World Turtle Day
23 May 2017
Today, the Department of Environmental Affairs joins the world in commemorating World Turtle Day. There are seven (7) species of marine turtles in the world, of which five (5) have been recorded in South Africa. These are the Leatherback, Loggerhead, Green, Hawksbill and the rarely seen Olive Ridley turtles. Two of these species, namely, the Leatherback and the Loggerhead turtles nests in South Africa, in the iSimangaliso Wetland Park. These nesting beaches are of critical importance to turtles because of their genetic distinction from other rookeries of the same species in the Western Indian Ocean. iSimangaliso, despite being a World Heritage Site, has also been chosen to be one of the sites of importance for sea turtle conservation under the Indian Ocean South East Asia Turtle Memorandum of Understanding (MOU) , of which South Africa is a member state.
Marine turtles lay large numbers of eggs in holes that they excavate with their hand flippers on dry, sandy beaches. The clutch is then covered and left to incubate with no parental care. The eggs take between 70 - 20 days to hatch. As with other reptiles, a temperature can determine whether an egg develops into a male or a female: male hatchlings are associated with lower temperatures and females with higher temperatures. When the turtles hatch, they dig to the surface and head immediately towards the sea. They spend the rest of their lives in the open ocean or shallow coastal waters, except when they return to the nest. As such they are highly migratory, often moving considerable distances between nesting and feeding areas. Turtles are long-lived and can take many years to reach breeding age (for example, loggerhead females first reproduce between 17 and 33 years of age), and in many cases nest every few years rather than annually.
The eggs in the nests, are in one of the most sensitive life stages of turtles. Turtle eggs are susceptible to crushing, burial, exposure, erosion, tides and/or storm inundation. As such trampling by humans or life stock has the potential to crush eggs or hatchlings ready for emergence while still in their nests. Natural events such as tidal or storm inundation of nests or the erosion or accretion of beaches are natural selective pressures ensuring the survival of the fittest turtles.
Sea turtles are affected by numerous anthropogenic impacts. These include degradation of coastal and marine habitats, oil spills, degradation of water quality (including the accumulation of marine debris and ocean acidification), incidental capture or by-catch in fishery practices (that is, shark nets, purse seine and longliners). Other impacts affecting sea turtles include mortality through diseases or parasite infestation and predation by land-based predators such as mongoose, jackal, honey badgers as well as pets (e.g. dogs).
Sea turtles have an ecological role in that they influence community diversity and structure by operating at multiple trophic levels as predators, prey, competitors, nutrient transporters, habitat modifiers and substrates for epibionts (an organism that lives on the surface of another living organism). Turtles can enhance benthic diversity, e.g. by feeding on sponges, they reduce their coverage of reefs that facilitate the growth of corals. They also actively rework the sediment on the sandy beaches while digging their nests and directly making significant nutrient contributions to nutrient-poor beaches through nesting and thus influencing beach food webs. Turtles may also play a role as ideal sentinel species for ecosystem changes because they use a range of habitats throughout their lives and interact with various threats throughout.
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