(From the Marine Dynamics Newsletter, September 2009)

September 2009 has certainly been the month of transition for our Great White Sharks in Gansbaai. It is difficult to know where to start with this month as so much has been happening! First of all, the sharks finally decided to move inshore to Joubertsdam - our summer shallows area. However, we did finish off our fantastic Dyer island winter season on a high. For almost a week the most stunning visibility allowed us some fantastic sightings of sharks around the island. Anchored in 15m of water, just in the lee of the island and adjacent to the channel mouth the visibility was so crystal clear we could make every individual rock, piece of reef and kelp forest on the sea floor! Even though shark numbers were fewer, seeing the great white shark in such immaculate crystal clear visibility is ultimately the most beautiful experience- and also quite a rarity in the Western Cape!

On the 6th of September we ran our first trip to the shallows after sitting the morning by the island and waiting a long time between sharks. As we motored over to Joubertsdam to lay anchor bright milky green water gleamed beneath us. With not even a five minute wait we got our first large black dorsal fin appear at the boat and they just kept on coming! All the sharks that followed were large females and between 3-4m long - plus they were extremely active. They investigated both the bait line and the decoy with avid interest. Our first trip we had 15 sharks in the shallows and are still sighting lots of sharks on trips there into October.

Familiar fins

Certainly a couple of dorsal fins have been familiar in September - particularly a large female with a white pigmentation patch or ‘rosie’ at the leading edge of the dorsal. This animal we think we had in September 2007 and named her Marilyn (because of the large beauty spot). Another distinctive shark in the area at the moment is called ‘Ike’ and has a large cluster of copepods by its tail. This shark is really active and mischievous - apparently it mouthed the camera of an underwater videographer working on another shark boat and swallowed the wide angle lens (oops!). We noticed after seeing the shark a couple of times her parasites seem to have either changed colour or fallen off as the patch has gone from a yellow colour to grey. This could also be the shedding of their eggs- as often these crustaceans have long trails behind them that look like tails but are actually egg cases. Hennie Otto the MD skipper is currently sampling copepods form other lamnid sharks in the area and working together with local fishermen and an expert from MCM to find out more about these creatures attaching to white sharks and other shark species in the area. There is always a possibility that the species of copepod on a shark can determine the body of water it has travelled through - another way of potentially tracking their movements?

Conditions and sizing

Strong South Easterly winds blew for the largest part of September. In Gansbaai this usually means upwelling and colder water with sometimes choppy conditions. At this time of year we see mainly females with very few males ever sighted at the inshore sight. Water temperature is usually slightly warmer closer inshore within bay systems. However during summer in Gansbaai the average is generally 12-13ºC. There are studies in Australia that confirm a documented spatial segregation between male and female great whites with only male sharks found at offshore islands predominantly where water temp is cooler. The females inshore are believed to prefer this locality possibly because they may be nurturing their young internally and the warmer temps aid in their development and growth rate. This is an interesting concept- and there is a lot of debate about our females sizes being mature or not. The common belief is that the females in Gansbaai are subadults. The largest white sharks in SA are found in False bay (predominantly large females 3.5m average). Judgement of size when the shark is in the water is usually just a comparison with a fixed reference such as the length of a boat or cage. Being too conservative about sizing sharks can quite easily happen.

Whales

We finally have plenty of Southern Right whales in the bay with lots of mother and calf pairs being sighted by our whale whisperer. The white calf (see last months newsletter) has been seen on numerous occasions well in to the month of October too. Occasionally both the mother and the white calf have been seen breaching together which must be such a spectacular sight! On the 24th to the 27th the Hermanus whale festival took place. Special thanks to Linda Chivell and her team from the Adventure Center and Fasttrax media who organised a big expo tent right in the middle of the festival with numerous guest speakers and conservationists invited to do talks to the public. Despite the odd bought of rain on the Saturday afternoon and the loud Mr motivator dance (positioned right next to the expo tent!) the event was a huge success and all who attended will agree Linda did a stunning job the whole set up looked excellent! Carting a life sized southern right whale model form Gansbaai to Hermanus is also not the easiest of things to do but was certainly worth the effort after the amount of attention it got and how astounded a lot of Jo public were to see what a whale actually look like when up close! Sanchia Chivell painted the life sized whale so beautifully its callosities even looked real and people had to touch just to see for sure! Well done to all and we very much look forward to next years event.

Dolphins

At the end of September Chris and Monique Fallows - two very well known shark operators and conservationists from False bay - emailed through some photographs they had of a pod of humpback dolphins nearby the harbour there. Some suspiciously familiar looking dorsal id’s were sent to myself and then forwarded on to Wilfred Chivell the Dyer island conservation trust manager and on to our PHD student from France Isabelle Dupre who is studying the humpback dolphins of Gansbaai. In the last months newsletter we mentioned how Isabelle had been and gone in August without seeing one of her dolphins in the area . Isabelle confirmed with much excitement that YES- these were the same humpbacks from Gansbaai and all of the animals were named and recognised individually! We would like to extend our warmest thanks to Chris and Monique who enabled the DICT and Isabelle to solve the missing link and identify the dolphins over there! Working together in the marine field can only benefit the future of the incredible marine animals found along the SA coastline and the more we liase between different fields and areas the better we can understand their movements.

Seabirds

We were very priviliged to have Lourien du Plessis from UCT join us on the shark boat at the end of September. Lourien is doing some fantastic work with seabirds. She has completed her PHD on the effects of fishing grounds and MPA’s in the west coast on gannets, penguins and other bird sp off St Croix and Bird island in PE. Interestingly her research showed that just by closing off a fishing area around bird island significantly decreased the distance the penguins would have to travel to feed. Lorien lectures at the university and is now starting a project on cormorants where she will be using Dyer island as one of her sample locations. It was really nice to have her on board and hear information and expertise on the birds. Her work also indicates how effective MPA’s can be if deployed in the right circumstances and maintained properly. The Penguins of Dyer Island were tracked with GPS loggers last year swimming as far as 50km in a day to access fish based food.