How many lakes does it take to feed an eagle?

Stop me if you think that you’ve heard this one before: a bird conservationist, a farmer, and a mathematician walk into a pub. The conservationist wants to bring back the white-tailed eagle. The farmer is aghast: white-tailed eagles eat lambs! The mathematician just responds “Oh, but won’t somebody please think of the fish!”

Perhaps this is not quite the premise you would expect for work in the Lake District, but there is some truth to the situation above. The Lake District is a sizable national park in northern England with varied terrain including valleys, hills and mountains (locally referred to as fells), forests, heathlands, grasslands, bogs, and, of course, lakes. It is also a major tourist location, a UNESCO (cultural) World Heritage Site, a major farming and forestry location and a major source of water for the outlying regions. Between the terrain, the traditions, the tourism, and the ecosystem services, it is no wonder that the residents, both people and animals, are feeling tugged in every which way.

There appear to be good intentions and frustrations on all fronts. For scientists and conservationists, the Lake District is a prized opportunity in Europe, and in England especially, to make a difference for many species. This includes the white-tailed eagle, which has a particularly complicated story. Is it rare? Yes and no; it is endangered in the Mediterranean, but of least concern in Europe. It has been resident in Britain before, and was also driven out by people before. Why this apparent persecution? Well, it was and still is considered a danger to livestock, and a danger to livestock is a danger to livelihoods. Some people want it back, some people do not. Many species have complicated relationships with humans, especially carnivorous birds.

What about local farmers? Of course farmers want to do their part for the environment around them; their past, present and future depend on the environment. There are complicated stories of local, if not indigenous, knowledge and ownership here, because these are people who have devoted their careers, lives and families to a mixture of environmental stewardship and working. The locals can tell stories about generations of their families working in and around the Lake District, tracing back hundreds of years, and it is hard to say that such ties and knowledge should be disregarded. It is also not quite clear that what outsiders like scientists and government want is actually good for the locals and their environment; it is all too easy to hear stories of things going wrong and it can be unclear if it is malice, incompetence, or merely competing priorities.

But there is another group of actors with an equally complicated historical interrelationship that marches through to the present day: industry and its provisioning of ecosystem services. Perhaps unsurprisingly, one of if not the largest ecosystem service supplied to nearby areas is water, starting with the growth of nearby cities like Manchester. With increasing urban demands for water over the last two centuries, natural lakes were transformed, such as Thirlmere or Haweswater, and artificial lakes created, such as Wet Sleddale, to function as reservoirs to supply millions of gallons of water.

Now, United Utilities acts as the major face of these reservoirs by owning Haweswater and Thirlmere amongst other reservoirs, making them both a major provider of water for the outlying region, but also an obvious target for if anything goes wrong. As a result, United Utilities has been both accused of being a major polluter as well as celebrated as a major partner in restoration works. Scepticism abounds.

This is not to say that water is the only industry or ecosystem service. Mining and tourism both have histories in the Lake District. Focusing on tourism, the number of visitors per year has been in the tens of millions for a decade now. While a prominent industry with benefits, it also brings problems including litter and environmental degradation. Managing industry, environment, governance, tradition, and all the local stakeholders is a complicated task.

So, with all of the ecosystem interactions and historical baggage, why might a mathematician ask instead about the fish? There are two threads worth discussing, both tied into PhD positions my collaborators and I are offering. First, species movement in the context of habitat restoration – the Lake District is a varied set of ecosystems that are interconnected and play host to multiple different species. When contemplating reintroduction or dispersal of species, especially across generations, we need to think about not just how far a species can travel, but where it will settle and what it will do to the other species when it settles. There are a variety of tools to approach this first problem with – we are starting with Condatis – but no model can encompass everything we might need and a general tool can be less useful than multiple specific tools. The crux of the issue is what happens when we need to prioritise habitat for multiple species simultaneously. If we have birds that move faster than and eat squirrels, can we put in place habitat interventions that enable both to persist? This project seeks not just to answer that question, but to make sure to provide a framework to answer it again and again in other contexts.

If the first question is what and where are the birds eating, the second question is what and where are the birds not eating, i.e. what happened to the fish in the lakes? Fishing was at one point a major industry in the Lake District. So it is clear that a sustainable population of fish not only was once present in parts of the Lake District, but it was large enough to support a major local industry from the 13th century until the 19th century. If the reason for the collapse of the industry could be identified and, if necessary, reversed, then it might be feasible to reintroduce fish species to the lakes. This comes back to the titular question as well. Currently, the lakes are relatively lacking in fish as demonstrated by the disappearance of fishing as an industry, which in some areas occurred quite recently, and those fish that remain are considered rare, such as the endangered Coregonus vandesius (Vendace) and the vulnerable Coregonus stigmaticus (Schelly). If the abundance of fish could be increased, however, then the lakes might be able to support ongoing and long term rewilding initiatives such as Wild Haweswater by supporting the local terrestrial ecosystems and the local economy.

White tailed eagle raftsund square crop from Wikimedia Commons by Christoph Müller, CC-4.0. If the lakes in the Lake District have enough fish, that might relieve pressure on other animals and revive a locally endangered industry simultaneously.

I’d also be remiss not to mention there’s a third project I’m advertising. If you do not like terrestrial animals and aquatic animals in England, perhaps you might be more interested in plants in South Africa! This project looks at the seemingly underappreciated carbon ecosystem services provided by savannas and grasslands, which have been targeted by tree planting schemes, and contributes to this crucial area of literature and policy by considering long historical times via pollen analysis. The goal is to determine what are the tradeoffs between tree cover, carbon stocks, and local stakeholder priorities and preferences.

All of these PhDs are open for application now, so please do get in contact or apply. And maybe next time you’re in a pub in Pooley Bridge, won’t you please think of the grass and fish?