Sardine Run 2010

April 23, 2010

Greetings once again sardine run followers. It is that time of the year again when we at UKZN, and anybody slightly interested in the sardine run, are filled with excitement, anticipation and even a slight sense of trepidation. The trepidation stems from the annual concern for the quality of the year’s event. We have not had a good sardine run since the epic 2004, when solid sardine run activity lasted well into August, and sporadic activity continued into September. 2005 was amazing for the 2 weeks that it lasted! Since then, activity along the KZN coastline has been very sporadic indeed.

This has not, however, been the case along the Wild Coast (south of Waterfall Bluff). Every year, during our sardine run research, we’ve encountered solid sardine run activity and have managed to achieve each year’s research aims. Initially these aims involved conducting aerial surveys along the wild Coast to investigate sardine distribution along the east coast. Recent years have seen us filming baitballs in an attempt to understand the feeding dynamics of sardine run predators. By the end of last year’s run, we’d obtained enough footage of baitballs, and are now conducting quantitative analysis this footage.

This year we are focussing our efforts on bronze whalers (Carcharynus brachyurus), known locally as copper sharks. These sharks have slipped below our research radar thus far, largely because of the difficulty in observing them. Thanks to the good folks at VEMCO (http://www.vemco.com), that is all about to change. VEMCO are supplying us with accoustic monitoring devices that we will “attach’ to bronze whalers. Attachment is the fun part. We will need to catch red-eye roundherring (Etrumeus spp.) using lures and then we will implant our sensors into these fish. The red-eye will then be fed to a chosen bronze whaler by a diver, who will then return to the boat. It is important that we do not disturb the shark during attachment, as this may affect its normal behaviour. Feeding the shark is the least invasive method of attaching the sensor, and will enable us to obtain biological information about the shark using simultenous video logging. The research team will then follow the shark using a hydrophone and conduct simultaneous boat-based predator surveys.

This VEMCO V9AP tags measures movement along 3 planes to determine a subject's movement in terms of its acceleration and depth.

Meanwhile, in the shark’s stomach, the sensor will be measuring depth, temprature and changes in the shark’s acceleration. The temperature measurement should allow us to determine when the shark is feeding, because when food is ingested, stomach temperature rises temporarily. All of this should provide much-needed insight into the role that these predators play in the sardine run phenomenon, and how much interaction there is between them and common dolphins.

taken from Chapter 4 of my thesis

It is still too early to make predictions about 2010 sardine movement up the coast. Each year during April and May we do see movement of fish up and down the SE coast, and there are, inevitably, false starts as sardine move eastwards, only to retract from their advances as conditions change. Our research has shown that movement is largely associated with cooling of continental shelf waters. Fish are often concentrated at the interface where cool water extending up the coastline meets warm Agulhas Current water that has invaded the continental shelf. If the cool water extends up the east coast, following upwelling in the Port Alfred region, then the chances of a good sardine run are enhanced. Let’s hope this is the case this year!

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