You have a Chionoecetes opilio (O. Fabricius, 1788) – Snow crab
Synonyms: Cancer opilio O. Fabricius, 1788; Chionoecetes behringianus Stimpson, 1857; Chionoecetes chilensis Streets, 1870; Peloplastus pallasi Gerstaecker, 1856
Common names: Snow crab, Queen crab (U.K., USA, CAN); Arktisk krabbe, (Stor) Grønlandsk krabbe (DK); Snøkrabbe (NO); Crabe des neiges (FR); Cangrejo de las nieves (SP); Kurzschwanz-krebs, Schneekrabbe (DE); Zuwai-gani (JP); Krab streegoon (RU)
Chionoecetes opilio is a large true crab (Brachyura) species with a carapace width of 90-140(150) mm for males and 55-85(95) mm for females. It has some similarity with the king crab (Paralithodes camtschaticus), such as the almost circular carapace and long, slender legs, which in the snow crab are equipped with low, rounded knobs or warts as well as short spines. Also, the snow crab has the usual 5 pairs of legs of which the first pair is the chelipeds. The rostrum is short, wide, and equipped with two horn-like spines. There is a triangular spine lateral to the green eyes. The chelipeds are relatively small and slender, shorter or equal to the walking legs. The colour varies from reddish brown to brownish red.
In the North Pacific, Bering Sea and Sea of Okhotsk there are three additional species of the genus Chionoecetes. One of them, the tanner crab, Chionoecetes bairdi Rathbun, 1924, has a carapace that is distinctly broader than long. The snow crab and tanner crab are capable of hybridizing in the Bering Sea (Johnson, 1976; Urban et al., 2002). The hybrids show a mosaic of characters from the two parent species. In Japan there is another closely related species, C. japonicus Rathbun, 1932 – the red snow crab, which is also an important fisheries species. In the Barents Sea only the common spider crab, Maja squinado (Herbst, 1788), can be mistaken for C. opilio. M. squinado has a more diamond-shaped carapace and a more spiny surface. Juvenile specimens might also be confused with the native species of Hyas. Both species of Hyas have carapaces that are distinctly longer than wide.
Chionoecetes opilio, ventral view. Photo by Kathe Rose Jensen
For further information on Maja squinado – common spider crab see:
For further information on Hyas araneus (Linnaeus, 1758) – the great spider crab see:
For further information on Hyas coarctatus Leach, 1816 – toad crab see:
Taxonomic note:Until recently Chionoecetes opilio was referred to the family Majidae, the spider crabs. However, according to World Register of Marine Species (WoRMS) this species belongs to the family Oregoniidae, as does the native North European species of Hyas. Prior to this change the Oregoniidae was only considered a subfamily of the family Majidae. The common spider crab, Maja squinado, also a native of North European waters, is presently in the family Majidae, subfamily Majinae, and all of the above are in the same superfamily, Majoidea.
Native area: Chionoecetes opilio is a native of arctic seas of the North Pacific to Japan and Korea, the Bering Sea, Alaska and west coast of Canada. It also includes the NW Atlantic coast of Canada to Maine, USA and the west coast of Greenland (Alsvåg et al., 2009).
Introduced area: Chionoecetes opilio was first detected in the Barents Sea in 1996 (Kuzmin, 2000). The first record from Norwegian waters was in 2003 (Alsvåg et al., 2009). Studies in the following years showed that juveniles as well as adults of both sexes and ovigerous females occurred in both the Russian and Norwegian EEZs (Alsvåg et al., 2009). Thus the species must be considered established in the Barents Sea. Genetic studies to identify the source population are under ways (Alsvåg et al., 2009).
Vector: Assumed to be ballast water (Kuzmin, 2000).
Chionoecetes opilio is a cold water species, living at depths from 20 to 700 m and water temperatures not exceeding 5° C (Elner & Beninger, 1992), except for mating migrations. Their life span is about 15 years. The snow crab is a predator of various invertebrates including crustaceans, bivalves, polychaetes, etc. (Wieczorek & Hooper; Squires & Dawe, 2003). Cannibalism also is an important cause of mortality (Lovrich & Sainte-Marie, 1997). Chionoecetes opilio constitutes an important part of the diet of skates in parts of its native area (Kuril Islands) (Orlov, 1998).
Growth during the first 10 instars is equal for males and females, but decreasing with increasing age (Robichaud et al., 1989). Like all processes in cold water, ecdysis is a slow procedure, shells softening about 6 weeks prior to molting, and hardening 2-8 weeks after shedding the exoskeleton (Jadamec et al., 1999).
Chionoecetes opilio is host to some commensal turbellarian flatworms, Ectocotyla hirudo (Levinsen, 1879) and E. multitesticulata Fleming & Burt, 1978, which are found in the gill chamber and on the gills, and Peraclistus oophagus (Friedman, 1924) (Fleming et al., 1981). In the Barents Sea the fish leech Johanssonia arctica (Johansson, 1898) has been found on some large specimens (Kuzmin, 2000). Older snow crabs have an increasing amount of epifauna, such as barnacles, serpulid worms, bryozoans, etc. (Savoie et al., 2007)
Reproduction: Size at sexual maturity seems to vary among populations. Robichaud et al. (1989) indicate 52-137 mm for males and 47-95 mm for females, whereas Sainte-Marie & Hazel (1992) indicate 40 mm carapace width as average for both sexes, and Elner & Beninger (1992) report a minimum carapace width of 51 mm for males and 41 mm for females, corresponding to age 5-10 years. Apparently there is a final "pubertal" molt at sexual maturity, and mature crabs do not molt after this (Elner & Beninger, 1992), but there is some discussion whether the differentiation of chelae or the presence of mature spermatophores are the best indicator for sexual maturity of male snow crabs. The chelae of the males increase proportionally more at this final molt and become relatively taller than before (Conan & Comeau, 1986; Comeau & Conan, 1992). This has also been illustrated in Jadamec et al. (1999). Males compete for access to females, and "adolescent" and newly molted adult males usually loose the battle to older, hard-shelled males (Rondeau & Saninte-Marie, 2001; Sainte-Marie et al., 2002). During the copulatory act the male turns the female upside down, and the male remains with the female until the eggs are spawned and attached to the pleopods several hours after copulation (Sainte-Marie & Hazel, 1992; Comeau et al., 1998; Jadamec et al., 1999). Females may store enough sperm for more than one egg clutch, but may also mate a second time after hatching of the first brood (Sainte-Marie & Carrière, 1995; Saninte-Marie et al., 2002). Eggs of one clutch are all fertilized by sperm from the same male (Urbani et al., 1998). Multiparous females are recognized by older carapace (with epifauna) and scars from the previous mating (Jadamec et al., 1999).
Eggs are brooded for more than one year (Charmantier & Charmantier-Daures, 1995). Fecundity depends on the size of the female as well as the locality, with small females (40-44 mm) in cold water (Chukchi Sea) carrying 13.000 eggs and large females (>80 mm) in warmer water (Gulf of St. Lawrence) carry about 115.000 eggs (Jewett, 1981). Eggs are bright orange at the time of spawning. Eye spots appear in the embryos after about 8-11 months, and the eggs change colour to dark brown or almost black as the eyes become more prominent (Jadamec et al., 1999).
Larvae hatch as prezoeae, and there are two zoea stages and one megalopa before metamorphosis to juvenile crabs. Zoea I lasts about one month at 9.5° C, but mortality under laboratory conditions is very high. Larvae also appear to be rather stenohaline (25-38 ppt), though lower and higher salinities can be tolerated for short time intervals (Charmantier & Charmantier-Daures, 1995). Both zoea larvae and juvenile crabs appear to be osmoconformers. Field observations indicate that zoea I to metamorphosis of first crab stage (instar I) takes 3-5 months (Robichaud et al., 1989).
In Japan spawning is between February and April (Makino, 2008). In eastern Canada the spawning period is December to April for the females spawning their first brood; for multiparous females it is April to June. There is a spring migration to shallow water, 4-20 m, for molting and mating (Hooper, 1986; Sainte-Marie & Hazel, 1992).
Most of the available information on impacts is on impacts of fishery in the native area. As it is an important species, much of the available information can be downloaded from various sources. For instance a book on biological field techniques (Jadamec et al., 1999) is available at http://seagrant.uaf.edu/bookstore/pubs/AK-SG-99-02.html
Fishery on the east coast of Canada began in the 1960s. The fishery increased rapidly in the 1990s when a moratorium was in place for benthic finfish fishery. Snow crab is a high value commodity, but costs as well as markets are unstable. Canadian fisheries regulations stipulate that only males can be caught and minimum size is 95 mm carapace width. Fishing areas are closed during molting season. Further regulation is by individual boat quotas and a limit on the number of traps (FRCC, 2005).
There is also a commercial fishery in Greenland. Here the minimum size is 90 mm carapace length, and as in Canada, only males can be caught. Other management measures are closed areas and short open seasons(Burmeister, 2000, 2002). Snow crabs are exported live from Greenland to Denmark for further distribution to the European market. This gives the opportunity for individuals to escape to the wild, but presumably water temperatures are too high for the snow crabs to survive.
Fishery in Alaska takes place during the winter in severe weather conditions. Here the minimum legal size in 79 mm carapace width, but usually males between 79 and 101 mm carapace width are also discarded. Due to the adverse weather conditions and the handling mortality in discards is very high (Warrenchuk & Shirley, 2002). This mortality is not presently taken into account when setting annual catch limits.
Fishery in Japan goes back several centuries. After a period of overfishing and overcapacity during the 20th century the fishery is now regulated and various measures for protecting stock and reproduction are in place. Snow crabs are fished by trawling and both males and females are fished. The minimum legal size is 90 mm carapace width (Makino, 2008).
Norwegian king crab fishers are not permitted to throw back snow crabs caught as by-catch. This is to prevent the further spread of the snow crab in the Barents Sea (http://www.sitnews.us/LaineWelch/021008_fish_factor.html, last accessed 10March 2015).
Like the king crab, Paralithodes camtschaticus, the snow crab may also be infected by micro-organisms of the genus Hematodinium sp., which cause the problem of "bitter crab" (Jadamec et al., 1999; Shields et al., 2005; Wheeler et al., 2007). Another lethal disease is the fungal infection by Trichomaris invadens, which cases the socalled "black mat" symptoms of reproductive bodies on the exosketeton (Jadamec et al., 1999). These diseases could possibly spread to native crustaceans.