Sexual maturity in females of deep-sea red crab Chaceon notialis (Brachyura, Geryonidae) in the southwestern Atlantic Ocean

Chaceon notialis is a brachyuran crab inhabiting the continental slope (250-1,000 m) off Uruguay in the southwestern Atlantic Ocean, constituting one of the main exploited stocks of deep-sea red crab in the world. The objective of this paper was to estimate size at morphological and physiological sexual maturity in females of Chaceon notialis in Uruguayan waters. Crabs were obtained from commercial samples taken in 1997 and 1998. For each individual, carapace width (CW) was measured and morphological (abdomen width and vulval features) and physiological (ovarian maturity) reproductive indicators were examined in order to estimate the size at sexual maturity. As the existence of a terminal molt still cannot be confirmed in females of C. notialis, we tested the alternative hypotheses that females: (1) have indeterminate growth and (2) exhibit a terminal molt. Hypothesis 1 was evaluated by fitting the logistic maturity function that provides the CW50% of females with mature vulvae, whereas hypothesis 2 was evaluated through the analysis of CW frequency distributions of morphologically and physiologically mature females. In addition, 50 pairs of female spermathecae were examined to determine if insemination had occurred; the carapace hardness of the individuals concerned was also noted. Two patterns of vulval morphology in females of C. notialis were observed for the first time: immature or ttclosedtt vulvae, and mature or ttopenedtt vulvae, respectively. Estimations of size at sexual maturity differed according to the hypothesis evaluated: under the assumption that females continue growing after the pubertal molt, mean sizes at morphological and physiological maturity (CW50%) were estimated as 70.2 mm and 71.7 mm, respectively. Alternatively, if females have a terminal molt, mean (± SD) estimates were 91.5 ± 8.5 mm and 91.1 ± 8.0 mm, respectively. Both scenarios clearly suggest synchrony between vulval and ovarian maturity. The species displays a soft mating system and most mature postmolt females lacks seminal contents in their reservoirs, in spite of evidence of successful mating (abrasion marks). This suggests that, due to selective exploitation of males, sperm supply may have become a limiting resource for the reproductive output of the population. Under the terminal molt hypothesis, females at the pubertal moult will be the only individuals in the population contributing to reproduction. Taking into account these findings, we suggest that the current regulations are reassessed, including the use of the terminal molt scenario for fishery management because it provides a precautionary framework in a situation where the life history of the targeted stock is data-limited.