Kelp forests and Seven gill sharks
Kelp forests and Seven gill sharks
Hidden and little talked about is a cove next to Miller’s Point off the west side of the False Bay in the Western Cape. The little dive nook lies between Pyramid Rock (34” 14,24’S; 18”28,72’E) and the shore. What makes this dive interesting is the diversity of life created by the interaction of kelp forests, rocks, sandy bottoms and the sea. By Richard Lomax.
Animals and plants you will encounter in this area are from the most simple to the most complex, and from modern to ancient species. It is a little museum-zoo in the ocean.
Winter is the best time to dive this spot when it is a warm (15°C) and there is good visibility. Plan to do the dive at a high tide. You can gain entry from the shore but a boat entry is easier. Drop off into a patch between the kelp close to the shore and sink slowly to the bottom, about 10m down. Take a bearing on Pyramid Point before descending – this is where you are heading. Wrap up warmly because you are going to be down there until your air runs low.
Once you have oriented yourself at the bottom, swim slowly through the kelp forests (Ecklonia maxima) and around the boulders towards Pyramid Rock. The warm winter sun filters through the water creating an eerily beautiful forest scene of straight stems with a gently waving overhead canopy. The sea bamboo stretches up, reaching to capture the light needed to make its food, and oscillates gently in the slight swell. Its tenacious roots anchor it to the bottom and its air filled body makes it float. It is tough and elastic to cope with the tidal action and the roughness of the sea. Unlike pine forests, this forest is full of life – don’t panic if a Seven gill shark (Notorynchus cepedianus) comes for a visit.
They share this cove with other critters and seem happy with divers swimming in their territory. A very different attitude to what humans’ would have if this was a ‘human’ ocean pool!
The Broad-nose seven gill is found around the world. For the most part, it appears to inhabit colder water, whilst its cousin, the Sharp-nose seven gill (H. perlo) occupies warmer water. It is unclear why the Seven gills like this little cove. It might be a resident community or transient individuals attracted to unknown characteristics of the area. Adult sharks of this species normally occupy much deeper water and have been found at depths of more than 500m, whilst juveniles occupy the shallows. The size of the Seven gills encountered (up to 2m) suggests that the occupants of this cove are adults.
Sharks take a long time to reach sexual maturity and it is primarily for this reason that shark numbers have been decimated – not enough sharks grow old enough to reproduce. For most sharks we have little or no idea how old they need to be before they are able to produce offspring. It appears that the male Seven gill reaches this age at approximately five years whilst the female may only become sexually mature after 11 years! The Seven gill is on the UN Red List.
I am not sure why this shark is so curious, but it will swim right up to you and bring its friends and relatives to look you up and down. Raggies (Carcharius taurus) and Great whites (Carcharodon caracharius) have also been seen in this cove whilst seals (Arctocephalus pusillius pusillius) are also common. As you meander your way through the kelp on the way to Pyramid Rock, also look out for the Six gill hag fish (Eptatretus hexatrema).
This species is much prettier swimming along than photographs make it out to be. Like the Seven gill, it is an ancient primitive. Encounters with these two species take one back along the evolutionary road to what the original sharks and eels looked like way back in time.
The Cuttlefish (Sepia vermiculata) is also common. It has the most amazing ability of being able to change its colouration to that of its surroundings. If you don’t follow it carefully it will disappear before your eyes. When it comes to colour change and camouflage, chameleons are beginners compared to this fellow.
Reflect for a moment on how diverse the animal sea kingdom is. The Cuttlefish belongs to the same family (Phylum) as a mussel. How would you feel if your second cousin lived in a shell stuck to a rock? But not all animals in this cove are big and scary, or even swim. Some look just like a plant. Apart from the Redfingers, the fish (Cheilodactylus fasciatus), this photograph shows three other animals. The beautiful Gorgonian twig coral (Homophyton verrucosum), Elegant featherstars (Tropiometra carinata) and purple and white Sea urchins (Echinoidea).
Look out for other animals along the way, such as the beautiful Strawberry anemones (Corynactis annulata). Ask yourself what the purpose of the red ring is? And why is the colour such a delicate blue on the outer edge, deepening to a purple on the inside?
There are reasons why this animal was designed this way, we just don’t know why. Pyramid Rock is a little zoo on its own. Sponges, starfish and hard and soft corals are abundabnt. Enjoy and watch the air before you run out!
When back on shore, reflect on the diversity of life that you have seen. The diversity is required so that the animal/plant can fill the niches created by the geology of the area and actions of the sea. But that is not where it ends. There is dependence between the species occupying the various niches that extends right up the evolutionary ladder to us humans. In further articles I would like to explore this dependence.
* Two Oceans, GM Branch, CL Griffiths, ML Branch, LE Buckley, Struik, 2007.
* A Field Guide to Marine Animals of the Cape Peninsula, Georgina Jones, SURG, 2008.
* Growth, age estimation and feeding of captive Sevengill Sharks, Notorynchus cepedianus, at the Monterey Bay Aquarium, G Van Dykhuizen and HF Mollet, Australian Journal of Marine and Freshwater Research 43(1) 297 - 318 doi:10.1071/MF9920297.
* Florida Museum of Natural History Ichthyology Department: Seven-gill Shark, Cathleen Bester.
* Sharp-nose seven-gill shark - Wikipedia, the free encyclopaedia.
Photographs by Bruce, Sabine and Timothy (Bubble Blowers members).
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