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Tourism development and environmental limitations at Heron Island, Great Barrier Reef
Journal of Environmental Management (t991) 33, 117-122
Tourism Development and Environmental Limitations at Heron Island, Great Barrier Reef T. A. Walker Department of Environment and Heritage, PO Box 5391, Townsville 4810, Australia Received 2 April 1990
Heron Island is an important sea-bird and sea-turtle breeding cay on the southern Great Barrier Reef. Human occupation over many decades has caused substantial degradation of the island and its fauna and flora. Examination of the history of anthropogenic impact on the island illustrates that environmental planning theory is no substitute for a sound knowledge of ecology and physical processes.
Keywords: Heron Island, Great Barrier Reef, black noddy (Anous minutus), wedge-tailed shearwater (Puffinuspacificus), tourism, sea-birds, flora.
1. Introduction Hill and Rosier (1989) recently discussed the relationship between breeding sea-bird populations and tourism development at Heron Island, a small sand cay at the southern end of the Great Barrier Reef. They noted that the increase in size of the black noddy (Anous minutus) colony over recent decades, the lack of evidence for a decline in wedgetailed shearwater (Puffinus pacificus) numbers and the similar population sizes of both species on the more-developed and less-developed halves of the island demonstrate coexistence between these birds and island development. Hill and Rosier (1989) argue that this information "contradicts some previous literature regarding the compatibility between development and sea-bird colonies on Heron Island and demonstrates that some sea-birds are able to compensate for loss of space through more concentrated nesting activity." The previous literature is not cited but the authors conclude with the general environmental philosophy that "future limitations cannot be placed on development because of inadequate knowledge about the impact of development on the key elements of the ecosystem." On the contrary, it is clear that limitations must be placed on development if knowledge of the environmental impact is inadequate. The alternative is to chance disaster. Heron Island already provides a text-book example of the results of allowing development without adequate environmental consideration. 117 0301~4797/91/060117 + 06 $03.00/0
~1 1991 Academic Press Limited
118
Tourism and environment at Heron Island
2. Heron Island
Heron Island was occupied in 1925 when a turtle soup factory commenced operations. The factory closed in 1928 and the buildings and lease were converted to a tourist resort in 1932. The present 280-bed resort (plus 90 staff) has developed gradually since the 1930s. A scientific field station commenced in 1951 and presently has 80-bed accommodation and 10 staff. Three buildings have been built since 1983 for field officers of the Department of Environment and Heritage. Measurements from aerial photographs show that 10% of the 14 ha surface of Heron Island is covered by buildings or concrete. A further 30% or more is alienated by roads, lawns, walkways, vehicle yards, gardens and dumps. Buildings were constructed on the lee margin of Heron Island with inadequate knowledge of the natural movement of sand cays. Some buildings were inevitably threatened by eroding beaches and a sea-wall was constructed in 1960 with inadequate knowledge of the environmental effects of such structures. The alignment of the wall accelerated beach erosion in adjacent areas, prompting further wall additions in subsequent years and thus further erosion problems (Flood, 1984). Since 1972, a sea-wall 250 m in length has surrounded the western end of the cay. Inadequate knowledge about the environmental impact of opening vessel access through the surrounding reef has allowed works causing serious interruption of sand movement around the cay. Initially, a gap was blasted in the reef rim in 1945, followed by a boat channel in 1966, then redredging of the infilled channel on a number of occasions (Flood, 1984), and, in 1988, by channel enlargement and excavation of a wider vessel harbour. The resulting altered hydrological patterns have promoted cay erosion and permanent loss of sand which is funnelled into the boat channel and eventually into deep water. Sand loss is particularly severe during tropical cyclones. Between 1936 and 1978 the northern shoreline of the cay retreated an average of 40 m (Flood, 1984). 3. Flora of Heron Island
The natural vegetation of Heron Island is predominantly Pisonia grandis forest. The remaining Australian stands of this remarkable and attractive island tree cover less than 180ha (Walker, in press), Previously, inadequate knowledge of the distribution of Pisonia forest has led to an assumption of abundance. Despite having a quarter of its forest felled, Heron Island supports the third largest of the surviving stands of this tree in Australia. Heron Island shares with Lady Elliot Island the distinction of having the highest number of weeds known for a cay on the Great Barrier Reef (Chaloupka and Domm, 1985; Walker, unpublished). Native plant species on both these resort islands are outnumbered by naturalized alien species. These invasions are a direct result of human activities including anthropochory, habitat modification and introduction of gardens (Chaloupka and Domm, 1985; Heatwole and Walker, 1989). 4. Fauna of Heron Island
Australia is one of the last refuges for globally declining sea-turtle populations and Heron Island supports one of the I0 largest nesting colonies of green turtles in eastern Australia. Inadequate knowledge of sea-turtle population dynamics allowed their hunting until low numbers of nesting adults prompted legislative protection in 1950. Human activities have greatly reduced the available turtle nesting area at Heron Island
T. A. Walker
119
by construction of a sea-wall barrier, by accelerating erosion of beaches, by building over and compacting nest areas and by alienating areas with heavy human traffic. The loss of nesting area, predominantly on the sunny side of the cay, gives rise to reduced numbers of female hatchlings which require a higher incubation temperature than males (Limpus et al., 1984). In addition, the lights from buildings disorient turtle hatchlings from rapidly reaching the safety of deep water. Ground-nesting terns, gulls or boobies breed on the southern half of the Great Barrier Reef on all 22 coral islands not impacted by commercial tourist operations or human habitation (Walker 1987). Heron Island is the only member of the southernmost Capricorn-Bunker Islands that no longer supports nesting of sea-birds or shore-birds on the surface of the ground. Eleven such species breed amongst the other 14 islands of this group, including two inhabited islands, Lady Elliot Island and One Tree Island, where sea-bird breeding areas are protected from human entry. Another island in the group, North West Island, has only recently seen a return of gull nesting following eradication of feral cats. The black noddy and wedge-tailed shearwater are the only breeding seabirds remaining at Heron Island although a small colony of black-naped Terns (Sterna sumatrana) nests on a shipwreck on Heron Reef. Anthropogenic impacts on nesting sea-birds cannot be assessed by counting nest densities as proposed by Hill and Rosier (1989), but must be determined from comparison of the breeding success of birds at natural and impacted sites. There are no comparative studies of breeding success of black noddies or wedge-tailed shearwaters available at Heron Island. Other factors relevant to these two species are discussed below.
5. Black noddy population A potential weakness of environmental planning at sea-bird colonies is failure to account for the cyclic nature of many sea-bird populations. Sea-birds experience wide natural population fluctuations as a result of variation in abundance of food, storms and disease. Fluctuations can be dramatic like the mass mortality along the Peruvian coast associated with episodic oceanographic E1 Nino events (Barber and Chavey, 1983). Less dramatic are the good years when sea-bird populations are greatly boosted by survival of many juveniles. Observations of the black noddy on the Capricorn-Bunker Islands over many decades indicate that there is a highly variable population. In most years, the population increases at a low or moderate rate, in some years it remains relatively constant or decreases due to low availability of food or bad weather, and from time to time there is high mortality from a tropical cyclone (Bustard, 1972; Kikkawa and Boles, 1976; pers. obs.) or epidemic. In July 1986 the Capricorn-Bunker Islands were devoid of black noddies following a massive die-off. At this time, only the small winter population was affected, but, had the epidemic occurred in summer, the southern Barrier Reef population might have been reduced to a few per cent of its size. This has almost certainly happened in the past. The important point is that black noddies do not have a static population and it cannot be considered as a constant in environmental planning. The increasing black noddy population at Heron Island may have a long way to go before it regains previous levels and this should be appreciated before decisions are made on further development affecting potential nesting habitat. Capricorn-Bunker Islands are not yet saturated with black noddies (Hulsman, 1984) and the establishment and growth of new colonies at One Tree Island and Lady Elliot Island in recent years
120
Tourism and environment at Heron Island
(Walker, 1986, 1989) indicates a period of expansion throughout the region. Numbers nesting at Heron Island are approaching a situation when competition for nest sites will limit future reproduction. A proposal to construct an airstrip on Heron Island in the late 1960s was rejected on ecological criteria (Heatwole, 1984) but, if the planning approach of Hill and Rosier (1989) had been used, this development might have proceeded. At that time, the black noddy population was small enough to be concentrated into the remaining trees around an airstrip. Such development would have precluded progression of the population to its present level. Another complication which must be considered in environmental planning relates to the existing "naturalness" of a site. There needs to be adequate knowledge that the site is not already damaged or deteriorated as a result of previous human activities. Did the increase in the black noddy population at Heron Island commence in the early 1960s coincident with removal of the rat infestation? Black noddies nested in only about 50 trees in 1927 (MacGillivray, 1928), and Cooper (1948) reported a similarly small colony in 1946 [the 50 pairs in 1910 cited by Hill and Rosier is an error from Kikkawa (1970), corrected in a subsequent article by Kikkawa and Boles (1976)]. The recent population increase to greater than 40 000 pairs is probably natural, but the possibility that it was previously constrained or reduced by nocturnal rat predation of nests (MacGillivray, 1928; Moulton, 1961; Bustard, 1972) cannot be overlooked. Introduced rats are implicated in depletion or extinction of island sea-bird colonies, including black noddy throughout the world (Atkinson, 1985). Prior to the 1970s, Heron Island birds were also subjected to feral cats, dogs and human occupants who dined on sea-bird eggs.
6. Wedge-tailed shearwater population The census of Shipway (1969) first showed that the density of shearwater burrows was higher by 37% or more in resort and research station areas compared with undeveloped regions of Heron Island. This density might be partly attributed to easy burrow access from roads, tracks and mown areas. In wet years, the forest clearings are choked with the garden escapee Euphorbia o'athophora that restricts approaches to burrows. The census of Hill and Barnes (1989) confirmed that low burrow densities are present in highly developed areas, but that high densities occur in partly developed or disturbed areas of Pisonia forest. Heron Island is capable of supporting a substantially greater number of burrows (presently over 16000 active burrows) before it reaches the density found nearby at North West Island (Hulsman, 1984). The same caution must therefore be exercised in planning for a cyclic shearwater population as for the black noddy population. Fluctuations in shearwater numbers are less visible because birds are hidden in burrows or remain at sea during daylight hours. They are susceptible to natural factors such as disease (Gilbert, 1925) but unlike black noddies they also suffer direct mortality from human activities. It is difficult to walk through nesting areas without collapsing burrows (crushing or suffocating the occupants) and this can be a problem if thousands of tourists visit a colony. Additionally, at Heron Island, there have been instances where regions of occupied burrows were bulldozed to make way for resort expansion (Moulton, 1961; Heatwole, 1984; pers. obs.).
7. Export of environmental problems Heron Island resort guests are taken on regular picnic trips to a nearby cay, Wilson Island, and consequently environmental problems are exported to this cay from Heron
T. A. Walker
121
Island. The issue of most concern is the impact on the roseate tern (Sterna dougallii) colony. This tern has a low global population and is threatened in the northern hemisphere. Its conservation status in the southern hemisphere is not known, but the largest breeding colony on the southern Great Barrier Reef has been recorded at Wilson Island. Further development at Heron Island will inevitably lead to higher visitation pressure on Wilson Island and perhaps other adjacent islands. Environmental problems result from daily sea-dumping of resort food scraps near Heron Island. As well as attracting sharks to the vicinity of scuba diving sites, the resort food scraps support hundreds of silver gulls (Larus novaehollandiae) that commute from adjacent islands where they prey on eggs and chicks of other nesting sea-birds (Walker, 1988). Tern colonies at these islands sometimes lose all of their clutches to gulls (Cooper, 1948; Hulsman, 1977).
8. Conclusion
Results of the environmental planning approach advocated by Hill and Rosier (1989) are already well illustrated at Heron Island. Following extensive development with inadequate knowledge or concern about environmental impacts, the island is permanently washing away, has the second lowest diversity of breeding sea-birds of any cay on the southern Great Barrier Reef, has the second highest number of weeds known for a coral island on the Great Barrier Reef, and sustains the largest Great Barrier Reef population of gulls. Most species o f sea-birds and shore-birds will abandon breeding colonies when impacted by human activities. There can be little doubt that seven or more species of seabirds and oystercatchers nested at Heron Island prior to human occupation. On the other hand, some species such as the black noddy and wedge-tailed shearwater are relatively fearless of people. If it can be demonstrated that human presence is not detrimental to the breeding success of these birds, then conditions for mutual coexistence on certain islands may be set. Such planning must ensure there is provision for the cycle of population expansion and reduction. The black noddy population is fast approaching saturation of the remaining habitat at Heron Island. Even without considering the black noddies and wedge-tailed shearwaters, there is more than adequate data to justify containment of further development at Heron Island. Effects on other components of the environment are considerable and there is a limit to the social carrying capacity of the cay. The environmental and social carrying capacities are not independent because most visitors to the island come to experience an attractive natural environment rather than social activities (in contrast with many other resorts). A survey of resort guests found that 57% were nature lovers, 18% were birdwatchers and 30% were photographers (categories not mutually exclusive; Environment Science and Services, 1986). Heron Island well illustrates the environmental damage that can result from occupation of coral cays and sea-bird breeding islands. On the Great Barrier Reef such damage can be minimized by directing tourism to the environmentally robust continental islands. These islands are more numerous, rarely have significant sea-bird or turtle colonies and usually do not require blasting or dredging of harbours. If general conservation theory and observation lead to erroneous conclusions that unjustly limit commercial development then the result is reversible when more adequate knowledge becomes available. The converse is unfortunately not often true. The approach advocated by Hill and Rosier (1989) must be rejected as a planning strategy. In
122
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planning for development caution.
in fragile environments
it is e s s e n t i a l t o e r r o n t h e side o f
References
Atkinson, I. A. E. (1985). The spread of commensal species of Rattus to oceanic islands and their effects on island avifaunas. In Conservation of Island Birds: Case Studies for the Management of Threatened Island Species (P. J. Moors, ed.), pp. 35-81. Cambridge: International Council for Bird Preservation. Barber, R. T. and Chavey, F. P. (1983). Biological consequences of E1 Nino. Science 222, 1203-1210. Bustard, H. R. (1972). Australian Sea Turtles: Their Natural History and Conservation. London: Collins. Chaloupka, M. Y. and Domm, S. B. (1985). Comprehensive regional survey of the terrestrial flora on coral cays in the Capricornia Section of the Great Barrier Reef Marine Park. Proceedings of the Royal Society of Queensland 96, 75 80. Cooper, R. P. (1948). Birds of the Capricorns--Great Barrier Reef. Emu 48, 107 126. Environment Science and Services (1986). User Survey Capricornia Section. Results o f Heron Island Resort Visitors Survey. Townsville: Great Barrier Reef Marine Park Authority Report. Flood, P. G. (1984). Changes in the Shoreline Position on Six Coral Cays, Capricornia Section, Great Barrier Reef Marine Park. Armidale: University of New England. Gilbert, P. A. (1925). The biology of North West Islet, Capricorn Group. Australian Zoologist 4, 210-226. Heatwole, H. (1984). The cays of the Capricornia Section, Great Barrier Reef Marine Park, and a history of research.on their terrestrial biota. In The Capricornia Section o f the Great Barrier Reef" Past, Present and Future (W. T. Ward and P. Saenger, eds), pp. 25~44. Brisbane: Royal Society of Queensland. Heatwole, H. and Walker, T. A. (1989). Dispersal of alien plants to coral cays. Ecology 70, 501-509. Hill, G. J. E. and Barnes, A. (1989). Census and distribution of wedge-tailed shearwater Puffinus pacificus burrows on Heron Island, November 1985. Emu 89, 135-139. Hill, G. J. E. and Rosier, J. (1989). Wedgetailed shearwaters, white capped noddies and tourist development on Heron Island, Great Barrier Reef Marine Park. Journal of Environrnental Management 29, 102114. Hulsman, K. (1977). Breeding success and mortality of terns at One Tree Island, Great Barrier Reef. Emu 77, 49-60. Hulsman, K. (1984). Survey of Seabird Colonies in the Capricornia Section of the Great Barrier Reef Marine Park, IlL Townsville: Great Barrier Reef Marine Park Authority Report. Kikkawa, J. (1970). Birds recorded at Heron Island. Sunbird 1, 34-48. Kikkawa J. and Boles, W. (1976). Seabird Island No. 15: Heron Island, Queensland. Australian Bird Bander 14, 1-6.
Limpus, C. J., Fleay, A. and Guinea, M. (1984). Sea turtles of the Capricornia Section, Great Barrier Reef. In The Capricornia Section of the Great Barrier Reef" Past, Present and Future (W. T. Ward and P. Saenger, eds), pp. 61 78. Brisbane: Royal Society of Queensland. MacGillivray, W. (1928). Bird-life of the Bunker and Capricorn Islands. Emu 28, 230--249. Moulton, J. M. (1961). Some observations on the Heron Island fauna. Atoll Research Bulletin 82, 15-16. Shipway, A. K. (1969). The numbers of terns and shearwaters nesting on Heron Island in 1965. Emu 69, 108109. Walker, T. A. (1986). The birds of Lady Elliot Island. Sunbird 16, 73-82. Walker, T. A. (I 987). Birds of Bushy Island (with a summary of the nesting status of bird species on southern Great Barrier Reef cays). Sunbird 17, 5~58. Walker, T. A. (1988). The population of the Silver Gull Larus novaehollandiae on the Capricorn and Bunker Islands. Corella 12, 113-118. Walker, T. A. (1989). Seabird Island No. 201: Lady Elliot Island, Great Barrier Reef, Queensland. Corella 13, 118-121. Walker, T. A. (in press). Pisonia islands of the Great Barrier Reef, I. The distribution, abundance and dispersal by seabirds of Pisonia grandis. Atoll Research Bulletin.
Tourism Development and Environmental Limitations at Heron Island, Great Barrier Reef T. A. Walker Department of Environment and Heritage, PO Box 5391, Townsville 4810, Australia Received 2 April 1990
Heron Island is an important sea-bird and sea-turtle breeding cay on the southern Great Barrier Reef. Human occupation over many decades has caused substantial degradation of the island and its fauna and flora. Examination of the history of anthropogenic impact on the island illustrates that environmental planning theory is no substitute for a sound knowledge of ecology and physical processes.
Keywords: Heron Island, Great Barrier Reef, black noddy (Anous minutus), wedge-tailed shearwater (Puffinuspacificus), tourism, sea-birds, flora.
1. Introduction Hill and Rosier (1989) recently discussed the relationship between breeding sea-bird populations and tourism development at Heron Island, a small sand cay at the southern end of the Great Barrier Reef. They noted that the increase in size of the black noddy (Anous minutus) colony over recent decades, the lack of evidence for a decline in wedgetailed shearwater (Puffinus pacificus) numbers and the similar population sizes of both species on the more-developed and less-developed halves of the island demonstrate coexistence between these birds and island development. Hill and Rosier (1989) argue that this information "contradicts some previous literature regarding the compatibility between development and sea-bird colonies on Heron Island and demonstrates that some sea-birds are able to compensate for loss of space through more concentrated nesting activity." The previous literature is not cited but the authors conclude with the general environmental philosophy that "future limitations cannot be placed on development because of inadequate knowledge about the impact of development on the key elements of the ecosystem." On the contrary, it is clear that limitations must be placed on development if knowledge of the environmental impact is inadequate. The alternative is to chance disaster. Heron Island already provides a text-book example of the results of allowing development without adequate environmental consideration. 117 0301~4797/91/060117 + 06 $03.00/0
~1 1991 Academic Press Limited
118
Tourism and environment at Heron Island
2. Heron Island
Heron Island was occupied in 1925 when a turtle soup factory commenced operations. The factory closed in 1928 and the buildings and lease were converted to a tourist resort in 1932. The present 280-bed resort (plus 90 staff) has developed gradually since the 1930s. A scientific field station commenced in 1951 and presently has 80-bed accommodation and 10 staff. Three buildings have been built since 1983 for field officers of the Department of Environment and Heritage. Measurements from aerial photographs show that 10% of the 14 ha surface of Heron Island is covered by buildings or concrete. A further 30% or more is alienated by roads, lawns, walkways, vehicle yards, gardens and dumps. Buildings were constructed on the lee margin of Heron Island with inadequate knowledge of the natural movement of sand cays. Some buildings were inevitably threatened by eroding beaches and a sea-wall was constructed in 1960 with inadequate knowledge of the environmental effects of such structures. The alignment of the wall accelerated beach erosion in adjacent areas, prompting further wall additions in subsequent years and thus further erosion problems (Flood, 1984). Since 1972, a sea-wall 250 m in length has surrounded the western end of the cay. Inadequate knowledge about the environmental impact of opening vessel access through the surrounding reef has allowed works causing serious interruption of sand movement around the cay. Initially, a gap was blasted in the reef rim in 1945, followed by a boat channel in 1966, then redredging of the infilled channel on a number of occasions (Flood, 1984), and, in 1988, by channel enlargement and excavation of a wider vessel harbour. The resulting altered hydrological patterns have promoted cay erosion and permanent loss of sand which is funnelled into the boat channel and eventually into deep water. Sand loss is particularly severe during tropical cyclones. Between 1936 and 1978 the northern shoreline of the cay retreated an average of 40 m (Flood, 1984). 3. Flora of Heron Island
The natural vegetation of Heron Island is predominantly Pisonia grandis forest. The remaining Australian stands of this remarkable and attractive island tree cover less than 180ha (Walker, in press), Previously, inadequate knowledge of the distribution of Pisonia forest has led to an assumption of abundance. Despite having a quarter of its forest felled, Heron Island supports the third largest of the surviving stands of this tree in Australia. Heron Island shares with Lady Elliot Island the distinction of having the highest number of weeds known for a cay on the Great Barrier Reef (Chaloupka and Domm, 1985; Walker, unpublished). Native plant species on both these resort islands are outnumbered by naturalized alien species. These invasions are a direct result of human activities including anthropochory, habitat modification and introduction of gardens (Chaloupka and Domm, 1985; Heatwole and Walker, 1989). 4. Fauna of Heron Island
Australia is one of the last refuges for globally declining sea-turtle populations and Heron Island supports one of the I0 largest nesting colonies of green turtles in eastern Australia. Inadequate knowledge of sea-turtle population dynamics allowed their hunting until low numbers of nesting adults prompted legislative protection in 1950. Human activities have greatly reduced the available turtle nesting area at Heron Island
T. A. Walker
119
by construction of a sea-wall barrier, by accelerating erosion of beaches, by building over and compacting nest areas and by alienating areas with heavy human traffic. The loss of nesting area, predominantly on the sunny side of the cay, gives rise to reduced numbers of female hatchlings which require a higher incubation temperature than males (Limpus et al., 1984). In addition, the lights from buildings disorient turtle hatchlings from rapidly reaching the safety of deep water. Ground-nesting terns, gulls or boobies breed on the southern half of the Great Barrier Reef on all 22 coral islands not impacted by commercial tourist operations or human habitation (Walker 1987). Heron Island is the only member of the southernmost Capricorn-Bunker Islands that no longer supports nesting of sea-birds or shore-birds on the surface of the ground. Eleven such species breed amongst the other 14 islands of this group, including two inhabited islands, Lady Elliot Island and One Tree Island, where sea-bird breeding areas are protected from human entry. Another island in the group, North West Island, has only recently seen a return of gull nesting following eradication of feral cats. The black noddy and wedge-tailed shearwater are the only breeding seabirds remaining at Heron Island although a small colony of black-naped Terns (Sterna sumatrana) nests on a shipwreck on Heron Reef. Anthropogenic impacts on nesting sea-birds cannot be assessed by counting nest densities as proposed by Hill and Rosier (1989), but must be determined from comparison of the breeding success of birds at natural and impacted sites. There are no comparative studies of breeding success of black noddies or wedge-tailed shearwaters available at Heron Island. Other factors relevant to these two species are discussed below.
5. Black noddy population A potential weakness of environmental planning at sea-bird colonies is failure to account for the cyclic nature of many sea-bird populations. Sea-birds experience wide natural population fluctuations as a result of variation in abundance of food, storms and disease. Fluctuations can be dramatic like the mass mortality along the Peruvian coast associated with episodic oceanographic E1 Nino events (Barber and Chavey, 1983). Less dramatic are the good years when sea-bird populations are greatly boosted by survival of many juveniles. Observations of the black noddy on the Capricorn-Bunker Islands over many decades indicate that there is a highly variable population. In most years, the population increases at a low or moderate rate, in some years it remains relatively constant or decreases due to low availability of food or bad weather, and from time to time there is high mortality from a tropical cyclone (Bustard, 1972; Kikkawa and Boles, 1976; pers. obs.) or epidemic. In July 1986 the Capricorn-Bunker Islands were devoid of black noddies following a massive die-off. At this time, only the small winter population was affected, but, had the epidemic occurred in summer, the southern Barrier Reef population might have been reduced to a few per cent of its size. This has almost certainly happened in the past. The important point is that black noddies do not have a static population and it cannot be considered as a constant in environmental planning. The increasing black noddy population at Heron Island may have a long way to go before it regains previous levels and this should be appreciated before decisions are made on further development affecting potential nesting habitat. Capricorn-Bunker Islands are not yet saturated with black noddies (Hulsman, 1984) and the establishment and growth of new colonies at One Tree Island and Lady Elliot Island in recent years
120
Tourism and environment at Heron Island
(Walker, 1986, 1989) indicates a period of expansion throughout the region. Numbers nesting at Heron Island are approaching a situation when competition for nest sites will limit future reproduction. A proposal to construct an airstrip on Heron Island in the late 1960s was rejected on ecological criteria (Heatwole, 1984) but, if the planning approach of Hill and Rosier (1989) had been used, this development might have proceeded. At that time, the black noddy population was small enough to be concentrated into the remaining trees around an airstrip. Such development would have precluded progression of the population to its present level. Another complication which must be considered in environmental planning relates to the existing "naturalness" of a site. There needs to be adequate knowledge that the site is not already damaged or deteriorated as a result of previous human activities. Did the increase in the black noddy population at Heron Island commence in the early 1960s coincident with removal of the rat infestation? Black noddies nested in only about 50 trees in 1927 (MacGillivray, 1928), and Cooper (1948) reported a similarly small colony in 1946 [the 50 pairs in 1910 cited by Hill and Rosier is an error from Kikkawa (1970), corrected in a subsequent article by Kikkawa and Boles (1976)]. The recent population increase to greater than 40 000 pairs is probably natural, but the possibility that it was previously constrained or reduced by nocturnal rat predation of nests (MacGillivray, 1928; Moulton, 1961; Bustard, 1972) cannot be overlooked. Introduced rats are implicated in depletion or extinction of island sea-bird colonies, including black noddy throughout the world (Atkinson, 1985). Prior to the 1970s, Heron Island birds were also subjected to feral cats, dogs and human occupants who dined on sea-bird eggs.
6. Wedge-tailed shearwater population The census of Shipway (1969) first showed that the density of shearwater burrows was higher by 37% or more in resort and research station areas compared with undeveloped regions of Heron Island. This density might be partly attributed to easy burrow access from roads, tracks and mown areas. In wet years, the forest clearings are choked with the garden escapee Euphorbia o'athophora that restricts approaches to burrows. The census of Hill and Barnes (1989) confirmed that low burrow densities are present in highly developed areas, but that high densities occur in partly developed or disturbed areas of Pisonia forest. Heron Island is capable of supporting a substantially greater number of burrows (presently over 16000 active burrows) before it reaches the density found nearby at North West Island (Hulsman, 1984). The same caution must therefore be exercised in planning for a cyclic shearwater population as for the black noddy population. Fluctuations in shearwater numbers are less visible because birds are hidden in burrows or remain at sea during daylight hours. They are susceptible to natural factors such as disease (Gilbert, 1925) but unlike black noddies they also suffer direct mortality from human activities. It is difficult to walk through nesting areas without collapsing burrows (crushing or suffocating the occupants) and this can be a problem if thousands of tourists visit a colony. Additionally, at Heron Island, there have been instances where regions of occupied burrows were bulldozed to make way for resort expansion (Moulton, 1961; Heatwole, 1984; pers. obs.).
7. Export of environmental problems Heron Island resort guests are taken on regular picnic trips to a nearby cay, Wilson Island, and consequently environmental problems are exported to this cay from Heron
T. A. Walker
121
Island. The issue of most concern is the impact on the roseate tern (Sterna dougallii) colony. This tern has a low global population and is threatened in the northern hemisphere. Its conservation status in the southern hemisphere is not known, but the largest breeding colony on the southern Great Barrier Reef has been recorded at Wilson Island. Further development at Heron Island will inevitably lead to higher visitation pressure on Wilson Island and perhaps other adjacent islands. Environmental problems result from daily sea-dumping of resort food scraps near Heron Island. As well as attracting sharks to the vicinity of scuba diving sites, the resort food scraps support hundreds of silver gulls (Larus novaehollandiae) that commute from adjacent islands where they prey on eggs and chicks of other nesting sea-birds (Walker, 1988). Tern colonies at these islands sometimes lose all of their clutches to gulls (Cooper, 1948; Hulsman, 1977).
8. Conclusion
Results of the environmental planning approach advocated by Hill and Rosier (1989) are already well illustrated at Heron Island. Following extensive development with inadequate knowledge or concern about environmental impacts, the island is permanently washing away, has the second lowest diversity of breeding sea-birds of any cay on the southern Great Barrier Reef, has the second highest number of weeds known for a coral island on the Great Barrier Reef, and sustains the largest Great Barrier Reef population of gulls. Most species o f sea-birds and shore-birds will abandon breeding colonies when impacted by human activities. There can be little doubt that seven or more species of seabirds and oystercatchers nested at Heron Island prior to human occupation. On the other hand, some species such as the black noddy and wedge-tailed shearwater are relatively fearless of people. If it can be demonstrated that human presence is not detrimental to the breeding success of these birds, then conditions for mutual coexistence on certain islands may be set. Such planning must ensure there is provision for the cycle of population expansion and reduction. The black noddy population is fast approaching saturation of the remaining habitat at Heron Island. Even without considering the black noddies and wedge-tailed shearwaters, there is more than adequate data to justify containment of further development at Heron Island. Effects on other components of the environment are considerable and there is a limit to the social carrying capacity of the cay. The environmental and social carrying capacities are not independent because most visitors to the island come to experience an attractive natural environment rather than social activities (in contrast with many other resorts). A survey of resort guests found that 57% were nature lovers, 18% were birdwatchers and 30% were photographers (categories not mutually exclusive; Environment Science and Services, 1986). Heron Island well illustrates the environmental damage that can result from occupation of coral cays and sea-bird breeding islands. On the Great Barrier Reef such damage can be minimized by directing tourism to the environmentally robust continental islands. These islands are more numerous, rarely have significant sea-bird or turtle colonies and usually do not require blasting or dredging of harbours. If general conservation theory and observation lead to erroneous conclusions that unjustly limit commercial development then the result is reversible when more adequate knowledge becomes available. The converse is unfortunately not often true. The approach advocated by Hill and Rosier (1989) must be rejected as a planning strategy. In
122
Tourism and environment at Heron Island
planning for development caution.
in fragile environments
it is e s s e n t i a l t o e r r o n t h e side o f
References
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