Tanner Crab

Tanner Crab
Latin Name

Chionoecetes bairdi/tanneri/angulatus

Group Name

Invertebrates

Taxonomy details

Habitat

There are three species of Tanner crab in British Columbia. Chionoecetes bairdi is the nearshore, relatively shallow water species, native to the Pacific coast of North America from Alaska to Oregon and is not generally found in the eastern Pacific, although there are reports of them occurring off Japan. Their major abundance in British Columbia appears to be the northern mainland inlets where they were fished commercially until 1993. There currently is no commercial fishery and recreational harvesters rarely encounter them because of their depth.

The other two species, Chionoecetes tanneri and Chionoecetes angulatus, are deepwater spider crabs (500 to 3000 metres) and are found along the continental slope from California, around the Aleutian chain, to Japan. Attempts to develop a commercial fishery for these two species in British Columbia have been unsuccessful.

Species Description

Tanner crabs are large, spider crabs with four pairs of slender, pointed walking legs and a pair of claws about the same size as their legs with two narrow, curved pincers. Their carapace (shell) is round and flattened, with two 'horns' on the front.

Chionoecetes bairdi - the shallowest of the three species - is brown in colour and has a rough, bumpy surface. Their undersides are pinkish orange to cream. These nearshore Tanner crabs grow to a maximum carapace width of about 140 millimetres in British Columbia, with males considerably larger than females. It is believed that they live up to 14 years.

The deepwater species, Chionoecetes tanneri (grooved Tanner crab) and Chionoecetes angulatus (angle Tanner crab) have bright orange shells with enlarged lobes over the gill region.

Tanner Crab (C. tanneri)

The deep water grooved tanner crab (Chionoecetes tanneri) is one of several species being considered for new fisheries off the coast of British Columbia. This proposal has been following the phased approach for new and developing fisheries. The program has been inactive since 2003 when the last experimental fishery took place. The fishery was not economically viable for the Tanner Crab Joint Venture Fishermen’s Association to continue.

The grooved tanner crab, Chionoecetes tanneri, is a large deep-water spider crab. Tanner crabs are Brachyuran crabs of the family Majidae, and genus Chionoecetes of which there are three species in B.C. Chionoecetes bairdi (Tanner crab), C. tanneri (Grooved Tanner crab) and C. angulatus (Angle Tanner crab).

This species resembles other spider crabs of the genus Chionoecetes, but is noted for its scarlet colour, deep chocolate eye colour, and the enlarged branchial lobes of the carapace with a deep groove between them (from which it derives its common name). The legs are longer and thinner than those of the Snow crab (Chionoecetes opilio) or the Alaskan Tanner (C. bairdi). It most closely resembles the other deep water crab of the same genus, C. angulatus or Angle Tanner.

Photo: Tanner with black spot growth (Photo: Jim Boutillier)

Photo: Tanner with black spot growth (Photo: Jim Boutillier)

Photo: Detail of one claw (Chionoecetes tanneri)

Photo: Detail of one claw (Chionoecetes tanneri)

Photo: Tanner crab with ruler (Chionoecetes tanneri)

Photo: Tanner crab with ruler (Chionoecetes tanneri)

C. tanneri are unique to the western Pacific where they occur from Mexico to the Gulf of Alaska at depths ranging from 53 - 1,944 m. In B.C., they are known from 458 - 1,784 m. Their theoretical bathymetric distribution is a narrow ribbon bounded by these depths along the continental slope.

Adult male distribution off Vancouver Island is between 580 and 670 m, while females occur deeper, between 670-720 m during most of the year. During late March to April however, it appears that females move shallower for the purpose of egg release and mating. Primiparous females, apparently, are not bred as softshell crabs as in other Chionoecetes, but as hardshell animals following a moult during the previous spring/summer period. It is likely that adult females are capable of producing at least 2 batches of eggs during their reproductive careers, although it is unclear whether they also use stored sperm to fertilize multiple egg clutches (as with most other majid crabs) or whether annual breeding is required.

Little is know about growth rates or the age structure for this species. Size distribution from samples taken off Vancouver Island are 100-174 mm for males and 94-138 mm for females. Data estimates of size at maturity are 112 mm carapace width (CW) for males and 88 mm CW for females. Detail of one claw (Chionoecetes tanneri) Tanner crab with ruler (Chionoecetes tanneri).

C. tanneri Assessment Program

The deep water grooved tanner crab (Chionoecetes tanneri) is being investigated as one of several species proposed as new fisheries off the coast of British Columbia. Investigation of the fishery potential of this species has been following the Phased approach for the provision of scientific information for new and developing fisheries (Perry et al. 1999). The assessment of the possibility of a C. tanneri crab fishery is currently in the second phase.

Following the Phase 0 review a number of information gaps were identified. These included:

Phase 1 recommendations for C. tanneri included:

DFO Trawl Surveys

Trawl surveys were completed by the DFO from the research vessel CCGS W.E. RICKER between 1999 and 2003, with supplementary trap surveys in the first three years. Trawl surveys took place on the west coast of North Vancouver Island, Queen Charlotte Sound, and the west coast of North and South Queen Charlotte Island.

Industry Trap Surveys

Industry completed distributional trap surveys of West Coast Vancouver Island in 1999/2000 and completed surveys off West Coast Queen Charlotte Island in 2003.

Experimental Fishing

Industry has conducted experimental fisheries in Pacific Fisheries Management Areas (PFMA) 125 and 126 between 1999 and 2003. Detailed fishing location, catch information and biological data were collected from each set, during the experimental fishery. Objectives of the experimental fishery were to:

These questions need examining because female Tanner crabs account for the greatest by-catch.

Photo: Many C. tanneri harvested (photo: Ken Fong)

Photo: Many C. tanneri harvested (photo: Ken Fong)

Photo: Experimental fishery (photo: Ken Wong)

Photo: Experimental fishery (photo: Ken Wong)

Photo: C. tanneri being loaded (Photo: Ken Fong)

Photo: C. tanneri being loaded (Photo: Ken Fong)

Photo: Experimental fishery (photo: Ken Wong)

Photo: Experimental fishery (photo: Ken Wong)

Tanner Crab (C. bairdi)

Chionoecetes bairdi or inshore Tanner crab is one species that is considered to have potential for a new commercial fishery. This consideration follows a phased approach to new and developing fisheries to ensure that any eventual commercial activity is biologically sustainable. The Wuikinuxv (Oweekeno) First Nation in collaboration with DFO explored the opportunity of developing a fishery for inshore Tanner crab throughout the Rivers Inlet system.

Fong, K.H. and J.S. Dunham. 2005. A progress report on the development of a new fishery for inshore Tanner crabs (Chionoecetes bairdi Rathbun, 1924) in Rivers Inlet, British Columbia. PSARC Working Paper. 2005-06: 90p.

G. Krause, G. Workman, A. Phillips. 2001. A Phase '0' Review of the Biology and Fisheries of the Tanner Crab (Chionoecetes bairdi). ( PDF)

Tanner crabs are members of the Phylum Arthropoda; Subphylum Crustacea; Class Malacostraca; Subclass Eucarida; Order Decapoda; Family Majidae; and Genus Chionoecetes. Members of the Family Majidae or true crabs are noted for having 4 sets of walking legs and 2 claws unlike members of the Family Lithodidae or king crabs which have only 3 pairs of walking legs. Only three species of Chionoecetes crabs (C. bairdi, C. tanneri, and C. angulatus) are found in British Columbia waters.

Members of the genus Chionoecetes share many morphological, physiological and reproductive features. C. bairdi is recognized for its orange-brown colour dorsally, pink-cream colour ventrally and relatively flat branchial areas (unlike the grooved Tanner crab, C. tanneri, and angle Tanner crab, C. angulatus, which are bright orange and have enlarged branchial lobes).

Chionoecetes bairdi are distributed in the eastern Pacific Ocean from Oregon to Alaska in depths of 0-400 m. In British Columbia they are found throughout the coast in both coastal inlets and offshore. C. bairdi occurs in abundance from northern British Columbia though the Aleutian chain to the Sea of Okhotsk and the Sea of Japan. They supports a major commercial fishery in Alaska where they are known simply as Tanner crabs.

Photo: Several C. bairdi (Photo: Ken Fong)

Photo: Several C. bairdi (Photo: Ken Fong)

In Alaskan waters, female tanner crabs are reported to pass through 12 instars before undergoing a terminal moult in about 5 years. Meanwhile, male Tanner crabs are estimated to pass through as many as 18 instars in about 6 years when reaching maturity, although the presence of a terminal moult in males remains debatable among researchers. The frequency and timing of moulting is likely dependent on water temperature, food availability and breeding behaviour.

Juvenile males and females are found at similar depths throughout the year until they near the moult to puberty when the distribution patterns diverge. Pubescent female tanner crabs have been observed in shallow inshore waters while mature, multiparous females were generally found in deeper waters. As the animals grow, males take up residence over a much larger bathymetric range than females but it appears that the majority of adult (male and female) Tanner crabs migrate to water deeper than 100 m after reaching maturity and mating for the first time. The sexes in Chionoecetes tend to segregate by depth except during the mating season. The reasons for segregation are not clear but may be the result of intraspecific competition as there is a marked sexual dimorphism.

Adults tend to be found buried in mud-sand substrates, a common behavior to many crab species that live in soft bottoms. Females are nocturnally active, during daylight hours they remain buried in the substrate, presumably as a defense against predators. Juveniles of both sexes and males are suspected of burying, but to what extent is unknown.

There are at least three major pathogens identified in Chionoecetes crabs. Bitter crab disease (BCD) is caused by a dinoflagellate parasite (Hematodinium spp.) in the hemolymph which produces a wasting disease ultimately resulting in death of the host. The disease also creates a bitter taste to crab meat rendering it unusable. Black mat disease is an encrusting fungus infection caused by the ascomycete Trichomaris invadens. The fungus forms a thick tar-like mass on infected individuals from which the name is derived, but also invades the cuticle and various deeper tissues and may prevent moulting and eventually causes death of the host. Nemertean worm egg predators are known to cause egg loss in Red King crabs and Tanner crabs species.

C. bairdi Assessment Program

Photo : C. bairdi, female and male (Photo : Ken Fong)

Photo : C. bairdi, female and male (Photo : Ken Fong)

In 2001, the Pacific Scientific Advice Review Committee (PSARC) accepted a Phase 0 review of the biology of C. bairdi. The review identified several basic information requirements needed to support the sustainable development of a C. bairdi fishery in B.C in a precautionary, risk averse manner. These include stock distribution, population size and life history characteristics.

Fisheries & Oceans Canada and the Wuikinuxv Nation partnered in carrying out a Phase 1 assessment of C. bairdi populations in Rivers Inlet and portions of Fitz Hugh Sound located in the central coast region of British Columbia. Several structured trap and trawl surveys were carried-out between 2004 and 2005.

There didn’t appear to be a sufficient population of marketable size crabs that would make this fishery economically viable although there wasn’t enough information available to make generalized statements of local stock composition of Tanner crabs in other areas outside of Rivers Inlet.

Crab Publications

Below are some selected publications by the Crab program.

Citations may include abstracts (HTML) or the full document may be available for viewing as an Adobe Acrobat file (*.pdf).

C. tanneri Publications

C. bairdi Publications