Reproductive cycle and conditioning of translocated scallops (Pecten maximus) from five broodstock populations in Norway

In Norway sea ranching depends on deployment of animals of local origin, and growers demand large spat outside the natural production season. To develop stock-specific production of juveniles, knowledge on local scallop reproductive cycle and performance in hatchery was needed. Broodstock sized scallops (Pecten maximus) were collected from 5 locations along the coast of Norway from 59°N to 65°N during 2004 and 2005, and translocated to natural sea location at 61°N. The reproductive cycles were characterised and the possibility of performing successful hatchery conditioning and spawning outside the natural reproduction cycle was investigated.Results showed that scallops from south-western Norway (3 locations) all had distinct season summer peaks in the reproductive cycles. Scallops from the northern part (2 locations) quickly rebuilt the gonad after spawning and seemed to have full gonads through most of the year. Gonad indices in the southern group varied between 5 and 15%, while in the northern group it was 10 to 25% of total tissue weight. Both in December and March most individuals (> 75%) in the southern group had empty gonads, while most individuals in the northern group were characterised as being in gonad maturation stages 3–6. There was no complete synchronous gonad development through the year, and most developmental stages were present at all times. Scallops from the southern locations showed small changes in gonad maturation after translocation to the new environment. Scallops from northern locations kept the original cycle, but seemed to spawn later in summer. Scallops from the 3 southern locations responded to conditioning methods in the hatchery from late autumn to spring, as did one of the northern populations, while the other northern population could not be conditioned in winter. Based on reproductive cycle and hatchery performance we suggest that scallops from the 5 locations belonged to 3 distinct different populations. The differences in timing of gametogenesis and response to conditioning environment have implications for spat production in the hatchery and must be accounted for in order to fulfil the requirements of site-specific spat for scallop sea ranching in Norway.