· Harvesting of eggs for human consumption.
· Reduction of the penguin’s food supply by commercial fishing.
· Oil pollution from oil tankers. This could devastate the major colonies. Oil tankers may illegally clean out their tanks as they pass round the Cape to fill up with oil in the middle east.
· Large-scale removal of guano in the 19th century has decreased the ability of penguins to construct nests through burrowing. This has led to increased competition for breeding space with larger animals such as seals. Penguins breeding on the mainland are vulnerable to mainland predators not found on islands, such as leopards, genets and domestic dogs and cats, and also to human disturbance unless the colonies are adequately fenced and patrolled.
CONSERVATION ACTION
All the islands where jackass penguins breed, except Robben Island, are protected as provincial nature reserves or fall within the West Coast National Park. However, there is competition with seals for the limited breeding space available on some islands, and some individual seals are known to kill and eat penguins. At Mercury Island seals have been successfully displaced from penguin breeding sites. At Dassen and Robben Islands steps have been taken to eliminate the feral cat populations.
Efforts have been made to protect the new mainland breeding colonies at Betty’s Bay and Simonstown. A 100-metre fence has been erected at Stony Point peninsula at Betty’s Bay, and this is successfully preventing human disturbance and attacks by predators. The colony has grown to more than 100 nesting pairs.
The South African National Foundation for the Conservation of Coastal Birds (SANCCOB) carries out valuable work in rescuing oil-soaked penguins (and other seabirds) and rehabilitating them back to the wild. SANCCOB has one of the world’s highest rates of success in saving oiled seabirds, primarily because penguins respond better to captivity and cleaning than do flying birds.
· ROBERTS’ BIRDS OF SOUTHERN AFRICA.
G.L. Maclean. John Voelcker Bird Fund, Cape Town, 1985.
· OCEANS OF LIFE OFF SOUTHERN AFRICA.
A. Payne and R. Crawford (eds). Vlaeberg Publishers, Cape Town, 1989.
· SECRETS OF THE SEAS.
Illustrated guide to marine life off southern Africa. A. Payne and R. Crawford (eds). Vlaeberg Publishers, Cape Town, 1992.
GREEN TURTLE
HABITAT : Primarily shallow-water zones with seaweed (algae) or seagrass, and require sandy beaches for nesting.
GEOGRAPHICAL SPREAD: Circum-tropical marine waters. Although very many nesting locations are known worldwide, most populations are depleted and many are declining, some have already been extirpated (e.g. in the Caribbean). Only about a dozen large populations with around 2,000 or more nesting females per year are known at present; these occur on Ascension, around western and northern Australia, Costa Rica, Europa and nearby islands in the Mozambique Channel, Pacific Mexico, Oman, Pakistan, and possibly the Philippines, Sabah and Sarawak.
CURRENT POPULATION: Assessment of Marine Turtle populations is very difficult. Attention is focused on nests and nesting females. Because females rarely nest every year, but more usually at two, three or four year intervals, and because it is not possible to determine what proportion of the total mature female population is at the nest beach in any given year, population estimates are typically not precise. It is further complicated by the fact that nesting numbers on individual beaches can show extreme variation from one year to another. In a good year over 10,000 females may nest on Europa, and up to 80,000 at Raine Island (Australia); these appear to be the only stable populations not heavily exploited.
SIZE: Average nesting female carapace length 80 to 110cm.
WEIGHT: Average nesting female 110 to 185kg..
AVERAGE LIFE EXPECTANCY: Potentially long-lived.
NORMAL DIET: Herbivorous; exclusively seagrass and seaweed (algae).
NORMAL LIFESTYLE: Hatchlings emerge mostly at night from eggs buried in beach sand and make their way to the sea. The Green Turtle forages in shallow, inshore waters. Aggregations of Green Turtles often occur over shallow-water seagrass pastures or other suitable feeding grounds. Migrating Green Turtles may travel 20 to 40km per day. It is suggested that migratory behaviour is particularly linked with herbivory, since the richest feeding grounds (notably sea grasses) are most often found in shallow areas of coastal deposition, and do not typically coincide with the best nesting grounds (often isolated predator-free island beaches). Females do not attain maturity in the wild for 15 to 50 years. After a period of two to five decades, females typically migrate to a nesting beach often used by aggregations of turtles. Females remigrate at intervals of three years, and may lay three clutches of 100 to 120 eggs.
PREVIOUS GEOGRAPHICAL SPREAD: As present but with more nesting sites.
REASONS FOR DECLINE: Although traditionally used as a food source by many littoral peoples, the primary cause of decline in Green Turtle populations is systematic commercial exploitation of eggs and adults, coupled with beach disturbance.
CURRENT THREATS: Heavily utilised in most of the range; adults and eggs for food, juveniles for curios, and adults also for hide and oil. Incidental catch causes much mortality. Local subsistence and local commercial exploitation appear to be having an increasing impact on sea turtle populations, as tribal cultures decline, modern technology (e.g. outboard motors) spreads, and human populations in the tropics increase.
CONSERVATION PROJECTS: Chelonia mydas is listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Appendix I listing requires that trade in the taxon and its products is subject to strict regulation by ratifying states and international trade for primarily commercial purposes is forbidden. Nominally protected by legislation in much of the range, however, in many areas the legislation is inadequately enforced. Some nesting beaches fall within National Parks or Nature Reserves and are accorded varying degrees of protection. Legislation should be enforced, more protected areas are required (for nesting beaches, internesting habitat, and other life cycle phases). The slow maturation period for Marine Turtles can mask the effects of exploitation and conservation action. It is possible to monitor the populations at some localities from the air or by boat. Since the Green Turtle is a migratory species, passing through the jurisdictions of many countries, international cooperation and regional agreements on conservation are highly desirable. Has bred in captivity, but large-scale closed-cycle captive breeding has not yet been demonstrated to be possible.
SPECIAL FEATURES: The Green Turtle is the largest of the hard-shelled sea turtles (the Leatherback Dermochelys can grow much larger) although size, weight, and carapace shape can vary markedly between different populations.
REFERENCES:
Groombridge, B. and Luxmoore, R. 1989. The Green Turtle and Hawksbill World Status, Exploitation and Trade. CITES Secretariat, Switzerland.
Groombridge, B. 1982. The IUCN Amphibia Reptilia Red Data Book: Testudines, Crocodylia, Rhynchocephalia. IUCN, Switzerland.