Reproductive cycle of Ensis magnus in the Ría de Pontevedra (NW Spain): Spatial variability and fisheries management implications

• Mesoscale differences in the reproductive cycle of E. magnus were investigated.
• The differences may arise from environmental conditions variability between beds.
• The size at which E. magnus reaches sexual maturity was estimated in 79 mm.
• The information obtained has been already applied in razor clam fishery management.

Mesoscale differences in the reproductive cycle of the commercial sword razor clam Ensis magnus ( Schumacher, 1817) were studied in six shellfish beds in the Ría de Pontevedra (NW Spain) between March 2008 and July 2010. The GCI accurately described the reproductive cycle as indicated by the histological analysis. Both methods showed that the reproductive cycle was similar at different sites and was characterized by a resting stage during summer and early autumn, initiation of gametogenesis in autumn and a period of successive spawning interspersed with gonad recovery during winter and spring. However, a 15-day to one month delay in advanced stages of gametogenesis and maturation was observed between the inner and the outermost site of the ria, as well as an extended spawning period in the outermost area. Lower bottom seawater temperatures at the outermost sites appeared to delay maturation and to prolong the spawning periods, whereas salinity fluctuations at the innermost sites appeared to reduce the length of the cycle. This study provides the first estimation of the size at which E. magnus reaches sexual maturity in the Iberian Peninsula, determined in 79 mm, and it is also the first work in determining the mesoscale variation in gonadal development of any species of the superfamily Solenoidea. The results highlight the importance of carrying out mesoscale studies of the reproductive biology in coastal fisheries resources. Some of the findings of the present study have already been applied in the rotation scheme of the fishery harvesting plan.