Thursday, September 28, 2006

Great White Sharks are going inshore False Bay

Great white sharks appear to be following their expected spring season migration into the inshore areas of False Bay, and researchers have appealed to sea users to be extra-vigilant in the coming weeks.The sharks' general movement away from Seal Island and into shallow coastal areas has been confirmed by shark spotters and from data downloaded from acoustic tags fitted to sharks, reported the multi-member Shark Working Group.Shark spotters have started reporting regular sightings this past week: There were white sharks off Muizenberg, St James and Fish Hoek last Friday, on Sunday and again on Tuesday. There was a sighting at Fish Hoek; and another shark was seen at St James on Wednesday.

On Saturday, five of the 35 acoustic receivers that monitor great white shark movements in False Bay were retrieved from the sea floor as part of the collaborative False Bay White Shark Ecology Project, funded by Save Our Seas Foundation and the department of environmental affairs and tourism. Experienced divers recovered four monitors at Muizenberg and one at Partridge Point, near Simon's Town. These receivers detect the presence of a great white shark tagged with an acoustic transmitter and store information, such as which individual sharks were in the area, when they arrived and departed, and how long they stayed for.

Sixty-four great whites have been tagged with the transmitters so far, including 18 tagged earlier this year.Most of these sharks were tagged during the winter months off Seal Island. Shark Working Group spokesperson Gregg Oelofse said the information retrieved from the receivers recovered on Saturday confirmed the results from last year's research and provided valuable information of great white shark behaviour in False Bay.

"Throughout the winter period, great whites were occasionally recorded on the Muizenberg receivers, but because of the low number of detections recorded, it appears as if most of the records were from sharks swimming more than a kilometre offshore," said Oelofse."However, since the end of August and early September, not only have more tagged sharks - six so far - been recorded in the area, but they are also starting to spend longer periods of time here, closer to shore, ultimately leaving Seal Island completely for the summer period. "This corresponds to a decrease in observations and records from the Seal Island receivers."

Based on last year's information and the data retrieved on Saturday, it was expected that white shark inshore activity would increase in the coming weeks, said Oelofse."What is clear is that this seasonal change is not unique to False Bay or recent in its occurrence."Similar behaviour is recorded in Gansbaai, Mossel Bay and even in California (United States). "And anecdotal evidence from fisherman and military exercises suggests it has been occurring in False Bay since the early 1900s."

The information collected by the shark spotters is being correlated to the records from the acoustic receivers. The shark spotted at Baileys Cottage on Friday was most likely a 3,5m female great white tagged at Seal Island in June. "The time that the shark was sighted by the spotters - at 2pm - correlates exactly with a record recorded by the acoustic receiver," said Oelofse.More sea floor acoustic receivers will be retrieved at Cape Hangklip, Pringle Bay and Gordon's Bay on Thursday, if weather conditions are favourable.

Next month, a large-scale inshore tagging operation is planned when researchers will attempt to place transmitters on about 10 great whites that are already swimming near inshore areas like Muizenberg and Fish Hoek."Based on last year's data as well as this year's most recent data, the Shark Working Group would like to ask people using the coast for recreation to be extra-vigilant, particularly over the next few months when the highest occurrence of inshore white shark activity is expected," said Oelofse.

"People are encouraged to use areas where shark spotters are on duty and to take the time to speak to them on the day they visit the beach to find out about recent sightings and activity as well as the current conditions which determine the effectiveness for shark-spotting. "People are also requested to please take the time to read the shark-spotting signs to inform themselves of the four-flag warning system used, as well as be aware of the use of a siren to close the beach".


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