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Impact of bottom trawling on deep-sea sediment properties along the flanks of a submarine canyon.

Martín J, Puig P, Masqué P, Palanques A, Sánchez-Gómez A - PLoS ONE (2014)

Bottom Line: Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears.Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites.This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea.

View Article: PubMed Central - PubMed

Affiliation: Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (ICM-CSIC), Barcelona, Spain.

ABSTRACT
The offshore displacement of commercial bottom trawling has raised concerns about the impact of this destructive fishing practice on the deep seafloor, which is in general characterized by lower resilience than shallow water regions. This study focuses on the flanks of La Fonera (or Palamós) submarine canyon in the Northwestern Mediterranean, where an intensive bottom trawl fishery has been active during several decades in the 400-800 m depth range. To explore the degree of alteration of surface sediments (0-50 cm depth) caused by this industrial activity, fishing grounds and control (untrawled) sites were sampled along the canyon flanks with an interface multicorer. Sediment cores were analyzed to obtain vertical profiles of sediment grain-size, dry bulk density, organic carbon content and concentration of the radionuclide 210Pb. At control sites, surface sediments presented sedimentological characteristics typical of slope depositional systems, including a topmost unit of unconsolidated and bioturbated material overlying sediments progressively compacted with depth, with consistently high 210Pb inventories and exponential decaying profiles of 210Pb concentrations. Sediment accumulation rates at these untrawled sites ranged from 0.3 to 1.0 cm y-1. Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears. Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites. This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea.

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Bathymetric chart of La Fonera (or Palamós) Canyon in the NW Mediterranean Sea.The main fishing grounds active on the canyon flanks are marked with grey points corresponding to Vessel Monitoring System (VMS) positions from Palamós harbour trawlers for the period 2007–2010 (see Puig et al., 2012 for details). Coring stations visited in this study are labelled based on their location in the northern flank (NF) or southern flank (SF), increasing their numbering with distance from shore. For further clarity, blue dots have been assigned to untrawled (control) and red dots to trawled sampling sites. Site NF-6 could not be sampled due to the extreme coarseness and compaction of surface sediments (see the text for details).
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pone-0104536-g001: Bathymetric chart of La Fonera (or Palamós) Canyon in the NW Mediterranean Sea.The main fishing grounds active on the canyon flanks are marked with grey points corresponding to Vessel Monitoring System (VMS) positions from Palamós harbour trawlers for the period 2007–2010 (see Puig et al., 2012 for details). Coring stations visited in this study are labelled based on their location in the northern flank (NF) or southern flank (SF), increasing their numbering with distance from shore. For further clarity, blue dots have been assigned to untrawled (control) and red dots to trawled sampling sites. Site NF-6 could not be sampled due to the extreme coarseness and compaction of surface sediments (see the text for details).

Mentions: La Fonera (or Palamós) submarine canyon (Fig. 1) is one of the most prominent submarine canyons incising the NE Spanish continental margin. The bifurcated canyon head opens very close to the coast, while its upstream (northern) flank cuts the continental shelf and upper slope transversally to the mean SW regional flow. In this way, the canyon intercepts and channelizes further offshore suspended particles that are transported by along-shore currents, resuspended during storms or episodes of dense shelf water cascading [11], [12], [13].


Impact of bottom trawling on deep-sea sediment properties along the flanks of a submarine canyon.

Martín J, Puig P, Masqué P, Palanques A, Sánchez-Gómez A - PLoS ONE (2014)

Bathymetric chart of La Fonera (or Palamós) Canyon in the NW Mediterranean Sea.The main fishing grounds active on the canyon flanks are marked with grey points corresponding to Vessel Monitoring System (VMS) positions from Palamós harbour trawlers for the period 2007–2010 (see Puig et al., 2012 for details). Coring stations visited in this study are labelled based on their location in the northern flank (NF) or southern flank (SF), increasing their numbering with distance from shore. For further clarity, blue dots have been assigned to untrawled (control) and red dots to trawled sampling sites. Site NF-6 could not be sampled due to the extreme coarseness and compaction of surface sediments (see the text for details).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4128664&req=5

pone-0104536-g001: Bathymetric chart of La Fonera (or Palamós) Canyon in the NW Mediterranean Sea.The main fishing grounds active on the canyon flanks are marked with grey points corresponding to Vessel Monitoring System (VMS) positions from Palamós harbour trawlers for the period 2007–2010 (see Puig et al., 2012 for details). Coring stations visited in this study are labelled based on their location in the northern flank (NF) or southern flank (SF), increasing their numbering with distance from shore. For further clarity, blue dots have been assigned to untrawled (control) and red dots to trawled sampling sites. Site NF-6 could not be sampled due to the extreme coarseness and compaction of surface sediments (see the text for details).
Mentions: La Fonera (or Palamós) submarine canyon (Fig. 1) is one of the most prominent submarine canyons incising the NE Spanish continental margin. The bifurcated canyon head opens very close to the coast, while its upstream (northern) flank cuts the continental shelf and upper slope transversally to the mean SW regional flow. In this way, the canyon intercepts and channelizes further offshore suspended particles that are transported by along-shore currents, resuspended during storms or episodes of dense shelf water cascading [11], [12], [13].

Bottom Line: Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears.Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites.This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea.

View Article: PubMed Central - PubMed

Affiliation: Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (ICM-CSIC), Barcelona, Spain.

ABSTRACT
The offshore displacement of commercial bottom trawling has raised concerns about the impact of this destructive fishing practice on the deep seafloor, which is in general characterized by lower resilience than shallow water regions. This study focuses on the flanks of La Fonera (or Palamós) submarine canyon in the Northwestern Mediterranean, where an intensive bottom trawl fishery has been active during several decades in the 400-800 m depth range. To explore the degree of alteration of surface sediments (0-50 cm depth) caused by this industrial activity, fishing grounds and control (untrawled) sites were sampled along the canyon flanks with an interface multicorer. Sediment cores were analyzed to obtain vertical profiles of sediment grain-size, dry bulk density, organic carbon content and concentration of the radionuclide 210Pb. At control sites, surface sediments presented sedimentological characteristics typical of slope depositional systems, including a topmost unit of unconsolidated and bioturbated material overlying sediments progressively compacted with depth, with consistently high 210Pb inventories and exponential decaying profiles of 210Pb concentrations. Sediment accumulation rates at these untrawled sites ranged from 0.3 to 1.0 cm y-1. Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears. Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites. This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea.

Show MeSH
Related in: MedlinePlus