For the past week, Sardines have been trapped along the Atlantic coast (and have washed up on Cape Beaches at Noordhoek and Scarborough). They moved into Houtbay and surrounding areas causing a frenzy of activity for fishermen, seals and dolphins. This has happened before but not in-recent memory and certainly not in such vast quantities, in November 2009 we saw a similar phenomenon with anchovies but that only lasted a single day. Steve Benjamin with photographers Jean Tresfon and Graham Fenwick headed out on Sunday morning to look for shoals of fish being predated on by seals. We found this in a small bay under Chapmans Peak drive. Here large pockets were trapped in shallow, clean water with hundreds of seals in pursuit. The seals seemed to favor the tiny loose shoals of 2-5 fish and these they chased like dogs after a tennis ball. I saw numerous seals biting sardines and not consuming them, a massacre of injured and flailing fish. The theory as to why the fish are trapped is that they were caught close to shore by a sudden cold snap in water temperature by a sudden strong SE wind. The thermal shock stressed the fish and predators took advantage. The fish were thin and weak, looking disoriented and lost. This experience was unique and rare and I am so glad we made the extra effort to get out there and get into the action. These events happen quickly and you just can’t put it off “till tomorrow”. In this environment there is no tomorrow, you must act now. Adventure divers put great effort and finances in traveling around the world to see unique marine events and one just happened on our doorstep. There are so many incredible wildlife experiences to be had right here in our regular coastal waters, if you know what to look for. Dare to dive in a different way…
From the Animal Ocean Newsletter: Click here for the full set of photos http://www.flickr.com/photos/jtresfon/sets/72157628107062155/
Regards
Jean
Jean Tresfon
Underwater Images & Surveys
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Comment from Editor: Dr Carl van der Lingen, a scientist from the Dept of Argiculture, Forestry & Fisheries, believes that the prevalence of Red Tide (gonyaulax polygramma – a phytoplankton) could also be influencing the sardines as the locations where sardines are inshore corresponds with the current distribution of redtide from Struisbaai to St Helena Bay. He contends that as the phytoplankton bloom reduces the oxygen levels in their immediate area, the sardines would shy away from red tide water and could end up being trapped too close to the shore.
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Fishermen as well as seals were making the most of this unusual sardine run today in Hout Bay, where many of the fish were trapped. The seals were feasting, but the fishermen were puling in sardines in great numbers, and we were able to buy a basket load for only R20. They will make a great braai and there are plenty to share.
Seeing thousands of shimmering sardines in the Komm and in the shallows all along Long Beach was an amazing expereince. We managed to catch a few which washed into a rock pool at high tide and were then trapped there at low tide. I have never seen a sardine run in CT before this, but some of the sea-wise locals happily filling up fish boxes in Kommetjie with leaping silver fish said that it has happened a few times in the past.
10’s of tons of sardines are washing up or being caught in the current cape sardine run. Although this is a lot of fish, it is a small fraction of the annual pelagic quota of 90 000 tons of sardines (As an aside, apparently the authorities at Koeberg were concerned that the sardines coming ashore north of Melkbosstrand could block the cooling intake of the reactors).
Marine Scientist and sardine expert, Dr Van der Lingen is concerned about the poor quality of the fish being washed up – fish from Hout Bay and Struisbay are very thin. Why? Sardines are not fussy feeders and can even eat some of the phytoplankton organisms in the bloom that is apparently trapping them inshore. One possibility is that as they try to feed on the phytoplankton, their gills become clogged causing them discomfort and resulting in them eating less.
Sardine runs worldwide are rare which makes the annual sardine run in winter off the KwaZulu Natal coast is a uniquely South African experience. Records of sardine runs along the East Coast date back to a Natal Mercury newspaper article of 4 August 1853. While the sardine runs in KwaZulu-Natal support a significant tourism, wildlife documentary, recreational fishing & diving industry, occurrences in the Cape are rare and the factors causing sardines to come inshore are different.
Red tide occurrences in the Cape are often a contributing factor as indicated by Dr van der Linden in relation to the current sardine run. There are records in the Cape of sardines and other fish washing inshore during red tide conditions as far back as 1962. In 2007 many fish washed up in Gordon’s Bay – not poisoned, but suffering from O2 depletion.
How healthy is the sardine population? Apparently research boats are currently at sea determining the recruitment rate of juvenile fish in order to determine the next season’s fishing quota.
In recent years sardine stocks have suffered 6 successive years of poor recruitment. This means that the natural replacement and growth of sardine stocks has been poor – apparently for natural environmental reasons. On a downward slide from a bumper year in 2000 when the stocks were estimated at 4 million tons, sardine stocks have declined as the mature fish shifted their spawning grounds eastward to the Central Agulhas Bank. Spawning so far east compromises the ability of the juvenile fish to reach the favourable nursery grounds off the West Coast of South Africa. As a result the recruitment of juvenile fish to replace adult sardine stocks has been low for a number of consecutive years.
Is this shift in spawning ground the result of a shift in ocean wind and currents – and is this a cyclical phenomenon OR is it related to Climate Change. If the latter, then the reduction of a valuable link in the marine food chin and a valuable protein source to humans should be cause for immediate and serious climate friendly change in human behaviour!! On the subject of Climate Change, the occurrence of red tide so early in the summer this year is also raising alarm bells. Experiencing how nature shifts her balance to readjust to changes has always been fascinating. As the demands of humans on Nature grows we are understanding increasingly that the natural environment is our economy – our ultimate resource base. . Thank-you to Dr van der Lingen for his telephone discussion providing the base information about the cape sardine run and recruitment of sardines. I hope that I have recorded it accurately. KimK