Expedition South Seas

JBL Expedition South Seas I and II

JBL Expedition South Seas I and II

Snorkelling in shallow water amongst sharks

Not all of the participants had already had encounters with sharks and so some felt uneasy when reef sharks were present while snorkelling. But in the evening we organised a specialist lecture on interactions with these elegant predators. Expedition leader and marine biologist Heiko Blessin informed the participants (and the crew) about the behaviour of sharks and their body language. Afterwards, the participants were much more relaxed when they encountered the hunters in just 40 cm of shallow water.

Both the divers and the snorkellers were enthusiastic about snorkelling in shallow water (up to 8 m deep). Many fish species, such as the blue-lined and spotted surgeonfish (Acanthurus lineatus & A. guttatus) can only be found down to a depth of 3 m.

Scuba divers will never be able to observe these fish species. The intra-species territorial behaviour of these surgeonfish species is very interesting and quickly makes it clear why the blue-lined surgeonfish can only be kept in aquariums of 2-3 m or more. Their life seems to consist exclusively of plucking algae and fighting.

Convict surgeonfish (Acanthurus triostegus) usually move in small groups through the shallow water areas (up to 8 m) of the fringing reefs. But they also occur in really large shoals of 120 animals (photo taking, print out and counting the fish).

Further interesting observations were made directly in the area where the waves break. There, the fore and back currents are extreme. A snorkeller can no longer hold on there. Only when there are V-shaped cuts in the fringing reefs is it reasonably safe for a snorkeller to stay between the breaking waves.

In these shallow water areas, it also becomes clear why sharks are so important in the reef ecosystem. They patrol the reef, even at a depth of 30 cm, where their bellies scrape over the coral. Careless, injured, sick or deformed fish are preyed upon. Healthy fish take cover between the corals in time. If humans continue to kill 100 million sharks a year for their fins for soup, the coral reef system will be under massive threat. Top predators have one of the most important functions in ecosystems!

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