Trawls

Trawl Fishing

             Catching stocks of demersal fish in commercial quantities in the Philippines using trawls became popular after the liberation period (1945-1946). During the first three years of operation, fishermen were satisfied with the efficiency of the beam trawl. Subsequently, they used otter boards to replace the wooden beam to increase opening of their nets. The adoption of the otter trawl by the fishing industry resulted in many improvements in its design, construction and operation.
             With the introduction of twin engines on trawlers in 1958, the trawling speed was increased to catch the fast swimming fish. Filipino fishermen continued to modify their trawl nets to have a higher vertical opening. In the latter part of 1966, the Norwegian type trawl was adopted by the industry.
             During the early part of the 1970s, a German trawl net was tried in Manila Bay. This was the Hermann Engel type with mouth circumferences of 294 x 160 mm mesh, and 418 x 160 mm mesh. It was made of pure nylon twine. The boat used had a gross tonnage of 44.9 tons and was propelled by 2 x 225 Hp Gray Marine engines. Other vessels have 40 gross tonnages and are powered by 2 x 250 Hp Cummins engines.
              The German, two-seam, high-opening trawl net was used by trawlers in Manila Bay and other trawl fishing grounds. This net increased the towing speed from 2.5 to 3.5 and 4 knots as wings and belly mesh sizes were bigger compared to the locally made net. The otter board measured 109 cm x 214 cm and weighed 90 kilos. In the fishing trials, the German trawl was more efficient catching 90.94 kg per hour while the locally made net was 32.48 kg. per hour.
              With the expansion of fishing operations to rough grounds, plastic roller bobbins and oval boards were tried. The set of plastic bobbins was 38 m long consisting of different bobbin sizes, chain link, cable wire, iron discs (washers) and rubber discs. The bobbins were directly attached to the ground rope by way of the chain links. The oval boards with three-slit opening weighed 326 kg. each, rigged with fore and aft rigid brackets. The chain back strop is provided with the block roller where the Kelly’s eye was also attached. Comparing the trawling speed of 3 knots with a rectangular board, the plastic bobbins and oval board registered a faster trawling speed of 3.5 to 3.7 knots. The oval board offers less resistance while the bobbins roll instead of plowing the bottom. The bobbin operations were considered successful in rough grounds with a harvest of big groupers and snappers.
             With the desire of fishermen to catch the semi-pelagic fish, more modifications have been introduced into the trawling industry. Wings and bellies now use 2 m or more mesh sizes to increase height opening and towing speed.
             Lately, in 1992, the bottom pair trawl was introduced by Chinese fishermen under a joint venture agreement. Each boat has a V-shaped steel-hull of 180.74 gross tonnage and is powered by three cummins diesel engines of 400 Hp. The trawling operation requires the synchronization of two vessels to pull the net. No trawl boards are used. The main species caught by bottom pair trawl during ten (10) days fishing operation in Northern Palawan is shown in Table 19.
             Presently, the otter trawl is the most effective fishing gear for catching demersal species in muddy-sandy bottom conditions. Additionally, it contributes some pelagic species. It is used both by the municipal and commercial fishermen. In the commercial sector, it can be seen that slipmouth dominated the catch at 14,328 MT or 25.61% of the trawl production in 1995 (Table 20). Noteworthy for consideration is the dominance of pelagic species such as sardines, mackerels, scad and anchovies which indicate the present high mouth opening of the gear.

TABLE 19 FISHING OPERATION IN NORTHERN PALAWAN

TABLE 20 MAJOR SPECIES CAUGHT BY COMMERCIAL TRAWL, 1995(METRIC TONS)

Total trawl commercial production = 55,949 metric tons.
Source : Fisheries Statistics 1995, Bureau of Agricultural Statistics.

Fishing Gear and Methods

         Trawl fishing in the Philippines can be grouped into three major categories:
   

   3.1 Otter Trawl
   3.2 Pair Trawl
   3.3 Beam Trawl