Estimating the underwater shape of tuna longlines with micro-bathythermographs

Mizuno, Keisuke and Okazaki, Makoto and Nakano, Hideki and Okamura, Hiroshi (eds.) (1999) Estimating the underwater shape of tuna longlines with micro-bathythermographs. La Jolla, CA, Inter-American Tropical Tuna Commission, 38pp. (Inter-American Tropical Tuna Commission Special Report, 10)

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An estimation method for the three-dimensional underwater shape of tuna longlines is developed, using measurements of depth obtained from micro-bathythermographs (BTs) attached to the main line at equally spaced intervals. The shape of the main line is approximated by a model which consists of a chain of unit length lines (folding-rule model), where the junction points are placed at the observed depths. Among the infinite number of possible shapes, the most likely shape is considered to be the smoothest one that can be obtained with a numerical optimization algorithm. To validate the method, a series of experimental longline operations were conducted in the equatorial region of the eastern Pacific Ocean, using 13 or 14 micro-BTs per basket of main line. Concurrent observations of oceanographic conditions (currents and temperature structure) were obtained. The shape of the main line can be calculated at arbitrary times during operations. Shapes were consistent with the current structure. On the equator, the line was elevated significantly by the Equatorial Undercurrent. It is shown that the shape of main line depends primarily upon the vertical shear and direction of the current relative to the gear. Time sequences of calculated shapes reveals that observed periodic (1-2 hours) oscillations in depth of the gear was caused by swinging movements of the main line. The shortening rate of the main line is an important parameter for formulating the shape of the longline, and its precise measurement is desirable.

Item Type: Monograph or Serial Issue
Title: Estimating the underwater shape of tuna longlines with micro-bathythermographs
Mizuno, Keisuke
Okazaki, Makoto
Nakano, Hideki
Okamura, Hiroshi
Series Name: Inter-American Tropical Tuna Commission Special Report
Number: 10
Number of Pages: 38
Date: 1999
Publisher: Inter-American Tropical Tuna Commission
Place of Publication: La Jolla, CA
Issuing Agency: Inter-American Tropical Tuna Commission
Subjects: Fisheries
Item ID: 5762
Depositing User: Joan Parker
Date Deposited: 18 Jun 2011 13:57
Last Modified: 29 Sep 2011 14:34

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