We’ve been doing surveys of a near-shore reef to test out the Trident ROV’s new potential as a research tool. Heres an example of what we see. The big schools of fish you’re seeing are Blacktail (with a black dot near the tail) and Strepie.
So last time I went into more detail then I initially planned explaining the ethics of chumming and bait roping. Today I wanted to explain the adrenaline rush that is a chum trip. Chum trip is the term for our boat shifts assessing the shark population. I’ll set the scene.
It’s a quiet morning, the wind is down, the sky is covered in a smattering of grey clouds with random patches of blue sky. You can hear the calls of the seals sounding something like a mix between a goat and Chewbacca, the repetitive lapping of the water against the boat, the random conversation of the interns. It seems like a calm relaxing day, but you’re intensely focused. The noise is all background chatter to you as you watch the Tuna head at the end of your bait rope bobbing in the water. You know at any second, the calm could be shattered. You’re standing on a little platform on the side of the boat with a metal railing against your legs holding the bait rope in two hands.
Suddenly you notice a change in the water. It’s bordering on imperceptible, you don’t even really have time to fully realize whats changed. But in an instant, you know whats coming. In that fraction of a second you yank hard on the rope as the water in front of you explodes. The tuna head leaves the water just as a great white shark bursts from the water a meter or so from you. In under a second you can go from staring at calm flat water to staring one on of the oceans top predators with its body from a half out of the water as it launches for your bait.
Its not always this intense, but this is a recount of one particularly memorable encounter I had with a white shark on a chum trips was like with Oceans Research. What I’m doing with the bait rope is a key part of our white shark population monitoring. It lures nearby sharks to the surface and hopefully close enough to record data on them. My goal is to make sure the sharks don’t get the baits.
What Happens When the Sharks Arrive?
When the first shark comes to the surface the first job falls to an intern working the camera. They’re job is to get a clear photo of the sharks fin for later identification. There are certain types of pigmentation on the sharks fin that persist throughout its life making them a useful method for identification. You can see what I’m talking about below.
We never officially record a shark on our data sheets until we get the first photo of it. We always aim to get the best fin shots possible, but sharks don’t always play ball. So we end up taking a lot of photos.
Before we even get the photo, my minds already working. This is likely to be our first recorded shark so I need to be recognize it. In those flashes of time I look first for identifying markers. Scratches, scars, hooks in the mouth and strange coloration are all things I need to be able to recognize a shark long term.
This helps when you’re up to shark eleven or twelve for a shift and suddenly, your spotters call out “shark threes back, and shark seven”. As you can imagine, it gets pretty fast paced at times.
What happens when we get a photo?
Thats when the shouting starts and the intern recording data gets anxious.
“absent all fin deformities and amputations”,
“Photos one to five are shark one”
“Video one is shark one”,
The person on data likely gets this yelled at them all at once from three different people. The first parts come from the field specialist on shift, its size class information and whether or not the shark has any significant damage to the fins. It’ll change depending on the shark. The third bit comes from the camera person at the front of the boat, so we know later which photos are of which shark. The last bit comes from the person manning the GoPro pole. What this is a long metal pole with a platform at the bottom and a gopro attached to the platform. We use this to work out a white sharks gender.
The only way to tell a white sharks gender is to look for the presence or absence of claspers on the sharks underside near the caudal fin. Claspers means it s a male, no claspers mean its a female. The Gopro pole lets us film the underside of the shark.
Sometimes these shifts can be incredibly fast paced, sometimes not, it depends on the sharks. But one thing that stays constant is the need for spotters. This is a job for two people who stand up on the observation platform and watch for sharks. As the bait roper, I rely heavily on these two. When I have the bait in the water, my focus narrows to about a meter square patch of water with the bait in the middle. I need the spotters calling out to me where sharks are, if they’re coming at the bait, what direction they’re coming from and how far out they are. Depending on the weather conditions, water visibility can range anywhere from one meter to six meters, So the spotters can definitely have a tough job.
The last job was touched on in the previous post, the chummer. The intern on chum is mixing a block of mashed up pilchard parts with sea water and pouring scoops into the water, its not glamorous but its important to attract sharks. It creates a scent trail (roughly 150m) as its carried away by the water that nearby sharks will be curious about it and come to investigate.
These shifts run in four hour blocks, twice a day (if the weathers right). The data from this trip has been the backbone of a PhD thesis and has lead several interesting discoveries.
What have we Learnt?
There has been a lot of really interesting science to come out of the chum trip data from Mossel Bay. Almost nothing was known about the sharks that lived there before this research. Now we know that the population is exclusively juvenile sharks and that they must leave the bay when they’re past a certain age. We now know the population is largely female with an increase in males during the winter. This seems to concur with other research around the world that suggests great white shark populations usually display strong gender segregation. In my opinion, one of the more interesting finds is that they utilize different habitats at different times of the year. In Summer and Autumn, they tend to congregate in coastal waters off the coast of Grootbrak and Kleinbrak, two rivers that enter Mossel Bay. In winter they congregate at Seal Island and in Spring they congregate at at Seal Island and another coastal site called Hartenbos. This seems to be likely due to changes in prey abundance throughout the year.
Its the habitat usage patterns like this that make me wonder whether similar research could be useful in Western Australia.
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.
So in the last post I talked about how in the process of testing a method for 3D mapping the underwater environment, we lost me GoPro. Well In the days following that little misadventure, there were two different attempts to find it. Both were trips came up empty. We assumed the current or a lucky Scuba diver had taken my camera and I’d even started researching the cost of a replacement. Fast forward to today.
We decided to go back to the same site. We were there because my ROV is going to be used in a study of fish abundance on a reef accessible from that site. We’d been having a slight problem though, we couldn’t find the reef…
We’d planned to do a more thorough search for the reef today. In addition to the ROV, I was going to go snorkel the area and search for the reef. I also wanted to make one final attempt at finding my lost GoPro. So while Mitch and Jesse got more practice on the ROV, I started my search. I found the area where we’d spotted the GoPro the previous weekend and I searched high and low, in among rocks, all over the place and drew the obvious conclusion that it was gone. I then turned to helping the ROV find this disappearing reef. I swam out in the direction I’d been described, and while I saw some beautiful fish in among the Dolos wall, I didn’t find a reef. I decided the last part of the attempt would be to swim the ROV out as far as it could go in the direction I’d just been swimming so see how far it could search.
So I swam back to the entry point where Mitch was sitting. Now there was a bit of surge today and the entry point is a bit rocky, so I was cautious about getting tossed on something sharp. Close to shore now and I suddenly found the water pushing me forward and I almost went face first into some rocks on the seafloor ahead of me. I put my hands out to steady myself, and as my face came close to these rocks, I saw into a gap between them and thought, “you gotta be s***ting me” and sure enough nestled down in between these two rocks sat my GoPro!. I quickly reached in and grabbed it before making my way up to the steps.
After a whole week, The GoPro had survived intact and still working. I’m yet to analyse the video.
On a side note, after talking to some locals, it looks like the reef may be too far for the ROV to reach it on the 25m tether I have. So we’re going to investigate other options
Stay tuned next week when the Ocean Research crew will hopefully be tagging a great white. I actually have to check with the boss as to whether I’m allowed to saw any more about that though…
Its finally time for robots
So a few people have assumed my time in South Africa is all exciting adventures. Its definitely exciting at times but I’m living in a small town with limited money so the weekends can be somewhat quiet. This weekend however was eventful as me and two other field specialists from Oceans decided to go and start getting some ROV piloting practice.
The ROV (essentially an underwater drone) is going to be used by Oceans Research to document the fish population of a near shore reef. The goal is to see how an ROV compares to other methods of data collection for similar projects. The first step was getting good at piloting.
So on Saturday afternoon, Jesse, Mitch and me gathered up our equipment.
We headed down to a small public access pier near the main harbor in Mossel Bay and got to diving. Now I figured, being so close to a heavily used boat slipway we wouldn’t see much. We’d genuinely planned it as a chance to get more piloting practice for some upcoming research. Boy were we wrong! we found a small reef and schools of fish all around! Some members of the general public came by curious about what we were doing so we enjoyed a bit of impromptu science communication about the reefs in the area. The kids especially were really fascinated.
There were heaps of fish for us to see and it proved to be a really fun first dive. I’d done some practice dives back home in a harbor. But it was a sandy area with little to see. This dive really opened my eyes to whats possible with this technology. I was really excited!
Hoping for a repeat performance of Saturdays success we decided to head on Sunday as well. This time we were deploying at a similar site nearby to the first at the site of a nearshore reef that we hoped to study with the ROV. Today was just a test. But it quickly turned into a bit of a misadventure.
We decided to test out a few new toys for the ROV. In hindsight we were maybe jumping the gun just a little bit. The first thing we tested was a special type of GoPro mount. The mount attached to the bottom of the ROV and allowed the GoPro to face straight down. This would allow us to shoot detailed footage of the seafloor which could in theory be turned into a 3D map of the seafloor.
So we deployed the ROV and headed out. We started alright, but the water was pretty choppy and we banged into a few rocks. When we got further out, we charged out into calmer water, we couldn’t find the reef which was pretty frustrating to say the least. So we figured we’d cut our losses, detach the GoPro attachment and just practice piloting a bit more.
SO I piloted the ROV back into the shore, Jesse picked it up and I’ve immediately said “Oh s***!” when I saw that GoPro was gone. The GoPro mount I’d 3D printed had snapped during one of those collisions with the rocks. Jesse was about to go jump in to try find it but I had a better idea.
I quickly pointed out that the second ROV attachment I’d prepared to test was a grabber claw. Here is a video of what I’m talking about.
Out of that, a rescue plan was born. Admittedly, it was a wildly optimistic plan: Use an untested grabber claw to search somewhat choppy water for a small camera we hope to grab in rapidly fading sunlight with an ROV we just barely knew how to pilot.
But we’re an optimistic bunch of , and much to our surprise we found the Camera!
And were we successful?
Sadly no, while we were able to find the GoPro (much to our surprise). The water was too choppy for the ROV to make an approach and grab it. It is close to shore so it is retrievable. Yesterday one of the Jesse tried to go for a swim to retrieve it. The visibility didn’t allow it. Another attempt will happen today, cross your fingers for me!
So things have been a bit quiet for me lately since I’ve been a bit sick but that doesn’t mean nothing cools been happening.
Recently, we took the interns out to take part in a citizen science project studying the breeding patterns of small sharks and skates found along the coastal waters here. Specifically we were down on the beach collecting their egg casings. The project is being run by Whale Coast Conservation. It covers around thirty different beaches on the Western Cape of South Africa. Anyone can take part in collections and the idea is that after two years, the pooled data will hopefully help us understand if certain species of egg laying shark breed at certain times of the year, and if they favor particular areas(Head to http://www.whalecoastconservation.org.za to find out more). This has obvious benefits for targeting conservation efforts. It also happens to make for a great afternoon out
But Back to the Sharks
Roughly 25% of know shark species lay eggs. But they dont look anything like what you’d imagine an egg to be, Here is an example.
This is just one example of the weird and wonderful shapes out there. The Port Jackson Shark, found in South Australia has corkscrew shaped eggs. There are others that look like leafy fronds, some that look like they have a tangled mess of string protruding from one or both ends and a wide array of other strange shapes. They don’t even feel like your typical chicken egg. They aren’t hard and easily smashed but instead have more of a tough leathery shell. But this all begs the question…
Well to answer that you need to think about the environment they’ve evolved in. When a chicken for example lays an egg, that egg will more or less stay in the same spot unless moved by someone else. Its not like a strong gust of wind will blow it away. The problem a chicken egg faces is air. Its pretty dry biologically speaking and an embryo needs to stay wet, so a thick, hard shell make sense from a protection point of view. But lets apply the same thinking to sharks. They live in a wet environment so they don’t need to invest in the extra protection of a rigid egg case. But more importantly, that gust of wind analogy suddenly has serious consequences in water. A strong water current could easily pick up a light shark egg and carry it far away. If that happened, the new born shark might find itself far from home and unable to survive. Thats where those weird shapes come in, they create ways for shark eggs to get caught on rocks, seaweed or anything else that might keep it in place.
So thats all for this post. As always, feel free to comment or ask questions, and most importantly share it around. Next week I should hopefully have some ROV dives to share!
So sorry to say it but I wont be jumping into shark science just yet. For my first day of field specialist training I was doing some inter-tidal surveys with the new interns to watch how a more experienced field specialist teaches it.
For those who don’t know the inter-tidal zone is basically that area where the land meets the sea, its an area where a heap of marine creatures live and its an area that can be very reactive to changes in climate, water quality and anthropogenic impacts.
As it turns out inter-tidal zone of Mossel Bay is in a particularly interesting area because of two large oceanic currents. The Agulhas current comes down the coast from the east and brings warm water. The Benguela current comes from the south bringing cold waters up the west coast of Africa. Mossel Bay sits smack dab in the middle. What this means is that while warm water environments typically have high species diversity but low abundance and cold water environments typically have low species diversity but high abundance. Mossel Bay gets the best of both worlds.
But back to the surveys, we were basically being kids exploring rock pools. But with the crucial distinction that we were writing down everything so it counts as science. What we did was lay out a long rope, then starting at the low tide mark, place a 1m x 1m square on the ground every 2.5m and count all the critters that we found inside.
This may not sound as fun as getting up close with Great whites but its incredibly interesting. In my case, I was particularly amazed by the limpets.
But whats that you ask?
A limpets a type of gastropod. Imagine a snail, except instead of living in a swirly shell, imagine it lives under a dome shell and you’re in the ball park. They look like this.
They spend their lives clinging to rocks in rock pools all around the world and while they look pretty mundane, they’re actually incredible!
Exhibit A: The Brown Limpet
Looks pretty dull, but this little guy can paralyze a starfish! Starfish living in these rock pools eat lots of things including some types of limpet. They manage to get under their shell and flip them over to feast on the unprotected underside. But this limpet carries a special toxin, and when the starfish makes contact with its flesh, it gets paralyzed while the limpet gets to make a sneaky getaway.
Exhibit B: The Star Limpet
I figured these guys needed a little highlighting as they have a tendency to blend into the background a bit. Whats cool about star limpets is these two are actually separated for a very good reason, they’re ultra territorial.
This is because star limpets actually tend a garden or algae all around them. You can see it fairly clearly with the limpet at the top of the photo. It cultivates and maintains an algae crop that it can feed from and if any star limpet dares enter its territory, there’ll be hell to pay! If a territory is invaded, the limpets will fight each other, trying to get their shell over the edge of the other before sucking onto the rock to crunch down on their opponents shell. Hopefully the snail on that top limpets rock is quick enough to escape!
Exhibit C. The Shield Limpet
So there is a fun story about these ones. Back when I interned with Oceans Research last year, during one of the inter-tidal survey sessions, one of the field specialists made an offer to me and a friend. “If you can pull that limpet off the rock, I’ll give you my van” he said. With our heads filled with visions of cheap trips up and down the coast on the weekends, we spent longer then I’d care to admit trying to win the van. I only found out on Thursday just how safe a bet that was for the field specialist when he pointed these out to me.
What I had thought were random markings on the rocks were actually grooves created by shield limpets shuffling around, and then suctioning onto the rock. With that kind of power I finally understood why we never had a shot at the van.
So there you have it
Hopefully you have a new found appreciation for these weird and wonderful critters, feel free to post questions in the comments sections and stay tuned for me next week!
Welcome to Ocean Minded. I’m going to use this to share some of the awesome science I’ll be doing out here in South Africa over the next four months. My time with Oceans Research is going to cover a wide variety of marine science including catching and tagging small sharks, collecting data on great whites monitoring dolphins (and possibly tagging them with drones), Intertidal surveys and ROV dives.
Check it out, share it around, comment and ask questions,learn stuff and most importantly, enjoy!