Posted on Sunday, 31 July 2005
Dear Shark Lovers
All I can say is WOW, what a month we have had. In June I spoke about how many sharks we were seeing around the boat and how few predatory events we had seen. The whole month we were expecting the sharks to start feeding on seals and it didn’t really happen. Well. It certainly happened in July. I have just been going through our field notes, and although I knew there was an extraordinary amount of activity I was overwhelmed to find that we recorded 471 separate predatory events, meaning an event where a shark was either successful or unsuccessful in catching a seal. The sharks were successful just under 50% of the time, which is in line with what we usually observe. Chris reckons that over a 14 day period we had in July is the most intense predatory activity that he has witnessed in the 10 years that he has observed sharks at Seal Island.
Over this time we saw 42 different events in one morning and had numerous days of 30 plus events. Sometimes there would be three and even sometimes 4 different events going on at the same time. We found it difficult to chose which one’s to go over to as just as one person would see one someone else would shout about a new event!
Although this is the highest amount of activity that we have ever recorded there are probably a few factors that contribute to this. These are that due to good weather we were able to be at the Island 26 out of 31 days and also perhaps we are getting better at spotting these events.
The most intense behaviour was taking place just before sunrise and the sharks were also more successful in these lower light levels. There was also definitely more seal movement before sunrise so coupled with the fact that these seals probably find it more difficult to pick up an approaching shark conditions were favourable for the sharks.
For 3 weeks we facilitated a BBC film crew. The crew had brought out a “home made” camera that could shoot 1000 frames per second and their number one aim was to film a predation sequence using this camera. It was extremely challenging as the camera could film for a maximum of 2,5 seconds before the footage needed to be downloaded onto a hard drive. This took about 15 minutes to download and as you can imagine it was very frustrating to not be able to film events during this time!
This 6-minute sequence will be part of a follow-up series to The Blue Planet. It will start airing at the end of 2005 as well as 2006, so this will definitely be something to look out for. You can imagine the detail that can be shown of a predation event filmed at 1000 frames per second!
As mentioned we had periods of very good weather and this always helps in picking up interesting details. Mostly it helps in being able to identify sharks at predatory events. These events happen exceptionally quickly, most times in less than 30 seconds. There is tremendous competition between sharks and we think that the seal carcass is consumed with no time wasted in case the carcass is lost to another shark. As you might well know larger sharks are dominant over smaller sharks. We had one instance where we watched a certain shark make a successful kill and about 1 minute later a larger shark with about the top third of its tail fin missing, pop up on the surface with the carcass, which it proceeded to consume. It was very easy to see that this was a different shark due to the injury of its tail fin, but most times we would probably miss this bit of information just because it is so difficult to identify the shark in this lightening fast event.
Guests very often ask us how often the sharks are feeding on seals, and it has always been a difficult question to answer. The most we have previously seen was Cuz who made 3 successful kills in 5 days. Again he is very easy to identify as he has a distinguishing dorsal fin. The day after we saw the shark with the injured tail fin steal the seal carcass we saw it attempt to catch a seal. We were fairly surprised that the shark was trying to hunt so soon after feeding. Not long after this we observed a large shark of about 3,7 meters (just under 13 foot) make a successful kill. She had a very easily identifiable feature in that her upper caudal lobe was badly lacerated. 11 minutes later and 900 meters (1/2 a mile) from where she made the first kill she made a second kill. It was undoubtedly the same shark and we were unbelievably excited to have had observed this. These sharks never fail to surprise me!
After this period of good weather we had a number of cold fronts roll through Cape Town. Most times this induces high predatory activity. This is most probably because there is more seal movement as many seals choose to return to the protection of Seal Island. We had the BBC with us during these cold fronts and although the sea was very rough they were keen to be out there.
On the first two days we saw intense predation. On day 3 and 4 it was impossible to get out as the sea was just too bad. But on day 5 it was barely manageable so we bounced our way to the Island only to get there and see absolutely nothing! The next 5 days after this were also very quiet, so maybe the sharks had had their fill. The last four days of July has again been incredibly busy with predatory activity and we have seen some awesome sights.
I am afraid that I cannot tell you all too much about which sharks we have been seeing around the boat simply because they have not been in the least bit interested in coming up to our boat. With all the hunting they are doing we imagine that they are just slowing down and conserving energy during the day. When some sharks have been at the boat they have been mostly “Drive-by’s”, basically one look at the tuna and they are off!
In other news we got some exciting feed back from a diamond ray that we tagged in December last year. 176 days later the ray was recaptured. It had travelled 1 577 kilometres (2 838 miles) up the South African east coast. It had also grown 100mm in this time. The best news is that it was re-released by the angler that had caught it so hopefully we’ll reencounter it in Cape Town one day.
We have uploaded some very good predation images on Photo’s of the Month as well as some very good breach images. So you may want check them out.
Otherwise I look forward to sharing more shark news with you all in August.