Snow Crab
Snow Crab
Tanner Crab/By Robert Shetterly Copyright © Blue Ocean Institute
Tanner Crab/By Robert Shetterly Copyright © Blue Ocean Institute

Snow and Tanner Crabs (U.S. and Canada)

Snow Crab (Chionoecetes opilio); C. bairdi; Grooved Tanner Crab (C. tanneri)

Sometimes known as Alaska Snow Crab, Atlantic Snow Crab, Queen Crab or Spider Crab.

These species are wild-caught.

Summary

Snow Crabs in Alaska are classified as overfished, owing to their low level of abundance. Although fishery managers have implemented rebuilding measures, it is too soon to tell if they are effective. Canadian Atlantic populations are considered healthy. Snow Crabs are caught in pots, which cause moderate damage to habitat, but generally have lower bycatch than other fishing methods.

Criterion Points
Life History 1.50
Abundance 1.50
Habitat Quality and Fishing Gear Impacts 2.25
Management 2.75
Bycatch 2.75
Final Score (average of criteria) 2.15
Color
Final Score Color
2.60 - 4.00
2.20 - 2.59
1.80 - 2.19
1.40 - 1.79
0.00 - 1.39

Last updated March 10, 2005.

Life History

Core Points (only one selection allowed)

If a value for intrinsic rate of increase (‘r’) is known, assign the score below based on this value. If no r-value is available, assign the score below for the correct age at 50% maturity for females if specified, or for the correct value of growth rate ('k'). If no estimates of r, age at 50% maturity, or k are available, assign the score below based on maximum age.

1.00
Intrinsic rate of increase <0.05; OR age at 50% maturity >10 years; OR growth rate <0.15; OR maximum age >30 years.
2.00
Intrinsic rate of increase = 0.05-0.15; OR age at 50% maturity = 5-10 years; OR a growth rate = 0.16–0.30; OR maximum age = 11-30 years.

Estimates of intrinsic rate of increase for the three species marketed as "Snow Crabs" are unavailable. Estimates of age at maturity are available for female and male Tanner Crabs: approximately 5 and 6 years of age, respectively. Snow Crabs and Tanner Crabs may live a maximum of approximately 14 years (ADF&G 1994).

3.00
Intrinsic rate of increase >0.16; OR age at 50% maturity = 1-5 years; OR growth rate >0.30; OR maximum age <11 years.

Points of Adjustment (multiple selections allowed)

-0.25
Species has special behaviors that make it especially vulnerable to fishing pressure (e.g., spawning aggregations; site fidelity; segregation by sex; migratory bottlenecks; unusual attraction to gear; etc.).

Snow, Tanner, and Grooved Tanner Crabs spend most of the year in aggregations, which makes them easier to catch (ADF&G 1994). Tanner Crab females are known to form high-density mating aggregations, or mounds, consisting of hundreds of crabs per mound (NMFS 2004).

-0.25
Species has a strategy for sexual development that makes it especially vulnerable to fishing pressure (e.g., age at 50% maturity >20 years; sequential hermaphrodites; extremely low fecundity).

After the eggs are fertilized, female Snow Crabs carry clutches of 50,000 to 400,000 eggs under their abdominal flap for just under a year (NMFS 2004).

-0.25
Species has a small or restricted range (e.g., endemism; numerous evolutionarily significant units; restricted to one coastline; e.g., American lobster; striped bass; endemic reef fishes).
-0.25
Species exhibits high natural population variability driven by broad–scale environmental change (e.g., El Nino; decadal oscillations).

Snow and Tanner Crab abundance in U.S. waters has been observed to fluctuate significantly over time according to fishery data and trawl surveys conducted by NOAA's National Marine Fisheries Service and the Alaska Department of Fish and Game. Such significant changes in abundance may reflect effects of ecosystem processes that control different life history stages and, ultimately, commercial fisheries for these species (NMFS 2004).

+0.25
Species does not have special behaviors that increase ease or population consequences of capture OR has special behaviors that make it less vulnerable to fishing pressure (e.g., species is widely dispersed during spawning).
+0.25
Species has a strategy for sexual development that makes it especially resilient to fishing pressure (e.g., age at 50% maturity <1 year; extremely high fecundity).
+0.25
Species is distributed over a very wide range (e.g., throughout an entire hemisphere or ocean basin; e.g., swordfish; tuna; Patagonian toothfish).

Snow Crabs are distributed throughout the North Atlantic as far south as Maine, on the continental shelf of the Bering Sea, in the Arctic Ocean, and in the Sea of Japan. Snow Crabs are not present in the Gulf of Alaska (NMFS 2004).

Tanner Crabs occur in the Gulf of Alaska, Aleutian Islands, and the Bering Sea. Tanner Crabs are concentrated around the Pribilof Islands and immediately north of the Alaska Peninsula and are found in lower abundance in the Gulf of Alaska (NMFS 2004).

+0.25
Species does not exhibit high natural population variability driven by broad-scale environmental change (e.g., El Nino; decadal oscillations).
1.50
Points for Life History

Abundance

Core Points (only one selection allowed)

Compared to natural or un-fished level, the species population is:

1.00
Low: Abundance or biomass is <75% of BMSY or similar proxy (e.g., spawning potential ratio).
2.00
Medium: Abundance or biomass is 75–125% of BMSY or similar proxy; OR population is approaching or recovering from an overfished condition; OR adequate information on abundance or biomass is not available.

In Alaska, abundance of Snow Crabs is determined by estimating the spawning biomass, or the total biomass of mature males and females. A maximum sustainable yield (MSY) for Snow Crabs is estimated by determining the minimum stock size threshold (MSST), or 50% of the mean total spawning biomass (SB) in a given period. Snow Crab populations with SB less than MSST are classified as overfished, regardless of the cause of low abundance (NPFMC 2000). In 2002, C. opilio, which supplies the majority of U.S. landings, fell below the MSST level. The East Bering Sea Grooved Tanner Crab population is considered to be overfished and no fishery occurs. Two Kodiak districts and all of Southeast Alaska have viable Tanner Crab fisheries at present (Kruse, G., pers. comm., 11/10/2004).

In Canadian waters, the Snow Crab population appears to be more abundant. The DFO considers Atlantic C. opilio to be healthy (DFO 2001). Studies conducted by the Department of Fisheries and Oceans show that Snow Crab populations are variable and subject to natural fluctuation. Increases and decreases in abundance are considered normal and are unrelated to other fisheries in Atlantic Canada. Some years, such as the 1999 fishing season in Newfoundland, present unusual above-average yields of Snow Crab (DFO 2004).

A medium score was awarded here to account for the difference in abundance between Alaska's snow crab populations and those off Canada.

3.00
High: Abundance or biomass is >125% of BMSY or similar proxy.

Points of Adjustment (multiple selections allowed)

-0.25
The population is declining over a generational time scale (as indicated by biomass estimates or standardized CPUE).

Studies show an overall decline in the abundance and size of snow crab throughout the Atlantic provinces of Canada (DFO 2004).

-0.25
Age, size or sex distribution is skewed relative to the natural condition (e.g., truncated size/age structure or anomalous sex distribution).
-0.25
Species is listed as “overfished” OR species is listed as “depleted”, “endangered”, or “threatened” by recognized national or international bodies.

Several populations of species sold as Snow Crabs are classified as overfished. On March 3, 1999, NOAA Fisheries declared the Bering Sea Tanner Crab population to be overfished because the population was below the MSST level (65 Federal Register 76175 December 6, 2000). On September 24, 1999, NOAA Fisheries declared the Bering Sea Snow Crab to be overfished (66 Federal Register 742, January 4, 2001).

-0.25
Current levels of abundance are likely to jeopardize the availability of food for other species or cause substantial change in the structure of the associated food web.
+0.25
The population is increasing over a generational time scale (as indicated by biomass estimates or standardized CPUE).
+0.25
Age, size or sex distribution is functionally normal.
+0.25
Species is close to virgin biomass.
+0.25
Current levels of abundance provide adequate food for other predators or are not known to affect the structure of the associated food web.
1.50
Points for Abundance

Habitat Quality and Fishing Gear Impacts

Core Points (only one selection allowed)

Select the option that most accurately describes the effect of the fishing method upon the habitat that it affects.

1.00
The fishing method causes great damage to physical and biogenic habitats (e.g., cyanide; blasting; bottom trawling; dredging).
2.00
The fishing method does moderate damage to physical and biogenic habitats (e.g., bottom gillnets; traps and pots; bottom longlines).

Typically, Snow Crabs are caught with large steel-mesh traps (also called pots) over a sandy seafloor, at depths ranging from 30 to 1500 feet (Neptune 2001; ADF&G 1994). Pots are usually baited with chopped herring and are left to soak and catch crabs for 1-3 days before being hauled aboard (ADF&G 1994).

The crab fisheries may impact benthic habitat through the setting and retrieval of pots. The extent of habitat impacts depends on the type of bottom habitat (U.S. National Marine Fisheries Service, 2004).

3.00
The fishing method does little damage to physical or biogenic habitats (e.g., hand picking; hand raking; hook and line; pelagic long lines; mid-water trawl or gillnet; purse seines).

Points of Adjustment (multiple selections allowed)

-0.25
Habitat for this species is so compromised from non-fishery impacts that the ability of the habitat to support this species is substantially reduced (e.g., dams; pollution; coastal development).
-0.25
Critical habitat areas (e.g., spawning areas) for this species are not protected by management using time/area closures, marine reserves, etc.
-0.25
No efforts are being made to minimize damage from existing gear types OR new or modified gear is increasing habitat damage (e.g., fitting trawls with roller rigs or rockhopping gear; more robust gear for deep-sea fisheries).
-0.25
If gear impacts are substantial, resilience of affected habitats is very slow (e.g., deep water corals; rocky bottoms).
+0.25
Habitat for this species remains robust and viable and is capable of supporting this species.
+0.25
Critical habitat areas (e.g., spawning areas) for this species are protected by management using time/area closures, marine reserves, etc.
+0.25
Gear innovations are being implemented over a majority of the fishing area to minimize damage from gear types OR no innovations necessary because gear effects are minimal.
+0.25
If gear impacts are substantial, resilience of affected habitats is fast (e.g., mud or sandy bottoms) OR gear effects are minimal.

Pots are generally set on soft bottom habitats with little biotic structure (Kruse, G., pers. comm., 11/10/2004).

2.25
Points for Habitat Quality and Fishing Gear Impacts

Management

Core Points (only one selection allowed)

Select the option that most accurately describes the current management of the fisheries of this species.

1.00
Regulations are ineffective (e.g., illegal fishing or overfishing is occurring) OR the fishery is unregulated (i.e., no control rules are in effect).
2.00
Management measures are in place over a major portion over the species’ range but implementation has not met conservation goals OR management measures are in place but have not been in place long enough to determine if they are likely to achieve conservation and sustainability goals.

The majority of Snow Crabs sold in the U.S. are caught in U.S. or Canadian fisheries, both of which have well developed management frameworks. Goals appear to be met in Canada's Atlantic waters, as Snow Crab population appears to be healthy (DFO 2001). Management measures include limited entry, total allowable catch limits, gear restrictions, minimum size limits, and area closures.

The state of Alaska manages crab stocks in the Bering Sea and Aleutian Islands through a federal Fishery Management Plan (NMFS 2004). However, despite strong management frameworks, substantial problems exist in the U.S. Snow Crab fisheries such as overcapitalization and overfishing (NMFS 2004). Appropriate management measures are in place, goals appear to be being met in Canadian fisheries, but Alaska rebuilding measures have not yet been demonstrated to be effective, so a score of 2 is awarded.

3.00
Substantial management measures are in place over a large portion of the species range and have demonstrated success in achieving conservation and sustainability goals.

Points of Adjustment (multiple selections allowed)

-0.25
There is inadequate scientific monitoring of stock status, catch or fishing effort.
-0.25
Management does not explicitly address fishery effects on habitat, food webs, and ecosystems.
-0.25
This species is overfished and no recovery plan or an ineffective recovery plan is in place.
-0.25
Management has failed to reduce excess capacity in this fishery or implements subsidies that result in excess capacity in this fishery.
+0.25
There is adequate scientific monitoring, analysis and interpretation of stock status, catch and fishing effort.

In the U.S. and Canada, where the vast majority of Snow Crabs in the U.S. market are caught, fishery independent surveys are conducted to assess Snow Crab populations (DFO 2004; NMFS 2001, 2004).

U.S. Snow Crab catches are continuously monitored using in-season industry reports, fish tickets and, in some cases, state fishery observers (NPFMC 1998a, 1998b). Snow Crab fishers are required to report bycatch on fish tickets (ADF&G 2001a; NPFMC 1998b). Enforcement is strict in U.S. Snow Crab fisheries (NPFMC 2000).

Canada’s Snow Crab fisheries are monitored via fisheries logbooks, landings surveys, dockside sampling, and at-sea observers (DFO 1999, 2001, 2002c). In the Southern Gulf of St. Lawrence (Canada’s largest Snow Crab fishery) at-sea observers cover 30% of days the fleets are on the water (DFO 1999). Bycatch of softshelled Snow Crab, known as "white crab" (Marine Institute 2002), is monitored by DFO managers, and Snow Crab fishers are requested to move out of any areas where white crab exceeds 20% of their take (DFO 1999).

+0.25
Management explicitly and effectively addresses fishery effects on habitat, food webs, and ecosystems.
+0.25
This species is overfished and there is a recovery plan (including benchmarks, timetables and methods to evaluate success) in place that is showing signs of success OR recovery plan is not needed.

On March 3, 1999, NMFS declared Bering Sea Tanner Crab to be overfished, because the stock was below the MSST of 94.8 million pounds. The North Pacific Fishery Management Council developed the rebuilding plan as Amendment 11, which NMFS approved on November 26, 2000 (65 Federal Register [FR] 76175 December 6, 2000). On September 24, 1999, NMFS declared Bering Sea Snow Crab to be overfished, because the stock was below the MSST of 460.8 million pounds. The Council developed the Snow Crab rebuilding plan as Amendment 14. NMFS approved the rebuilding plan on December 28, 2000 (66 FR 742, January 4, 2001). Each rebuilding plan contains a rebuilding harvest strategy, bycatch control measures, and habitat protection measures. The rebuilding harvest strategies are the main components of these rebuilding plans and provide for the rebuilding of the stocks (NMFS 2004).

A 3 to 10 year rebuilding plan for the Snow Crab population in the Bering Sea is currently in progress. Under the plan the fishery is required to close if the population falls below 50% MSST (AFSC 2002).

+0.25
Management has taken action to control excess capacity or reduce subsidies that result in excess capacity OR no measures are necessary because fishery is not overcapitalized.

The U.S. National Marine Fisheries Service is proposing management changes to the Bering Sea and Aleutian Islands crab fishery to address problems of excess capacity and derby- style races for fish (NMFS 2004).

2.75
Points for Management

Bycatch

Core Points (only one selection allowed)

Select the option that most accurately describes the current level of bycatch and the consequences that result from fishing this species.

The term, "bycatch” used in this document excludes incidental catch of a species for which an adequate management framework exists.

The terms, “endangered, threatened, or protected,” used in this document refer to species status that is determined by national legislation such as the U.S. Endangered Species Act, the U.S. Marine Mammal Protection Act (or another nation's equivalent), the IUCN Red List, or a credible scientific body such as the American Fisheries Society.

1.00
Bycatch in this fishery is high (>100% of targeted landings), OR regularly includes a “threatened, endangered or protected species.”
2.00
Bycatch in this fishery is moderate (10-99% of targeted landings) AND does not regularly include “threatened, endangered or protected species” OR level of bycatch is unknown.

Bycatch in Alaska Bering Sea Snow Crab fisheries is estimated by state fisheries observers and reported in annual management reports.

Various species of crab are harvested in the Canadian Atlantic Provinces. Snow Crab make up the majority of the landings, but other species include Spider-toad, Jonah, Rock, Red and Porcupine Crab, octopus, and flatfish (DFO 2004; NMFS 2004).

The Alaska crab fisheries catch a small amount of other species as bycatch. These species include octopus, Pacific Cod, Pacific Halibut, and other flatfish. All bycatch is discarded. Typically, low levels of bycatch of these species do not impact their abundance (NMFS 2004).

The vast majority of bycatch in the crab fisheries are females of the target species, sub-legal males of target species, and non-target crabs (NPFMC 2000). All bycatch of non-legal crabs are discarded at sea (NMFS 2004). A majority of the unwanted catch in Bering Sea Snow Crab fisheries are legal males that are a bit smaller than the industry demands (Pengilly et al., 2001). Bycatch of non-crab species in pot gear is usually comprised of an occasional octopus or large fish. However, a quantitative estimate of bycatch relative to targeted landings was not available at the time of this evalation. Because of injuries or stress sustained in capture, it is assumed that about 25% of discarded Snow Crabs will die; as C. opilio is thought to be more susceptible to discard mortality than other Chionoecetes species, this is considered a maximum discard mortality for all Bering Sea Chionoecetes fisheries (Pengilly et al. 2001).

Pot gear potentially can cause mortality to benthic species when pots settle to the bottom and when they are hauled back to the surface. Lost pots cam also impact benthic species by continuing to capture and kill them, known as ghost fishing (U.S. National Marine Fisheries Service, 2004). All crab pots, however, are required to have biodegradable twine to allow escape from lost pots (Kruse, G., pers. comm., 11/10/2004).

3.00
Bycatch in this fishery is low (<10% of targeted landings) and does not regularly include "threatened, endangered or protected species."

Points of Adjustment (multiple selections allowed)

-0.25
Bycatch in this fishery is a contributing factor to the decline of “threatened, endangered, or protected species" and no effective measures are being taken to reduce it.
-0.25
Bycatch of targeted or non-targeted species (e.g., undersize individuals) in this fishery is high and no measures are being taken to reduce it.
-0.25
Bycatch of this species (e.g., undersize individuals) in other fisheries is high OR bycatch of this species in other fisheries inhibits its recovery, and no measures are being taken to reduce it.
-0.25
The continued removal of the bycatch species contributes to its decline.
+0.25
Measures taken over a major portion of the species range have been shown to reduce bycatch of “threatened, endangered, or protected species” or bycatch rates are no longer deemed to affect the abundance of the “protected” bycatch species OR no measures needed because fishery is highly selective (e.g., harpoon; spear).
+0.25
There is bycatch of targeted (e.g., undersize individuals) or non-targeted species in this fishery and measures (e.g., gear modifications) have been implemented that have been shown to reduce bycatch over a large portion of the species range OR no measures are needed because fishery is highly selective (e.g., harpoon; spear).

Alaska State regulations prescribe gear modifications to inhibit the bycatch of small crab, female crab, and other species of crab. Gear modifications include escape rings, tunnel size, and a requirement that crab pots be fitted with a degradable escape mechanism (NMFS 2004).

The state of Alaska has attempted to reduce bycatch of other non-targeted crabs in directed crab fisheries through various management measures. For example the season for Grooved Tanner Crab in the Bering Sea has been held in conjunction with other fisheries (i.e Bristol Bay Red King Crab and Snow Crab) to reduce bycatch of legal-size Grooved Tanner Crab. Another example is gear modifications to reduce crab bycatch of non-targeted crab species, i.e. escape rings and tunnel height restrictions. ADF&G has also taken action to eliminate all bycatch by keeping the Pribilof District Red King Crab season closed to eliminate all Blue King Crab bycatch. In addition, harvest strategies developed for Bering Sea King and Tanner Crab stocks since the mid-1990's account for assumed incidental harvest and handling mortality of non-retained crabs in the determination of the harvest rate on mature or legal sized males (NMFS 2004).

To reduce bycatch, both the U.S. and Canada require that all crab pots have escape devices for sublegal size crabs and that metal traps have release mechanisms to reduce ghost fishing if the trap is lost (ADF&G 1996; Pengilly 2003; Donaldson 2003).

+0.25
Bycatch of this species in other fisheries is low OR bycatch of this species in other fisheries inhibits its recovery, but effective measures are being taken to reduce it over a large portion of the range.

Snow crabs are taken as bycatch in Alaska bottom trawl fisheries. Snow Crabs are identified as prohibited species in this fishery, however, and are protected through the use of area closures and prohibited species caps (Kruse, G., pers. comm., 11/10/2004). Small amounts of Tanner Crab are taken as incidental catch in California and Oregon groundfish trawl fisheries (McCrae 1994).

+0.25
The continued removal of the bycatch species in the targeted fishery has had or will likely have little or no impact on populations of the bycatch species OR there are no significant bycatch concerns because the fishery is highly selective (e.g., harpoon; spear).

There are low levels of bycatch in Snow Crab fisheries, and the continued removal of the bycatch species is not believed to impact their population abundance. The Alaska crab fisheries catch a small amount of other species as bycatch. These species include octopus, Pacific Cod, Pacific Halibut, and other flatfish. All bycatch is discarded. Typically, low levels of bycatch of these species do not impact their abundance (NMFS 2004).

2.75
Points for Bycatch

References

Alaska Department of Fish and Game (ADF&G). 1994. Tanner Crabs. ADF&G Wildlife Notebook Series. Available at: http://www.adfg.state.ak.us/pubs/notebook/shellfsh/tanner.php.

Department of Fisheries and Oceans Canada (DFO). 1993. Snow Crab. Available at: http://www.mi.mun.ca/mi-net/fishdeve/crab.htm.

DFO. 2004. Snow Crab. Available at: http://www.dfo-mpo.gc.ca/media/backgrou/2003/snowcrab_e.htm.

DFO. 2002. Pacific Crab Commercial Harvest Plan, 2002. Available at: http://www-comm.pac.dfo-mpo.gc.ca/english/publications/crab.pdf.

McCrae, J. 1994. Grooved Tanner crab, Chionoecetes tanneri. Oregon Developmental Series; Oregon Department of Fish and Wildlife. Available at: http://www.hmsc.edu/odfw/devfish/sp/Tanner.html.

National Marine Fisheries Service (NMFS). 2004. Landings, import and export sources. Available at http://www.st.nmfs.gov/.

NMFS. 2004. Draft Environmental Impact Statement for Bering Sea and Aleutian Islands Crab Fisheries. Juneau, AK, USA.

NMFS. 2001. Bering Sea and Aleutian Islands Crab Fisheries Management. Available at: http://www.fakr.noaa.gov/sustainablefisheries/crab/.

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