Can sharks adapt to changing seas?

Show Notes

Our oceans are changing dramatically – not just with climate change, but also in how it is being used and exploited by humans. In this episode, we ask shark movement experts Prof. David Sims and Freya Womersley, who work on the Global Shark Movement Project, what these changes mean for sharks and how their distribution and behaviour might change in response. Can sharks adapt? Or will it spell further trouble for our elasmobranchs?

We begin the episode as we always do, by asking David and Freya about their most memorable experiences in the ocean (04.56) – one is 32 years ago, and the other involves ‘layers of sharks’! David then talks about the Global Shark Movement Project (09.17), a collaboration of over 150 scientists from across the world, working to collect and analyse data on pelagic shark distribution and space use in relation to environmental and anthropogenic threats. Freya is working with some of this data for her PhD, and she tells us some of the key questions she is hoping to answer with her thesis (13.23), which include the potential threat of vessel collision to whale sharks and shifts in future pelagic shark distribution in response to climate change.

Now pelagic sharks are notoriously difficult animals to study – they don’t stay in one place, travel huge distances, and go places humans can’t. So how do we even begin to understand how they move about and use our oceans? David gives us the tagging 101 (18.06), explaining how this technology works and the information they give us about the sharks location including depth, light level, temperature and pressure. We even learn what its like to get an ‘email’ from a basking shark! (20.50). Freya also explains how this technology has advanced to get even smaller, more streamlined, and include environmental variables like oxygen concentration and even the capacity to record video (22.10).

With that in mind, our conversation moves on to some of the most prominent findings from the Global Shark Movement Project. First, we learn about the effect of Oxygen Minimum Zones (OMZ) – areas where levels of oxygen are declining rapidly – on blue and mako sharks (23.44). David describes how these sharks were migrating to an OMZ off the west coast of Africa and hanging about above it. During this time, their maximum daily dive depth – which is usually as much as 1,700m – decreased significantly, and they were feeding on ‘hypoxia-tolerant’ cephalopods (species that can cope with low levels of oxygen). This suggests blue sharks in particular may be able to withstand mild hypoxic conditions, but only for a short time, and only up to a certain temperature. We discuss whether this means that this species could adapt to climate change – but there are a couple of caveats to this, including the overlap of warming temperatures and fishing ‘hotspots’ with OMZs, which David explains in detail (29.00). In short, the sharks were ‘sandwiched’ between a layer of warmer water above and low oxygen beneath, and longline fishing fleets were exploiting this aggregation rendering the sharks more vulnerable to fishing pressure.

We then ask Freya to look into her ‘crystal ball’ and tell us what other changes we might expect to see (33.56). This of course is a question we’re still answering, but there are a few predictions we can make for pelagic sharks in particular. She explains that because these sharks are so wide-ranging, we can assume they may have an advantage in being able to seek out areas that are favourable to them and may, for a short time, be able to move away from intolerable areas. How they move will depend on many different complex variables – temperature, oxygen levels, prey distribution – and we are starting to see some of these changes already, as species shift in response to already warming seas. But, we do not yet know what the impact of these shifts will be on the sharks, how they will overlap with other anthropogenic threats – like fishing and boat traffic – and how sustainable they are under prolonged climate change. Future marine scientists…consider this your call to action!

We round off this episode by asking Freya to talk about her fascinating research on another kind of shark adaptation – the amazing healing capabilities of whale sharks (43.34). Freya uses the occurrence of boat-inflicted injuries (like lacerations from propellors) as a measure of human-shark conflict, which is a useful proxy especially in locations like the Maldives, where there are many marine tourism operations. Freya has discovered that whale sharks can heal remarkably quickly from injury, and we discuss the complexities of this finding – yes, it could mean that whale sharks are more resilient, but what are the physiological and behavioural implications of injury? And should sharks have to adapt to human stressors in the first place? This takes us to the end of our conversation, where we talk about how we can use this data to improve management practices and policy to better protect sharks now, and in the future (49.30).

About our guests

David Sims

Professor David Sims is a Senior Research Fellow at the Marine Biological Association (MBA) Laboratory in Plymouth, UK, and Professor of Marine Ecology at the University of Southampton’s National Oceanography Centre (NOCS). His research focuses on movement ecology and conservation of marine predators and he is best known for bio-logging studies of shark behaviour to identify essential habitats. He also leads the Global Shark Movement Project involving over 150 scientists from 25 countries. He has authored more than 180 scientific papers including numerous articles in Nature, Science and PNAS. He is the recipient of several research awards, including the Zoological Society of London’s Marsh Award and the Fisheries Society of the British Isles’ FSBI Medal.

Freya Womersley

Freya is a researcher based at the Marine Biological Association (MBA) Laboratory in Plymouth, UK, where she is approaching the final year of a PhD. Her PhD, which is in partnership with the University of Southampton and funded by UK Research and Innovation (UKRI), uses data from the Global Shark Movement Project (GSMP) to explore broad-scale movements, ecology and conservation opportunities related to pelagic sharks. Her main focus is on developing techniques to identify global distributions and quantify human threats both in the present day and future oceans, with an aim to provide evidence that can be used to better protect declining populations.

Global Shark Movement website ; Marine Biological Association website