Clutch fullness index as an early indicator of overexploitation of the Southern King Crab: Implications for fisheries management

Abstract

Southern king crab is a high-value fishing resource commercially exploited in the Argentine Patagonia (south 44° S) since 2004. The ovigerous mass size of females, estimated as the clutch fullness index (CFI), has been used as a proxy for qualitative fecundity and an indicator of population health. In 2015, the use of CFI allowed the early detection of signs of overexploitation of the Southern king crab. This study aimed to assess temporal variations in the CFI in relation to fishing effort and management measures. Data were collected from commercial vessels between January and May from 2012 to 2020 in the Central Patagonian Sector (comprising the San Jorge gulf and adjacent shelf waters, 43°30′- 48°S). The Correspondence Analysis and hierarchical cluster analysis showed that the CFI varied among years. The variation of the CFI was opposite to the fishing effort. The CFI decreased between 2015 and 2017 (from 80% of females with 100% CFI in 2014 to 43% in 2017), and increased since 2018 (from 57% in 2018 to 78% in 2020). This is probably due to the implementation of two new management measures (extended closed season and the regulation of an annual catch quota). Two indicators of L. santolla reproductive status are proposed based on empirical data. The first one is the proportion of non-ovigerous mature females during the incubation period, which could reflect a male shortage during the mating period must not exceed 10% and the second one is the proportion of females with a complete clutch must be greater than 40%. The CFI variations and the proposed indicators can constitute an alternative to the crabs traditional management.