How do marine animals navigate the ocean?
The global ocean is a vast place, spanning the entire planet and tens of thousands of kilometres deep. Many marine animals undertake huge migrations across the ocean, but there are no signposts or google maps…so how on earth do they know where to go? In this episode, we delve into the incredible world of sensory and cognitive ecology to understand how sharks, rays, whales and a host of other critters navigate the underwater world with scientists Jesse Granger and Kyle Newton. Jesse and Kyle ask big questions about how animals find their way around, mainly focussing on the possible ways that they are able to detect and use the earth’s magnetic field to orientate themselves.
Of course, we begin where we always do – with our guest’s most memorable experiences in the ocean [4.00]. We then ask Jesse and Kyle how they came to study the cool and pretty unusual fields of magnetoreception and animal navigation – turns out they both have a passion for physics [6.08]! Jesse discusses her journey from an early interest in how light interacts with the human eye, to studying diatoms and finally to the earth’s magnetic field and how animals use this to navigate. Kyle tells us about his career path as a marine biologist, gaining experience at the Bimini shark lab and as a freelance photographer before discovering his passion for magnetoreception in sharks.
We then get stuck into the question of today’s episode – how do marine animals navigate the oceans? This is still a relatively new field with lots yet to be discovered, but we discuss some of the main theories as to how marine life finds its way around [12.52]. Jesse and Kyle explain that it’s important to think of scale when answering this question. For example, if you’re trying to find something nearby, sight or smell might be most useful. But if you’re trying to locate something or travel across large distances, then other sensory or cognitive cues are more appropriate. As far as we understand, these are fairly limited – either something celestial, like stars or the sun, or the earth’s magnetic field. The latter can be pretty complicated, but don’t worry! Jesse and Kyle explain exactly what they mean by the magnetic field in simple terms, and break down its individual components [18.31]. Picture a bar magnet – like the ones you might have used in high school – but on a much bigger scale! It’s why your compass needle swings towards the north. We don’t feel this because the earth’s magnetic field is actually pretty weak (your average fridge magnet is stronger!), as Jesse explains [23.38]. So how do animals even detect this?
Kyle emphasises that no one has yet found an actual receptor on an animal that definitely detects the magnetic field, but tells us about the three main hypotheses as to how this may be done in nature [25.00]. This includes electroreceptors, like those found in sharks and rays, and photoreceptors, the cells that respond to light. But the truth is – we just don’t know! As Jesse says, it’s like searching for a needle in a needlestack…
Next, we talk about the specific questions Kyle and Jesse are focussing on. Kyle talks about his research with yellow stingrays, a small species of ray that he thinks can detect magnetic cues [33.56]. His studies include behavioural conditioning (essentially training the stingrays to solve mazes, find magnets, and move in response to magnetic stimuli!) to test for these cues. He also talks about similar studies in other species of elasmobranchs, like bonnetheads, that suggest these animals can detect the tiniest of cues from the magnetic field to navigate around the oceans. Jesse also discusses her research looking at how other species use magnetic inclination to cross the world, using computer models to simulate long-distance migrations [41.51]. She looks at what happens when there are changes, or shifts, to the magnetic field, and how this affects animal navigation – in other words, what happens when something goes wrong? This includes massive solar storms, where the sun gives out a lot of energy all at once, affecting the magnetic field. She has found that whale strandings correlate with solar storms, which suggests that disruptions to the magnetic field have an impact on whale navigation [45.30]. However, Jesse emphasises that correlation isn’t causation – we don’t know this for certain, but it seems likely.
We carry on this discussion by looking at other ways animal navigation may be disrupted – such as signals from our electronic devices [46.46] and the magnetic ‘noise’ given off by the large electrical cables for renewable energies, which are laid on the seabed [48.00]. The latter is the focus of Kyle’s current work at Oregon State University, and we finish this episode by talking about weighing up the environmental benefits of renewables with the potential negative impacts on marine species that use magnetic cues to get around.
Jesse Granger is a fourth-year Ph.D. candidate in Sonke Johnsen’s lab at Duke University. She primarily studies animal navigation and orientation, with a focus on how animals use the earth’s magnetic field to navigate.
You can find out more about her work by following @JesseGranger6 on Twitter or heading to https://sites.duke.edu/jngranger/.
Dr Kyle Newton is a Research Associate in the Big Fish Lab at Oregon State University. Kyle is a sensory and cognitive ecologist that uses machine vision and learning, biologging and telemetry techniques to understand, monitor, and mitigate the impact that human activities have on the physiology and behaviour of marine wildlife. He is particularly interested in how the electromagnetic field noise generated by offshore energy infrastructure impacts the foraging and navigation behavior of electrically and magnetically sensitive species, such as sharks, rays, skates, teleosts, and decapod crustaceans. Kyle is an avid scuba diver, novice surfer, academic gypsy, and all-time professional cat dad.
Follow @SharkMagneto on Twitter for more updates on Kyle’s work!