July 2010 Shark Bytes
Posted on Saturday, 31 July 2010
Dear Shark Lovers,
The more time I spend with the shark the more I realise how difficult it is to understand these magnificent creatures!
We have had a great month at Seal Island but it has just been a little different from previous seasons.
We normally observe and record our most intense predator/prey interactions from the start of July to about mid August but this month has been different. We have noticed that the numbers of predatory events are down by at least 60% which is obviously a significant decrease.
One of the glaringly obvious reasons is that there have been little to none of the young of the year seals returning from the feeding grounds to Seal Island in the early hours of dawn. This means that there has been very little opportunity for the sharks to attempt to hunt. Remembering that the young of the year seal is the first choice for the sharks 85% of the time this has probably caused a problem.
That said this year has seen up to 11 boats at Seal Island looking for predations on some weekends that no doubt limit the sharks ability to detect incoming and outgoing seals. The boats also often block the seals as they are not experienced in working in the area. There has also once again been a large amount of decoy towing at Seal Island and on the mornings where the decoys are being towed before sunrise we have seen a noticeable decrease in predation. It is for this reason that we try to avoid towing decoys during active feeding periods.
The sharks are still going after the large groups of seals that depart the Island but the success rate has been minimal and only every few days are we seeing even one successful feeding event. Historically we have noted that the sharks are far less successful on these large groups, probably because there is no single target the shark can lock on and also because there are many eyes watching out for an approaching Great white shark.
An interesting study was recently published showing that a seal was able to detect the vortices of their prey (fish) with their whiskers which greatly enhanced their ability to hunt. We have documented countless times seals springing out of the water before the shark comes hurtling through the group and for nearly five years now Chris has hypothesized that the seals are detecting the approaching bow wave of pressure ahead of the shark as a early warning of an impending attack. In Ultimate Air Jaws this was actually what he was trying to see but the action happens so fast it is invisible to the naked eye. So, these observations has made us think that the seals can most likely detect the pressure wave of water as the Great white propels itself into the middle of a group. This split second warning may make a huge difference between life and death.
Many of the attempted predatory events this July have just been a rush from below and we have not even seen the shark…but we know from the boil on the surface and the behaviour of the seals that a shark has been on the prowl.
Despite the low number of events we did have our best photographic opportunity this season. Chris had spotted a shark breach fairly far from the Island. En route to check it out a shark breached on a seal about 80 meters in front of us. As such we were onto the event for the second follow up from the shark. The shark breached completely out of the water with its mouth wide open but missing the lucky seal by a mile. Chris was fortunate to capture this spectacular event on camera.
It will be very interesting to see what happens in the next couple weeks. I would think that the predation activity has to kick off sometime…but who knows!
We have been mindful about towing the decoy this month. With the lack of single seals moving around the Island we had to be pretty careful that the sharks did not waste too much energy with no reward by jumping on the decoy. Even so we were still getting hits after only towing for limited periods.
Most of Cape Town has been wondering where winter is this year. There have been so many beautiful days devoid of the usual wind and rain. This has meant many calm days on anchor at Seal Island, perfect for watching Great white sharks gently cruise around the boat.
Despite the lack of predatory events we have had good numbers of sharks around the boat, averaging 8 sharks per trip and a lot of days with 10 plus sharks. The good weather has meant that the viewing from the surface has been fantastic. The notorious Cruella has visited us a number of times with her heart-stopping lunges for the bait and/or decoy.
One thing we have noticed is that there has not been a high turn around of different individual sharks, and the same ones have spent most of the month with us. Of course this could have a lot to do with the lack of feeding.
One of the sharks hanging around was a particularly pleasant 3.4 meter shark we have called Nikita. She loves the cage and almost always just circles the cage and then occasionally has a look at the decoy or boat. All the guests love her as she is such a great shark to dive with.
For the whole month we thought she was a female but then 2 days ago she inverted and we got a real good look under her pelvic fins...turns out she is a male! So much for being shark experts!
We have had fantastic guests this month. The tail end of the World Cup Football meant a lot more Spanish fans on the boat that we had a lot of fun with. We have also many of our Seal Island “locals” who return each year, so it is great to have old friends spending some sharky moments with us again as well as all the new friends we have made.
Killer Whales & Other Cetaceans
After our great sightings this year of Killer whales we are constantly on the look out for them in False Bay. Towards the end of the month we came across a school of about 250 common dolphins en route to Seal Island. After about 10 minutes with them their relaxed manner changed completely out of the blue as they turned into a writhing mass of petrified dolphins.
Of course having observed this behaviour before we knew it meant that their nemesis was around….Unfortunately we could not spend too much time with them as we needed to get to Seal Island for our Afternoon trip. When we got back to Simonstown later that afternoon we heard that the Killer whales were sighted again in Fish Hoek bay, about 5 miles from where we saw the dolphins. So, we are back on super high killer whale alert.
We have come across a high number of Brydes whales in False Bay and also the first few sightings of the Southern Right Whales that return each year. We always spend time spotting for various whales on dolphins en route to the Island so it is great to have success and our guests really enjoyed the encounters.