Maja squinado

The European Spider Crab

Biology and Fishery

Funds for spider crab research were provided by the Jersey Department of Agriculture and Fisheries

Adult male spider crab (Maja squinado)

Spider crabs in commercial holding tanks

Measuring juvenile spider crabs at sea

Hauling spider crab traps on the research vessel 'Howard Davis'

CONTENTS

CLASSIFICATION AND DISTRIBUTION OF MAJA SQUINADO
  • PHYLUM
  •   CRUSTACEA
  • CLASS
  •   MALACOSTRACA
  • ORDER
  •   DECAPODA (Latreille, 1803)
  • SUBORDER
  •   BRACHYURA (Latreille, 1803)
  • SECTION
  •   OXYRHYNCHA (Latreille, 1803)
  • FAMILY
  •   Majidae   (Samouelle, 1819)
  • GENUS
  •   Maja   (Lamarck, 1801)
  • SPECIES
  •   squinado   (Herbst, 1788)

    The family Majidae, containing approximately 900 species, is widely distributed in marine waters (Brownell et al, 1977). Although the vast majority of majid crabs are small and have no direct economic importance, some species support commercial fisheries (Brownell et al, 1977). Commercially exploited majids include the Canadian snow crab (Chionoecetes opilio ) (Bailey & Elner, 1989) and the common European spider crab (Maja squinado ). Maja squinado   is the sole European representative of the subfamily Majinae (Ingle, 1980) and is the largest of approximately 66 species of majid crabs occurring in the north-eastern Atlantic (Brownell et al, 1977) Maja squinado   is essentially a Boreal species, with a latitudinal distribution extending from 15-60°N (Ingle, 1980). M. squinado   has a patchy distribution throughout its range. An effective northern limit of 52°N exists for commercially exploitable densities of M. squinado , and established fisheries exist as far north as the English Channel, Irish Sea and South West Ireland (Fig 1.1); M. squinado   also supports commercial fisheries in northern Spain (Galicia), Portugal and in the Adriatic Sea. Maja squinado   is not exploited commercially below 30°N. There is considerable seasonal and demographic variation in the depth distribution of Maja squinado   (De Kergariou, 1976; De Kergariou & Veron, 1981). In general, depth distribution during the summer is coastal, extending from 20-30m up to the low water mark and even into the intertidal zone (Anon, 1929; De Kergariou, 1976), whereas during winter most M. squinado   are found at depths of around 50m - 90m and occasionally down to 120m (De Kergariou, 1984). Aggregations of subsections of the M. squinado   population (e.g. `juveniles' or `recently-moulted adults') are often found in discrete areas of different depths (Mtimet, 1991). Generally, juveniles have a shallower distribution than adults, often occurring in well-defined, shallow inshore `nursery areas'. Recently- moulted adults tend to have a shallower distribution than the adults which did not moult in the current season (De Kergariou & Veron, 1981). As a result of their migratory habit, however, representatives of all subsections of the population may be found at the same depth at certain times of the year. Predominantly, Maja squinado   is found in areas where the seabed is flat and composed of soft substrata, and crabs have been observed partially buried in areas of suitably soft substrata (Stevcic, 1968b). Some M. squinado   (particularly large adult males) may occur in areas where the seabed is very rocky, particularly during their seasonal migrations (De Kergariou, 1984).

    BIOLOGY OF MAJA SQUINADO

    Life Cycle

    Maja squinado   has a life cycle of between 5 - 8 years, consisting of two main phases (growth and reproductive phases) separated by a final moult (De Kergariou, 1984). The growth phase consists of a planktonic larval phase (Schlegel, 1911; Lebour, 1927) followed by a benthic juvenile phase (Teissier, 1935; Carlisle, 1957; Hartnoll, 1963; Latrouite & Le Foll, 1989). The planktonic larval phase is shorter and less complicated than that of many other non-majid species of crab (Lebour, 1927; Brownell et al, 1977). The total duration of the growth phase in M. squinado   is thought to be between 2 - 3 years (Latrouite & Le Foll, 1989; Le Foll, 1993). Adult crabs may live for up to six years after their terminal moult (Le Foll, 1993).

    Larval Development

    The planktonic larval development of Maja squinado , consisting of two zoeal stages and one megalopa stage, takes approximately 2-3 weeks (from hatching to settlement of the first post-larval stage)(Schlegel, 1911; LeBour, 1927, 1928). Interannual and geographical variations in the timing and number of peak occurrences of planktonic larvae of M. squinado   have been noted. Typically, areas (and years), of lower ambient seawater temperature have fewer, and later, peaks of occurrence than those at higher water temperature (Stevcic, 1971; Ingle, 1980; Martin, 1980, 1983, 1985). In waters around The Channel Islands, planktonic larvae of M. squinado   have been detected from the beginning of July until the end of November, generally reaching a peak of occurrence between August and September (Martin, 1980, 1983, 1985) The first zoeal stage of M. squinado   is preceded by a transitory pre- or protozoeal stage during which the larva is surrounded by an embryonic membrane; the membrane is shed within 1 or 2h of hatching to give the first zoeal stage. This latter stage (approximately 2.5mm in length; green and black in colour) lasts for approximately 5 days and is strongly photopositive (Schlegel, 1911). In the Normano-Breton Gulf (Fig. 2.1), stage 1 zoeae are present typically between early July and late November, with peak abundances occurring during late August or early September (Martin, 1985). According to Martin (1980, 1983, 1985), the appearance and disappearance of stage 1 larvae of M. squinado   off Plogoff (North Biscay) occurs slightly earlier than in the Normano- Breton Gulf. The rate of larval development varies with seawater temperature, being faster at higher seawater temperatures (De Kergariou, 1971). Thus variations in timing and duration of occurrence of M. squinado   larvae observed by Martin (1980, 1983, 1985) may be correlated with differences in seawater temperatures between years and areas sampled. The second zoeal stage (approximately 3mm in length; same colouration as the first zoea) has a duration of 4-5 days, during which it remains strongly photopositive (Schlegel, 1911; LeBour, 1927, 1928). In the waters of the Normano-Breton Gulf, stage 2 zoeae are present over the same period as stage 1 zoeae, although peak abundance of stage 2 zoeae is generally slightly later than for stage 1 zoeae (Martin, 1985). According to LeBour (1927, 1928), the megalopa of M. squinado   is slightly smaller (2.4mm in length) than the second zoeal stage, however, Schlegel (1911) stated that the megalopa of this spider crab was slightly larger than the preceding stage. It seems likely that Le Bour (1927) confused the megalopa of another crab with that of M. squinado   (Le Foll, 1993). The duration of the megalopa of M. squinado   is between 8-9 days (Schlegel, 1911), during which time the larvae become increasingly photonegative. In the Normano-Breton Gulf (South-Western English Channel), megalopae of M. squinado   have been detected in the plankton from August to November (Martin 1985). The first benthic stage (juvenile) emerging from the megalopa is also strongly photonegative.

    Juvenile (growth) phase

    The developmental stages between the morphologically distinct planktonic larval and the adult phases of Maja squinado   are known as "juveniles". In most cases, duration of the juvenile stage of M. squinado   is approximately two years (Mtimet, 1991) although a minority may take between 2 - 3 years to complete the juvenile phase (Le Foll, 1993). The first postlarval (juvenile) stage measures approximately 1.28mm (carapace width) and possesses the characteristic "spider crab" appearance of later stages (Schlegel, 1911; Le Foll, 1993). Juvenile growth is slightly allometric which results in minor morphometric differences between early and late stage juveniles (Teissier, 1934, 1935). The number of moults which occur between the initial settlement of the first benthic postlarval stage and the onset of the first winter, when juvenile M. squinado   achieve an average of between 10-15mm carapace length, is unknown (Le Foll, 1993). Two moults are thought to occur in the second year and moult increments during the juvenile phase are relatively large (33%) for males and females (Le Foll, 1993). In the course of successive juvenile moults, the male size range becomes progressively greater compared with females of the same age (Le Foll, 1993). The end of the juvenile stage is marked by a final `maturity' (`terminal') moult, at which time sexual maturity is achieved and pronounced morphometric changes occur; no further moulting occurs after this terminal moult. The moult increment at the maturity moult in M. squinado   is smaller than for preceding moults (29%) for males and females (Le Foll, 1993).

    Adult (reproductive) phase

    One result of the terminal moult is the functional degeneration of the `Y' organ (Carlisle, 1957), which, in Maja squinado   is thought to be responsible for production of the moult-inducing hormone, 20-hydroxy ecdysone (Skinner, 1985). After the terminal moult, the gonads become enlarged and fully functional (Brosnan, 1981), and certain obvious external morphometric changes occur. For example, the chelae of males become greatly enlarged, and the female abdomen becomes enlarged and modified for egg carrying compared with juveniles. Immediately after the terminal moult, adult spider crabs are typically bright orange or red, however, this colour gradually fades with time to a dull reddish-brown. Also with age, the carapace and legs become increasingly worn and covered with epibiotic fouling organisms. Irreparable wear of the carapace probably contributes to the limited post-terminal moult life span (3 - 6 years) of spider crabs (Le Foll, 1993). In the Normano-Breton Gulf, adult males range in size from 85 to 200mm carapace length (mean = 138mm) and adult females from 80 to 170mm (mean = 128mm) carapace length (Mtimet, 1991; Le Foll, 1993). These measurements were collected using scallop dredges, a technique known to give a representative sample of the adult spider crab population (Le Foll, 1993). Males have a more variable size than females (Le Foll, 1993), and average size of Maja squinado   is known to increase with decreasing latitude (Gonzalez-Gurruriân, pers. comm.).

    DIET

    Larval

    No work has been published concerning the natural diet of the planktonic stages of Maja squinado, however, diets suitable for laboratory rearing of these stages have been described (LeBour, 1927). Larvae were reared successfully from egg to megalopa (but no further) utilizing a diet of oyster larvae (0.17 - 0.18mm hinge width), Teredo   larvae (0.05 - 0.06mm in length) and Pomatoceros   larvae (0.08mm in diameter); diets consisting of `wild caught' diatoms and small copeopods were unsuitable for larval development (LeBour, 1927). Schlegel (1911) successfully reared M. squinado   from egg to postlarva, but gave no details of the food used. Le Foll (1993) successfully reared M. squinado   from egg to adult, using techniques and diets developed for lobsters, which typically include a diet of Artemia salina   nauplii (or mixed wild-caught plankton) seawater temperatures of 15-25°C, salinity of approximately 35ppt and low light levels (Phillips & Sastry, 1980).

    Juvenile and Adult

    Maja squinado   has an omnivorous diet (Stevcic, 1968a; Brosnan, 1981; De Kergariou, 1974, 1984), with algae and molluscs forming the essential dietary items (De Kergariou, 1974, 1984). Marine algae consumed are predominantly members of the Rhodophyceae, including Corallina   (Brosnan, 1981), Griffithsia   (Carlisle, 1957), Ceramium   and Polysiphonia   (Le Foll, 1993), and the Phaeophyceae (various species of Laminaria ) (De Kergariou, 1974). Bivalve molluscs such as Mytilus   (Brosnan, 1981; De Kergariou, 1974), and gastropod molluscs such as Buccinium   (De Kergariou, 1974) are often consumed. In addition to molluscs, a wide range of other animals feature in the diet of M. squinado , including polychaetes, echinoderms (sea urchins such as Paracentrotus , brittle stars and starfish including Marthasterias , and Asterias ), crustaceans and fish (Stevcic, 1968a; De Kergariou, 1974; Brosnan, 1981). Although differences in diet have been reported for Maja squinado   from different areas, the catholic dietary requirements of this species (Stevcic, 1968a) suggests that it is opportunistic and consumes whatever range of food is available in each area. Omnivory is a particularly well-suited dietry strategy of migratory crustaceans which are likely to encounter a wide variety of potential food items while crossing different habitats in the course of their seasonal migrations (Latrouite, pers. comm.) Dietry preferences may, however, exist between different spider crab stages. For example, inclusion of Rhodophyceae in tanks used for juvenile M. squinado   improved survival rates (Le Foll, 1993), whereas adult crabs have been successfully maintained in aquaria using diets from which plant material was entirely absent (Brosnan, 1981).

    REPRODUCTION
    Unlike many other species of Crustacea which require the female to moult into a soft condition prior to mating, Maja squinado   is able to copulate while the female is hard (De Kergariou, 1971; pers. obs.). De Kergariou (1975) and Stevcic (1973) observed copulation between males and hard shelled females on the French Atlantic coast and in the Adriatic Sea respectively. Generally, mating occurs during the summer months. For example in Ireland, copulation occurred from May to July (Brosnan, 1981) and De Kergariou (1984) noted that copulation was frequent from the end of June onwards on the French coast. In all the observations of Brosnan (1981), male and female M. squinado in copula   were either of similar size, or the male was larger and copulation typically lasted for several hours after which time the crabs separated. Various authors have cited evidence establishing the presence of spermathecae (or bursa copulatrix   ) in Maja squinado   (Carlisle, 1957; Brosnan, 1981; De Kergariou, 1984). Some authors argue that M. squinado   has no ability to store sperm in the spermathecae from a single mating for subsequent fertilization of several spawnings. A major argument against long-term storage of sperm in the spermathecae, is that ovigerous females, with eggs in the final stage of embryonic development, have been observed in copula, both in captivity and in the natural environment (Stevcic, 1967; De Kergariou, 1975, 1984) and have spawned subsequently, 3 or 4 days after hatching their first brood (De Kergariou, 1971). De Kergariou (1975) stated further that ovigerous females, which were kept separate from males during the incubation of their first brood, also spawned a second time but the eggs were non viable. In addition Lang (1973) held adult females in captivity in the absence of males and observed a successful second spawning, suggesting that storage of sperm in the spermathecae for fertilization of multiple spawnings does indeed occur in M. squinado. This conclusion receives further support from recent work in Spain, which has shown that adult female M. squinado, held in aquaria, spawned successfully up to five times after a single mating (Gonz”lez-Gurruri”n, pers. comm.)   . In the English Channel and on the French Atlantic coast, ovigerous female spider crabs occur from February to October (De Kergariou, 1975), however, the majority of females carry eggs from May to September (Carlisle, 1957; De Kergariou, 1984). Conflicting reports concerning the number of times a female spawns each year probably arise because observations have been made in different areas or in different years (with consequently different temperature regimes). Stevcic (1967) suggested that three spawnings occur each year in the relatively warm Adriatic Sea and De Kergariou (1971, 1984) suggested that females spawn twice each year on the French coast. Martin (1980, 1983, 1985) detected a single spawning in some years and two in others in the same geographical area as De Kergariou (1971). As De Kergariou (1971) established a linear relationship between the duration of egg development and the ambient seawater temperature, it follows that the ambient seawater temperature will influence the number of spawnings that can be accommodated each year. In cases where females spawn more than once a year, successive spawnings occur within 72h of the hatching of the previous brood (De Kergariou, 1984). It is unclear whether discrete spawning areas exist, however, aggregations of ovigerous females have been observed in shallow (<10m) coastal embayments during the early summer months (pers. obs.). The duration of egg development has been cited variously as 43-47 days at 15°C (Brosnan, 1981), and 47 and 74 days at 16.8°C and 14.0°C respectively (De Kergariou, 1971). Initially, eggs are orange and become increasingly pigmented during development, being brown just prior to nocturnal hatching (De Kergariou, 1971; Brosnan, 1981). The number of eggs carried by a single female Maja squinado   is directly proportional to female body size, and varies between 45,000 and 400,000; an "average sized" female of 128mm carapace length (CL)(650g wet weight) carries between 150,000-155,000 eggs (De Kergariou, 1971, 1984). It should be noted, however, that, as is the case with other crustaceans, the number of eggs spawned is a function of female age and seawater temperature at the time of spawning as well as female size (De Kergariou, 1971). De Kergariou (1971) suggested that low spawning temperatures result in large numbers of relatively small eggs and that the opposite (small numbers of relatively large eggs) occurs at higher spawning temperatures. Seawater temperatures above 22°C are fatal for developing eggs of M. squinado   (De Kergariou, 1971).

    MIGRATIONS
    A notable feature of the biology of Maja squinado   in the Normano-Breton Gulf is their seasonal migrations. Work carried out by Latrouite & Le Foll (1989) indicated that newly-moulted adult   M. squinado   undertake an autumn/winter migration from coastal nursery areas to offshore sites where they overwinter in depths of more than 50m (Fig. 1.3). Adult M. squinado   return to the coastal nursery areas during the spring (Latrouite & Le Foll, 1989). These migrations may be an evolutionary mechanism to avoid mortality resulting from excessive cooling of shallow coastal waters during the winter months (Le Foll, 1993).

    COMMERCIAL EXPLOITATION OF MAJA SQUINADO

    The European commercial spider crab fisheries

    Maja squinado   is exploited by a number of countries throughout its geographical range (north-eastern Atlantic and Mediterranean). In the north-eastern Atlantic, intensive spider crab fisheries are operated in England, Eire, France, The Channel Islands, Spain, Portugal and Morocco (Brosnan, 1981; De Kergariou, 1984; Le Foll, 1993). Maja squinado   is also exploited in the Adriatic Sea by Italy and the former Yugoslavia (Brosnan, 1981). Capture methods involve predominantly the use of traps and tangle nets, although crabs may be taken by trawls (De Kergariou, 1984), divers and various artisanal methods of hand gathering in shallow waters and intertidal areas. According to FAO statistics, the total annual catches of Maja squinado   over the period 1974 to 1990 ranged from a maximum of 11,849 tonnes (in 1977) to 3,699 tonnes (in 1990); the average annual landing over the period 1985 to 1990 was 4,110 tonnes (Gonzâlez-Gurruriân, 1993). The main countries contributing to these FAO landing statistics are France, the United Kingdom, The Channel Islands, Spain, Portugal and Yugoslavia (Gonzâlez-Gurruriân, 1993). France contributes more than 65% of the total catches of M. squinado   and at least 85% of the annual French landings are taken from the Normano-Breton Gulf and western English Channel coast of the Brittany Peninsula (Latrouite, pers. comm.). Unfortunately, the reliability of these FAO landing statistics for M. squinado   are open to question, as are official national landings (Gonzâlez-Gurruriân, 1993). For example, Le Foll (1993) estimated landings of 4,169 tonnes for the French western English Channel fishery (1986) for M. squinado , while official landing statistics for the same period and the same area were for 1,862 tonnes. It is likely that the statistics for the spider crab fisheries in other countries suffer similar variation and should also be treated with caution (Gonzâlez-Gurruriân, pers. comm. ). Most of the countries which exploit Maja squinado   adhere to the European Community minimum legal size for this species of 120mm CL. In addition, other regulations are applied to the national management of fisheries for M. squinado. These include fishery closures to protect spider crabs during the moulting season (France and The Channel Islands), and non -specific closures and restrictions on taking ovigerous females (Spain).

    History of the Jersey spider crab fishery

    Although the common spider crab, Maja squinado   has been consumed in Jersey for many years, prior to the development of a commercial fishery (in the late 1970's), spider crabs were traditionally gathered only in summer either from the shore at low water or occasionally from pots set to catch lobsters. Nicolle (1893) documented this seasonal gathering of spider crabs in his description of crustaceans in Jersey:

    "This list of marketable crustaceans would be sadly incomplete, were mention omitted of the large spider crab (Maja squinado), of which cartloads may be seen in summer in the markets. On a bright summer day at spring tide even women and children are constantly to be seen eagerly tramping up and down in shallow water at low tide among the Zostera beds, feeling for their prey with their feet."

    Some gathering of spider crabs continued well into the 20th century and instances of particular abundance were noted by Islanders. In June1929, the Jersey Evening Post   contained the following description of shore gathering of spider crabs:

    "At the present time, the bays around the island are infested with spider crabs, particularly St. Ouen's Bay which seems to be swarming with them. Every tide sees the `spiders' advancing into the bay in hordes, the sands seeming literally alive with them. Large numbers are left, as the tide recedes, among the rocks where one can catch as many as it is possible to carry away. They run to a large size, specimens of 5lbs and over being quite common. Numbers of people go down to the area around the Rocco Tower at every tide and bring the crabs away by the sackful, catches of seventy and over being common. A well informed resident of L'Etacq informed us this morning that such a thing has never been known before within the memory of even the oldest inhabitants, and the supply does not seem by any means to be nearing exhaustion, notwithstanding the thousands that have been caught."

    In retrospect, two main factors have contributed to the decline of the summertime inshore abundance of spider crabs upon which the tradition of shore gathering was based. Firstly, the winter of 1962-1963 was extremely severe by Jersey standards and seawater temperatures dropped well below the normal level and remained below 5°C for the majority of January, February and March 1963 (Jersey Meteorological Office data). As seawater temperatures of 6°C (or below) are lethal for spider crabs (Le Duff, 1989), it seems probable that the abnormally low seawater temperatures recorded in the winter of 1962-1963 reduced the spider crab stocks to low levels (Le Duff, 1989). After this severe winter, spider crabs were only seen occasionally around Jersey shores until 1967 (Dunn et al, 1967). Secondly, a commercial fishery for spider crabs was established in The Channel Islands in the late 1960's and expanded considerably in the late 1970's. It is probable that this increased fishing effort contributed substantially to the decline in crab numbers. These two factors probably combined to reduce the numbers of crabs appearing inshore each summer. Certainly, large-scale shore gathering has not been possible in recent years, even though the landings of Maja squinado   from the Normano-Breton Gulf increased by 40% between 1988 and 1991 (Le Foll, 1993) as a result of strong recruitment during this period (Mtimet, 1991). It should be noted that the decline in inshore abundance of spider crabs during the summer months results not from recruitment overfishing but rather from the interception of migrating crabs, preventing them from reaching inshore areas in the high numbers seen in previous years. Such interception fishing arises from crabs being caught in traps and nets during their migrations between overwintering areas and inshore areas, and from being caught by vessels fishing in the overwintering areas. Certainly, large numbers of juvenile M. squinado   can still be found in the inshore nursery areas during the summer months (Mtimet, 1991; Le Foll, 1993), indicating that the cycle of recruitment remains unbroken.

    The modern commercial Jersey spider crab fishery

    Interest in the commercial potential of stocks of Maja squinado   around Jersey began during the late 1960's as lobster fishermen, confronted with declining lobster catches, started to look for alternative species to supplement their incomes (Dunn et al, 1967). The commercial fishery for M. squinado   expanded considerably until the mid 1970's. The number of Jersey vessels targeting M. squinado   has remained relatively constant since the early 1980's, although fishermen suggest that the number of traps in use has doubled since 1980. This commercial fishery is based upon the export of live spider crabs to France and Spain in `vivier' vessels and `vivier' lorries. Unfortunately, Jersey catch data for Cancer pagurus   and Maja squinado   were combined until the 1980's, so no historical record of spider crab landings exists. During the 1980's, however, annual spider crab landings remained relatively stable, averaging 150 tonnes (Fig. 1.4). The annual landed value of declared Jersey catches (over the period 1988-1992) varied between £220,000 and £460,000 (average value of £300,000 per annum). In 1990, Jersey landings increased by about 30% (Fig. 1.4) probably as a result of strong recruitment of M. squinado   in the Normano-Breton Gulf during the early 1990's (Mtimet, 1991). Declared Jersey landings of M. squinado   represent some 4% of the total landings of this species from the entire Normano-Breton Gulf region (Latrouite, pers. comm.). It should be noted, however, that the reliability of these statistics may be questionable, mainly because landing returns are voluntary. The seasonal variations in ex-vessel price for Maja squinado   (Fig. 1.5) reflect the traditional seasonal demand for this species in southern Europe (centered around the festivals of Easter and Christmas), and seasonal variations in landings related to migrations and changes in catchability of this species associated with seawater temperature (Chapter 3). The Jersey fleet exploiting Maja squinado   has `full-time' and `part-time' components. The current full-time fleet consists of approximately 90 vessels in the 5-15m range (predominantly in the 8-12m range) each with 2-4 crew. These vessels which fish up to 12 nautical miles from Jersey, catch spider crabs throughout the year but specifically target spider crab when the price is favourable (particularly around Christmas and Easter). The majority of the full-time fleet use traps to catch M. squinado. Each vessel uses between 300 and 600 `inkwell' traps, depending on vessel size. At least 30 of the larger full-time vessels also use tangle nets (stretched mesh size of 300mm) and the total length of tangle net used varies from 5 to 20km. The use of tangle nets is becoming increasingly popular with the Jersey fleet. The part-time fleet consists of 130 small (5-6m) vessels (1 or 2 crew) which fish within 3 nautical miles of the island and which catch M. squinado   only during the summer months when crabs are inshore. The fishing method for M. squinado   by part-time vessels is almost exclusively restricted to inkwell traps and, in most cases part time vessels use less than 50 traps. The vast majority of the Jersey landings of M. squinado   are accounted for by the full-time fleet. Management measures used to regulate the Jersey fishery for Maja squinado   are limited to the European Community minimum legal size for this species of 120mm CL and a two to three month closed season during the autumn (used to protect recently moulted crabs which are common at this time of year). The closed season for M. squinado   is restricted currently to the Normano-Breton Gulf. During the latter half of the 1980's, Jersey fishermen became concerned; that they were only able to maintain catches of M. squinado   at levels observed in previous seasons by increasing fishing effort (number of traps). As a result of these concerns, a study of the biology and fishery of M. squinado   around Jersey was initiated in 1990.

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