Conversion of southern rock lobster (Jasus edwardsii) carapace length to tail width for enforcement of size limits

Abstract

The morphometric relationship of carapace length (CL) to tail width (TW) of southern rock lobster (Jasus edwardsii) was determined to assist enforcement of existing minimum size limits and also to enable the development of an upper size limit in Tasmania. Data were collected from southern rock lobsters in the wild and at processors and used to develop a system for measuring TW which reduces measurement error. Linear regression was used to define the relationship between CL and TW for males (TW = 0.4107x+14.058, R2=.9236, n=1003) and females (TW=0.5756x+2.2884, R2=.9323, n=503). Logistic regressions provide the TWs associated with the probability (0.5, 50 and 95%) of a lobster having a carapace equal to or more than the theoretical size limits. Regional differences in the morphometric relationship were evident but would not prevent the use of size limit based on TW if a conservative probability value were used.