The snow crab, Chionoecetes opilio, is a crustacean found predominantly in the cold, deep waters of the North Atlantic and North Pacific Oceans. Often called the Queen crab, this species is highly valued for its delicate meat and is the focus of major commercial fisheries. The size a snow crab achieves determines its economic value. Snow crabs grow slowly to reach their full adult dimensions.
Defining the Maximum Dimensions
The standard measurement for a mature adult snow crab is the width of its carapace, the hard, upper shell covering its body. Maximum sizes are primarily observed in mature males, as they continue to molt and grow larger than females. A large, commercially harvested male snow crab will typically have a carapace width between 3.7 and 6.5 inches (9.4 to 16.5 cm).
The length of the legs is proportionally much greater than the body size; a large male can have a leg span that extends to nearly 3 feet (1 meter) across. These large males, the primary target of commercial fishing, generally weigh between 1.1 and 3.0 pounds (0.5 to 1.35 kg). Commercial regulations often set a minimum size, such as 3.7 inches (95 mm) in carapace width, to ensure only mature individuals are harvested.
The Significant Difference Between Male and Female Size
Snow crabs exhibit pronounced sexual dimorphism, meaning there is a clear difference in size and form between adult males and females. Males are significantly larger, often growing to be nearly twice the size of their female counterparts. While large males can reach a maximum carapace width of 6.5 inches (16.5 cm), females rarely exceed 3.7 inches (9.5 cm) in width.
The mature female’s body shape is characterized by a wider, more rounded abdominal flap, necessary for carrying her egg clutch. Females stop growing entirely once they reach reproductive maturity, undergoing a single, final molt that prevents further size increase. This biological limit means females do not attain the large size and weight required for commercial harvesting, typically weighing only around 1.1 pounds (0.5 kg).
Growth Through Molting: The Path to Maturity
Snow crabs, like all crustaceans, grow by shedding their rigid outer shell, a process called molting or ecdysis. Since the hard exoskeleton does not expand, growth occurs in steps immediately after the old shell is shed and before the new shell hardens. This process allows the crab to increase its carapace width by roughly 50% and nearly double its weight with each successful molt during its immature phase.
A snow crab will molt frequently when young, sometimes twice a year, before slowing to an annual molt as it matures. The crab must absorb seawater to expand its body and crack open the old shell along a seam, a vulnerable period when it is exposed to predators.
The path to maturity ends with a terminal molt, the final shed of the crab’s life. Once a crab undergoes this final shed, it achieves sexual maturity and ceases to grow. For males, this terminal molt can occur over a wide size range, resulting in the largest individuals that are targeted in the fishery.