June 21st 2010

June 29, 2010

Common dolphins, Delphinus capensis. photo: Will Robbins

A very promising start for today’s research, with patches of foraging birds off Poenskop (the north end of PSJ Bay). There were nice concentrations of diving gannets, with at least 800 birds feeding between Port St Johns and Mntafufu River. Unfortunately, although there were quite a few common dolphins feeding, they did not isolate a patch of fish into a stationary baitball. We need a stationary ball with predators, and particularly sharks, feeding upon it before we can deploy our transmitters. Consequently, we spent the greater part of the morning doing exploratory dives to check whether the activity below the water line matched the chaos above. Regrettably, it didn’t.

diving Cape gannet, Morus capensis. photo: Will Robbins

One particularly noteworthy item: there were lots of bottlenose dolphins amongst this feeding activity. At one stage of the morning’s activity, we followed a pod of bottlenose dolphins with birds diving regularly above them, but at no stage did the bottlenose dolphins show any indication that they would form a bait ball. There were quite a few oil slicks and some smell of sardine on the water, so we were very hopeful. Unfortunately, the activity died down and by 11h00 one would never have suspected that anything had happened during the morning, if one did not notice the rafts of birds sitting and digesting what little food they were able to gather during the craziness.

Sea Surface Temperature 21st June 2010. image courtesy of MRSU

The activity from earlier this month seems to have all but disappeared. This is disappointing, but very interesting nonetheless. From the satellite images taken during this period, one can see that shelf temperatures have increased with all activity restricted to the southern end of the Wild Coast, where one can see nice cool temperatures. It seems very likely that the passing Natal Pulse from earlier this month allowed a limited amount of sardine through, which resulted in some netting on the KZN South Coast, but the warming of temperatures seems to have retarted the impetus of the main shoals, which appear to the languishing on the southern Wild Coast.

Because of the lack of activity, and because we need stationary baitballs for us to deploy our tags, we have decided to take a hiatus from the sardine run, and do some serious FIFA World Cup fan mongering!!! We intend to return to the Wild Coast on the 4th July, unless the activity gets going earlier…

June 20th 2010

June 29, 2010

Happy father’s day, and although there was not one father to be found on our boat, we had a very happy day indeed. Unfortunately, it was not happy scientists’ day, as it was very, very quiet on the sardine run front. The happiness came instead from the perfect Wild Coast weather, the clear water, the jumping humpack whales, charging common dolphin pods and flashy bonitos feasting upon our red-eye roundherring offerings.

Port St Johns sunrise. photo: Vic Peddemors

We launched today through a mighty Mzimvubu sunrise to quiet seas and even quieter skies. The million dollar question was which direction to travel: south to Brazen Head or north to Mbotyi. Neither direction looked particularly promising, although, travelling northwards we did find plenty of gannets, schools of dolphins and pockets of fish (mostly red-eye roundherring and mackerel). We also passed oil slicks on the water with the distinctive smell of sardine. But no feeding pockets of predators. Very strange indeed. All the ingredients for some serious predatory feeding are there, but nothing is happening. Instead we filled our day with tracking a pod of about 300 dolphins 30 kilometers up the coast (and collecting some valuable data on their movements) and diving with some dusky sharks.

dusky shark, Carcharhinus obscurus. photo: Will Robbins

You can see, from the trackline posted below, that common dolphins swim up the coast in a zig-zag when foraging. What the trackline does not show, is how suddenly the whole pod changes direction to forage in the new direction, and how the shape of the pod changes. It was a very interesting exercise, indeed.

tracking common dolphin foraging

June 18th 2010

June 18, 2010

apologies for not being up to date. Still battling with the internet connection here (PSJ hippie-villie left behind the technology curtain).

will try to do our stuff today, on the blog tomorrow.

Not much action for us today – cool water was found at Mbotyi with all the activity that we managed to find.

more tomorrow

June 17th 2010

June 18, 2010

battling with the slow internet here. please check out my pdf…

June 17th 2010

June 16th 2010

June 16, 2010

June 16th 2010

Due to the terribly slow internet here in PSJ, I’ m attaching today’s blog as a pdf. HOpefully it is quicker like this. grrrrrrr.

During early June we had the first reports of sardine run activity off Port St Johns. Rod Haestier, our skipper for the 2010 sardine run, was dillegently stocking up the larder for our trip and was kind enough to phone me and let me know of the activity. The baitfish were mostly east coast roundherring (“red-eye”) and mackerel, but there was some sardine mixed in with them. There was plenty of predator activity with the usual birds diving and dolphins gorging themseves. What was particularly encouraging was the presence of many sharks at the surface. The activitywas so promising that the KZN Sharks Board lifted their shark nets and drumlines along the lower KZN South Coast. Over the past week, the activity seemed to be slipping south, to the Brazen Head area, just south of Port St Johns, but yesterday there were fresh reports of sardine off Waterfall Bluff. So, 2010 sardine run has started. Historically speaking, this year’s run is almost a month early. We head down on Friday, and we’re champing at the bit!!!

Why has the run started early this year? Let us look at satellite images (obtained from the Marine Remote Sensing Unit (MRSU) at http://www.afro-sea.org.za/) from the 6th June (Fig. 1):

Fig. 1. Sea surface temperature conditions along the South African east coast on the 6th June 2010
In Fig. 1, the star indicates Waterfall Bluff. You can see that a thin strip of cool water ( < 21 C) reaches up to Waterfall Bluff, indicating temperatures suitable for sardines to occur.  What is particularly interesting about this image, is the large meander in the Agulhas Current to the south of Waterfall Bluff (indicated by the black box). This meander appears to be a phenomenon called a “Natal Pulse”. Usually the Agulhas Current flows more or less parallel with the coastline between Durban and East London. This can be seen in the orange strip of warm water in Fig. 1. On a handful of occasions during the year, a large meander, called a Natal Pulse, forms off Durban and travels southwards at about 20 km per day. Interestingly, these meanders circumscribe cool, upwelled water (also visible in Fig. 1). Over the past 2 weeks, or so, I’ve been following the southward progress of the meander, visible in Fig. 1. The presence of the meander has coincided with the early arrival of the sardine run, and may well be partly responsible for the cool conditions and activity we’re seeing now. But wait, that’s not all… scroll down now and you will see a free image of chlorophyll a concentration (Fig. 2), also from the MRSU:

Fig. 2. South African east coast chlorophyll a concentration, 6th June 2010

When one compares Figures 1 and 2, one can see that the meander is associated with both cooler conditions and elevated chlorophyll a (chl a) conditions. Chl a is the green pigment found in all photosynthesising plants, and in single celled algae in oceans (see Figure 2). “Flowing” northwards from the base of the meander are elevated chl a concentrations, suggesting good feeding conditions for zooplankton, upon which sardine largely feed, besides feeding on algae themselves. Clearly visible in both images are strong thermal and chl a fronts, conditions which sardine are known to prefer. It is intriguing that the early occurrence of the 2010 sardine run may be explained using satellite imagery, and the case for using these tools to predict sardine presence continues to be built following our efforts from last year. More to follow…

Sardine Run thesis

May 1, 2010

I recently graduated here at UKZN with my doctoral degree. You can download my sardine run thesis by clicking the link below.

O’Donoghue_PhDthesis (9Mb)

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!

Well what do you know, those little slithery suckers have finally arrived in Durbs. Nice to see cool water stretching all the way up the east coast to KZN!!!!!

BIG REQUEST FROM DENNIS KING: DOES ANYBODY HAVE A PHOTO OF A COPPER SHARK (BRONZE WHALER) FOR HIS MULTI-MEDIA FISH GUIDE????
PLEEEEAAAASSSSEEEE???

I’ll be out on the Natal Bight measuring things, so won’t be on the blog for some time now. The good news is that the thesis is at the printers. toot toot!!

over for the year

July 13, 2009

So the rsmarinesa website is still offline, and I haven’t downloaded the satellite images for this year’s run. When I do, I will do a synoposis of the run, but that is low on the list of priorities. Although everybody is packing up for the year, the run continues in Port St Johns. Now would be the time to get a little team together and charter a boat down there. You will get activity for the new few weeks, and there’ll be nobody else there.

prey species on the run

prey species on the run

We would like to thank Craig and his staff from Scuba Addicts who kindly provided us with air refills during the sardine run, and would like to thank all other boat operators who participated in the sharing of information about the location of sardine run activity, and for their courtesy in observing etiquette around baitballs. Their behaviour ensured that this year’s run remained an enjoyable experience with no bun fights around baitballs. thanks everybody!!!

film crew gets ready

film crew gets ready

For me, it’s back to the grindstone. Our field trip was a great success thanks to that last fantastic day. Now comes the grind: capturing and analysing all that data (but it is an interesting grind, make no mistake!).
I’ll be blogging again next year, when we’ll be putting critter cam and all sorts of groovy motion sensors on bronze whaler sharks to get a handle on how they feed. It should be an awful lot of fun, as well as serious science, so please join us again during early June 2010.
all the best
Sean