Where did the Gansbaai sharks go?

Great White Shark blue half breachGansbaai is one of three great white shark cage diving hotspots in the world and the only location with all year round shark activity. That was until January 2016. For the first time in the shark cage diving history of Gansbaai the white sharks mysteriously disappeared.

For over a week the eight shark cage diving operators launched extensive search attempts in different parts of the bay but all without success. Neither marine biologists or fisherman could explain the unusual phenomena.

alison_towner (1)Alison Towner, a local marine biologist, has been working with sharks in the Gansbaai area for a number of years and her explanation for the mystery therefore seem the most plausible.

Seasonality: December, January and February are generally quieter months in terms of white shark numbers in Gansbaai.

Migration: Satellite tracking show that the majority of white sharks sighted in Gansbaai migrate along the east coast in summer, as far as Mozambique

Environmental conditions: We are currently in the middle of a major ‘El Nino’ event, with abnormal climate conditions. As a result, ocean temperatures are warmer along many coasts. This may alter the species on which white sharks prey and thus they will follow them into other areas.

shark_eating_a_whalesDeceased whales: If a whale carcass washes up or is nearby the area the white sharks may well be attracted to it from miles away. There have been various deceased whale carcasses recorded in the Western Cape lately, including a rare sperm whale and three humpback whales in Cape Town.

Trauma might trigger a flight response: When a white shark is killed, often other sharks in the area will pick up the bio chemical signal from the rotting carcass which usually sinks, and cause the sharks to leave the area. An observation was made that a white shark was hit in Gansbaai by a Trans Agulhas racing boat this December, while the animal was basking at the surface.

Bottomline: White sharks are highly migratory apex predators. They do not live for extensive time periods in coastal areas. These regions provide seasonal rest and refuel pit stops for them. They are certainly not resident animals conditioned into an area for us to dive with.

Original Article by: Alison Towner, Marine Biologist, Marine Dynamics Tours

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