People's Democratic Republic of Yemen: Evaluation of Soil Status in some of the major agricultural areas in PDRY

Land and Water Division

People's Democratic Republic of Yemen: Evaluation of Soil Status in some of the major agricultural areas in PDRY

Consultant's report.

Year of publication 1983

Pages 106 p.

Author Land and Water Division

Product type Project

Category Programme / project report

Edition 1

Full item page

Language English

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Third report of mesh selection studies conducted in the People's Democratic Republic of Yemen on the cuttlefish Sepia pharaonis 1983

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The results of a third cod-end mesh selection trial involving the alternate haul method are described. All cod-ends were made from single braided polyetheylene, and the mesh sizes used were 7.0 cm, 10.3 cm, 12.4 cm, 14.1 cm, 15.2 cm, and 16.9 cm; the smallest size being taken as the standard against which the others were compared. The relationship between the 50% selection lengths and mesh sizes, was found not to be different from those of the earlier two trials; combining the results from all t rials gave: 50% selection length (cm) = 2.15 x mesh size (cm) - 9.34; whose correlation coefficient is highly significant (at P<0.05).
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Prediction of the annual catch of cuttlefish from the People's Democratic Republic of Yemen during 1982 1982

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The beginning of the season catch per standard fishing effort is used to predict a 5000 tons catch of cuttlefish during 1982 for the People's Democratic Republic of Yemen. The estimation procedures included determining the catch per standard fishing effort in May 1982, from the operational statistics of a non-standard vessel, plus knowledge of the relative fishing power of the vessel. This value was then used to obtain an initial prediction of the annual catch from the relationship (y = 1.8 + 0. 5 x) where y is the annual catch in thousand tones, and x is the May catch per unit effort in tones per standard fishing day. The initial prediction was subsequently adjusted to account for the fishing effort regime expected to apply during 1982 being substantially different from that applying during the earlier years of the fishery.
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Second report of mesh selection studies conducted in the People's Democratic Republic of Yemen on the cuttlefish Sepia pharaonis 1982

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This paper describes a repeat of an earlier study by the authors, concerning the mesh selection properties of trawl cod-ends of various mesh sizes on the cuttlefish Sepia pharaonic. A brief resume of the findings is as follows: the estimated 50% selection lengths with 95% confidence limits for single braided polyethylene cod-ends of 12.4 cm, 13.6 cm and 16.8 cm mesh sizes were 17.87+0.28 cm, 20.74+- 0.53 cm and 26.95+-1.07 cm; the 50% selection lengths and selection ranges were very similar to t hose obtained in the earlier study in respect to the 12.4 cm cod-end, but higher in respect to the 13.6 cm cod-end; the 16.8 cm cod-end had not been previously used; the previously held assumption that the 50% selection lengths and cod-end mesh sizes were proportionally related was seen as inappropriate, and hence also the estimation of selection factors; the more appropriate relationship was seen to be one of non-proportional linearity, and the regression equation considered most compatible wit h the observations as 50% selection length (cm)=2.03 mesh size(cm) -7.41; for a chosen value of the 50% selection length, this equation gives substantially different values for the choice of appropriate cod-end mesh size, than the selection factors estimated from the earlier study.