False Bay (Afrikaans: Valsbaai) is a body of water in the Atlantic Ocean between the mountainous Cape Peninsula and the Hottentots Holland Mountains in the extreme south-west of South Africa. The mouth of the bay faces south and is demarcated by Cape Point to the west and Cape Hangklip to the east. The north side of the bay is the low-lying Cape Flats, and the east side is the foot of the Hottentots Holland Mountains to Cape Hangklip, which is at nearly the same latitude as Cape Point. The bay is approximately square, with roughly the same length from north to south as from east to west, and the southern side open to the ocean. The seabed generally slopes gradually down from north to south, and is mostly fairly flat unconsolidated sediments. Much of the bay is off the coast of the City of Cape Town, and it includes part of the Table Mountain National Park Marine Protected Area and the whole of the Helderberg Marine Protected Area. The name "False Bay" was applied at least 300 years ago by sailors returning from the east, who confused Cape Point and Cape Hangklip, which are somewhat similar in profile when approached from the southeast. False Bay is at the extreme western end of the inshore Agulhas marine ecoregion, which extends from Cape Point to the Mbashe river over the continental shelf, in the overlap zone between Cape Agulhas and Cape Point, where the warm Agulhas Current and the cooler South Atlantic waters mix. The continental shelf is at its widest in this ecoregion, extending up to 240 km (150 mi) offshore on the Agulhas Bank, but is considerably narrower off False Bay. This ecoregion has the highest number of South African marine endemics and is a breeding area for many species. The transition between the Agulhas ecoregion and the cooler Benguela ecoregion is at Cape Point, on the western boundary of False Bay. False Bay also contains South Africa's largest naval base at Simon's Town (historically a base for the Royal Navy), and small fishing harbours at Kalk Bay and Gordon's Bay.
Description and location
The western side is bordered by the Cape Peninsula, and this stretch of coastline includes the smaller Buffels Bay, Smitswinkel Bay, Simon's Bay, and Fish Hoek Bay. At Muizenberg, the coastline becomes relatively low and sandy and curves east across the southern boundary of the Cape Flats to Gordon's Bay, to form the northern boundary of False Bay. From Gordon's Bay, the coastline swings roughly south and zigzags along the foot of the Hottentots Holland Mountains to Cape Hangklip, which is at nearly the same latitude as Cape Point. The highest peak on this side is Kogelberg at 1,269 m (4,163 ft). The bay is approximately square-shaped with wobbly edges, with roughly the same length from north to south as from east to west (30 km (19 mi)), with the entire southern side open to the ocean. The area of False Bay has been measured at about 1,090 km2 (420 sq mi), and the volume is approximately 45 km3 (11 cu mi) (with an average depth of about 40 m (130 ft)). The land perimeter has been measured from a 1:50,000-scale map at 116 km (72 mi). The eastern and western shores of the bay are very rocky and even mountainous; in places, large cliffs plunge into the water. Notable peaks associated with the bay include Koeëlberg (1,289 m (4,229 ft)), which rises from the water itself and forms the highest point of the Kogelberg, as well as Somerset Sneeukop (1,590 m (5,220 ft)) and Wemmershoek Peak (1,788 m (5,866 ft)), which are clearly visible across the bay. Some of the highest peaks visible across False Bay include Du Toits Peak near Paarl (1,995 m (6,545 ft)), Klein Winterhoek Peak near Tulbagh (1,995 m (6,545 ft)), Mostertshoek Peak at the Western extreme of the Michell's Pass (2,008 m (6,588 ft)) and Groot Winterhoek Peak North of Tulbagh (2,077 m (6,814 ft)). The northern shore is defined by a very long, curving, sandy beach. This sandy northern perimeter of the bay marks the southern edge of the Cape Flats. The bay is 30 km (19 mi) wide at its widest point. Suburbs of Cape Town stretch right across the Cape Flats, from Simon's Town halfway down the Cape Peninsula to the north-eastern corner at Gordon's Bay. There are also two small towns of the Overberg region on the east coast of the bay, Rooiels and Pringle Bay.
Coastal landmarks The coastal landmarks visible from offshore in False Bay, listed clockwise from Cape Point to Cape Hangklip, are:
Bottom morphology
The bottom morphology of False Bay is generally smooth and fairly shallow, sloping gently downwards at about 3 m per km from north to south, so that the depth at the centre of the mouth is about 80 m (260 ft). The bottom is covered with sediment, ranging from very coarse to very fine, with most of the fine sediment and mud in the center of the bay. The main exception is a long ridge of sedimentary rock that extends southward from off the Strand to approximately level with the mouth of the Steenbras River. The southern tip of this ridge is known as Steenbras Deep. There is one true island in the bay, Seal Island, a barren and stony outcrop of granite about 200 m (660 ft) long and with an area of about 2 ha (24,000 sq yd). It is about 6 km (3.7 mi) south of Strandfontein and is less than 10 m (33 ft) above sea level at its highest point. Many small rocky islets extend above the high-water mark, and other rocks and shoals that approach the surface. The largest of these, and the most significant navigational hazard in the bay, is Whittle Rock, a large outcrop of granite about halfway into the bay and a quarter of the way across from the Cape Peninsula (34°14.846′S 18°33.714′E), which is about 1 km (0.62 mi) in diameter and rises from a fairly flat sand bottom at about 40 m (130 ft) to within 4 m (13 ft) of the surface. There are smaller outlying granite reefs scattered to the south, east, and west of Whittle Rock, and more smaller granite reefs to the northwest. Most of the reefs on the western side of the bay are composed of granite from the Peninsula pluton. Still, east of Seal Island, they are generally sandstone, either of the Table Mountain series, or of the underlying Tygerberg formation. Whittle Rock reef can refract large south easterly storm waves, increasing their size in the vicinity of Kalk Bay harbour. Other shoal areas include the granite reefs at Roman Rock in Simon's Bay, hard sedimentary or metamorphic rock at York shoal and hard sandstone at East shoal, and several isolated granite outcrops which are too deep to be navigational hazards in the western part of the bay. The palaeo-drainage of the bay is split between the western side of the bay and the eastern side by the relatively durable contact zone between the Peninsula granite and the Tygerberg sediments, with deep valleys cut into the bedrock during the glacial maximum, which have since been filled with sediments. The drainage of the west side passed to the west of Seal Island, Whittle Rock, and Rocky Bank. The east side was drained by a valley between Seal Island and East Shoal, and another valley to the east of Steenbras Ridge, which joined east of Rocky bank and exited the bay between Rocky Bank and Hangklip Ridge. Outside the bay, but influencing the wave patterns in it, Rocky Bank is an extensive area of relatively flat sandstone reef between 20 and 30 m (66 and 98 ft) deep on the top, sloping down on all sides, but mostly to the south and east, where the depth can exceed 100 m (330 ft). A long underwater sandstone ridge sweeps across the eastern side of the mouth from Cape Hangklip towards the southwest, which is believed to affect water circulation in the bay. On the west side, a relatively shallow area of granite reef extends beyond the Cape Peninsula, with one major navigational hazard at Bellows Rock and a lesser one somewhat closer inshore at Anvil Rock.
Bathymetry
The bathymetry of False Bay differs from that of the west side of the Cape Peninsula. The west coast seabed tends to slope down more steeply than in False Bay and, although the close inshore waters are also shallow, the 100 m (330 ft) contour is mostly within about 10 km (6.2 mi) of the west coast, while the entire False Bay is shallower than about 90 m (300 ft). The bottom of the bay slopes down relatively gradually from the gently sloping beaches of the north shore to the mouth, and has a fairly even depth from east to west except close to the shorelines, with three major features disrupting this gentle slope. These are Seal Island, Whittle Rock, and the Steenbras ridge. Just outside the bay, there is a large shoal area at Rocky Bank, and a large ridge extending south-west from Cape Hangklip, which channels cold, nutrient-rich water into the west side of the bay during upwelling events.
Geology
The three main rock formations are the late-Precambrian Malmesbury Group (sedimentary and metamorphic rock), the Peninsula granite, a huge batholith that was intruded into the Malmesbury Group about 630 million years ago, and the Table Mountain group sandstones that were deposited on the eroded peneplain surface of the granite and Malmesbury series basement about 450 million years ago. The sand, silt, and mud deposits were lithified by pressure and then folded during the Permian–Triassic Cape Orogeny to form the Cape Fold Belt, which extends along the western and southern coasts of the Western Cape. The present landscape is due to prolonged erosion, which has carved deep valleys, removed parts of the once-continuous Table Mountain Group sandstone cover from the Cape Flats, and left high residual mountain ridges.
At times, the sea covered the Cape Flats and Noordhoek valley, the Cape Peninsula was then a group of islands, and False Bay and the Cape Flats a strait. During glacial periods, the sea level dropped, exposing the bottom of False Bay to weathering and erosion; the last major regression left the entire bottom of False Bay exposed. During this period, an extensive system of dunes was formed on the sandy floor of False Bay. At this time, the drainage outlets lay between Rocky Bank and Cape Point to the west, and between Rocky Bank and Hangklip Ridge to the east.
Waves, tides, water circulation, and temperature Swell entering the bay is predominantly the product of the westerly winds blowing over the Southern Ocean. The prevailing swell is about 12 to 25 seconds in period from the southwest, with an average height of about 3 m (9.8 ft). It impinges directly on the east coast of the bay, amplified by refraction over Rocky Bank in the region near the Steenbras River mouth, where rogue waves may occur. Further west, the swell refracts and diffuses around a fairly large shoal area around Cape Point, and is moderately to severely attenuated by the time it reaches the western shores. Waves along the north coast of the bay between Macassar and Muizenberg generally break by spilling as the slope is gradual. In summer, strong south-easterly winds blow over a fetch partly limited by the width of the bay and generate short-period wind waves of around 6 seconds and 2 m (6.6 ft) height, and produce multiple lines of breakers along the north shore. Where the slopes are steeper, rip currents may form, posing a hazard to swimmers. Northward propagating long period waves are focused in the northeast and northwest parts of False Bay by refraction effects over the shoal waters of Rocky Bank in the mouth of the bay, with measured heights of waves in the area between Steenbras mouth and Kogelbaai being up to twice the height of the waves in the Muizenberg to Strandfontein region for the prevailing southwesterly open ocean swell. The focusing effect is mostly on swells with a period of 13 seconds or more, and a direction between 210° and 245° true. The smaller and shallower reef at Whittle Rock towards the west side of the bay has a similar but lesser effect, and can focus longer period south-easterly waves on Kalk Bay. This is unusual, and associated with a cut-off low-pressure system causing the south-easterly winds to blow for an unusually long time over enough fetch to develop a sea sufficiently for it to be refracted by the shoal area. Wave height of southwesterly swells decreases from west to east along the north coast of False Bay from around Macassar to Gordon's Bay due to the effects of refraction and friction of the wave base on larger areas of offshore reef before reaching the shoreline. Tides are regular, semi-diurnal, and relatively weak, and there are no strong tidal currents. Maximum tidal range at Simon's Town is 2 m (6.6 ft) at the highest astronomical tide, with a minimum range of about 0.56 m (1.8 ft) at mean neap tides. When large waves break at Macassar on a high tide, the beach is known to be dangerous for swimming, and beach erosion is increased. The circulation patterns in False Bay are variable over time, with seasonal and longer-term cycles. There are cold-water upwelling events associated with south-easterly winds in summer, and periodic intrusions of warm-water eddies from the Agulhas Current along the south coast, both of which contribute to biodiversity. Four main surface circulation patterns have been observed in False Bay. Wind is the dominant forcing influence on surface circulation, with tidal and inertial currents of secondary importance, mainly when the winds are weak. Gordon's Bay is in the wind shadow of the Hottentots-Holland Mountains for south easterly winds, and this causes a semi-permanent anticyclonic eddy and associated anticlockwise gyre, in the opposite direction to the usual cyclonic circulation of the main part of the bay. A clockwise rotation driven by the south-easterly winds mostly occurs during summer. This circulation is partly set up by the west-northwesterly flow south of the bay, which splits at Cape Point. The northerly component sets up flow towards the equator on the western shores. South-easterly winds cause this clockwise pattern to dominate. North-westerly winds cause an anti-clockwise circulation, with an eastward current flowing south of the Bay and entering at Cape Hangklip. When there is no strong wind forcing, tidal forcing can occur on the incoming and outgoing tides. A fairly uniform northward flow occurs during flooding tides, and southward during ebbing tides, with bathymetry affecting the flow direction in shallow areas. These currents are most noticeable along the coastline and in the shallow northern parts of the bay between Simon's Town and Gordon's Bay. In the deeper areas of the mouth of the bay, tidal and inertial currents appear to contribute to the variability of the deeper part of the water column, along with the effects of wind forcing. Wave energy focused by the various shoal areas outside and inside the bay is a driver of nearshore currents, particularly in the northern parts of the bay.
In summer, False Bay is thermally stratified, with a vertical temperature range of 5 to 9 °C (41 to 48 °F) between the warmer surface waters and the cooler waters below 50 m (160 ft). In contrast, in winter, the water column is nearly constant in temperature at all depths. The development of a thermocline is strongest around late December and peaks in late summer to early autumn. In summer, the south easterly winds generate a zone of upwelling near Cape Hangklip, where surface water temperatures can be 6 to 7 °C (43 to 45 °F) colder than the surrounding areas, and bottom temperatures below 12 °C (54 °F). In the summer to early autumn (January–March), cold water upwelling near Cape Hangklip causes a strong surface temperature gradient between the south-western and north-eastern corners of the bay. In winter, the surface temperature tends to be much the same everywhere. In the northern sector, surface temperatures vary a bit more (13 to 22 °C (55 to 72 °F)) than in the south (14 to 20 °C (57 to 68 °F)) throughout the year. Surface temperature variation from year to year is linked to the El Niño–Southern Oscillation. During El Niño years, the South Atlantic high is shifted, reducing the south-easterly winds, so upwelling and evaporative cooling are reduced, and sea surface temperatures throughout the bay are warmer, while in La Niña years, there is more wind and upwelling and consequently lower temperatures. Surface water heating during El Niño increases vertical stratification. The relationship is not linear. Water density dynamics are mostly temperature dependent, with only weak influences from salinity. The major influence on the temperature distribution is wind-driven upwelling and advection of cold water, which is most notable north-west of Hangklip and less marked near Gordon's Bay, due to strong south-easterly winds, with isolation as a secondary effect, mostly in the shallow waters of the northern and north-easterly regions. Waves may have a greater influence on nearshore temperatures than wind. Upwelling outside the bay along the coast east of Hangklip can also supply cold water to the bay.
Rivers and drainage
Drainage into False Bay can be considered from four watersheds: the east-flowing streams of the southern Cape Peninsula, the Cape Flats, the Helderberg basin, and the south-westwards drainage of the Hottentots-Holland mountains of the Overberg, extending south as far as Cape Hangklip. The eastward draining rivers of the Southern Peninsula are generally fairly short and steep, and some, such as the Silvermine and Elsje rivers, have valley bottom wetlands at the coast. The Buffels River flows from a small spring to its mouth in Buffels Bay; the Klawersvlei River flows northwest from behind the mountains above Miller's Point over the plateau behind Simon's Town, before turning east over the escarpment and a high waterfall, entering the bay near the Simon's Town railway station; the Elsjes River flows from the Red Hill plateau to enter False Bay from the Glencairn valley; and the Silvermine River, originally known as the Esselstein River, drains the valley south of the Steenberg mountains and flows east across the Steenberg Plateau, then south through the Silvermine Valley before crossing the coastal Fish Hoek plain to enter False Bay at Clovelly on the north side of Fish Hoek Bay. Between these short and fairly steep streams, rainwater runoff generally flows directly down the mountainside into the bay. The Sandvlei catchment drains the east side of the mountains north of Muizenberg and south of the Liesbeek catchment into False Bay: Sandvlei (Zandvlei) is the largest of eight estuaries on the False Bay coastline, with an area of about 155 ha (0.60 sq mi). The Westlake, Keysers, and Sand rivers feed it. The southern Diep River flows from the mountains above Constantia to Little Princessvlei, which drains into the Sand River, which flows into the northeast of Sandvlei. The Westlake River, also known as the Steenberg or Raapkraal River, originates on the slopes of the Steenberg and flows through the Kirstenhof wetlands into the north-west of Sandvlei. The Keysers River and its tributaries, the Grootbosch, Spaanschemat, and Prinseskasteel rivers, rise on Constantiaberg. The upper reaches of the Spaanschemat River are known as the Glen Alpine Stream, which originates below Constantia Nek and is joined by the Eagles Nest Stream. Historically, the Cape Flats was partly covered in wetlands, particularly during winter, and retained much of its rainfall. Many of these wetlands have been destroyed by canalization and infilling to provide residential space. Many of the remaining perennial vleis are at the southwest side of the region (Zeekoevlei, Rondevlei, Zandvlei, etc.) and drain into the bay at Muizenberg through the estuary at Zandvlei. There is also groundwater seepage through the sand along the bay's north coast. The Elsieskraal River and the Black River catchment drain to the northwest into Table Bay, and do not affect False Bay. The Diep River catchment drains into Zandvlei, and Zeekoevlei and its catchment also drain to Zandvlei at times. The Eerste River and its tributary, the Kuils River, drain into False Bay on the north coast, west of the Helderberg basin watershed. They drain part of the Cape Flats, but most of the catchment of the Eerste River is in the Stellenbosch district, between the Helderberg and Stellenbosch Mountains, and the Jonkershoek Valley. The catchment of the Lourens River is in the Helderberg region. It is the region's largest river. The source is in Diepgat Ravine, in the Hottentots Holland Mountains. It is joined by minor tributaries from Landdroskloof and Sneeukopkloof in its upper reaches. The river flows in a south-westerly direction between the Helderberg and Schapenberg, through Somerset West and Strand, to a small estuary on the coast of False Bay. Its overall length is about 20 kilometres. The Soete River is a small river that may have originally been part of the Lourens River system, diverting floodwater through an alternative route to the bay. Sir Lowry's River drains the south side of Schapenberg and the west side of the Hottentots Holland south of Schapenberg. It enters the bay in Gordon's Bay. The Steenbras River catchment is to the east of the Hottentots Holland mountains, and almost all of its water is retained by the upper and lower Steenbras Dams, which are a significant part of the municipal water supply to the City of Cape Town. Steenbras River mouth is south of Gordon's Bay. The Rooiels River enters False Bay at Rooiels Beach. It drains a small catchment area in a nature reserve in the mountains of the southwest of the Overberg district.
Water quality The nutrient contribution to False Bay surface waters from upwelling appears to exceed that from terrestrial sources via runoff and groundwater seepage. Still, pollutants from terrestrial sources can persist and adversely affect coastal ecosystems and recreational activities. Mixing with offshore water has a significant effect on surf zone and inshore water quality. The effects of microbial processes on inshore water quality and the relative contribution of anthropogenic nutrient sources remain unknown but are likely to be increasing.
History
In pre-colonial times, False Bay, along with most of the Southern African coast, provided sustenance to the Khoisan or Khoekhoen tribe, who collected seafood from the shores and deposited the shells in middens along the coast, which indicate use over the past 10,000 years. Bartolomeu Dias first referred to the bay, in 1488, as "the gulf between the mountains". The name "False Bay" was first used at least three hundred years ago by sailors who confused the bay with Table Bay to the north. According to Schirmer, the confusion arose because sailors returning from the east (the Dutch East Indies) initially confused Cape Point and Cape Hangklip, which are somewhat similar in form. Hangklip was known to early Portuguese seafarers as Cabo Falso, or False Cape, and the bay's name derives from the cape. Commercial fishing was started in the late 17th century, soon after settlement by the Dutch. In 1672, the Dutch warship Goudvinck was stationed at the Cape and was instructed to survey False Bay, but it is not known how much was done before it was recalled. Simon van der Stel, who was appointed commander of the station in 1679, sailed False Bay in November 1687 on the galiot De Noord, took the earliest recorded soundings, and described the islands, reefs, and shoreline of the bay. By the end of the 17th century, the general bathymetry was known. The Whittle Rock reef is named after a lieutenant Whittle of the Royal Navy, who surveyed parts of False Bay after HMS Indent was damaged off Miller's Point, soon after the first British occupation of the Cape in 1795. Commercial fishing has been practiced in False Bay since the late 1600s. Over time, a range of fishing methods have been prohibited in False Bay. Demersal trawling, purse seining, and gillnetting were introduced in the 19th century but have been stopped because they deplete stocks, conflict with other fisheries and users, and damage the environment. Illegal gillnetting is still a problem. Penguin eggs were collected until 1968, whaling operations took place until 1975, seals were hunted for fur until 1984, and guano was collected until 1991. All of these activities had a severely detrimental effect on the targeted populations and are now illegal. Commercial abalone diving has been severely restricted due to overfishing, but illegal exploitation continues. Recreational abalone extraction has been discontinued. There have been symposia in 1968 and 1989 on the socio-ecological importance of False Bay, with reviews of the bay's oceanography and biology, as well as of human impacts on it.
Shipwrecks
Over the years, several ships have been wrecked in False Bay due to weather, war, navigational errors, other accidents, or intentional scuttling. These include: Wrecked:
1691: Portuguese warship Sarpine, wrecked near Hottentot's Holland.
25 August 1778: British East Indiaman Colebrooke, wrecked south of the Steenbras River mouth, at 34°13.871′S 18°50.588′E 7 October 1786: Dutch East Indian schooner Catwyk aan Rhyn, driven ashore in a gale in Simon's Bay without loss of life. 16 October 1788: French frigate Pénélope. 16 May 1789: Dutch ship Drietal Handelaars. 28 September 1800: Sloop Benjamin, lost with all hands at Gordon's Bay. 1803: Dutch warship HNMS Bato, burned and sank in Simon's Bay at 34°10.998′S 18°25.560′E c. 2 September 1805: English East Indiaman Brunswick, wrecked at Long Beach in Simon's Bay at 34°10.880′S 18°25.607′E. 1810: British East Indiaman Euphrates, struck Whittle Rock but was repaired. 29 July 1816: Brig-sloop HMS Zebra (1815), was stranded, but not wrecked, in Simon's Bay; it was eventually wrecked on 2 December 1840, when a heavy gale drove it ashore and wrecked it off Mount Carmel near Haifa. 29 July 1816: Frigate HMS Revolutionnaire, stranded in Simon's Bay, but could not have been wrecked as it was broken up on 4 October 1822 after further service. 18 October 1816: Brig Camille, wrecked at Muizenberg beach. 1818: Vrouw Ida Alida, wrecked at Muizenberg. 25 October 1821: Waterloo, wrecked at Fish Hoek. 1823: Wooden sailing schooner Cockburn, wrecked on Muizenberg beach. Alternative dates from 3 to 6 April have been cited. 29 June 1828: Padang, wrecked in Simon's Bay. 12 July 1829: Phoenix, wrecked at Phoenix Shoal off Boulders Beach, Simon's Town on 19 July 1829 at 34°11.388′S 18°26.898′E. 10 January 1839: French whaler Le Protee, wrecked at Strandfontein. 27 July 1839: Barque Admiral Cockburn, wrecked at Muizenberg beach. 28 July 1841: Schooner Felix Vincidor, wrecked at Muizenberg beach. 12 February 1847: Robert, sprang a leak and was beached without loss of life near Gordon's Bay. 13 January 1850: Slaving barque Rowvonia, wrecked in Simon's Bay. 16 July 1862: Prussian barque Johanna Wagner, wrecked at Zandfontein near Muizenberg. November 1878: Benefactress, wrecked at Lourens River mouth, The Strand. 9 August 1897: Schooner Nukteris, wrecked at Buffels Bay just north of Cape Point. 21 November 1914: British turret steamer SS Clan Stuart, ran aground at Glencairn, 34°10.303′S 18°25.842′E HMS Trident, struck Whittle Rock and sank. Scuttled:
MV Rockeater, scuttled as an artificial reef in Smitswinkel Bay on 15 December 1972 at 34°16.127′S 18°28.890′E SAS Pietermaritzburg, scuttled as a recreational dive site just north of Millers Point at 34°13.303′S 18°28.465′E SAS Good Hope, scuttled as an artificial reef in Smitswinkel Bay at 34°16.054′S 18°28.850′E SAS Fleur, scuttled in central False Bay north of Whittle Rock at 34.1805°S 18.5649°E / -34.1805; 18.5649 SAS Transvaal, scuttled as an artificial reef in Smitswinkel Bay at 34°16.005′S 18°28.761′E SAS Bloemfontein, scuttled in central False Bay at 34.2443°S 18.6659°E / -34.2443; 18.6659 MFV Princess Elizabeth, scuttled as an artificial reef in Smitswinkel Bay at 34°16.068′S 18°28.839′E MFV Orotava, scuttled as an artificial reef in Smitswinkel Bay at 34°15.998′S 18°28.774′E Muizenberg Trawler wrecks, ST Bulby and ST Iolite, scuttled off Muizenberg at: Western trawler wreck: 34°07.006′S 18°31.219′E Eastern trawler wreck: 34°06.996′S 18°31.360′E ST Godetia, scuttled as an air-force training exercise off Macassar at about 34.1°S 18.73°E / -34.1; 18.73. SATS General Botha, scuttled in central False Bay east of Whittle Rock by gunfire from a battery at Simon's Town at 34°13.679′S 18°38.290′E
Climate
The climate is Mediterranean, with warm, dry summers and cool, damp winters. In winter, gales and storms from the northwest are common and can be ferocious. False Bay is exposed to southeasterly winds in summer and its waters are approximately 6 °C (43 °F) warmer than those of Table Bay, owing to the influence of the warm Agulhas Current. The La Niña phase of the El Niño–Southern Oscillation cycle tends to increase rainfall in this region in the dry season (November to April).
Winds The winds strongly influence the waves and water circulation and, through them, the sea surface temperature. The wind follows a characteristic pattern that shifts in latitude with the seasons and tracks the Rossby waves as they move eastwards over the southern ocean. A southwesterly wind follows the passage of a cold front as the anticyclone moves east and merges with the South Atlantic High, producing strong south-easterly winds. The high pressure cell moves further over the tip of Africa and splits off the South Atlantic High, with weakening south easterly winds, followed by a coastal low with north-westerly wind before the next cold front, bringing cool, wet westerly wind which passes around Table Mountain and converges as a northerly wind over the bay. The South Atlantic High shifts latitude with the seasons, following the sun, which causes large variations in the wind pattern throughout the year. In summer, it moves south, and south-easterly winds dominate, with average strength in January and February. During winter, the northward shift allows the fronts to extend farther north, with stronger northwesterly winds and more frequent, heavier rain. The winter winds tend to be strongest in June and are generally northwesterly. The transition periods are April and September. The El Niño–Southern Oscillation (ENSO) affects the winds and rainfall over this region. Sea surface temperatures off the west and south coasts of South Africa are affected by ENSO via changes in surface wind strength. During El Niño, the south-easterly winds driving upwelling are weaker, which results in warmer coastal waters than normal, while, during La Niña, the same winds are stronger and cause colder coastal waters. These effects on the winds are part of large-scale influences on the tropical Atlantic and the South Atlantic High-pressure system, and changes to the pattern of westerly winds further south. There are other influences not known to be related to ENSO that are similarly important. Some ENSO events do not lead to the expected changes. Local variations in wind direction and strength are caused by interaction with the mountains on both sides of the bay. South-easterly winds are accelerated northwest of Cape Hangklip, and a distinct wind shadow can develop in the lee of the Kogelberg mountain. Northwesterly winds accelerate over Table Mountain and approach the bay from varying directions depending on the local topography. Temperature differences between land and water can also produce diurnal variations of wind speed and direction, particularly in summer. Eastward-moving atmospheric Rossby waves move across the area at 3 to 20 day intervals, mostly in winter from May to September. The subtropical ridge is replaced by coastal lows, followed by northwesterly winds and frontal troughs that bring rain, stormy winds and seas, onshore transport, downwelling on the eastern shores, and mixing.
Ecology and marine life
False Bay is at the extreme western end of the inshore Agulhas marine ecoregion which extends from Cape Point to the Mbashe River over the continental shelf, in the overlap zone between Cape Agulhas and Cape Point where the warm Agulhas Current and the cooler South Atlantic waters mix. The continental shelf is at its widest in this ecoregion, extending up to 240 km (150 mi) offshore on the Agulhas Bank, but is considerably narrower off False Bay. This ecoregion has the highest number of South African endemics and is a breeding area for many species. There are several important commercial fisheries in this region. The transition between the Agulhas ecoregion and the cooler Benguela ecoregion is at Cape Point, on the western boundary of False Bay. There are two marine protected areas in False Bay: the Table Mountain National Park Marine Protected Area (TMNPMPA) lies on both sides of the Cape Peninsula, and so is partly in False Bay, and the Helderberg Marine Protected Area is off Macassar on the northern shoreline of the bay. There are concerns about the effect the disappearance of great white sharks in False Bay will have on the local ecosystem, as the sharks serve as the main predators of the local Cape fur seal population. A government-appointed panel has reported that the appearance of orcas, commercial fishing, and climate change are likely the major contributing factors to the mass exodus of the sharks.
Reef ecosystems Six feeding groups have been identified among the common suprabenthic fish species of False Bay, based on diet comparisons. These are: generalised benthic carnivores. carnivorous benthic browsers, herbivorous benthic grazers, midwater predators on small invertebrates, benthic macro-predators, and predators on small benthic invertebrates. These groups appear to eat mostly reef-dwelling prey, with the small amount of sand-dwelling prey assumed to be from areas adjacent to the reef. Feeding occurs mostly when water temperatures exceed 13 °C (55 °F). There is some dietary overlap between species but, in most cases, each species has a dietary niche, reducing competition for food within the assemblage.
Habitat types The benthic habitat types listed for False Bay in the National Biodiversity Assessment are:
Fauna
The marine animals of False Bay are diverse. The more popularly known species, which are a tourist draw, include white sharks, abalone, African penguins, snoek, yellowtail, many over-exploited line fish species and west coast rock lobster. Besides the resident species and several known migrants, the waters of the MPA are occasionally visited by vagrants carried in by the eddies of the Agulhas Current, which can bring tropical and subtropical specimens normally resident thousands of kilometres away. Fauna found in the area include:
Great white shark Cape fur seal Southern elephant seal (vagrant) Broadnose sevengill shark Cetaceans Southern right whale Humpback whale Bryde's whale Pygmy right whale Heaviside's dolphin Dusky dolphin Indo-Pacific bottlenose dolphin Indo-Pacific humpback dolphin Long-beaked common dolphin Killer whale (orca) Cape clawless otter Cape gannet African oystercatcher Whitecrested cormorant Crowned cormorant Cape Cormorant Grey heron Jackass penguin Hartlaub's gull Kelp gull Greyheaded gull Caspian tern Comon tern Sandwich tern Swift tern Damara tern
Seaweeds
Seaweeds are thousands of species of macroscopic, multicellular, marine algae of varied taxonomic classification. The term includes some types of Rhodophyta (red), Phaeophyta (brown) and Chlorophyta (green) macroalgae. The seaweed ecology is unusually varied for an area of this size, as a result of the meeting of two major oceanic water masses near Cape Point, comprising two coastal marine bioregions. The ecology of the west or "Atlantic Seaboard" side of the Cape Peninsula is noticeably different in character and biodiversity to that of the east, or "False Bay" side. Both sides are classified as temperate waters, but there is a significant difference in average temperature: the Atlantic side is noticeably colder.
Algal blooms
False Bay has a high incidence of dinoflagellate blooms that may produce toxins or accumulate as red tides. The water retention and stratification of late summer and autumn produce the environment most conducive to harmful algal blooms. Algal blooms tend to propagate clockwise with the circulation, and may become trapped in the Gordon's Bay eddy for extended periods. Brown discoloration in the surf zone along the north shore is frequently due to persistent blooms of the non-toxic diatom Anaulus australis, which is provided with nutrients from groundwater seepage through the sand bottom and river outfalls containing waste water from the nearby sewage purification systems.
Marine protected areas
The Table Mountain National Park Marine Protected Area is an inshore marine protected area around the Cape Peninsula. It was proclaimed in Government Gazette No. 26431 of 4 June 2004 in terms of the Marine Living Resources Act, 18 of 1998. The MPA is of value for conservation of a wide range of endemic species, and has considerable economic value as a tourist destination. It encloses a large number of recreational dive sites visited by residents and tourists from further afield. The shark and whale-watching tourism industries are also represented, and there are several popular surfing spots. The MPA is mainly a controlled zone where extractive activities are allowed under permit, with six small no-take zones. The MPA is administrated by the Table Mountain National Park, a branch of SANParks. The marine ecology is unusually varied for an area of this size, as a result of the meeting of two major oceanic water masses near Cape Point, and the park extends into two coastal marine bioregions. The ecology of the west, or "Atlantic Seaboard," side of the park is noticeably different in character and biodiversity from that of the east, or "False Bay," side. Both sides are classified as temperate waters, but there is a significant difference in average temperature: the Atlantic side is noticeably colder. This MPA contains culturally significant fish traps, historical wrecks, and traditional fishing communities, and is also important for commercial fisheries. Part of the West Coast rock lobster industry takes place within the MPA, as do recreational and subsistence fishers, and an illegal poaching industry that mostly targets abalone, rock lobster, and territorial line fish from the no-take zones. The Helderberg Marine Protected Area is a small marine conservation area on the north-eastern side of False Bay, between the mouths of the Lourens River in the Strand, and the Eerste River in Macassar. The Helderberg MPA is located in the warm-temperate Agulhas bioregion. The shoreline is a sandy beach with mobile dunes, and the seabed is a low sandstone reef with kelp beds and sand sediments. The areas nearest to the river mouths are in relatively poor condition, due to pollution of the river water. The beach inside the MPA is the most pristine part of the north shore of False Bay. The City of Cape Town administrates the MPA.
Economic value The harbours and slipways support the South African Navy, a small fishing industry, and a larger recreational boating community, including yachts, recreational fishing boats and recreational diving boats.
Harbours There are harbours at:
Simon's Town Simon's Town naval base, with dry dock and syncrolift facilities False Bay Yacht Club (marina and club trailer and travelift slipways, NSRI station 10) Kalk Bay (commercial fishing harbour, with rail slipway for repairs) Gordon's Bay (commercial fishing harbour, yacht club marina, NSRI station 9, and public trailer and rail slipways) Harbour Island marina (recreational boating marina and public trailer slipway)
Other slipways Buffels Bay (public trailer slipway inside the TMNP) Miller's Point (public trailer slipway for recreational and commercial ski-boats) Rumbly Bay (public trailer slipway for recreational ski-boats Rooiels (private