Evidence for a permanent establishment of the snow crab (Chionoecetes opilio) in the Barents Sea

In the Atlantic the snow crab (Chionoecetes opilio) is naturally distributed on the northwestern side, i.e. eastern Canada and west Greenland. Until recently, there have been no observations of snow crab in eastern Atlantic. However, in 1990s single and occasional reports were made of crabs captured in the eastern part of the Barents Sea, presumably introduced through ballast water. Special attention during the annual bottom-trawl surveys in the Barents Sea during February 2004–2006 were given to include recordings of snow crab to evaluate if the introduced species has succeeded to establish a self-sustaining population in this region. Recordings of snow crabs were systematically noted and biological measurements carried out. The results confirm previous Russian observations of snow crabs in the northern region of Gåsebanken. In addition, a significant number of crabs were also found in the central region of the Barents Sea, mainly in deeper waters from 180 to 350 m depth. The sizes ranged from 14 to 136 mm carapace width. All females above 70 mm were berried with fertilised eggs. A major fraction (31% in 2005; 76% in 2006) of the crabs consisted of juveniles below 50 mm CW, providing evidence for successful recruitment. The small-sized crabs were exclusively found in Gåsebanken, identifying the main recruiting area at present for snow crab in the Barents Sea. The results obtained show that the snow crab is now adapted to the northeast Atlantic.     

New microsatellite markers for the snow crab Chionoecetes opilio (Brachyura: Majidae)

Five microsatellite markers were developed for the snow crab (Chionoecetes opilio) and polymerase chain reaction conditions and/or primer sequences of three previously developed microsatellites were adapted for fluorescent labelling analysis. All loci were analysed in 449 individuals from 11 sampling sites in the northwest Atlantic. The high degree of polymorphism exhibited by these microsatellites (mean of 34 alleles per locus and mean observed heterozygosity of 0.76) suggests that they will be suitable for spatial and temporal genetic analysis of C. opilio populations.     

Changes in embryonic development and hatching in Chionoecetes opilio (snow crab) with variation in incubation temperature

Water temperature affects the distribution, movement, and reproductive potential of female snow crab, Chionoecetes opilio. Ovigerous females of C. opilio from the eastern Bering Sea were held at five temperatures (-1, 0, 1, 3, and 6 degrees C) in the laboratory while their embryos developed from gastrula to hatching. The duration of incubation increased by 105 d (30%) with decreasing temperature; however, a switch to a 2-year duration of embryo incubation was not observed. For females held at 6, 3, and 1 degrees C, their embryos underwent a short period of diapause late in development; no diapause was observed for embryos of females held at 0 or -1 degrees C. Successful extrusion of a subsequent clutch and hatch timing comparable with that observed in the eastern Bering Sea indicated that temperatures of 0 to 3 degrees C may be optimal for multiparous female reproduction. We demonstrated that a switch from 1-year to 2-year reproduction cannot be triggered by changing the thermal regime after several months of embryonic development. The timing of female movement from colder to warmer waters may be important for maintaining population reproductive potential during the recent phase of warming and contraction of cold-water biomes in the Bering Sea.     

Biochemical indicators of muscle growth in the snow crab Chionoecetes opilio (O. Fabricius)

This study examined the relationships between muscle growth rate, the activity of metabolic enzymes and the RNA:DNA ratio, in adult snow crabs Chionoecetes opilio. After moulting, crabs were assigned to three feeding rations to attain a range of tissue growth rates. Muscle growth rate, estimated by the variation in dry tissue content per ml of merus of the first walking leg, was positively correlated with changes in muscle cell number, as evaluated by the DNA content per ml of merus. However, no significant correlation was detected between growth rate and the variation in muscle cell size, the latter being estimated by the change in the protein:DNA ratio. This is due to the fact that, in starved crabs, a reduction in the number of cells is partly compensated by a size increment of the remaining ones. This phenomenon also weakened the overall relationship between muscle growth rate and the phosphofructokinase (PFK) capacity per ml of merus. The simple correlation between those two variables was significantly positive for animals which increased their mass of muscle but insignificant for those which were loosing muscle mass. The lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome c oxidase (CCO) capacity per ml of merus did not match growth rate. The significant simple correlations that were detected between growth rate and the various enzyme activity expressed per g of protein, per μg of DNA and per g of dry mass did not hold when partial correlations were computed. Variations in muscle cell size were related to adjustments in the quantity of RNA per cell, as depicted by the RNA:DNA ratio. Since muscle growth was not correlated with the variation in muscle cell size, it was not correlated with the RNA:DNA ratio either.     

Population genetic analysis and origin discrimination of snow crab (Chionoecetes opilio) using microsatellite markers

Major habitats for the snow crab Chionoecetes opilio are mostly found within the northwest Atlantic and North Pacific Oceans. However, the East Sea populations of C. opilio, along with its relative the red snow crab (C. japonicas), are two of the most important commercial crustacean species for fisheries on the east coast of the Korean Peninsula. The East Sea populations of C. opilio are facing declining resources due to overfishing and global climate change. Thus, an analysis of population structure is necessary for future management. Five Korean and one Russian group of C. opilio were analyzed using nine microsatellite markers that were recently developed using next-generation sequencing. No linkage disequilibrium was found between any pair of loci, indicating that the markers were independent. The number of alleles per locus varied from 4 to 18 with a mean of 12, and allelic richness per locus ranged from 4.0 to 17.1 across all populations with a mean of 9.7. The Hardy–Weinberg equilibrium test revealed significant deviation in three out of nine loci in some populations after sequential Bonferroni correction and all of them had higher expected heterozygosity than observed heterozygosity. Null alleles were presumed in four loci, which explained the homozygosity in three loci. The pairwise fixation index (F _ST ) values among the five Korean snow crab populations did not differ significantly, but all of the pairwise F _ST values between each of the Korean snow crab populations and the Russian snow crab population differed significantly. An UPGMA dendrogram revealed clear separation of the Russian snow crab population from the Korean snow crab populations. Assignment tests based on the allele distribution discriminated between Korean and Russian origins with 93 % accuracy. Therefore, the snow crab populations around the Korean Peninsula need to be managed separately from the populations in Bering Sea in global scale resource management. Also, this information can be used for identification of snow crab origin which is problematic in worldwide crab trade.     

A review of factors contributing to the decline of Newfoundland and Labrador snow crab (Chionoecetes opilio)

The Newfoundland and Labrador (NL) snow crab resource, presently the basis of the most important commercial fishery in the region, is in decline. Short-, mid-, and long-term recruitment prospects are deemed poor in most areas. Fishery declines have been most apparent in the north, beginning in the mid- to late 2000s, but are expected to begin in the more productive southern areas in the near future. A multitude of emergent theories to explain the resource decline have been hypothesized as contributing factors, including fishing, trawling impacts, seismic activities, disease, predation, and increasing temperature. This study comprehensively reviews and qualitatively relates the results of recent research and literature on each of these factors. We find that several factors may be contributing to a lack of recruitment in the stock, but diminishing productivity resulting from a warming oceanographic regime is the primary cause of the resource decline. Further, we postulate that trends occurring in the snow crab stock are indicative of a broader-scale ecological regime shift occurring along the NL shelf.     

Pathology of Hematodinium infections in snow crabs (Chionoecetes opilio) from Newfoundland, Canada

Bitter crab disease (BCD) of snow crabs, Chionoecetes opilio, is caused by a parasitic dinoflagellate, Hematodinium sp. The disease has shown an alarming increase in prevalence in the commercial fishery in eastern and northeastern areas of Newfoundland and Labrador since it was first recorded there in the early 1990s. We documented histopathological alterations to the tissues in snow crabs with heavy infections of Hematodinium sp. and during sporulation of the parasite. Pressure necrosis was evident in the spongy connective tissues of the hepatopancreas and the blood vessels in most organs. In heavy infections, little remained of the spongy connective tissues around the hepatopancreas. Damage to the gills varied; in some cases it was severe, particularly during sporulation, involving apparent thinning of the cuticle, loss of epithelial cells, and fusion of the membranous layers of adjacent gill lamellae. Affected lamellae exhibited varying degrees of distention with a loss of trabecular cells, hemocyte infiltrations, and swelling or "clubbing" along the distal margins. Large numbers of zoospores were located along the distal margins of affected lamellae suggesting that sporulation may cause a lysis or bursting of the thin lamellar cuticle, releasing spores. Pressure necrosis, due to the build up of high densities of parasites, was the primary histopathological alteration in most tissues. Hematodinium infections in the snow crab are chronic, long-term infections that end in host death, during sporulation of the parasite.     

Pattern and causes of a temperature-dependent gradient of size at terminal moult in snow crab (Chionoecetes opilio) along West Greenland

Geographic variation in size of male and female snow crabs (Chionoecetes opilio) was investigated along the west coast of Greenland to test the hypothesis that size at terminal molt (=adulthood) is temperature dependent. A total of 81,490 snow crabs were collected in small-mesh traps in Disko Bay (68–69°N) and six sites near Sisimiut (66–67°N) in May and June from 2000 to 2005. Average bottom temperature over the study period ranged from −0.8 to 3.2°C across the sampling sites. Mean carapace width was positively correlated with temperature in both sexes, a pattern often described as a converse Jame’s cline. We infer that temperature per se is the causative factor and discount season length, food availability or density as ultimate causes of the cline. Temperature effects on body size of crabs apparently result from a change in the number of instars before terminal molt. This interpretation is supported by size frequency analysis showing that in general crabs were larger at instar in a colder than in a warmer site. We briefly discuss the implications of our findings for population reproductive potential and the effectiveness of a fixed legal size limit in protecting some adult males from exploitation at different temperature regimes.     

Predicting the distribution and ecological niche of unexploited snow crab (Chionoecetes opilio) populations in Alaskan waters: a first open-access ensemble model

Populations of the snow crab (Chionoecetes opilio) are widely distributed on high-latitude continental shelves of the North Pacific and North Atlantic, and represent a valuable resource in both the United States and Canada. In US waters, snow crabs are found throughout the Arctic and sub-Arctic seas surrounding Alaska, north of the Aleutian Islands, yet commercial harvest currently focuses on the more southerly population in the Bering Sea. Population dynamics are well-monitored in exploited areas, but few data exist for populations further north where climate trends in the Arctic appear to be affecting species' distributions and community structure on multiple trophic levels. Moreover, increased shipping traffic, as well as fisheries and petroleum resource development, may add additional pressures in northern portions of the range as seasonal ice cover continues to decline. In the face of these pressures, we examined the ecological niche and population distribution of snow crabs in Alaskan waters using a GIS-based spatial modeling approach. We present the first quantitative open-access model predictions of snow-crab distribution, abundance, and biomass in the Chukchi and Beaufort Seas. Multi-variate analysis of environmental drivers of species' distribution and community structure commonly rely on multiple linear regression methods. The spatial modeling approach employed here improves upon linear regression methods in allowing for exploration of nonlinear relationships and interactions between variables. Three machine-learning algorithms were used to evaluate relationships between snow-crab distribution and environmental parameters, including TreeNet, Random Forests, and MARS. An ensemble model was then generated by combining output from these three models to generate consensus predictions for presence-absence, abundance, and biomass of snow crabs. Each algorithm identified a suite of variables most important in predicting snow-crab distribution, including nutrient and chlorophyll-a concentrations in overlying waters, temperature, salinity, and annual sea-ice cover; this information may be used to develop and test hypotheses regarding the ecology of this species. This is the first such quantitative model for snow crabs, and all GIS-data layers compiled for this project are freely available from the authors, upon request, for public use and improvement.     

Biomolecular characterization of allergenic proteins in snow crab (Chionoecetes opilio) and de novo sequencing of the second allergen arginine kinase using tandem mass spectrometry

Snow crab (Chionoecetes opilio) proteins have been recognized as an important source of both food and occupational allergens. While snow crab causes a significant occupational allergy, only one novel allergen has recently been fully characterized. The muscle proteins from snow crab legs were profiled by SDS-PAGE. Several of these proteins were characterized using tandem mass spectrometry. Five proteins were identified; sarcoplasmic Ca-binding (20kDa), arginine kinase (40), troponin (23kDa) and α-actine (42kDa) and smooth endoplasmic reticulum Ca(2+)ATPase (113kDa). Immunoblotting using serum of sixteen allergic patients resulted in strong reactivity with the 40-kDa protein in seven patients (43%). This protein was purified by chromatography and subsequently de novo sequenced using matrix assisted laser desorption ionization and electrospray tandem mass spectrometry. We identified a second important allergen, arginine kinase, in snow crab, designated Chi o 3. Based on identity and homology analysis, using bioinformatics tools, a signature peptide was identified as a chemical surrogate for arginine kinase. The suitability of this signature peptide was tested for analytically representing the arginine kinase, by performing a multi-reaction monitoring tandem mass spectrometry approach on actual air filter samples collected from a simulated crab processing plant.     

Isolation and characterization of polymorphic microsatellite markers in the red snow crab (Chionoecetes japonicus)

A total of 12 polymorphic microsatellite DNA loci were isolated from the red snow crab, Chionoecetes japonicus (Brachyura: Majidae), one of important fisheries resources in the Far East. The number of alleles observed at each locus ranged from two to 19, with the observed and expected heterozygosities of 0.125-0.875 and 0.156-0.949, respectively, suggesting these loci to be a useful molecular marker for population analysis in this species. Of the 12 loci, seven also were available for genotyping of the snow crab, Chionoecetes opilio, implying these loci as a useful molecular marker in the genus Chionoecetes.     

Dynamics of snow crab (<Emphasis Type="Italic">Chionoecetes opilio</Emphasis>) movement and migration along the Newfoundland and Labrador and Eastern Barents Sea continental shelves

This study uses survey and tagging data and cluster analysis to interpret dynamics of ontogenetic movements and seasonal migrations in snow crab (Chionoecetes opilio) along the Newfoundland and Labrador (NL) continental shelves. Most historic literature from Atlantic Canada suggests snow crab undertake small-scale ontogenetic movements while observations of seasonal migrations had been near-exclusive to the inshore. Information on both types of movement in the most spatially expansive offshore region of Atlantic Canada, in NL, was lacking. We find that that both ontogenetic movements and seasonal migrations occur in most areas of the NL offshore, with ontogenetic movements generally down-slope and seasonal migrations generally up-slope. Conservative estimates of average ontogenetic movements range from 54 to 72 km for both males and females in the largest offshore regions while seasonal migrations are slightly smaller, with two independent studies on the Grand Bank producing average estimates of 43–46 km and an adjacent tagging study in a smaller inshore bay producing an average estimate of 25 km. Ontogenetic movements appear associated with a search for warm water while seasonal migrations appear associated with both mating and molting in shallow water. On average, morphometrically mature crab of both sexes move less vertical distance than morphometrically immature crab during seasonal migrations. We investigate plausible explanations for ontogenetic movements and spring migrations and detail how bottom temperature affects crab distribution and life history dynamics. We further document movement patterns from tagging studies on the burgeoning snow crab stock in the Eastern Barents Sea toward establishing consistencies in species behaviour on the global scale. Finally, we discuss explanations for historical disparities in the literature between scales of movement for snow crab in the Eastern Bering Sea of Alaska versus Atlantic Canada and advance perspectives on life history theory for the species.     

Variable mate-guarding time and sperm allocation by male snow crabs (Chionoecetes opilio) in response to sexual competition, and their impact on the mating success of females.

Two laboratory experiments investigated mate guarding and sperm allocation patterns of adult males with virgin females of the snow crab, Chionoecetes opilio, in relation to sex ratio. Although females outnumbered males in treatments, operational sex ratios were male-biased because females mature asynchronously and have a limited period of sexual attractiveness after their maturity molt. Males guarded females significantly longer as the sex ratio increased: the mean time per female was 2.9 d in a 2 males:20 females treatment compared to 5.6 d in a 6 males:20 females treatment. Female injury and mortality scaled positively to sex ratio. Males that guarded for the greatest number of days were significantly larger, and at experiment's end had significantly smaller vasa deferentia, suggesting greater sperm expense, than males that guarded for fewer days. In both experiments, the spermathecal load (SL)--that is, the quantity of ejaculate stored in a female's spermatheca--was independent of molt date, except in the most female-biased treatment, where it was negatively related. The SL increased as the sex ratio increased, mainly because females accumulated more ejaculates. However, similarly sized males had smaller vasa deferentia and passed smaller ejaculates, such that, at a given sex ratio, the mean SL was 55% less in one experiment than in the other. Some females extruded clutches with few or no fertilized eggs, and their median SL (3-4 mg) was one order of magnitude smaller than that of females with well-fertilized clutches (31-50 mg), indicating sperm limitation. Males economized sperm: all females irrespective of sex ratio were inseminated, but to a varying extent submaximally; each ejaculate represented less than 2.5% of male sperm reserves; and no male was fully exhausted of sperm. Sperm economy is predicted by sperm competition theory for species like snow crab in which polyandry exists, mechanisms of last-male sperm precedence are effective, and the probability that one male fertilizes a female's lifetime production of eggs is small.     

Some observations on moulting, growth and maturation of krill (Thysanoessa inermis) from the Barents Sea

The moulting interval of the euphausiid Thysanoessa inermisfrom the Barents Sea was found to be temperature dependent withinthe range of 1.5–8.0°C. Each moult accounted for a2.1% loss of dry body wt, equivalent to a 1.2–1.3% lossof body carbon or nitrogen. During 5 months of observation bothbody length and secondary sexual characters (thelycum and petasma)of specimens varied greatly, including positive and negativegrowth periods and progression and regression of maturity stages.Characteristics of eggs spawned by one female are described.     

Red king crab (Paralithodes camtschaticus) in the Barents Sea: a comparative study of introduced and native populations

Red king crab (Paralithodes camtschaticus) was introduced into the Barents Sea in the 1960-1970s. Its present habitation area spans on the coastal zone from Hammerfest (Northern Norway) to the Barents Sea Funnel in the north-east of the Kola Peninsula. We studied the polymorphism of a mitochondrial gene encoding cytochrome oxidase (COI) and five nuclear microsatellite loci in four samples from the Barents Sea and two donor populations from the Western Kamchatka and Primorye. No decrease in the genetic diversity of the introduced populations was detected. Microsatellite assay demonstrated that the sample from Varrangerfjord was distinct from the rest five populations. However, no significant differences between the rest samples were found. Possible reasons underlying this phenomenon are discussed.     

Families in space: relatedness in the Barents Sea population of polar bears (Ursus maritimus)

The kin structure and dispersal pattern of polar bears ( Ursus maritimus ) of the Barents Sea was investigated during the spring mating season using two complementary approaches. First, individual genotypes based on the analyses of 27 microsatellite loci of 583 polar bears were related to field information gathered from 1146 bears in order to reconstruct the animals' pedigrees and to infer geographical distances between adult bears of different relatedness categories. According to the data, the median natal dispersal distance of the male animals was 52 km while that of the females was 93 km. Second, the relatedness of pairs of adult bears was estimated and correlated to the geographical distance between them. The female dyads had a much stronger kin structure than the male dyads. The 'pedigree approach' revealed a male kin structure which could not be detected using the 'relatedness approach'. This suggests that, on a broader scale, effective dispersal is slightly male biased. Despite fidelity to natal areas, male-mediated gene flow may nevertheless prevent genetic differentiation. Males might occasionally shift their home range which could therefore lead to a male-biased breeding dispersal. Our results showed that a nonterritorial species such as the polar bear that has a high dispersal potential, lives in a highly unstable environment and migrates seasonally is still able to exhibit a distinct kin structure during the mating season.     

Conflict between two inshore fisheries: for whelk (Buccinum undatum) and brown crab (Cancer pagurus), in the southwest Irish Sea

Landings from the whelk fishery in the southwest Irish Sea rose from 63 t in 1990 to 6587 t in 1996 although landings declined to 2919 tonnes in 1998. Whelk are caught in pots baited with a combination of dogfish Scyliorhinus spp and brown crab Cancer pagurus. The input of bait crab is estimated at 7.2% of whelk landed. Most of the crab comes from southeast Ireland where some of it is a by-product of the claw fishery; some is targeted as bait crab, and this includes sub-size or recently moulted individuals. Fishing effort has been increasing on brown crab for human consumption also and there is concern about the sustainability of the crab fishery. Alternative bait trials examined a number of readily available fish species, some of them offals, whose attractiveness was evaluated by reference to crab and dogfish: whitefish (whiting and cod), pelagic species (mackerel and scad) and blue mussel. An artificial bait ration which included some crab meat, but 60% less than its natural equivalent, proved as effective as natural bait crab. A bait which consisted of a single species was less successful than two species fished together and some of the combinations (notably of whitefish) performed very effectively. Pelagic species performed poorly. The trade in brown crab for human consumption will always produce some form of discards which should be used; extending its use in an artificial bait is desirable.