Dr Nathan Hart is an expert in comparative neurobiology and specialises in animal sensory systems. He completed his PhD on colour vision in birds at the University of Bristol, UK, before moving Australia in 1999. He’s since worked on the visual systems of various animals, and more recently has been working with sharks. We interviewed him about his very interesting career history.
How did you end up in science and research?
I’ve always loved the natural world, and so I went to Bristol University to study Biology. After completing my degree, I did a PhD, also at Bristol, that combined a couple of my interests: birds and vision / optics. It was there that I really became a neuroscientist by studying the retina. The retina, as you may know, is part of the central nervous system, arising from the forebrain during development. Neurons in the retina are organised into distinct layers that make it very convenient to study. In fact, the retina has been referred to as ‘Nature’s brain slice’ because it is such an accessible part of the central nervous system, and using it we have learnt a lot about how simple neural circuits process complex information. During my PhD, I discovered some fascinating things, such as how birds can see ultraviolet (UV) light and have far better colour vision than we do. That’s how I got into neuroscience and sensory biology in particular.
How did you progress through your field of speciality?
I started to become more focused on mechanistic neuroscience: the nuts and bolts of how things work in the visual system; how we detect shapes and colours, for example. I’m particularly interested in how animals detect and discriminate objects. The work we’re doing at the moment is related to how sharks detect their prey visually; what is it about the shape of an object that tells a shark ‘yes, that’s prey, go on and bite it’ as opposed to a non-prey object. We can apply that approach to all different aspects of their sensory biology, including electroreception, hearing and smell, so it’s not just about vision.
Sharks must be particularly interesting for you with their extra senses?
They are. They’re a lot harder to work on than birds for lots of different reasons, but they capture your imagination as they have these different senses that we lack, such as electroreception and the lateral line. We also know so little about their behavior in the wild: where they go, what they do, and why. It’s only now with the increased effort being made in the tagging and tracking of sharks that we’re getting an idea of what they’re doing below the water, and we can begin to tie up the anatomy and physiology that we measure in the lab with their natural behaviours.
So do you think it’s harder to study an animal in the water than on land or in the air?
Yes, especially for the experiments we do that involve physiology. We will often take a shark into the lab, anaesthetise it and then record the response of the eye to different visual stimuli (lights and patterns), so we can establish how good its vision is, what colours it can see, and the fine detail it can discriminate. That’s much easier to do with an air breathing animal. Once you have an aquatic animal you need to have a more complex life support system that can supply oxygenated water to the gills while conducting the experiments. It’s logistically much harder, especially with larger sharks, and of course it’s harder to observe aquatic animals in their natural habitat.
Do you ever carry out experiments in a not-so-natural environment, like an aquarium or zoo?
We have done a little bit of research with captive sharks, but it’s hard to know how comparable their behavioural responses are when in captivity compared to when they are in the wild. However, there are some fundamental things we can study, like eye movements as a shark swims, which is one of the things my post doc Laura Ryan is studying at the moment.
Do you consider yourself more of a biologist or a conservationist?
More of a biologist. Fundamentally, we want to know how the nervous system works and how animals perceive the world around them. However, shark conservation is definitely an applied outcome of our current research on shark deterrents. If we can find reliable ways for people to avoid getting bitten by sharks, then we won’t need to have so much culling of shark populations and we see that as a really positive outcome for the work we’re doing.
I recently read that the Australian government are carrying out a population assessment to determine how many large shark species are around the Australian coastline in order to justify the culling.
I am not familiar with the study that’s going on. My understanding is that we don’t really have a great idea of how many sharks are present in Australian waters. Things like tiger sharks and bull sharks are not protected so anyone can catch them, but white sharks are protected by legislation. No one really knows how many there are and the tagging effort is so limited that we don’t fully understand their movements either. I can’t see them lifting the protection for white sharks any time soon, but the WA government managed to find a loophole to kill white sharks if they felt it was in the public’s interest to do so. You also can’t stop them getting caught on drumlines and in nets.
So you’re against the culling?
I am against the culling, but I understand why it’s in place. As a scientist working in this area, you understand the odds and the risks involved better than most, but when you enter the ocean you still wonder about sharks being there. So you have to be able to understand that the general public can be frightened, especially when the media gets involved. So I am against culling, but I understand that the government have a duty of care to keep people safe. They’re between a rock and a hard place. You tend to find that the people in the government who are making the decisions are often very pro shark but they have to do their job and deal with many different points of view.
From a science point of view, do you think it’s possible that culling could work?
Well, if you get rid of all the sharks, no one will get bitten. At some point, it would be a benefit. However, the recent culls in Western Australia in response to the attacks there didn’t really catch any white sharks. They caught a lot of tiger sharks and other bycatch, but it would probably have had little or no effect on the risk of being bitten by a white shark, which was the species implicated in the majority of the attacks that occurred there. They say there have been no attacks on the netted beaches on the East Coast, so maybe it does work there, but at some point you do have to think about the cost to the environment. However, it’s hard to weigh up the value of people’s lives against the lives of all the wildlife that gets caught in the nets, and so it’s a very emotive subject.
I think it’s good that people like yourself are looking at alternative methods to deter sharks. I read about ecobarriers in some parts of Australia.
That’s right. They’re trying, but one of the problems is that the barriers can’t be used on high energy beaches as they get knocked around and washed ashore; bearing in mind that they can cost $1mil each, it’s very expensive. Most people you talk to who aren’t staunchly anti-sharks really want to find a solution and are asking what works in terms of personal deterrents. I think if you can give them convincing evidence something works, they’d use that as an alternative to the nets. There are lots of people who want to do the right thing, but so little has been proven scientifically to work.
Do you have an ultimate goal in your research or career?
Good question. I think there’s so much to know about the brain that it’s hard to say that you’re going to get to some ultimate point of having a global understanding of how it works. But it’s a very exciting time in the field of neuroscience at the moment, in that there are a lot of very advanced technical tools that are allowing us to link behaviors with the activity of single neurons and the role of specific genes. So for the first time in the history of the field, everything is starting to come together to a point where we can really understand the different neural circuits that drive particular behaviours. We’re a long way off doing that with sharks, but we’re at a stage where we’re getting some real insight in lab mice and rats. I’d like to be part of that movement and contribute to that greater understanding of how the brain works and how we can take that information and use it.
What’s your favourite species of animal, and why?
Well as fun as it is working on sharks, I have a real soft spot for birds, which is how I started my scientific career. As a group they are incredibly diverse it terms of habitat, morphology and behaviour, and this is reflected in the different adaptations we see in their visual system. Most birds have four types of cone (colour) photoreceptors in their eye and so they have amazing tetrachromatic (4-channel colour vision); they can also see UV, have this incredible sense of motion detection and far better spatial vision than we do. From a scientific perspective, they’re fascinating. So, I think that birds as a group would be my favourite. Really, I’m an accidental shark biologist. I did a little bit of research that showed some sharks are completely colour blind, and I didn’t expect to keep working on them for as long as I have. However, we’ve really tried to help with the shark attack problem and funding has been available to allow us to keep working in that area. Coming to South Africa to work with them is an amazing thing to do.
We have some amazing bird species too.
Well that’s right, if only I had the time to check them out!
You recently published the paper “Electrophysiological measures of temporal resolution, contrast sensitivity and spatial resolving power in sharks”. How would you explain this study to the lay person?
This was work that Laura did as part of her PhD under my supervision. What we’re interested in is understanding, from the shark’s perspective, how they perceive the world. For example, we want to know what detail they can detect in the image of the world that falls on their retina. Humans have very good spatial or detail vision; by contrast, most fish have relatively poor detail vision. If you can imagine someone who’s very short-sighted taking off their glasses, that’s what it’s like for a lot of fish. So understanding where sharks fall on that spectrum between very good vision and very poor vision is useful, because it tells us what they can detect from a particular distance, and that may help us to design vision-based shark deterrents. We also want to know how quick their eyes are, which is why we measure temporal resolution. If you take the analogy of a camera, most people know about shutter speed. If you want to stop the motion you use a fast shutter speed. Eyes work in the same way and, depending on species, capture images at different rates; if they don’t do it fast enough, the image captured will be blurred as the motion ‘smears’ the image across the retina. If you’re an animal that needs to detect or hunt fast moving prey, you tend to have a fast eye. White sharks and marlin have a counter-current blood circulation system, so they are able to warm different part of their body, even their eyes and their brain, potentially to speed up the physiological responses of neurons and help them gain faster vision. We were looking at benthic sharks for that particular paper, but it was nice to have that as a counter-point to some of the other work that’s been done in the past
What can you tell us about your other past research?
As someone who spends a lot of time working on colour, the fact that many sharks are colour-blind is fascinating because there are very few vertebrate animals that are completely colour-blind. There might be some sharks that can see colour—we’ve only looked at a handful of species—but so far all of the sharks we’ve looked at have only one type of cone photoreceptor in their eyes, which they use under bright light; this means that they lack the machinery for colour vision because you need at least two different types of cone (humans have three, which are sensitive to red, green and blue light, respectively). The only other group of marine vertebrates to lack colour vision are marine mammals such as dolphins, whales and seals. Sharks and marine mammals are very separate in terms of their evolutionary history. Sharks as a group are over 400 million years old and of course have always lived in the water. Marine mammals, on the other hand, evolved from land-dwelling ancestors and returned to the ocean maybe 50 million years ago. This is a clear example of convergent evolution in visual system ‘design’ and perhaps tells us that large marine predators probably have very little use for colour vision. For us, that’s been one of the most interesting discoveries in recent years. Intriguingly, most stingrays have more than one type of colour receptor and as expected they’ve got good colour vision. We’ve conducted some behavioural experiments with stingrays where we’d train them to swim up and tap different coloured cards. They’re very intelligent animals, even though they’re so ancient and people think of them as very basic animals.
Some of the prey of sharks and marine mammals can be colourful. Why do you think that is if the predators are colour-blind?
If you’re a shark or a killer whale hunting fast moving prey, probably the most important thing is the brightness contrast of the prey against the background, especially in dimly lit or turbid water. Detecting the outline or shape of an object and detecting its motion doesn’t usually require colour vision. In fact, having a retina capable of detecting colour may make it harder for you to detect things like motion and brightness because you’re taking up space in the retina with cells that are specifically involved in colour discrimination. If you get rid of those, it might improve certain aspects of visual performance and make you a more efficient predator.
But that’s theory?
That’s entirely theory, based on some pretty sound knowledge of how the retina works.
What has been your most important scientific finding?
I think, taken as a whole, it would be how variable the visual system is across the animal kingdom. As humans, we tend to think that we have pretty good senses and that we perceive the world around us very accurately and completely. But if you look, for example, at the very ‘primitive’ lampreys—jawless vertebrates that evolved around 500 million years ago—they have pentachromatic (5-channels) colour vision that is likely far better than our own. In fact, most animals see the world very differently from humans and conveying that to the wider scientific community and the general public has probably been my most important contribution.
What animal was the most fun to work with?
Definitely white sharks. How often do you get to tease white sharks by towing things behind a boat? Working with sharks is definitely fun. Scientifically, what we’re doing at the moment are very simple experiments, but they’re very enjoyable to do and get me out of the lab!
What has been your biggest challenge?
Going to nice places and sitting in a dark room! The type of work I do on the visual system often means I have to keep animals in a darkroom during the experiments. I’ve been to lots of lovely coral islands to work on fishes but had to sit in a makeshift darkroom for three of four weeks at a time while everyone else is out on a boat getting a tan! In terms of my career, the most challenging thing has been navigating the scientific career path. When you are a post doc, you have to apply for funding for your salary every two to three years. It’s a tough career. I am lucky enough to have a permanent job now, but I spent 17 years as a post doc. You’re always wondering where the next lot of money is going to come from and it makes it hard to concentrate on the science you want to do and it makes it hard to plan out your life. All of the science and research I’ve done has been fantastic and largely successful, and I haven’t bumped into too many problems along the way.
Is there a reason you pick Mossel Bay for some of the aspects of your past research?
We are interested in scientifically testing shark deterrents and have been doing that for a few years. Mossel Bay seems to have a reliable population of white sharks that are readily accessible. Oceans Research has been incredibly helpful in facilitating that research. It’s a great place to come and do research, both because of the people that are here and the convenience of working with sharks that are just five minutes away. They have white sharks in Australia but it’s harder to find a concentrated aggregation of sharks and it’s actually more expensive to do this work in Australia. We have a limited budget and we need it to go a long way. We have to do a lot of boat trips to get sufficient interactions with the sharks.
Do you hope your research will aide in conservation?
In order to make a project like this work, it had to have lots of different aspects. One of them is getting students involved who can work on the basic biology. We’re interested in that question of how the sharks sense the world around them, but the main goal for the funding is to come up with a solution that will prevent the need for culling. We want to equip people with technology that’s scientifically tested and reliable so that they won’t feel frightened in the water. We have to educate people that there will always be risks but if you give them confidence that the technology they’re using has been tested, works and will significantly reduce the risks, they won’t be calling for shark culling. That will undoubtedly help in shark conservation because people will care more about the sharks and this may lead to the removal of drumlines and nets. If you can get all of the surfing community on board, for example, using a type of technology which means they are safe on the sea, ultimately fewer and fewer people will have negative interactions with sharks. That will keep feeding back into the population and people will be wondering why they were ever afraid of sharks.
Would you encourage your kids to pursue a career in science?
It’s a tough career but everybody should follow their passion and do what makes them happy. If my children were going to pursue a career in science I would encourage them to do that, but I hope that I could give them insight into what the career of a scientist is, what they should expect and how to excel in that field. A lot of very successful scientists today are the children of scientists, and I don’t think that’s a coincidence. Coming from a non-scientific background I had a lot more learning to do about the politics of universities; the need for networking and being strategic about what you do and who you do it with. I would be happy if my children want to go into science, but if they want to become and doctor or a lawyer that’s fine too. I wouldn’t dissuade them from science just because it’s a tough career.