Sexual maturity of the deep-sea royal crab Chaceon ramosae Manning, Tavares & Albuquerque, 1989 (Brachyura: Geryonidae) in southern Brazil

Abstract

The royal crab Chaceon ramosae is one of the three species of deep-sea crabs currently exploited in Brazil. The royal crab fishery started in 2001 with foreign vessels that were extensively monitored by observers and tracked by satellite. A management plan implemented in 2005 was based only on biomass dynamics, as biological knowledge of the resource was limited at that date. Samples taken aboard were used to determine size at first sexual maturity for males and females by studying the use of allometric growth of chelae and abdomen in relation to carapace width (CW), the proportion of females with opened vulvae and eggs in the pleopods, and males showing copula marks on the first ambulatory legs. Morphometric maturity was attained, on average, at 12.1 cm (males) and 10.7 cm (females). The CW50% was estimated to be 10.9 cm and 12.2 cm for females, respectively considering the vulva condition and eggs in the pleopods, and 13.6 cm for males. By size class, the maximum estimated proportions of ovigerous females by size class was 0.4 and of males with copula marks was 0.6, suggesting a bi-annual reproductive cycle for individuals of the species. The size composition analysis showed that immature individuals may comprise up to 70% of the catches. These results indicate the need to consider enhanced trap selectivity and lower mortality of ovigerous females as new and immediate goals to improve resource management.