Reproductive cycle of the New Zealand geoduck, Panopea zelandica, in two north island populations

The reproductive cycle of the ~ew Zealand geoduck, Panopea zelandica (Quoy & Gaimard, 1835), was studied over a 22 month period at two sites in northern l\'ew Zealand: Kennedy Bay, Coromandel, and Shelly Bay, Wellington. Standard histological analysis, measures of oocyte diameters, and gonadosomatic indices (GS1s) were used to describe the timing of g-ametogenic development and spawning. Sex ratios and size at sex~al maturity were also assessed for both populations. Gametogenesis in both populations began in late autumn, with spawning beginning during spring in Kennedy Bay and in late SUllll11er in Shelly Bay. The difference in the timing of spawning was attributed to latitudinal gradients in temperanrre as both populations spawned when water temperatures reached 15°C approximately. Monthly mean oocyte values and GSIs closely followed the patterns evident in the histological analysis of the reproductive cycle. However, monthly mean munber oLeggs/follicle indicated that a small amount of spawning may begin earlier than indicated by histology. Sex ratios were equal in Shelly Bay, but there were significantly more males than females in Kennedy Bay. This was attributed to a large cohort of small males present in Kennedy Bay. Males in both populations matured earlier than females. \\Thether geoducks are protandric or the sexes have different growth needs to be investigated. The data presented here suggest that GSIs may be of use to marine fanners wanting a quick and easy method for assessing the reproductive state of potential broodstock