Sorry I’ve been a little quiet. I’ve been busy with work and admittedly had a little writers block but I thought it was about time to answer a question I was getting a lot before I came over here:
“I know you’re studying sharks… but what does that actually involve?
It’s a good question with a slightly long winded answer.
Why we do it?
A good starting point is understanding what we’re hoping to achieve. Essentially it’s a population census, yep that thing the Australian government botched a few years back, except its done more frequently and… well…. better.
We’re seeing how the population changes over time. We’re looking at things like the male to female ratio, how many individuals of different size-classes live in the bay? how long do they live in the bay? and is the population increasing or decreasing?
It all takes place during what’s known here, as “A chum trip”. It starts with a field specialist, a boat skipper, and ideally seven interns head down to the harbor and taking a boat ride out to a place called seal island.
Seal island was once upon a time, a penguin colony with the seals instead living on the beach, but then coastal development forced the seals off the beach and they took over the island, the penguin populations are now found in Capetown and Port Elizbeth. But I digress.
When we get on site and anchor, we have several jobs for our interns that I’ll get into later. Two of the keys roles are chum and bait roper. The intern on chum defrosts and mixes a frozen block of pilchards through a large tub of water and periodically pours scoops of this pungent mix into the ocean. The fish oils in the chum create a smell trail that sharks will come to investigate. The last and most exciting job is called bait roping, and as a field specialist, this is my role when I’m on shift. For this, we attach a tuna head to a long line of rope with a small float to keep it near the surface, then we chuck it in the water. The goal here isn’t to feed the sharks, but to create a physical target that they’ll investigate bringing them close enough that we can record data on them.
Sounds ethically dubious?
The short answer is no. But its important to understand why. The two main ethical concerns that arise from chumming practises are:
- Aren’t you luring sharks close to beaches where they might endanger humans?
- Aren’t you conditioning sharks to come to you for food?
I’m not going to defend all chumming practices everywhere but I firmly believe (based on evidence) that when done correctly, it doesn’t present a problem. Here is why:
We only go where the sharks already are so we aren’t going to lure them anywhere. We have three main sites, seal island and two locations near the eastern coast of the bay. Tagging and tracking has shown that the sharks frequent all three locations irrespective of chumming and Seal Island specifically has been identified as a hunting ground for the sharks. So we only go where the sharks already are, and just encourage them to come a little closer.
By conditioning, what I mean is this. If the sharks grow to associate boats and/or cage diving humans (a neutral stimulus), with eating a tuna head off a bait rope (a positive stimulus). They’re going to learn to associate the two and start interacting with boats and people even when no bait rope is present. Here in the Western Cape, there was a multi-year program monitoring the practice in the cage diving industry to assess the problem. The nature of the different stimuli (positive, negative, neutral etc) was confirmed first by observers noting that the overwhelming majority of shark interactions with the boats were specifically targeted on the bait rather than other non-edible stimuli like the boat or dive cage.
They noted that in Mossel Bay, individual sharks could be positively identified for periods lasting up to around 60 days. This would mean they would be exposed to boats long enough to a conditioned response to arise… if they were positively rewarded. This positive reward is identified by the shark via their senses of sight and smell (remember they can sense electricity too). They found from observing shark interactions with the cage diving boat, sharks only successfully got the bait 25% of the time. During this study, the chumming and bait roping procedure was replicated on a research vessel. They were able to keep the sharks to just a 7% success rate! The next question to ask is then, is this enough to condition them? The study showed that at several of the bays being studied, Sharks spent progressively less time around the boat over time, the complete opposite of what positive conditioning would do. Furthermore, monitoring of tagged sharks in the bay showed that sharks in close proximity to the boat failed to be visually identified nearly 50% of the time! So they weren’t even coming close to the boat when presented with a clear positive stimulus. One possible explanation for this is that the chum slicks typically only travel around 150m without any wind.
This isn’t to say sharks can’t be conditioned. The study noted four sharks that were unusually successful at getting the bait. These sharks did exhibit a positive conditioning response but they were far and away, the exception not the rule. Speaking from my experience with Oceans Research, sharks don’t consistently get the bait, when they do, its rarely the same shark repeatedly and in the rare case that it does happen, we don’t see that shark day after day getting more food. This means that conditioning is a very unlikely to occur due to chumming and bait roping.
With the ethics covered, tune in for part 2 where I’ll go into the detail of what we do out on the water and how to ID a great white shark.