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Aerial census of whale sharks (Rhincodon typus) on the northern KwaZulu-Natal coast, South Africa
Fisheries Research 84 (2007) 41–46
Aerial census of whale sharks (Rhincodon typus) on the northern KwaZulu-Natal coast, South Africa Geremy Cliff a,∗ , Michael D. Anderson-Reade a , Andrew P. Aitken b , Graeme E. Charter a , Victor M. Peddemors a,1 b
a Natal Sharks Board, Private Bag 2 Umhlanga 4320, South Africa Zoology Department, University of Cape Town, Rondebosch 7700, South Africa
Abstract A project was initiated to assess the potential for dedicated whale shark diving on the northern KwaZulu-Natal (KZN) coast of South Africa. Between October 2001 and September 2002, 12 aerial surveys were conducted along 350 km of the coastline immediately south of the South Africa/Mozambique border. Only eight whale sharks were seen, with a sighting rate of 0.21 sharks per 100 km of coastline. Another 13 surveys were completed during the summers of 2003/2004 and 2004/2005 and a total of 30 sharks were sighted, with a mean sighting rate of 0.69 sharks per 100 km of coastline. The density of sharks was highest in the far north where it averaged 1.05 sharks per 100 km between January and May but this value is considered too low to support dedicated whale shark diving. Local dive operators and light aircraft pilots confirmed the scarcity of whale sharks in the region. The mean sighting rate from three flights along 950 km of southern Mozambique coastline in March was 5.6 sharks per 100 km of coastline. Reasons for the marked regional differences in shark density are not apparent but the paucity of sharks in northern KZN waters may be linked to a recent increase in sightings off the Kenyan coast. © 2006 Elsevier B.V. All rights reserved. Keywords: Whale shark; Rhincodon typus; Abundance; Distribution; Aerial survey
1. Introduction The whale shark Rhincodon typus (Smith, 1828) has a circumtropical distribution. It appears to be a highly nomadic and migratory species, with some long distance movements, probably timed to coincide with blooms of plankton (Compagno, 2001). In recent years whale sharks, as the world’s largest fish, have been recognised for their eco-tourist value. Dedicated whale shark diving is now offered at several locations, where occurrences of whale sharks are seasonal and predictable. These locations include Ningaloo Reef in Western Australia, the Galapagos Islands, the Sea of Cortez and Baja California in the eastern Pacific, and the islands in the Andaman Sea off western Thailand (Colman, 1997). In some of these localities spotter planes are used to locate the sharks for the dive boats. Encounters with whale sharks in South Africa often take place in Maputaland, the northernmost section of KwaZulu-Natal ∗
Corresponding author. Tel.: +27 31 5660412; fax: +27 31 5660499. E-mail address: [email protected] (G. Cliff). 1 Present address: Discipline of Zoology (Westville), School of Biological & Conservation Sciences, University of KwaZulu-Natal, P. Bag X54001, Durban 4000, South Africa. 0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.11.012
(KZN; this province was formerly known as Natal) (Fig. 1). The region enjoys clear, warm water, which supports prolific coral growth. This has attracted a large number of dive charters, most of which are based at Sodwana. Diving with whale sharks has generally been the result of opportunistic encounters with sharks. In the mid-1990s, with the aid of microlight aircraft, dive operators started offering dedicated whale shark diving along a 20 km stretch of the Mozambique coastline immediately north of the South African border. Beckley et al. (1997) quantified sightings made by these dive operations in 1994 and 1995. In 2001 the Natal Sharks Board (NSB) was requested by the Branch: Marine and Coastal Management of the Department of Environmental Affairs and Tourism to assess the potential for dedicated whale shark diving on the South African coast. As part of this assessment the NSB undertook aerial surveys to determine the number and distribution of whale sharks on the northern KZN coast, with the Maputaland coast being the primary study area. The low sightings resulted in a further 2 years of funding to continue the surveys. This paper documents the sightings of whale sharks made between October 2001 and March 2005. Data from three surveys into southern Mozambique are also presented.
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G. Cliff et al. / Fisheries Research 84 (2007) 41–46
discharge substantial quantities of sediment into the sea, particularly during the summer rainy season and the water is permanently turbid (Martin and Flemming, 1988). South of the Tugela River, where 40 km of coast was surveyed, these sediment loads are reduced and water clarity averages 5–6 m in the dry winter months (NSB, unpublished data). 2.2. Survey techniques
Fig. 1. The KwaZulu-Natal coast showing the study area to the north and its position relative to the rest of South Africa (inset).
2. Materials and methods 2.1. The study area The northern KZN coastline from Durban to the Mozambique border is a relatively straight one, devoid of embayments, gulfs or islands (Fig. 1). It is a moderate energy coast, exposed to swell waves and semi-diurnal tides with a range of 0.5–1.75 m (Schumann, 1988). Most of the shoreline is sandy beach, interspersed with rocky outcrops. The most important oceanographic feature is the Agulhas Current, one of the world’s major western boundary currents, which originates at about 28◦ S and flows in a south-easterly direction, roughly steered by the edge of the continental shelf. The core of the current generally flows offshore of the shelf but its influence can be felt inshore (Lutjeharms, 2004). Longshore coastal currents are predominantly winddriven (Schumann, 1988). The Maputaland coast is 190 km long and extends from the Mozambique border to Cape St. Lucia (Fig. 1); the continental shelf is only 2–7 km wide and the slope is steep. There are two large contiguous marine protected areas, the Maputaland MPA (proclaimed in 1986) and St. Lucia MPA (proclaimed in 1979), both of which now fall in the world heritage site known as the Greater St. Lucia Wetland Park, which extends some 5 km out to sea. The coastal region is a flat, sandy plain with few large rivers, so the sea contains little silt and is generally clear. Most of the nearshore reefs are topped with prolific growths of both soft and hard corals, as there are no true coral reefs in KZN and mean monthly nearshore water temperatures range from 22 to 28 ◦ C (Schleyer and Celliers, 2003). Between Cape St. Lucia and the Tugela River mouth (120 km), there is a gentle bight in the coastline and the shelf widens to a maximum width of 45 km. Several large rivers
Light aircraft have proved successful in locating whale sharks close inshore along the KZN coast (Beckley et al., 1997). A top wing aircraft was flown coastwise from Ballito, 44 km north of Durban, to the South Africa/Mozambique border and back, covering approximately 350 km of coast (Fig. 1). Surveys generally commenced at 07:30–08:00 h and terminated at 14:30–15:30 h. The flight was conducted at a speed of 184 km/h (100 knots) and at an altitude of 305 m (1000 ft). On each flight there were two observers, who were seated on the left side of the aircraft, and a data recorder. Flights took place when viewing conditions were optimal (light winds and minimal cloud), but this was extremely difficult to achieve along the entire survey area. The survey was aborted when viewing conditions deteriorated (Beaufort scale of wind >3) and, as a result, there were some flights on which less than the full 350 km of coastline was surveyed. The GPS position of each shark, its direction of travel relative to the coastline (north, south, inshore or offshore) and approximate length (using vehicles on the beach as a guide) was recorded. Reports of large numbers of whale sharks, within 1 km of the shore (Beckley et al., 1997), greatly influenced the choice of flight path. On the northbound leg the flight track was approximately 1750 m offshore, so that the observers searched the strip between 750 and 1500 m offshore, allowing for the dead space directly below the aircraft. On the southbound, return flight the aircraft flew inland of the shoreline, and the inshore strip out to 750 m was searched. Only sharks observed on the southbound flight were used to determine abundance, thereby avoiding the possibility of counting the same shark twice. Three surveys were undertaken along 950 km of coastline in southern Mozambique, as far as Vilanculos (Fig. 2). The same flight path along the KZN coast and the same search routine were followed. In view of the distances covered, the return flight along the northern KZN coast was at least 2 days after the northbound flight and it was generally far earlier in the day. 3. Results 3.1. Whale shark sightings: northbound flights In the first period (2001–2002) only two sharks were seen on 12 northbound flights. In the second period (2003–2005) five sharks were seen on 3 of the 13 flights. These sightings were not used in any of the subsequent analyses. 3.2. Whale shark sightings: southbound flights Eight sharks were seen on 12 surveys between October 2001 and September 2002 (Table 1). These flights were spread
G. Cliff et al. / Fisheries Research 84 (2007) 41–46
Fig. 2. Map of South Africa and Mozambique.
throughout the year. No sharks were sighted on seven flights. Sighting rates ranged from 0 to 0.86 sharks per 100 km of coastline, with a mean of 0.21 sharks per 100 km of coastline. Between March 2003 and March 2005 13 flights were undertaken in the warmer months (Table 1). A total of 30 whale sharks were seen, with no sharks encountered on four flights. The sighting rates varied from 0 to 4.35 sharks per 100 km, with a mean
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Fig. 3. Seasonality of whale shark sightings on the northern KZN coast and their distance from the Mozambique border.
of 0.69 sharks per 100 km. The overall sighting rate for the 5 year study was 0.46 sharks per 100 km of coastline. 3.3. Geographical and seasonal distribution All but 1 of the 38 sharks were seen within 150 km of the Mozambique border (Fig. 3). The solitary exception was seen
Table 1 Details of surveys conducted and whale sharks sighted on southbound flights along the northern KZN coast Date 23-October-2001 20-November-2001 18-December-2001 22-January-2002 12-February-2002 27-February-2002 19-March-2002 12-April-2002 15-May-2002 2-July-2002 20-August-2002 18-September-2002
Distance traveled (km)
No. seen
Density sharks/ 100 km
Estimated length (m)
Time (h)
– – 6 4 – 4 – – 6–7, 5, 5 5, 4 – –
– – 11:22 14:01 – 11:31 – – 10:17 to 11:03 11:01, 11:20 – –
250 350 350 350 230 350 350 260 350 350 350 350
0 0 1 1 0 1 0 0 3 2 0 0
0 0 0.29 0.29 0 0.29 0 0 0.86 0.57 0 0
3890
8
0.21
350 350 275 350 350 230 350 350 350 350 350 350 350
9 1 1 1 4 10 1 0 0 2 1 0 0
2.57 0.29 0.36 0.29 1.14 4.35 0.29 0 0 0.57 0.29 0 0
Subtotal
4355
30
Grand total
8245
38
Subtotal 27-March-2003 7-November-2003 28-November-2003 19-December-2003 24-January-2004 25-February-2004 5-April-2004 29-April-2004 18-November-2004 18-January-2005 10-February-2005 2-March-2005 14-March-2005
Heading→N
Heading→S
– – – 1 – 1 – – 1 1 – –
– – 1 – – – – – 2 1 – –
4
4
2 – – – 3 10 – – – 2 1 – –
4 1 1 1 1 – 1 – – – – – –
0.69
22
13
0.46
26
17
– 4 – 4 – – 4 – – – 5–6 – –
10:55 to 11:10 9:45 14:21 11:22 7:35 to 7:39 12:39–12:55 11:31 – – 10:26–10:44 13:12 – –
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G. Cliff et al. / Fisheries Research 84 (2007) 41–46
Fig. 4. Mean monthly densities of whale sharks on the northern KZN coast. Vertical lines represent standard error of the mean. Inserted values represent the number of flights conducted in that month.
close to the southern end of the survey. The most sharks seen on a single survey was in February (10) and March (9), with respective densities of 4.35 and 2.57 sharks per 100 km (Table 1). When the results from each month’s surveys were combined, the highest densities were in February (1.03 per 100 km) and May (0.86 per 100 km) (Fig. 4). Although only five flights were conducted between May and October, there was some evidence of a seasonal pattern, in which, with the exception of April, sharks were most common in the first 5 months of the year. 3.4. Size, direction of travel, grouping and time of day The sharks were estimated to be 4–7 m long (Table 1). All but 3 of the 38 sharks were travelling parallel to the coast, with no significant difference in direction (p = 0.12, n = 35). All 10 sharks sighted on 25 February 2004 were heading north. The greatest concentration was seven sharks in 3 km of coast on 25 February 2004, when the sharks were well spaced and did not appear to be swimming together. Sighting times ranged from 07:35 to 14:01 h, with 79% of sightings in the 3-h period from 10:00 to 13:00 h (Table 1). 3.5. Sharks in Mozambique A survey was conducted along 950 km of southern Mozambique coastline in March 2004 and repeated twice in March 2005. Shark densities were very similar on the three flights, ranging from 4.3 to 5.9 sharks per 100 km, with a mean of 5.6 sharks per 100 km. The sharks were concentrated in a relatively short (<200 km) section of the coast, most noticeably on 1 March 2005, with 54 sharks along some 50 km of coast. A focal point for these aggregations was the coastline around Ponta Tofo (23◦ 52 S; Fig. 2). The sharks were at the surface, swimming in all directions, with no sign of any grouping behaviour. Time did not permit recording direction of travel nor circling over the sharks to make further observations. 4. Discussion The sighting rate of 0.21 sharks per 100 km of KZN coastline in 2001/2002 is extremely low. In 2003/2005 this figure
increased to 0.69 sharks per 100 km during the warmer months, when there appeared to be a greater likelihood of sharks being present. In contrast, Beckley et al. (1997) reported sightings of 50–100 sharks per 100 km of coast on three occasions. In January 1980, 54 sharks were recorded during a coastal flight between Sodwana and Cape Vidal, a distance of 64 km. Immediately south of Durban 95 sharks were sighted in January 1994 within 1 km of the shoreline along 110 km of coast. In much the same area 49 sharks were sighted in January 1996 on 73 km of coastline. Unfortunately there are no other published records of dedicated whale shark counts on the KZN coast and the three reports probably represent exceptional situations. Dive operators at Sodwana and in southern Mozambique reported that whale sharks were common in the mid-1990s, when dedicated whale shark viewing was introduced in the extreme south of Mozambique, but since 1999 viewing has been poor (Aitken, unpublished). One dive operator at Sodwana has used a microlight aircraft to spot whale sharks in the summer of 2004/2005, with sightings of only 11 sharks in each of the 3 months from December to February (Bester, personal communication). The concentration of sharks in the extreme north of KZN is to be expected. The animals are tropical and the water along the Maputaland coast is warm and clear, which enhances the sharks’ visibility from the air. It is not surprising that no sharks were seen between Cape St. Lucia and the Tugela River mouth, given the prevailing high turbidity inshore. It is not known how this turbid water affects the southward movement of the sharks. The sharks may move offshore to skirt the turbid water, which is generally restricted to within 2–4 km of the coast, which could explain why large numbers have been seen from Durban southwards in the summer rainy season (see above and Beckley et al., 1997). The stranding of three sharks in highly turbid water just north of Richards Bay (Fig. 1) (Beckley et al., 1997) suggests that some of the sharks must remain close inshore as they head south rather than moving offshore to avoid the silt. The highest density of sharks was in February, followed by May, although the latter was the result of a single flight. This pattern is not entirely in keeping with the reports from dive operators at Sodwana (Aitken, unpublished) and divers (Beckley et al., 1997) in which sightings were most frequent between November and January. This discrepancy may be an artefact of the low densities. There is insufficient information to comment on the influence of time of day on the movements of the sharks and their presence at the surface. Taylor (1996) reports that on Ningaloo Reef more sharks were present on the surface between 10:00 and 14:00 h, rather than after 14:00 h. It is fortuitous that most of the southbound flights were completed before 14:00 h. The sighting of four sharks between 07:35 and 07:39 h was on a return flight from Mozambique and was far earlier than normal, as most southbound flights commenced after 10:00 h. The reported lengths of 4–7 m were very rough estimates and indicate that largely immature animals enter KZN. These
G. Cliff et al. / Fisheries Research 84 (2007) 41–46
sizes were possibly underestimates, given that stranded sharks in KZN ranged from 5.9 to 9.2 m (Beckley et al., 1997) and the dive operators at Sodwana report that the vast majority of the sharks sighted are less than 9 m, typically 6–8 m (Aitken, unpublished). The direction of travel did not conform to the pattern of animals undertaking a southward movement or range extension at the onset of summer, returning to the tropics as the water cools. The prevailing inshore currents, which are largely winddriven (Schumann, 1988), may have the greatest influence on the direction of travel. All the sightings, particularly the large numbers in relatively small areas in southern Mozambique, indicate that this species is a solitary one and that large aggregations are probably a response to a localised abundance of food rather than an innate schooling behaviour. The density of sharks on the Mozambique coast is an order of magnitude higher than that on the northern KZN coast. The distribution of animals along this coast is extremely patchy, being concentrated around Ponta Tofo. This area is well known among divers for its concentrations of whale sharks. Cliff (unpublished) reported that a group of divers observed what they estimated to be “about 100 whale sharks milling around about 1–1.5 km offshore.” In early 2005 divers reported large aggregations of sharks over a period of several weeks. On some occasions the sharks swam slowly with closed mouths. On others they swam much faster, with open mouths, often breaking the surface and therefore presumably feeding. There is no published evidence that there are higher concentrations of prey along this particular section of coast to account for the highly localised distribution. The whale shark aggregations on Ningaloo Reef are highly seasonal, from March to May, in response to coral spawning and subsequent increase in production of zooplankton (Taylor, 1996). It is therefore not surprising that large numbers of whale sharks were spotted in the Ponta Tofo area during the three flights in March, although divers report that sharks may be present in far smaller numbers throughout the year. Another factor that could contribute to enhanced plankton production would be upwelling of cooler, nutrient-rich water. Lutjeharms (2004) refers to two upwelling cells on the central and southern Mozambique coast, one to the extreme north off Angoche and the other off Maputo Bay to the south (Fig. 4), both too far away to exert any obvious influence on the nearshore waters in the vicinity of Ponta Tofo. 5. Conclusions At this stage there is no indication of what oceanographic conditions might have changed during the last 5 years to explain the paucity of whale sharks on the KZN coast. It is tempting to attribute some of this decline to human-induced impacts, such as hunting, elsewhere in the whale shark’s range, but the international trend appears to one of reduced harvesting and increased protection for the species. The higher densities in southern Mozambique are encouraging, but these appear to be long standing ones, making it difficult to accept that the large numbers of sharks which were encountered in KZN
45
waters in the past (Beckley et al., 1997) simply remained off the Mozambique coast during the study period. Further north, Kenya and, to a lesser extent, Tanzania have seen an unprecedented increase in whale shark sightings in the last few years, which has coincided with a similar increase in mantis shrimp populations (Watson, 2004; Steffensen, 2005). It is possible that sharks, which would have ventured south and ultimately ended up in the waters of KZN, have remained well to the north. Given that any dedicated whale shark diving industry would be based on the Maputaland coast, the density of whale sharks along this 190 km stretch of coastline between December and May was 1.05 sharks per 100 km of coastline. Although this figure is higher than that for the entire northern KZN, it is still too low to justify establishing a dedicated whale shark diving industry there. Nevertheless, legislation has been passed to protect whale sharks from possible harassment in the Greater St. Lucia Wetland Park. Aerial surveys in northern KZN will continue in the summer of 2005/2006. If additional funding can be obtained, the surveys should be repeated in southern Mozambique and the reasons for and the extent of the aggregations in the Ponta Tofo area should be investigated. Acknowledgements Most of the flying costs were funded by the Branch: Marine and Coastal Management (MCM) Co-ordination of the Department of Environmental Affairs and Tourism. The authors wish to acknowledge the assistance of those who acted as a second observer on the flights and Sabine Wintner in the preparation of the manuscript, and to thank Herman Oosthuizen of MCM for initiating the project. The enthusiasm of Rob and Sam Bester of Gypsea Dive Centre, Sodwana is acknowledged. References Beckley, L.E., Cliff, G., Smale, M.J., Compagno, L.J.V., 1997. Recent strandings and sightings of whale sharks in South Africa. Environ. Biol. Fish. 50, 343–348. Colman, J.G., 1997. A review of the biology and ecology of the whale shark. J. Fish Biol. 51, 1219–1234. Compagno, L.J.V., 2001. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2: bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). In: FAO Species Catalogue for Fishery Purposes, no. 1, vol. 2. Food and Agriculture Organization of the United Nations, Rome, 269 pp. Lutjeharms, J.R.E., 2004. The coastal oceans of south-eastern Africa. In: Robinson, A.R., Brink, K.H. (Eds.), The Global Coastal Ocean: Multiscale Interdisciplinary Processes (The Sea: Ideas and Observations on Progress in the Study of the Seas). Harvard University Press. Martin, A.K., Flemming, B.W., 1988. Physiography, structure and geological evolution of the Natal continental shelf. In: Schumann, E.H. (Ed.), Coastal Studies off Natal, South Africa. Lecture Notes on Coastal and Estuarine Studies, vol. 26. Springer-Verlag, New York, pp. 11–46. Schleyer, M.H., Celliers, L., 2003. Biodiversity on the marginal coral reefs of South Africa: what does the future hold? Zool. Verh. 345, 387– 400. Schumann, E.H., 1988. Physical oceanography off Natal. In: Schumann, E.H. (Ed.), Coastal Studies off Natal, South Africa. Lecture Notes on Coastal and Estuarine Studies, vol. 26. Springer-Verlag, New York, pp. 101– 130.
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Smith, A., 1828. Descriptions of new, or imperfectly known objects of the animal kingdom, found in South Africa. South African Commercial Advertiser 3, 2. Steffensen, M., 2005. Whale Shark “East Africa’s Mystery”. Africa Wild, Africa Wild Publishing, Johannesburg, South Africa, pp. 58–67.
Taylor, J.G., 1996. Seasonal occurrence, distribution and movements of the whale shark, Rhincodon typus, at Ningaloo Reef Western Australia. Mar. Freshwater Res. 47, 637–642. Watson, R., 2004. Living Submarines, vol. 27. SWARA The magazine of the East African Wild Life Society, Nairobi, Kenya, pp. 42–47.
Aerial census of whale sharks (Rhincodon typus) on the northern KwaZulu-Natal coast, South Africa Geremy Cliff a,∗ , Michael D. Anderson-Reade a , Andrew P. Aitken b , Graeme E. Charter a , Victor M. Peddemors a,1 b
a Natal Sharks Board, Private Bag 2 Umhlanga 4320, South Africa Zoology Department, University of Cape Town, Rondebosch 7700, South Africa
Abstract A project was initiated to assess the potential for dedicated whale shark diving on the northern KwaZulu-Natal (KZN) coast of South Africa. Between October 2001 and September 2002, 12 aerial surveys were conducted along 350 km of the coastline immediately south of the South Africa/Mozambique border. Only eight whale sharks were seen, with a sighting rate of 0.21 sharks per 100 km of coastline. Another 13 surveys were completed during the summers of 2003/2004 and 2004/2005 and a total of 30 sharks were sighted, with a mean sighting rate of 0.69 sharks per 100 km of coastline. The density of sharks was highest in the far north where it averaged 1.05 sharks per 100 km between January and May but this value is considered too low to support dedicated whale shark diving. Local dive operators and light aircraft pilots confirmed the scarcity of whale sharks in the region. The mean sighting rate from three flights along 950 km of southern Mozambique coastline in March was 5.6 sharks per 100 km of coastline. Reasons for the marked regional differences in shark density are not apparent but the paucity of sharks in northern KZN waters may be linked to a recent increase in sightings off the Kenyan coast. © 2006 Elsevier B.V. All rights reserved. Keywords: Whale shark; Rhincodon typus; Abundance; Distribution; Aerial survey
1. Introduction The whale shark Rhincodon typus (Smith, 1828) has a circumtropical distribution. It appears to be a highly nomadic and migratory species, with some long distance movements, probably timed to coincide with blooms of plankton (Compagno, 2001). In recent years whale sharks, as the world’s largest fish, have been recognised for their eco-tourist value. Dedicated whale shark diving is now offered at several locations, where occurrences of whale sharks are seasonal and predictable. These locations include Ningaloo Reef in Western Australia, the Galapagos Islands, the Sea of Cortez and Baja California in the eastern Pacific, and the islands in the Andaman Sea off western Thailand (Colman, 1997). In some of these localities spotter planes are used to locate the sharks for the dive boats. Encounters with whale sharks in South Africa often take place in Maputaland, the northernmost section of KwaZulu-Natal ∗
Corresponding author. Tel.: +27 31 5660412; fax: +27 31 5660499. E-mail address: [email protected] (G. Cliff). 1 Present address: Discipline of Zoology (Westville), School of Biological & Conservation Sciences, University of KwaZulu-Natal, P. Bag X54001, Durban 4000, South Africa. 0165-7836/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2006.11.012
(KZN; this province was formerly known as Natal) (Fig. 1). The region enjoys clear, warm water, which supports prolific coral growth. This has attracted a large number of dive charters, most of which are based at Sodwana. Diving with whale sharks has generally been the result of opportunistic encounters with sharks. In the mid-1990s, with the aid of microlight aircraft, dive operators started offering dedicated whale shark diving along a 20 km stretch of the Mozambique coastline immediately north of the South African border. Beckley et al. (1997) quantified sightings made by these dive operations in 1994 and 1995. In 2001 the Natal Sharks Board (NSB) was requested by the Branch: Marine and Coastal Management of the Department of Environmental Affairs and Tourism to assess the potential for dedicated whale shark diving on the South African coast. As part of this assessment the NSB undertook aerial surveys to determine the number and distribution of whale sharks on the northern KZN coast, with the Maputaland coast being the primary study area. The low sightings resulted in a further 2 years of funding to continue the surveys. This paper documents the sightings of whale sharks made between October 2001 and March 2005. Data from three surveys into southern Mozambique are also presented.
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G. Cliff et al. / Fisheries Research 84 (2007) 41–46
discharge substantial quantities of sediment into the sea, particularly during the summer rainy season and the water is permanently turbid (Martin and Flemming, 1988). South of the Tugela River, where 40 km of coast was surveyed, these sediment loads are reduced and water clarity averages 5–6 m in the dry winter months (NSB, unpublished data). 2.2. Survey techniques
Fig. 1. The KwaZulu-Natal coast showing the study area to the north and its position relative to the rest of South Africa (inset).
2. Materials and methods 2.1. The study area The northern KZN coastline from Durban to the Mozambique border is a relatively straight one, devoid of embayments, gulfs or islands (Fig. 1). It is a moderate energy coast, exposed to swell waves and semi-diurnal tides with a range of 0.5–1.75 m (Schumann, 1988). Most of the shoreline is sandy beach, interspersed with rocky outcrops. The most important oceanographic feature is the Agulhas Current, one of the world’s major western boundary currents, which originates at about 28◦ S and flows in a south-easterly direction, roughly steered by the edge of the continental shelf. The core of the current generally flows offshore of the shelf but its influence can be felt inshore (Lutjeharms, 2004). Longshore coastal currents are predominantly winddriven (Schumann, 1988). The Maputaland coast is 190 km long and extends from the Mozambique border to Cape St. Lucia (Fig. 1); the continental shelf is only 2–7 km wide and the slope is steep. There are two large contiguous marine protected areas, the Maputaland MPA (proclaimed in 1986) and St. Lucia MPA (proclaimed in 1979), both of which now fall in the world heritage site known as the Greater St. Lucia Wetland Park, which extends some 5 km out to sea. The coastal region is a flat, sandy plain with few large rivers, so the sea contains little silt and is generally clear. Most of the nearshore reefs are topped with prolific growths of both soft and hard corals, as there are no true coral reefs in KZN and mean monthly nearshore water temperatures range from 22 to 28 ◦ C (Schleyer and Celliers, 2003). Between Cape St. Lucia and the Tugela River mouth (120 km), there is a gentle bight in the coastline and the shelf widens to a maximum width of 45 km. Several large rivers
Light aircraft have proved successful in locating whale sharks close inshore along the KZN coast (Beckley et al., 1997). A top wing aircraft was flown coastwise from Ballito, 44 km north of Durban, to the South Africa/Mozambique border and back, covering approximately 350 km of coast (Fig. 1). Surveys generally commenced at 07:30–08:00 h and terminated at 14:30–15:30 h. The flight was conducted at a speed of 184 km/h (100 knots) and at an altitude of 305 m (1000 ft). On each flight there were two observers, who were seated on the left side of the aircraft, and a data recorder. Flights took place when viewing conditions were optimal (light winds and minimal cloud), but this was extremely difficult to achieve along the entire survey area. The survey was aborted when viewing conditions deteriorated (Beaufort scale of wind >3) and, as a result, there were some flights on which less than the full 350 km of coastline was surveyed. The GPS position of each shark, its direction of travel relative to the coastline (north, south, inshore or offshore) and approximate length (using vehicles on the beach as a guide) was recorded. Reports of large numbers of whale sharks, within 1 km of the shore (Beckley et al., 1997), greatly influenced the choice of flight path. On the northbound leg the flight track was approximately 1750 m offshore, so that the observers searched the strip between 750 and 1500 m offshore, allowing for the dead space directly below the aircraft. On the southbound, return flight the aircraft flew inland of the shoreline, and the inshore strip out to 750 m was searched. Only sharks observed on the southbound flight were used to determine abundance, thereby avoiding the possibility of counting the same shark twice. Three surveys were undertaken along 950 km of coastline in southern Mozambique, as far as Vilanculos (Fig. 2). The same flight path along the KZN coast and the same search routine were followed. In view of the distances covered, the return flight along the northern KZN coast was at least 2 days after the northbound flight and it was generally far earlier in the day. 3. Results 3.1. Whale shark sightings: northbound flights In the first period (2001–2002) only two sharks were seen on 12 northbound flights. In the second period (2003–2005) five sharks were seen on 3 of the 13 flights. These sightings were not used in any of the subsequent analyses. 3.2. Whale shark sightings: southbound flights Eight sharks were seen on 12 surveys between October 2001 and September 2002 (Table 1). These flights were spread
G. Cliff et al. / Fisheries Research 84 (2007) 41–46
Fig. 2. Map of South Africa and Mozambique.
throughout the year. No sharks were sighted on seven flights. Sighting rates ranged from 0 to 0.86 sharks per 100 km of coastline, with a mean of 0.21 sharks per 100 km of coastline. Between March 2003 and March 2005 13 flights were undertaken in the warmer months (Table 1). A total of 30 whale sharks were seen, with no sharks encountered on four flights. The sighting rates varied from 0 to 4.35 sharks per 100 km, with a mean
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Fig. 3. Seasonality of whale shark sightings on the northern KZN coast and their distance from the Mozambique border.
of 0.69 sharks per 100 km. The overall sighting rate for the 5 year study was 0.46 sharks per 100 km of coastline. 3.3. Geographical and seasonal distribution All but 1 of the 38 sharks were seen within 150 km of the Mozambique border (Fig. 3). The solitary exception was seen
Table 1 Details of surveys conducted and whale sharks sighted on southbound flights along the northern KZN coast Date 23-October-2001 20-November-2001 18-December-2001 22-January-2002 12-February-2002 27-February-2002 19-March-2002 12-April-2002 15-May-2002 2-July-2002 20-August-2002 18-September-2002
Distance traveled (km)
No. seen
Density sharks/ 100 km
Estimated length (m)
Time (h)
– – 6 4 – 4 – – 6–7, 5, 5 5, 4 – –
– – 11:22 14:01 – 11:31 – – 10:17 to 11:03 11:01, 11:20 – –
250 350 350 350 230 350 350 260 350 350 350 350
0 0 1 1 0 1 0 0 3 2 0 0
0 0 0.29 0.29 0 0.29 0 0 0.86 0.57 0 0
3890
8
0.21
350 350 275 350 350 230 350 350 350 350 350 350 350
9 1 1 1 4 10 1 0 0 2 1 0 0
2.57 0.29 0.36 0.29 1.14 4.35 0.29 0 0 0.57 0.29 0 0
Subtotal
4355
30
Grand total
8245
38
Subtotal 27-March-2003 7-November-2003 28-November-2003 19-December-2003 24-January-2004 25-February-2004 5-April-2004 29-April-2004 18-November-2004 18-January-2005 10-February-2005 2-March-2005 14-March-2005
Heading→N
Heading→S
– – – 1 – 1 – – 1 1 – –
– – 1 – – – – – 2 1 – –
4
4
2 – – – 3 10 – – – 2 1 – –
4 1 1 1 1 – 1 – – – – – –
0.69
22
13
0.46
26
17
– 4 – 4 – – 4 – – – 5–6 – –
10:55 to 11:10 9:45 14:21 11:22 7:35 to 7:39 12:39–12:55 11:31 – – 10:26–10:44 13:12 – –
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G. Cliff et al. / Fisheries Research 84 (2007) 41–46
Fig. 4. Mean monthly densities of whale sharks on the northern KZN coast. Vertical lines represent standard error of the mean. Inserted values represent the number of flights conducted in that month.
close to the southern end of the survey. The most sharks seen on a single survey was in February (10) and March (9), with respective densities of 4.35 and 2.57 sharks per 100 km (Table 1). When the results from each month’s surveys were combined, the highest densities were in February (1.03 per 100 km) and May (0.86 per 100 km) (Fig. 4). Although only five flights were conducted between May and October, there was some evidence of a seasonal pattern, in which, with the exception of April, sharks were most common in the first 5 months of the year. 3.4. Size, direction of travel, grouping and time of day The sharks were estimated to be 4–7 m long (Table 1). All but 3 of the 38 sharks were travelling parallel to the coast, with no significant difference in direction (p = 0.12, n = 35). All 10 sharks sighted on 25 February 2004 were heading north. The greatest concentration was seven sharks in 3 km of coast on 25 February 2004, when the sharks were well spaced and did not appear to be swimming together. Sighting times ranged from 07:35 to 14:01 h, with 79% of sightings in the 3-h period from 10:00 to 13:00 h (Table 1). 3.5. Sharks in Mozambique A survey was conducted along 950 km of southern Mozambique coastline in March 2004 and repeated twice in March 2005. Shark densities were very similar on the three flights, ranging from 4.3 to 5.9 sharks per 100 km, with a mean of 5.6 sharks per 100 km. The sharks were concentrated in a relatively short (<200 km) section of the coast, most noticeably on 1 March 2005, with 54 sharks along some 50 km of coast. A focal point for these aggregations was the coastline around Ponta Tofo (23◦ 52 S; Fig. 2). The sharks were at the surface, swimming in all directions, with no sign of any grouping behaviour. Time did not permit recording direction of travel nor circling over the sharks to make further observations. 4. Discussion The sighting rate of 0.21 sharks per 100 km of KZN coastline in 2001/2002 is extremely low. In 2003/2005 this figure
increased to 0.69 sharks per 100 km during the warmer months, when there appeared to be a greater likelihood of sharks being present. In contrast, Beckley et al. (1997) reported sightings of 50–100 sharks per 100 km of coast on three occasions. In January 1980, 54 sharks were recorded during a coastal flight between Sodwana and Cape Vidal, a distance of 64 km. Immediately south of Durban 95 sharks were sighted in January 1994 within 1 km of the shoreline along 110 km of coast. In much the same area 49 sharks were sighted in January 1996 on 73 km of coastline. Unfortunately there are no other published records of dedicated whale shark counts on the KZN coast and the three reports probably represent exceptional situations. Dive operators at Sodwana and in southern Mozambique reported that whale sharks were common in the mid-1990s, when dedicated whale shark viewing was introduced in the extreme south of Mozambique, but since 1999 viewing has been poor (Aitken, unpublished). One dive operator at Sodwana has used a microlight aircraft to spot whale sharks in the summer of 2004/2005, with sightings of only 11 sharks in each of the 3 months from December to February (Bester, personal communication). The concentration of sharks in the extreme north of KZN is to be expected. The animals are tropical and the water along the Maputaland coast is warm and clear, which enhances the sharks’ visibility from the air. It is not surprising that no sharks were seen between Cape St. Lucia and the Tugela River mouth, given the prevailing high turbidity inshore. It is not known how this turbid water affects the southward movement of the sharks. The sharks may move offshore to skirt the turbid water, which is generally restricted to within 2–4 km of the coast, which could explain why large numbers have been seen from Durban southwards in the summer rainy season (see above and Beckley et al., 1997). The stranding of three sharks in highly turbid water just north of Richards Bay (Fig. 1) (Beckley et al., 1997) suggests that some of the sharks must remain close inshore as they head south rather than moving offshore to avoid the silt. The highest density of sharks was in February, followed by May, although the latter was the result of a single flight. This pattern is not entirely in keeping with the reports from dive operators at Sodwana (Aitken, unpublished) and divers (Beckley et al., 1997) in which sightings were most frequent between November and January. This discrepancy may be an artefact of the low densities. There is insufficient information to comment on the influence of time of day on the movements of the sharks and their presence at the surface. Taylor (1996) reports that on Ningaloo Reef more sharks were present on the surface between 10:00 and 14:00 h, rather than after 14:00 h. It is fortuitous that most of the southbound flights were completed before 14:00 h. The sighting of four sharks between 07:35 and 07:39 h was on a return flight from Mozambique and was far earlier than normal, as most southbound flights commenced after 10:00 h. The reported lengths of 4–7 m were very rough estimates and indicate that largely immature animals enter KZN. These
G. Cliff et al. / Fisheries Research 84 (2007) 41–46
sizes were possibly underestimates, given that stranded sharks in KZN ranged from 5.9 to 9.2 m (Beckley et al., 1997) and the dive operators at Sodwana report that the vast majority of the sharks sighted are less than 9 m, typically 6–8 m (Aitken, unpublished). The direction of travel did not conform to the pattern of animals undertaking a southward movement or range extension at the onset of summer, returning to the tropics as the water cools. The prevailing inshore currents, which are largely winddriven (Schumann, 1988), may have the greatest influence on the direction of travel. All the sightings, particularly the large numbers in relatively small areas in southern Mozambique, indicate that this species is a solitary one and that large aggregations are probably a response to a localised abundance of food rather than an innate schooling behaviour. The density of sharks on the Mozambique coast is an order of magnitude higher than that on the northern KZN coast. The distribution of animals along this coast is extremely patchy, being concentrated around Ponta Tofo. This area is well known among divers for its concentrations of whale sharks. Cliff (unpublished) reported that a group of divers observed what they estimated to be “about 100 whale sharks milling around about 1–1.5 km offshore.” In early 2005 divers reported large aggregations of sharks over a period of several weeks. On some occasions the sharks swam slowly with closed mouths. On others they swam much faster, with open mouths, often breaking the surface and therefore presumably feeding. There is no published evidence that there are higher concentrations of prey along this particular section of coast to account for the highly localised distribution. The whale shark aggregations on Ningaloo Reef are highly seasonal, from March to May, in response to coral spawning and subsequent increase in production of zooplankton (Taylor, 1996). It is therefore not surprising that large numbers of whale sharks were spotted in the Ponta Tofo area during the three flights in March, although divers report that sharks may be present in far smaller numbers throughout the year. Another factor that could contribute to enhanced plankton production would be upwelling of cooler, nutrient-rich water. Lutjeharms (2004) refers to two upwelling cells on the central and southern Mozambique coast, one to the extreme north off Angoche and the other off Maputo Bay to the south (Fig. 4), both too far away to exert any obvious influence on the nearshore waters in the vicinity of Ponta Tofo. 5. Conclusions At this stage there is no indication of what oceanographic conditions might have changed during the last 5 years to explain the paucity of whale sharks on the KZN coast. It is tempting to attribute some of this decline to human-induced impacts, such as hunting, elsewhere in the whale shark’s range, but the international trend appears to one of reduced harvesting and increased protection for the species. The higher densities in southern Mozambique are encouraging, but these appear to be long standing ones, making it difficult to accept that the large numbers of sharks which were encountered in KZN
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waters in the past (Beckley et al., 1997) simply remained off the Mozambique coast during the study period. Further north, Kenya and, to a lesser extent, Tanzania have seen an unprecedented increase in whale shark sightings in the last few years, which has coincided with a similar increase in mantis shrimp populations (Watson, 2004; Steffensen, 2005). It is possible that sharks, which would have ventured south and ultimately ended up in the waters of KZN, have remained well to the north. Given that any dedicated whale shark diving industry would be based on the Maputaland coast, the density of whale sharks along this 190 km stretch of coastline between December and May was 1.05 sharks per 100 km of coastline. Although this figure is higher than that for the entire northern KZN, it is still too low to justify establishing a dedicated whale shark diving industry there. Nevertheless, legislation has been passed to protect whale sharks from possible harassment in the Greater St. Lucia Wetland Park. Aerial surveys in northern KZN will continue in the summer of 2005/2006. If additional funding can be obtained, the surveys should be repeated in southern Mozambique and the reasons for and the extent of the aggregations in the Ponta Tofo area should be investigated. Acknowledgements Most of the flying costs were funded by the Branch: Marine and Coastal Management (MCM) Co-ordination of the Department of Environmental Affairs and Tourism. The authors wish to acknowledge the assistance of those who acted as a second observer on the flights and Sabine Wintner in the preparation of the manuscript, and to thank Herman Oosthuizen of MCM for initiating the project. The enthusiasm of Rob and Sam Bester of Gypsea Dive Centre, Sodwana is acknowledged. References Beckley, L.E., Cliff, G., Smale, M.J., Compagno, L.J.V., 1997. Recent strandings and sightings of whale sharks in South Africa. Environ. Biol. Fish. 50, 343–348. Colman, J.G., 1997. A review of the biology and ecology of the whale shark. J. Fish Biol. 51, 1219–1234. Compagno, L.J.V., 2001. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2: bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). In: FAO Species Catalogue for Fishery Purposes, no. 1, vol. 2. Food and Agriculture Organization of the United Nations, Rome, 269 pp. Lutjeharms, J.R.E., 2004. The coastal oceans of south-eastern Africa. In: Robinson, A.R., Brink, K.H. (Eds.), The Global Coastal Ocean: Multiscale Interdisciplinary Processes (The Sea: Ideas and Observations on Progress in the Study of the Seas). Harvard University Press. Martin, A.K., Flemming, B.W., 1988. Physiography, structure and geological evolution of the Natal continental shelf. In: Schumann, E.H. (Ed.), Coastal Studies off Natal, South Africa. Lecture Notes on Coastal and Estuarine Studies, vol. 26. Springer-Verlag, New York, pp. 11–46. Schleyer, M.H., Celliers, L., 2003. Biodiversity on the marginal coral reefs of South Africa: what does the future hold? Zool. Verh. 345, 387– 400. Schumann, E.H., 1988. Physical oceanography off Natal. In: Schumann, E.H. (Ed.), Coastal Studies off Natal, South Africa. Lecture Notes on Coastal and Estuarine Studies, vol. 26. Springer-Verlag, New York, pp. 101– 130.
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Smith, A., 1828. Descriptions of new, or imperfectly known objects of the animal kingdom, found in South Africa. South African Commercial Advertiser 3, 2. Steffensen, M., 2005. Whale Shark “East Africa’s Mystery”. Africa Wild, Africa Wild Publishing, Johannesburg, South Africa, pp. 58–67.
Taylor, J.G., 1996. Seasonal occurrence, distribution and movements of the whale shark, Rhincodon typus, at Ningaloo Reef Western Australia. Mar. Freshwater Res. 47, 637–642. Watson, R., 2004. Living Submarines, vol. 27. SWARA The magazine of the East African Wild Life Society, Nairobi, Kenya, pp. 42–47.