Albatross predation of juvenile southern blue whiting (Micromesistius australis) on the Campbell Plateau

Dietary samples collected at Campbell Island in summer 1997 indicate that southern blue whiting (Micromesistius australis) formed the bulk of the food of black‐browed albatrosses (Diomedea melanophrys impavida) during the chick‐rearing period. Birds preyed upon a single size class of fish with a mode at 80–90 mm standard length; fish were 4–5 months old and belonged to the 0+ age group. Satellite tracking showed that, when performing trips of short duration, adult albatrosses foraged within the 1000 m depth contour in the subantarctic zone north of Campbell Island. The feeding ecology of albatrosses thus suggests that juvenile (0+) southern blue whiting are pelagic and occur in dense schools in the top 5 m of the water column over the Campbell Plateau during the summer months. The high reliance of birds on juvenile southern blue whiting during the chick‐rearing period has implications for the management of the southern blue whiting fishery and the conservation of black‐browed albatrosses and other marine predators occurring in the New Zealand subantarctic area.     

The food and feeding of seven fish species from the Campbell Plateau,New Zealand

The food and feeding habits of hoki (Macruronus novaezelandiae), southern blue whiting (Micromesistius australis), javelin fish (Lepi‐dorhynchus denticulatus), ling (Genypterus blacodes), smooth rattail (Coelorinchus aspercephalus), silverside (Argentina elongata), and small‐scaled notothenid (Notothenia microlepidota) sampled from the Campbell Plateau in 1979 were examined. The importance of prey items in the diet has been assessed by an ‘index of relative importance’, which combines measurements of frequency of occurrence, number, and weight of prey. Hoki, southern blue whiting, and javelin fish are pelagic feeders. Hoki preyed largely on natant decapod crustaceans, amphipods, and myctophid and photichthyid fishes. The main prey of southern blue whiting were amphipods, natant decapods, and euphausiids. Javelin fish fed on natant decapods, amphipods, and small squid. Seasonal and regional differences in feeding, and dietary changes with length of fish were evident. Ling, smooth rattail, silverside, and small‐scaled notothenid are predominantly benthic feeders. Ling preyed on natant decapods, macrourid fishes, and small hoki. The diet of rattail comprised natant decapod crustaceans, opal fishes (Hemerocoetes spp.), and poly‐chaetes. Silverside fed almost solely on salps. Salps, amphipods, brachyuran crustaceans, and opal fishes were the main prey of small‐scaled notothenid.     

Batch fecundity and spawning frequency of southern blue whiting (Micromesistius australis) in the southwest Atlantic Ocean

The reproductive biology of southern blue whiting (Micromesistius australis) inhabiting waters of the southwest Atlantic Ocean (52°‐53°S and 57°‐62°W) was studied through histological analysis of the ovaries. During 2003, the spawning peak occurred at the beginning of September south of the Malvinas Islands. Batch fecundity of this species ranged from 35 000 (41 cm total length, TL) to 245 000 (62 cm TL) oocytes and relative batch fecundity was 122 ± 43 (Mean ± SD, n = 24) oocytes per gram somatic weight. The average proportion of mature females with stage‐0 post‐ovulatory follicles was 0.25 for September 2003, which indicated a spawning frequency of 4 days during the peak of the season. Large females produced more egg batches than small spawners during the same period, but no significant relationship was found between oocyte dry weight and female size of southern blue whiting.     

Resource partitioning by two large planktivorous fishes Micromesistius australis and Macruronus magellanicus in the Southwest Atlantic

The ontogenetic, seasonal, bathymetric and regional variations in the feeding spectrum of 922 specimens of southern blue whiting Micromesistius australis and 512 specimens of hoki Macruronus magellanicus were studied on the Falkland Islands’ shelf (Southwest Atlantic) between November 1999 and April 2003. A total of 49 different prey items were found in the stomach contents of the two species, with the hyperiid Themisto gaudichaudii and Euphausiacea being amongst the most important prey. Although the species composition did not change over fish size, the proportions of individual prey items in their diets did, with an increase in T. gaudichaudii and Euphausiacea with increasing fish size in southern blue whiting. The opposite occurred in hoki. Seasonal variations in the diet were found to mirror the seasonal abundance of prey around the Falkland Islands for the two species. Intra-specific differences in the diet of both predators reflected the distribution of prey, which in turn was determined by the water structure in the two regions sampled, leading to very different diets. In the limited time that the two species occupied the same space there was little or no competition resulting in almost total segregation of their trophic niches in space and time.     

The diet of Patagonian hake Merluccius australis polylepis and its daily ration of Patagonian grenadier Macrouronus magellanicus

The diet of the Patagonian hake Merluccius australis polylepis in 1986 was determined by analysis of stomach samples collected from commercial trawl catches. The major prey items were Patagonian grenadier Macrouronus magellanicus and, to a lesser extent, southern blue whiting Micromesistius australis. Large (81–100 cm) hake are mainly piscivorous and consume more grenadier than smaller (51–80 cm) hake. The smaller hake feed both on fish and invertebrates. There was no difference by sex in terms of stomach contents. The daily feeding cycle was also investigated from samples collected during 1991. Hake feed principally on 1-, 2-, and 3-year-old grenadier, which they seem to catch mainly at night. The daily ration of grenadier was between 0,043 and 0,26 per cent of body mass (1,692–9,849 g). The results are similar to those for other hake species in terms of composition of the diet, daily feeding cycle and daily ration.     

Genetic variability of the blue and red shrimp Aristeus antennatus in the Western Mediterranean Sea inferred by DNA microsatellite loci

Genetic variation at eight microsatellite loci was studied in nine populations of the blue and red shrimp Aristeus antennatus to investigate whether distinct stocks are present in the Western Mediterranean Sea. A high level of gene flow and no evidence of genetic partitioning were discovered. No significant variation was found (F_ST = 0.00673, P-value = 0.067) even when shrimps from exploited and those from deep-water unexploited grounds were compared. No evidence of reduction or expansion of population size in the recent past was found, as indicated by the bottleneck and interlocus g-tests. Our results are consistent with previous studies using mitochondrial gene methods and allozymes, indicating that, for this species, extensive pelagic larval dispersal and adult migration are probably responsible for the genetic homogeneity observed. In particular, due to a different bathymetric distribution of males and females, reported to be associated with different water masses and hence with possible differential dispersal capacity between sexes, the hypothesis of sex-biased dispersal was tested. Mean values of corrected assignment indices and mean relatedness values were higher for males, suggesting that females are the more widely dispersing sex. Molecular assessment of A. antennatus from the Western Mediterranean provides data of biological and evolutionary interest for the successful management of such a highly valuable fishery resource.     

多鳞(Sillago sihama)鱚4个野生地理群体的微卫星标记分析

采用微卫星DNA分子标记方法对中国南部沿海多鳞鱚(Sillago sihama)广西北海、广东湛江、汕尾及海南三亚4个野生地理群体进行了遗传多样性及遗传分化等研究。结果表明:(1)用于研究的34对微卫星引物在4个群体中具有丰富的多态性,有效等位基因数介于1.71—20.46之间,多态信息含量PIC介于0.40—0.95之间。4个群体总的平均期望杂合度(He)为0.598,观测杂合度(Ho)为0.572,SY群体的杂合度最大(He=0.606,Ho=0.623),SW群体的最小(He=0.586,Ho=0.508)。(2)群体间F-统计量分析表明,群体遗传分化处于高度分化水平(Fst平均值为0.306);基于奈氏遗传距离(DA)构建的NJ和UPGMA聚类树均显示地理位置相邻的群体聚在一起。     

Trophic ecology of black scabbardfish,Aphanopus carbo in the NE Atlantic—Assessment through stomach content and stable isotope analyses

The black scabbardfish is a deep water species of high commercial interest in the NE Atlantic. Specimens were collected from commercial trawls to the west of the British Isles and from longliners operating near Madeira between September 2008 and May 2010. Stomach content analysis was confined to samples from the northern area, because of a high number of empty stomachs from Madeira. Stable isotope analyses identified that black scabbardfish feeds on species with epipelagic and benthopelagic affinities. For the west of British Isles, the δN values were significantly different between seasons suggesting a change in the diet throughout the year. Black scabbardfish have higher δN and δC values compared with other co-occurring benthopelagic feeders and lower nitrogen values than the true benthic predators and/or scavengers. Comparison with stable isotope analysis in samples from Madeira indicated that black scabbardfish feed at a similar trophic level and has the same trophic niche width in both areas, assuming similar baseline isotope compositions. The diet in the northern area comprised fish (68% N), crustaceans (22% N) and cephalopods (15% N) with blue whiting (Micromesistius poutassou) constituting 40% of the prey. Seasonal shift in diet was observed, with a predominance of blue whiting (70%) in the first quarter of the year, shifting to a more diverse diet in the remainder of the year. These results indicate that the diet of black scabbardfish is closely linked with the seasonal migration of blue whiting and that they likely select prey in proportion to availability. This study demonstrates that the combined used of both methods can elucidate the trophic ecology of black scabbardfish, in situations where conventional methods alone provide insufficient data.     

Geographic structure of European anchovy: A nuclear-DNA study

Atlantic–Mediterranean anchovies were genetically characterized at two polymorphic nuclear loci (intron 6 of two creatine-kinase genes) and compared to reference Engraulis albidus and E. encrasicolus samples from the northern Western Mediterranean to provide new insights into their geographic structure. Northeastern Atlantic anchovy, represented by one sample from the Canary archipelago and one sample from the Alboran Sea, were genetically distinct from Mediterranean E. encrasicolus (Weir and Cockerham's ^θ = 0.027–0.311), indicating geographic isolation from either side of the Almería–Oran oceanographic front. Generally smaller genetic differences were evident among anchovy populations from different sub-basins in the Mediterranean (^θ = − 0.019–0.116), the genetic differences between Black Sea and Ionian Sea/Aegean Sea anchovies being the strongest (^θ = 0.002–0.116). There was no evidence of the presence of E. albidus in our samples outside Camargue (northern shore of the Western Mediterranean). However, a sample from the southern Western Mediterranean appeared to be genetically intermediate between E. albidus and Mediterranean E. encrasicolus, indicating possible hybridization. Anchovy from the Benguela current system off southern Africa possessed allele frequencies characteristic of E. albidus at one locus and Northeastern Atlantic anchovy at the other locus, suggesting past introgression.     

洞庭湖水系五强溪水库光泽黄颡鱼(Pelteobagrus nitidus)遗传多样性的AFLP分析

为了了解沅水五强溪大坝阻隔对光泽黄颡鱼可能造成的遗传多样性影响,采用AFLP分子标记技术,对沅水五强溪水库库区和沅水下游两个光泽黄颡鱼野生群体进行了遗传多样性分析。9对选择性引物在两个光泽黄颡鱼群体中,共扩增出1243个位点,多态位点1091个,多态位点比率为87.77%。其中库区和沅水下游群体多态位点比率分别为85.41%、83.25%,观测等位基因数分别为1.854±0.592、1.803±0.622,有效等位基因数分别为1.597±0.381、1.574±0.377,Nei’s多样性指数分别为0.220±0.211、0.207±0.195,Shannon’s信息指数分别为0.330±0.305、0.302±0.338;两个群体内的平均遗传距离分别为0.124±0.072、0.119±0.057,群体间的平均遗传距离为0.127±0.100。两个群体的遗传参数比较不存在显著差异(P0.05)。聚类分析显示,UPGMA系统树没有依据群体而形成明显的两大分支。以上结果表明,五强溪水库库区和沅水下游两个光泽黄颡鱼群体的遗传多样性丰富,光泽黄颡鱼种群遗传结构对水库大坝阻隔的响应不明显。     

Population structure of the thornback ray (Raja clavata L.) in British waters

Prior to the 1950s, thornback ray (Raja clavata L.) was common and widely distributed in the seas of Northwest Europe. Since then, it has decreased in abundance and geographic range due to over-fishing. The sustainability of ray populations is of concern to fisheries management because their slow growth rate, late maturity and low fecundity make them susceptible to exploitation as victims of by-catch. We investigated the population genetic structure of thornback rays from 14 locations in the southern North Sea, English Channel and Irish Sea. Adults comprised < 4% of the total sampling despite heavy sampling effort over 47 hauls; thus our results apply mainly to sexually immature individuals. Using five microsatellite loci, weak but significant population differentiation was detected with a global F_ST = 0.013 (P < 0.001). Pairwise F_st was significant for 75 out of 171 comparisons. Although earlier tagging studies suggest restricted foraging distances from home areas, the absence of genetic differentiation between some distant populations suggests that a substantial fraction of individuals migrate over wide areas. Autumn/winter locations appear to have a lower level of differentiation than spring/summer, which could be due to seasonal migration. Management and conservation of thornback ray populations will be challenging as population structure appears to be dynamic in space and time.     

羊栖菜养殖品系DNA指纹图谱的研究

对羊栖菜(Hizikia fusiformis (Harv) Okamura)养殖中常见的3个品系进行了DNA指纹分析及遗传变异的研究,构建了其遗传指纹图谱,分析了不同种群的遗传关系,为羊栖菜的种质鉴定及选育提供了理论依据.运用RAPD分子标记技术,对5个羊栖菜的种群中共125个个体进行了分析,从300个引物中筛选出12条随机扩增引物共扩增135个位点,多态位点比率为84.4%.从中选择了4个多态性位点,构建了DNA指纹图谱.相关结果对羊栖菜遗传选育和种质鉴定等有参考价值.     

Genetic and morphological variation of the lanternfish Lampanyctodes hectoris (Myctophiformes: Myctophidae) off southern Africa

Genetic and morphological variation within the southern African population of Lampanyctodes hectoris was analysed. A total of 15 enzymes, encoding 22 isozyme loci, was examined (n = 327); seven were polymorphic. The percentage of polymorphic loci ranged from 13.6 to 27.3%. The mean heterozygosity was generally low and ranged from 0.003 to 0.005. Genetic divergences between specimens from four areas along the west coast of southern Africa were negligible, genetic distance values (D) ranging from 0 to 0.00011. The results showed the population of L. hectoris to be genetically invariant. Principal Component Analysis was performed separately on ratios of 13 morphometric and 6 meristic variables (n = 446), and there was evidence of extensive overlap between fish from all areas. However, discriminant analysis suggested some morphological variability within this population. Although genetically the population of L. hectoris seems to be homogenous, morphologically it appears to be variable. A combination of these results suggests that there is no clear genetic basis for the slight morphological differentiation within the population.     

Multi-element otolith chemistry of juvenile sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) in the Thames Estuary and adjacent coastal regions

Estuaries are regarded as valuable nursery habitats for many commercially important marine fishes, potentially providing a thermal resource, refuge from predators and a source of abundant prey. To assess the extent of estuarine use by juvenile (0+) common sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) we: (1) developed techniques to distinguish between estuarine and coastally-caught juveniles using otolith chemistry; and (2) examined the accuracy with which multi-elemental signatures could re-classify juveniles to their region of collection.High-resolution solution-based inductively coupled plasma mass spectrometry (HB-SB-ICPMS) was used to quantify 32 elements within the juvenile otoliths; 14 elements occurred above detection limits for all samples. Some elemental distributions demonstrated clear differences between estuarine and coastally-caught fish. Multivariate analysis of the otolith chemistry data resulted in 95–100% re-classification accuracy to the region of collection. Estuarine and coastal signatures were most clearly defined for sole which, compared to bass and whiting, have low mobility and are less likely to move from estuarine to coastal habitats between larval settlement and later migration to adult stocks. Sole were the only species to reveal an energetic benefit associated with an estuarine juvenile phase. The physiological ability of bass to access upper estuarine regions was consistent with some elemental data, while the high mobility and restricted range of whiting resulted in less distinct otolith chemistries.     

Catch, survey and life-history data for shrimp (Pandalus borealis) off Jan Mayen

The Jan Mayen area has an extreme environment with low temperatures and infrequent, but abrupt temperature changes. The shrimp population here is considered to be on its edge of distribution. The life-history parameters are in the same range as in other high-latitude shrimp populations and are characterized by slow growth, large size at maturation and extended longevity. Irregular and sporadic commercial exploitation limit fishing mortality and give the population life-history parameters not previously seen in other areas. The Jan Mayen shrimp are large compared to, e.g., the Barents Sea shrimp and can reach a maximum carapace length (L_max) of 37 mm and an age of 10–11 years. The large size at sex transformation (L₅₀, >24 mm) and analyses of length–frequency distributions indicate that the shrimp may be 6–7 years of age before changing sex. The change in L_max and L₅₀ observed during the study period is probably caused by increased natural mortality due to sudden temperature changes or due to increased predation, rather than increased growth rates. The life-history strategy of shrimp in the Jan Mayen area can be explained by factors such as depth, temperature and population density variations caused by fluctuation in recruitment and mortality.The shrimp fisheries in the Jan Mayen area began in the late 1970s and reached an annual landing of 2000 tonnes in 1985, and since then landings have oscillated around 500 tonnes depending on a combination of factors. The survey indices of stock biomass varied between 3000 and 6600 tonnes. For most years, the highest shrimp densities are at a depth of 200–299 m, while large shrimp (and therefore also female shrimp) are dominant at depths greater than 300 m.Fish community data were studied as the composition of the demersal fish community is an integrated response to environmental conditions and as predation affects the shrimp stock. Polar cod and capelin are the most abundant fish species in the study area. A high number of blue whiting was registered in 1979, but the number declined in 1980 and 1981 as temperature decreased. During the surveys in 1994 and 1995, no blue whiting was registered. A few individuals were found again in the 1999 samples. The number of Greenland halibut has declined from the beginning of the 1980s to the 1990s.     

四种鳕鱼的形态学研究

本文对蓝鳕 (Micromesistius poutassou)、远东宽突鳕 (Eleginusgracilis)、大西洋鳕(Gadusmorhua)和太平洋鳕 (G. macrocephalus)等 4种经济鳕鱼类进行了细致的观察 ,对其分节及量度特征进行了测定分析 ,发现所测数据与国内外资料存在一些差异 ;并补充描述了各种的鼻孔、牙齿等形态特征。统计检验表明 :蓝鳕的第 1臀鳍鳍条数、鳃耙数与其他鳕鱼存在显著差异 ;远东宽突鳕的脊椎骨数与其他鳕鱼存在显著差异 ;大西洋鳕和太平洋鳕在上述性状上的差异不明显 ,但 2者的体色有明显差异。从形态特征聚类分析图得知宽突鳕属与鳕属亲缘关系近 ,而蓝鳕属与鳕属亲缘关系远。     

Biochemical‐genetic and meristic evidence that blue and copper moki (Teleostei: Latridae: Latridopsis) are discrete species

Specimens of blue moki Latridopsis ciliaris (Forster in Bloch & Schneider, 1801) from New Zealand were shown to differ from specimens of copper moki Latridopsis forsteri (Castelnau, 1872) using two genetic methods—allozymes and muscle proteins. Allozyme techniques revealed fixed differences between blue and copper moki at 4 out of 15 loci. There was a genetic distance of 0.31–0.34 between population samples of the two colour morphs. The two morphs were also distinguished by iso‐electric focusing of muscle proteins. Meristic characters, counted in the specimens studied with genetic markers, revealed diagnostic markers in tubed lateral line scales and scales in the lower transverse series. It is concluded that specimens of blue moki from New Zealand and copper moki from New Zealand and Tasmania are valid species.     

中国对虾选育群体“黄海1号”和野生群体不同组织基因组DNA甲基化的MSAP分析

DNA甲基化在调节动物生长发育和组织分化中发挥了重要作用。本研究主要从酶切、预扩和选扩等方面优化了中国对虾DNA甲基化分析的MSAP技术,给出了适合中国对虾MSAP分析的最近反应程序和体系,并采用该技术分别对中国对虾选育群体"黄海1号"和野生群体的肌肉、鳃和血细胞三种组织基因组DNA的CCGG甲基化水平进行分析。研究结果表明,中国对虾野生群体肌肉、鳃和血细胞的DNA甲基化比例分别为23.1%、22.3%和19.7%,选育群体"黄海1号"肌肉、鳃和血液的甲基化比例分别为21.4%、19.6%和18.9%。鳃组织的DNA甲基化水平在两群体中差异极显著(P <0.01),肌肉间的甲基化水平差异显著(P <0.05),而血细胞中甲基化水平差异不显著(P >0.05)。中国对虾野生群体和"黄海1号"同一组织间的甲基化水平不同(P ≤ 0.05),而不同组织间的甲基化水平也各不相同(P ≤ 0.05)。DNA甲基化多态性分析表明,野生群体和选育群体"黄海1号"的鳃和血细胞组织的甲基化多态性比例变化明显,而肌肉组织甲基化水平较稳定,这些变化趋势与CCGG位点的甲基化和去甲基化有关。     

Biochemical‐genetic variation in a wild and a cultured population of the greenshell mussel,Perna canaliculus

A wild and a cultured greenshell mussel (Perna canaliculus) population were compared for biochemical genetic variation at seven polymorphic and four monomorphic allozyme loci. Significant heterozygote deficiencies were observed for all polymorphic loci (La—1, La—2, Lap, Lgg—1, Lgg— 2, Pgi, and Pgm) for both populations (except the Pgi locus of the wild mussel population). Genotypic disequilibrium was calculated for both populations: genotypic frequencies were significantly non‐random at three pairs of loci among the wild mussels, and significantly non‐random at three different pairs of loci among the cultured mussels. All six pairs of loci which exhibited significant genotypic disequilibrium involved amino‐peptidases, suggesting that these loci form a linkage group, and that neither the Pgi nor the Pgm loci are associated with this group. Exact tests for population differentiation based upon population‐specific allele distributions indicated that four of the polymorphic loci were significantly heterogeneous among the two populations, whereas the remaining three polymorphic loci were not. Based upon the private allele system, the number of migrants (N _m) between the populations was estimated to be 2.009, which, according to the private allele system, represents a high level of gene flow. These findings are discussed with regard to the population biology and genetic structure of this species.