How Trawling Works

kelolalaut.com - Trawling is one of commercial fishing methods that works by pulling a large fishing net through the water with one or more boat. The net that use in this methods is called trawl, and the boat that used for trawling is called trawler. This trawler boat has many different size, from small boat to a large factory trawler. The trawling process can be carried out by one or two trawlers (pair trawling).

There are two types of trawling, which is bottom trawling and midwater trawling. This method is facing two major problems that has been noticed because it is causing seabed damage (especially bottom trawl methods) and by-catch. Some solution of this problems has been introduced such as changing the mesh and net structure to minimize the by-catch. The preservation seabed and fish spawning ground are managed by various regulation in some countries.  

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Bottom Trawl

Bottom trawl or also called by demersal trawl are used to catch fish and prawns that live on or near the sea floor. The catch include flathead, pink ling, blue grenadier, silver warehou and prawns. Bottoms trawl has trawl boards/doors that made of timber or steel to keep the mouth of the net open on the bottom. Bottom trawl are designed differently depending on the target of the catch.

The main issue with the bottom trawling is this type of gear can catch unwanted species of sea creatures. This is known as by-catch and it is monitored by on-board fishery observers. Others problem is it can cause significant damage to the sensitive habitat like corals, sponges, and seagrass if it trawled. To prevent this damage, management arrangement like specify the area of fishing ground are used. 

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Midwater Trawl

Midwater trawl is use to catch fish in the water column and are used to catch various pelagic fish species. Midwater trawl nets may incorporate acoustic technology to tell the position of the net in the water column, the opening/spread of the net and the volume of fish that entering the net. This gear is often used to catch small pelagic fish like mackerel and sardine. Midwater trawling is involves towing a net behind a boat, the net then connected to the boat by the warp wires. The opening of the net is spread by using two large boards known as otter boards. 

Midwater trawl nets mostly shaped like a cone with wide opening to catch the fish and narrow end called cod end where fish are collected. Midwater trawl has minimal impact on the environment because it doesn’t directly come in contact with sea floor. But sometime there are some by-catch or unwanted species that get caught as well.

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