Quantification of bottom trawl fishing damage to ancient shipwreck sites

Bottom trawl fishing is among the most destructive anthropogenic pressures acting on benthic ecosystems, but the full extent of the damage is undocumented because of the limited number of deep-sea observations of impacted regions (e.g., Brennan et al., 2012Brennan et al., , 2016. As part of its continuing ocean exploration mission, in 2011, E/V Nautilus conducted a remotely operated vehicle (ROV) survey along a transect in a submarine canyon in the Mediterranean's Alboran Sea off southern Spain at depths ranging from 1,200 m to <300 m . This exploration along the South Alboran Ridge offered the opportunity to directly observe with video the bathymetric extent and intensity of recent trawling damage to the seafloor in this area. This dive revealed large furrows running in multiple directions caused by trawl doors scraping across the seabed. Little biological activity was evident in the depth ranges where these scars were observed. The destructive nature of bottom trawl fishing should be viewed with the same public affront as subaerial clearcutting of forests and strip-mining. The only difference is that the ocean hides trawl damage from the public eye. The more we explore the deep sea, repeatedly map the seafloor with sonar, and observe the seabed and its ecosystems with video captured by ROVs, the greater we can understand the full impacts of trawling.The deleterious and nonselective damage that trawling operations cause to the seabed has been a subject of concern and debate among ecologists and fisheries managers for decades (e.g., Caddy, 1973;Jones, 1992;DeAlteris et al., 1999;Demestre et al., 2015). Bottom trawls have a long-lasting impact beyond their removal of large quantities of fish from the ecosystem, including bycatch. Trawling destroys benthic habitats and hard ground for invertebrates, smooths over seabed morphology, and resuspends sediments (e.g., Watling and Norse, 1998;Ivanović et al., 2011;De Juan and Demestre, 2012;Lucchetti and Sala, 2012;Norse et al., 2012;Martín et al., 2014a). In the Mediterranean, the trawl fleet works along both the continental shelf and the continental slope. Trawls catch many species, although only some of them are targeted, including blue whiting (Micromesistius poutassou), hake (Merluccius merluccius), red mullet (Mullus spp.), octopus (Octopus vulgaris and FIGURE 1. The ROV transect began at nearly 1,200 m on flat, muddy seabed, with small mounded burrows and clear bioturbation. Below 850 m, no trawl marks are evident. Macrofauna, including rattail fish, sea urchins, crabs, and blackmouth catshark, were observed in the area. FIGURE 2. At 0530 GMT, Nautilus crossed paths with a trawling vessel and caused the team to slow the ROV transect. When the vehicles reached the area the where the fishermen were operating, fresh trawl marks were visible on the seabed. New trawl marks are crisscrossed with older scars, although all appear recent, with rectangular-shaped edges rather than the U-shaped scars that develop once they become partially filled in with sediment. FIGURE ...

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Bathymetric Extent of Recent Trawl Damage to the Seabed Captured by an ROV Transect in the Alboran Sea

Brennan

Canals

Coleman

et al. 2015

Oceanog

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“…Research has shown that those ancient wrecks that lie within the trawling exclusion zone are mostly or fully intact, whereas those lying outside the limit have suffered significant damage from trawls (Brennan et al ., : 64–67; Krumholz and Brennan, : 130; Brennan et al ., : 84). In addition, the better‐preserved wrecks, serving as artificial reef habitats, demonstrated more abundant fish populations and biodiversity compared to those degraded by trawling (Krumholz and Brennan, : 131–132; Brennan et al ., : 87). With these data, a strong case can be made that the creation of marine protected areas with a high concentration of shipwrecks can result in both improved protection of maritime cultural sites and an increase in fish population in adjacent fishing grounds through adult fish spillover.…”

Section: Discussionmentioning

confidence: 99%

“…These showed that the site changed significantly, with >95% of the artefacts moved, including a conspicuous notched timber now missing. Calculations from comparing the two survey data sets indicated that more than 15m 3 of material was removed from the site between visits (Brennan et al ., : 83–87).…”

Section: Expedition Background and Methodologymentioning

confidence: 99%

“…In partnership with Turkish colleagues, the expedition adopted the principle of in situ preservation as a first option in accord with the UNESCO Convention for the Protection of the Underwater Cultural Heritage (UNESCO, 2001) and implemented a non-intrusive, non-sampling mode of survey and mapping. Eregli E, the oldest of the 12 wrecks, was mapped after its initial discovery in 2011, then remapped the following year (Davis et al, 2014;Brennan et al, 2016) (Fig. 2).…”

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The Ereğli E Shipwreck, Turkey: an early Hellenistic merchant ship in the Black Sea

Davis

Brennan²,

Opaiţ³

et al. 2017

International Journal of Nautical Archaeology

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A shipwreck from the early 3rd century BC was discovered in the Black Sea's suboxic depths off Ereğli, Turkey, during the 2011 E/V Nautilus expedition. Remote investigation revealed the trawl‐damaged remains of a merchant ship carrying multiple amphora types associated with Aegean and Pontic production areas. Also discovered were elements of the ship's hull that show evidence of both pegged mortise‐and‐tenon and laced construction. The wreck provides crucial archaeological evidence for both maritime connectivity and ship‐construction methods during a period of political and economic transition.

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“…Bottom trawling has destructive effects on priority habitats (e.g., coral community, coralligenous formations, seagrass beds) which are targets for conservation actions [12][13][14]. In addition, marine geoarchaeological sites have also been heavily impacted by trawl-fishing [15,16]. The amount of the damage done depends on the spatial extent and the frequency of trawling [17].…”

Section: Introductionmentioning

confidence: 99%

Automatic Detection of Trawl-Marks in Sidescan Sonar Images through Spatial Domain Filtering, Employing Haar-Like Features and Morphological Operations

et al. 2019

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Bottom trawl footprints are a prominent environmental impact of deep-sea fishery that was revealed through the evolution of underwater remote sensing technologies. Image processing techniques have been widely applied in acoustic remote sensing, but accurate trawl-mark (TM) detection is underdeveloped. The paper presents a new algorithm for the automatic detection and spatial quantification of TMs that is implemented on sidescan sonar (SSS) images of a fishing ground from the Gulf of Patras in the Eastern Mediterranean Sea. This method inspects any structure of the local seafloor in an environmentally adaptive procedure, in order to overcome the predicament of analyzing noisy and complex SSS images of the seafloor. The initial preprocessing stage deals with radiometric inconsistencies. Then, multiplex filters in the spatial domain are performed with multiscale rotated Haar-like features through integral images that locate the TM-like forms and additionally discriminate the textural characteristics of the seafloor. The final TMs are selected according to their geometric and background environment features, and the algorithm successfully produces a set of trawling-ground quantification values that could be established as a baseline measure for the status assessment of a fishing ground.

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Quantification of bottom trawl fishing damage to ancient shipwreck sites

Cited by 33 publications

References 28 publications

Bathymetric Extent of Recent Trawl Damage to the Seabed Captured by an ROV Transect in the Alboran Sea

Bathymetric Extent of Recent Trawl Damage to the Seabed Captured by an ROV Transect in the Alboran Sea

The Ereğli E Shipwreck, Turkey: an early Hellenistic merchant ship in the Black Sea

Automatic Detection of Trawl-Marks in Sidescan Sonar Images through Spatial Domain Filtering, Employing Haar-Like Features and Morphological Operations

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