The Decreasing Strength of Set Nets During the Submersion Period, and the Minimum for Utility

Abstract

A general practice with the operation of otoshi ami, the most prevalent type of trap nets in this country, is to provide two units of the net, each one serving under water from 10 to 60 days after the other (Fig. 2). The procedure will be repeated all through the season so that the net fabrics may be protected from deterioration. However, a close obser vation would reveal that the strength of thread woven into the fishing net gradually declines with the lapse of time until reaching beyond a minimum of utility when the life of the net comes to an end. In this regard it should be reminded here that in case of synthetic fiber nets having gained prevalence, the threads presumably have not to be so strong as natural fiber threads, as the former is more durable than the latter. For that reason it is important for designing and operating a net to know the minimum strength of various net materials in c luding both natural and synthetic fibers.