Assessment of size at maturity and gonad index methods for the scallop Pecten novaezelandiae

Abstract

Size at sexual maturity and gonad indices appropriate for measuring reproduction were examined in the scallop Pecten novaezelandiae at two sites in the Hauraki Gulf, New Zealand. Size at maturity was assessed using gonad visual grading and allometric calculation methods. Size of the smallest mature individual varied from 52 to 59 mm shell height between sites. In general, 50% of scallops were mature at 60 mm and 100% were mature at 65 mm. Small differences in size at maturity between sites may be related to differences in environmental conditions that affect growth rates. Our results were broadly similar to those reported from the South Island, however direct comparisons were compromised by the wide range of methods and definitions used in previous studies. Here we applied a method that directly scaled gonad mass to shell height, removing the need for a reference mass, and combined it with an objective method to establish size at maturity that will facilitate future comparisons.