Use of derrick scales for weighing live fish

Abstract

In Norway purse seine catches of saithe are usually sold to the factories alive. The fish is transported in boats specially constructed for the transport, i.e. well-boats. The saithe is weighed when transferred to these well-boats. The usual method of weighing has been to transfer the saithe by a dip net to a perforated container placed on a balance scales. Last year, however, a few well-boats started using a scales hanging from the derrick hook above the dip net, and the weight of each load could be read off immediately. In this study the above methods of weighing saithe were compared, taking into account the accuracy of the methods, the mortality rate of the saithe, and time and effort involved in the process. Both systems of weighing were used on board a well-boat in which the well was divided into two separate compartments; and each load weighed was controlled after transport to land. No difference in accuracy could be detected between the two methods of weighing, but the use of derrick scales seems to give a slightly better survival rate and, furthermore, this method saves both time and effort.