Preservation potential of Irish Sea shipwrecks

The UK has a rich maritime heritage, stretching back over 23,000 years. It’s impossible to tell the story of our islands without talking about our relationship with the sea. This maritime past is becoming increasingly important. People are more aware of our exploitation of the sea and topics such as colonialism, slavery and immigration.

 Unpath’d Waters  aims to increase interaction with the UK’s maritime heritage by making it easier to research and easier for the public to discover and share stories in new ways.

A lack of high-quality remotely sensed data and limited research means our maritime heritage remains poorly understood. Thousands of shipwrecks around the UK coastline have been identified incorrectly or remain unknown. The 'Science and the Sea' work package is developing new methods to help solve this problem. These methods will accelerate maritime research activity and support the development of research tools designed to improve the management of UK wreck sites. Focussing on vessels lost in the Irish Sea, we’re developing methods to refine wreck site identification and methods for integrating marine scientific data with the historic record and maritime collections.

Another task for this work package is to investigate the preservation potential of the Irish Sea wrecks, with a view to underwater cultural heritage (UCH) management. As UCH is a finite resource, it is important to understand the risk historic wreck sites are under in response to increased anthropogenic and natural forcing.

Human impacts typically include trawling and ocean engineering (subsea cables, pipelines, turbines), while physical, chemical and biological processes acting in the water column and seabed naturally deteriorate wreck sites. Climate change is magnifying these natural effects.

We use acoustic remote sensing to locate and identify wreck sites, and use the resultant data to build high-definition digital models of the wrecks. You can read all about how we locate and identify wrecks in our  StoryMap #1 . When combined with environmental variables, we can model the preservation potential of these wreck sites, and assess potential risks.

Many environmental and anthropogenic processes influence site formation and preservation. Some of the key physical, bio-chemical and anthropogenic variables are: depth, substrate, salinity, dissolved oxygen, temperature, hydrodynamics, and fishing intensity.

We developed three simple preservation models, based on burial and/or exposure of UCH, and perceived threat from natural and anthropogenic processes:

Model 1 assumes the preservation potential of material buried beneath the seabed is solely dependent upon substrate conditions. As noted above, bottom type is arguably the most important variable in terms of wreck site formation, as substrate controls not only the depth of burial of UCH, but also imparts primary control on many of the other environmental variables that impact site formation. Variable weighting: 100% substrate.

Model 2 assumes the preservation potential of semi-exposed and shallow buried material is dependent upon substrate conditions and seabed fishing intensity. For example, the Nephrops fishery in the Irish Sea west is economically the most important in ICES Division VIIa and is mainly prosecuted by vessels from UK (Northern Ireland) and Ireland. This fishery occurs throughout the year and does not exhibit major inter annual changes in seasonal pattern (AFBI, 2020). Furrow marks from gear (otter doors) typically bite 20 cm into seabed.  Variable weighting: 50% substrate, 50% fishing intensity (otter trawls).

Model 3 assumes the preservation potential of fully-submerged exposed material is dependent upon substrate and oceanographic conditions. A further assumption of this model is that if these UCH sites are known to fishers, they are avoided by benthic fishing gear for fear of damage or loss. Some researchers argue that wrecks are heavily impacted by commercial fishing practices, others are less convinced.  Variable weighting: 50% substrate, 20% velocity, 10% DO, 10% salinity, 10% temperature.

We assess the risk category for each wreck site in the shipwreck databases by classifying them according to Model 3, where individual sites inherit their risk from the model output. Variable weighting: 50% substrate, 20% velocity, 10% DO, 10% salinity, 10% temperature

As part of Unpath'd Waters, Bangor University collected multibeam sonar data from over 150 wreck/obstruction sites that are listed on the UK Hydrographic Office database, including 60 sites in the Bristol Channel, 26 sites off the coast of South Wales and 63 located between the Isle of Man and Northern Ireland. 

The data from the Isle of Man wrecks were first to be examined. The resultant digital elevation models (DEMs) have a spatial resolution 0.5 m, and allow us to assess the structural integrity of the wrecks. In the next phase of research, the archaeological record (as imaged in the multibeam echosounder data) will be compared against historic ship's plans to positively identify as many of the wreck sites as possible.

Read about the methods we use to locate, image and identify shipwrecks using multibeam echosounders in   StoryMap #1 .