Dietary composition of juvenile Dissostichus eleginoides (Pisces, Nototheniidae) around Shag Rocks and South Georgia, Antarctica

A diet analysis of the Patagonian toothfish Dissostichus eleginoides, trawled in the South Georgia Islands area in March–April 1996, was carried out by frequency of occurrence (F%) and coefficient Q (%) methods. The samples consisted chiefly of immature specimens, with predominant length ranges of 30–70 cm (TL). Fish was by far the main food on the shelves of Shag Rocks and South Georgia, accounting for about 70% of prey. Krill appeared as secondary food, although its importance was overestimated by the frequency of occurrence method. Cephalopods and mysids were infrequent in the stomachs, and only at Shag Rocks and South Georgia, respectively. Lepidonotothen kempi, Champsocephalus gunnari and Chaenocephalus aceratus constituted the main fish prey and their variability between Shag Rocks and South Georgia depended on their local abundance. The large proportion of fish exhibiting stomachs full or close to fullness (together 62%) suggests that feeding intensity of the species was high.     

Distribution of cephalopods recorded in the diet of the Patagonian toothfish (Dissostichus eleginoides) around South Georgia

The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around South Georgia was analysed from stomach contents collected between March and May 2000. Cephalopods occurred in 7% of D. eleginoides stomachs. A total of 363 cephalopod beaks were found, comprising 16 cephalopod species, of which 15 had not been previously recorded in the diet. Octopodid A (probably Pareledone turqueti) was the most important cephalopod species by number of lower beaks (36 beaks; 20.2% of the lower beaks) and Kondakovia longimana was the most important in terms of estimated mass (76% of the cephalopod component). When the cephalopod component of D. eleginoides was compared with other predators between March and May 2000, D. eleginoides fed more on octopods (25% of the lower beaks) than black-browed and grey-headed albatrosses (<1% of the lower beaks). The low frequency of the squid Martialia hyadesi in the diet of D. eleginoides around South Georgia was also noticed in the diet of albatrosses, and suggests that M. hyadesi was not present in these waters in 2000 (probably due to migratory movements or reproduction failure), despite being a candidate for commercial exploitation. The presence of the squid Mesonychoteuthis hamiltoni in the diet of D. eleginoides and being caught by a longline hook whilst presumably feeding on D. eleginoides, may indicate that juveniles of Mesonychoteuthis hamiltoni are prey of D. eleginoides adults, and when Mesonychoteuthis hamiltoni reach a large size as adults, they become the predator.     

Interannual variability in reproductive traits of the Patagonian toothfish Dissostichus eleginoides around the sub‐Antarctic island of South Georgia

Commercial fisheries data, collected as part of an observer programme and covering the period 1997–2014, were utilized in order to define key reproductive traits and spawning dynamics of the Patagonian toothfish Dissostichus eleginoides at South Georgia. Multi‐year spawning site fidelity of D. eleginoides was revealed through the identification of previously unknown spawning hotspots. Timing of female spawning was shown to have shifted later, leading to a shorter spawning duration. A decrease in length and mass of female and male spawning fish and a reduced number of large spawning fish was found, evidence of a change in size structure of spawning D. eleginoides. During the study period fewer later maturity stage females (including spawning stage) were observed in conjunction with increased proportions of early stage female D. eleginoides. The findings are discussed in the context of reproductive success, with consideration of the possible effects such spawning characteristics and behaviours may have on egg and larval survival. This work presents the first long‐term assessment of D. eleginoides spawning dynamics at South Georgia and provides valuable knowledge for both the ecology of the species and for future fisheries management of this commercially important species.     

Distribution and reproduction of the Patagonian toothfish Dissostichus eleginoides Smitt around the Falkland Islands

Population characteristics of the Patagonian toothfish Dissostichus eleginoides were investigated based on material collected from both trawl and longline fisheries in Falkland Islands' waters. The fish occurred between 56 and 2122 m and attained 225 cm total length ( L _T). Males matured earlier, L _T at 50% maturity was 86 cm for males v . 90 cm for females. Subadult fish foraged at depths of <600 m, whereas adult Patagonian toothfish lived at >600 m. Spawning occurred on slopes of the Burdwood Bank at c . 1000 m depth with a minor peak in May, and a major peak in July to August. Males arrived at the spawning grounds first. Between spawning peaks both sexes remained around the Burdwood Bank with males occurring at greater depths than females. The Patagonian toothfish in south‐east Patagonia and the Falkland Islands had a long juvenile and sub‐adult period in the relatively shallow and warm waters of the outer shelf and upper slope unlike that of juveniles in other Patagonian toothfish populations. The migratory life style of the south‐west Atlantic population is probably very different from that of other populations, which tend to be resident as they are inclined to inhabit the waters around oceanic islands and sea mounts with narrow shelf areas.     

Mackerel icefish size and age differences and long‐term change at South Georgia and Shag Rocks

This study analysed the total length ( L _T)‐frequency distribution of mackerel icefish Champsocephalus gunnari at South Georgia and Shag Rocks from nine bottom trawl surveys at South Georgia and eight at Shag Rocks between 1987 and 2002. The estimated mean L _T of age‐classes 1+, 2+, 3+ and 4+ years during January were, respectively, 14·7, 23·5, 29·8 and 35·1 cm at South Georgia. Age‐classes 1+, 2+ and 3+ years were 18·3, 26·2 and 33·8 cm at Shag Rocks. The derived Bertalanffy growth parameters for South Georgia were: L _∞ = 51·7 cm, k  = 0·27 and t ₀ = −0·26. The mean L _T of each age‐class of C. gunnari at Shag Rocks was significantly larger than at South Georgia, equivalent to c . 5 months growth, although the annual growth in L _T was similar. This is further evidence that C. gunnari hatched earlier at Shag Rocks. At South Georgia, the mean L _T of age‐classes 1+ and 3+ years were correlated, and significantly decreased between 1987 and 2002, and were smaller following warmer summers. This decrease in the size of C. gunnari may be the result of reduced food availability linked to climate warming.     

Parasites of the Patagonian toothfish, Dissostichus eleginoides Smitt 1898, in different parts of the Subantarctic

The parasite faunas of the Patagonian toothfish Dissostichus eleginoides from six locations around the Southern Ocean were studied and compared. Thirty-two parasite taxa were found. Ten parasite species are reported from D. eleginoides for the first time and some other previously reported species were new locality records. Sample size at Shag Rocks was sufficient to examine the effect of intrinsic host factors, including sex and length, on the parasite fauna and these results are discussed here. Some parasite species were found only in certain areas. Sørensens similarity index indicated that the parasite faunas at Heard, Maquarie and Prince Edward Islands were the most similar, while those from the Ross Sea was the most dissimilar. There may be a gradual decrease in parasite diversity the further east the samples were collected around the Southern Ocean.     

Spatio‐temporal dynamics in maturation and spawning of Patagonian toothfish Dissostichus eleginoides on the sub‐Antarctic Kerguelen Plateau

This study investigated maturation and spawning of Patagonian toothfish Dissostichus eleginoides in the Heard Island and McDonald Islands (HIMI) fishery on the Kerguelen Plateau in the Indian Sector of the Southern Ocean based on gonads and otoliths collected between 2004 and 2015 and using histological analyses and calibration of macroscopic staging criteria. Dissostichus eleginoides at HIMI spawn throughout the austral late autumn and winter months of May–August and spawning activity is concentrated on slopes along the west and south of the plateau around HIMI at depths of 1500–1900 m. Comparison between histological analyses and macroscopic gonad staging indicated that many fish that had spawned, as indicated by the presence of post‐ovulatory follicles, returned to a resting stage which was macroscopically indistinguishable from maturing fish. Furthermore, the occurrence of females of all size classes with low gonado‐somatic index and low macroscopic gonad stage during the spawning season suggested that a proportion of mature females did not spawn every year. Age‐at‐maturity estimates, based on the assumption that fish of macroscopic stages ≥2 were mature, decreased between the 2004–2009 and 2010–2015 periods for both sexes. The magnitude of this temporal variation in age at maturity, however, varied between gear types and fishing depths and variable sampling regimes probably influenced these variations. This study highlights the importance of correct interpretation of macroscopic gonad stages and understanding the influence of fishery operations on estimations of life‐history parameters.     

Aspects of body size and gonadal histology in the Antarctic toothfish, Dissostichus mawsoni, from McMurdo Sound, Antarctica

Twenty-eight specimens of the large notothenioid Dissostichus mawsoni were dissected after capture on a set line near the southern limit of its range in McMurdo Sound, Antarctica. Total length (L _T) averaged 127.3 cm (range 90–162 cm) and weight (W ) was 26.7 kg (range 10.4–60.3 kg). The length-weight relationship was W=3.44×10⁻⁵ L _T ^2.85 (n=28, r ²=0.96). Subcutaneous lipid thickness averaged 2.6 mm and showed no difference due to sex, but a significant weak relationship to W and L _T. Hepatosomatic index (I _H) was 1.6% for females and 1.7% for males; gonadosomatic index (I _G) was 0.9% for females and 0.2% for males. Although specimens were large and sexually mature, the histology indicated that the gonads of this November sample were in a resting stage. Testes lacked spermatids and spermatozoa. Oocytes were in the previtellogenic stage (91.2%) or in the first stage of vitellogenesis (8.8%). A few atretic oocytes and empty follicles indicated that some females in this sample had spawned previously. A summary of the life-cycle is also presented. Accepted: 27 September 1999     

Variations in the parasite fauna of the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), with length, season, and depth of habitat around the Falkland Islands

The parasite fauna of Dissostichus eleginoides was examined from locations around the Falkland Islands. In total, of 11,362 individual parasites of 27 taxa were recovered from 105 fish. Two species, Ceratomyxa dissostichi and Sphaerospora dissostichi, represent new host records. The nematode Ascarophis nototheniae and the larval acanothocephalan Corynosoma bullosum were found to be new locality records and add to the knowledge of the biogeography and host specificity of parasites on the Patagonian Shelf. There were no significant differences in the mean abundance and prevalence of parasites recovered between sexes. Therefore, sex was not considered in further analysis and the data were pooled. Cysts of unknown etiology (CUE), the monogenean Neopavlovskioides georgianus, the larval acanthocephalan Corynosoma bullosum, and the digenean Neolepidapedon magnatestis had significant positive correlations with increasing host length. The larval Trypanorhynch cestode Grillotia erinaceus and the digenean Elytrophalloides oatesi showed significant negative correlations with increasing host length. CUEs, N. georgianus, the digenean Gonocerca physidis and E. oatesi showed statistically significant prevalence between summer, winter, and spring. The effect of depth on parasite communities was also examined, initially using a linear discriminant function analysis. The prevalence of individual parasites was then compared between depth strata using the chi-square test. The parasite communities on the shelf and deep water (> 1,000 m) were found to be different, whereas those caught at intermediate depths on the shelf slope were found to have parasite communities that were intermediate, containing a mixture of shelf and deeper-water parasites. The causes of the variations in parasite faunas in association with these intrinsic and extrinsic factors are discussed.     

Changes in the structure and cell composition of the thymus as a result of dosed physical loads

By means of histological and morphometrical methods normal age involution of the thymus has been studied, as well as its changes under conditions of dosed physical loadings. The experiment has been performed in 92 non-inbred white male rats. At adaptation of the organism to the loadings, involution of the gland decelerates, and at an insufficient adaptation--accelerates. This is, probably, the cause of decreasing protective forces of the organism.     

Distribution and ecology of <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis> (Channichthyidae) around South Georgia and Shag Rocks (Southern Ocean)

Chaenocephalus aceratus (Family Channicthyidae) is one of the dominant species of demersal fish living on the South Georgia shelf where it is caught in low numbers as by-catch in the mackerel icefish and Antarctic krill commercial fisheries. Data collected during 14 demersal fish surveys, from 1986 to 2006, are analysed to investigate biomass, distribution, growth and diet. Biomass estimates from a swept area method ranged from 4,462 to 28,740 tonnes on the South Georgia and Shag Rock shelves although few fish were caught at Shag Rocks. Analysis of length frequency data indicated that growth was fast in the first five years with males and females attaining lengths at first spawning of 440 mm TL and 520 mm TL. The diet was comprised of fish and crustaceans, with an ontogenetic shift in diet from Euphausia superba and mysids to benthic fish and decapods observed to begin at 250 mm TL. In larger fish (>500 mm TL) the diet was dominated by fish. C. aceratus diet is sufficiently different from the other species of channichthyids around South Georgia to suggest that these species have undergone resource partitioning.     

气候环境因子和捕捞压力对南海北部带鱼渔获量变动的影响

带鱼(Trichiurus japonicas)是南海北部的重要经济鱼类,其渔获量的变化不仅与捕捞压力有关,还与气候环境变化有关.为了研究气候变化和捕捞对南海北部带鱼渔获量变动的影响,使用长时间序列渔业统计资料和气候变化数据对1956-2006年的南海北部带鱼渔获量变动进行了分析.南海北部的带鱼渔获量变化可划分成因捕捞效应所产生的趋势变化和因气候环境变化所导致的渔获量变动.捕捞效应所产生的趋势变化可用Fox模型拟合,Fox模型拟合结果显示南海北部带鱼渔获量与捕捞努力量关系显著(P＜0.01),说明捕捞压力的增长显著影响到南海北部带鱼渔获量的变化.移除捕捞效应所产生的趋势变化后,渔获量变动与中国南方降雨、南海北部海表水温、南海北部夏季季风以及南海北部冬季季风等气候因子呈显著正偏相关(P＜0.04),与热带气旋影响指数呈显著负偏相关(P＜0.03),这种相关说明南海北部带鱼渔获量变动还受气候环境因子的影响.南海北部带鱼渔获量可用捕捞努力量和气候变量来拟合,且拟合效果显著(R2=0.958,P＜0.01),表明南海北部带鱼渔获量的变动归因于捕捞压力的单调增长和气候环境的变化.在南海北部的捕捞压力维持在现有水平下,未来的气候变化和人类活动引起营养盐的增加都可能有利于南海北部带鱼渔业产量的增加,且由于未来极端天气事件的频繁发生,可能还会引起带鱼渔获量的变动幅度加剧.     

Species composition and ecology of dinoflagellates from the Southern Ocean near South Georgia

Dinoflagellates were identified and counted from preserved verticalnet haul samples collected from a station grid centred on SouthGeorgia in austral summer 1981 –1982. All species werescarce in comparison with diatoms, the dominant large-celledmicroplankton. Dinophysis antarctica Balech was the most abundantand widespread species. Maximum dinoflagellate numbers werefound at stations forming a belt to the south and west of theisland. Whilst previous analysis of diatom community compositionhad revealed distinct species associations, no differences inspecies composition between this region and areas of low dinoflagellateabundance could be resolved. Since both heterotrophic and photoautotrophictaxa were found in the samples, it is difficult to identifyenvironmental features which could act on most of the dinoflagellatetaxa. The large-scale pattern of dinoflagellate distributionmay reflect the pattern of water circulation along the edgeof the South Georgia continental shelf.     

Changes in the blood-testis barrier as a result of streptococcal sensitization

Permeability of the histo-hematic barrier in the guinea pig and mouse testes immunized with streptococci has been studied radiometrically and luminescent microscopically with application of labelled bovine serum albumin, human gamma-globulin and blue dye preparations. The permeability of the hemato-testicular barrier increases on the 7th--30th day after immunization. Test-preparations penetrate from the vessels of the intercanalicular connective tissue layers through the membrane of the convoluted tubules. The testicular autoantigen is revealed in blood. The disturbance in permeability of the hemato-testicular barrier precedes or coincides in time with the developing destruction of the testicular spermatogenic elements.     

Changes in cyclic AMP concentration of the rat preoptic region as a result of long term exposure to cold

The cAMP concentration in the preoptic region was studied in rats during exposure to low ambient temperature (Ta: -10 degrees C) and after return to control Ta (22 degrees C). With respect to control cAMP concentration, changes were observed consisting of a decrease (delta cAMP: 4.19 /+- 0.15 pM/mg Pr; p < 0.001) at low Ta and an increase (delta cAMP: 1.40 /+- 0.13 pM/mg Pr; P < 0.05) after return to control Ta. In contrast, cortical cAMP concentration decreased both at low Ta (delta cAMP: 2.94 /+- 0.09 pM/mg Pr; P < 0.005) and after return to control Ta (delta cAMP: 3.21 /+- 0.09 pM/mg Pr; P < 0.001). such cAMP changes in the preoptic region may be related to different activation levels of thermoregulatory and sleep mechanisms.     

Changes in the speed of ants as a result of aggressive interactions

Subordinate ant species utilize different tactics to reduce competition with the stronger, larger and more aggressive individuals of a dominant species. In our experimental study, we assessed the behavioral response of individual workers of 4 subordinate ant species during their co‐occurrence with workers of a single dominant species. Contrary to most classical experiments focused on aggressive interactions, we assessed workers’ speed as a crucial factor in the outcome of co‐occurrence. Generally, there was a large intraspecific variation in the speed of the studied species—each had slow and fast individuals. Workers of all studied species moved faster just after interaction, suggesting that contact between 2 hostile workers is a stressful stimulus, generating a behavioral reaction of increasing speed. Also, the number of aggressive contacts experienced by a given individual positively affected its speed. Moreover, workers which were fast when exploring territory were also fast after interspecific interactions. The duration of aggression was significantly reduced by the speed and body size of a subordinate species worker—the more quickly a worker reacted and bigger it was, the shorter was the time of cumulative aggression. To our knowledge, this is the first study of this type to be conducted on ants and we conclude that speed is an overlooked and important characteristic of species and also individuals, therefore it should be considered as a driver of patterns of co‐occurrence in ant assemblages.     

Changes in the myocardium of fetuses and newborn infants as a result of hypoxia

Myocardium has been investigated in 68 human fetuses and newborns suffered from intrauterine acute and prolonged hypoxia, occurred as a result of various maternal, fetal and placental diseases. Under acute hypoxia only reactive changes of the contractile myocardium appear. They are demonstrated as degeneration of muscle fibers and appearance of scattered foci of necrosis in cardiomyocytes. Under a prolonged hypoxia, besides analogous reactive changes, compensatory hypertrophy of some part of cardiomyocytes is noted; this is manifestation of a compensatory-adaptive reaction of the myocardium.