Trawling

A preliminary mass-balance trophic model was constructed for the coastal fisheries ecosystem of the West Coast of Peninsular Malaysia (0 - 120 m depth). The ecosystem was partitioned into 15 trophic groups, and biomasses for selected groups were obtained from research (trawl) surveys conducted in the area in 1987 and 1991. Trophic interactions of the groups are presented. The network analysis indicates that fishing fleets for demersal fishes and prawns have a major direct or indirect impact on most high-trophic level groups in the ecosystem.

The biological effect of fishing bans in tropical waters is considered. In the Philippines, the Samar Sea was closed to trawlers in November 1976; a fishery survey was carried out to monitor possible changes in the fish stocks. In spite of the ongoing activities of a few small trawlers, the biomass of fish in the Samar Sea increased constantly during the survey period. Thus, it is concluded that the imposition of a trawling ban is a suitable tool in tropical waters to protect the vital interests of the sustenance fishery by helping heavily exploited fish stocks to recover.

Demersal surveys from the southwest coast of India were analyzed to determine the general pattern of distribution of demersal species assemblages in the area. Seasonality is pronounced, indicating three major periods, pre-monsoon, monsoon and post-monsoon. Each of the periods is characterized by different oceanographic circulation patterns that mainly determine the pattern of distribution of species assemblages. Spatial analysis confirmed that the Wadge Bank has the highest potential for producing good quality fish.

Yield-per-recruit analyses were performed on catch data of the Ivory Coast trawl fishery in order to identify the mesh size and levels of fishing effort most approprate. Results show that at present levels of fishing mortality an increase of age/size at first capture would bring about a large increase in yield-per-recruit for all species considered. Management implications regarding increasing mesh size are considered.

Average towing speed by Dutch beam trawlermen has fallen substantially between 2002 and 2009. Changes in towing speed are related to changes in oil price. The price of their valuable main target species (sole, Solea vulgaris) did not influence towing speed. The aim of this Short Communication is to explore the hypothesis that changes in trawling speeds are directly related to changes in oil price using time-series data.

A mass-balance steady-state trophic model of the coastal fisheries ecosystem off the West Coasts of Sabah and Sarawak, Malaysia (10 - 60 m depth) was constructed using the Ecopath software. The ecosystem models were partitioned into 29 ecological/trophic groups. The input values (e.g. biomasses) for selected groups were obtained from the research (trawl) surveys conducted in the area in 1972. The estimated mean trophic level of the fisheries catch for both models is about 3.3.

The Ecopath approach and software were used to construct a trophic model of the coastal fisheries ecosystem of the southwest (SW) coast of India. The model consisted of 11 ecological groups and used estimated landings from all areas along the southwest coast (based on the sample surveys conducted by Coastal Marine Fisheries Research Institute for the years 1994, 1995 and 1996). The trophic model suggests high catch levels, particularly for the large and medium predators, demersal feeders and detritivores.

Thailand is currently one of the ten largest fishing nations in the world. In 1996, fish production reached 3.7 million t with 90% of the production coming from the marine fisheries sector and 10% from inland fisheries. Thai fishing operates in four fishing grounds namely, the Gulf of Thailand, the Andaman Sea, the South China Sea and the Bay of Bengal. However with the establishment of the Exclusive Economic Zone (EEZ) in 1977, Thailand lost over 300 000 km2 of traditional fishing grounds.

Bangladesh has an exclusive economic zone (EEZ) of 164 000 km2 and a continental shelf area of 66 440 km2. Artisanal (small scale) fisheries extend from the coast to 40 m while industrial (commercial scale) fisheries operate beyond 40 m depth. The coastal fisheries of Bangladesh exploit a complex multi-species resource. There are 18 demersal and pelagic species, seven species of larger pelagic and 10 shrimp species that are commercially important among the fishes exploited.

Sri Lanka is an island country with a land area of 65 610 km2. With the declaration of the exclusive economic zone (EEZ) in 1976, the country gained sovereign rights over an ocean area of 536 000 km2 and EEZ extending from 24 to 200 nm. The continental shelf is about 26 000 km2 with an average width of around 22 km, and the coastline is 1 100 km long. The total annual fish production of Sri Lanka was 25 000 t in 1952 and 269 850 t in 1998. Major fish species caught in Sri Lankan waters are skipjack, blood fish, yellow fin tuna, mullet, shark, trevally, Spanish mackerel, prawns, lobsters.