How might pollution impact sharks?
SHOW NOTES
Plastics. Oil spills. Ghost nets. Industrial chemicals. Pesticides…the list of man-made pollutants that have found their way into the ocean is endless. But scientists are only just beginning to understand the true extent of our impact on marine life. Fish biologist and SOSF project leader Franco Cristiani is investigating the effects of harmful pollutants on chondrichthyans, using the American elephant fish (a chimaera) as a model species. We invited Franco onto World of Sharks to discuss this important research and learn about the potential consequences of marine pollution on the reproductive health, immune function and overall survival of sharks and their relatives.
But before diving into our core topic, we take some time to get to know Franco and where his passion for sharks came from. An experience that particularly stands out for Franco was his first trip to the Galapagos, where he was able to dive with schooling hammerheads [6.12]. After years of studying for a degree in the biological sciences, Franco had had enough of books and wanted to be close to the animals that had inspired him to go to university in the first place: sharks. Franco’s fascination with sharks started early, around the time other children were discovering dinosaurs [10.46]. In a now common theme for this podcast, the movie Jaws captured Franco’s young mind and inspired him to learn more about these creatures. That passion has continued to this day. Now studying for a PhD, Franco believes that the more you learn about sharks, the more that fascination grows.
It was a love for sharks that drove Franco towards the area of research he is in now. Learning about the threats currently facing sharks, and wanting to help find solutions to these problems, led him to the field of marine pollution [12.52]. Very little is known about the impact of pollutants on marine organisms, especially chondrichthyans. But given the extent of human-generated pollution in the ocean, Franco and his supervisors felt this was an important question to answer.
But what do we mean by ‘marine pollution’ [16.06]? In a general sense, the term applies to all man-made (e.g. non-natural) substances that end up in the ocean, either directly or indirectly, which can have a negative effect on the organisms that live there. Something that might immediately spring to mind is plastics, especially macro-plastics – the larger plastic items that we usually see on the news, like disposable bottles, coffee cups and shopping bags that wash up on beaches or collect in tidelines. Footage of vast quantities of plastics and other debris floating around the sea, looking like a mega-swarm of jellyfish, or entangling and choking charismatic marine animals has frequently gone viral. It’s an impact we can clearly see with our own eyes, something we can’t ignore. Even walking along the beach at low tide is a reminder of our plastic footprint on the earth. Franco believes this is why campaigns to ban single-use plastics and clean up the ocean has gathered so much momentum, because of the startling, arresting nature of such footage. But it’s also the substances we can’t see that need our attention. For example, persistent organic pollutants like pesticides and herbicides are invisible to us, but their impact is far-reaching. These substances have been used for decades, to assist in farming and other industries, and have slowly leached into the ocean via surface run-off, carried by rainfall, rivers, and waste disposal. Some have even been banned on land due to their harmful properties. But despite no longer being manufactured their legacy continues in the ocean, where everything is part of one long, continuous cycle. These compounds do not break down easily, tending to stay around for extremely long periods of time. And, as Franco points out, new substances and compounds are created to replace the prohibited ones. He says that ‘it’s like a wheel that’s never going to stop’ [18.32].
A huge part of the problem is how little we know about how pollutants move around the ocean, and the long-lasting effects of such chemicals on marine life [19.29]. The first question we have always asked is ‘how will these substances affect us?” rather than how they will impact the other species we share the planet with. Even if some substances may be safe for us below certain concentrations, how they accumulate in the ocean and get passed between organisms, is what Franco finds most worrying. A common misconception is that because the ocean is so vast, any chemicals dumped in it will be diluted to a point where any potential negative effects are negligible. But the migratory nature of many marine species, the dynamics of ocean currents and processes, and the sheer amount of pollutants that are already present in the ocean make this a far more complex and difficult problem than we might first imagine.
Disentangling the effects of harmful pollutants on sharks, rays and chimaeras is also inherently difficult [22.76]. There are ethical reasons against testing the impacts of chemical substances on captive animals. In the wild, aside from the challenges of collecting samples from live animals, there is also the difficulty in figuring out whether a particular substance is affecting the animal. Franco describes the ocean as a kind of pollutant “soup”, where lots of different chemicals are all mixing with one another. But it is a very important question to try and answer. As top predators, sharks and their relatives are particularly susceptible to the harmful effects of pollutants. The substances accumulate as you go up the food chain, meaning that those nearing the top are more likely to have a higher concentration of harmful chemicals present in their tissues than those further down. Additionally, sharks, rays and chimaeras are generally long-lived, allowing more time for harmful substances to accumulate in their bodies, and they also have a hard time processing these compounds [26.15]. As Franco explains, such compounds tend to be ‘lipophilic’, meaning they combine with or dissolve in fats. They can attach to organs like the liver, spleen or gonads, where they can also interact with and even mimic the body’s natural enzymes and hormones. This can have detrimental effects on the immune and reproductive systems, eventually hampering the animal’s capability for survival.
But exactly how these compounds are processed in the body, and their long-term effects, is information that is lacking for sharks, rays and chimaeras [28.35]. We don’t have the luxury of time – that is, waiting around to see what the eventual impact of these pollutants will be – and so Franco is interested in understanding what concentrations of certain pollutants place species in the ‘danger zone’, where their reproductive and immune capacity may be compromised.
The city of Puerto Madryn in Argentina (or, more specifically, the Golfo Nuevo, the body of water that borders the city and connects to the South Atlantic Ocean) is the perfect study site for Franco to explore the effects of marine pollution on chondrichthyan fishes [30.22]. Not only are there numerous species of sharks, rays and chimaeras, but Puerto Madryn is a growing city, which brings its own challenges in terms of pollution as the area becomes increasingly urbanised. To the north of the city also lies the Península Valdés, a UNESCO World Heritage Site and globally significant for the conservation of marine mammals.
Franco is using the charismatic American Elephant Fish Callorhinchus callorynchus as a model species [35.24]. This curious, strange-looking creature is actually a chimaera – a close relative of the sharks and rays (you can listen to our episode on chimaeras here to find out more about them!). Perhaps the strangest thing about them is their elongated, fleshy snout that they can use to probe the seafloor in search of food, much like an elephant’s snout! They also have very well-developed electroreception to detect food buried in the sand, and use their plate-like teeth to crush shellfish, bivalves and molluscs.
Franco admits they look quite alien-like, but also thinks they are beautiful in their own way, with large pectoral fins that he describes as ‘wing-like’. They are usually found on the seafloor, in waters over 1,000m deep, which means they can be pretty hard to find. But, in spring and summer, the elephant fish come closer into shore to lay their eggs. During this time they are much more susceptible to fishing pressure, but also easier to study for researchers like Franco. The fact that they migrate vertically (from deep to shallower waters), rather than over great distances across the world makes them an ideal study species to observe the impacts of pollution on chondrichthyans.
In order to catch an elephant fish and get the samples he needs, Franco has to conduct most of his fieldwork in the dead of night, when they are most active [42.45]. He is mainly collecting blood samples, but also weighs and measures the fish before releasing it back into the sea. Then, as quickly as possible, Franco gets the samples back to the lab for analysis. Sometimes, he is up until 3 or 4 in the morning! He tests the blood samples for the concentration of certain pollutants, and looks at the levels of different hormones and enzymes. Sometimes, if an elephant fish has been caught and landed by fishermen, Franco is sometimes able to obtain the whole fish to examine the organs, and look for any evidence of damage, which he can then also use as data for his studies.
Franco is still in the middle of his research, and doesn’t have any concrete analyses he can share just yet [51.25]. But what he can share is that they have detected aromatic hydrocarbons – compounds that can be found naturally in plants and the human body, but are also used in the manufacture of plastics, solvent glues, and explosives – and a specific insecticide called ‘chlorpyrifos’. Evidence of these compounds were found in the gills, liver and gonads. But what long-term impact these pollutants have had on the overall health of the fish are yet to be uncovered. Franco still has some work to do before he can share his conclusions, but it certainly sounds like the results will be interesting, if somewhat concerning.
But, there are some things that we can do now to help the problem of pollution [55.12]. One of the most significant actions we can take is to be responsible consumers, being aware of what we buy and dispose of – in other words, where do the products come from, how are they made, and where do they go once we’re done with them? Another important action is to use your voice. Speaking to friends and family, using social media, and writing to your local government representatives – there are all actions we can take that cumulatively, will make a difference.
You can follow along with Franco’s research here: https://saveourseas.com/project-leader/franco-cristiani/
ABOUT OUR GUEST
FRANCO CRISTIANI
Since childhood Franco has felt passionate about marine life and particularly for sharks. His vocation to marine biology persisted through time and, after a long journey, he now finds himself conducting a PhD scholarship studying the effects of anthropic pollutants, such as endocrine disruptors, in the reproductive and immune system of chondrichthyans. During his career Franco got involved in many shark conservation projects such as the first tagging program in the New Gulf, Peninsula Valdes; the biology monitoring of whale sharks in Cebu, Philippines and the white shark’s conservation program at Guadalupe Island among other small projects.
His goals for the near future are focused on his PhD research, and education and awareness of shark conservation around the region. Franco believes in the integrative way of working between scientists and other stakeholders such as recreational fishermen, tourism agents, park rangers, educators and communicators, in order to find solutions and generate knowledge concerning sharks and marine environments. Franco is very keen on outreach and communication. As a biologist, he feels strongly that he has the responsibility of taking the word not only to scientific journals but also to the rest of society and specially to future generations.
