Seasonal Abundance, Size Composition, and Growth of Rock Crab, Cancer Antennarius Stimpson, Off Central California

Abstract

Bimonthly crab trapping and tagging efforts off the central coast of California from August 1976 to April 1981 yielded data on over 9,000 adult Cancer antennarius, the northeastern Pacific crab. Female crabs were most abundant during autumn, the period of warmest water temperatures along central California, but males exhibited no clearly defined seasonal abundance trends. Ovigerous females were prevalent during winter, resulting in the subsequent dispersal of pelagic larvae during spring and early summer. Rock crabs attain sexual maturity about 2 years after settlement, at a size of 60-80 mm carapace width. Adult crab growth averages 16.7% in carapace width and 57.7% in body weight after a single molt, with intermolt periods of up to 16 months duration. Maximum size may exceed 150 mm in carapace width and 900 g in body weight after 5 or 6 years making C. antennarius a desirable sport and commercial fishery species. Tag returns averaged 6.3% while tag loss, as detected by a scar on the epimeral suture of recaptured crabs, was 14.4%. Nearly half of all recaptured crabs were recovered at their original release site after 2-18 months, although migratory distances of 7 km were recorded for several individuals. The northeastern Pacific crab Cancer antennarius Stimpson is an edible crab common along the central Californian coast of North America, and ranges from Oregon to Baja California (Garth and Abbott, 1980). Three sympatric species of Cancer, all commonly referred to as rock crab, inhabit the central Californian coast: C. antennarius (rock crab), C. productus Randall (red crab), and C. anthonyi Rathbun (yellow crab). Of these, C. antennarius is the most abundant in shallow waters of the outer rocky coast. In central and southern California these three species have supported a small sport and commercial fishery for over thirty years (Frey, 1971). Despite its common occurrence and commercial importance, the Pacific crab has received little attention in the scientific literature beyond descriptions of larval development (Mir, 1961; Roesajadi, 1976), laboratory behavior (Krekorian et al., 1974), molt cycle dynamics (Spaziani et al., 1981), and brief accounts of its general biology (Schmitt, 1921; Ricketts et al., 1968; Garth and Abbott, 1980). The objective of the present study was to document several aspects of an adult C. antennarius population including: 1) seasonal abundance, 2) sex ratio, 3) size composition, 4) molting and spawning periods, 5) individual growth rates, and 6) migratory behavior.