Report of the ICES/ICNAF Working Groups on Selectivity Analysis

The results of selectivity experiments provide the basis for the minimum mesh size regulations in force in both the ICES and ICNAF areas. The study of selectivity has been in progress since at least 1927 but most of the work on this subject has been done since 1950. The majority of the experiments concentrated on defining selection factors for particular species in relation to the chemical nature of the netting yarn used, this being the main factor used in determining differentials. The introduction of new synthetic materials for netting yarns has not only demanded continuous updating of these regulations but has also resulted in a call for a reassessment of the principles upon which they are based as different net materials with apparently dissimilar physical properties have been shown to have similar selectivities. 

To reassess the position ICES and ICNAF formed two Working Groups whose terms of reference called for a review of the whole field of selectivity, taking into account all factors involved. The results of the Working Groups are presented in this report. Not only does it provide an up-todate review of the whole field and cover many aspects of selectivity which have been largely ignored but it also includes an extensive bibliography and a very comprehensive summary of selectivity data for NEAFC Regions 1 and 2 and the whole of the ICNAF area.