Reproduction and Development: Adult females brood thousands of embryos underneath their tail flap for about a year's time. When the embryos are fully developed they hatch as swimming larvae, but they are still susceptible to the movements of tides and currents. After feeding on plant and animal plankton for several months and undergoing several body changes with each molt, the larvae settle to the ocean bottom and molt into nonswimmers, looking for the first time like king crabs as we normally think of them, except they are smaller than a dime. Red king crabs settle in waters less than 90 feet deep.
Growth: Because a crab's skeleton is its shell (made mostly of calcium), it must molt its shell in order to grow. Juveniles molt many times in their first few years, then less frequently until they reach sexual maturity in four or five years. Adult females must molt in order to mate but males do not. Adult males often skip a molt and keep the same shell for one or two years. Red king crabs can grow very large with the record female and male weighing 10.5 and 24 pounds, respectively. These large crabs were estimated to be 20-30 years old. The male's leg span was nearly 5 feet across.
Movements: Adult red king crabs exhibit near shore to offshore (or shallow to deep) and back, annual migrations. They come to shallow water in late winter and by spring the female's embryos hatch. Adult females and some adult males molt and mate before they start their offshore feeding migration to deeper waters. Adult crabs tend to segregate by sex off the mating-molting grounds. Red, blue, and golden king crabs are seldom found co-existing with one another even though the depth ranges they live in and habitats may overlap. Adult male red king crabs in the Kodiak area have been known to migrate up to 100 miles round-trip annually, moving at times as fast as a mile per day.