BIOTIC Species Information for Nephrops norvegicus
|Researched by||Lizzie Tyler||Data supplied by||University of Sheffield|
|Refereed by||This information is not refereed.|
|Reproductive Season||Summer to Autumn||Reproductive Location||As adult|
|Reproductive frequency||Annual episodic||Regeneration potential||No|
|Life span||6-10 years||Age at reproductive maturity|
|Generation time||See additional information||Fecundity|
|Egg/propagule size||Fertilization type||Internal|
|Reproduction Preferences Additional Information||Longevity
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.
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 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 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.
The fecundity of Nephrops norvegicus is variable and different methods have been used to estimate Nephrops fecundity (Abelló & Sardá, 1982) for example:
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).
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).
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,|