Dyer Island Nature Reserve

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General Information

Status:

Global IBA (A1, A4i, ii, iii)

Province:

Western Cape

Protection:

Fully Protected

Size:

390 ha

Number:

SA120

Additional Info

  • Site description

    Covering c. 20 ha, Dyer Island is one of two low-lying islands situated 4.7 km south-east of Danger Point; the nearest harbour is at Kleinbaai/Franskraal, just south of Gansbaai. Its coastline is rugged, with some low rocky areas spreading inland. This flat, low-lying island reaches 7 m a.s.l. at its highest point and is covered by a pebble surface with little sand. The mixed vegetation consists primarily of species of the Mesembryanthemaceae family and exotic weeds. In the south-eastern section of the island are several buildings that house the island staff, boats and stores. The smaller Geyser Island also forms part of the IBA and Dyer Island Nature Reserve.

    Dyer Island is approximately 20 hectares and is one of two low-lying islands situated 4.7 km south-east of Danger Point; the nearest harbour is at Kleinbaai/Franskraal, just south of Gansbaai. Its coastline is rugged, with some low rocky areas spreading inland. This flat, low-lying island reaches 7 m a.s.l. at its highest point and is covered by a pebble surface with little sand. The mixed vegetation consists primarily of species of the Mesembryanthemaceae family and exotic weeds. In the south-eastern section of the island are several buildings that house the island staff, boats and stores. The smaller Geyser Rock also forms part of the IBA and Dyer Island Nature Reserve.

    Birds

    CapeNature has recorded 12 seabird and five terrestrial species breeding on the island (Birss et al. 2012). Unfortunately, as in the cases of other island IBAs in the Western Cape that have been gazetted specifically for their seabirds, these species have shown major declines from the numbers recorded in the original IBA description (Barnes 1998).

    The African Penguin Spheniscus demersus population at Dyer Island is in rapid decline. Although the island supported some 72 500 birds in 1976, it is thought that the population may have fallen below 3 000 pairs by 1997. It now numbers approximately 1 000 breeding pairs.

    The discovery of Leach’s Storm Petrel Oceanodroma leucorhoa in several of the stone walls on the island in October 1995 was the first evidence of a procellariiform breeding in southern Africa. In November 1996 at least 19 birds were heard calling from within the walls and one was found to be incubating an egg. It was estimated that 8–9 pairs were breeding. In early February 1997 the nest contained a month-old chick and chicks were heard calling from two other nests, confirming breeding for this species.

    In 1996, after an absence of some 25 years, Roseate Tern Sterna dougallii, which breeds regularly only at two other islands in southern Africa (Bird and St Croix Islands, part of the Algoa Bay Islands IBA, SA095), attempted to breed again at Dyer Island. The attempt failed, it is suspected as a result of human disturbance. However, in subsequent years the species remained on the island and a small breeding colony persists. Caspian Tern Sterna caspia has also been recorded breeding on the island and has been listed as an additional IBA species.

    Many other species breed on this island, including large numbers of Cape Cormorant Phalacrocorax capensis (approximately 12% of the species’ population) and small numbers of White-breasted Cormorant P. lucidus, Bank Cormorant P. neglectus and Crowned Cormorant P. coronatus. Numbers of Bank and Cape Cormorants have declined in recent years, while numbers of Crowned Cormorant seem to have remained stable. Several large colonies of Hartlaub’s Gull Chroicocephalus hartlaubii and Swift Tern Thalasseus bergii breed on the island. Sandwich Tern T. sandvicensis, Common Tern Sterna hirundo, Arctic Tern S. paradisaea and Antarctic Tern S. vittata all form large mixed tern roosts with the breeding Swift Terns.

    Dyer Island is also estimated to hold more than 1% of the world’s African Black Oystercatcher Haematopus moquini population.

    IBA trigger species

    Globally threatened trigger species are African Penguin (975 breeding pairs; Crawford et al. 2012), Bank Cormorant (nine breeding pairs; Crawford et al. 2012), Cape Cormorant (24 000 breeding pairs; Crawford et al. 2012) Crowned Cormorant (266 breeding pairs; Crawford et al. 2012) and African Black Oystercatcher (21 breeding pairs; Birss et al. 2012). Regionally threatened species are Roseate Tern (15–30 breeding pairs; Birss et al. 2012) and Caspian Tern (four breeding pairs; Birss et al. 2012).

    Congregatory species with more than 1% of the population represented are Cape Cormorant and African Black Oystercatcher. More than 0.5% of the population of Hartlaub's Gull (160 breeding pairs; Birss et al. 2012) and Swift Tern (500 breeding pairs; Birss et al. 2012) are present on the island.

    Other biodiversity

    The waters around Dyer Island hold a large population of great white shark Carcharodon carcharias.

    Conservation issues

    Threats

    The main focus of conservation on this island nature reserve is the seabird colonies, which are the reason for the island being given IBA status (Barnes 1998). The threats facing the seabirds on Dyer Island are not dissimilar to those impacting other colonies around the east and west coasts of South Africa. In particular, the seabirds are impacted by an increase in competition for food resources. Competition with commercial fisheries, especially purse-seining for surface-shoaling fish such as anchovy Engraulis capensis and pilchard Sardinops sagax, has been implicated as one of the most significant factors causing seabird population declines in the region. Anchovy recruitment was impaired and stocks were greatly reduced between 1989 and 1990, which may have triggered mass penguin emigration. It is thought that birds that used to breed at Dyer Island may have relocated to Stony Point, Boulders Beach, Robben Island and as far east as St Croix in the Algoa Bay Islands IBA, where the populations are growing steadily. It has been recommended that marine reserves with a radius of 25 km be created around important breeding islands. Commercial fishing should be banned or restricted within these zones. Regulations of this type may prevent the local depletion of food resources that contributes to low breeding success and may precipitate mass desertion of these colonies.

    Loss of suitable breeding habitat for seabirds and degradation of habitat by pollution are also threats. Pollution incudes both chronic and catastrophic oil pollution by crude oil or other pollutants that spill into the ocean when tankers run aground and break open, wash their tanks, dump cargo or pump bilge. Chronic plastic pollution also occurs and can result in birds either becoming entangled in plastic that washes up on the breeding islands or ingesting plastic when they are foraging in the open ocean.

    Another threat is disturbance due to uncontrolled tourism activities, in conjunction with disturbance that can be generated through monitoring activities. CapeNature is very aware of the latter issue and ensures that negative impacts are minimal. Tourism to the reefs around the island to see great white shark is increasing and the industry needs to be carefully monitored. Landings on the island are currently not permitted. Several introduced species also occur on the treeless Dyer Island, including 15 exotic plants, which are mostly small weeds and forbs.

    The Cape fur seal Arctocephalus pusillus population on nearby Geyser Island has been growing steadily. There has been an increase in the number of cases of seals mauling and killing penguins and Cape Cormorant fledglings. Certain ‘rogue’ individuals seem to be the principal agents of this mortality and it is important that management action be introduced to eliminate the animals responsible. Furthermore, increased seal numbers, coupled with the animals’ ability to outcompete and displace birds at breeding islands, pose a major threat to all breeding seabirds.

    The poaching of abalone Haliotis asinina and other marine resources, potential outbreaks of disease and the impacts of climate change are also noted as threats to the seabirds. An outbreak of an epizootic occurred in 2002, affecting five offshore islands in the Western Cape. Since then, outbreaks of avian cholera Pasteurella multocida have occurred annually on Dyer Island. However, these outbreaks are carefully monitored and managed by CapeNature staff in order to reduce seabird mortalities.

    Conservation action

    Dyer Island is State-owned and administered and managed by the Walker Bay office of CapeNature based in Hermanus. This status affords the island the necessary protection, management planning and associated resources required for long-term conservation. A number of actions deal with all the aspects of conservation management at this site, as laid out in detail in the Dyer Island Nature Reserve Complex Protected Area Management Plan of 2012. These actions include (but are not limited to) finalising the legal status and reserve expansion as far as possible; co-operative governance with all relevant government departments and other agencies; ecosystem and biodiversity monitoring and management; law enforcement and compliance; infrastructure management and maintenance; and disaster management.

    Seabird populations on specific islands are seldom stable over long periods and they go through spells of flux. The most important island at any one time may be of minimal significance a few decades later. It is imperative that the entire network, including other IBAs of the Western Cape and Eastern Cape where threatened birds breed or could breed, is suitably protected.

    Related webpages

    www.capenature.co.za

    Dyer Island Conservation Trust: http://www.dict.org.za/index.php

    Contact

    If you have any information about the IBA, such as a new threat that could impact on it, please send an e-mail to iba@birdlife.org.za or call BirdLife South Africa +27 (11) 789 1122.

    Page last updated

    Friday, 23 January 2015

    Further Reading

    Adams NJ. 1991. Patterns and impacts of oiling of African Penguins Spheniscus demersus 1981–1991. Biological Conservation 68: 35–41.

    Birss C, Geldenhuys D, Waller L, Cleaver-Christie G. (eds). 2012. Dyer Island Nature Reserve Complex Management Plan 2013-2018. Unpublished report. Cape Town: CapeNature.

    Branch WR. 1991. The herpetofauna of the offshore islands of South Africa and Namibia. Annals of the Cape Provincial Museum (Natural History) 18: 205–225.

    Brooke RK, Prins A.J. 1986. Review of alien species on South African offshore islands. South African Journal of Antarctic Research 16: 102–109.

    Cooper J. 1981. Biology of the Bank Cormorant, Part 1: Distribution, population size, movements and conservation. Ostrich 52: 208–215.

    Cooper J, Berruti A. 1989. The conservation status of South Africa’s continental and oceanic islands. In: Huntley BJ (ed.), Biotic diversity in southern Africa: concepts and conservation. Cape Town: Oxford University Press. pp 239–253.

    Cooper J, Brooke RK. 1986. Alien plants and animals on South African continental and oceanic islands: species richness, ecological impacts and management. In: Macdonald IAW et al. (eds), The ecology & management of biological invasions in southern Africa. Cape Town: Oxford University Press.

    Cooper J, Hockey PAR, Brooke RK. 1983. Introduced mammals on South and South West African islands: history, effects on birds and control. In: Cooper J (ed.), Proceedings of the Symposium on Birds of the Sea and Shore, 1979. Cape Town: African Seabird Group. pp 179–203.

    Cooper J, Williams AJ, Britton PL. 1984. Distribution, population sizes and conservation of breeding seabirds in the Afrotropical region. ICBP Technical Publication No. 2.

    Crawford RJM. 1995. Conservation of southern Africa’s breeding seabirds. Birding in Southern Africa 47: 106–109.

    Crawford RJM, Altwegg R, Barham BJ, Barham PJ, Durant JM, Dyer BM, Geldenhuys D, Makhado AB, Pichegru L, Ryan PG, Underhill LG, Upfold L, Visagie J, Waller LJ, Whittington PA. 2011. Collapse of South Africa’s penguins in the early 21st century. African Journal of Marine Science 33(1): 139–156.

    Crawford RJM, Cooper J, Shelton PA. 1982a. Distribution, population size, breeding and conservation of the Kelp Gull in southern Africa. Ostrich 53: 164–177.

    Crawford RJM, David JHM, Williams AJ, Dyer BM. 1989. Competition for space: recolonising seals displace endangered, endemic seabirds off Namibia. Biological Conservation 48: 59–72.

    Crawford RJM, Dyer BM. 1995. Responses by four seabird species to a fluctuating availability of Cape Anchovy Engraulis capensis off South Africa. Ibis 137: 329–339.

    Crawford RJM, Dyer BM, Brooke RK. 1994. Breeding nomadism in southern African seabirds: constraints, causes and conservation. Ostrich 65: 231–246.

    Crawford RJM, Dyer BM, Kotze PGH, McCue S, Meÿer MA, Upfold L, Makhado AB. 2012. Status of seabirds breeding in South Africa in 2011. Cape Town: Department of Environmental Affairs, Branch Oceans & Coasts.

    Crawford RJM, Shelton PA. 1978. Pelagic fish and seabirds interrelationships off the coasts of South West and South Africa. Biological Conservation 14: 85–109.

    Crawford RJM, Shelton, PA. 1981. Population trends for some southern African seabirds related to fish availability. In: Cooper J (ed.), Proceedings of the Symposium on Birds of the Sea and Shore, 1979. Cape Town: African Seabird Group. pp 15–41.

    Crawford RJM, Shelton PA, Brooke RK, Cooper J. 1982b. Taxonomy, distribution, population size and conservation of the Crowned Cormorant Phalacrocorax coronatus. Gerfaut 72: 3–30.

    Crawford RJM, Shelton PA, Cooper J, Brooke RK. 1983. Distribution, population size and conservation of the Cape Gannet Morus capensis. South African Journal of Marine Science 1: 153–174.

    Crawford RJM, Williams AJ, Hofmeyer JH, Klages NTW, Randall RM, Cooper J, Dyer BM, Chesselet Y. 1995c. Trends in African Penguin Spheniscus demersus populations in the 20th century. South African Journal of Marine Science 16: 101–118.

    Crawford RJM, Williams AJ, Randall RM, Randall RM, Berruti A. & Ross GJB. 1990. Recent population trends in Jackass Penguins Spheniscus demersus. Biological Conservation 52: 229–243.

    Frost PGH, Siegfried WR, Cooper J. 1976. Conservation of the Jackass Penguin (Spheniscus demersus). Biological Conservation 9: 79–99.

    Furness RW, Cooper J. 1982. Interactions between breeding seabird and pelagic fish populations in the southern Benguela region. Marine Ecology Progress Series 8: 243–250.

    Hockey PAR, Hallinan J. 1981. Effects of human disturbance on the breeding of Jackass Penguins Spheniscusdemersus. South African Journal of Wildlife Research 11: 59–62.

    Morant PD, Cooper J, Randall RM. 1981. The rehabilitation of oiled Jackass Penguins Spheniscus demersus, 1970–1980. In: Cooper J (ed.), Proceedings of the Symposium on Birds of the Sea and Shore, 1979. Cape Town: African Seabird Group. pp 267–301.

    Rand RW. 1963. The biology of guano producing seabirds: a composition of the colonies on the Cape Islands. Division of Sea Fisheries Investigational Report No. 43. Cape Town: Department of Commerce and Industries.

    Randall RM, Randall BM. 1980a. Status and distribution of the Roseate Tern in South Africa. Ostrich 51: 14–20.

    Randall RM, Randall BM, Bevan J. 1980b. Oil pollution and penguins: is cleaning justified? Marine Pollution Bulletin 11: 234–237.

    Shelton PA, Crawford RJM, Cooper J, Brooke RK. 1982. Distribution, population size and conservation of the Jackass Penguin Spheniscus demersus. South African Journal of Marine Science 2: 217–257.

    Siegfried WR. 1982. Ecology of the Jackass Penguin Spheniscus demersus, with special reference to conservation of the species. National Geographic Society Research Reports 14: 597–600.

    Summers RW, Cooper J. 1977. The population, ecology and conservation of the African Black Oystercatcher Haematopus moquini. Ostrich 48: 28–40.

    Underhill LG, Crawford RJM, Wolfaardt AC, Whittington PA, Dyer BM, Leshoro TM, Visagie J. 2006. Regionally coherent trends in colonies of African penguins Spheniscus demersus in the Western Cape, South Africa, 1987–2005. African Journal of Marine Science 28(3–4): 697–704.

    Waller LJ, Underhill LG. 2007. Management of avian cholera Pasteurella multocida outbreaks on Dyer Island, South Africa, 2002–2005. African Journal of Marine Science. 29(1): 105–111.

    Whittington PA. 1996. Voices in the walls. Africa – Birds & Birding 1(3): 13.

    Whittington PA, Dyer BM. 1995. A new breeding seabird for Africa? Bird Numbers 5: 18–19.

    Whittington PA, Dyer BM, Crawford RJM. 1998. Leach’s Storm Petrel: further news from the islands. Bird Numbers 7(1): 20–21.

    Whittington PA, Dyer BM, Crawford RJ, Williams AJ. 1999. First recorded breeding of Leach’s storm petrel Oceanodroma leucorhoa in the Southern Hemisphere, at Dyer Island, South Africa. Ibis 141(2): 327–330.

    Williams AJ, Steele WK, Cooper J, Crawford RJM. 1990. Distribution, population and conservation of Hartlaub’s Gull Larus hartlaubii. Ostrich 61: 66–76.

    Wilson RP, Wilson MTP, Duffy DC. 1988. Contemporary and historical patterns of African Penguin Spheniscus demersus: distribution at sea. Estuarine, Coastal and Shelf Science 26: 447–458.

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