Using Shark Scales to Unlock the Secrets of Historical Shark Communities on Coral Reefs

Post provided by Erin Dillon

Close your eyes for a second and imagine a coral reef. What do you think the shark community on that reef looked like historically?

Grey reef sharks on Palmyra Atoll’s forereef. ©Darcy Bradley.

Perhaps you imagined a remote reef with high shark abundance like Fakarava, French Polynesia or Palmyra Atoll, Northern Line Islands. Maybe you thought of a marine protected area such as Jardines de la Reina National Park in Cuba. Or perhaps you relied on your own memories from snorkeling on reefs in the past or photos of reefs taken decades ago.

The answer to this question depends on a reef’s location, given that shark abundances can vary with primary productivity and other oceanographic features. It also depends on which time period you chose as your reference point. Shark abundances can fluctuate over the course of a few hours – as well as over days to years to decades and beyond. Even if you chose the same time and place as the person before you, you might have come up with a slightly different answer. This variation in how we determine baselines – overlaid on a backdrop of natural variation in shark communities over space and time – can contribute to differing perceptions about what’s natural or what a depleted population can possibly be restored to.

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