Bottom trawling

Global catch from bottom trawling has been estimated at over 30 million tonnes per year, an amount larger than any other fishing method.

An early reference to fishery conservation measures comes from a complaint about a form of trawling dating from the 14th century, during the reign of Edward III.

The net had maskes of the length and breadth of two men's thumbs[11] The response from the Crown was to "let Commission be made by qualified persons to inquire and certify on the truth of this allegation, and thereon let right be done in the Court of Chancery".

However, in the closing years of that century a type of vessel emerged that was capable of towing a large trawl, in deeper waters.

The reason for this peculiarity is that the destruction caused by the first trawl resulted in many dead and dying organisms, which temporarily attracted a large number of additional species to feed on this moribund mass.

A slightly different approach was developed where the "Utase Ami" or "trawled bottom net" was deployed from a sideways sailing boat.

[12] Bottom trawling has been widely implicated in the population collapse of a variety of fish species, locally and worldwide, including orange roughy, barndoor skate, shark, and many others.

These can be simple structures like "square mesh panels", which are easier for smaller fish to pass through, or more complicated devices, such as bycatch grills.

[14] Also, the repetitive passage of trawling gear over the same areas creates long-lasting, cumulative impacts that modify the cohesiveness and texture of sediments.

It can be asserted nowadays that due to its recurrence, mobility and wide geographical extent, industrial trawling has become a major force driving seafloor change and affecting not only its physical integrity on short spatial scales but also imprinting measurable modifications to the geomorphology of entire continental margins.

[23] Bottom trawling can both resuspend and bury biologically recyclable organic material, changing the flow of nutrients and carbon through the food web and thereby alter geomorphological landscapes.

[30] Multiple large-scale reviews on bottom trawling have noted that there is a great need for further studies that properly examine the effects of nutrient and toxin remobilization as well as carbon cycling,[31][32] in order to better estimate greenhouse gas emissions and hence the impact on climate change.

[33] The Secretary General of the United Nations reported in 2006 that 95 percent of damage to seamount ecosystems worldwide is caused by deep sea bottom trawling.

[34][35] A study published in Current Biology suggests a cutoff of 600 metres (2,000 ft) is a point which ecological damage increases significantly.

[36] An estimated 370 million tonnes a year of carbon dioxide stored in seafloor sediment is released by bottom-trawling fishing.

[52] The North East Atlantic Fisheries Commission (NEAFC) also recently closed four seamounts and part of the mid-Atlantic Ridge from all fishing, including bottom trawling, for three years.

All countries fishing in the region (accounting for about 25 percent of the global ocean) agreed to exclude bottom trawling on high seas areas where vulnerable ecosystems are likely or known to occur until a specific impact assessment is undertaken and precautionary measures have been implemented.

Palau President Tommy Remengesau has called for a ban on destructive and unregulated bottom trawling beyond national jurisdictions.

[53][54] Palau has been joined by the Federated States of Micronesia, the Republic of the Marshall Islands, and Tuvalu in supporting an interim bottom trawling ban at the United Nations.

The Celtic Explorer , a research vessel engaged in bottom trawling
Otter trawl
Pelagic (midwater) otter trawl. 1: trawl warp, 2: otter boards, 3: longline chains, 4 hunter, 5: weights 6: headline with floats, 7: pre-net, 8: tunnel and belly, 9: codend
Short clip of a bottom trawl of a lake and the large amounts of debris produced
Satellite image of trawler mud trails off the Louisiana coast
(A) The coral community and seabed on an untrawled seamount. (B) The exposed bedrock of a trawled seamount. Both are 1,000–2,000 metres (3,300–6,600 ft) below the surface.