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SECTION
3 NATURAL RESOURCES CAPITAL STOCK
| 3.3 |
Agriculture
and Fisheries |
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| Pressures
on Mariculture |
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| 3.3.2.5 |
From
1980 to 1997, 481 red tides have been recorded
with most occurring in the eastern WCZs
of Tolo Harbour and Channel (48% of occurrences),
Mirs Bay (16%), Port Shelter (13%) and the
Southern WCZ (13%). A more detailed breakdown
of red tide occurrences since 1990 is included
in Annex F3,
for Hong Kong waters and for beaches. The
data from this table show that the greatest
incidence of red tides is from the months
of December to May with no discernible pattern
in the number or percentage of these occurrences
at bathing beaches. The annual numbers of
red tide occurrences have declined since
the start of the decade. In 1998, harmful
algal blooms resulted in significant losses
to the mariculture industry through several
fish kill events. Mariculture feeding practices
are thought to have lead to an accumulation
of nutrients on the seabed underneath the
mariculture rafts. The presence of such
nutrient rich sediments may at times encourage
algal blooms in the area which, when they
collapse, may result in depressed levels
of dissolved oxygen affecting the cultured
fish in the cages. Factors such as coastal
development, pollution and red tides (mainly
Harmful Algal Blooms) could be considered
as pressures acting on mariculture. Coastal
development may result in direct loss of
mariculture areas if the area is to be reclaimed
in order to provide additional land for
development. Construction activities associated
with coastal development could impose indirect
impacts to mariculture through deterioration
in water quality (eg elevation in sediment
levels) which, if serious, could cause fish
kills and hence a reduction in mariculture
production. However, pressures from coastal
development on mariculture are now unlikely
to be severe since gazetted Fish Culture
Zones (FCZs) are identified as sensitive
receivers when assessing environmental impacts
of a proposed project. It is understood
that under no circumstances should insurmountable
impacts to FCZs arising from proposed projects
be allowed to occur and, where necessary,
appropriate mitigation measures should be
implemented. Consequently, pressures from
coastal development are unlikely to have
influential impacts on the long term sustainability
of mariculture operations.
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| 3.3.2.6 |
Pollution
arising from the marine discharge of domestic
and agricultural wastes could lead to depletion
of dissolved oxygen in the water column
due to active decomposition of organic matter
and proliferation of micro-organisms. If
such perturbations to water quality are
serious and occur near mariculture areas,
subsequent impacts on production may occur.
However, with the implementation of pollution
abatement measures and the long-term monitoring
of marine water quality undertaken by the
EPD (since 1986), water quality conditions
have been closely tracked and undesirable
changes to water quality can be detected
and prevented. Consequently, insurmountable
impacts to mariculture arising from effluent
discharges are not expected.
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| 3.3.2.7 |
Red
tides, particularly Harmful Algal Blooms,
are known to impose pressures on mariculture
through their impact to cultured fish (see
Paragraphs 5.2.1.15 and 5.2.1.16 for effects
of red tides on water quality). In Hong
Kong, occasional damage by red tides on
mariculture has been recorded in the past
years. According to the AFCD Study on Red
Tide Monitoring and Management in Hong Kong,
there have been a total of 19 red tide related
fish kills recorded during the period 1975
to 1997 (Anderson et al 1999). On average,
there has been about one fish kill per year
with a maximum of four reported in 1980
and 1982. Most (79%) of the bloom-related
fish kills were reported from the Tolo Harbour/Channel
and Junk Bay/Port Shelter areas. Damage
by red tides on mariculture, though occasional,
can be disastrous. In March - April 1998
widespread algal blooms (caused by a red
tide species, tentatively identified as
Gyrodinium sp. hk98) caused fish kills at
many of the FCZs in Hong Kong. This is reflected
in a large decrease in annual production
of fish reared in Hong Kong from 2,960 tonnes
in 1997 to 1,200 tonnes in 1998. Therefore,
occasional red tides occurrences could have
short-term impacts on the sustainability
of mariculture but long-term influences
are not expected.
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Pressures
on Capture Fisheries Resources
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| 3.3.2.7 |
Recent
studies (ERM 1998a) suggest that intensive
fishing pressure, coupled with Hong Kong's
rate of infrastructure development and population
growth which has resulted in marine habitat
destruction and increased pollutant discharges
to the marine environment, have had an adverse
effect on the fisheries resources in Hong
Kong waters. Large-scale reclamation works
first initiated in the late 1980s have resulted
in the loss of important coastal fish habitats,
in particular spawning and nursery grounds
which support critical life stages. During
the same period, coastal water quality has
worsened due to construction activities and
increased industrial, sewage and other point
source discharges from the resulting development. |
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| 3.3.2.8 |
While
development and pollution effects have undoubtedly
contributed to this decline, fishing pressure
has also been a factor. Despite the decline
in marine fish stocks, Hong Kong's seabed
is even now subjected to heavy fishing pressure
which not only captures even juvenile fish
but also physically damages the seabed. Over
the past few decades, many fishers have converted
from traditional "junk"-style vessels
to more effective trawlers which are capable
of offshore fishing in Mainland waters. Therefore,
an increasing number of commercial fishers
are looking to distant waters to support their
activities and the HKSARG is currently assessing
the potential for developing a true offshore
fishing industry. |
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| 3.3.2.9 |
The
growth of the mariculture industry has in
some ways contributed to the decline of the
capture fisheries. Small or otherwise low
value fish captured by trawl in Hong Kong's
inshore waters are ground into fish meal and
used as feed at the mariculture rafts. In
turn the demand for high value table fish
has been in part met by the local mariculture
industry and in part by importation of live
reef fish from other areas of Southeast Asia.
This trade is somewhat controversial since
many operations deploy dynamite or cyanide
to stun and capture fish with the undesirable
side effects of killing coral and other small
fishes. It is thought that Hong Kong's extraordinary
demand for live marine fish, estimated at
60% of the total world demand, is perpetuating
the use of destructive fishing techniques
in countries which catch and supply these
fish (WWF 1999). Destructive fishing operations,
which are illegal in Hong Kong, have also
been reported locally, both outside and within
Marine Parks. |
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| 3.3.2.10 |
In
response to the degradation of Hong Kong's
own fisheries resources, the fishing and seafood
industries have already adapted to utilise
new sources of supply such as mariculture,
offshore fisheries, and live reef fish imports.
Despite the degradation of inshore fisheries
resources, they are still used to support
the local mariculture industry. For these
reasons, the remediation of Hong Kong's capture
fisheries natural capital stock is less a
question of sustainability than one of maximising
the value of the resource through careful
management. In addition to providing an economic
return, this enhancement is also expected
to realise benefits in terms of ecological
resources natural capital stock (Section
4) as well as scientific, existence and
recreational value of the stock (Section
7). |
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