPTER 16
ENVIRONMENTAL ISSUES IN THE GULF OF
THAILAND
GULLAYA WATTAYAKORN
1. INTRODUCTION
The Gulf of Thailand is a semi-enclosed tropical sea located in the South China Sea
(Pacific Ocean), surrounded by the countries Malaysia, Thailand, Cambodia and
Vietnam. The Gulf covers roughly 320,000 km². The boundary of the Gulf is
defined by the line from Cape Camau in southern Vietnam (just south of the mouth
of the Mekong River) to the coastal city of Kota Bharu on the east coast of
Peninsular Malaysia. It is relatively shallow; the mean depth is 45 m, and the
maximum depth only 80 m. The general shape of the Gulf’s bottom topography can
be considered elliptic parabolic. It is separated from the South China Sea by two
ridges that limit water exchanges with the open South China Sea. The first extends
southeast from Cape Camou for about 60 nautical miles with an average sill depth of
less than 25 m. The second ridge, which extends off Kota Bharu for approximately
90 nautical miles, has an average sill depth of 50 m. There is a narrow, deeper
channel between the two ridges with the observed depth of 67 m (Emery and Niino,
1963). The Gulf may be divided into two portions, Upper Gulf and Lower Gulf. The
Upper Gulf at the innermost area has an inverted U-shape. The Upper Gulf is the
catchment basin of four large rivers on the northern side and two on the western
coast. Numerous rivers discharge freshwater and sediment into the Gulf. Among
them, the Chao Phraya River has the biggest volume transport next to the Mekong
River. The average runoff per year of the Chao Phraya is 13.22 x 103 and that of
3
also discharged from these rivers, promoting primary productivity in the Gulf
Seasonal circulation in the Gulf of Thailand, deduced from oceanographic data
measured in 1993-1994, suggested that circulation the Gulf is generally weak and
variable. The mean circulation in the Gulf is forced by the South China Sea and not
by the local wind as previously suspected, a phenomenon particularly marked during
the Northeast monsoon when Mekong River water enters the lower Gulf
(Wattayakorn et al., 1998). During January to February, currents throughout the
Gulf are at their weakest, with little mixing of Upper and Lower Gulf water masses.
© 2006 Springer. Printed in the Netherlands.
the Mekong is 326 x 10 3
km . It is estimated that a considerable amount of nutrients is
3
km
(Piyakarnchana et al., 1990).
250 GULLAYA WATTAYAKORN
From March to August, anticyclonic (clockwise) circulation predominates in the
Lower Gulf, and penetrates into the Upper Gulf. In September, the circulation
direction reverses to cyclonic in the Lower Gulf, initially producing cyclonic current
in the Upper Gulf; by November the flow in the Upper Gulf becomes anticyclonic
(Figure 2). On the whole, the Gulf of Thailand is poorly flushed. In the Upper Gulf,
little mixing occurs between coastal and offshore waters. As a consequence of these
comparatively static conditions, contaminants discharged into the Upper Gulf may
accumulate. Variability in current directions may also result in the return of
contaminants that were initially flushed from an area.
Figure 1. Map of the Gulf of Thailand, showing major rivers discharging into the Inner Gulf.
The innermost part of the Gulf, in the vicinity of Bangkok, extends from Ban
Pak Thale, Phetchburi Province, in the west, north and east past the mouths of the
Maeklong, Thachin, Chao Phraya, and Bangpakong Rivers, to the town of Chonburi
in the southeast (Figure 1), is a large area of intertidal mudflats around the shores of
a huge, shallow sea bay forming the estuary of the four major rivers. The area
formerly supported extensive mangroves. While the largest areas have now been
cleared for aquaculture and salt pans, much secondary mangrove still remains and is
usually found as a narrow (10-l00 m) fringe along the seaward margins. Extensive
areas of low scrub are found in the brackish marshes along the landward edge. In
places, the open shrimp ponds and salt pans extend two to three km inland and,
together with the offshore mudflats, provide an important feeding and roosting area
ENVIRONMENTAL ISSUES IN THE GULF OF THAILAND 251
for many thousands of shorebirds (Erftemeijer and Jugmongkol, 1999). They are
also important fish breeding and nursery grounds, where many species reproduce.
The barriers on most major rivers, such as dams, weirs, and hydropower structures,
also have a major impact on migratory species that swim upriver to spawn.
Figure 2. Sketch of the water circulation in the Gulf of Thailand, deduced from the
oceanographic data during 1993–1994. (Adapted from Wattayakorn et al., 1998).
The Gulf of Thailand is an important resource to the national economy of
Thailand that receives income from the Gulf fishing industry, tourism and port
252 GULLAYA WATTAYAKORN
operations. Bangkok is the economic center of Thailand. The human population
density is extremely high, and there is an increasing amount of heavy industry,
especially extending eastwards from Bangkok along the lower reaches of the Chao
Phraya River. The Port of Bangkok, at the mouth of the Chao Phraya River, is the
transportation life-blood of the country. It serves as the main egress point for
agricultural export products from the country’s interior as well as access for raw
materials such as fertilizer, grain, steel and oil products. In addition, several deep sea
ports within the Gulf have been constructed to facilitate the huge increase in sea
transport of import and export cargoes. The deep sea port at Laem Chabang provides
relief to the congestion in Bangkok, while the ports at Songkhla and Map Ta Phut
offer ocean shipping alternatives to industries and resources within the Gulf of
Thailand.
Thailand’s population increased from 23 million in 1961 to 65 million by 2004.
The rapid increasing population with associated industrialization and economic
development in the coastal areas in the past two decades has resulted in construction
and planning of many coastal development projects. Many of these developments
have altered local coastal and estuarine processes, which have caused changes in the
shoreline and sediment processes. In addition, the Gulf of Thailand has been a
receptacle for agriculture; lumbering; ports and shipping; fishing and aquaculture;
human settlement; recreation and tourism for a long time. The marine waters and
coastal areas of Thailand, therefore, have been threatened by both the forces of
nature as well as by human activities. Foremost among these threats are siltation;
pollution from domestic and industrial wastes; heavy metals; agrochemicals,
particularly pesticides; pollution resulting from oil spills from tankers and from
onshore and offshore drilling for oil and minerals. In addition, the vast ecosystems
of mangrove forests, coral reefs, and intertidal flora and fauna of the country are
threatened by the conversion and/or reclamation of land for multipurpose uses and
by recreational activities. Therefore, the problems of the marine environment in the
Gulf of Thailand may be broadly divided into those of overexploitation of fisheries,
loss of habitats, and pollution. This paper will briefly deal with specific items under
these three headings.
2. OVER-EXPLOITATION OF FISHERIES RESOURCES
The Gulf of Thailand is among the productive areas of the South China Sea in which
Thai people are dependent on marine fisheries. The rising demand for fish from the
increasing population, for food and export, has led to the rapid increase in marine
fishery production in the country, especially in the seventies and eighties. In the
Gulf of Thailand, most of the pelagic fishery except Indian mackerel is fully
exploited. Almost all demersal stocks are also overfished including fish, shrimp,
squid, cuttle fish, and others (FAO, 1995). Overfishing of the inshore and coastal
waters has also been reported in many technical publications (Chullasorn and
Chotiyaputta, 1997; Jirapanpitat, 1992).
The marine capture fisheries in the Gulf are characterized by the use of multi-
gear by a large number of small-scale fishermen, to exploit a large number of fish
and other aquatic organisms. The Gulf trawl fisheries suffer from overcapacity, due
ENVIRONMENTAL ISSUES IN THE GULF OF THAILAND 253
to their uncontrolled growth in the late 1960s - early 1970s. Statistics from the
Department of Fisheries have shown that the coastal and inshore fishery resources
have been fully exploited since the early seventies (Supongpan, 1996). The massive
increase in trawling effort that occurred from the early 1960s on, and which resulted,
in the early 1980s, in a strong decline in catch per effort (CPUE), from about 290
Night-time CPUE has also declined drastically to less than half of its earlier value
from 57 in 1976 to about 21 in 1995 (Eiamsa-Ard and Amornchairojkul,
1997). Captured fisheries statistics (1986-1995) of Suratthani indicate that fishery
production of Bandon Bay area was greatly declined during this period. Most of
fish production was mainly trash fish resulting from excessive fishing effort, capture
of undersize fish as well as the destructive nature of the push net which was used as
the main fishing gear in the area (Wattayakorn et al., 1999). Changes in the species
and size composition of the catch are other clear evidence of the onset of
overfishing. Chullasorn and Chotiyaputta (1997) reported that the catch from trawl
surveys shows that 30% to 40% consists of trash fish. Of this trash fish, 30%
comprised of juveniles of commercially important species. Due to overfishing and
the resulting decreased availability of fish, subsistence and artisanal fishermen are
often forced into destructive fishing techniques such as blast fishing and poisons.
The use of such fishing techniques can result in lasting deleterious impact to the
marine environment, especially to coral reefs.
3. DEGRADATION OF COASTAL ECOSYSTEMS
3.1. Mangroves
Approximately 60% of the current population in Thailand (roughly 39 million
inhabitants) lives in coastal towns and villages. This leads to rapid coastal
development for industries and housing, and extensive coastal habitat destruction
and loss. Mangrove destruction is the most obvious and has probably had the
greatest loss. With Thailand’s developing economy, since the 1960s the mangrove
forests along the Gulf of Thailand have been reduced by 50-80% (Table 1). Mainly
shrimp farms, hotels, growing cities and other coastal developments, have replaced
them. Estimates of the amount of mangrove conversion due to shrimp farming vary,
but recent studies suggest that up to 50-65% of Thailand’s mangroves have been lost
to shrimp farm conversion since 1975 (Aksornkoae and Tokrisna, 2004; Charuppat
and Charuppat, 1997; Dierberg and Kiattisimkul, 1996). Mangroves are still being
cut down for agriculture, aquaculture, and coastal construction but at a much lower
rate. For example, mangrove forest in the Bandon Bay area was depleted by 30%
during the period of 1993-1998 as compared to 87% during 1961-1986, most of
which has been converted to shrimp ponds (Wattayakorn et al., 1999).
The high profits of shrimp farming resulted in the increase in the number of
shrimp farms and culture areas from about 6,000 farms in 1987, taking up an area of
45,000 hectares, to 28,000 farms covering 79,000 hectares in 1999 (DOF, 2001).
in 1963 to about 50 in the 1980s a nd 20-30 kg h-1
in the 1990s. kg h-1
kg h-1
kg h-1kg h-1
254 GULLAYA WATTAYAKORN
Rapid expansion of intensive shrimp farming along the coast, some of which
involved clear-cutting of mangrove forests, has caused many environmental
problems such as poor coastal water quality, deteriorating of marine resources, and
saltwater intrusion into nearby agricultural areas. The catastrophic collapses of
several shrimp farms in the Upper Gulf of Thailand in 1989 were attributed to poor
water quality originated from industrialization within the watersheds and to
pollution from the farms (Dierberg and Kiattisimkul, 1996). Many shrimp ponds are
abandoned after they become unprofitable, leaving vast areas unsuitable for
agriculture or other aquaculture activities.
Table 1. Comparison of the mangrove areas in Thailand in 1975 and in 1996. (Adapted from
Charuppat and Charuppat 1997).
Mangrove area 1975
(rai)*
1996
(rai)*
Decrease
(rai)*
Gulf of Thailand 756,250 216,741 539,509
Eastern Region:
Trat, Chantaburi, Rayong, Chonburi,
Chachoengsao 306,250 79,113 227,137
Central Region:
Bangkok, Samut Prakarn, Samut Sakhon,
Samut Songkhram, Petchburi, Prachuab Khirikhan 228,875 34,057 194,068
Southern Region:
Chumphon, Suratthani, Nakhon Si Thammarat,
Phattalung, Songkhla, Pattani 221,125 103,571 118,304
Note: 1 rai = 0.16 hectare
3.2. Coral reefs
Coral reefs are under stress in many areas in the Gulf, especially those near shallow
shelves and dense populations. Storms and monsoon waves are the major natural
causes of coral reef damage. Typhoon Gay hit southern Thailand in 1989 and caused
major damage to some reefs. Extreme low tides and coral bleaching are other natural
phenomena causing severe damage. The erosion that has resulted from logging has
killed coral reefs by increasing the turbidity of coastal waters, such that the coral
polyps no longer have enough light to photosynthesize metabolites and may even be
buried by increased sedimentation. Over 60% of all major reef groups in the Gulf of
Thailand have less than 50% live coral cover and there is increased algal growth
because of nutrient pollution from the land, including near the major tourist resorts
of Pattaya Bay and Samui Island (Chansang and Phongsuwan, 1993). Other
anthropogenic disturbances on localized coral reefs in the Gulf are boat grounding
and destructive fishing methods such as the use of dynamite and bottom-trawlers
(Sudara and Patimanukasem, 1991). Loss of coral reefs has long-term implications
because of the time that they take to recover.
ENVIRONMENTAL ISSUES IN THE GULF OF THAILAND 255
3.3 Seagrass beds
Seagrass beds are the least studied marine habitats compared to coral reefs and
mangroves. Seagrass beds in Thailand are more abundant in the Andaman Sea than
in the Gulf of Thailand. However, no comprehensive evaluation on the seagrass
cover in the country has been undertaken to date. Species of seagrass such as
Enhalus acoroides, Halodule pinifolia, and Halophila ovalis were reported in the
Gulf of Thailand. A survey of seagrass around Samui Island found degraded
seagrass beds in those areas where there were considerable industrial construction,
shrimp farming and land development (Poovachiranon et al., 1994). It is apparent
from the site surveys that economic activities are the main factor affecting seagrass
4. COASTAL AND MARINE WATER POLLUTION
Pollution has considerably degraded the coastal and marine environment, including
estuaries, of Thailand over the past three decades. Coastal and marine water
pollution in Thailand is mainly due to direct discharges from rivers, surface runoff
and drainage from port areas, domestic and industrial effluent discharges through
outfalls and various contaminants from ships. Urban centers in Thailand are often
located on coasts and estuaries and much of the domestic wastes and garbage is
dumped directly into the shallow coastal environment. Hence, rivers are generally
heavily contaminated with municipal sewage, industrial effluent and sediments.
The primary sources of marine-based pollution are offshore oil and gas
operations, wastes from maritime transportation, shipping and oil spills. For land-
based pollution, the primary sources are domestic sources, industrial development
and tourism areas, especially beach resorts and agriculture and aquaculture activities
(Piyakarnchana et al., 1990). Land-based sources contribute some 70% of the
pollutants, mostly from domestic sources. An estimated volume of more than
200,000 tonnes of waste quantified as BOD is discharged into the Gulf each year
(Chongprasit and Srinetre, 1998). A smaller quantity of industrial waste consisting
of the
land-based contaminants are delivered into the Gulf by the four large rivers at
the head of the Upper Gulf. In general, water quality is lower than acceptable
standards in the Inner Gulf region, especially at the mouths of the four major rivers,
the popular tourist spots along the coast, and near certain islands. Water quality is
deteriorating due to increasing inputs of nutrients from the increased use of
fertilizers in agriculture, the mariculture industry and from household sewage. This
chapter will address some current problems i.e. eutrophication (red tides) and oil
pollution in the Gulf of Thailand.
4.1. Red Tides
Primary production prevailing in the Gulf of Thailand is known to be relatively high,
with a recent boost by increased nutrients from rivers and shrimp farms, which in
turn leads to increasing occurrences of phytoplankton blooms (or “red tides”),
depletion (Nateekanjanalarp and Sudara, 1992).
of more toxic chemical substances is also released into the Gulf. About 50 %
256 GULLAYA WATTAYAKORN
oxygen depletion events, food poisonings and other pollution effects, particularly in
the Inner Gulf (Eiamsa-Ard and Amornchairojkul, 1997; Longhurst, 1998;
Piyakarnchana, 1999).
The occurrence of red tides in Thailand was first reported in 1957. In the past,
red tides were regarded as natural phenomena and there was no serious impact of red
tides on the marine environment or organisms. However, its frequency has been
increasing in recent years. Noctiluca scintillans and Trichodesmiun erythraeum were
the two species of plankton that frequently bloom in the Inner Gulf (Suvapeepan,
1995). Blooming of Noctiluca sp. usually changes the apparent color of water into
dark green. The bloom of Trichodesmium sp. changes the apparent color of seawater
into yellow green color and then to red brown. The algal blooms caused by both
species of phytoplankton have no direct harmful effects on fish and shellfish.
However the heavy blooms can result in sudden reduction of dissolved oxygen and a
high amount of ammonia concentration in the water, which in turn sometimes lead
to fish kills. A large bloom of Noctiluca sp. caused a mass mortality of fish at
Sriracha Bay in August, 1991 and along the Pattaya Bay in August, 1992 (Sukasem,
1992). Blooming of diatoms i.e. Rhizosolenia sp. and Chetoceros sp. was also
reported to occur as a result of eutrophication in the Inner Gulf (Suvapeepan, 1995).
According to the survey by the Aquatic Resources Research Institute,
Chulalongkorn University (2003), 97 incidents of red tides were recorded in the
Gulf of Thailand from 1957 to 2001. To date, there is only one incident of paralytic
shellfish poisoning (PSP) recorded in Thailand, in May 1983 after consuming the
contaminated green mussels (Perna viridis) in the red-tide area of the Pranburi River
mouth. Sixty-three people were ill and one died because of this incident
(Tamiyavanish, 1984). The causative organism of that incident could not be
established. Since then, all the phytoplankton blooms recorded in Thailand are
harmless to humans.
4.2. Oil pollution
Oil pollution in the Gulf of Thailand has risen with industrial development in coastal
regions. The shipping of oil coupled with increasing emphasis on offshore oil
exploration makes the Gulf of Thailand extremely vulnerable to oil pollution.
Wattayakorn (1986, 1987 and 1991) has reported chronic petroleum hydrocarbon
contamination in coastal waters. Pollution was believed to originate primarily from
the discharge of oil from small coastal boats, via urban, industrial, refinery and
sewage effluent. Additional oil contamination could also originate from maritime
transportation of crude and refined oil through the region, as a result of the discharge
of ballast water from tankers. Increased pollution in the form of tarballs and oil
slicks has been observed in the past years (Wattayakorn et al., 1998). The
deleterious effects on the marine environment and living resources as a result of the
growing frequency of oil spills (due to both constant deballasting activities and
accidents such as collision in shallow waters) have caused public concern and
gained widespread attention in environmental protection in Thailand.
The accidental oil spills have been frequently reported along oil transport routes,
at points of discharge and loading of oil carriers. There have been over 50 oil spill
ENVIRONMENTAL ISSUES IN THE GULF OF THAILAND 257
accidents reported to occur in the Gulf during 1973-2002. Frequent spills were
found at the mouth of the main entrance to the Bangkok Port (Chao Phraya River
mouth) and Laemchabang Port (Chonburi Province). These oil spills represent the
greatest source of petroleum related pollution in the Gulf. These incidents are
expected to continue because of insufficient understanding of navigational routes
and inadequate contingency plans. A list of large oil spill accidents that have
occurred recently in the Gulf can be found in the Table 2.
Table 2. Recent major oil spill accidents in the Gulf of Thailand.
Date Oil type
Volume
(tonnes) Location Cause
6 Mar 1994 Diesel 400 Chonburi Province Collision of tanker and
container vessel
30 Oct 1996 Crude Oil 160 Rayong Province Leaking during loading
15 Jan 2002 Diesel oil 230 Chonburi Province Grounding
17 Dec 2002 Bunker Oil 230 Chonburi Province Collision of tanker and
container vessel
Under normal operations, most cargo and oil/gas ports are not major sources of
pollution. Only in fishing ports, where regulations on pollution control are difficult
to implement on small boats, is oil pollution from fuel/lubrication oil dumping and
bilge water discharge seen. Fishing ports exist in every coastal province and they are
usually near to major urban areas, thus making it difficult to separate the
contribution from the two sources. There are probably over 40,000 fishing boats of
various sizes registered and operating in the Gulf of Thailand. The used lubricating
oil from these fishing boats is believed to be illegally dumped into the sea. In
addition, leaks and spills of fuel (diesel) oil during filling and transfer also occur.
There is insufficient institutional and administrative capacity to ensure
environmentally responsible maritime practices. There is also a prevalence of
inadequate skills to detect, control and enhance areas of spills.
5. MANAGEMENT APPROACHES
Despite the growing awareness and concern of the public, coastal and other aquatic
ecosystems continue to be degraded by pollution and unsound forms of utilization.
Scientists have been conducting research and monitoring activities on the Gulf for
decades. These activities were typically geared for a specific need, limited in
coverage, and failed to provide an overall picture of the Gulf's condition. There is
still a poor understanding of the biological, physical, chemical and socio-economic
In addition, politicians and the general public are not aware of the potential value of
marine science to society.
However, several measures have been taken for protection and conservation of
marine resources in the Gulf. Since 1972, trawlers are prohibited from an area
within 3 km from the shoreline, and within a perimeter of 400 m of any stationary
fishing gear. In 1984, an area of about 26,400 km2 in the Gulf was declared as a
conservation area, prohibiting fishing by all gear types during spawning season from
258 GULLAYA WATTAYAKORN
15 February to 15 May (Phasuk, 1994). To provide protection of endangered and
threatened species, the Department of Fisheries issued regulations prohibiting the
catching of sea turtles, the collection of their eggs and the export of sea turtle shells.
Catching of dugongs and collection of corals are also prohibited. The Department of
Fisheries also emphasizes the rehabilitation of fishing grounds, and promotes
artificial reef projects to create protected habitats for marine life. However,
enforcement of these regulations is far from effective (Phasuk, 1994). Royal
Forestry Department (RFD) has also established and managed several marine
national parks, and prohibited some fishing activities in certain areas.
Economic measures have been introduced to support the prevention of
environmental problems. Incentives such as import tax reduction for
environmentally friendly equipment and machines, recognition for companies that
operate in an environmentally friendly manner, and use of the polluter pays principle
(PPP) to encourage voluntary action on pollution prevention in private companies.
An environmental fund was set up and managed effectively as a financial support
for environmental liability and cleanup. The budget derived from the energy
conservation fund was also used to conduct the energy saving campaign.
Other government activities undertaken include education and the dissemination
of environmental knowledge through the media. The government also encourages
more involvement from the private sector and non-government organization
(NGOs). Many obsolete environmental laws and regulations were amended to suit
the current situation. Moreover, the government attempted to issue several
significant laws such as the Community Forest Act and Water Resource Act. The
Thai government has shown its commitment to international environmental
problems by finalizing its ratification of the Convention on Biodiversity while
implementing the other ratified conventions. These activities will all help to alleviate
environmental problems in the future.
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