Page:Dungeness Crabs of Glacier Bay.pdf/2

 no spines on the top side of their carapaces (shells).
 * The carapace does not grow in the continuous, gradual manner of animals with internal skeletons ­ such as fish and mammals.
 * They can live between 8-­13 years and reach a size of 10­-plus inches.
 * Within 2­3 years, crabs are sexually active. At 4­5 years, they have grown to the legal harvest size (6 ¼ across the shell and 2­3 pounds in weight).

Prior to and during molting, crabs absorb water into their body tissues, which expands the body to a larger size causing the shell to split. The soft, newly­molted crab emerges from the old shell and seeks shelter while its new shell hardens. Complete hardening of the new shell takes about 6 weeks for adult crabs. It takes a little longer for the crab to fully replace the absorbed water with new body tissue, such as muscle.

Adult males and females in a population tend to molt at different times, so that the males will be hard-­shelled and able to mate when the females molt. During the first 2 years (10–11 molts) the crabs shed their shell several times a year, increasing in size with every successive molt. After molting, the new, paper­thin shell is vulnerable to puncture, so the crab hides by burying itself in the sandy bottom for several days. Most males molt during the summer months but the time can vary greatly by area and year.

Once grown, mature males that have recently molted can be found sometimes in large groups (aggregates). Aggregates can be found in depressions or trenches usually approximately 1 meter deep and 5 meters wide. These habitat features may offer increased protection from predation. The rarity of such features in the habitat may also explain why the crabs, usually solitary, gather there. These groups seem to suggest a selfish herd or schooling phenomenon in which individuals gain protection in numbers through greater watchfulness and confusion of predators. Another explanation for these groups can be found in the fact that in 3 recently observed male aggregates, the distance from the nearest known female assembly averaged 200 meters, a lot closer than would be expected to occur randomly. Juveniles live in intertidal and shallow subtidal areas, hiding underneath or among plants, rocks, shell debris and eelgrass beds. Juveniles also prefer cooler waters than adults. Adult crabs prefer eelgrass beds and sandy or muddy substrate. Breeding occurs in nearshore areas and females usually move to deeper water to hatch eggs.

When the female molts, she is ready to be mated with a male who protects her while mating. Mating occurs in the late spring or early summer. The eggs are not fertilized until the female