Growth, maturity, and mating of male southern king crab (Lithodes santolla) in the Beagle Channel, Argentina

Growth, maturity, and mating of male southern king crab (Lithodes santolla) in the Beagle Channel, Argentina

G.A. Lovrich, J.H. Vinuesa, and B.D. Smith

Growth, maturity, and mating of male southern king crab (Lithodes santolla) in the Beagle Channel, ArgentinaThis is part of Crabs in Cold Water Regions: Biology, Management, and Economics
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Description

Until the early 1990s, Lithodes santolla constituted the main target species of the mixed fisheries of the southern tip of South America. In the Beagle Channel, Argentina, the fishery is regulated mainly by a fishing season that extends between January and October, and by the exclusive extraction of males of a legal size >110 mm of carapace length (CL). It is essential to know whether animals protected by this regulation are able to reproduce, and thus guarantee the continuity of the fishery. Due to the lack of fishery controls, the fishery was overexploited and closed in 1994. As part of fishery rehabilitation, a growth model was also needed. We studied growth per molt of male Lithodes santolla crabs larger than gonadal maturity (ca. 70 mm CL) by a size frequency analysis jointly with molt increment data. Increment-at-molt was independent of the crab size and averaged 11.4 (±1.7) mm CL. The growth factor significantly decreased with premolt size, from 12.0-15.8% to 7.5-9.5% of premolt size in crabs ca. 75 and 130 mm CL, respectively. We found 8 molt instars that satisfactorily explain the size frequency distributions. Male crabs 73.5-105 mm CL molt twice a year in autumn and spring, whereas crabs >105 mm CL molt only once, each autumn. Hence, male L. santolla probably reach the legal size 2 years later than attaining the size at morphometric maturity (SMM), and enter into the fishery stock at their 7th-8th year. SMM calculated with the routine MATURE (Somerton 1980) strongly depended on the choice of chela dimension and the inclusion of smaller crabs in calculations. The best estimation of SMM was 75.4 (±4.8) mm CL. To determine the functional (= behavioral) maturity size, we studied the constitution of mating pairs. In mating couples, most of males were larger than females, size of mating males and females correlated positively, and only males >94.2 mm CL participated in the pairs. Hence, the present legal size for the fishery could be interpreted as adequate.

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