||Calibrated Mask-Bar for Underwater Measurement of Fish.
Swenson, W. A. ;
Gobin, W. P. ;
Simonson, T. D. ;
||Wisconsin Univ.-Superior. Center for Lake Superior Environmental Studies.;Environmental Research Lab.-Duluth, MN.
||EPA-R-812215 ;EPA-R-810934; EPA/600/J-88/461;
Measuring instruments ;
Underwater equipment ;
Diving suits ;
Breathing masks ;
||Most EPA libraries have a fiche copy filed under the call number shown. Check with individual libraries about paper copy.
The paper describes a method for measuring fish under water by using a diving mask equipped with a calibrated mask-bar. The calibrated mask-bar consists of a plexiglass strip with calibration marks spaced 3.22 mm (1/8 in) apart, mounted to a diver's mask by aluminum straps. Relationships between calibration mark counts made by underwater observers and the length of objects were described by regression analysis. Measurements of stationary objects were accurate to within + or - 5%. Estimates of fish length under field conditions were generally accurate to within + or - 10%. Mean lengths calculated from multiple mask-bar measurements were consistent with those calculated from measurement of captured fish. (Copyright (c) by the American Fisheries Society 1988.)