The application of fecundity estimates to determine the spawning stock biomass of Irish Sea Nephrops norvegicus (L.) using the annual larval production method

Abstract

. 2002. The application of fecundity estimates to determine the spawning stock biomass of Irish Sea Nephrops norvegicus (L.) using the annual larval production method. -ICES Journal of Marine Science, 59: 109-119.Ovigerous female Nephrops were collected by trawl and creel and maintained in individual containers over the nine-month incubation period to investigate aspects of fecundity. Females which extruded eggs in captivity shortly after capture provided an estimate of mean realised fecundity of 104.3 eggs g 1 live weight (s.e.=2.7). Egg loss during incubation, estimated by sampling ovigerous females from research trawl hauls at different times of year, was 36.7 eggs g 1 (s.e.=3.3). A similar value was obtained by monitoring individuals kept in the hatchery. Mean effective fecundity at the time of hatching was estimated as 67.6 eggs g 1 (s.e.=4.3) and is the difference between the number of eggs extruded (realised fecundity) and egg losses during incubation. The abundance of larvae at development stages I, II, and III was estimated over a series of surveys using high-speed plankton samplers. Abundance values were converted to daily production values using relationships between temperature and stage-duration. Annual larval production by stage was estimated by fitting Gaussian curves to the survey estimates. The mortality rate of larvae (Z=0.033 d 1 ; s.e.=0.006) was estimated from the values of annual production by stage, using a maximum likelihood method. Annual production at hatching, estimated as the intercept of the mortality curve, was 440 10 9 larvae (s.e.=62 10 9 ). The biomass of mature female Nephrops in the western Irish Sea in 1995 was estimated from annual larval production and mean fecundity to be 6290 t (CV=0.17). The current ICES estimate of female SSB in 1995 of 7750 t, obtained from analysis of commercial catch data, lies within the 95% confidence limits for the ALP estimate. This indicates that current estimates of fishing mortality for female Nephrops in the Irish Sea may be robust.

Climate-induced changes in the North Sea Decapoda over the last 60 years

“…Although the relationship between larval abundance and the size of benthic populations has not been generally established for invertebrate macrofauna, larval surveys are a longestablished means of estimating the spawning stocks of decapods (Briggs et al 2002). While Pandalus and Nephrops are sampled poorly by the CPR, fisheries data -which show that landings of these predatory species (ICES 2006) and Cancer (Heath 2005) have increased markedly in the North Sea -are consistent with a general increase in decapod larval abundance (Kirby et al 2008), which may be indicative of changes in the North Sea benthos.…”

Reproductive Biology of Female Norway Lobster, Nephrops norvegicus (Linnaeus, 1758) Leach, in Icelandic Waters During the Period 1960–2010

“…The number of eggs was shown to vary from 800 to 5000, but no specific relationships were given between female size and egg number. More recently, a number of authors have studied fecundity and female size relationships at one or more stages of external egg development (Abelló and Sardà, 1982;Allonso-Allende, 1979;Briggs et al, 2002;Chapman and Ballantyne, 1980;Farina et al, 1999;Farmer, 1974b;Froglia and Gramitto, 1979, 1981Gramitto and Froglia, 1980;Nichols et al, 1987;Orsi Relini et al, 1998), while others have estimated the fecundity from the number of oocytes of mature ovaries (Fontaine and Warluzel, 1969;Morizur and Rivoalen, 1982;Smith, 1987;Thomas, 1964;Tuck Figure 2.54 Monthly female sex ratio (%) by denoted geographical areas ranging from SW Iceland to the Aegean Sea (for references, see Table 2.9). et al, 2000).…”

Behaviour influences larval dispersal in shelf sea gyres: Nephrops norvegicus in the Irish Sea

“…Mortality of N. norvegicus larvae is highly complex, due to predation and parasites (Farmer 1975). Although estimates of average daily larval mortality rates are available (Nichols et al 1987, Dickey-Collas et al 2000a, Briggs et al 2002, little is known about how mortality varies spatially and temporally. Mortality is therefore neglected entirely in this investigation.…”