BULLETIN OF MARINE SCIENCE, 67(3): 1025–1042, 2000 CORAL REEF PAPER DAMAGE ON SOUTH AFRICAN CORAL REEFS AND AN ASSESSMENT OF THEIR SUSTAINABLE DIVING CAPACITY USING A FISHERIES APPROACH Michael H. Schleyer and Bruce J. Tomalin ABSTRACT Coral reefs in a marine reserve at Sodwana Bay (27°30'S) make it a premier dive resort. Corals are at the southern limits of their African distribution on these reefs which are dominated by soft corals. The coastline is exposed and turbulent. An assessment of the degree to which sport diving damages the reefs is needed for their management. This study showed that recognizable diver damage is generally concentrated in heavily dived areas. This damage and that of unknown cause probably attributable to divers exceeded natural damage on the reefs, despite the normally rough seas. Fishing line discarded in angling areas also caused considerable damage by tangling around branching corals which become algal fouled and die. Heaviest damage was caused in isolated areas by a minor crown-of-thorns outbreak. A linear regression indicated that 10% diver damage occurs at 9000 dives per dive site p.a. Taking uncertainty into account, a precautionary limit of 7000 dives per dive site p.a. was recommended. Further recommendations are that the reefs be zoned in terms of their sensitivity to diver damage, depth and use by divers according to qualification, and a ban be placed on the use of diving gloves to reduce handling of the reefs. The complexity and beauty of coral reefs make them an attractive and valuable re- source for ecotourism (Davis and Tisdell, 1995). However, many corals are fragile and susceptible to damage, making an assessment of the sustainable diving capacity of the reefs and the damage caused by sport-diving essential for their management. While the effects of other human activities on coral reefs have been well documented (e.g., coral mining and dynamite fishing; Brown 1986, 1987; Alcala and Gomez, 1987; Wells and Alcala, 1987), relatively few studies have focused on the deleterious effects of sport div- ing. These were reviewed by Davis and Tisdell (1995), who found that most were focused on spear-fishing and snorkelling, with the least attention being given to SCUBA diving. In situations in which ideal diving conditions are encountered, such studies can be based on observations of diver behavior, the most comprehensive in this regard being those of Rouphael and Inglis (1995, 1997) which were undertaken on the Great Barrier Reef. However, research on the subject is more often based on a comparison between the damage found on heavily dived reefs relative to undived areas (see Davis and Tisdell, 1995), absolute quantification normally being difficult to accomplish. One quantitative study established that fast-growing, branching corals suffer the most damage in the Red Sea (Riegl and Velimirov, 1991). The level of damage is directly related to the susceptibility of the coral species (Riegl and Velimirov, 1991; Hawkins and Roberts, 1992; Rouphael and Inglis, 1995, 1997; Allison, 1996) and diving intensity (Hawkins and Roberts, 1997; this study). Much diver damage on reefs is unnecessary and can be avoided by modifying diver behavior (Rouphael and Inglis, 1995; Allison 1996; Medio et al., 1997; Hawkins and Roberts, 1997), limiting diving to the sustainable diving capacity of the reefs (Davis and Tisdell, 1995; Hawkins 1025 1026 BULLETIN OF MARINE SCIENCE, VOL. 67, NO. 3, 2000 and Roberts, 1997) and zoning them in terms of their sensitivity to damage (Rouphael and Inglis, 1995). Schleyer (1995, 1999, in press) reviewed the structure and limited extent of coral reefs in South Africa. All fall in conservation areas and are only used for recreational game fishing and sport diving. The reefs are considered a valuable yet vulnerable resource but only became the subject of extensive research in the last decade. Sport diving increased six-fold between 1987 and 1996 on the most accessible of the three reef complexes; how- ever only a superficial examination of reef damage was undertaken in this period (Riegl and Cook, 1995) in tandem with the baseline studies. Alarmist articles on the incidence of diver damage appeared in the press with the increase in diving during this period. A holistic approach was recommended by Schleyer (pers. correspond., 1995, 1999, in press) for the management of the South African reefs. This approach incorporated fea- tures such as the inclusion of breeding refugia and the restriction of diving on reefs vul- nerable to damage, to divers of advanced qualification. However, no information was available on the sustainable diving capacity of the reefs, leaving the management guide- lines incomplete. This study was thus undertaken to quantify damage on the accessible reefs and establish their sustainable diving capacity. Conceptually, we believe that diver damage on coral reefs can be considered equivalent to fishing mortality caused in a fishery and hence the techniques of fisheries stock as- sessment can be used (for an introduction to fisheries science see Hilborn and Walters, 1992). Diver damage will be a function of diving intensity (effort in a fishery) and behav- ior (selectivity and fishing power). Catch per unit effort in a fishery could be considered equivalent to diver ‘satisfaction’. Average diver satisfaction would decline with increased diving intensity due to perceptions of crowding and obvious diver damage. The equiva- lent in a fishery is the inevitable decline in catch per unit effort with increasing effort. Note that as fisheries managers have to accept that any level of fishing will result in some decline in stock size, managers of coral reefs will have to accept that if diving is to be allowed, some level of damage to corals will occur. The question in both cases is how much decline in stock size or increase in damage is ‘acceptable’. In fisheries this is ad- dressed by assessing the predicted total yield versus effort function. Total yield in a fish- ery would be equivalent to total diver satisfaction (the product of the number of dives and the average satisfaction per dive). We would expect satisfaction to reach an asymptote at an intermediate amount of diving, followed by a decline as diving intensity increases (as does total yield in a fishery). As in fisheries, sport diving generates considerable income to the private sector and the state. In this case, the local nature conservation service ob- tains the bulk of its non-state income from the Sodwana resort. A ‘common’ resource is used by visitors to the Sodwana Bay National Park and, if unrestricted access to the coral reefs is allowed, a “tragedy of the commons” could result (Hardin, 1968). Although fisheries science has a long history and deterministic models are well estab- lished, recent developments have emphasized the role of uncertainty in this science (sum- marized in Hilborn and Peterman, 1996). It is recognized that fishing effort may only explain a small proportion of the variability in the size of a harvested stock. Similarly, it is likely that factors other than diving may cause more spatial and temporal variability in damage to corals (e.g., natural predation, storms, other anthropogenic effects). However, in common with fisheries managers, managers of coral reefs have very little control over factors other than diving intensity (fishing effort) and therefore our analysis focuses on the single factor which is controllable. The other factors can be considered to cause un- SCHLEYER AND TOMALIN: DAMAGE ON SOUTH AFRICAN CORAL REEFS 1027 certainty around the estimation of the effect of diving intensity and we therefore consid- ered it more important to incorporate uncertainty into our analysis than to produce a complex model of the effect of diving intensity. In summary, three fisheries stock assessment concepts were adopted for the analysis of the effects of diving on the reefs: the precautionary approach (FAO, 1995) incorporating the use of limit reference points (Caddy and Mahon, 1995), quantification of trade-offs and the incorporation of uncertainty into risk analysis (Hilborn and Walters, 1992). In this case, a trade-off was considered between maximizing the number of dives per site and minimizing the risk of ‘significant’ damage due to human activity. We did not at- tempt to quantify ecological damage, but considered diver damage to be significant when it was noticed by sports divers. This level was then used as a precautionary limit reference point (FAO, 1995). As the matter is an aesthetic issue, we emphasize the proportion (%) of total damage caused by divers and not the absolute amount (damage per unit area). The trade-off between diving intensity and the amount of diver damage was quantified using cumulative risk curves because the relationship was uncertain. MATERIALS AND METHODS Visual estimates of reef damage were made in the central of three reef complexes in northern KwaZulu-Natal which is accessible from tourism facilities and a launch site at Sodwana Bay (Fig. 1). The northern complex is relatively inaccessible while the one to the south falls in a sanctuary not open to the public. The central complex is thus a focus of marine recreational activity. Records of the total number of dives and boat launches made in this complex are kept by the local conservation authority, the KwaZulu-Natal Nature Conservation Service (KZNNCS). The damage estimates were made by SCUBA divers undertaking drift dives on the reefs between September 1994 and November 1995. A three decimal GPS (Navstar XR4G) fix was taken on entry and termination of all but the shortest dives and a record was kept on underwater slates of damage to any sessile organism in a 2 m path as the dive progressed. The length of shorter dives was obtained from direct measurements. The observations were thus made within a transect belt of approximately known area.