Trawling and fishing impacting underwater cultural heritage sites

The results of trawling on a seabed

Fishing has always been one the main reasons for the human kind to roam and venture the seas. Fishing and fishers are an inseparable part of maritime archaeology.

Ancient fishing sites are of great archaeological interest, as for instance net weights and fishing hooks from historic periods are a source of knowledge both on fishing and on the site in question. But often fishing has also a negative impact on submerged sites.

The impact of fishing activity on shipwrecks is similar to the impact of the agriculture on land archaeological sites. Fishers have the best knowledge of their area and have been, up until the advance of new technologies at least, the prime discoverers of sites. Fishing, however, has also often been the cause of negative impact on cultural heritage sites. More often than not, the communication and understanding between fishers and archaeologists is very poor. Harsh reproaches can be the result, whereas an open dialogue of heritage professionals and professionals in the fishing industry would be helpful.

Trawling activities are today a major issue concerning the preservation of underwater cultural heritage. Its impact on the sea floor of the Italian coasts of the North Adriatic Sea for example is particularly devastating. The "rapido" and the "turbossofiante" are tools used by the Adriatic fishing fleets. The "turbosoffiante"  tows a big box, weighting 350 kg over the seabed to fish mussels. It does however also, thanks to a water dredger, excavate the seafloor producing a trench two meters large and at least 30 cm deep. It is obvious that this tool destroys everything it meets. The good news is, that sites begin to be recorded and can sometimes be avoided by the fishing industry. More such efforts are needed.

 

Two opinions and case studies below:

 

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

Michael Brennan, University of Rhode Island, USA (Text)

 

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 area.

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

Carlo Beltrame, Università Ca' Foscari Venezia

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.

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