Trawling and fishing

The compatibility of heritage protection and fishing practice

Thijs Maarleveld, President of ICUCH, Professor at the University of Southern Denmark (Chair)

Fishing has been one of the major reasons for humanity to roam the coasts and venture at sea. Fishing sites are important archaeological sites and all other sites at sea have been impacted by fishing through the ages. Net weights and fishing hooks from all periods following a site’s formation are the typical add-on to any assemblage and a source of knowledge both on fishing and on the site in question. Fishing is therefore an inseparable part of maritime archaeology. However, the relationship of present-day archaeologists with modern fishermen is a bit more ambiguous than with their forebears. There is a very positive side to it. Fishermen have local knowledge which is indispensable for maritime archaeologists. Moreover, they are the prime discoverers of sites, or at least they have been until swath bathymetry and integration of geophysical databases became available and fishing techniques were adapted to consume less fuel and thus to impact the sea bottom. However, the impact of bottom fisheries on the seabed has been an undeniable factor long before heritage protection was considered a serious issue, and continues to be so now that it is. It is a situation with uncomfortable side effects, as it was used as an excuse for less than responsible heritage approaches. And more often than not, there is little communication and understanding between fishermen and archaeologists working in the same area. Harsh reproaches are sometimes the result, whereas an open dialogue and relationship of heritage professionals and professionals in the fishing industry would be more helpful.

Quantification of trawl damage to premodern shipwreck sites: csae studies from the Aegean and Black Seas

Michael Brennan, University of Rhode Island, USA

(Text) (from minute 7)

The past four years of exploration by the E/V Nautilus off the Aegean and Black Sea coasts of Turkey have located 40 pre-modern shipwrecks, ranging from Archaic Greek to early 19th century. More importantly, these wrecks also range in their state of preservation, due in large part to the amount of damages to each site by bottom trawling activities. Analysis was conducted of the damage reflected by each wreck site, the extent and intensity of trawl scars visible in side-scan sonar mapping, and the proximity of each site to the coast and other areas of fishing restrictions. In the Black Sea, these results are correlated with evidence of anoxic events caused by internal wave activity at the oxic/anoxic interface, reflected by the preservation of wooden shipwrecks. These data show areas of the Turkish coast where sites are more severely threatened or where they may have already been eradicated. Damage reflected by the dispersal of wooden timbers or by broken ceramic cargos indicates areas that may be aided by additional establishment and enforcement of marine protected areas.

Impact of trawling and fishing on underwater cultural heritage sites - the Dutch experience

Thijs van Kolfschoten & Margot Kuitems, Leiden University, Netherlands

Since the fishery fleet was modernized in the 1950s, the amount of fossil material collected from the bottom of the North Sea increased considerably and thousands of fossil terrestrial mammalian remains as well as hundreds of Palaeolithic and Mesolithic artefacts have been collected. The southern part of the North Sea, in particular, is rich in mammal fossils. Analyses indicated the occurrence of at least four faunal assemblages that differ in composition and age. The oldest assemblage dates from the Early Pleistocene. A second assemblage dates from the late Early Pleistocene or early Middle Pleistocene. The most numerous are the finds with a Late Pleistocene age and the most recent faunal assemblage dates from the early Holocene. Archaeological sites e.g. in England, located at the western edge of the North Sea basin indicate that the North Sea faunal associations except for the oldest one, date from a period that hominids were present in the region. However, the context of the zoological record and the Palaeolithic and Mesolithic artefacts collected by trawling and fishing, is unknown. Still these finds should be regarded as an important part of our Archaeological Heritage and we should invest in methods to increase our knowledge about the context.

The perspective of the fishing industry on the impact of trawiling and fishing on submerged heritage

Philip Macmullen, Sea Fish Industry Authority, UK


In UK waters, as well as in the rest of Europe, the fishing industry has to come to terms with spatial planning. Awareness of underwater cultural heritage issues hitherto has generally been quite low. The southern North Sea has regularly yielded Ice Age- or land bridge-related artefacts but there has been no real perception of the existence of heritage sites per se; if recovered objects have received any sort of media coverage it has been on a par with recovered mines or other 20th century ordnance. The occasional reports of wreck-related ‘catches’ have been in the same category.
Seafish has operated its Kingfisher Charts department for over 50 years and has built up a huge database of seabed obstructions or ‘fasteners’. Virtually the entire fleet co-operates in this endeavor with the result that ‘coming fast’ is now quite an unusual occurrence.
Spatial planning, increasing recognition of the importance of heritage sites, dramatic advances in vessel monitoring systems (VMS), and moves to codify good practice in fishing all now offer the potential for a more systematic approach to marine heritage protection. This presentation outlines the potential and means by which it could be achieved.

The impact of the fishing trawling on the shipwrecks along the Italian coast of the North Adriatic sea

Carlo Beltrame, Università Ca' Foscari Venezia

© UNESCO/A. Vanzo
Shipwreck of Mercure

The impact of the fishing trawling activity on the sea floor of the Italian coasts of the North Adriatic Sea is particularly devastating. It has been calculated that from the introduction of the fishing ships with engine, every square meter of the sea bottom has been covered at least three times. The impact of the fishing activity on the shipwrecks is similar to the impact of the agriculture on the land archaeological sites. The "rapido" and the "turbossofiante" are the tools used by the Adriatic fishing fleets. The first one is composed by four rectangular metal boxes with iron teeth on the bottom which are the entrance of the nets. These boxes are towed with chains and they drag on the sea floor impacting the sand for at least some centimeters deep. They are able to damage the obstacles and they are quite strong to move heavy objects for long distances.

The site of the shipwreck Mercurio, which is a brig sunk in the 1812 during the battle of Grado, lies 7 miles off the delta of the Tagliamento River 17 meters deep. It is a well preserved and coherent wreck when it was discovered in 2001, protruded from the sand with only a tumulus of concretions and some iron carronades all around it. The discovery of the site occurred thank to the "fishing" of a carronade, weighting one ton, which was recovered by one of the boxes of the rapido. Another box was lost because it got caught on another carronade. There is suspect that other carronades have been moved for some meters on the sea bottom by other fishing trawls.

The "turbosoffiante" is the most destructive tool. The ship tows a big box, weighting 350 kg, for the fishing of the mussels which, thanks to a water dredger, excavates the seafloor making a trench two meters large and at least 30 cm deep. It is obvious that it destroys everything it meets.

The first side scan sonar tracing made in 2001 shows clear traces of the circular passages of both these fishing tools. We do not know which has been the damage made before our arrival but we can say that after 2001 no important impact has been recorded although sometimes the fishermen cross the site "forgetting" that there is a shipwreck. This summer, fishermen working 50 meters from the wreck, while the excavation was open and the site was exposed, have been found.

One of the most impressive examples of the effects of the passage of fishing trawl over an ancient shipwreck is the Roman wreck of Grado. Before the recovery, the shipwreck was located 5 miles off Grado and was 15 meters deep. When it was discovered, they found a level of amphoras without the necks. We can say that the typical effect to the passage of the trawls on the cargos of amphoras is their decapitation. On the Grado shipwreck it has been supposed that an upper level of amphoras have been completely destroyed by the trawls.

There is a very well preserved shipwreck 13 km off Caorle at a depth of about 33 meters. It has been protected for two millenia by a thick layer of concretions. The concretions have covered at least two strata of amphoras still in situ with a capsule. In the past years, the passage of trawls has created some holes in the concretion which allow us to see the cargo. The artificial protection made by metal nets and sand bags have been strappate more time by the continuous passage of the trawls. Even with this impact, the thick layer of concretion actually is the best protection against the trawls although sample-excavations made by the Archaeological Superintend have partially compromised this equilibrium.