Chionoecetes bairdi Rathbun, 1893  Common name(s):  Tanner crab, Southern tanner crab, snow crab, cobbler crab
Synonyms: Chionoecetes opilio (those found south of Alaska)
Phylum Arthropoda Subphylum Crustacea Class Malacostraca Subclass Eumalacostraca Superorder Eucarida  Order Decapoda Infraorder Brachyura Family Oregoniidae (formerly in Family Majidae)
	Chionoecetes juvenile captured at 250-300 foot depth in San Juan Channel.  Carapace width 2.75 cm.
	(Photo by: Dave Cowles, July 2011)

How to Distinguish from Similar Species: Chionoecetes tanneri (C. angulatus?) has a rostrum which turns dorsally.  It is mainly found at depths below 1000 m. style="font-style: italic;">C. opilio is an arctic species common near the Aleutian Islands, with carapace length and width nearly equal and less spines on the carapace.  Most other crabs from family Majidae, which look similar, have a carapace longer than wide (except for Mimulus foliatus, in which the carapace margins are expanded into winglike flanges).

Geographical Range: Northern Alaska to central Oregon

Depth Range:  6 to 475 m

Habitat: Subtidal, Sandy or muddy bottoms

Biology/Natural History: This crab is harvested commercially in Alaska as the snow crab, although that harvest is mostly of the relative C. opilio.  Predators include sea otters in Alaska.  The egg masses of this species may be parasitized by a tiny Nemertean worm Carcinonemertes regicides.  A leech, Notostomium cyclostoma, which feeds off fishes lays its eggs on the crab carapace.  The leeches do not appear to feed on the crab.  It may also be parasitized by the dinoflagellate Hematodinium.  This crab has a terminal molt. Females reaching their terminal molt breed for the first time while still soft from molting, but can breed again while still hard. They store sperm (from male spermatophores) in their spermatheca. Males first produce spermatophores when about 45 mm carapace width, but larger males produce more spermatophores. Females may become sexually mature by about 55 mm carapace width but may be as large as 85 mm carapace width (Paul, 1992). 

References:

General References:
  Hart, 1982
  Lamb and Hanby, 2005
  O'Clair and O'Clair, 1998

Scientific Articles:
Myers, T.C.,  T.M. Botelho, T.M. Koeneman, S. Short, and K. Inamura, 1990.  Distribution of bitter crab dinoflagellate syndrome in southeast Alaskan Tanner Crabs Chionoecetes bairdi.  Dis. Aquat. Org. 9: pp. 37-43 

Paul, A.J., 1992. A review of size a maturity of male tanner (Chionoecetes bairdi) and King (Paralithodes camtschaticus) crabs and the methods used to determine maturity. American Zoologist 32: pp. 534-540

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

This closeup shows the rostrum, the spines on the anterolateral margins of the carapace, the chelipeds, and the eye pattern.  Photo by Dave Cowles, July 2011.

A photo of another individual clearly shows the small spines lining the anterolateral carapace.  Captured by Kirt Onthank by SCUBA at about 20 m depth at night in Burrows Bay.  Photo by Dave Cowles, August 2015
 

These images of the underside of a male show the shape of the abdomen and the specialized first pleopods underneath. Carapace width on this individual is 3.5 cm.  Photos by Dave Cowles, August 2015
Ventral abdomen	Abdomen folded back to show pleopods

A dorsal view of the same individual.

And the ventral side

This closeup of the chelae shows that the chelipeds are relatively short but with small spines and granules.  The base (palm) of the propodus is swollen and slightly elongated.  The fingers of the chelae are long and narrow and are serrated with sharp teeth.

A view of the mouth.