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When discarded from bottom trawl fisheries, survival of Nephrops norvegicus may be sufficiently high that this species can be exempted from the EU Landing Obligation. In three studies, Nephrops were sampled from trawlers in northern European waters, and the fate of individuals monitored for a minimum of 13 days in onshore tanks. Winter estimates of captive survival (means ± 95% confidence intervals), including immediate mortality during catch sorting, were 62 ± 2.8% for the West of Scotland, 57 ± 1.8% for the Farne Deeps (North Sea), and 67 ± 5.4% for the Skagerrak. The Farne Deeps fishery is not active in summer, but captive survival rates in summer in the other two areas were reduced to 47 ± 3.4% for West of Scotland and 40 ± 4.8% for the Skagerrak. Linear modelling of the West of Scotland and Skagerrak data suggested that higher survivals in winter were related to colder water or air temperatures, although temperatures during captive observation may also have had an impact. Net modifications in the Skagerrak study had an effect on survival, which was higher for Nephrops sampled from nets equipped with the more selective Swedish sorting grid compared to Seltra trawls.

Expeditious uptake of quad-rig trawling in the economically important Irish fishery for Nephrops norvegicus outpaced technical understanding of this newly introduced gear. The main driver for its introduction is increased catch rates of Nephrops. Higher Nephrops discard rates associated with quad-rig trawling are likely to be problematic under the landing obligation unless size selectivity can be improved. Catch comparison methods are suitable for assessing the performance of fishing gear modifications to reduce discards. Utilizing a quad-rig potentially increases the number of gears that can be included in a catch comparison study to four but current modeling methods are limited to two gears. Our study provides a new general multinomial mixed effects modeling framework that can be applied to two or more gears, elucidates how case-specific and choice-specific covariates may influence catch at length, and facilitates discussion on appropriate gear based management measures. Application of the method to catches from four different cod-end mesh sizes revealed significant effects of carapace length, catch weight and net position, on the numbers of Nephrops retained in each cod-end. Results suggest that management measures which specifically address different catch profiles associated with different numbers of trawling rigs are required to optimize Nephrops size selectivity.

The European Common Fisheries Policy has in its 2013 reform increased in complexity, such as a call for coherence with the Marine Strategy Framework Directive and a landing obligation, posing new requirements and challenges to managers, scientists and the fishing industry. Therefore, re-evaluations of current practice are important as a basis for management actions. The Swedish fishery for Norway lobster (Nephrops norvegicus) in the Kattegat–Skagerrak area provides an interesting case study of relevance to emerging policies. Sprung from an unbalance in available fish- and Nephrops quotas and an ambition to protect coastal areas, the current fishery has been directed towards three separate fisheries (mixed trawling, directed trawling using a sorting grid and creeling). Studying direct and indirect effects from alternative Swedish quota allocations among gear types is therefore interesting. Accordingly, a screening study was conducted, taking into consideration area-gear interactions in catch rates, to compare the three different fisheries regarding quantified pressures on the target species, the by-catch species, and on the seafloor, as well as to qualitatively discuss social and economic dimensions. In the next step, alternative quota allocations were studied. In Swedish fisheries, we show that creeling offers a substantial reduction of fishing mortality of both undersized Nephrops and fish and a reduced seafloor pressure per landed kilo of Nephrops. Given that the fishing areas in many cases may be interchangeable between gears, allocating a larger quota share to creels in the Swedish fishery would therefore contribute to the integration of fisheries- and environmental management as called for in the new policies.

Øresland, V., and Ulmestrand, M. 2013. European lobster subpopulations from limited adult movements and larval retention. – ICES Journal of Marine Science, 70: 532–539. Adults and larvae of the European lobster, Homarus gammarus, were studied within and around the Swedish Kåvra lobster reserve (2.2 km2). Tagging of 4016 lobsters within the reserve showed that the lobsters have limited movement out of the reserve. Only 58 lobsters (1.4% of all tagged lobsters) were recaptured ≥1 km from the reserve and 5658 recaptures were obtained inside the reserve. Light trap catches showed that stage 1 larvae had a peak occurrence during

Pampoulie, C., Skirnisdottir, S., Hauksdottir, S., Olafsson, K., Eiríksson, H., Chosson, V., Hreggvidsson, G. O., Gunnarsson, G. H., and Hjorleifsdottir, S. 2011. A pilot genetic study reveals the absence of spatial genetic structure in Norway lobster (Nephrops norvegicus) on fishing grounds in Icelandic waters. – ICES Journal of Marine Science, 68: 20–25. Stock structure of Norway lobster off southern Iceland was investigated using 12 microsatellite loci. No genetic method detected significant genetic differentiation among the locations sampled, even among Icelandic samples and an out-group from Scotland. Testing the power of resolution of microsatellite loci, the loci and sample sizes used were sufficient to detect significant genetic differentiation with confidence. The lack of genetic structure is discussed in terms of the level of gene flow, recent isolation of populations, and the statistical power of the experimental design.

Madsen, N., and Valentinsson, D. 2010. Use of selective devices in trawls to support recovery of the Kattegat cod stock: a review of experiments and experience. – ICES Journal of Marine Science, 67: 2042–2050. The spawning-stock biomass of cod (Gadus morhua) in the Kattegat area is at a historically low level. Throughout the past decade considerable efforts have been devoted to research on improving both species and size selectivity of the trawls used in the mixed demersal fishery in the area, because this provides a valuable management tool for reducing the bycatch of cod and reducing mortality, and thus helping to rebuild the depleted stock. Gear research in the area has been focused on devices that allow for continued exploitation of the Norway lobster (Nephrops norvegicus) and flatfish, but minimizing the bycatch. We review the results of previous and continuing experiments with various codend mesh sizes, mesh configurations, escape windows, sorting grids, sorting frames, and separator panels, but also changes in whole-trawl designs. Based on our review, we compare and discuss the gear-related technical measures and their effectiveness in maintaining a commercial fishery on viable stocks, yet protecting cod. We discuss the results in relation to changes in legislation and experience with implementation of new selective devices in recent years. We also discuss ways to create stronger incentives for fishers to participate in gear research and to increase acceptance of more selective gears.

Frandsen, R. P., Madsen, N., and Krag, L. A. 2010. Selectivity and escapement behaviour of five commercial fishery species in standard square- and diamond-mesh codends. – ICES Journal of Marine Science, 67: 1721–1731. The Danish fishery for Nephrops (Nephrops norvegicus) is often conducted in a mixed-species setting, characterized by high rates of discards of several target species, including Nephrops and cod (Gadus morhua). Experiments were conducted to investigate and compare the selective properties of a standard 70 mm square-mesh codend (standard SMC) and a standard 90 mm diamond-mesh codend (standard DMC). Selectivity estimates for five commercial species are provided for both codends. The standard SMC yielded higher estimates of length at 50% retention/mesh size (hereafter SF) for Nephrops and roundfish than did the standard DMC, but no effect of codend type on SF was found for plaice (Pleuronectes platessa). Moreover, a novel codend cover design allowed assessment of the preferred direction of escapement in the codend. Whiting (Merlangius merlangus) and Nephrops showed pronounced, but opposite, vertical preference in the direction of escapement, with whiting escaping upwards and Nephrops downwards. A significant (p < 0.05) difference in the direction of escapement between the two codends was found for haddock (Melanogrammus aeglefinus) and whiting. Owing to the relatively small catches, the outcome is probably most applicable to Nephrops-directed fisheries under similar conditions, and caution should be taken not to extrapolate the results to other fisheries.

Campbell, N., Allan, L., Weetman, A., and Dobby, H. 2009. Investigating the link between Nephrops norvegicus burrow density and sediment composition in Scottish waters. – ICES Journal of Marine Science, 66: 2052–2059. Nephrops norvegicus is a burrowing decapod, found in the North Atlantic and Mediterranean Sea at depths of 10–1200 m, and currently the most valuable species taken by the commercial fishing industry in Scotland. It constructs and inhabits extensive burrow complexes in suitable muddy sediments. Owing to its variable emergence patterns, catch rates from traditional trawl surveys are not considered a good indicator of population size. Nephrops populations around Scotland are assessed using an underwater television (UWTV) survey method. Sediment samples are collected at the end of each UWTV deployment. This study focuses on two areas off the coast of Scotland and investigates the accuracy of the sediment maps used for assessment purposes, and the relationship between Nephrops burrow density and sediment composition, over the period 2002–2007. Nephrops have a stock-specific relationship with the sediment they inhabit, which retains the same form through fluctuations in population size.

Campbell, N., Dobby, H., and Bailey, N. 2009. Investigating and mitigating uncertainties in the assessment of Scottish Nephrops norvegicus populations using simulated underwater television data. – ICES Journal of Marine Science, 66: 646–655. Nephrops norvegicus is a commercially significant decapod crustacean that excavates and inhabits burrows in muddy sediments throughout the Northeast Atlantic and Mediterranean Sea. Because of its variable emergence behaviour, traditional surveys are considered a poor indicator of the status of its populations, and underwater television (TV) survey methods have been developed. The approach involves towing a TV camera over patches of muddy sediment and counting the number of Nephrops burrow complexes within a known area. Assuming a 1:1 rate of occupancy, the average population density can be estimated. This is raised to the known area of suitable sediment to give a measure of population size. Recently, underwater TV surveys have been used to provide absolute measures of abundance for a number of Nephrops stocks in the North Sea and Northeast Atlantic. It is therefore imperative to identify, quantify, and control for uncertainties in this process. Previous workers have suggested that visual recognition of Nephrops burrows and “edge effects”, where single openings of burrow complexes at the sides of the viewed transect are counted, are important sources of uncertainty. This study shows edge effects to be responsible for an overestimation of population size of between 4 and 55%, depending on the width of the field of view and the mean size of the burrow complex. This overestimation is countered to some extent by variability in burrow entrance structure, which leads to Nephrops burrows going unrecognized. The scales of these errors are discussed in relation to observed sediment softness, sediment distribution, and burrow dimensions from sites around Scotland.

Milligan, R. J., Albalat, A., Atkinson, R. J. A., and Neil, D. M. 2009. The effects of trawling on the physical condition of the Norway lobster Nephrops norvegicus in relation to seasonal cycles in the Clyde Sea area. – ICES Journal of Marine Science, 66: 488–494. The fishery for Norway lobster, Nephrops norvegicus, is the most valuable in Scotland, but few studies have examined the physical condition of the animals trawled. This study aimed to determine the extent of physical damage caused by trawling to Nephrops in the Clyde Sea area in relation to trawl duration, sex, size, and moult stage. Longer trawls (2.5–4 h) corresponded to increased damage in “hard” (intermoult) Nephrops compared with short (1 h) or very short (15 min) trawls, but there was no correlation in “soft” (late intermoult or recently moulted) or “jelly” (immediate post-moult) Nephrops. This effect appeared to be limited to Nephrops with a carapace length (CL) of 20.0–29.9 mm. Seasonal effects were also observed, with numbers of jelly Nephrops highest in May 2006, corresponding to a peak in female prevalence in the catches, an increase in the mean CL of females, and greater damage in females. The proportion of females was higher than males from May to September 2006, and it is suggested that this corresponds to female emergence patterns. As quality will be low, it may be pertinent to avoid fishing during the peak emergence period to maximize the quality and profitability of catches.

Ungfors, A., McKeown, N. J., Shaw, P. W., and André, C. 2009. Lack of spatial genetic variation in the edible crab (Cancer pagurus) in the Kattegat–Skagerrak area. – ICES Journal of Marine Science, 66: 462–469. The stock structure of the edible crab (Cancer pagurus L.) in the Kattegat and Skagerrak was investigated using eight microsatellite DNA loci. Replicate samples, collected 4–6 years apart, were derived from the Kattegat (Grove Bank, 57°N) and the Skagerrak (Lunneviken, 59°N), plus a geographical outgroup sample from the Norwegian Sea (Midsund, 62°N). Genetic differentiation among samples, estimated as global FST = 0.002, was significant (p = 0.03) when the statistical test was based on allele frequencies, but not when based on genotype frequencies. Moreover, all single- and multilocus pairwise tests between samples were non-significant. An analysis of molecular variance, AMOVA, did not reveal significant differentiation between spatial (Kattegat vs. Skagerrak) or temporal (2001/2002 vs. 2006/2007) groups of samples. Power analysis suggested that the loci and sample sizes employed conferred a power of >90% of detecting even low (true FST = 0.002) levels of population structure. Low spatial and temporal genetic structure might be explained by either or both of (i) high levels of contemporary gene flow in the area attributable to adult migration or larval dispersal or both factors taken together, and (ii) patterns of historical gene flow persisting among recently founded large populations.

Smith, I. P., and Jensen, A. C. 2008. Dynamics of closed areas in Norway lobster fisheries. – ICES Journal of Marine Science, 65: 1600–1609. A dynamic, age-structured population model was developed to investigate the potential effects of introducing a closed area to a fishery for a species with limited adult mobility and planktonic dispersal of larvae, using biological and fishery information from a Norway lobster fishery in eastern Scotland. Simulated closure of part of the fishing grounds led to a long-term increase in total biomass and recruitment to the fished zone, but the larval subsidy did not compensate for the loss of fishing ground, and fishery yield was reduced under all modelled combinations of closed-area size and prior fishing effort. Concentration of effort in the fished zone and increased recruitment there led to reduced average size, and therefore value, of animals in the catch, as well as increased destruction of biomass by discarding undersized lobsters. Implementation of a closed area also led to oscillations in stock biomass, recruitment, and yield over several years after the closure, particularly with large closed areas and high fishing effort.

Morello, E. B., Froglia, C., and Atkinson, R. J. A. 2007. Underwater television as a fishery-independent method for stock assessment of Norway lobster (Nephrops norvegicus) in the central Adriatic Sea (Italy). – ICES Journal of Marine Science, 64: 1116–1123. Norway lobster is of great commercial importance throughout the NE Atlantic and Mediterranean, where it lives in burrows in muddy sediments. The fact that the species is caught in commercial gear only when it emerges from its burrow and the absence of hard structures available for age determination complicate the application of normal fishery-dependent stock-assessment methodologies. This study provides more evidence of the usefulness of underwater television surveys as a fishery-independent technique to assess the Nephrops stocks of the Adriatic Sea. The results are compared with those of previous studies, and the advantages and disadvantages of using such methodology discussed in an Adriatic context.

Allozyme starch gel electrophoresis was used to investigate the genetic structure of Nephrops norvegicus populations in an extended sampling scheme. Nine populations from the North Sea and Aegean Sea were sampled and analysed using ten enzymatic systems corresponding to 15 putative loci. Values of heterozygosity were similar between Atlantic and Mediterranean population samples, ranging from 0.165 to 0.187. Genetic distance estimates, FST analyses and tests for genetic differentiation revealed a heterogeneous genetic structure within the sampling area of N. norvegicus. No evidence was found of past separation of Atlantic and Mediterranean populations, agreeing with the results of previous allozymic and mitochondrial genetic studies of N. norvegicus. Data are compared with genetic studies of other marine crustaceans and fish, and the implications for management of N. norvegicus stocks are discussed.

Harris, R. R., and Ulmestrand, M. 2004. Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers e mortality and damage seen in simulation experiments. e ICES Journal of Marine Science, 61: 127e139. The Kattegat/Skagerrak Nephrops fishery is unusual in that animals normally live in high salinities (33e34 psu) but are raised through a low salinity surface layer and, if discarded, descend back through it to the sea bed. In other open-sea Nephrops fisheries, such low salinity exposure is rare. Physiologically the species is described as being marine stenohaline, i.e. intolerant of reduced salinities, and a lower salinity limit of 29e30 for its distribution has been suggested. Using CTD data from the Anholt E hydrographic station, near to known Nephrops grounds, a knowledge of hauling times (including washing the cod-end with surface water) and of the sinking rate of Nephrops, we simulated conditions experienced by the catch in this fishery. We also included a period of emersion (air exposure) on deck during sorting or reshooting the trawl. Blood electrolytes, body mass changes and simple behavioural responses were examined before and after the simulation over a 5-day period. ‘‘Discarded’’ Nephrops experienced significant haemodilution and gained mass rapidly. Animals showed slow rates of ‘‘tail-flipping’’, or absence of responses to stimulation, in the period immediately following return to salinity 33 seawater, although many showed recovery later. Delayed effects included abdominal stiffness, swelling and further mortalities (25e42% overall). Controls (exposed to 33 psu seawater only) showed good survival and vigorous responses, even with a period of emersion. The effects of salinity exposure, which are additional to the stresses of being trawled, on the fitness of discarded animals were evaluated. Our results suggest that Nephrops discard mortality in this fishery is significantly higher than past estimates and is due to the stress of this brief exposure to low salinity surface water.

An underwater television technique was used to investigate burrow density of Nephrops norvegicus in a large semi-enclosed bay in the west central Aegean. Pagasitikos Bay has the shallowest occurrence of Nephrops in high densities in Greek waters with an estimated population area of 376 km2. As trawling is by law prohibited in the bay, Nephrops is fished only by bottom nets. Burrow densities were estimated seasonally (May, August and November 1998 and February 1999) by video sled transects at nine stations around the bay. Bottom trawls were undertaken to estimate animal abundance, mean individual carapace length and mean weight. Total stock estimate (number and weight) was undertaken for 100 and 75% burrow occupancy with the ground delimited by the 60 m contour. Annual removal by fishermen was estimated to be 1.5–2% of the stock. Densities were found to be higher than in other Greek Nephrops grounds. Variations in burrow density were found both between stations and within stations over time, with an overall decrease in density in 1999. The decrease in density during 1999, in conjunction with an increase in mean carapace length from the trawl catches was attributed to an eutrophication event evidenced by a flock layer settling onto the seabed and causing, in the worst cases, patches of anoxic surface sediments. The event was most probably the result of high nutrient run-off into the bay.

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.

Parameter values for the von Bertalanffy growth model are estimated for Nephrops norvegicus in the Skagerrak on the Swedish west coast using analysis of length frequency distribution from commercial catches and tag-recapture data. The asymptotic lengths (L) for males and females are estimated from size distributions using a modified Powell-Wetherall plot. The tagging experiment was conducted with Floy streamer tag and analysed in a ‘‘forced’’ Gulland-Holt plot to estimate the growth coefficient K for males. The estimates of L (72.9) and K (0.138) for males differ from those currently used in the ICES assessment for this area (76 and 0.16, respectively), and the results are discussed in relation to sensitivity to reference points from analytical stock assessments and possible implications for management decisions.

The two major field methods (body colour and pleopod index) for the diagnosis of infection in the Norway lobster, Nephrops norvegicus by the dinoflagellate parasite Hematodinium were compared. Using the more reliable method, the pleopod index, which scores infection severity on a four-point scale, infection prevalence data were collected from a single fishing ground in the Clyde Sea area, western Scotland over a continuous period of 31 months. Peak infection prevalence occurs during the spring and is highest in small N. norvegicus [mean carapace length 28.1 (0.67) mm in females and 30.9 (0.50) mm in males] and in females. Mean infection severity increased from 1.050.03 during the low season (July–December) to 2.590.19 by the end of the main infection season (May), highlighting the progressive nature of patent infection over time. Infection prevalence is synchronous between the sexes in some seasons but not in others. Additionally, the proportion of recently moulted, infected males in the late season extends the duration of peak infection prevalence in certain years. Data from two adjacent fishing grounds in the Clyde Sea area also show that infection prevalence depends upon the population structure at a given site – the site with smaller animals showing the higher prevalence. An evaluation of methods for monitoring Hematodinium infection suggests that the pleopod method gives the most accurate estimation of prevalence in field-caught lobsters. 2001 International Council for the Exploration of the Sea

An investigation into the effect of Nephrops norvegicus bioturbation on the acoustic indices of RoxAnn™ was carried out over three commercial fishing grounds; the Firth of Forth, Moray Firth and the North Minch. The results obtained in the present study suggest that the relationship between burrow density and the acoustic output of RoxAnn™ is significantly more complicated than was previously reported. The differences in the findings in the present study and those previously reported are discussed.

Tuck, I. D., Atkinson, R. J. A., and Chapman, C. J. 2000. Population biology of the Norway lobster, Nephrops norvegicus (L.) in the Firth of Clyde, Scotland II: fecundity and size at onset of sexual maturity. – ICES Journal of Marine Science, 57: 1227–1239. The fecundity and size at onset of sexual maturity of Nephrops norvegicus was estimated at different locations within the Firth of Clyde, S.W. Scotland. The ‘‘potential’’ fecundity was estimated from oocyte counts in mature ovaries, while estimates of ‘‘actual’’ fecundity were made from counts of the eggs attached to the pleopods of ovigerous females. Size at onset of maturity of Nephrops norvegicus was estimated from the study of primary (ovary maturity and eggs on pleopods) and secondary (allometric) sexual characteristics. Relationships between potential fecundity and female carapace length were found to conform to a power function (F=aL b ). Comparison of the logarithmic formulations of the relationships for seven locations revealed no differences in power terms, but there were significant differences in the constants. Results suggested that differences in fecundity mainly reflected a geographical variation in oocyte volume (expressed in terms of mean dry weight) which appeared to be related to growth. Where growth rate was characterized by a low value for the asymptotic length of the carapace (L), females appeared to have smaller oocytes and larger size-specific fecundity. Estimates of size at onset of sexual maturity varied over small geographic scales (tens of km) and ranged between 21–34 mm carapace length for females and 29–46 mm for males, the estimate obtained from the different approaches being similar. Size at onset of maturity was positively related to L (p

The growth of Norway lobster (Nephrops norvegicus) from the bay of Biscay was modelled through the succession of moults and intermoult periods. First, parameters related to each of these processes were estimated for each sex and maturity stage. Moult increment was modelled as a linear function of carapace length, and regression parameters were estimated. For females, intermoult period was assumed to depend on maturity stage whereas for males it was assumed to be constant throughout their life. Mean intermoult periods were estimated from radiometric data. The estimations relied on bootstrap procedures that take into account both measurement error and individual variability. In a second step, 500 individual growth curves were simulated using previous parameter estimates. Finally, an age-length key was calculated from simulation outputs, yielding median age-at-length as well as corresponding confidence interval.

Around Scotland, coastal stocks of the commercially important Norway lobster (Nephrops norvegicus), particularly those within the Clyde Sea Area (CSA), have for some years been known to be infected by syndiniid dinoflagellate endoparasites of the genus Hematodinium. The prevalences of infected Norway lobsters in trawl samples from the CSA are reported for 1992-1995, together with similar data from a range of Scottish west coast sites in 1992, and from the Irish Sea in 1994 and 1995. In the CSA, infection prevalences declined after 1992 and were higher than those recorded in other sampled areas. Infection by Hematodinium was confined to the first half of the year, peaking in the spring and early summer, with medium-sized and female lobsters showng the highest prevalence. Comparison between CSA sites suggests that infection may be influenced by factors directly related to Nephrops age rather than size. In addition to the usual diel variability in catch, in spring male Nephrops showed diel variability in Hematodinium prevalence in trawl samples (being higher in the midnight samples). Females showed no diel variation in prevalence. Underwater television surveys of Nephrops burrow density and data on commercial landings indicate a decrease in Nephrops abundance in the last decade, which might in part reflect the higher levels of infection by Hematodinium during this time.

Size increase at moult, duration of the intermoult period, and moulting seasonality of the Norway lobster Nephrops norvegicus oV Galicia (NW Spain) were studied in the laboratory. At a mean pre-ecdysis carapace length, CL, of 35 mm the absolute moult size increment (MI) was 2.1&1.1 mm (mean&s.d.) in males and 1.7&0.7 mm in females. This corresponded to percentage moult increments (PMI) of 6.2 and 5.5% in males and females, respectively. There was a significant positive linear relation between MI and CL in males but not in females. Percentage moult increments in males were constant throughout the CL range examined (21‐54 mm), but in females a significant negative linear relationship was detected between lnPMI and CL. In both sexes the growth at moult decreased with increasing holding time under laboratory conditions, especially in the case of ecdyses taking place after more than 1 year in captivity. In males, MI was lower in smaller holding tanks. Duration of the intermoult period was similar in both sexes (180&80 days in males and 174&65 days in females), and increased significantly with increasing CL. Moulting seasonality was not marked, but two moulting seasons in autumn‐winter and spring‐summer were recorded. The information obtained in the present study was compared with available data for the Norway lobster in other geographical areas in the NE Atlantic and Mediterranean. ? 1998 International Council for the Exploration of the Sea

19 pages, 9 figures, 2 tables, The spatial distribution and biomass of Nephrops norvegicus were assessed by trawling over commercial fishing grounds ('Serola', off Barcelona, Spain) during two surveys (spring and fall 1991), using geostatistical methods. The surveys were set 6 months apart, in order to analyse possible seasonal differences. In the present surveys, Norway lobster was caught between 200 and 600 m depth, with peak abundance at about 400 m. The analysis of the structure of spatial correlation by means of semivariograms showed that densities of Nephrops norvegicus were spatially autocorrelated and lobster populations were distributed in high-density patches 6 to 9 km in diameter. No spatial segregation per biological category (size or sex) was detected. The semivariograms were consistent for all biological categories. A strong linear relationship between local mean and standard deviation (proportional effect) was modelled by the relative semivariogram. Relative experimental semivariograms were fitted to a spherical model. The shape of the semivariogram, and the spatial autocorrelation structure of Norway lobster populations, remained stable over the two surveys. The density of Nephrops norvegicus available to the experimental gear was mapped by point kriging. Highdensity patches of different biological categories exactly conformed and remained stable over the two surveys, showing a certain intra-annual stability. However, mean densities and overall abundance (computed by global kriging) decreased sharply in the fall survey. This was accounted for by means of knowledge on the biology of the species for the same area. The biological characteristics of Nephrops populations in the area studied are similar to those of other Mediterranean and Atlantic populations, hence our results are not restricted to the study area. We conclude that the geostatistical analysis approach, which takes into consideration the spatial autocorrelation structure of the populations, is adequate for the direct biomass estimation and assessment of Nephrops harvestable stock

The density, size composition and growth of Nephrops norvegicus were examined at six sites in part of the Firth of Clyde, SW Scotland, between 1990 and 1992. Sampling was carried out using small mesh trawls and by an underwater television camera. The growth of male Nephrops at each site was investigated by analysis of length-frequency distributions using the computer program “Multifan”. Estimates of Nephrops density at each station were obtained from TV counts of burrows and from relative trawl catch rates. Both density measures were correlated and showed a similar pattern between stations, although burrow counts exceeded trawl catches by roughly two orders of magnitude. Marked geographical variations were recorded in both the growth (L 0nfin; and K) and density parameters, and L ∞ was found to be inversely correlated with burrow density, suggesting that growth may be density-dependent. The weighted annual mean carapace length of Nephrops in trawl samples was significantly correlated with L ∞ , suggesting that mean size data may provide a useful indicator of growth variability within and between populations. On the other hand, the maximum carapace length (L max ) of Nephrops in samples was found to provide an unreliable estimate of L ∞ . The results are discussed in relation to possible environmental influences on growth and population density.