trawl


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Related to trawl: trawl net

trawl

Sea fishing
1. a large net, usually in the shape of a sock or bag, drawn at deep levels behind special boats (trawlers)
2. a long line to which numerous shorter hooked lines are attached, suspended between buoys
3. Angling another word for troll (sense 2)

Trawl

 

a pass fishnet towed through the water by a special ship, called a trawler; it is designed to catch fish such as cod, haddock, banded sea perch, and other marine life.

A trawl is a conical sack of netting that is held open by rigid elements (a beam trawl) or by the hydrodynamic forces that arise when the trawl is moved (an otter trawl). The second type predominates in modern fishing. In trawling, the fish enter the mouth of the trawl and are drawn into the cod, which is the narrow end part. After the trawl is hauled on board the trawler, the cod is untied and the fish are unloaded into the hold or onto the deck.

There are several types of trawls, such as benthic, bathypelag-ic, midwater (which catch fish in the midwater, or pelagic zone), and general-purpose. The headropes of the largest trawls are up to 150 m long; the vertical opening of such nets is 30–35 m, and the horizontal opening is 50 m. These trawls pass up to 6,000 cu m of water per sec. Light and electric current are used to prevent the fish from leaving the area of the trawl. Fishing is made more efficient by the use of instruments to monitor the trawl. Such instruments make it possible to keep track of the trawl opening, the level of trawling, and the accumulation of fish in the net. The manufacture of trawls from synthetic materials, such as olefin polymers and polyamides, makes possible a reduction of the hydrodynamic resistance of the trawl and an increase in its wear-resistance and service life.

REFERENCE

Fridman, A. L., M M. Rozenshtein, and V. N. Lukashov. Proektirovanie i ispytanie tralov. Moscow, 1973.

V. V. RANENKO

trawl

[trȯl]
(engineering)
A baglike net whose mouth is kept open by boards or by a leading diving vane or depressor at the foot of the opening and a spreader bar at the top; towed by a ship at specified depths for catching forms of marine life.

trawl

To sift through large volumes of data (e.g. Usenet postings, FTP archives, or the Jargon File) looking for something of interest.
References in periodicals archive ?
where NTV and NMV represent the numbers of trawl vessels and main catch vessels, respectively; PTV and PMV are powers of trawl vessels and main catch vessels; RELE is released number of larval crab, SST is the sea surface temperature.
These values are higher than reported in most other post-discard studies in Nephrops trawl fisheries (Castro et al.
Usually, an indicator of the fishing effort used in trawl fisheries corresponds to the time and duration of the trawling (Kotwicki et al, 2001); however, this effort unit is not related to the technological features of the trawl that produces the fishing mortality.
If, however, a fish is able to swim fast enough and long enough to outpace a survey trawl, sampling efficiency will be reduced.
Except for the grouping of by-catch by species in order to detect fish preference behavior among the dolphins, by-catch was discarded in a manner similar to other commercial shrimp trawl vessels.
Likewise, the ideal vessel required to tow the most-used trawl in 1995 (46'semi-balloon model) was compared with that of 2010 (37' Korean model).
The device also became easily clogged with debris that caused the trawl to become deformed, resulting in the capture of turtles and the loss of shrimp.
Because of the importance of a sustainable use of marine resources, a traditional trawl and a modified trawl were tested in the Gulf of Tehuantepec, Mexico, in order to assess efficiency on by-catch reduction in shrimp trawling; cruises were carried out during commercial and shrimp ban seasons.
Dew said official trawl bycatch figures are low because none of the catcher boats carried observers in those days, and only about a quarter of processor vessels carried observers.
Another effort involves a private sector buyout of trawl boats that have been damaging the Monterey Bay National Marine Sanctuary for several decades now.
Truancy trawls will be held nearly every day in Middlesbrough town centre and the districts as part of the three-week national campaign.
of deep-sea fish and corals upon which they thrive are depleted and their habitats severely damaged by the fishing industry, which drags trawl nets along the bottom.