Sharks, Sharks, Everywhere

Apr 20, 2016

There are literally tens of thousands of sharks that come down and spend the winter right off our beaches here in Southeast Florida. Add to that the fact that Florida beaches are very popular for tourists and locals. Those are the ingredients that have made Florida the world's leader in shark attacks. 

Blacktip sharks are a medium sized shark. They’re maybe just about six feet long at the most. They are primarily fish eaters, and they will come down, spend the winter down here (South Florida) where the temperature is preferred. And then they'll follow that preferred temperature up the coast in the spring. So they migrate farther north and spend the summers off the Carolinas before coming back here again the next year.

Carcharhinus melanopterus: blacktip reef sharks are grey or brown on the dorsal area and white on the ventral. The tips of each of its fins are black with a lighter band lying just below the black
Credit https://bioweb.uwlax.edu/bio203/f2013/berry_nich/adaptation.htm / Organismal Biology at University of Wisconsin - La Crosse

  I'd imagine as a researcher that you spend a lot of your time up close with underwater species. Why did you want to get this bird's eye view of blacktip sharks?

Well, for many years I would get inquiries from the local media saying that their news helicopters had seen large numbers of the sharks (from above). I told them all it is is a migration that happens every year. No big deal. But when I had the opportunity to do the flying myself and see the animals I said this is really ripe for exploration. And the best way to address this, to cover a large area of the coast, is to do it by airplane and get this bird's eye view. And that's really the best way to count the numbers of sharks and see how many there are and when they're here. And that's what we started back in 2011.

And besides getting the count, what else do you learn from that vantage point?

It's so interesting because we get not only how many sharks are here but also their spatial distribution. Do we see more around inlets or are they, you know, on the inside of the reef, or where are they located? And we also get an idea of the density.  Sometimes there are very tight patches with lots of sharks and then large stretches of coastline with no animals at all. So that top-down view really gives us this perspective that we don't get when we're down on the water.

Dr. Stephen M. Kajiura, Florida Atlantic University
Credit FAU / https://www.youtube.com/watch?v=xCTsjqeV4lw
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Reading on your biography, your area of expertise is in the sensory biology of sharks and other species. But, what exactly does that mean and what is it you're trying to understand about sharks?

So my training is primarily in understanding how the animals perceive the world around them through their vision, their sense of smell, their electro-receptors -- things of that nature. And one of the big questions is, how were these animals able to make these long-distance migrations over largely unmapped terrain and still come back to the same spot. And here's where I think it's interesting because you can tie together their ability to use the earth's magnetic field, this magneto reception, to use that as a mechanism to help them home in. And that's sort of bringing together the migratory study as well as the sensory study. That's my actual background.

When it comes to shark attacks, they don't see us, right? It's something else that they're sensing about us.

Well, that's only partially true. So what's happening here in Southeast Florida, we are really fortunate to have such beautiful clear water. For the most part the sharks can come up to you and see -- Oh that's a person, that's not a fish, I'm not going to bite that. And they'll leave us alone. But in contrast, if you go farther north, New Smyrna or Daytona leads the state in the number of bites on people and most of those are blacktip sharks. The water up there is much more murky. So the shark may hear the splashing and thrashing and go to investigate, but they can't quite see -- is that a person or a fish? They sense the water's turbulence or take a bite, and it turns out, oh, that's a person's hand. Well, that's too bad, but by then  the damage has been done.

You know sharks are amazing species from the standpoint when you look at evolution. It's a creature that's existed for hundreds of millions of years and survived numerous extinction-level events. The current sharks are very similar to their ancestors dating back 60 million years. Why is this species so durable?

You know, I like to think of it that evolution got it right in the first place. If you have a design that's robust and able to respond to changing environments relatively well, then it's going to persist. If you're extremely specialized, you may be more prone to being wiped out by extinction. But if you've got this generalized body plan that can do so many different things I think you've basically got this buffer and this built in insulation which enables you to be successful,  and I think that's what we're seeing with the sharks.

How many different species (of sharks) exist off Florida waters, especially here in South Florida?

Of the more than 400 shark species worldwide, we have several of them right here and in South Florida -- 25, 30-plus. In addition to those, ones that you're likely to encounter, there are a large number of individuals that are found in deep water, sharks that we're never going to see and that you're specifically targeting. So there are probably well in the range of 50 different shark species in South Florida, which we'd only see regularly maybe half of those.

Just some of the sharks that can be seen off Florida's coast.
Credit Fish and Wildlife Conservation Commission / http://www.eregulations.com/florida/fishing/saltwater/sharks/

According to the University of Florida's international shark attack file, 2015 saw a record number of shark attacks worldwide, 98. Florida was again by far the leader. They predict the numbers are only going to grow because the population of humans grows and more people want to be in the water. Is there a way to make beaches safer for people and sharks?

I think one of the best ways to try and make everyone safer is through public education, informing the public that the sharks are there and what sort of conditions are most likely conducive to a person being bitten by a shark. So for example - dusk or dawn when you've got relatively poor lighting may be difficult for the shark to discern if that shiny flashy thing is a fish or is it the palm of someone's hand? So stay out of the water under those conditions. Informing the public about what the risks are when they have the greatest chance of being bitten, that's really the best way to keep the public safe.

There was a study on the over-fishing of sharks. It states that roughly 100 million sharks are killed annually and the big reason is the fishing for shark fins. What happens to sea life and the food chain if the shark population is destroyed?

The sharks really occupy the top of the food pyramid. So if you don't have those top-level predators, basically keeping in check, that next layer down in the food chain, what you'll see is that next layer can proliferate. And they will potentially have an impact on the layer under them and you have this cascading effect. By reducing the number of sharks you may actually end up throwing off the balance of the entire ecosystem. It's really important that this ecosystem has been stable for a very long time and humans have only started making a big impact in it in the last maybe, few decades. We are providing this enormous impact. And evolution is not just going to catch up. We're simply too strong an impact too quickly. I think that one of the biggest concerns is that by having these sharks reduced in population we could be seeing huge effects, which nature's simply not able to keep up with.

Do you remember your first ever encounter with a shark?

In fact I was scuba diving in Bonaire and I looked behind one of the other divers and I saw, like a truck go by, and I thought that's cool. I didn't think much of it. When I mentioned it to my friend, he said we never see those; that's amazing that your very first dive here and you saw the shark and we've never seen them. And so I thought that was fun. That was my first real encounter diving with a shark.

When I was in college I spent a lot of time on a surfboard and I remember my first encounter with a shark, and it was beautiful and frightening all at the same time. It was a small shark, maybe six feet. I was on a nine-foot surfboard so maybe I thought I had that advantage. As cool as that was, I think to myself I'm glad it wasn't a great white. Is that fear because of the fact that movies like 'Jaws' have kind of put that in our minds, or is that a justifiable fear because maybe the great white is just really ferocious?

You know, there are a couple of different ways of looking at this. One is certainly the media has portrayed these animals as very aggressive and they always show the big nasty teeth and things of that nature which, you know, plays into our basic fear of being eaten. And so to that extent, yes, the media's played a large role in the public perception of the animals. But at the same time recognize that humans have only started going into the water in the last hundred years or so. We are not an aquatic species and so we are always naturally apprehensive of being in that environment. It's not our native environment. The fear of being bitten is genuine. I think it harkens back to our fundamental evolutionary makeup.

I bring it up also because of the fact that I saw a story recently of someone spotting a great white shark four miles off the coast of South Florida. Is the great white shark the kind that swims around this area?

In fact, the great white is found right here in South Florida. We see them here in the wintertime. We have evidence from some studies where whites sharks tagged off New England have been detected right down here. And so we know they're making this migration down here and then going back up north again. It might even be that maybe they're maybe they're feeding on the blacktips when they're down here as well. I mean the backtips are prey for larger sharks.