Trawling has been recognised as a profoundly damaging practice with lasting negative consequences on seabed ecology and marine life since its first mention in a 1376 parliamentary petition. Mobile fishing gear (including any dredge, trawl, or similar device) is used to tow or push a net with a boat to catch fish. Bottom trawling, in particular, grew from a need to keep up with declining fish stocks and developed further with technological changes and increased demands, though it created ‘anger and resentment’ within the fishing communities (Bolster, 2012, p. 236). All three trawling revolutions—invention, mechanisation, and later deep-water expansion—have been met with controversy and pushback by the public and environmentalists alike (Roberts, 2008).

There is no doubt that trawling has decimated fish stocks globally which has brought hardship on fishing communities. Today’s boats must work an estimated 17 times harder than in the past because there are literally fewer fish in the sea (Roberts, 2012; Thurstan et al., 2010). Every year trawlers plough areas of the seabed roughly equal to half of the world’s continental shelves and convert the rich seafloor below into a bleak landscape of flat nothing (Watling & Norse, 1998). With one pass by a trawler, boulders can be displaced, large epifaunal invertebrates removed and damaged, and sediment re-suspended (Freese et al., 1999). Yet little has been done to seriously limit the practice and protect the underwater landscape.

Crucially, archaeological impacts and data are also missing from biological reports and published articles on the practice. Trawling also has dramatic impacts on maritime archaeology sites, though these effects are less well known. The seafloor landscape includes historical information and sites of cultural significance. Bottom trawling does not just destroy the physical fish habitats—important shipwrecks and artefacts are lost too and ostensibly have been since the inception of trawling. Trawling gear damages wrecks when their nets snag and are tangled with shipwreck structures, often destroying components, and the trawl doors and chains can destroy and scatter artefacts and vessel components (Brennan, 2016). Archaeologists have recently begun raising awareness about the impact of trawling on their sites, and more work is needed.

Although legislation that limits trawling can help biological communities rebound, the archaeological material lost can never be recovered. And although efforts to illustrate sustainability in seafood, such as the Marine Stewardship Council stamp, may attempt to show safe fishing practices, one can never be sure of the wider harm being done, especially to Underwater Cultural Heritage (UCH). Despite decades of research and protests against trawling from fishery scientists and marine ecologists, archaeologists have only recently begun examining this industry’s impacts to UCH sites.

This book serves as a call for action to address the threats to our Ocean Heritage from the destructive activities of bottom trawling. In the follow up to his seminal work The Unnatural History of the Sea, conservationist Callum Roberts writes in The Ocean of Life that the ‘impacts [of trawling in this case] are discussed in isolation at different meetings and by different people, who never quite see the overall picture’ (Roberts, 2012, p. 6). He is referring to different people within the marine scientific fields such as those focused on fishery sciences or pollution. His point holds true, though, with a group of people many do not consider: Ocean Heritage professionals. Underwater Cultural Heritage is an integral part of both cultural heritage and natural heritage, thus making it a shared Ocean Heritage which must be considered part of a Marine Spatial Planning programme that should ban bottom trawling at UCH sites.

1.1 The Importance of Our Ocean Heritage

1.1.1 Cultural Heritage

The stories of our societies and our ancestors are wrapped in intangible connection with the ocean and preserved on the seafloor as artefacts, shipwrecks, and remains of those lost or buried at sea. Marine global heritage has largely been based on natural features, and the inextricable link between natural and cultural has been ignored. However, UCH functions in a shared space of natural and cultural heritage: Ocean Heritage. Bottom trawling impacts this Ocean Heritage and harms both natural and cultural objects on the seafloor.

Coastal trawling is particularly destructive to UCH since it is where most known wrecks are located and is where nearly all submerged landscapes, the continental shelf where submerged prehistoric sites are located from time periods of lower water levels, are situated (Evans et al., 2014; Bailey et al., 2017). However, there is also a massive amount of ecological damage from trawling in coastal waters. Coastal seas are some of the most ecologically productive areas, with delicate plants, marine life, and complex ecological systems. A 2021 report found that trawling is most intense in the territorial (12 nautical miles offshore) seas of coastal states (Steadman et al., 2021; Pauly et al., 2020) (Fig. 1.1).

Fig. 1.1
A world map depicts the relative intensity of various types of fishing along the world's coastlines. The intensity is highest in all coastal areas around the world.

The relative intensity of all types of fishing around the coast is illustrated here in tonnes per square kilometre. (Source: Pauly D., Zeller D., Palomares M.L.D. (Editors), 2020. Sea Around Us Concepts, Design and Data (seaaroundus.org) printed under Creative Commons Attribution Non-Commercial 4.0 International License)

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As technology improves, archaeological investigation will move further out to the deep sea, and those sites must be protected from trawling too. The deep-water sites are also valuable resources since, being inaccessible for so long, they have had the least anthropogenic damage. Remotely Operated Vehicle (ROV) technology has allowed previously impossible deep-sea exploration and has revealed both beautiful, complex habitats as well as shipwrecks that have been already damaged by trawlers. For example, in the Black Sea and Turkey’s Mediterranean, Aegean, and Black Sea shores (Brennan et al., 2016), there is evidence of trawl damage on deep-water wrecks. Ereğli E, one of the oldest deep-water wrecks yet discovered in the Black Sea, could have been one of the most significant wrecks in the area, but by the time it was found in 2011, it had already been nearly destroyed by trawling (Brennan et al., 2016).

1.1.2 Natural Heritage

Trawling also does extensive damage to the seafloor and ecosystems within it, as will be discussed in Chap. 2. The effects have been likened to clear cutting a forest. Structural components of fish habitats are removed, and biodiversity is lost. For example, the North Sea has been heavily fished for centuries, and this increased significantly in the 1900s (Frid et al., 2000). Information from published and unpublished sources dating back 60 years shows that fishing has influenced the benthic communities of the North Sea, with a definite change in composition of the benthos coinciding with increased rates of trawling (Frid et al., 2000).

Important deep-sea sites have been destroyed before scientists have even been able to study them. In deeper waters, fauna is less adapted to changes and disturbances to their environment. The effects of trawling here take decades, not years, to be recovered (Jones, 1992). The morphology of the seafloor is changed over time, as trawl gear displaces sediments and reduces the original complexity (Puig et al., 2012). Bottom trawling has become a driver of deep seascape evolution and is comparable to areas destroyed by large-scale agricultural ploughing (Puig et al., 2012).

1.1.3 Underwater Cultural Heritage as Both Natural and Cultural

UCH can support ecological marine biodiversity and helps boost sea connectivity. A paper by Kirstin S. Meyer-Kaiser and Calvin H. Mires coined the term ‘Maritime Heritage Ecology’, a field that must be further explored (Meyer-Kaiser & Mires, 2022) and the importance of which is highlighted in chapter 6. This is because cultural heritage and natural heritage are intertwined. UCH can support ecological marine biodiversity and helps boost sea connectivity. Natali Pearson and Benjamin Thompson argue that it is beneficial for sites with high UCH and high natural heritage to co-occur and be used strategically together (Pearson & Thompson, 2023).

Over time, shipwrecks come into equilibrium with the marine environment around them and become part of the benthic topography (Brennan et al., 2016). Trawling destroys this equilibrium, which often has been balanced for centuries (Brennan et al., 2013). Shipwrecks function as artificial reefs and are crucial to habitats. They provide shelter for juvenile species, add hard materials to an otherwise soft seafloor, and can be as indispensable to the seafloor ecology as a natural coral reef or seamount. Waters around protected wrecks have been documented to produce higher fish population and biomass than in areas of high trawling with no structures on the seafloor (Brennan, 2016; Krumholz & Brennan, 2015). Through this process of ‘spill over’, protected shipwrecks can help increase the strength of surrounding fish stocks. Thus, shipwrecks should not be viewed solely in a cultural significance context. They are part of the natural ocean landscape as well and our Ocean Heritage.

Trawling can also cause damage to potentially polluting shipwrecks (PPWs) and further hurt the seabed ecosystem (Brennan et al., 2023). The topic of PPWs is covered in Michael Brennan’s edited volume Threats to Our Ocean Heritage: Potentially Polluting Wrecks and a recent article highlight, through case studies, the risk to oil-containing shipwrecks posed by trawling (Brennan et al., 2023).

It is difficult to map the history of trawling on sites, as many visible trawl scars on the seabed fade over time, rendering them invisible to an archaeologist investigating the site. There have been a few regional studies in recent years, though, that clearly illustrate the danger faced by historic sites. In this book, after an introduction to the history of bottom trawling and the ecological damage caused by mobile fishing gear, Maria Peña Ermida highlights the legal context within which bottom trawling sits, and advocates for the precautionary principleFootnote 1 and duty to protect UCH within the marine environment.

Next, case studies from some archaeological sites destroyed by trawling are used to illustrate the destructive nature of the practice. Michael Brennan begins the case study section with an overview of his extensive work highlighting trawl damage in the Mediterranean and discussing more recent scholarship. The work done by Brennan and the team in Turkey presents a method ‘to truly quantify change to a shipwreck site over time by bottom trawling’ by conducting return visits and repeated surveys to sites. It is proposed that ‘more work like this is needed to illustrate the threat posed to shipwrecks’.

The chapter from Jan Majcher, Rory Quinn, Gert Normann Andersen, and David Gregory explores the impact of bottom trawling on individual shipwreck sites. The authors discuss shipwrecks as process-response systems, which over time reach a state of quasi-equilibrium that can be disrupted by the physical disturbance of bottom-contact fishing. They draw on examples from recent geophysical surveys carried out in the Irish, Baltic, and North Seas, examining the potential of contemporary geophysical techniques in tracking changes at underwater sites induced by bottom trawling. Furthermore, knowledge gaps related to the impact of bottom-contact fishing on UCH are identified, as well as the challenges associated with addressing them. It can be difficult to directly detect evidence of disturbance on dynamic seafloors, but detailed examination of wreck distribution may provide some clues to whether structural damage to the ship can be attributed to bottom trawling. The chapter concludes with the authors advocating for more case studies to better understand the impact of fishing on shipwreck sites.

Calvin Mires, Benjamin Haskell, and Kirstin Meyer-Kaiser use a US National Marine Sanctuary, Stellwagen Bank (SBMNS), as a case study to show the complexities of protecting UCH at risk for trawling while also working within unique situational requirements. SBMNS is in New England, where fishing activities are an integral part of many people’s livelihoods and have been since long before the sanctuary. Additionally, as a national sanctuary, Stellwagen’s management is also bound to facilitate public and private activities, like fishing, while also protecting the sanctuary’s resources, like Ocean Heritage. Along with providing images that show trawling’s negative impacts on both natural and cultural heritage, the authors also deliver a case study that highlights the voice of fishers in the area, and the needs of all stakeholders. They show the necessity to integrate maritime historical ecology into management systems because the Ocean Heritage that needs protection encompasses both natural and cultural resources. They also suggest that ‘UCH offers many opportunities to understand ocean processes, and its archaeological and ecological roles are intertwined’. Maritime Heritage Ecology (MHE) is part of a solution for Stellwagen’s trawling management dilemma.

Ben Ferrari, Antony Firth, David Gregory, and Louise Sanger also discuss a road to safeguard Ocean Heritage from trawling in a way that, crucially, also safeguards fishers. They highlight the ‘shared concerns between heritage managers and other stakeholders in the context of a complex marine management and stewardship environment’, and the needs for both evidence-based characterisations of the impacts of fishing, and their integration into consideration of site formation. They introduce three exciting new initiatives focused on this: The European Research Council’s Project ENDURE, Lloyd’s Register Foundation’s work on UCH protection in the context of engineering a safe, sustainable ocean economy, and Historic England’s work to engage with fishers to mitigate damage to UCH and develop better management regimes. They tie their work to the notion of a rapidly growing Blue Economy and the future strains that will be placed on ocean systems in the decades to come. This leads to the conclusion of this volume, where possible steps forward are discussed and a call to action is made.

1.2 Steps Forward

Underwater policies formulated to manage offshore fishing based on cultural preservation are lacking. Archaeologists are significantly behind benthic ecologists and fishery management professionals in advocating for regulation. Some trawling restrictions have been placed after backlash in the 1990s when ecologists and fisheries experts, well aware of the dangers of trawling, lobbied for more restrictions. This research and advocation for regulation is a good start but needs more activism led by archaeologists. There is a preferred policy for in situ preservation considered as a first option in the 2001 UNESCO Convention but some practical measures for site managers to address the threats from bottom trawling are needed. If in situ preservation is to be supported, moorings should be added so that shipwrecks, when left in place, can become artificial reefs. However, what is needed most is for states and international fishing organisations to ban bottom trawling at and around identified UCH sites, as has already been done for some seamounts. Most importantly, trawling damage should not be allowed as a justification for salvage by treasure-hunting companies either, as Michael Brennan discusses in Chap. 8.

These results cannot be achieved without the voice and support of the fishing community. Wrecks can also present problems to fishers. When nets snag, gear is lost or ruined and can be costly to replace. Shipwrecks can also endanger the lives of those onboard vessels. In Britain, from 1976 to 2005, around 16 vessels capsised after gear was snagged on obstructions, and many lives were lost (Atkinson, 2012). Although some shipwreck sites have only been found because of fishers’ reports, there is no requirement for them to do so. A clearer partnership between archaeologists and fishers is needed and archaeologists must understand the context fishers operate in to communicate effectively.

The steps we take to minimise trawling damage to Ocean Heritage can pave the way for other important ocean exploitation. Climate change will continue to threaten our ocean (for example, sea-level-rise sinking previously terrestrial sites) and we know ecologically why it is important to protect the ocean. While there are many unknowns regarding deep-sea biodiversity and ecosystem services, what we do know clearly points to vast and far-reaching damage. In other words, we know enough from the existing trawling damage that tells us we should stop similar practices, like seabed mining, immediately.

We must use precautionary measures, explained by Maria Peña Ermida in Chap. 3 and not start further exploitative practices. This is particularly important when talking about the deep-sea, since it is often left out of conversations about the ocean, which in turn have been left out of discussions about climate and environment. In fact, these things are all crucial and deeply connected. We cannot predict what sites are yet to be discovered and which are historically significant. Trawling is a danger, both to fish populations and habitats, as well as cultural landscapes. There should not be a choice between humans and the natural world. Restrictions must be passed as soon as possible to prevent further destruction to our Ocean Heritage.