Scientific Excellence • Resource Protection & Conservation

Scientific Excellence • Resource Protection & Conservation • Benefits for Canadians 2 Underwater Wo rld

arious crab species are adapted to world; even the small and unprepos- V a wide range of habitats off sessing green crab was a favorite in CRABS OF THE Canada's eastern coastline, from the Victorian London a century aga and is ATLANTIC COAST intertidal zone to the deep waters of the still eaten in Spain. One probable continental slope. However, des pite answer is that the cost of pioneering a OF CANADA their variety and abundance, Atlantic fishery, developing processing tech- Canadian crabs have hitherto remained niques and marketing routes for the largely underutilized. Currently, the crabs has appeared commercially unat- snow crab is the sole fully exploited tractive compared to the rewards from crab species, constituting a major other more traditional Atlantic fisher- resource in terms of bath landings and ies. Difficulties associated with fishing value. There is only small-scale trap- crab traps in deep, offshore waters, ping of the extensive jonah crab and gear conflicts with established fisheries Fig. 1 (or Frontispiece). Northwest rock crab stocks and essentially no and complications posed by the possi- Atlantic crab claws: form adapted to function. A. northern stone crab: a commercial landings of deep-sea red bility of by-catches of the more lucra- strong claw with blunt teeth designed crab, toad crab, northern stone crab, tive lobster have presented further for cracking heavily armored prey; porcupine crab or green crab. problems. B. snow crab: a slender, fine-toothed Each of the crab species has its own However, with overharvesting in but powerfully-muscled claw for chip- unique flavor and texture (even the some of the traditional fisheries, ping open mollusc shells and tearing smallest crabs are perfectly edible industry is being encouraged to diver- apart brittlestars; C. deep-sea red crab: although somewhat fiddly). Consider- sify and utilize the crab by-catch from a fast-action claw with sharp serrated ing that the crabs offer _delectable existing fisheries as well as start pilot teeth for biting and cutting softer- eating experiences as well as being fisheries directed exclusively for crab. bodied prey; D. jonah crab: a heavy claw extremely nutritious (the raw white An increased world market demand for able to exert slow but substantial forces ideal for crushing the shells of mol- meat contains about 20 per cent pro- crab products, created by collapses in luscs, sea urchins and crustaceans: tein, 1 to 2 per cent minerais, little fat the massive Alaskan crab fisheries, has E. rock crab: a 'generalist' claw, capable and hardly any carbohydrate), why are raised crab prices and further height- of opening shells as well as capturing they underutilized? ened the probability of an expanded and tearing apart agile, softer-bodied Certainly, crab species appear more Canadian crab fishery. Since crabs are prey. widely harvested in other parts of the likely to increase in commercial importance, it is particularly appropriate to summarize crab biology, ongoing research and the characteristics of the predominant species found in the Canadian Atlantic.

Crab Biology Crabs are decapod crustaceans (10-legged and having a crust or shell), a wide grouping that includes shrimps and lobsters. Many species of crabs are abundant, grow large and have a high and nutritious meat yield from their body and legs. Such properties have made them a favorite food for man and a target of heavy exploitation.

Moulting and Growth Being invertebrates (without back- bones), crabs rely on a hard external shell for skeletal support and protection. Despite the shell being jointed and somewhat flexible, al! crabs must cast off their old shell (a process known as moulting or ecdysis) in order to grow. Once the old shell has been shed, the wrinkled, soft crab takes up QL 626 U53 1989 Elner, R.W. EMAR LIBRARY 1 0 1 Crabs of the Atlantic coast _u_n_de-rw_a_ e_r_w__r _d ______FI Ss... H of Canada 118963 05014765 c.1 MB R3T 2N6 CANADA .

water and swells to its larger size within Reproduction a few hours. The new shell gradually For many crab species in the north- hardens and more muscles and tissue west Atlantic, mating usually takes grow inside, although it may take place between a newly-moulted, soft- several months for the crab to regain shelled, mature female and a larger its former shell hardness and condi- hard-shelled, mature male. The male tion. As crabs grow aider, they moult carries the female around before her Jess frequently and their percentage moult and may continue to protect her growth increment diminishes as well. for several days after copulation. The Fig. 2. Snow crab (Chionoecetes Since all the bard parts of the crab, male's behavior, as well as being of opilio). internai as well as external are lost at considerable survival value to the vul- moulting, no tell-tale indicators (such nerable female, serves to guard his as scale and otolith rings in fish) remain genetic investment against the death of to accurately age the animal. Hence, the female and displacement by other the age of a crab of a given size can males. Subsequently, the female only be backcalculated from estimates extrudes many thousands of fertilized of frequency of moulting and growth eggs onto the swimmerets under her per moult. Accurate information on abdomen. age is basic to much fisheries biology, Typically, larger females of a crab and the difficulty in obtaining this species carry more eggs than smaller information for crustaceans remains a females; a large female rock crab may fundamental problem. carry 330,400 eggs. The eggs usually hatch during the warmer months of the year and free-swimming larvae are Life Style released. The larvae may spend from The life style of a crab species is one to several months in the plankton uniquely reflected in the form taken by and moult through a number of stages its 10 legs. The first pair are modified before settling down on the sea bed and into conspicuous claws which, accord- moulting to the first crab stage. Ocean ing to the crab's feeding habits, have currents can transport larvae consider- evolved as optimal tools for the various able distances from their hatching crushing, cutting, digging, pinching, place. The massive mortalities that rasping and snatching actions required occur during the larval stages tend to to capture and devour prey. Contrary be compensated for by the vast to popula_r belief, most northwest numbers of larvae produced. Atlantic crabs are not simply "scav- engers" but predominantly carnivores with well-defined preferences for prey Crab Research such as mussels, snails and brittlestars. Since the early 1960s, fisheries Claws are also used in burrowing, biologists from provincial and federal fi ghting and, interestingly, signalling. governments, as well as from univer- Claw signais are a universal decapod sities, have been carrying out research '' language' ' and displays serve into crab. The work has been con- variously to ward off rivais for terri- ducted for a variety of purposes, to tory, repel would-be predators and estimate stock abundance and size attract mates; ail without recourse to composition, growth rate, reproduc- Fig. 3. Rock crab (Cancer irroratus). physical contact. Some crabs have tive pattern, movement, and exploita- achieved greater flexibility by having tion rate. However, all the work has a one large claw adapted for one major common aim in providing an accurate purpose, for example, crushing heavily picture of the crab resources so that armored molluscs or dis play, and the they can be properly managed. other smaller claw adapted for, say, Traps, beam trawls and towed under- snatching small agile prey. Although water camera sledges are used from the remaining four pairs of legs are government research vessels and com- modified most for movement, be it bur- mercial vessels under charter to assess rowing, climbing, swimming or walk- crab densities on the bottom. Tagging ing, they can also serve for feeding and techniques have been refined to pro- grasping. duce reliable tags that will be retained 4 Underwater World

when a crab moults. Such moult- fishermen, and placed the species retainable tags are expected to supply fourth in landed value in the Canadian valuable information on stock bio- Atlantic fishery behind cod, lobster mass, exploitation and growth, as well and scallop. The 37 ,255 t of snow crab as long-term movements. The ecology landed in 1983 had a record value in and population dynamics of juvenile excess of $53 million. snow crab are being subjected to Distribution - West Greenland to special investigation through beam Maine and from Alaska to Siberia; trawl surveys and stomach analyses of from 20 to 700 m. Commercial concen- the groundfish which feed on crab. trations occur on soft bottom around Continued research on the larval and Cape Breton, Newfoundland and in Fig. 4. Jonah crab (Cancer borealis). juvenile stages of crab remains a prior- the western Gulf of St. Lawrence, ity if the factors influencing growth especially from 70 to 280 m. Occa- and recruitment to the fishery are to be sionally found in the Bay of Fundy. understood. If commercial stock size Description - Somewhat flattened and production could be regularly walking legs that are two to three times predicted from larval and juvenile as long as carapace; almost circular abundances, fishery managers could carapace; pale brownish above, yellow- more effectively optimize exploitation ish below. Males reach a maximum of the resource. carapace width of 150 mm, a leg spread Commercial crab catches are moni- of approximately 0.9 manda weight of tored regularly at landing points 2.0 kg; females are not commercially throughout Atlantic Canada and sales fished as they attain a maximum receipts are analyzed. Sampling is also carapace width of only 47 to 95 mm. carried out at sea onboard licensed crab vessels and commercial vessels, such as seiners, that have a crab by- ROCK CRAB, Cancer irroratus (sand catch. Most importantly, data are crab, purple crab) analyzed from fishermen's logbooks. Where there has been a market, The logbooks provide critical details Canadian lobster fishermen have been such as daily catch weight, number and landing rock crab by-catches for type of traps hauled, trap location, and decades, although landings hardly soak time. When considered with the exceeded 230 t per annum prior to commercial catch sampling data, the 1973. However, with greater demand logbooks provide a vital means of and occasional directed fisheries for assessing stock size, exploitation rate, rock crab, landings have since risen; in and stock dynamics. To this end, the 1983 approximately 500 t of rock crab continued cooperation of fishermen in were caught (valued at about $111,000) maintaining accurate logbooks is principally from the Northumberland essential. Strait. The sustainable annual rock The following overviews and de- crab yield from the southern Gulf of scribes nine species of crabs likely to be St. Lawrence has been estimated at encountered in Atlantic Canada. 1360 to 2270 t. Nevertheless, despite effective crab traps having been developed to exclude a lobster by- Fig. 5. Deep-sea red crab (Geryon SNOW CRAB, Chionoecetes opilio catch, the relatively small size of this quinquedens.) (spider crab, queen crab, zuwai crab) crab, its low meat yield and high pro- The exploitation of snow crab in cessing costs have so far hindered Atlantic Canada started in 1960 with development of a wide-spread directed small incidental by-catches by ground- fishery. fish draggers off Gaspé, Quebec. How- Distribution - Labrador to South ever, since the inception of a directed Carolina. Found from low water to trap fishery in 1966, after exploratory 600 m; commonest in shallow water, vessels located extensive stocks in the especially in bays. Highly abundant in Gulf of St. Lawrence, annual landings the southern Gulf of St. Lawrence, have increased rapidly. Peak catches of although plentiful along the coastline over 47 ,000 metric tons (t) in 1982 were of Newfoundland, Nova Scotia and worth more than $43 million to the in the Bay of Fundy. Most frequently Unde rwate r World 5

encountered on open sand or sand- a small-scale pilot fishery existed on mud bottoms. the Scotian Shelf edge in the early Description Nine, shallow, 1970s. However, fisheries have been smooth-edged marginal teeth along established for this large attractive crab each side of the front edge of the along the Atlantic coast of the United carapace; marginal teeth pointed at States and off the west coast of Africa widest part of carapace; surface of sin ce 1973. Recent exploratory surveys claws and carapace relatively smooth indicate a trappable resource in excess (compared to jonah crab); background of 2700 t of large male crabs along the colour variable above, generally yellow- Scotian Shelf edge from the Fundian brown, with overlay of minute purple Channel to Sable Island. The flavor Fig. 6. Green crab (Carcinus or crimson spots; pale yellow under- and texture of deep-sea red crab meat maenas). neath; up to approximately 140 mm is excellent and the species shows real carapace width and 0.25 kg in weight. commercial potential, particularly in conjunction with the directed trap fishery for jonah crab. JONAH CRAB, Cancer borealis Distribution - Nova Scotia to Cuba; (white crab) commonly from 40 to 2000 m. Very There have been intermittent small abundant in patches along edge of the landings of jonah crab by-catches by continental slope from western Scotian lobster fishermen in the Bay of Fundy Shelf to Georges Bank at depths of 180 and off southern Nova Scotia since the to 550 m. Occurs in the Bay of Fundy. mid 1960s. Canadian jonah crab land- Found on mud, sand or hard bottoms. ings in 1983 amounted to approximate- Description - Carapace squarish; ly 204 t, with 90 t being accounted for usually deep orange or red; five mar- by a newly-instigated directed pilot ginal teeth along each side of the cara- fishery on the Scotian Shelf. With high pace; walking legs long and slender; catch rates by the directed fishery in males reach a maximum carapace width 1984 and processing difficulties (due to of approximately 180 mm and a weight the jonah crab's hard brittle shell) of nearly 1.4 kg . being overcome, the commercial fore- cast for this fine-flavored crab appears promising. GREEN CRAB, Carcinus maenas Distribution - Occurs from Nova (shore crab, harbor crab, japanese crab) Scotia to South Carolina; from low The green crab, in addition to offer- water to over 800 m. Dominant crab ing some limited opportunities for species at intermediate depths away exploitation, is particularly renowned from shore off Nova Scotia; present in as a serious pest of other shellfisheries. the Bay of Fundy. Not recorded from Probably introduced from Europe in Gulf of St. Lawrence. ships' bilges, the green crab was Description - Similar to rock crab, restricted to shores south of Cape Cod but carapace outline more rounded, until the late 1800s. Aided by general legs relatively shorter but claws more warming trends, the species has slowly massive than rock crab; nine, rectan- spread northwards until its present day gular, rough-edged marginal teeth on distribution extends into the Bay of each side of the front edge of the Fundy and along the Atlantic coast of carapace; surface of claws and cara- mainland Nova Scotia. A rapacious pace rough; background colour vari- predator of clams, mussels and oysters able but generally yellow-brown above on both sides of the north Atlantic, the Fig. 7. Northern stone crab (Lith- and yellowish below. Up to approxi- green crab is also a pugnacious com- odes maja ). mately 180 mm carapace width and petitor with lobsters and other crab 0.4 kg in weight. species for prey and space. The green crab's small size probably precludes anything other than localized, casual DEEP·SEA RED CRAB, Geryon harvesting of the largest individuals for quinquedens food; however; it is of minor commer- There are presently no Canadian cial importance as a bait for sport landings of deep-sea red crab although fishermen in the United States and Europe. 6 Underwater World

Distribution - Abundant along the theless of concern to shellfish culturists Atlantic coast of Nova Scotia to Bay of because of its pestiferous nature. In the Fundy to New Jersey. Commonest crab southern Gulf of St. Lawrence, mud on rocky shores, occurs intertidally crabs feed on small oysters attached to and subtidally to about 10 m. spat collectors. Although the average Description - Carapace colour dark predation rate by an individual mud green to brown, sometimes with white crab is probably no more than one or black patches; five prominent mar- oyster every 2 days, the large numbers ginal teeth along each side of carapace. of the crabs magnify their impact and Claws usually unequal; posterior pair make control measures desirable. Fig. B. Mud crab (Neopanope sayi). of legs compressed with marginal Distribution - Gulf of St. Lawrence hairs. Males reach a maximum cara- to Florida; abundant during the sum- pace width of about 85 mm and weight mer months in bays around Prince of 0.2 kg . Edward Island, occasionally encountered around Nova Scotia and the Bay of Fundy. Occurs on soft mud bottoms NORTHERN STONE CRAB, to about 10 m. Lithodes maja (spider crab) Description - Carapace oval shaped, Concentrations of the northern stone dark reddish-brown in colour. Males crab on the southern Scotian Shelf have have markedly unequal claws with the occasionally been subject to small-scale fingers dark brown or black. A small, exploratory trapping by offshore stout crab reaching no more than lobster and jonah crab vessels. 27 mm across the carapace. Although meat from these striking crabs is apparently delicious, the shells are reported to be extremely hard. The TOAD CRAB, Hyas sp. (policeman overall distribution of high concentra- crab, sea toad, spider crab) tions of northern stone crab appears so The ubiquitous toad crabs are com- limited as to preclude either a long- mon by-catch in the existing lobster term directed fishery or a by-catch and snow crab fisheries and could also fishery; however, the species might be form an incidental catch to developing a target for periodic pulse fishing by crab fisheries. Although unattractive crab and lobster vessels when catches ''in-the-shell'' and unlikely to warrant of more traditional crustaceans are directed harvesting, the extracted meat low. from the by-catch of larger toad crabs Distribution - Newfoundland to might form a worthwhile supplement New Jersey and northwestern Europe; to lobster and other crab catches. from 65 to 800 m. In the Gulf of Distribution - Widespread on both St. Lawrence it appears to live in sides of the north Atlantic; from low deeper, warmer water than the snow water to about 1650 m; in the Gulf of crab. Occurs in Bay of Fundy and on St. Lawrence and Bay of Fundy, around the Scotian Shelf. Very abundant in Newfoundland and Nova Scotia. Very patches at intermediate depths. common in places, mostly at inter- Distribution - Resembles snow crab mediate depths, overlaps rock crab and in size and general shape but readily snow crab zones. identified by the numerous prominent Description - Uneven carapace sur- Fig. 9. Toad crab (Hyas sp.). spines on its carapace and legs; face; four pairs of round, tubular carapace slightly longer than wide; walking legs. Carapace approximately long spiny rostrum; orange/ red in 1 1 /3 times longer than wide; up to a colour; only 3 pairs of walking legs maximum carapace width of about apparent. Up to approximately 100 mm 100 mm and a spread of 450 mm; carapace width with a leg spread of maximum weight approximately 0.7 kg. 600 mm and a weight of 1.4 kg.

PORCUPINE CRAB, Neolithodes MUD CRAB, Neopanope sayi grimaldii (spiny spider crab) (Caribbean mud crab) There is so little information on the Too small to command gastro- distribution, abundance and life nomical interest, the mud crab is never- history of the porcupine crab that Underwater World 7

forecasts as to its commercial potential Miller, R.J. 1976. North American are very tenuous. Concentrations of crab fisheries: regulations and their the porcupine crab are probably so rationales. Fishery Bulletin 74: sporadic that it is improbable any long- 632-633. term directed or by-catch fisheries could develop. However, as for the Scarratt, D.J., and R. Lowe. 1972. northern stone crab, it is possible that Biology of rock crab (Cancer intermittent landings may occur if crab irroratus) in Northumberland Strait. or lobster fishermen decide to occa- Journal of the Fisheries Research sionally retarget onto commercial Board of Canada 29: 161-166. patches of these extraordinary looking beasts. Warner, G.F. 1977. The biology of Fig. 10. Porcupine crab (Neolithodes Distribution - Both sides of the crabs. Van Nostrand Reinhold grima/dii). north Atlantic; 100 to 2000 m. Occurs Company, New York: 202 p. in patches at intermediate depths on the Scotian Shelf. Not recorded from Text: Gulf of St. Lawrence or Bay of Fundy. Robert W. Elner Description - Similar to northern Department of Fisheries and Oceans stone crab but extremely prominent Fisheries Research Branch spines on carapace and appendages. Biological Station Reaches a maximum carapace width of St. Andrews, New Brunswick approximately 100 mm, a leg spread of E0G 2X0 760 mm and a weight of 1.4 kg.

Claw Illustrations: Further Reading: Lori V. Colpitts Bailey, R. 1981. The Atlantic snow Dalhousie University crab. Department of Fisheries and Halifax, Nova Scotia Oceans, Underwater World Factsheet UW 81 / 006E: 8 p.

Elner, R.W. 1981. Diet of green crab, Carcinus maenas (L.) from Port Hebert, southwestern Nova Scotia. Journal of Shellfish Research 1: 89-94.

Elner, R.W., and A.B. Stasko. 1978. Mating behavior of the rock crab, Cancer irroratus. Journal of the Fisheries Research Board of Canada 35 : 1385-1388 .

Haefner, P .A. 1977. Aspects of the biology of the jonah crab, Cancer borealis Stimpson, 1859 in the mid- Atlantic Bight. Journal of Natural History 11: 303-320.

McElman, J.F., and R.W. Elner. 1982. Red crab (Geryon quinquedens) trap survey along the edge of the Scotian Shelf, September 1980. Canadian Technical Report of Fïsheries and Aquatic Sciences 1084: 12 p. QL 626 U53 1989 8 Underwater World Elner, R.W. Crabs of the Atlantic of Canada coast- 1189 63 05014765 C . l

Underwater Worid factsheets are brief illustrated accounts of fisheries resources and marine phenomena pre- pared for public information and education. They describe the life history, geographic distribution, utilization and population status of fish, shellfish and other living marine resources, and I or the nature, ongm and impact of marine processes and phenomena.

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