Sex Ratio, Size at Reproductive Maturity, and Reproduction of the Hawaiian Kona Crab, Ranina ranina (Linnaeus) (Brachyura, Gymnopleura, Raninidae)

Abstract

Sex ratio and size at reproduction of Ranina ranina (Linnaeus) in
\nHawaii were investigated. A sample of 1596 Kona crabs collected over 1 year in
\nHawaiian waters was examined to determine sex ratio and size at reproduction.
\nMales constituted 55 percent of the overall samples and a similar proportion
\nin all size classes. Males attain a larger maximum size than do females and have
\nmature spermatozoa when their carapace length exceeds 60 mm. Secondary sexual
\ncharacteristics in the male develop at a carapace length of about 75 mm.
\nFemales are ovigerous from May to September. Most ovarian growth occurs
\nbetween February and May. In May, at the beginning of the spawning season, the
\nnumber of eggs ovulated is a function of maternal body size: a 25-percent increase
\nin carapace length is associated with a 200-percent increase in number of eggs
\novulated. This is not so later in the spawning season (August-September). Larger
\nfemales appear to ovulate at least twice each season, with the primary effort going
\ninto the first ovulation. The smallest 5-mm size class in which at least 50 percent of
\nthe females are ovigerous during the spawning season is 70.0-74.9 mm in carapace
\nlength. The mean minimum size of ovigerous females is 86 ± 8 mm in this dimension.
\nThe spermatheca in females is open to the outside at carapace lengths exceeding
\n60 mm.
\nEighteen crabs with carapace lengths less than 65 mm were captured. Half (31.9
\nmm-42.6 mm) were white in color and were all immature; the remaining half
\n(43.6 mm-61.1 mm) were the usual orange color and all of these exhibited active
\ngametogenesis. This correlation of color with size may be of significance for
\nreproductive behavior.