If you’ve ever felt a sense of calm at a Cape Town beach, knowing that there’s someone stationed up top ready to let you know if a shark pops past, then you have Shark Spotters to thank.

Through a combination of dedicated spotters and drones, they have put many minds at ease, but the organisation does far more than make swimming safer for all of us.

They have also, in conjunction with a team of researchers from the University of Cape Town and Rhodes University, spent nine years studying the white shark population at Seal Island.

That would be the Seal Island in False Bay, where you might be treated to the spectacular sight of a great white breaching in pursuit of a seal.

Alison Kock, a marine biologist who serves as an executive committee member for Shark Spotters, outlined some of what the research team found in a great piece on The Conversation.

Some of that below:

How big is South Africa’s white shark population? Nobody really knows: estimates range from 500 to more than 1200. This is an important question because the species is under enormous pressure. South Africa’s sharks come from two genetic lineages – one related to Australia and New Zealand, and one found only in waters around its coastline…

Apart from doing a “head count” of sharks, we noticed a fascinating trend. Seal Island is mostly used by juvenile and sub-adult sharks. But once the sharks – particularly females – reach maturity (around 33-years-old) they are rarely seen in the area again. This partly confirms what we already knew: Seal Island is an important habitat for one segment of the white shark population and needs to be conserved.

The mature white sharks, meanwhile, must be using other habitats to feed and reproduce. But we don’t know where those habitats are, and that’s a problem – without knowing what their chosen habitats are and what threats they might face in those areas, we can’t offer informed recommendations about conserving either the animals or their habitats. We can’t conserve what we don’t know.

During the course of the study, the team recorded 1 105 shark sightings, using photo ID to identify 303 unique individuals. Of those 303, most were never seen in the area again, which points to a population that is largely transient:

More on those female sharks in the area:

The most surprising finding was that after visiting Seal Island consecutively for between two and three years, female sharks approaching sexual maturity were rarely seen again. Overall few mature females and no pregnant females were recorded at Seal Island. This suggests that Seal Island is a seasonal feeding ground for young white sharks rather than a nursery area or adult gathering site.

Whilst Kock and her fellow researchers are somewhat in the dark about where these sharks go once they have left False Bay, they do know where they’ll start looking:

Satellite tracking has provided us with our first clue. The trackers suggest that the South West Indian Ocean islands and deep oceanic habitats off the continental shelf are areas where we can start looking. These are spaces ranging from a few hundred to a couple of thousand kilometres away from South Africa’s coast.

You might not be keen to get too up close and personal with one of nature’s apex predators, but there’s no denying that they play a vital role in the ocean’s ecosystem.

Just remember this – they feed on a variety of squids, fish, seals, and other shark species, and we really aren’t all that tasty.

A shout out to all those at Shark Spotters for the work that they do. You can find out more about their organisation here.

[source:conversation]