Growth of juvenile southern king crabs (Lithodes santolla) in San Jorge Gulf, Southwestern Atlantic Ocean

Abstract

The southern king crab (SKC), Lithodes santolla, supports a lucrative fishery in San Jorge Gulf (SJG), Argentina and its adjacent area in the southwestern Atlantic Ocean. However, despite its commercial value, biological data on the SKC in SJG are scarce. In this study, we analyzed the growth of early juvenile SKCs by combining field and laboratory data. Sampling was carried out monthly in shallow waters in the central area of SJG (44°–46 °S). The sex and molt stages of SKC were recorded and the carapace length (CL) was measured. Individuals in premolt were taken alive to the laboratory to measure the molt increment. Size frequency distribution was used to assess modal progression, whereas the molt increments determined in the laboratory were used to verify the modal groups identified. Juvenile SKCs had molting activity throughout the year with no synchronization of the molt cycle observed. The molt increment ranged from 0.37 to 8.86 mm and the relative increment varied between 7.13 and 48.29 %. A total of 17 post-settlement modal groups were recognized: nine within the first year post-settlement, four within the second and three within the third. A wide variability in CL was recorded within the same annual class, which could be due to the absence of molting synchrony and the wide range of molt increment. Our results suggest that both male and female SKCs reach maturity four and a half years after settlement and that males recruit to the fishery seven years after settlement (at 110 mm CL).