The might Mzimvubu Estuary
It’s now Sunday evening and it’s back to the blog for me. Yesterday the blog was given a miss as it was rugby time, followed by beer drinking time, followed by a trip to the local “night-spot”, which turned out to be really, really pleasant: the local marimba band (a wooden xylophone) was practicing, and they were truly awesome. Some old timer came in to the pub with a baby samango monkey on his shoulder. These monkeys look very similar to their cousins, the vervet monkeys (who recently starred on their own satellite television series), but samangos are much less common. I’m not going to enter into a debate on the virtues (or lack thereof) of keeping a wild orphaned animal as a pet and letting it drink coke out of a bottle at a bar, but I will say that Port St Johns is one of those places where this kind of thing is not out of the ordinary.
on the run from dawn
So today we did our usual early morning launch and found that a lot of the activity was close inshore, that is, less than 3 km from shore. We did, however, also find our usual activity out on the 80 – 100 m depth line, about 6.5 km from shore. Once again it looked like little bait balls, and not wanting to scare off any predators, I hopped in alone and filmed a ball for over 30 minutes. The viz was not fantastic, so I won’t upload any of it to show. One interesting event, however, was the arrival of a little school of what looked to be bonito with an entourage of 4 decent-sized bronze whalers (by decent, I mean bigger than me). It was interesting to see them circle the ball once, and then to see the fish swim off into the gloom. The sharks, unfortunately, then chose me to circle around, but lost interest after the third or fourth roundabout, and also departed. The bait ball was being worked by the common dolphins – there was one easily identifiable large individual whose mouth (or beak) did not close properly. He spent a lot of time swimming around the bait ball, often pushing it in a direction. Intermittently, between 4 and 8 common dolphins would rush the ball and feed. When this happened, the few gannets that were in attendance generally also attacked the ball.
After the dive we followed some activity further out, in water deeper than 200 m, hoping to get in on clean water. There was a lot of activity with plenty of diving and another Bryde’s whale. Things were looking very positive, but the problem was that the activity was moving really rapidly, with diving starting up in one place, continuing for about 10 – 15 dives, and then moving off to another place. This would have been the dolphins moving around and feeding in different locations. The birds are very dependent upon the dolphins when feeding. It was interesting that the fish were not balling. We could see that the dolphins were feeding by the amount of scales in the water. Eventually some of the fish were forced to the surface, and we could see that they were very small. There was also no tell-tale smell of sardine, so we suspect that the dolphin were feeding on anchovy, which are generally smaller than sardine. They were also more than 2 km further from shore than our previous sardine shoals, and this agrees with data collected during the 2005 hydroaccoustic cruise, which found that anchovies are usually found further from shore than sardines.
Gannets waiting for common dolphins to start feeding again
Throughout the afternoon we watched wave after wave of feeding common dolphin pods moving northwards. Typically, the feeding would start up, and all birds in the sky would hone in on the action. Within 5 minutes, there was usually over 200 birds diving noisily of the dolphins, and then within a further 5 minutes, they would all be sitting on the water and the brief feeding session would be over. However as soon as the next session started, they would take off and go through the routine again. They did this all afternoon, which is unusual; because once gannets have been feeding successfully they sit on the sea surface for at least 2 hours to digest their prey. We suspect that either a) they were not feeding successfully or b) their food was not as nutritious as sardine or c) both of the above. It’s probably c) both of the above, and their prey was probably anchovy.
juvenile gannet with adults
Incidentally, we’ve seen plenty of juvenile gannets. Previously, during predator surveys of the sardine run, juvenile gannets comprised between 3 and 6 % of the total number of gannets sighted. This year, there seems to have been more than that. Hopefully it’s a sign that juvenile mortality over the past breeding season has been lower than the usual very high percentage. Juvenile gannets have dark plumage as they have not yet attained the brilliantly contrasting black and white plumage of the adults. When they are moulting into their adult plumage, their heads change to white first, and they look quite funny with a brown body and white head.
So what has happened to the sardine run? Well, this morning, all the boats that are based at Mbotyi headed south to Port St Johns. I therefore suspect that there is very little activity north of Waterfall Bluff, and that is bad news for the sardine run in KZN. It’s looking bleak, but don’t give up yet. On our way in to shore, in water depths from 115 to 60 m, we passed over a lot of sardine, but it was all on the bottom. There is too much warm water above, and they’re sitting down below in the cool water where they are safe(ish). We need the dolphins to bring them up to the surface in a baitball if we want any action now, alternatively, we need cool upwelled water to entice them up. Keep watching the satellite images, and be reassured, the sardine are still around, southwards of Waterfall Bluff at least!
