Trawling Operations Research Articles

えびひき網のえい網時間が漁獲効率に与える影響

A shrimp Metapenaeopsis acclivis (RATHBUN) is caught commercially as a bait for long-line fishing in the western part of Wakasa Bay off Kyoto Prefecture. The shallow parts of the area of less than 40m depth are optimal area of distribution of this species. Beam trawlings were conducted experimentally in this area in May and October 1982. The fishing boats employed had a displacementof 3 gross tons with a 35 H. P. engine. The times of trawling operations were 15, 30, 45, 60, 75, 90 and 120 minutes per haul at a speed of 1-2 knots and three kinds of nets with different cod-end in stretched mesh size, 13.0mm, 14.3mm, 15.8mm, together with a cod-end cover of 4mm mesh size, were alternately used.Catches of shrimp in number increased linearly with the protraction of towing duration. The difference in catches between May and October depended upon the shrimp density, which in October seemed to be about 1.8 times as much as in May.Shrimps ranged from 15mm to 95mm in total length. There appeared to be a prominent group in the size distribution of shrimp in May and two prominent groups in October regardless of the towing duration. The mesh selectivity in May was sharper than that in October as a whole, because of a large number of small sized shrimps in October. In the case of rather longer towing duration than 45 minutes, the marked differences of sharpness of mesh selectivity were not discerned. As the mesh size of cod-end used became smaller, the selectivity was sharpened when towing duration were shorter than 30 minutes.

The Exploitation of African Fisheries

Substantial fisheries exist on the major lakes and rivers of Africa. The seas off the western coast of Africa are amongst the most productive in the world but the eastern coasts are relatively poor. Lake Victoria is used as a case study to demonstrate how overfishing of some stocks, such as Sarotherodon esculentus, has occurred, how it could have been predicted by conventional models developed from temperate demersal fisheries and how the situation could be improved. The difficulties of assessing multispecific fisheries, i.e. where the whole community is exploited, are dealt with particularly in relation to proposed trawling operations in the lakes. Conflict between the trawl and artisan fisheries seems inevitable. Some shortcomings of fish culture and stocking programmes are discussed and attention is drawn to the increased activities of dealers in ornamental fish and the emerging problem of pollution. Our ignorance of how river fisheries operate is considerable. Tentative estimates of yield and models of river fisheries are only just beginning to appear. It is evident that the factors involved are very different from those of lake fisheries. Off the western sea board, the coastal states are at a severe disadvantage. Not only are the products of the major industrial fisheries off South Africa and Morocco exported to the developed countries but the majority of the catch from tropical waters is taken by foreign long-range fleets. The difficulties of Ghana in establishing a distant-water fleet for food fish are contrasted with the success of the South Koreans in establishing a world-wide tuna industry mainly for export. The importance of developing the long-range capability to take advantage of the probable general increase in territorial waters is emphasised. Some of the problems associated with management of tropical demersal and pelagic stocks are dealt with and questions are raised as to the approach required to deal with these when development is the priority.

Fishery Development and Management in Thailand

After a period of stabilization lasting more than 20 years, the Thai sea fisheries developed rapidly during the past decade through the introduction of trawl fishing. Suitable nets and fishing techniques were demonstrated and introduced in the course of a German bilateral aid project. This new input, together with a high level of technical abilities among the fishermen, the availability of sufficient capital to finance a trawler fleet of more than 2,500 boats, and adequate support from the Thai Government, resulted in rapid development of trawling from small vessels. Landings were about 600,000 metric tons of groundfish from the coastal area in 1970. About half of this is for human consumption, the remainder mostly being used fresh for duck food or, after processing, as chicken food. The level of development achieved has unfortunately meant that the moderately rich bottom-fish resources of the Gulf of Thailand have become overexploited. In 1971 the catch per unit of effort had decreased to only a quarter of the original, making trawling operations only marginally economic. This points up the difficult problem of the control of fishing effort, which the Government of Thailand, no less than other nations, has not yet been able to resolve satisfactorily.

Occurrence of American Eels, Anguilla rostrata, in Waters Overlying the Eastern North American Continental Shelf

Eleven reproductively maturing specimens of the American eel, Anguilla rostrata, were collected during three independent off-shore trawling operations. Three females were taken on December 5, 1967 southeast of the mouth of Chesapeake Bay in 10–13 fathoms, one male and one female on November 5, 1969 southeast of Cape Cod in 35–45 fathoms, and six females east of Assateague Island on December 22, 1971 in 5 fathoms. Morphometrical analysis showed that the specimens were within the range of "silver" phase of Anguilla rostrata. Gonadal observations were made on all specimens.

New records of Sargassum hawaiiensis Doty and Newhouse (Sargassaceae, Phaeophyta), a deep water species

Sargassum hawaiiensis Doty and Newhouse was described in 1966 from a fragmentation specimen dredged from a depth of 50 m off Oahu, Hawaii. Until recently, no further collections have been available for study. In 1968 and 1971 new material was collected from Penguin Banks off Molokai, Hawaii, during shrimp trawling operations by the National Marine Fisheries Service vessel “Townsend Cromwell”. The specimens were obtained from depths of 183 and 200 meters.A complete description of the species is given, which differentiates it from the three other species of Sargassum recognized from Hawaii. Sargassum hawaiiensis is distinguished by a combination of characteristics, these being: simple spines on some branches, terete vesicle petioles, muticous and spherical vesicles and bifurcate receptacles with narrow sterile bridges.

Fishes Rarely Caught in Shrimp Trawl

During a three year study made of the offshore waters of Mississippi the author became interested in the fishes "rarely caught" in shrimp trawls. This report concerns all data for the project, which was carried out during 1967, 1968 and 1969. The only characteristic common to the following species is the rarity with which they are taken in regular shrimp trawling operations. Some are by no means rare in terms of total number available in the Gulf of Mexico, but it is worthwhile to report data collected as compared to others taken thirty-nine to forty-one years ago in nearby Louisiana. (Gunter, 19G5). Later Gunter (1941) listed certain rare fishes from Texas taken in both inside and outside waters. The data given here concern only offshore stations, which extended farther out than any previously reported from this coast.

The taxonomy of the monogenetic trematode Plectanocotyle gurnardi (v. Ben. & Hesse)

Specimens of Plectanocotyle gurnardi were obtained by the writer from the gills of Trigla cuculus L. and T. gurnardus L. during trawling operations at the Irish Atlantic Slope fishing grounds in August 1938 and July 1939. One specimen of Plectanocotyle gurnardi was collected from a Trigla gurnardus and seven specimens of the same parasite from eight specimens of T. cuculus, the greatest degree of infestation encountered being 3 parasites per host fish. Plectanocotyle gurnardi has been recorded previously, under one or other of the synonyms listed above, from Trigla gurnardus by van Beneden & Hesse (1863), T. Scott (1901, 1905), A. Scott (1904), Lebour (1908), and Little (1929); from T. lucerna L. by A. Scott & Little; and from Trigla ‘sp.’ by Monticelli (1899). It will be noted that the present records of the parasite are from its usual host T. gurnardus and from a new host T. cuculus.

LXVI.—Natural History Notes from the Royal Indian Marine Survey Ship ‘Investigator,’ Commander T. H. Heming, R. N., commanding.—Series III., No. 5. An Account of the Trawling Operations during the Surveying-season of 1900–1901

(1901). LXVI.—Natural History Notes from the Royal Indian Marine Survey Ship ‘Investigator,’ Commander T. H. Heming, R. N., commanding.—Series III., No. 5. An Account of the Trawling Operations during the Surveying-season of 1900–1901. Annals and Magazine of Natural History: Vol. 8, No. 48, pp. 517-526.

Report of a Trawling Cruise in H.M.S. “Research” off the South-west Coast of Ireland

The cruise, of which the zoological results are given in this report, was undertaken at the suggestion of Capt. Wharton, R.N., F.R.S. hydrographer to the Admiralty, who kindly advised me that H.M.S. “Research” was to make a fresh series of soundings off the entrance to the Channel, and put me in communication with the captain of the ship. To Capt. Aldrich I am indebted for unbounded hospitality. and attention whilst I was on board, and I take this opportunity of expressing my most hearty thanks both to him and to the officers on board for the hospitality and kindness which they afforded me, and, for the help which they gave me in the trawling operations. The “Eesearch” is a paddle vessel of 520 tons register, built last year for the express purpose of surveying, and provided with a steam winch, deep-sea trawls and dredges, and 1000 fathoms of wire rope, with accumulators and accessory tackle. The available space on board was limited; there was no separate cabin at my disposal, so Capt. Aldrich most kindly made me his guest and gave me a berth in his own cabin, and I was given as much room, as could possibly be allowed for storing my bottles and other apparatus.