Chionoecetes opilio

Chionoecetes opilio, is a species of snow crab, also known as opilio crab or opies, is a predominantly epifaunal crustacean native to shelf depths in the northwest Atlantic Ocean and north Pacific Ocean. It is a well-known commercial species of Chionoecetes, often caught with traps or by trawling. Seven species are in the genus Chionoecetes, all of which bear the name 'snow crab'. C. opilio is related to C. bairdi, commonly known as the tanner crab, and other crab species found in the cold, northern oceans. Snow crabs have equally long and wide carapaces, or protective shell-coverings, over their bodies. Their tubercles, or the bodily projections on their shells, are moderately enclosed in calcium deposits, and they boast hooked setae, which are rigid, yet springy, hair-like organs on their claws. Snow crabs have a horizontal rostrum at the front of the carapace; the rostrum is basically just an extension of the hard, shell covering of the carapace and it boasts two flat horns separated by a gap. They have triangular spines and well-defined gastric and branchial regions internally. Snow crabs also have little granules along the border of their bodies, except their intestinal region. Concerning their walking legs, their first three are compressed; their chelipeds, or pincers, are usually smaller, shorter, or equal to their walking legs. Snow crabs are iridescent and range in color from brown to light red on top and from yellow to white on the bottom, and are bright white on the sides of their feet. Snow crabs are native to the Northwest Atlantic and the North Pacific. In the Northwest Atlantic, they are found in the areas near Greenland, Newfoundland, in the Gulf of St. Lawrence, and on the Scotian Shelf. In the North Pacific, this crab is found in areas ranging from Alaska to northern Siberia, and through the Bering Strait to the Aleutian Islands, Japan, and Korea. In 1996, they were recorded in the Barents Sea for the first time. They are considered an invasive species there, but how they arrived there is unclear. Another commercially important species, introduced deliberately to the same region, the red king crab, already has established itself in Barents Sea. Similarly, snow crabs likely will have an adverse effect on the native species of the Barents Sea. Snow crabs are found in the ocean's shelf and upper slope, on sandy and muddy bottoms. They are found at depths from 13 to 2,187 m (43 to 7,175 ft), but average is about 110 m (360 ft). In Atlantic waters, most snow crabs are found at depths of 70–280 m (230–920 ft). Where male and female snow crabs are found in the ocean, depths may vary. Small adult and senescent adult males occur mainly at intermediate depths over much of the year, while large and hardy adult males are found mostly at depths greater than 80 m (260 ft). Adult females are gregarious and congregate at depths of 60–120 m (200–390 ft). Snow crabs mainly reside in very cold waters, between −1 and 5 °C (30 and 41 °F), but can be found at temperatures up to 10 °C (50 °F). C. opilio crabs eat other invertebrates in the benthic shelf, such as crustaceans, bivalves, brittle stars, polychaetes, and even phytobenthos and foraminiferans. Snow crabs also are scavengers, and aside from preying on other benthic shelf invertebrates, they prey on annelid worms and mollusks. Males typically prove to be better predators than mature females, and prey type depends upon predator size, with the smallest crabs feeding mainly on amphipods and ophiuroids, while the largest crabs feed mainly on annelids, crustacean decapods, and fish. Cannibalism is practised at times among snow crabs, most frequently by intermediate-sized females. The snow crab grows slowly and is structured according to its size. At least 11 stages of growth for male crabs are recognized. Usually, the male crabs are almost twice the size of the female crabs. Males can grow up to 16.5 cm (6.5 in) in carapace width, while females can grow up to 9.5 cm (3.7 in). Male carapaces are usually about 7 cm (2.8 in) in width and length, with the female carapace usually close to 5.5 cm (2.2 in) in width and length. Males caught in commercial fisheries generally weigh 0.5–1.35 kg (1.1–3.0 lb) and females generally about 0.5 kg (1.1 lb). Off the coast of Newfoundland, two amphipod species – Ischyrocerus commensalis and Gammaropsis inaequistylis – have been found to live on the carapace of the snow crab.