Sardine run

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NASA map of the Agulhas Current showing the levels of primary production during 2009. This is a measure of how much food was available for the spawning sardines.

The sardine run of southern Africa occurs from May through July when billions of sardines – or more specifically the Southern African pilchard Sardinops sagax – spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa. Their sheer numbers create a feeding frenzy along the coastline. The run, containing millions of individual sardines, occurs when a current of cold water heads north from the Agulhas Bank up to Mozambique where it then leaves the coastline and goes further east into the Indian Ocean.

In terms of biomass, researchers estimate the sardine run could rival East Africa's great wildebeest migration.[1] However, little is known of the phenomenon. It is believed that the water temperature has to drop below 21 °C in order for the migration to take place. In 2003, the sardines failed to 'run' for the third time in 23 years. While 2005 saw a good run, 2006 marked another non-run.[2]

The shoals are often more than 7 km long, 1.5 km wide and 30 metres deep and are clearly visible from spotter planes or from the surface.

Sardines group together when they are threatened. This instinctual behaviour is a defence mechanism, as lone individuals are more likely to be eaten than large groups.

Causes of the sardine run[edit]

Netting a shoal of sardines (dark patch in the water)

The sardine run is still poorly understood from an ecological point of view. There have been various hypotheses, sometimes contradictory, that try to explain why and how the run occurs.

A recent interpretation of the causes[3] is that the sardine run is most likely a seasonal reproductive migration of a genetically distinct subpopulation of sardine that moves along the coast from the eastern Agulhas Bank to the coast of KwaZulu-Natal in most years if not in every year.

The migration is restricted to the inshore waters by the preference of sardine for cooler water and the strong and warm offshore Agulhas Current, which flows in the opposite direction to the migration, and is strongest just off the continental shelf. A band of cooler coastal water and the occurrence of Natal Pulses and break-away eddies make it possible for sardine shoals to overcome their habitat constraints. The importance of these enabling factors is greatest where the continental shelf is narrowest.

The presence of eggs off the KwaZulu-Natal coast suggests that sardine stay there for several months and their return migration during late winter to spring is nearly always unnoticeable because it probably occurs at depths where the water is cooler than at the surface.

In some years there does not appear to be a sardine run. This may be because it is not detected by coastal observers either because it actually does not occur due to high water temperatures and/or other hydrographic barriers, or the migration may occur farther offshore and possibly deeper due to unusual conditions.

Oceanographic influences[edit]

Sardine prefer water temperatures between 14 and 20 °C.[4] Each southern winter the nearshore sea temperature along the South African south east coast drops to within this range. Along the KwaZulu-Natal coast, sardine may be found in water warmer than 20 °C. It was hypothesized that factors beside temperature may influence the movement of sardine along the KwaZulu-Natal coastline, One of these factors may be predation pressure.

Oceanographic regions of the KwaZulu-Natal coast[edit]

The KwaZulu-Natal coast includes varied oceanographic regions, each influenced by distinct environmental forces.[5]

  • The continental shelf waters of the KwaZulu-Natal Mid to Lower South coasts are dominated by the warm Agulhas Current which flows toward the south west. This water has a mean winter temperature of 23 °C and the current speed is often more than 1m/s within 5 km of the coast.
  • The Agulhas Current follows a very constant path. The main stream is just offshore of the continental shelf break most of the time, which suggests that conditions are normally unsuitable for sardines along that part of the coast.
  • Local winds do not appear to have much effect on the currents.
  • Sardine move closer to shore as they travel northwards along the coast, but it is not known whether this is due to environmental conditions or biological conditions.
  • There is a persistent cyclonic gyre, known as the Durban Eddy where warm Agulhas Current water flows onto the shelf and the resulting inshore current direction is from south to north. This section of coast may be considered a transition from the wind-dominated section of the continental shelf to the north, to the Agulhas Current dominated section of shelf to the south.
  • The North Coast section of continental shelf is considerably wider (>40km) than that of the south coast(roughly 15 km). This causes the Agulhas Current to flow farther offshore, and current conditions over the shelf are more variable. Wind appears to be a dominant influence in ths region. Longshore north-easterly or south-westerly winds precede currents of similar direction by roughly 18 hours. Sea temperature is often lower and nutrients higher than along the South Coast. [6]
  • The North Coast would seem to be more suitable habitat for sardine, but it is not known to what extent they use it.

These distinct regions may affect sardine distribution and movement.

Oceanographic variables and sardine presence[edit]

Some oceanographic variables have been found useful for describing conditions influencing sardine presence.[5]

  • Water temperature has an inverse and highly significant influence. This is consistent with the preferred temperature range of sardine.
  • Sea currents have a significant effect, with calm current conditions most favourable for sardine presence and moderate current speeds from north to south most detrimental. As sardine movement during the run is northwards, this counter-current effect is expected.

Other conditions associated with sardine presence are:[5]

  • Increasing atmospheric pressure: sardine presence appears to be higher during periods between the cold fronts along the KwaZulu-Natal coast. These periods have calm atmospheric conditions and slow nearshore currents.
  • Large swells and low water clarity associated with cold fronts have a negative effect on sardine presence.
  • Wind direction, wind speed, current direction, air temperature and rainfall all significantly affect sea surface temperature and consequently sardine presence. *Current and wind direction effects dominated, with north-easterly wind and currents from north to south resulting in cooler sea surface temperatures.
  • North-easterly winds cause the surface water layer to move away from shore (Ekman veering), allowing the cool water to reach the surface, and south-westerly winds push warm Agulhas Current surface water towards the shore causing inshore temperatures to increase, which would negatively impact upon sardine presence.
  • Increasing maximum air temperature, south-easterly (onshore) winds, wind speeds in excess of 6 m/s, and rainfall, all result in warmer sea surface temperatures.
  • Strong south-easterly winds and rainfall are associated with the passage of frontal systems, which would push warm surface waters shoreward resulting in warmer sea surface temperatures.
  • Frequent light north-westerly land breezes: When north-westerly land breezes are the strongest winds of the day they have a cooling effect on sea surface temperature. This cooling should be greatest in the vicinity of the surf zone where mixing is most effective. Sardine are often sighted close inshore during early mornings, suggesting that they could be attracted by cooler conditions found there.

Summary: Oceanographic predictors of sardine presence[edit]

Favourable:

  • Decreasing sea surface temperature
  • Calm current conditions
  • Light north-westerly land breezes
  • Stable atmospheric conditions.

Unfavourable:

  • Increasing sea surface temperature
  • Moderate north to south currents
  • Large swells
  • Turbid water

North-easterly and north-westerly winds and north to south currents have a cooling effect upon nearshore sea surface temperatures, but south-easterly winds and increasing air temperatures cause nearshore sea surface temperature warming.

Predators[edit]

External images
Images of the sardine run

Dolphins (estimated as being up to 18,000 in number, mostly the Common Dolphin Delphinus capensis, but also the Bottlenose Dolphin Tursiops aduncus) are largely responsible for rounding up the sardines into bait balls. These bait balls can be 10–20 metres in diameter and extend to a depth of 10 metres. The bait balls are short lived and seldom last longer than 10 minutes. Once the sardines are rounded up, sharks (primarily the Bronze Whaler, but also Dusky Shark, Grey Nurse Shark, Blacktip Shark, Spinner Shark and Zambezi Shark), game fish (including Shad/Elf a.k.a. Bluefish, King Mackerel, Garrick, Geelbek and Eastern Little Tuna) and birds (like the Cape Gannet, cormorants, terns and gulls) take advantage of the opportunity.

Cape Fur Seals follow the shoals up the Eastern Cape coastline as far as Port St Johns.

Predators as predictors of sardine presence[edit]

The Cape gannet is the predator species most closely associated with sardine presence along the Eastern Cape and KwaZulu-Natal coastline and is the most useful indicator of sardine run activity.

Sharks and large gamefish presence is also strongly associated with sardine presence during the run, but as they are not as easily observed from the surface they are not as useful a predictor of sardine presence

The presence of common dolphins inshore along the east coast during winter is significantly associated with sardine presence and common dolphin can be considered the third most useful species for predicting sardine presence.

The resident population of bottlenose dolphin does not appear to associate with the sardine run, whereas the migrant stock does. This may explain why the bottlenose dolphin is less likely to predict sardine presence.[5]

Record of predators[edit]

2005 records: In June and July of 2005 the avian and mammal predators included Bryde’s whale Balaenoptera edeni, African penguin Spheniscus demersus, Cape cormorant Phalacrocorax capensis which were predominantly found in the cooler southern part of the region. Peak sardine run activity occurred within 4 km of shore at the northward limit of a strip of cool water (<21 °C) stretching along the East Coast. The principal predators at this stage were common dolphins Delphinus capensis and Cape gannets Morus capensis.[7]

Economic importance[edit]

Sardines caught off Amanzimtoti, South Africa

Tourism[edit]

The recent interest in the sardine run has had significant impact on the local economy. The run has become important to tourism and is considered to be one of the main attractions in KwaZulu-Natal during the winter holiday period. Both local and international tourists are attracted to the spectacle and are provided with opportunities to participate in activities such as dive charters and boat based predator viewing tours.

The KwaZulu-Natal Sharks Board and East Coast Radio, facilitate a ‘Sardine Run Hotline’, which provides information on the position and movement of sardine shoals. Information is also provided on the internet.[8]

The Sardine Run Association (www.thesardinerunassociation.org) has been formed to provide a link between tour operators, tourists, non-governmental organisations, scientists, and local and national governments.

Fishery[edit]

The sardine run also supports a small-scale, seasonal beach seine fishery.

History[edit]

Th oldest known record of the run is a mention in the Natal Mercury newspaper of 4 August 1853. More recently, the run has been the subject of natural history documentaries (e.g. the BBC’s Nature's Great Events) and printed popular media (e.g. National Geographic).[8]

The 2011 run[edit]

Pilot shoals were netted at Hibberdene on 20 June 2011, while the main shoal was sighted near Port St. Johns. Small pockets of sardines were seen between Mfazazana and Margate. About 25 crates of sardines were hauled out from the first netting at Hibberdene.[9] A further 33 crates of sardines were netted, and were sold at R700 per crate or R30 per dozen sardines. The 58 crates were sold "within minutes".[10] An attempt was also made to net sardines at Banana Beach. About 500 Common Dolphins and numerous sharks were noted near Margate. Shark nets had been removed between Umgababa and Port Edward.[9]

Sardines were netted at Park Rynie on 21 June 2011. Some large nets of 200–300 baskets of sardines were taken. The baskets sold at R600 each. A large gathering of sardine predators was seen off Port Grosvenor on the Wild Coast. Thousands of Cape Gannets and dolphins were seen in a continuous line of about 6km between Brazen Head and just north of the Umtata River. It is suspected that this year's shoal is "massive", and will produce a "bumper run". Shark nets have been removed to the south of Durban. The first shoals were expected to reach Amanzimtoti on 23 June 2011.[11] The main shoal was still near Port St Johns.[12]

On 22 June 2011, a "few" baskets were netted at Umgababa beach, and a "handful" of baskets were netted at Warner Beach in the afternoon. Sardines were also netted at Isipingo, where 14 baskets were hauled out. The sardines therefore reached the Amanzimtoti area a day earlier than predicted.[13]

Rough seas (with waves up to 4.7 m) caused by strong winds associated with a cold front kept the sardines from the shore on 23 June 2011. Pockets of sardines were seen far out to sea off the Bluff. The rough water and far distance of the sardines from shore made it impossible for the fish to be netted. No dolphin or bird activity was seen in the Durban area associated with the sardines. The main shoal was still suspected to be off the Eastern Cape coastline,[14] with a report of some sardines still seen near Port St Johns on 22 and 23 June 2011.[15]

Durban beaches were the scene of most netting activity on 27 June 2011. "Hundreds of baskets" of sardines were hauled onto the beaches in 13 nets. The price per basket was R350 in the morning, but later in the afternoon the price had dropped to R120 per basket.[16] Each net contained in excess of 300 baskets of sardines, with one net containing around 500 baskets.[17] Sardines were also netted at Umhlanga, Port Shepstone, Margate, Umgababa, and Port Edward. Cape Gannets and other seabirds were seen "plunging from considerable heights" to catch the sardines, especially on the South Coast.[18] Most of the sardines were netted along the Durban beaches as this was the area of calmest waters; swells along the KwaZulu-Natal coastline were around 2.5 m.[19] Shark nets had been removed from Salt Rock to Port Edward, and bathers were requested to consult with lifeguards before entering the water.[17] Meanwhile a baby dolphin washed up on the beach at Scottburgh, with a gash behind its "flipper" (the photo showed a gash between the dorsal fin and the tail) that exposed the spine. The "weeks old" dolphin was taken to a nearby paddling pool, but authorities later euthanased it due to the severity of the injuries.[20] Speculation was that the dolphin had been injured by a shark, or by a boat propeller; possibly related to the sardine run.

Swells dropped to 1–1.5 m on 28 June 2011, allowing more netting of sardines. Sardines were netted at Amanzimtoti; on the main beach and at Chain Rocks.[19] A 22 year old American marine biology student (research diver) named Paulo Edward Stanchi was attacked by a large Dusky Shark while diving at Aliwal Shoal Marine Protected Area. The group of divers had encountered a pocket of sardines when a 3m long Dusky Shark bit Mr Stanchi on his left leg and hands. Mr Stanchi managed to free himself from the shark, and was treated on the diving boat before being transported to Rocky Bay, where medics stabilised him. He was then airlifted to Nkosi Albert Luthuli Hospital, where he underwent surgery. Dusky Sharks generally live offshore, but come closer to the shore during the sardine run. The annual sardine run allowed more Dusky Sharks in the Aliwal Shoal MPA than usual, but there was no reason for them to show any more interest in divers than usual. Mr Stanchi had been wearing split fins with black and grey stripes, and this may have looked like a small shoal of fish to the shark.[21][22] Meanwhile a woman in her 40s broke her leg in the frenzy at Amanzimtoti when the sardines were netted. The woman is believed to have been trying to get some of the sardines when she "stepped wrong" and fractured her leg. Paramedics stabilized her before transporting her to hospital.[23]

5 July 2011 was a "quiet day" for the sardine run. "Plenty of birds" were seen diving at Karridene close to the shore. 50 crates of sardines were taken at Umgababa in the early afternoon, while a net of sardines pulled in at Karridene contained some Garrick. More Garrick were caught by fishermen at Karridene, but in general there was little other game fish activity. There was reported to be a "massive shoal" of sardines off Coffee Bay in the Eastern Cape.[24]

On 15 July 2011, 100 baskets were netted at Pennington. It was difficult to predict the sardines' movements as they were staying offshore.[25]

On 20 July 2011, 300 baskets of sardines were netted at Pennington in the morning. There were lots of gannets off Ballito, and "quite a bit of fish" between Park Rynie and Mtwalume.[26]

A strong cold front hit South Africa towards the end of July, causing land surface temperatures to drop below 10 °C over much of the country.[27] Heavy snow falls were experienced in high lying areas, including Nottingham Road, Mooi River and Newcastle in the Midlands, while Van Reenen’s Pass was snowed in.[28] The cold front caused swells of up to 4 meters on the KwaZulu-Natal coast and a 25 to 30 knot wind with rough sea conditions.[29][30] A ship called the Phoenix ran aground at Salt Rock, Ballito on 26 July 2011 because of the rough conditions.[29][30] This cold front may have put an end to the 2011 Sardine Run.

See also[edit]

References[edit]

  1. ^ Marine Scientists Scratch Heads Over Sardines. Reuters. August 30 2004
  2. ^ Sardine Run[dead link]
  3. ^ P Fréon et al. (2010). "A review and tests of hypotheses about causes of the KwaZulu-Natal sardine run". African Journal of Marine Science 32 (2): 449–479. doi:10.2989/1814232X.2010.519451. 
  4. ^ Barange M, Hampton I (1997). "Spatial structure of co-occurring anchovy and sardine populations from acoustic data: implications for survey design". Fisheries Oceanography 6 (2): 94–108. doi:10.1046/j.1365-2419.1997.00032.x. 
  5. ^ a b c d SH O’Donoghue, L Drapeau, SFJ Dudley and VM Peddemors (2010). "The KwaZulu-Natal sardine run: shoal distribution in relation to nearshore environmental conditions, 1997–2007". African Journal of Marine Science 32 (2): 293–307. doi:10.2989/1814232X.2010.501587. 
  6. ^ Lutjeharms JRE, Valentine HR, van Ballegooyen RC (2000). "The hydrography and water masses of the Natal Bight, South Africa". Continental Shelf Research 20 (14): 1907–1939. doi:10.1016/S0278-4343(00)00053-4. 
  7. ^ SH O’Donoghue, PA Whittington, BM Dyer and VM Peddemors (2010). "Abundance and distribution of avian and marine mammal predators of sardine observed during the 2005 KwaZulu-Natal sardine run survey". African Journal of Marine Science 32 (2): 361–374. doi:10.2989/1814232X.2010.502640. 
  8. ^ a b CD van der Lingen, JC Coetzee and L Hutchings (2010). "Overview of the KwaZulu-Natal sardine run". African Journal of Marine Science 32 (2): 271–277. doi:10.2989/1814232X.2010.501581. 
  9. ^ a b Padayachee, K. The Mercury: First Trickle of Sardines Netted, June 21, 2011.
  10. ^ Krishna, C. Upper Coast Fever: The sardines are finally here! Early arrivals netted on local beaches, June 24, 2011.
  11. ^ Langa, L. The Mercury: Bumper sardine run could be just around the corner, June 22, 2011.
  12. ^ Medley, L. Daily News: Sardines head for Amanzimtoti, June 22, 2011.
  13. ^ South Coast Sun: Early sardine surprise on Upper South Coast, June 24, 2011.
  14. ^ Daily News: Feeling Swell, June 23, 2011
  15. ^ Shane's Fishing Blog: Sardine Run 2011, retrieved 24 June 2011.
  16. ^ The Mercury: Rich Bounty, June 28, 2011.
  17. ^ a b The Citizen: Sardine run at fever pitch off South Coast, 29 June 2011.
  18. ^ Daily News: Sardines all along the coastline, June 27, 2011.
  19. ^ a b Daily News: Swells drop and sardines are there!, June 28, 2011
  20. ^ Upper Coast Fever: Little Lost Stranger, July 1, 2011.
  21. ^ South Coast Sun: Shark attacks diver off Aliwal Shoal, July 1, 2011.
  22. ^ Sampson, B. The Citizen: Family to visit US shark Attack victim, 30 June 2011
  23. ^ South Coast Sun: Sardine frenzy sees woman break her leg, July 1, 2011.
  24. ^ Daily News: Quiet Day disappoints anglers, but main shoal on its way, July 6, 2011.
  25. ^ Waterworth, T. The Independent on Saturday: Fishing Tragedy Averted, 16 July 2011.
  26. ^ Medley, L. Daily News: Sardine surges almost at an end, July 20, 2011
  27. ^ IOL News: Cold front hits SA: http://www.iol.co.za/news/south-africa/cold-front-hits-sa-1.1108277, retrieved 23 August 2011.
  28. ^ The Ridge Online: Cold front hits Durban, retrieved 23 August 2011.
  29. ^ a b Fishing Corner: SHIP RUN AGROUND – AT SALT ROCK, retrieved 23 August 2011.
  30. ^ a b George Herald: NSRI on stand-by throughout the night for ship run aground – Ballito, retrieved 23 August 2011.

External links[edit]