2.                  Mitigation objectives

 

2.1       Site Specific Target Habitats

 

2.1.1        The principal aim of the mitigation is the provision of suitable habitat for target species, rather than the restoration of specific habitats of intrinsic ecological value. Accordingly, the habitat target for the mitigation areas is the enhancement, creation and maintenance of at least 27.1 ha of fishponds and 4.9 ha of marshland in Favourable Condition for target Species of Conservation Importance.

 

2.1.2        It is recognised that using only avifauna as the measure of success of the managed wetland is unreliable because of the highly temporal nature of the species and the uncertainty of the impact of external factors such as availability of food sources, human disturbance and predator activity, on avifauna activity. In addition to avifauna, other more stable targets (with less temporal variation) have therefore been set, that reflect the habitat requirements of the target species. Such targets include the increase in shallow feeding areas, benthic composition, water quality, fish stocks and vegetation status and distribution. These habitat related targets are described in Section 2.4.

 

2.1.3        The definition of Favourable Condition of the habitat is dependent on the target species for mitigation and their specific requirements. These are described below.

 

2.2              Site Specific Target Species

 

2.2.1        Although avifauna are not considered to be the most reliable indicator of success, it is recognized that they are a key component of the ecosystem and need to be monitored as such. A full list of species that are considered to be targets for the mitigation measures and recommended measurable performance targets for each are listed below in Table 2.1. Species are considered to be targets for the Lok Ma Chau Station area mitigation area either if they are Species of Conservation Importance occurring within the area to be impacted by the construction of the Lok Ma Chau Station and the Spur Line within the Deep Bay Wetland Conservation Area or are good indicators of overall wetland ecological value (e.g. dragonflies and amphibians). Definition of Species of Conservation Importance follows the EIA Report (BBV 2000) with the following exceptions. Eurasian Otter which is restricted to the Deep Bay area in Hong Kong where it is rare (Reels 1996) has been added to the list as a consequence of a sighting made of this species during baseline fieldwork during winter 2000-01. This species is considered to be “Regionally Threatened” by Fellowes et al. (in press). Similarly, Chinese Bullfrog, which was recorded during baseline fieldwork during 2000-01, has been included as a Target Species in view of its Regionally Threatened status (Fellowes et al. in press) and its being an appropriate ecological indicator species.

 

2.2.2        This list of target species (and hence other aspects of the HCMP) will require amendment in the light of any changes to the list of Species of Conservation Importance that may be included in final EIA for the revised Spur Line alignment.

 

2.2.3        Regularly occurring wetland species that are either globally threatened, regionally important or threatened in Hong Kong, because they have a restricted range and/or are declining in numbers, are considered to be the main Target Species and are, therefore, the principal focus for the wetland mitigation design and long-term management requirements.

 

2.2.4        The baseline survey showed that Greater Spotted Eagle did not occur regularly within the Lok Ma Chau station area during 2000-01. Nevertheless it is considered to be a key target species since it is globally threatened and its Hong Kong population is restricted to the Deep Bay area and is regionally important. Moreover, the baseline survey showed that its habitat requirements could be accommodated within the proposed wetland mitigation area without compromising objectives for other species.

 

2.2.5        As described in the EIA report, large species of ardeid, such as Great Egret and Little Egret, as well as Black-faced Spoonbills and the globally threatened Imperial Eagle and Greater Spotted Eagle are likely to be most susceptible to disturbance from the operation of the railway and station. Therefore, because these species may not fully benefit from the mitigation measures being placed alongside the station, mitigation within the more distant fish ponds will be additionally targeted to these species.

 

2.2.6        In contrast, many smaller species of birds, particularly reedbed passerines, reptiles, amphibians and invertebrates are unlikely to be affected by disturbance or the presence of the large railway station buildings. Mitigation alongside the station complex will therefore focus on the creation of reedbed and other marshland habitats that will benefit such species.

 

2.2.7        It is considered that the provision of wetlands habitats that are suitable for the wide range of target species listed below will also create suitable habitats for a wide range of other taxa and contribute to the overall ecological and biodiversity value and integrity of the Wetland Conservation area.

 


Table 2.1

Wetland mitigation performance targets for target species in the

Lok Ma Chau / San Tin Station area

 

Species

Target

Notes

SPECIES OF CONSERVATION IMPORTANCE

Globally Threatened Species

Black-faced Spoonbill

Doubling of baseline.*

Regular occurrence during winter 2000-01 but not previously.

Greater Spotted Eagle

Recorded.

Not at present a regularly occurring species but included as a target species (c.f. para. 2.2.2).

Imperial Eagle

Recorded.

 

Japanese Yellow Bunting

Recorded at least one year in four.

Not a regularly occurring species in the area. Irregular occurrence in Hong Kong.

Regionally Important Species

Eurasian Otter

Recorded on average once per 12 month period.

Target reviewed if additional fieldwork shows that it is of regular occurrence in the area.

Black-winged Stilt

Doubling of baseline.*

 

Common Teal

Doubling of baseline.*

 

Eurasian Coot

Doubling of baseline.*

Not regular in the area to be impacted by the station or the mitigation area, though regular in the Lok Ma Chau area.

Great Cormorant

Doubling of baseline.*

 

Chinese Pond Heron

Doubling of baseline.*

 

Great Egret

Doubling of baseline.*

 

Grey Heron

Doubling of baseline.*

 

Little Egret

Doubling of baseline.*

 

Red-billed Starling

Doubling of baseline.*

 

 Chinese Bullfrog

Doubling of baseline.*

 

Locally Important Species

Common Snipe

Doubling of baseline.*

 

Common Stonechat

Doubling of number of birds recorded in other commercially operated fishponds in the area.

 

Pallas’s Grasshopper Warbler

Doubling of number of birds recorded in other commercially operated fishponds in the area.

Not regular in the area.

Pintail Snipe

Doubling of number of birds recorded in other commercially operated fishponds in the area.

Species not separable in the field.

Swinhoe’s Snipe

Zitting Cisticola

Doubling of number of birds recorded in other commercially operated fishponds in the area.

 

ECOLOGICAL INDICATOR SPECIES

Dragonflies

Agriocnemis spp.

Onychargia atrocyana

Ischnura senegalensis

Ceriagrion auranticum

Anaciaeschna jaspidea

Nannophya pygmaea

Nannophyopsis clara

Brachydiplax chalybea

Brachythemis contaminata

Orthetrum luzonicum

Neurothemis tullia

Neurothemis fulvia

Palpopleura sexmaculata

Rhodothemis rufa

Rhyothemis variegata

Urothemis signata

30% of species present and breeding after 2 years and 60% of species present and breeding after 5 years.

Indicator species for freshwater marsh.

Anax guttatus

Anax parthenope

Ictinogomphus pertinax

Sinictinogomphus clavatus

Epopthalmia elegans

 60% of species present and breeding after 5 years.

Species of large ponds with permanently high water levels (unable to tolerate seasonal drain down due to larval stage of more than one year).

Amphibians

Bufo melanostictus

Kalophrynus interlineatus

Microhyla ornata

Microhyla pulchra

Polypedates megacephalus

Rana guentheri

Rana limnocharis

Rana macrodactyla

Rana taipehensis

 

50% of species present and breeding after 2 years; 75% of species present and breeding after 5 years.

Indicator species for freshwater marsh habitat. Note that Rana rugulosa is treated separately as a Key Target Species.

 

Note: Black-naped Oriole, Richard’s Pipit and Japanese Quail are not included as target species as these do not use the target wetland habitats.

 

*          Baseline considered to be taken from waterfowl counts in HK BWS Ramsar Site Waterbird Monitoring Programme. Control sites will be selected for monitoring and the data collected during the monitoring will be used, in addition to the baseline data, for comparison of bird usage in the enhanced fish ponds.

 

 

2.3              Specific Requirements for Target Species

 

2.3.1        All target species are freshwater specialists, or wetland specialists. Some of these have more specific habitat requirements, and although the design caters for such species the range of micro-habitats, water levels, and vegetation types will provide foraging or roosting habitat for all target species (see Table 2.3).

 


Table 2.3

 

Summary of Habitat Requirements of Target Species of Conservation Importance

 

Key: habitat important for F = Foraging; R = Roosting; B = Breeding.

 

Species

Deep water

Shallow water

Muddy vegetation free margins

Reedbeds

Other emergent / marsh vegetation

Bare or sparsely vegetated bunds

Amphibians

 

F,B

F,B

F,B

F,B

 

Reptiles

 

F

F

F

F

F,B

 Eurasian Otter

F

F

F

F

F

 

Black-faced Spoonbill

 

F

F

 

 

R

Greater Spotted Eagle

 

F

 

 

F

F

Imperial Eagle

 

F

 

 

F

F

Japanese Yellow Bunting

 

 

 

F,R

F,R

F

Red-billed Starling

 

 

F

 

F

F

Great Cormorant

F

 

 

 

 

 

Chinese Pond Heron

 

F

 

F,R

F

 

Great Egret

 

F

 

 

F,R

 

Little Egret

 

F

 

 

F

 

Common Teal

F

F

 

F,R

 

 

Eurasian Coot

F

F

 

 

 

 

Black-winged Stilt

 

F

F

 

 

 

Grey Heron

 

F

 

 

F

 

Northern Hobby

 

 

 

 

 

 

Pheasant-tailed Jacana

 

F

 

 

F

 

Common Snipe

 

 

F

 

F,R

 

Pintail Snipe

 

 

F

 

F,R

 

Swinhoe's Snipe

 

 

F

 

F,R

 

Richard's Pipit

 

 

F

 

 

F

Bluethroat

 

 

F

F,R

F,R

 

Common Stonechat

 

 

 

F,R

F,R

F

Zitting Cisticola

 

 

 

F,R

F,R

 

Chestnut Bittern

 

F

 

 

F,R

 

Pallas's Grasshopper Warbler

 

 

 

F,R

F,R

 

2.3.2        Detailed accounts of the habitat requirements of main Target Species are provided below.

 

            Black-faced Spoonbill

 

2.3.3        Black-faced Spoonbills have been subject of a number of studies in Hong Kong (notably Anon. (1999), Melville et al. (1999), Anon (in prep.a), Anon (in prep.b)). In addition, when it was discovered during baseline fieldwork that Black-faced Spoonbills were utilising drained ponds  at Lok Ma Chau during winter 2000-01, their use of this area was subject to additional specific survey efforts (BBV 2001a, BBV in prep.).

 

2.3.4        Black-faced Spoonbills are tactile feeders. Feeding takes place in turbid water bodies with a flat or gradually sloping fine sediment bottom with water depths from 5 – 23 cm. (Yu and Swennen 2001). In Hong Kong these requirements are met in the intertidal mudflats in Deep Bay, as well as in fish ponds and gei wai. The relative importance of intertidal areas and fish ponds and gei wai is influenced by tidal regime and pond management, with the latter habitats being particularly important during adverse weather and when ponds are drained for harvesting (Anon in prep.a, Yu and Swennen 2001). Black-faced Spoonbills largely feed on small prey items, especially shrimps Palaemonetus sp. and Mosquito Fish Gambusia affinis, but larger prey items such as Tilapia Oreochromis mossambicus are also eaten, especially when these are readily available in partially drained ponds (Leader 1998, Yu and Swennen 2001).

 

2.3.5        Black-faced Spoonbills will be major beneficiaries of the rotational drain down of ponds and, since these will provide areas free of disturbance, with turbid water of an appropriate depth for foraging and plentiful food. Together with Ardeids, the detailed design and management of ponds will be specifically targeted at the requirements of this species.

 

Greater Spotted Eagle

 

2.3.6        Habitat utilisation in the Deep Bay area was studied during winter 2000-01 (BBV 2001b). Greater Spotted Eagles are a winter visitor to Hong Kong and are present from late October to early April. Their distribution in Hong Kong is restricted to the Deep Bay area, with the notable exception that they roost at night in hills to the south; with most birds apparently roosting in the Castle Peak area during winter 2000-01 (Carey et al. 2001, BBV 2001b). As with Imperial Eagle, observations during winter 2000-01 showed that the most important area for this species was Mai Po, with secondary foci at Tsim Bei Tsui and Nam Sang Wai. Together these areas accounted for 86% of records (BBV 2001b). In contrast to the distribution of Imperial Eagles, during this study there were no records from Lok Ma Chau; indeed there were very few records from east of  Mai Po. This species is scarcer in Hong Kong than Imperial Eagle (Carey et al. 2001); the frequency of sightings during winter 2000-01 was approximately half that of Imperial Eagle (BBV 2001b).

 

2.3.7        The pattern of occurrence was related to the presence of abundant waterbirds on ponds (especially wild ducks). Despite the presence of large numbers of waterbirds (including ducks) the intertidal zone is not utilised. Trees are required for daytime loafing or hunting perches and the study in winter 2000-01 suggested that, in comparison with Imperial Eagle, this species is less likely to occur in extensive open active fish pond areas

 

2.3.8        Greater Spotted Eagles do not, technically, meet the criterion of regular occurrence in the Lok Ma Chau area required for inclusion on the list of Key Target Species as this species was not recorded regularly there during winter 2000-01 (BBV 2001a, BBV 2001b). However, it is proposed that this species be included as a Key Target Species for the reason that it is Globally Threatened (BirdLife International 2000)n and has habitat requirements which can be accommodated within the mitigation area without compromising any other mitigation objectives (in fact the mitigation proposals are identical to those required for Imperial Eagle).

 

2.3.9        Greater Spotted Eagles will be attracted to concentrations of waterbirds, especially ducks, which will provide a source of food. They are likely to avoid areas adjacent to the LMC Station as well as the eastern part of the mitigation area where human activities associated with the presence of the Spur Line and the Boundary Crossing point will deter use. Accordingly, it is proposed to maintain ponds 1 and 2 (shown in Figure 4.1 in the Design Section, these ponds are those most remote from the station) with shallow to moderate water levels throughout the winter to provide suitable feeding and loafing habitat for ducks; thus providing a potential food source for Greater Spotted Eagles in an undisturbed area.

 

            Imperial Eagle

 

2.3.10    Habitat utilisation in the Deep Bay area was studied during winter 2000-01 (BBV 2001b). Imperial Eagles are a winter visitor to Hong Kong and are present from late October to early April. Their distribution in Hong Kong is restricted to the Deep Bay area, with the notable exception that they roost at night in hills to the south; with most birds apparently roosting in the Castle Peak area during winter 2000-01 (Carey et al. 2001, BBV 2001b). Observations during winter 2000-01 showed that the most important area for Imperial Eagles is Mai Po Nature Reserve, with Ma Tso Lung being the second most important area. Together, these two areas accounted for 66% of sightings during the study. Tsim Bei Tsui, Nam Sang Wai and Lok Ma Chau were sites of similar secondary importance, with Lok Ma Chau accounting for 8% of sightings.

 

2.3.11    The pattern of occurrence was related to the presence of abundant waterbirds on ponds (especially wild ducks), with a secondary factor being an avoidance of developed and disturbed areas. Despite the presence of large numbers of waterbirds (including ducks) the intertidal zone is not utilised. Trees are required for daytime loafing or hunting perches, but ponds surrounded by continuous large trees (as at parts of Nam Sang Wai) are avoided.

 

2.3.12    Imperial Eagles will benefit from the reduction in human disturbance arising from the management of the mitigation area. They will also be attracted to concentrations of waterbirds, especially ducks, which will provide a source of food. However, Imperial Eagles are likely to avoid areas adjacent to the LMC Station as well as the eastern part of the mitigation area where human activities associated with the presence of the Spur Line and the Boundary Crossing point will deter use. Accordingly, it is proposed to maintain ponds 1 and 2 (see Figure 4.1) with shallow to moderate water levels throughout the winter to provide suitable feeding and loafing habitat for ducks; thus providing a potential food source for Imperial Eagles in an undisturbed area.

           

Black-winged Stilt

 

2.3.13    The following is based on non-systematic observation in Hong Kong including observations at Lok Ma Chau during winter 2000-01 (BBV 2001a). In Hong Kong, Black-winged Stilts are restricted to fresh or brackish water habitats, favouring large disused fish ponds in the Deep Bay area and bloodworm ponds in Long Valley. Black-winged Stilts are recorded in Hong Kong throughout the year, but have not been known to breed; the small numbers present in summer presumably being non-breeding individuals or early returning migrants (Carey et al. 2001). Distribution on the Deep Bay area is somewhat erratic with flocks opportunistically utilising ponds which are of a suitable depth for feeding (c. 5 – 15 cm water depth) as this species rarely forages whilst swimming (Cramp and Simmons 1983). There is also some evidence that birds may move several kilometres between feeding and roosting areas in Hong Kong, with birds which roost in the Deep Bay area during the day flying to Long Valley to feed at night (BBV 2001c).

 

2.3.14    Black-winged Stilts feed predominantly on aquatic invertebrates, especially insects. Food is taken by wading in open water and invertebrates are taken from on and below the water surface and from aquatic vegetation (Cramp and Simmons 1983). Black-winged Stilts will benefit from shallow open water areas overlying soft mud with aquatic vegetation sparse or absent.

 


Common Teal

 

2.3.15    The following is based on non-systematic observation in Hong Kong including observations at Lok Ma Chau during winter 2000-01 (BBV 2001a). Common Teal are winter visitors to Hong Kong and are present between September and April. Though there are occasional records from other wetland sites; the majority of Common Teal are found in Deep Bay. Within Deep Bay favoured habitats are intertidal creeks amongst mangroves, gei wai and well-vegetated ponds, especially those with abundant growth of the facultative wetland grass Paspalum distichum. A common denominator in these preferences is the presence of mud or shallow water feeding areas in proximity to cover. More open wetland habitats such as active fish ponds, intertidal mudflats and Deep Bay itself are less favoured by Common Teal than most other duck species in Hong Kong – it is probably not co-incidence that this species is a frequent prey item for raptors including Greater Spotted and Imperial Eagles.

 

2.3.16    Diet of Common Teal has not been studied in Hong Kong; however elsewhere in its range it is considered to be omnivorous, filtering invertebrates and seeds from water or soft mud whilst either walking or swimming. Seeds are often particularly important in winter (Cramp and Simmons 1977).

 

2.3.17    Common Teal will benefit from the provision of suitable feeding and loafing areas at ponds 1 and 2 in Figure 4.1 (where water levels at shallow to moderate levels and Paspalum distichum will be established to provide food and cover) and the freshwater marsh areas.

 

            Eurasian Coot

 

2.3.18    The following is based on casual observation in Hong Kong. Eurasian Coots are primarily winter visitors to Hong Kong, but a few individuals are usually seen in summer and breeding has been recorded. In Hong Kong, Eurasian Coots are largely restricted to the Deep Bay area, where the largest numbers are present in the open waters of the bay itself. Small numbers are found on brackish and freshwater ponds and gei wai where these have extensive marginal and emergent vegetation, especially reeds Phragmites spp.

 

2.3.19    Diet has not been systematically studied in Hong Kong, but elsewhere in its range this species is omnivorous with plant matter (vegetative parts and seeds of aquatic plants) predominating (Cramp and Simmons 1980). In Hong Kong, Eurasian Coots are regularly attracted to grain provided for waterfall at Mai Po NR.

 


2.3.20    This species will benefit from the provision of feeding areas and shelter in the freshwater marsh. The diversity of marginal and emergent vegetation and management of water levels will maintain suitable conditions for this species throughout the year and may encourage more individuals to remain in summer and perhaps to breed.

 

            Great Cormorant

 

2.3.21    Great Cormorants are winter visitors to Hong Kong and are economically important as the numbers of this fish-eating species which occur in Deep Bay are perceived to have a significant impact on the profitability of commercial fish farming. Studies of the wintering ecology of Great Cormorants in Hong Kong, their impact on fisheries and possible preventative measures are in progress but have not been published.

 

2.3.22    Great Cormorants in Hong Kong roost communally. There are currently two roosts in the Deep Bay area: at Mai Po NR and at Nam Sang Wai. Cormorants disperse to feed; either in Deep Bay itself or on fish ponds. They use both active and inactive ponds, but avoid small ponds, especially those surrounded by trees or adjacent to sources of human activity. They readily take advantage of fish concentrations, including the provision of “trash fish” (Tilapia) in ponds at Mai Po NR to divert feeding pressure from commercial ponds.

 

2.3.23    Great Cormorants will benefit considerably from the provision of ponds stocked with “trash” fish when the water level is high. Management of ponds for this species will, thus, accord with that proposed for Black-faced Spoonbills and Ardeids: cormorants will utilise ponds when they are full, whilst the other species will largely benefit when they are drained. A subsidiary benefit of encouraging cormorants to use stocked ponds in the mitigation area is that they will be diverted from commercial ponds thus reducing conflict with fish farmers and avoiding the need for more drastic deterrence measures.

 

            Chinese Pond Heron

 

2.3.24    Chinese Pond Herons are found in Hong Kong throughout the year. Habitat utilisation has been studied in Hong Kong by Young (1994) who showed that birds breeding at the Mai Po Village egretry fed mainly around fish ponds. Individuals typically forage solitarily along the edges of open water areas or areas within sparse or short vegetation. They utilise open areas such as intertidal mudflats or drained down ponds less than larger Ardeid species in Hong Kong. Chinese Pond Herons breed colonially, either on their own or with other Ardeid species. Nests are often placed in bamboos Bambusa spp. Breeding adults largely forage within 3 km of their colonies (Young and Cha 1995).

2.3.25    Chinese Pond Herons will benefit from the provision of shallow open water areas or shallow water areas with partial vegetation cover up to around 300 mm in height. As such, they are likely to utilise all edge areas so long as vegetation is not too dense or water too deep to prevent successful foraging. Currently the closest egretry to Lok Ma Chau is at Mai Po Village, a distance of 2 km. Whilst this is within the foraging range of breeding Chinese Pond Herons, it is possible that the provision of suitable breeding habitat at Lok Ma Chau would benefit this species (a former egretry at Lok Ma Chau was abandoned in 1993 possibly due to increased disturbance from the vehicle Boundary Crossing Point (Young and Cha 1995)). Accordingly, it is proposed to plant of clumps of Bambusa vulgaris (which will also fulfill a screening function) along the northern fringe of the mitigation area.

 

            Great Egret

 

2.3.26    Great Egrets are one of the scarcer breeding Ardeids in Hong Kong, but numbers are much greater in winter (Young and Cha 1995). Habitat utilisation has been studied in Hong Kong by Young (1994) who showed that whilst this species feeds on drained ponds and gei wai, intertidal mudflats are significantly more important as feeding habitat. Despite these habitat preferences, Great Egrets will benefit to some extent from the provision of shallow water feeding areas on stocked ponds and will take advantage of drained ponds.

           

Grey Heron

 

2.3.27    Grey Herons have bred in Hong Kong, but this species is primarily a winter visitor (Young and Cha 1995). Habitat utilisation has been studied in Hong Kong by Young (1994) who noted that this species is predominantly a crepuscular feeder in Hong Kong and primarily uses gei wai as a daytime roost; but also utilises fish ponds for feeding. Grey Herons will benefit from the provision of shallow water feeding areas on stocked ponds and will take advantage of drained ponds. They are also likely to benefit from areas free of human disturbance, which will be suitable as daytime roost sites.

 

Little Egret

 

2.3.28    Little Egrets are found in Hong Kong throughout the year. Habitat utilisation has been studied in Hong Kong by Young (1994) and Cornish (1996). These studies showed that Little Egrets in Hong Kong feed primarily in fish pond and intertidal mudflat areas. Little Egrets feed opportunistically on fish remaining when ponds are drained and are often the most abundant Ardeid species in such feeding concentrations. Breeding birds typically forage within 3 km of egretries (Young 1994), which may be situated either in bamboos or a variety of tree species.


2.3.29    Little Egrets feed by wading and will benefit from the provision of shallow water feeding areas in ponds and shallow water areas in the marsh so long as vegetation is not too dense. In addition Little Egrets are likely to be one of the main beneficiaries of the proposed management regime for the ponds as they will readily take advantage of the availability of fish as ponds are drained. Like Chinese Pond Herons, Little Egrets may benefit from the provision of bamboo clumps along the northern boundary of the mitigation area, which will provide suitable breeding sites.

 

            Red-billed Starling

 

2.3.30    Red-billed Starling is a winter visitor to Hong Kong, occurring in large flocks in the northwest New Territories. The wintering population in Hong Kong is considered probably to be of international importance for this species (Carey et al. 2001). Red-billed Starlings are omnivores and feed around fish ponds, wet agricultural areas (especially where these are contaminated by effluent from pig farms), edges of reedbeds and both natural and artificial drainage channels. They readily take advantage of spilled food provided for fish or ducks. Much food is obtained on the ground but they also frequently feed in trees where they consume insects and fruit (though their gape size is too small to permit them to take most fruits of Melia azedarach, the most frequent fruiting tree around fish ponds).

 

2.3.31    This species will benefit from sparely vegetated fringes to ponds and marsh areas, especially where these are close to tree and shrub areas adjacent to the drainage channels and the station perimeter. It will also benefit from the proposed tree and shrub planting which will provide fruit and invertebrate food and shelter.

 

            Chinese Bullfrog

 

2.3.32    This large frog species is thought to be in marked decline locally and drastic decline regionally, and has therefore been rated as of Potential Regional Concern by Fellowes et al. (in press). It is commonly sold in food markets in Hong Kong and in southern China. It is a species closely associated with areas of wet agriculture, and breeds in ponds and marshes. The species is present but not common at Lok Ma Chau.

 

2.3.33    Chinese Bullfrogs feed on insects and small frogs and rodents (Karsen et al., 1998). They will benefit from provision of permanent and, particularly, seasonal marsh habitat (from which predatory fish are absent), with good development of emergent and/or edge vegetation and variable, but generally shallow, depth. Presence of prey items such as odonate larvae and other frog species will also encourage establishment of this species.

 


2.4              Habitat Condition Targets

 

2.4.1        As described in the EIA Report (BBV 2000) it is considered that the most appropriate form of wetland mitigation in the San Tin / Lok Ma Chau area is the enhancement of fish ponds over the majority of the mitigation area. Currently the large biogeographically important populations of herons and egrets that use fishponds in the Deep Bay area primarily feed on the abundant small non-commercial fish and invertebrates (termed ‘trash fish’) that thrive as a by-product of the highly productive commercial fish-farming systems. These include Gambusia affinis (Mosquito Fish), Macrobrachium nipponense (a prawn) and Oreochromis mossambicus (a species of Tilapia).

 

2.4.2        However, these food resources are generally only readily available to birds when the ponds are drained down for fish harvesting during the winter. Furthermore, only a small proportion of fish ponds are drained at one time and only for short periods. The spatial distribution of birds feeding on ponds is therefore highly dynamic and variable as birds move between fish ponds as they are drained. When recently drained, such fish ponds may contain many hundreds of feeding egrets, herons and other waterbirds. Consequently, a large area of fish ponds is required to support the bird populations and avoid ‘feeding bottlenecks’.

 

2.4.3        When ponds are full, their use by birds is severely limited due to their relatively steep sides, deep water and their frequent lack of marginal vegetation. These characteristics also limit their biodiversity interest for other taxa groups. The main objective of enhancing fish ponds would therefore be to:

 

           Increase the value of fish ponds to Black-faced Spoonbills, herons and egrets outside harvesting periods (i.e. draw-down), by increasing food resources and food availability and by reducing disturbance effects. Enhancement of the value of fish ponds to such birds outside harvest periods could reduce the potential for ‘feeding bottlenecks’ thereby possibly reducing the area of fish ponds needed to support the population.

 

          The management regime proposed is expected to benefit other species of conservation importance that currently use fishpond habitats. For example, the managed wetlands, at Mai Po which include areas of former fishponds have been shown to support significantly higher densities of Greater Spotted and Imperial Eagles than occur in commercial fishponds (ref baseline report). Both are globally threatened. In addition, the provision of a less homogonous wetland area and the resultant increase in habitat diversity within the Lok Ma Chau fishponds will provide habitat for other species that are generally rare within commercial fishponds. The areas of reeds and marsh will be more suitable for small migrant passerines that the habitats available at present. For example, Pallas’s Grasshopper Warbler, a species that prefers dense rank vegetation and avoids open and  sparse habitats would benefit.

 

           Increase their overall biodiversity value and suitability for other non-bird Species of Conservation Importance, such as some mammals including Eurasian Otter, amphibians and reptiles, whilst maintaining their current important functions for herons, egrets and other water birds.

 

2.4.4        Figure 1.2 indicates the location of the proposed area of enhanced fishponds. These will be placed away from the buildings to minimise disturbance impacts from the railway station and others sources such as the Lok Ma Chau border crossing. They would also be contiguous with the main area of fishponds in the WCA and Ramsar site as a whole. Maintaining a contiguous area for compensation which is linked with an existing area of recognised conservation importance is of significant ecological value.

 

2.4.5        The specific fish pond habitat targets for the mitigation area are:

 

           Enhancement and maintenance of a total of 27.1 ha of fishponds (including essential structures, e.g. water control structures, and other habitats e.g. bunds).

 

           > 20% of the fish pond area (excluding bunds and ponds that are dry for maintenance) consists of shallow water (i.e. < 10cm depth).

 

           Target plant species (see below) comprise >50% cover on > 20% of the area of fish pond bunds and islands.

 

           Undesirable invasive species and exotic species are < 10% of vegetation cover.

 

           Plant cover is <5% on > 75% of the area of fish pond bunds and islands.

 

           70-80% of the fish pond area (excluding bunds and ponds that are dry for maintenance) is under traditional polyculture fish pond management systems (see below for fish farming operation specifications).

 

           10 - 30% of the fish pond area (excluding bunds ponds that are dry for maintenance) is set-aside from fish farming and is under specific conservation management (see below for specifications).


2.4.6        The fishpond enhancement measures will be supported by the creation of some areas of reedbed and marshland habitat alongside the station buildings (Figure 1.2). These habitats will be established alongside the station complex to function as a barrier to disturbance and as shelter/cover for smaller herons, crakes, passerines, amphibians, reptiles and mammals. This marshland habitat will also have a high carrying capacity for several such target Species of Conservation Importance as well as providing habitat for some that at present occur in the area only in small numbers (see Table 1.2).

 

2.4.7        The specific marshland targets for the mitigation area are:

 

          Creation and maintenance of a total of 4.9 ha of marshland habitat (including essential structures, e.g. water control structures, and other habitats e.g. bunds) in Favourable Condition. Marshland habitats are defined as wetlands (i.e. where wetland hydrological conditions or wetland soils are present or where wetland plants are dominant) with shallow water (average < 1m) and wetland plant species cover greater than 30% of the area.

 

           Wetland plant species (as defined in monitoring SOPs; see EM & A Manual) comprise over >90%  of established vegetation.

 

           Undesirable invasive species and exotic species are < 10% of vegetation cover.

 

           The average depth of water (outside drawn down periods for maintenance) is 20 – 50 cm.

 

           The percentage of open water (i.e. unvegetated water) is 5 - 30%.

 

           Exposed soils are wet and soft (with penetrability of less than 6 kg F), outside drawn down periods for maintenance, over 75% of the area.

 

2.4.8        An additional area of reedbed will also be created alongside the station for water clean-up purposes. This habitat will provide additional habitat for reedbed species, potentially including smaller herons, bitterns and various passerines, but is not part of the specific mitigation measure documented in this HCMP.

 

 

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