Nephrops norvegicus

Researched ByLizzie TylerData Supplied ByUniversity of Sheffield
Refereed byThis information is not refereed.
Taxonomy
Scientific nameNephrops norvegicusCommon nameNorway lobster
MCS CodeS1402Recent SynonymsNone
PhylumCrustaceaSubphylum
SuperclassClassEumalacostraca
SubclassEucaridaOrderDecapoda
SuborderPleocyemataFamilyNephropidae
GenusNephropsSpeciesnorvegicus
Subspecies  
Additional InformationAlso known as the Dublin Bay prawn, scampi and langoustine.
Taxonomy References Howson & Picton, 1997, Fish & Fish, 1996, Ingle, 1997, Sardà, 1995, Connor et al., 1997(a)
General Biology
Growth formArticulateFeeding methodPredator, Scavenger
Mobility/MovementSwimmer, Crawler, BurrowerEnvironmental positionDemersal, Infaunal
Typical food typesNephrops is an opportunistic predator feeding on crustaceans, molluscs and to a lesser extent polychaetes and echinoderms.HabitFree living
BioturbatorFlexibilityLow (10-45 degrees)
FragilityIntermediateSizeMedium-large(21-50cm)
HeightInsufficient informationGrowth RateSee additional information
Adult dispersal potential10-100mDependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
Additional InformationTypical abundance
Early fisheries investigations revealed marked geographical variability in the abundance and size of individual Nephrops in trawls (Cole, 1965; Thomas, 1965a). In Loch Torridon, Chapman & Rice (1971) reported densities of Nephrops of 1 ind. /7.8 m² in 1968, whereas in 1969 it was 1 ind. /5.5 m². The density of two populations of Nephrops norvegicus was reported for two sites on the west coast of Scotland in the Clyde and the Sound of Jura (Thomas, 1965a). In the Sound of Jura the population of Nephrops norvegicus consisted mainly of small Nephrops below 30 mm carapace length (CL) at an estimated density of approximately 1 ind. /m². The density of Nephrops in the Clyde was much lower (approximately 1 ind. /4m²). Reasons for such variability in density, size and growth rates, are listed below.

  • Physical factors such as the nature of the substratum and its suitability for burrowing (Bailey & Chapman, 1983).
  • A change in climate could lead to variable recruitment through changes in mortality rates of early life stages, for example, differences in sea temperature and wind induced wave action might affect the survival of larval Nephrops either directly or by regulating food supply.
  • Patchy settlement of larvae (Bailey & Chapman, 1983).
  • Different levels of fishing effort / intensity (Bailey & Chapman, 1983). However variations in fishing effort may only be partly responsible for variations in abundance (Tully & Hillis, 1995) as differences were observed in some areas before the pressure of significant fisheries (Thomas, 1965a).
Mobility
Although Nephrops norvegicus is capable of swimming, it is a crawler more than it is a swimmer.

Sociability
Although Nephrops norvegicus are essentially solitary animals, multiple occupancy can occur in the burrows (Marrs, pers. comm.).

Growth
Like other crustaceans, Nephrops norvegicus must moult, shedding their hard exoskeleton, to grow. Nephrops contain no annually marked structures, such as the otoliths found in fish, so the estimation of growth rates, age and maximum age has proved to be particularly difficult in this species.

Growth (and fecundity) in Nephrops norvegicus are known to vary geographically and have been shown to be negatively correlated with burrow density (Tuck et al., 1997). Thus, growth rate appears to be density-dependent, and is also thought to be related to food availability. For example, Tuck et al. (1997) found growth was correlated with infaunal biomass. This suggests that nutritional stress occurs in populations with slower growing individuals. Growth of Nephrops may also be influenced at high densities through social behaviour changes (Cobb et al., 1982). Parslow-Williams et al. (2001) found evidence that nutritional limitation was occurring in Nephrops norvegicus from a site in the Clyde Sea with a high population density, compared to another site with a low density of individuals.

Information on the growth rate of lobsters is very limited (Thomas,1965c). Despite being one of the most studied decapods, the area of age and growth estimation is still one for which there is no standard methodology (Castro, 1995). A number of studies have estimated the growth rate of Nephrops norvegicus:

  • Thomas (1960; cited in Thomas, 1965c) estimated an average growth rate of 5.7% for males and 6.2% for female Nephrops based on eight moults that occurred in an aquarium;
  • Thomas (1965c) estimated an average moult increase in carapace length of 7.1% for male Nephrops. Thomas (1965c) suggested that increases in length decreased as male Nephrops grew but this was not observed in female Nephrops (Thomas, 1965c);
  • whereas, Höglund (1942; cited in Farmer, 1975) stated that individuals 10-15 cm in total length grew by 4 mm per moult;
  • however, under natural conditions Barnes & Bagenal (1951) concluded that Nephrops moult at least once a year but gave no data for the rates of growth.
Thus mature females about 23 mm CL and mature male Nephrops about 26 mm CL are around 2-3 years old in Irish waters (Marine Institute, 2001). The minimum landing size for Nephrops in Irish waters is >70 mm (total size) and >20 mm CL therefore individuals would range from 1.5 to 3 years old (Marine Institute, 2003).

Size
Nephrops norvegicus grows to a maximum total length of 25 cm (including the tail, carapace and clawed legs), although is normally between 18-20 cm (Fish & Fish, 1996). The generally recognized standard measurement for Nephrops norvegicus is carapace length (CL). The maximum recorded CL of Nephrops was 80 mm (Marine Institute, 2001). However, in recent years Nephrops with carapaces larger than 60 mm are rare (Marine Institute, 2001).

Environmental position
Nephrops norvegicus construct extensive shallow and branching burrows in soft sediments such as fine or silty mud at depths of 20-800 m. Burrows may be up to 10 cm in diameter, over a metre long and penetrate the sediment to a depth of 20-30 cm (Rice & Chapman, 1981). Nephrops norvegicus usually remain within their burrows by day and emerge at sunset to forage during the night but in deeper water this activity is reversed and individuals are more active by day (Chapman & Rice, 1971). In laboratory conditions, large males are less inclined to make burrows than females and small males, which may account for the higher proportion of large males that are caught in small catches (Andersen, 1962; cited in Farmer, 1974a, b).

Feeding
Representatives of most invertebrate phyla have been found in the foregut of Nephrops norvegicus. Most studies show that Nephrops norvegicus feeds primarily on crustaceans but also molluscs and to a lesser extent polychaetes and echinoderms (Parslow-Williams et al., 2002). Although a crustacean diet has a lower energy content that some of the other faunal groups, they do provide a source of essential minerals such as calcium (Ennis, 1973). Any differences in diet appear to be due more to changes in prey abundance than to prey preference (Parslow-Williams et al., 2002) indicating that the species is an opportunistic predator. The size range of prey eaten by Nephrops norvegicus was investigated by Thomas & Davidson (1962) who found that the minimum food particle size ingested was 1 mm, and the maximum for hard particles such as bits of shells was 5 mm. They also found that larger soft bodied organisms like polychaetes could also be ingested if taken in lengthways.

Loo et al. (1993) suggested that Nephrops could filter feed, allowing Nephrops to extend the size range of its food items. Farmer (1974d) reported that the expodites of the various mouth parts of Nephrops in most cases bore plumose setae, which when waved continuously produced water currents. Farmer (1974d) suggested that this behaviour was for cleaning suspended food particles away from the mouth. During another study Nephrops norvegicus were kept in small tanks containing fluorescently-marked food particles comprised of the brine shrimp Artemia salina. These food particles were found in the gills, stomach and intestine of Nephrops. Loo et al. (1993) suggested that this provided effective evidence of filter-feeding. However, this feeding may be more 'micro-raptorial' rather than strictly filter-feeding (Parslow-Williams et al., 2002). During periods of food scarcity, females spend a prolonged period in their burrows and suspension feeding is thought to occur (Loo et al., 1993).

Diel variation in feeding rates have been observed indirectly in Nephrops norvegicus. Catch rates of lobsters has always varied depending on the time of day with peak catches at dawn and dusk. Only those lobsters that have emerged from their burrows are caught in the trawls and, since it is assumed that they emerge mostly to forage (Chapman, 1980), catch patterns indicate diel patterns of feeding behaviour. The stomach contents of animals sampled by Parslow-Williams et al., (2002) indicated a feeding peak around dawn but not around dusk, although animals were out of their burrows. Sampling is complicated by the fact that satiated animals will return to their burrows and be unavailable for capture.

Supports which species
The rare British Fries' goby Lesueurigobius friesii shares the burrows of Nephrops norvegicus. The minute Cycliophoran Symbion pandora is a unique sessile animal less than 1 mm long that was found in the mouth parts of Nephrops collected in Denmark and the first of its kind to be described. Symbion pandora has a basal attachment disc and an anterior ciliated food gathering organ (Conway Morris, 1995).

Barnes & Bagenal (1951) recorded large numbers of Balanus crenatus living on Nephrops norvegicus in the Clyde area. The following species have been observed on specimens of Nephrops norvegicus from the Irish Sea: Triticella koreni, Balanus crenatus, Electra pilosa, Eudendrium capillare, Sabella pavonina, Serpula vermicularis and a forminiferan probably Cyclogyra sp. (Farmer, 1972; cited in Farmer, 1975). The polychaete Histriobdella homari has been observed on the pleopods of two Nephrops norvegicus from the Irish Sea and Clyde Sea (Briggs et al., 1997).

Predators
Nephrops norvegicus is preyed upon by numerous white fish some of which are listed below.

  • In Scotland the stomach contents of cod was examined. Results showed that 80% of cod had Nephrops norvegicus amongst their stomach contents (Thomas, 1965b).
  • Nephrops was also found in 52% of the thornback ray Raja clavata that were sampled (Thomas 1965b).
  • In the Clyde, Nephrops was found in 51% of the small spotted catshark (dogfish) Scyliorhinus canicula that were sampled (Gordon & De Silva, 1980).
Biology References Loo et al., 1993, Tuck et al., 1997, Parslow-Williams et al., 2002, Thomas & Davidson, 1962, Ennis, 1973, Chapman, 1980, Aréchiga et al., 1980, Simpson, 1965, Thomas, 1965a, Bailey & Chapman, 1983, Tully & Hillis, 1995, Cobb et al., 1982, Farmer, 1974b, Aréchiga & Atkinson, 1975, Anderson, 1962, Atkinson, 1989, Marine Institute, 2001, Thomas, 1965b, Cole, 1965, Conway Morris, 1995, Barnes & Bagenal, 1951, Farmer, 1975, Chapman & Rice, 1971, Farmer, 1974d, Castro, 1995, Marine Institute, 2003, Thomas, 1965c, Parslow-Williams et al., 2001, Briggs et al., 1997, Rice & Chapman, 1981, Hayward & Ryland, 1990, Julie Bremner, unpub data
Distribution and Habitat
Distribution in Britain & IrelandCommon around most British coasts but not apparently recorded for the English Channel, the Bristol Channel or the Western Approaches. Populations also exist to the north east of Scotland on the Fladen Ground.
Global distributionNephrops norvegicus is widely distributed on muddy substrata throughout the north-east Atlantic from Iceland in the north to Morocco in the south. The species is found in the Mediterranean and is abundant in the Adriatic.
Biogeographic rangeNot researchedDepth range200 - 800 m
MigratoryNon-migratory / Resident
Distribution Additional InformationMigration
Tagging experiments have shown that Nephrops norvegicus do not migrate large distances (Marine Institute, 2001). In laboratory mesocosms individuals displayed very territorial behaviour, aggressively defending their burrows (Marine Institute, 2001).
Substratum preferencesMud, Muddy sand, Sandy mudPhysiographic preferencesOffshore seabed
Biological zoneLower Infralittoral, Upper Circalittoral, Lower CircalittoralWave exposureSheltered, Very Sheltered, Extremely Sheltered, Ultra Sheltered
Tidal stream strength/Water flowWeak (<1 kn), Very Weak (negligible)SalinityFull (30-40 psu)
Habitat Additional Information
AMBI Group (Borja et al., 2000)I 
Distribution References Fish & Fish, 1996, Ingle, 1997, Sardà, 1995, Foster-Smith, 2000, Bruce et al., 1963, Connor et al., 1997(a), BODC, 1998, CEFAS, 2001, JNCC, 1999, Picton & Costello, 1998, Marine Institute, 2001, NBN, 2002, Hayward & Ryland, 1990, Julie Bremner, unpub data
Reproduction/Life History
Reproductive typeGonochoristic Developmental mechanismPlanktotrophic
Reproductive SeasonSummer to AutumnReproductive LocationAs adult
Reproductive frequencyAnnual episodic Regeneration potentialNo
Life span6-10 yearsAge at reproductive maturity
Generation timeSee additional informationFecundity
Egg/propagule sizeFertilization typeInternal
Larvae/Juveniles
Larval/Juvenile dispersal potentialSee additional informationLarval settlement periodInsufficient information
Duration of larval stage1-2 months  
Additional InformationLongevity
In the Irish Sea, Nephrops norvegicus individuals are not thought to live more than 8 or 9 years. In other areas, such as the Porcupine Bank, they may survive over 15 years (Marine Institute, 2001).

Age and size at sexual maturity
Tuck et al. (2000) found that, in the Firth of Clyde, age at the onset of sexual maturity was relatively constant between different study sites but varied between sexes. In general, the age at onset of maturity was 4 - 4.5 years in males and 3 - 3.5 years in females. The size (carapace length) at sexual maturity was found to be positively correlated to asymptotic length and negatively correlated to adult density and ranged from 21 - 34 mm in females and 29 - 46 mm in males (Tuck et al., 2000). The authors suggested that there may exist a minimum size threshold under which males may be too small to reproduce.

Reproduction
A full description of reproduction can be found in Jorgensen (1925). Most Nephrops stocks in British waters have an annual reproductive cycle (Marine Institute, 2003). Sexually mature Nephrops of both sexes moult towards the end of spring and into the summer. Mating takes place while the female is still 'soft' (Farmer, 1975) directly after the female has moulted and before the hardening of the new exoskeleton (Marrs, pers. comm.). Once fertilized the eggs are then carried on the females abdomen for 8-9 months, during which time the females tend to remain in their burrows.

Egg loss
Egg loss is common in crabs, lobsters, shrimps and prawns (Tuck et al., 2000). Reasons for egg loss include failure of the eggs to attach to the pleopods at oviposition, predation, and loss of eggs from the pleopods during the long developmental period (Kuris, 1991). In the Moray Firth a comparison between females with recently spawned eggs and females where the eggs were about to hatch suggested that 32 - 51 % of the eggs are lost during development and that this proportion is larger in smaller individuals (Chapman & Ballantyne, 1980).

Ovary resorption
Ovary resorption has been attributed to a number of factors in other decapods, including lack of fertilization, starvation, hormone deprivation and incorrect photoperiod (Aiken & Waddy, 1980; Sastry, 1983; Adiyodi & Subramoniam, 1983). The timing of ovary resorption after the spawning period, suggests that it occurs in females whose ovaries were not sufficiently developed to spawn at the suitable time. Whatever the cause, resorption is thought to be a mechanism for conserving or recycling nutrients.

Fecundity
The fecundity of Nephrops norvegicus is variable and different methods have been used to estimate Nephrops fecundity (Abelló & Sardá, 1982) for example:
  • Eiriksson (1970) estimated the fecundity of Nephrops norvegicus from eggs that were carried on the female abdomen and from the oocytes of mature ovaries. It was also reported (where this method had been used) that the number of eggs carried on the abdomen by the female is lower than the number of oocytes in the ovaries. In an average size female (35 mm CL), it was estimated that around 1,500 eggs were present in the ovaries compared to the 1,000 eggs attached to the pleopods of recently 'berried' females (Eiriksson, 1970). 'Berried' females are those females that carry their eggs on their abdomens.
  • Farmer (1974a) and Chapman & Ballantyne (1980) estimated the fecundity of Nephrops norvegicus from eggs carried on the abdomen by females.
  • Thomas (1964 cited in Abelló & Sardá, 1982) estimated the fecundity from the oocytes of mature ovaries.

In all investigations, the number of eggs was found to be directly proportional to the size of the female. Farmer (1974c) suggested that it was more accurate to estimate the fecundity from the eggs that are carried by the females because very often the oocytes are reabsorbed during the process of sexual maturation. However, it must also be noted that the number of eggs on the abdomen diminishes during incubation mainly due to predation (Morizur, 1979; cited in Abelló & Sardá, 1982).

Egg hatching
During incubation it is generally thought that ovigerous females tend to remain within their burrows (Farmer, 1975). Females Nephrops come out of their burrows to allow their eggs to hatch and the larvae to escape from April -June (Farmer, 1974c).

Dispersal potential
Hillis (1968) reported that larvae of Nephrops norvegicus in the Irish Sea were dispersed by the local hydrographical conditions but they generally remain in the hatching areas of adults without being transported long distances. The main concentration of larvae in the Irish Sea were found in and near deep water. Hillis (1968) also suggested that there was a more easterly distribution of older larvae.

In the Irish Sea a gyre (circulating water mass) forms during the spring and summer, which coincides with the period when Nephrops larvae are present in the plankton. The gyre retained the larvae in the vicinity of the parent population, rather than being carried off by currents into areas of unsuitable substratum (Hill et al., 1996, 1997). This phenomenon has also been observed in the Adriatic and Clyde Sea (Marrs, pers. comm.). In addition to gyres, muddy sediments have also been associated with high densities of Nephrops norvegicus (Marrs, pers. comm.).
Reproduction References Tuck et al., 1997, Aiken & Waddy, 1980, Adiyodi & Subramoniam, 1983, Sastry, 1983, Farmer, 1974a, Dickey-Collas et al., 2000a, Thompson et al., 1986, Nichols, 1987, Chapman & Ballantyne, 1980, Eiriksson, 1970, Abelló & Sardá, 1982, Thorson, 1946, Hillis, 1968, Hill et al., 1996b, Hill et al., 1997, Marine Institute, 2001, Dickey-Collas et al., 2000b, Farmer, 1975, Tuck et al., 2000, Kuris, 1991, Julie Bremner, unpub data, Relini & Relini, 1989