Isbell, Chester and Burnett, Russel (2012) Fisheries Science and Environmental Issues with Fishing. Academic Studio, Delhi, India. ISBN 9788132307099
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Abstract
Automatic fish counters are automatic devices for measuring the number of fish passing along a particular river in a particular period of time. Usually, one particular species is of interest. One important species studied by fish counters are Atlantic salmon. This species is of interest owing to its ecologically vulnerable status and anadromous lifestyles. Fish counters can be divided into three principal types: resistive counters, optical counters, and hydroacoustic counters. A resistive counter is associated with an in-river structure, such as a Crump weir. The resistivity of a fish is lower than that of water. So, as fish cross this barrier, they pass embedded electrodes, and the difference in resistivity disturbs the field established in the vicinity of the electrodes, altering inter-electrode resistance. With three electrodes these disturbances can then be measured by a Wheatstone bridge, or other means, to detect the size and direction of travel of the fish. Fish counters of this type are used widely in Scotland to census populations of Atlantic salmon. where comparison with closed circuit television shows around a 97% detection late. An optical counter is also associated with an in-river structure. However, rather than pass electrodes, in an optical counter the fish interrupt some of a number of vertically arranged beams of light. The pattern of beam-breaks can be used to determine the size, profile, and direction of motion of the fish The performance of optical counters has been determined by studies, under various conditions, to be greater than 90%. Optical counters can also distinguish the size of fish more accurately than other counter types and so are particularly useful where a mixture of species inhabit a river (for example rivers where salmon mix with sea trout). The key disadvantage of optical counters is the small penetration of the beams through the water, restricting their use to narrow river features or in-river structures, such as fish ladders.
| Item Type: | Book |
|---|---|
| Subjects: | S Agriculture > SH Aquaculture. Fisheries. Angling |
| Divisions: | Electronic Books |
| Depositing User: | Esam @ Hisham Muhammad |
| Date Deposited: | 02 Jan 2024 06:12 |
| Last Modified: | 02 Jan 2024 06:12 |
| URI: | http://odlsystem2.utm.my/id/eprint/4330 |
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