Bivariate and multivariate analyses of allometric relationships between chela size and carapace size of snow crab, Chionoecetes opilio, show that mature males are recognizable by morphometry. The most simple procedure is to plot logarithms of chela height (Ch) against logarithms of carapace width (Lc). Data from mature and immature males fit into two distinct ellipses with parallel major axes. The discriminant function Y = −0.78893 loge. Lc + 0.614488 logeCh + 1.76051 will assign individuals to the correct groups in 99% of cases (for mature males: Y > 0). Spermatophores are present in the vasa deferentia of all males larger than 60 mm Lc. The molt to morphometric maturity occurs later at Lc sizes ranging from 60 to 120 mm; it is identified as final. Only morphometrically mature males larger than 96 mm Lc have been observed to mate efficiently with multiparous females in intermolt and be functionally mature. In the catch, as many as 40% of males larger than the minimal legal size of 95 mm can be immature.

The growth and spatial distribution of postlarval snow crab (Chionoecetes opilio) from a relatively unexploitated stock in Bonne Bay, Newfoundland (Gulf of St. Lawrence), were described from the analysis of size distributions from trawls and a dredge sampled between 1988 and 1993. Immature crabs molted twice a year for instars I-V and then molted annually until females reached a terminal molt at maturity (instar X or XI) and males a juvenile stage (instar VIII). Thereafter, juvenile males could molt to another juvenile size, skip a molt, or achieve a terminal molt at the onset of the morphometric differentiation of their claws depending on the relative abundance of mature males. The life expectancy of females and males was 13 and 19 years, respectively. Males should recruit to the commercial size of 95 mm carapace width at instar XII, 9 years or more after settlement. Relative abundance of early benthic to commercial-size individuals suggests that small immature crabs (instar V) migrate from shallow rocky to deep muddy bottoms. The patchy spatial distribution observed for the snow crab appeared to be determined more by substrate and intraspecific factors than by depth. Seasonal movements to shallow waters by larger animals was related to density- and temperature-dependent factors associated with the reproductive and growth cycle.

The relationship between chela height (CH) and carapace width (CW) of male snow crab, Chionoecetes opilio, goes through three allometric stages. The "immature stage" (mostly < 34 mm CW) evolves into a "juvenile stage" (34–120 mm CW) through a "juvenile molt" defining a change in allometry marked by an angular point around 34 mm CW. Fifty percent of males reach gonad maturity, defined by the presence of spermatophores inside the vasa deferentia, at an estimated size of 34 mm CW) The third allometric stage, "morphometrically mature," is separated from the juvenile stage by a "molt to morphometric maturity" at sizes ranging from 50 to 120 mm CW. Juvenile males have smaller claws than morphometrically mature males of the same size. This secondary sexual character is justified by a specific behavior of the males holding the pereipods of the female in one chela during precopulatory embrace. Male snow crab efficiently mate in nature with intermolt multiparous females only after reaching morphometric maturity. Therefore, the presence of spermatophores is not the sole determinant factor necessary for male copulation. Juvenile males larger than the minimum legal size of 95 mm CW are harvestable before, they may efficiently mate.

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.1998 International Council for the Exploration of the Sea

Two trawl surveys designed for geostatistical analysis were made in spring and fall 199 1 on Nephrops norvegicus fishing grounds off Barcelona, Spain. High-resolution geostatistical techniques-a new tool for analyzing species assemblages-were used to map and assess species abundances. Of the 43 decapod crustacean species collected, the spatial structures of the nine most abundant were analyzed and mapped by kriging. The maps of abundance drawn by kriging showed that the populations within the depth range of a species were not spread uniformly but were segregated in areas of high density. The locations of high concentration patches were generally mutually exclusive between pairs of species. The depth-related zonation of the megafauna1 assemblage studied was complemented by a strong alongshore spatial heterogeneity. The spatial structure revealed by the geostatistical analysis, namely local dominance by one or a few species and a spatial pattern of high-density patches, made it difficult to predict the relative species composition at a given place, thus challenging the concept of a community of ecologically interacting decapod crustaceans over the continental slope. Local factors, such as canyon-mediated hydrographic processes and sediment resuspension, helped account for the horizontal heterogeneity in the spatial distribution of decapod crustaceans.