The history and status of oyster exploitation and culture in South Africa. ABSTRACT Both wild and cultivated oysters are consumed in South Africa. Edible wild oysters include Striostrea margaritacea, Saccostrea cucullata, Ostrea atherstonei, and O. algoensis, all of which occur along the south and east coasts, but not on the west coast. Wild oysters are exploited commercially, recreationally, and by subsistence fishers, with S. margaritacea being by far the most intensively targeted species. Commercial harvesting of S. margaritacea takes place along the southern Cape coast and in KwaZulu-Natal (KZN), with the southern Cape hosting 102 of the 145 commercial pickers. Data on total annual commercial catch of oysters in the various harvesting areas are presented, but these are minimum estimates, because collectors do not always comply with harvesting regulations or fully report catches. Subsistence harvesting remains largely unmanaged, except in KZN, and is particularly prevalent in the eastern Cape Province. The culture of oysters is dependent on imported Crassostrea gigas spat, mostly from Chile. Accurate annual oyster production statistics are only available since 1985, although approximately 2 million C. gigas oysters are known to have been cultured annually throughout the 1970s and early '80s. Since then, production increased steadily from 1985 to 1991, peaking at some 8 million individuals, then declined to 2-4 million individuals from the mid 1990s onward. Although the market for oysters has grown, production has not kept up with demand, largely because of a lack of suitable locations for oyster culture. Finding suitable sites for cultivation
along the northern Cape Province coast and establishing local oyster hatcheries for C. gigas are suggested as future priorities for the industry. KEY WORDS: Crassostrea gigas, Striostrea margaritacea, oyster, culture, exploitation, South Africa INTRODUCTION The South African coastline extends 3,100 km from the Namibian border (28[degrees]S, 16[degrees]E) in the west to that of Mozambique (26[degrees]S, 32[degrees]E) in the east. Its main features are the cold Benguela Current off the west coast and the warm Agulhas Current off the south and east coasts, resulting in a strong east-to-west decline in temperature that determines the distribution patterns of many marine organisms (Brown & Jarman 1978, Branch & Griffiths 1988, Emanuel et al. 1992). Various families of oysters occur along the South African coastline and are listed by Kilburn and Rippey (1982), but only members of the family Ostreidae are of commercial interest in this region, which is too temperate for culture of pearl oysters of the family Pteriidae. Four indigenous oysters, belonging to three genera of Ostreidae, occur in South Africa namely, Striostrea margaritacea and Saccostrea cucullata (previously known as Crassostrea margaritacea and C. cuccullata respectively), Ostrea atherstonei and O. algoensis (Kilburn & Rippey 1982). In addition, the introduced Pacific oyster Crassostrea gigas is widely farmed and has become naturalized in estuaries along the south coast (Robinson et al. 2005). In the following account we outline the distribution patterns and characteristics of these species and review the history of oyster
exploitation and culture in the region. DISTRIBUTION PATTERNS, CHARACTERISTICS, AND HABITAT PREFERENCES The Cape rock oyster S. margaritacea ranges from False Bay to Mozambique (Fig. 1) and is a large, heavy oyster, growing to 180 mm in shell length (Branch et al. 2005). The deep, multilayered, cup-shaped lower valve is cemented to the substratum and the thin, flat upper valve is usually marked with fine radially striated conchiolin externally (Kilburn & Rippey 1982). This conchiolin, together with the iridescent mother-of-pearl to gold shell interior and smooth, uncolored valve margins distinguish this species from S. cucullata (Robinson et al. 2005). S. margaritacea is common on rocky reefs from low water to about 5 m depth (Kilburn & Rippey 1982) and is the most common indigenous oyster species in the western Cape and the most economically important native oyster in the region (Branch et al. 2005). The Natal rock oyster S. cucullata ranges from Algoa Bay to KwaZulu-Natal (KZN) (Fig. 1) and is smaller than S. margaritacea, reaching only 70 mm in shell length (Branch et al. 2005, Robinson et al. 2005). The lower valve is deeply hollowed below the hinge and is cemented to the rock, whereas the upper valve is relatively flat. Unlike S. margaritacea, the radial threads are absent, the shell interior is noniridescent whitish gray, and the valve margins black with undulating folds (Kilburn & Rippey 1982). S. cucullata form a conspicuous belt on rocks in the upper midtidal zone, and are known to thrive under muddy conditions, colonizing the roots of mangrove trees and even reeds (Kilburn & Rippey 1982, Branch et al. 2005). The red oyster O. atherstonei ranges from Saldanha Bay to the south
coast of KZN (Fig. 1), grows to a maximum shell length of 105 mm, and has a shallow lower valve that is not hollowed below the hinge. Its color ranges from purplish brown to wine red. Individuals inhabit sheltered reefs on the open coast, mainly below the low tide level. O. atherstonei provide excellent eating, but do not form beds and are therefore of little commercial importance (Kilburn & Rippey 1982, Branch et al. 2005). The Cape weed oyster O. algoensis ranges from False Bay to East London (Fig. 1) and is relatively small, delicate, and flattened, growing to only 45 mm in shell length. The internal margin bears distinct chomata in the hinge region and the exterior is either smooth or has weak radial folds. The exterior is yellow or yellowish gray, with black or purplish rays, and the interior a very pale brownish yellow to greenish gray. O. algoensis are found in pools or in the mouths of estuaries and are often attached to the underside of intertidal rocks (Kilburn & Rippey 1982), but are too small to be of commercial interest. [FIGURE 1 OMITTED] The introduced Pacific oyster C. gigas is the most important commercially marketed oyster globally and in South Africa, and is quite similar in appearance to S. cucullata and S. margaritacea, with which it is often confused. It is characterized by a noniridescent white to off-white shell interior, has at least 1 adductor scar that is purple, and has undulating valve margins that usually show no coloration, although a few may be mauveblack (Robinson et al. 2005). C. gigas is usually larger than S. cucullata and S. margaritacea, reaching a maximum
size of 200 mm. Naturalized populations are known only from the Breede, Goukou, and Knysna Estuaries on the southern Cape coast (Fig. 1). The largest wild population (>180,000 individuals) is found in the Breede Estuary, whereas the other estuaries each support populations of less than 1,500 individuals (Robinson et al. 2005). The origins of these populations are unknown, but they may have became established as a result of trial introductions carried out by the former Division of Sea Fisheries of the Department of Trade and Industries. Naturalized individuals inhabit the low intertidal zone and to a depth of 1 m (Robinson et al. 2005). EXPLOITATION OF WILD OYSTERS Indigenous people have exploited shellfish resources in South Africa for thousands of years, as evidenced by the numerous shell remains found in prehistoric middens (Thackeray 1988, Van Andel 1989). However, oyster shells have not been reported from these middens, indicating that they were not exploited at that time (Parkington et al. 1988, Thackeray 1988, Jerardino & Yates 1996, Halkett et al. 2003, Jerardino et al. 2008). In the modern era, commercial, recreational, and subsistence harvesting of wild oysters all occur, both along the southern Cape coast and in KZN. S. margaritacea is the only species that is commercially targeted, whereas this and S. cucullata are the main species harvested for recreational and subsistence purposes. The directorate of Marine and Coastal Management (MCM) of the Department of Environment Affairs and Tourism (DEAT) is the primary government institution responsible for management of both recreational and commercial oyster fisheries along
the Southern Cape coast. In the province of KZN, the local conservation authority, Ezemvelo KwaZulu-Natal Wildlife, is responsible for management on behalf of MCM. Prior to 2002, the oyster fisheries in these 2 regions were managed as separate entities, but after 2002 they have been managed as a single national fishery and 4 commercial oyster-harvesting areas have been recognized (i.e., southern Cape coast, Port Elizabeth, KZN North, and KZN South (DEAT 2006); Fig. 1). No legally sanctioned commercial harvesting occurs along the remainder of the south and east coasts, although oysters do occur there (Fig. 1). Recreational collectors are required to apply for a permit and are allowed a maximum of 25 oysters per day, which can be collected by hand, or with a specified implement (blade or flat edge not exceeding 40 mm and not less than 1 m in length) (DEAT 2008/ 2009). Details of the spatial and temporal exploitation patterns of each species are provided in the following sections. Striostrea margaritacea Southern Cape Coast and Port Elizabeth The oyster, S. margaritacea is collected for small-scale commercial, recreational, and subsistence use along the southern Cape coast and throughout the eastern Cape Province (Cockcroft et al. 2002). Previously, regulations were implemented for harvesting oysters along the southern Cape coast (e.g., 25 oysters per picker per day), but the fishery was still poorly managed, because no licensing and submission of catch returns were implemented (Dye et al. 1994). Currently, a license is required to harvest oysters commercially and the southern Cape houses 102 of the 145 pickers used in South Africa. Commercial pickers are
required to complete catch return forms on a regular basis, indicating the number of oysters collected and the number of outings undertaken. Commercial harvesting is managed by limiting the number of pickers, with no daily bag limit, and effort is split across areas according to the extent of accessible oyster reef (DEAT 2006). The fishery is further controlled by a closed season from December 15 to January 5 to limit conflict between the commercial oyster sector and recreational harvesters during this peak holiday season (DEAT 2006). There are only 3 legal commercial pickers in Port Elizabeth and no in situ harvesting of oyster beds is practiced there, with only washed-up oysters collected (DEAT 2006). Levels of exploitation, are, however, still high along the rest of the eastern Cape as a result of recreational and extensive subsistence harvesting (Kiepiel & Quinlan 1997, Robertson & Fielding 1997, Britz et al. 2001, Cockcroft et al. 2002). The total commercial catch of oysters along the southern Cape coast and Port Elizabeth region has declined steadily since the earliest records in 1972 (Fig. 2). Reasons for this could be either a decrease in stocks of S. margaritaeea resulting from overexploitation, or implementation of stricter regulations. These official figures are, however, not considered totally reliable, because pickers often fail to submit catch--return forms (Madikaza, MCM, pers. comm.); thus, actual catches are almost certainly higher than reported here. Subsistence harvesting of S. margaritacea also occurs along the southern Cape coast, without any firmly enforced conservation legislation (Siegfried et al. 1994, Griffiths & Branch 1997). The
oysters are not usually consumed by fishers themselves, but rather are sold to generate an income. Hence, it has been suggested that these harvesters should be considered as small-scale commercial, rather than subsistence, fishers (Branch et al. 2002, Clark et al. 2002). As a result, in 2002, limited commercial oyster rights were allocated to empower a number of former subsistence fishers who were previously prevented from legally selling their harvests (DEAT 2006). KwaZulu-Natal In KZN, S. margaritacea are collected for small-scale commercial, recreational, and subsistence purposes (Cockcroft et al. 2002). The most important beds occur on the north coast and are harvested by 25 pickers, compared with only 15 pickers on the south coast (Schleyer & Kruger 1990, DEAT 2006). The oyster fishery in this province has operated for more than a century, and evidence of harvesting comes from as early as 1894 (Thompson 1913). The fishery is separated into a "local trade" (commercial) fishery and a "visitor" (recreational) fishery. The former is currently the only commercial intertidal fishery along the KZN coast (De Bruyn 2006). The commercial fishery was initially managed by dividing the coastline into 3 separate harvesting regions; in the mid 1950s, these regions were divided into 9 zones (De Bruyn 2006). In 1998, this was again revised, reducing the 3 regions to 2, with 5 zones in each, following recommendations from Schleyer (1988) and Schleyer & Kruger (1991) (Fig. 3). Harvesting is controlled by a rotational system that operates over a 5-y period. Two adjacent zones are consecutively harvested, each for 1 y, first by recreational fisheries and then by
commercial fisheries, and are then left fallow for the following 3 y (De Bruyn 2006). Both commercial and recreational fisheries are managed by licenses, subject to the submission of catch--returns, which provide useful statistics for managers. Prior to 1998, a daily bag limit of 50 oysters per recreational permit per day was allowed, but this has since been reduced to 25 oysters per permit per day in an effort to prevent overexploitation. The commercial regulations have also changed. Prior to 1999, 5 pickers were allowed per license, after which "half" and "full" licenses, allowing between 5 pickers and 12 pickers, were issued. Currently, pickers are registered individually. Bag limits per license have decreased from 960 oysters per picker per day to 190 oysters per picker per day. Harvesting gear has also changed. Historically, women and girls entered the water to depths not greater than their chests and pried oysters from the rocks, locating them by feel, or by sight, if the water was clear. The use of diving gear was prohibited; thus, only oyster populations in the intertidal and near-subtidal zones were exploited during spring low tides. Harvesting is now undertaken predominantly by men, who use masks and snorkels and are able to exploit oysters in water up to 1.5 m deep. They are, however, still restricted from using fins or flotation devices, and this prevents the subtidal "seed" stock or "mother beds" from being exploited (Dye et al. 1994, De Bruyn 2006). [FIGURE 3 OMITTED] Prior to the implementation of the new zonation system in 1998, stocks of S. rnargaritacea were diminishing in KZN. Overfishing,
combined with cyclical population changes and environmental variation probably played a role in this decline (Schleyer & Kruger 1990). De Bruyn et al. (2008) found that the abundance of the stock increased since the new rotational harvesting system was introduced in 1998, indicating a recovery. Nevertheless, Figure 4 indicates that the total annual commercial catches of S. margaritaeea have progressively declined since the mid 1980s, probably as a result of lower effective effort. Apart from commercial and recreational oyster fisheries, subsistence harvesting of S. margaritacea and other oysters, such as S. cucullata, also exists in KZN (Kyle et al. 1997). Data on informal fishing activities are not available, because no control has been implemented in the past. Currently, however, a management plan for subsistence fisheries in KZN has been drawn up, and controls are in the process of being implemented. Saccostrea cucullata Eastern Cape Province Most subsistence fishing in South Africa takes place along the heavily populated east coast (Clark et al. 2002, Cockcroft et al. 2002). The coast of the eastern Cape Province is relatively undeveloped, and the unspoiled nature of the surroundings has attracted many visitors and tourists, who encourage subsistence fisheries by creating a market for marine resources, including oysters (Kiepiel & Quinlan 1997, Robertson & Fielding 1997). S. cucullata have been heavily exploited by subsistence and recreational fisheries along this coastline (Kyle et al. 1997, Cockcroft et al. 2002). Hockey and Bosman (1986) compared exploited and protected sites (reserves) and found that exploited sites
exhibited greater species richness, but the size and density of exploited species, including S. cucullata, were diminished in exploited areas. The removal rates of this species have been estimated at 9-l1/[m.sup.2]/y (Dye 1989). Despite initial indications to the contrary, Dye et al. (1994) suggested that the recruitment of this species in the eastern Cape Province was so poor that no exploitation should be permitted. During the past decade, exploitation levels of S. cucullata in the eastern Cape Province have been moderate compared with those of S. margaritacea, which are also collected commercially. In 2001, the stock of S. cucullata was considered to be "variable to good," and the species was not viewed as an immediate research priority (Britz et al. 2001). [FIGURE 4 OMITTED] KwaZulu-Natal Saccostrea cucullata occurs in great densities in KZN, but is only targeted by recreational and subsistence fishers (Cockcroft et al. 2002). Subsistence fishers exploit this resource for a variety of purposes, including food, ornamentation, and traditional medicine. Harvesting is carried out mostly by women or children and, although oysters are not collected as often as mussels, they are still one of the main species harvested, with 5 t of S. cucullata and S. margaritacea being collected in KZN North between 1988 and 1994 (Kyle et al. 1997). However, only S. margaritacea may be harvested commercially (De Bruyn 2006). Ostrea atherstonei and Ostrea algoensis These oysters are not currently exploited in any significant
numbers, although failed attempts at culturing both species have been made in the past (Korringa 1956). They occur in KZN, but numbers are too scarce to warrant targeted collection (Schleyer, pers. comm.). In Langebaan Lagoon, deposits of O. atherstonei shells have fossilized, forming extensive oyster beds (Grindley 1969, Compton 2001), indicating that these oysters must have occurred in great numbers in the past. Changes in ocean currents, brought about by a decrease in sea level, are thought to be the reason for their mass mortality (Scott 1951). The extensive gravel oyster bed in Langebaan Lagoon used to be dredged commercially for agricultural lime, with 3 million t of lime being processed by an oyster shell factory that ceased operations before 1970 (Tankard 1976). Crassostrea gigas Wild populations of C. gigas have recently been reported in estuaries along the southern Cape coast. Holidaymakers have been observed collecting C. gigas in the Breede River Estuary (Robinson et al. 2005), although exploitation rates have not been quantified. Conservation legislation currently protects these populations. However, even though the authorities are aware of its invasive nature, no action has been taken. Based on the preceding information, it is evident that, although commercial and recreational harvesting of oysters in South Africa are controlled to a variable extent, the subsistence sector, which is an active role player in contributing to the exploitation of stocks, has been largely ignored. In the past, subsistence fishers had no legal access to marine resources and were therefore classified as poachers
(Cockcroft et al. 2002). This changed with the introduction of the white paper on fisheries and the Marine Living Resources Act in 1998, which recognized subsistence fishing for the first time in South Africa (DEAT 1997, DEAT 1998). Authorities have, however, only recently started managing the subsistence sector, and this fishery is still uncontrolled along large parts of the South African coastline, most notably on the eastern Cape. Despite management efforts in this region since the early 1990s (Fielding et al. 1994), active management occurs only in the southwestern half of the province around Port Elizabeth. Currently no fishery managers, or researchers, are based in most of the relatively inaccessible and underdeveloped eastern area, where poaching of marine resources remains rife (Britz et al. 2001). OYSTER CULTURE Aquaculture in South Africa's marine environment is underdeveloped. This is largely as result of the generally linear and wave-exposed nature of the coastline, which contains few significant estuaries, or sheltered bays, suitable for culture operations. Until recently, there has also been a lack of government investment and promotion. However, aquaculture facilities for high-value species, such as oysters, have become relatively well established through private-sector initiatives (Britz et al. 2001). These ventures were, however, not easily established, and oyster culture in South Africa has a long history, fraught with many difficulties. Early European settlers noticed the masses of indigenous oysters (probably S. margaritacea) along the south coast (Korringa 1956), and attempts at culturing oysters were made as early as 1673. It was not,
however, until 1948 that the first commercial company was founded in Knysna, and attempts at farming S. margaritacea were made (Hecht & Britz 1992). During these pioneer stages, the majority, if not all, attempts at establishing the culture of S. margaritacea failed (Thompson 1913). Reasons for failure were the translocation of this species outside its natural range; lack of knowledge of the conditions required for growth, fattening, and reproduction; and unanticipated environmental conditions, such as freshwater intrusion and shifting sands (Thompson 1913, Korringa 1956). Fortunately, these failed attempts did not completely discourage early pioneers and, in 1888, the "Act to promote the cultivation of oyster fisheries and the discovery of pearl-bearing oysters" was established (Korringa 1956). Because the main problem during these early periods of oyster culture appeared to be insufficient knowledge on culturing indigenous oysters, representatives from the United Kingdom, with ample knowledge on oyster culture, visited South Africa in 1894. Soon thereafter, exotic oysters, such as the European flat oyster Ostrea edulis, were imported. These early attempts at introducing exotic oysters were, however, also unsuccessful. The majority of the imported oysters died shortly after arrival, probably as a result of poor shipping conditions and predation in their new environment. These failed attempts proved discouraging, and oyster culture ventures were subsequently delayed for a long period (Korringa 1956). In 1946, interest was renewed in the Knysna Estuary as a suitable location for oyster culture, the main driving force being a growing
local demand for oysters, because the supply of indigenous oysters taken from the rocks was proving insufficient. Artificial collectors (stakes and asbestos roofing tiles) were first set out and results appeared promising as S. margaritacea spat began to settle on the collectors. These promising results led to the formation of the Knysna Oyster Company, Ltd. Nonetheless, culturing of S. margaritacea was never established, and O. edulis and the Portuguese oyster Crassostrea angulata were imported from Europe instead. Rearing of these imports was, however, unsuccessful, because these species proved sensitive to sand abrasion (Korringa 1956). After years of experimental trials of importing exotic oysters, South Africa now follows the global trend of importing the much hardier Pacific oyster C. gigas. Spat have previously been imported from France, England, and Chile, but are currently only sourced from Chile. Imports from France have recently been banned, as a result of the contagious herpes virus affecting oysters there. C. gigas spat was imported to the Knysna Estuary as early as 1973, and this species has since become the only oyster to be cultured on a commercial scale (Hecht & Britz 1992). The main reason for its preference over S. margaritacea is its faster growth rate (Hecht & Britz 1992). C. gigas can attain market size within 9-11 mo from 2 g seed, whereas S. margaritaeea takes 3 y (DEAT 2006, De Bruyn 2006). This is, however, site dependent, with C. gigas reaching market size after 24 mo on intertidal racks at Knysna. Currently, oyster farms and nurseries require an operational permit from MCM. Details and locations of current oyster nurseries and marine and estuarine farms are provided in the following sections.
Nurseries Oyster nurseries located in Walvis Bay (Namibia), Kleinsee, Paternoster, and Jeffrey's Bay (Fig. 1) have been in existence for approximately 5 y. These nurseries import C. gigas spat of less than 5 mm in length from Chile, after which they are kept in an upwelling facility for approximately 2 mo. When they reach approximately 20-25 mm, they are placed in plastic mesh cages and suspended in the upper part of the water column in dams and ponds (in the case of Kleinsee and Paternoster), or in the sea (at Walvis Bay). The seed oysters are rigorously cleansed and graded until they reach the required size for translocation to the various grow-out farms. This takes 3-8 mo, depending on site-and season-specific environmental conditions. Marine Oyster Farms Three marine-based farms are currently operational in the region (Fig. 1). Oyster farming activities in Alexander Bay commenced in 1994. The farm is situated inside the well-secured property of Alexkor, a state-owned diamond mining area in the northern Cape Province. Two clams are present on the farm, and C. gigas are grown in baskets from seed to market size in the 3.5-ha south dam, adjacent to the sea. Water is pumped from the sea into the dam, which is 10 m above sea level, and from there it drains to a lower dam and back to the sea. An average monthly production of 65,000 oysters is sold all over South Africa under different labels. Alexander Bay has also recently begun operating as a nursery, supplying part-grown oysters to the farm in Algoa Bay. The Saldanha Bay-Langebaan Lagoon system is the only large sheltered bay along the South African west coast and is a key site for
the South African mariculture industry (Jackson & McGibbon 1991, Tonin 2001). Mussel cultivation has been the main mariculture activity in this area since 1985. Oyster culture in the region was initiated by the Fisheries Development Corporation, which ran an experimental oyster farm in Langebaan Lagoon, but this was closed down approximately 20 y ago, when the site was incorporated into the newly established West Coast National Park. Oyster-growing trials in the main bay and an artificially created dam adjacent to the ore-loading jetty began around that time. The dam-based operation was commercialized and operated until 2005, whereas the current operation in the bay itself began in 2005. Three established oyster farms currently exist (Probyn et al. 2001, Tonin 2001). The culture cycle at the biggest farm begins with the purchase of C. gigas juveniles (25-35 g in total wet weight each) from nurseries. These are placed in specially designed plastic mesh cages and are suspended in the upper few meters of the water column in the southern, more exposed part of the bay. The oysters are removed from the sea on a regular 2-mo cycle, size graded, and cleaned of fouling organisms that could inhibit growth. It takes, on average, 3-4 mo for these juvenile oysters to attain a market size of 45-120 g total wet weight, depending on specific market preferences. Oyster farming activities in Algoa Bay were initiated during the late 1980s. The culture cycle at this farm begins with the translocation of juvenile oysters, approximately 4 mo old, from the Knysna Estuary. Oyster operations in the bay, as well as in Knysna, are owned by the same South Cape Oysters Company. The reason for the translocation of oysters from Knysna Estuary relates to unfavorable conditions, such as
floods, which result in low salinity levels (Warman 2001). Oysters are therefore only grown here for 4 mo, after which they are translocated to Algoa Bay, where conditions are considered more suitable. In the bay, oysters are cultured in a longline system moored in 10 m of water. Ropes of 150 m are strung with stacks of approximately 5 bags each at 1-m intervals. Of the 250 ha of sea area set aside for mariculture purposes at this location, 52 ha are leased to oyster farmers (Tonin 2001). Oysters grown in these waters reach market size after only 3-4 mo and are then returned to Knysna Estuary, where they are kept in holding tanks until purchase. Estuarine Oyster Farms South Africa has very few large, permanently open estuaries suitable for mariculture. Oyster culture in the Knysna Estuary was initiated in 1946, and efforts were concentrated on the indigenous S. margaritacea. A hatchery was developed and the first batch of S. margaritacea was reared in 1970. However, because of subsequent problems and the extremely slow growth rate of this species (3 y to reach market size), the hatchery was closed and it was decided to import C. gigas spat (Solomons, pers. comm.). As recently as 2001, 18 ha of the estuary were used for the cultivation of C. gigas, and it was regarded as the center of oyster production in South Africa (Tonin 2001). Since then, oyster production in Knysna has declined and has instead become concentrated in Saldanha Bay and Algoa Bay. Oyster spat are purchased from the Jeffrey's Bay nursery and are grown on racks in 6-mm mesh bags for the first 2-4 mo. They are then brought back to land, where they are mechanically size graded and sorted, and then translocated to
Algoa Bay. The Knysna Oyster Company is, therefore, no longer a significant producer, and it functions only as a nursery for the Algoa Bay operation. Most of the 18 ha previously leased for cultivation are no longer being used. The oyster farm in the Swartkops Estuary is comprised of floating wooden lattices in a tidally flushed pond linked to the main estuary via a shallow sandy channel. The seed oysters are glued individually to the wooden laths, which are nailed together in a lattice and floated in the pond. The oysters are then allowed to grow to market size before the lattices are pulled ashore and the oysters removed. [FIGURE 5 OMITTED] History of Oyster Production Approximately 2 million C. gigas were produced annually throughout the 1970s and early '80s (Hecht & Britz 1992), but accurate annual oyster production statistics are only available since 1985 (South African Molluscan Shellfish Monitoring and Control Program database). Overall oyster production in South Africa has fluctuated considerably during that time, increasing to a peak of approximately 8 million in 1991, then decreasing to 2-4 million by the mid 1990s and remaining relatively stable during the past decade (Fig. 5). During the late 1980s, a productive farm was established in Algoa Bay that operated for a few years, producing several million oysters a year, before it closed in the early 1990s. This, together with the significant decline in production in the Knysna Estuary, resulted in the decrease in production observed. After this period, the new farm in Algoa Bay, along with improved production on the west coast at Alexander Bay and Saldanha Bay
oyster farms, offset the earlier declines and led to a stabilization of total production. According to Alexkor Limited (2003), the market for cultivated oysters in South Africa has grown steadily during the past decade, but production has not kept up with demand. Compared with other countries, South Africa is a minor producer. The main reason for this is that relatively few places along the coastline are suitable for culturing oysters. CONCLUSIONS The management of South African oyster fisheries has concentrated on the commercial and recreational harvesting of S. margaritacea, whereas subsistence harvesting of oysters has been (and still is, to some degree) largely ignored in most harvesting areas. This lack of management may be detrimental to oyster stocks, because subsistence harvesting may be having substantial negative impacts on stocks. Subsistence fishers are the most difficult to manage, because coastal dwellers have collected marine resources freely without restrictions for many decades. Particularly in most of the eastern Cape Province, this sector remains largely unmanaged. Management plans for resource use, as well as levels of enforcement and monitoring capacity, are better developed in KZN. Thus, management of subsistence fisheries in KZN may differ from what is practical in the eastern Cape. For example, daily bag limits of S. margaritacea or S. cucullata may be appropriate and enforceable in KZN, whereas an overall limit on a basket of resources (oysters, mussels, and limpets) may be more practical and enforceable in the eastern Cape (Cockcroft et al. 2002). If it were decided to manage the subsistence sector of the eastern Cape, additional resources would
be required, because there is a severe shortage of reliable and trustworthy enforcement officers in this region. Tourists in the area should also be discouraged from purchasing illegally collected resources, because this would lower the demand on already heavily exploited stocks. MCM is currently developing a system to ensure that the data from subsistence fisheries are properly recorded. The culture of oysters can provide additional socioeconomic benefits from marine resources. This is particularly important, because most wild fisheries in South Africa are maximally or overexploited and offer little opportunity for growth. Efforts should be concentrated on finding more suitable sites for farming C. gigas. Many argue that the South African coastline is too exposed to the elements for aquaculture purposes. However, abandoned diamond-mining dams along the northern Cape coastline have long been regarded as having significant potential for mariculture, but there has been little progress toward realizing this potential. The primary reasons for this are a shortage of available expertise, failure to attract investors to the area, and the remote location and distance to market (Alexkor Limited 2003). Setting up oyster farms in popular tourist spots, such as Gansbaai, along the south coast, is almost impossible because of public pressure, as holidaymakers do not look favorably on unsightly mariculture operations in these areas (Warman 2001). These very same tourists, however, contribute to the demand for oysters in South Africa. Estuaries situated in impoverished coastal areas along the southern Cape coast also constitute promising sites for oyster farming and could play a role in making rural communities meaningful role-players in South African oyster production.
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Published on Mar 9, 2018
Published on Mar 9, 2018
ABSTRACT Both wild and cultivated oysters are consumed in SouthAfrica. Edible wild oysters include Striostrea margaritacea, Saccostreacucull...