首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The distribution and abundance of jellyfish of the family Ulmaridae was studied based on the data of trawl surveys conducted in the Sea of Okhotsk (1998–2006) and the Sea of Japan (2003) in the fall. The jellyfish Aurelia aurita mainly inhabits the waters of the Sea of Japan, while in the Sea of Okhotsk small quantities of this species were recorded in southern areas, and solitary individuals, off North Sakhalin. Aurelia limbata tends to shelf waters of the Sea of Okhotsk, being less abundant in the southern deepwater area and in the Sea of Japan. Phacellophora camtschatica, in contrast, aggregates mostly over deep basins, whereas in shallow areas a significant quantity of this species was found only off West Kamchatka. In the northern Sea of Okhotsk, the species A. limbata dominated in biomass and abundance among Ulmaridae. During the studied period, its biomass varied from 27 to 803 kg/km2 and its abundance varied from 69 to 1706 ind/km2. In the southern Sea of Okhotsk, as a rule, P. camtschatica prevailed (1–16 kg/km2 and 6–46 ind/km2). In the Sea of Japan, the most abundant species was A. aurita (29 kg/km2 and 104 ind/km2). The jellyfish size structure in catches is presented.  相似文献   

2.
This study assessed the possibility of using drift and subtidal seaweeds from St Lawrence Island, Alaska (lat. 63°N) for sale by the native population after simple processing. Over 125 km of coastline were surveyed for distribution of both drift and subtidal seaweeds. Drift seaweed wet weight densities ranged from 0.2 to over 9 kg m−2, with an average of over 4 t km−1 in the areas sampled. Attached, benthic seaweed densities ranged from 0.15 to 0.32 kg m−2. Thirty and 35% of the biomass was composed of Agarum cribrosum and species of Laminaria, respectively, both as drift and as benthic seaweed. Data from tagged Laminaria indicated that growth rates were relatively slow for most of the year. The drift seaweed resource on the coasts south and west of the city of Gambell appeared to have good potential for a small-scale commercial harvest. (*author for correspondence)  相似文献   

3.
Food handouts from visitors to Mt. Emei, in The People’s Republic of China, have considerably increased the diversity of food available to an indigenous population of Macaca thibetana.Some 43% of the feeding time was spent at the trail area frequented by tourists. Ranging behavior was of two kinds: wandering around within the group’s most densely used areas and making peripheral excursions between the areas. Three kinds of trail-area use were observed: three-group overlapping, two-group overlapping, and exclusive. M. thibetanatended to use sheltered sites for sleeping, to ensure safety and/or to keep dry in a rainy habitat. Exclusively and successively used sleeping sites were noted. The average size of the home range per group was 3 km 2; the average population density for the entire range was 13/km2, and the biomass was 109 kg/km2. The population may be growing, a possibility that is also supported by previous analyses using data on group composition.  相似文献   

4.
According to the data of trawl catches performed by the R/V “TINRO” in the upper epipelagic zone (0–50 m) of Pacific waters off the Kuril Islands from June 2 to July 8, 2012, the abundance of nekton was the lowest for the recent 9 years; thus, its density in 2012 (1.5 t/km2) was lower than the average value for the 2004–2012 period (2.40 ± 0.39 t/km2). The major portion of the nekton biomass was formed by pacific salmon (706 000 tons, or 43.6%); their role grows abruptly during pre-spawning migrations of pink salmon, whose proportion reached 29.8% (483 000 t). In 2012, the recorded biomass of pre-anadromous pink salmon was as high as those in the previous 3 years, and even higher than the estimate of 2010 (479 800 t), which is the largest value for even-numbered years. The value of 2012 also was comparable with the estimates for the previous odd-numbered year, 2011, when the total biomass of the species constituted 496 500 t. Chum salmon stands out among other salmon for its record-high biomass (192 700 t, 11.9%), which was twice as high as that in 2011. The biomass and the share of the mesopelagic fish complex was the lowest (286800 t, 17.7%) since 2004. Among other fish species, Kuril groups of walleye pollock also had a substantial biomass (381 200 t, 23.5%). The total biomass of squid (225 300 t, 13.9%) was lower than the value of 2011 (326 300 t, 14.8%) owing to the decline in the biomass of Boreopacific gonate squid by 90 000 t.  相似文献   

5.
ABSTRACT Given recent actions to increase sustained yield of moose (Alces alces) in Alaska, USA, we examined factors affecting yield and moose demographics and discussed related management. Prior studies concluded that yield and density of moose remain low in much of Interior Alaska and Yukon, Canada, despite high moose reproductive rates, because of predation from lightly harvested grizzly (Ursus arctos) and black bear (U. americanus) and wolf (Canis lupus) populations. Our study area, Game Management Unit (GMU) 20A, was also in Interior Alaska, but we describe elevated yield and density of moose. Prior to our study, a wolf control program (1976–1982) helped reverse a decline in the moose population. Subsequent to 1975, moose numbers continued a 28-year, 7-fold increase through the initial 8 years of our study (λB1 = 1.05 during 1996–2004, peak density = 1,299 moose/1,000 km2). During these initial 8 hunting seasons, reported harvest was composed primarily of males ( = 88%). Total harvest averaged 5% of the prehunt population and 57 moose/1,000 km2, the highest sustained harvest-density recorded in Interior Alaska for similar-sized areas. In contrast, sustained total harvests of <10 moose/1,000 km2 existed among low-density, predator-limited moose populations in Interior Alaska (≤417 moose/1,000 km2). During the final 3 years of our study (2004–2006), moose numbers declined (λB2 = 0.96) as intended using liberal harvests of female and male moose ( = 47%) that averaged 7% of the prehunt population and 97 moose/1,000 km2. We intentionally reduced high densities in the central half of GMU 20A (up to 1,741 moose/1,000 km2 in Nov) because moose were reproducing at the lowest rate measured among wild, noninsular North American populations. Calf survival was uniquely high in GMU 20A compared with 7 similar radiocollaring studies in Alaska and Yukon. Low predation was the proximate factor that allowed moose in GMU 20A to increase in density and sustain elevated yields. Bears killed only 9% of the modeled postcalving moose population annually in GMU 20A during 1996–2004, in contrast to 18–27% in 3 studies of low-density moose populations. Thus, outside GMU 20A, higher bear predation rates can create challenges for those desiring rapid increases in sustained yield of moose. Wolves killed 8–15% of the 4 postcalving moose populations annually (10% in GMU 20A), hunters killed 2–6%, and other factors killed 1–6%. Annually during the increase phase in GMU 20A, calf moose constituted 75% of the predator-killed moose and predators killed 4 times more moose than hunters killed. Wolf predation on calves remained largely additive at the high moose densities studied in GMU 20A. Sustainable harvest-densities of moose can be increased several-fold in most areas of Interior Alaska where moose density and moose: predator ratios are lower than in GMU 20A and nutritional status is higher. Steps include 1) reducing predation sufficient to allow the moose population to grow, and 2) initiating harvest of female moose to halt population growth and maximize harvest after density-dependent moose nutritional indices reach or approach the thresholds we previously published.  相似文献   

6.
A census of wild Yakushima macaques (Macaca fuscata yakui) was carried out in a 23-km2 area of the western coast of Yakushima Island, Japan. We analyzed the census data to investigate changes in monkey distribution associated with the vertical distribution of vegetation. In the lowland coastal zone of 0–300 m above sea level (a.s.l.), 4.8 troops and 62.4–99.8 monkeys are estimated to have existed per km2. In the mountainside zones of 300–900 m a.s.l., the troop density decreased to 1.3–1.6 troops/km2. Since there was no difference in size between the coastal and mountainside troops, population density should decrease with altitude to about 30–36 monkeys per km2. On the other hand, 2.4 troops and about 36 monkeys were estimated to have inhabited per km2 in the mountain summit zone of 900–1,323 m a.s.l. Nature Conservation College  相似文献   

7.
Zusammenfassung Die durch Kartierung 1973–1975 ermittelte Siedlungsdichte der Elster(Pica pica) in Nordost-Bayern betrug 0,18 Nester/km2. Die höchste Dichte wurde in Ortschaften mit Baumbestand erreicht (bis 4,5 Nester/km2). 39,9 % aller Nester befanden sich in, 60,1 % außerhalb von Ortschaften; ihre Dichte und Verteilung zeigen Tab. und Abb.
Abundance and habitat selection of the magpie(Pica pica) in northern Bavaria
Summary By mapping 1972/73 and 1974/75 in 23 study areas from 43,8 to 550 km2 (= 9649 km2) the abundance of the magpie amounted 0,18 nests/km2. Magpies reached highest densities within villages with many trees (up to 4,5 nests/km2). 39,9 percent of all nests were recorded within villages and 60,1 percent in the country side. For details about magpie's density and distribution within their habitats see table and fig.
  相似文献   

8.
Summary The early spring distribution of seabirds, pinnipeds and cetaceans was quantitatively determined in the northern Weddell Sea during the EPOS 1 cruise of the icebreaking RV Polarstern. Two hundred and ninety-one half hour counts were made in the Antarctic region between October 18 and November 16, 1988 (+94 counts in sub-antarctic and sub-tropical water). The bird populations were dominated by the Adélie Penguin Pygoscelis adeliae, which represented 90% of the birds counted in the closed pack ice (CPI), with a mean density of 31 penguins per km2. Crabeater seal Lobodon carcinophagus, the most common pinniped, had a mean density of 1.2/km2 in the CPI with local concentrations reaching 14/km2. Expressed as biomass, mean values of about 90 kg/km2 were found in the whole Antarctic zone for seabirds, 50 for seals, and 35 for baleen cetaceans. Densities were higher in the CPI: 140, 180 and 115 kg/km2 respectively, were found for birds, pinnipeds and baleen whales, and lowest in open water (8 kg/km2 for the birds, 0.2 for the pinnipeds and no whales). A minimum value of food intake by seabirds and marine mammals was estimated to be 2.7 mg C/m2/day for the Antarctic zone (4.1 in the CPI). Taking into account that pinnipeds density and cetacean food uptake are underestimated, and that Antarctic seabirds consume much more fish than generally suspected, a minimum krill production of 16 mg C/m2/day is proposed for the Antarctic zone: 22.5 in the CPI, 3 in open water, and intermediate values in the marginal ice zones.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation  相似文献   

9.
The biomass of arboreal folivorous primates in Africa and Asia is related to an index of mature leaf quality: the ratio of protein-to-fiber concentration. Investigations have considered variation in folivore biomass and forest composition among sites separated by hundreds or thousands of km. However, large variation in folivore abundance has been documented over much smaller spatial scales. We quantify the degree to which the average protein-to-fiber ratio of mature leaves of the 20 most abundant tree species predicts the biomass of western red colobus (Piliocolobus trephosceles) and black-and-white colobus (Colobus guereza) over very small spatial scales. Four sites within Kibale National Park, Uganda, varied markedly in forest structure. Colobine biomass varied among sites from 191 to 2675 kg/km2 and was related to the average protein-to-fiber ratio of mature leaves of the 20 most abundant tree species at each site. We examined the generality of the relationship between protein-to-fiber ratios and colobine abundance by adding our biomass and leaf chemistry values to previously published values to produce 9 comparable sites. At these locations, colobine biomass varied from 84 to 2675 kg/km2 (mean biomass among sites = 910 kg/km2), and mean protein/fiber ratios varied from 0.167 to 0.577. Colobine biomass was related to the protein-to-fiber ratios of mature leaves (R 2 = 0.616, P = 0.012).  相似文献   

10.
Based on a bottom trawl survey, it is shown that in Karaginskii and Olyutorskii bays of the western part of the Bering Sea, Lycodes raridens is a typically elittoral species, since it was recorded at depths of 52–120 m, and the majority of individuals of this species were found in the range of depths 50–100 m. The maximum concentrations of Lycodes raridens were 139 ind./km2 or 98 kg/km2, whereas the average values of the distribution density of this species were 7.8 ind.km2 or 5.4 kg/km2. In Karaginskii and Olyutorskii bays, Lycodes raridens is represented by individuals with a length of 16–86 cm, weight of 34–4510 g, at the age of 1+ to 7+, although fish with a length of 30–50 cm, weight of 100–1000 g, and age of 3+–4+ dominate. The data obtained suggest that in the autumn or autumn-winter period, the study species spawns in the western part of the Bering Sea. The dominant food of Lycodes raridens here are amphipods, polychaetes, bivalves, and decapods; by occurrence and the relative content in the stomach (% of weight), amphipods (as a rule, Melita spp.) and bivalves (Yoldia spp. and Macoma sp.) dominate. Lycodes raridens is a benthophage in which, at the early stage of the life cycle, gammarids prevail in food; with growth, its diet becomes more diverse due to bivalves, polychaetes, and decapods.  相似文献   

11.
The spawning biomass of Australian anchovy Engraulis australis in gulf and shelf waters of South Australia was compared using the daily egg production method (DEPM). The total survey area was 128 700 km2 with recorded spawning areas in gulf and shelf waters of 4898 and 44 618 km2, respectively. High egg densities in the warm, shallow gulf waters were produced by small, young (<1 year old) E. australis that spawned relatively small batches of eggs (c. 855) approximately every 3 days. In cooler, deeper shelf waters, where larger, older E. australis are found, lower egg densities occurred despite individuals producing much larger batches of eggs (c. 15 572) approximately every 7 days. In shelf waters, the highest densities were recorded at inshore sampling stations. Spawning appeared to peak between 0000 and 0100 hours. Females were more abundant than males in samples from both gulf and shelf waters with sex ratios of 0·61 and 0·56, respectively. The spawning biomass of E. australis in shelf waters was 101 522 t, whereas the estimate for gulf waters was 25 374 t. Due to the differences in mean size of the spawning females, however, c. 6 × 109E. australis were present in each region. The results support the hypothesis that variability in habitat conditions may directly influence E. australis reproduction. A large reserve of young fish in the relatively stable gulf environment may increase the resilience of the E. australis population in South Australia to unfavourable interannual changes in offshore environmental conditions.  相似文献   

12.
Group size, density and biomass of large‐bodied diurnal mammal species in the Réserve de Faune du Petit Loango, Gabon (now Parc National de Loango) was determined over a 12‐month period using standard line‐transect methods. Petit Loango encompasses a range of distinct habitat types, including coastal scrub, savanna, swamps and disturbed and mature forest. Such intact coastal habitats are increasingly rare on the Central‐West African coastline. Faecal censusing indicated highest forest elephant (Loxodonta africana cyclotis) and buffalo (Syncerus caffer nanus) ecological densities at the extreme coast (2.48 and 1.29 km−2 respectively), probably reflecting high intensity of use of this habitat. Ape density was comparable with that at other Central African study sites at 1.01 individuals km−2. Mean total biomass of diurnal primates, elephants and other ungulates over the 20 km2 site was 3290 kg km−2. Forest elephants and red river hogs (Potamochoerus porcus) constituted the bulk of the biomass, at 67% and 14% respectively. Primates made up 5% of the biomass. This is the first estimation of mammal density and biomass over an annual cycle at a Central African coastal site, and provides baseline data for long‐term studies in such habitats and to aid habitat and wildlife management decisions.  相似文献   

13.
A study on species composition, distribution, and population density of cercopithecids in the Campo-Ma’an area, Southwestern Cameroon, was undertaken from December 1997 until August 2000. A total of 665.5 km of line transects was used for the census. Thirteen diurnal primate species including five endangered species (Gorilla g. gorilla, Pan troglodytes, Mandrillus sphinx, Colobus satanas, Cercocebus torquatus) were recorded in the Campo Forest, the greatest part of which is a logging concession.Cercopithecus nictitans (1.43 groups/km2),C. cephus (1.13 groups/km2),C. pogonias (0.81 groups/km2), andC. torquatus (0.51 groups/km2) occurred at medium frequencies compared to figures from other Central African study sites. Mandrill densities estimated (0.27 groups/km2) show that the area is very important for the conservation of this rare species. Guenon densities found inside areas with a high level of human activities did not differ significantly from densities estimated in areas with a lower level of human activities.C. torquatus densities were significantly higher in the areas with a low level of human disturbance and encounter rates withLophocebus albigena also indicate a preference of less disturbed areas. Mangabeys are thus likely to be adversely affected by human activities in the area. In the Ma’an Forest, which has not been logged yet, ten species were confirmed. The population densities of two guenons (C. nictitans andC. cephus) were estimated to be twice as high in the unlogged forest area as compared to the logged forest of Campo. Other species are rarer in the Ma’an Forest than in the Campo Forest. Although mangabeys are adversely affected by human activities, the results still indicate that selective logging may be compatible with the conservation of cercopithecids, if a reduced damage logging concept and antipoaching measures are implemented. Increased hunting activities following logging operations will definitely have a negative longterm impact on primate populations in the Campo-Ma’an area if no further, more effective conservation measures will regulate wildlife use in future.  相似文献   

14.
The Sinnamary is a small tropical river (250 km long, watershed of 6500 km2) where a dam is to be impounded in 1994.The extent of naturally periodically flooded areas along the Sinnamary river is estimated by using remote sensing (Landsat TM satellite data) and botanical groupings are described on in situ observations, ground truth and collections. The fish assemblages of these areas are described and their density estimated by rotenone sampling. The role of this ecotone to fish populations is discussed.The extent of the inundated areas appears to be greater than previously estimated by classical mapping.As expected, the fish fauna is mostly composed of fish juveniles and adults of dwarf (< 3 cm) and small (< 15 cm) species. Large predators where not found. Due to these characteristics, fish are abundant but their biomass is low in naturally inundated areas. However, juveniles of some species found only in these zones. Therefore their adult populations will probably be very sensitive to any modification of these land/water ecotones.  相似文献   

15.
1. Young (0+) Arctic grayling (Thymallus arcticus) have the potential to control the trophic structure of Arctic tundra streams through consumption, nutrient excretion and the modification of prey behaviour. The effect of young grayling on three trophic levels (algae, invertebrates and fish) was investigated by manipulating fish density and by fertilizing the river with phosphorus (P). 2. Nutrients, epilithic chlorophyll a, benthic invertebrates and fish biomass were measured within each fish density treatment (0, 4, and 40 fish m–2) within the P-limited reference zone and the P-enriched fertilized zone of the Kuparuk River, Alaska. 3. Epilithic chlorophyll a increased with increased fish density in both reference and fertilized zones, while mayfly density decreased with increased fish density in the fertilized zone only. Final mean mass of young grayling in the 40 fish m–2 cages was lower than mean mass in the 4 fish m–2 cages. 4. Young grayling may produce a top-down cascading trophic effect in areas where nutrients are not limited. 5. River nutrient status and river discharge may modify the strength of top-down control by young grayling.  相似文献   

16.
On the basis of long-term (1981–2008) observations, it was shown that, in the northwestern part of the Sea of Japan, sea raven Hemitripterus villosus is a common species with low, but stable numbers and it is a part of elittoral ichthyocenoses. During the year it performs wintering, feeding, and spawning migrations within the shelf and the upper part of the continental slope occurring from almost the water’s edge to a depth of 550 m. Highest density of sea raven is observed in Peter the Great Bay and the lowest is observed off the coasts of northern Primorye. Maximum length of H. villosus in the northwestern part of the Sea of Japan reaches 57 cm, and the modal group of fish consists of fish with a length of 25–45 cm (75%). In Peter the Great Bay, in the summer period, individuals with a length of 11–50 cm feed mainly on mass fish species; the value of daily ration of H. villosus varies from 1.6 to 3.2% of body weight, averaging 2.5%. According to an expert estimate, the biomass of sea raven in the northwestern part of the Sea of Japan reaches 2000 t.  相似文献   

17.
The Northern Ireland Hare Survey documented the distribution of the Irish Hare (Lepus timidus hibernicus). Historical game bag records and other, more contemporary, records of hare distribution were examined. These data indicate how numbers of L. t. hibernicus may have changed over the last 140 years. The results of the Northern Ireland Hare Survey suggested that L. t. hibernicus was widespread throughout Northern Ireland. Current average densities are no more than 0.65 hares/km2. Game bag records indicate that hare densities may have been much higher in the past, with a maximum of 138 hares/km2 recorded on Crom Estate, Co. Fermanagh, in 1864. Evidence from hare distribution recorded during the Northern Ireland Rabbit Survey indicates that hare numbers declined between 1984 and 1994. Evidence from all sources suggests that L. t. hibernicus has declined in abundance substantially, with present total population estimates for Northern Ireland ranging from 8250 to 21 000 individuals. Flushing data indicate that rushes and hedgerows are important diurnal resting areas for hares. While the principal reason for the decline in numbers of L. t. hibernicus in Northern Ireland is not clear, more species‐rich pasture and provision of areas of cover, such as rushes, may arrest further declines, or indeed promote numbers of hares, particularly in lowland areas.  相似文献   

18.
Crustacean zooplankton data were compiled from long-term observational studies at seven large shallow Florida lakes, to determine whether there are general characteristics in regard to species composition, body size, and biomass. In particular, we examined whether patterns in body size and species richness fit empirical models developed by Stanley Dodson. The lakes included range in size from 125 to 1730 km2 and encompass mesotrophic to hyper-eutrophic conditions. We found that zooplankton biomass was strongly dominated by one species of calanoid copepod—Arctodiaptomus dorsalis. Large daphnids were absent, and Cladocera assemblages were dominated by small taxa such as Ceriodaphnia, Chydorus, and Eubosmina. The total number of species of pelagic cladocerans (8–12) was consistent with Dodson’s predictions based on lake area. The average size of crustacean zooplankton in Florida lakes is small in comparison with temperate communities. A. dorsalis is the smallest calanoid copepod in North America, and the mean length of Cladocera (0.6 mm) is consistent with Dodson’s results that size decreases from temperate to tropical zones. Total biomass of crustacean zooplankton was very low, ratios of zooplankton to phytoplankton biomass (0.01–0.1) are among the lowest reported in the literature, and the zooplankton displayed short-lasting early spring peaks in biomass. Cladocera were almost entirely absent in spring and summer. Factors known to occur in Florida lakes, which appear to explain these characteristics of biomass, include intense fish predation and high summer water temperature.  相似文献   

19.
Common carp is cheap and prolific in Australian waters and is regarded as an aquatic environmental pest. In order to add value to this fish species, surimi and kamaboko was prepared from common carp and its rheological and microstructure characteristics were compared with those produced from Alaska pollock and threadfin bream. Temperature sweep tests were run under 100-Pa stress and 0.1-Hz frequency, obtained from linear viscoelastic ranges of all tested fish gels. Storage modulus (G′) thermographs of all samples consisted of two positive peaks and a plateau zone in between. The sol-gel transition was completed at about 53 and 61 °C for these Alaska pollock and threadfin bream gels, respectively, whereas it was recorded at about 69 °C for common carp gel. At these temperatures, G′ of Alaska pollock gel was recorded at 330 kPa, which was 71% and 88% greater than that from threadfin bream and common carp gels, respectively. Furthermore, Alaska pollock and threadfin bream gels had greater gel strength than the gel prepared from common carp surimi. Textural quality could be associated with cross-linking in the gel network. From scanning electron microscopy studies, the microstructure of Alaska pollock gel matrix had about 15,450 polygonal structures per square millimeter with an average area of about 9 μm2. For threadfin bream and common carp gels, the polygonal structures were larger and 12% and 39% fewer, respectively, than those of Alaska pollock gel. However, these results cannot be only attributed to the species variation among tested fish as some other factors such as harvest location, physiological state, handling and processing method, etc. were not considered in this study.  相似文献   

20.
We studied Orthoptera, Dermaptera, and Blattodea of the Białowieża Forest (Poland) in order to assess (1) the minimum patch size of open habitat necessary for each species, (2) the role of linear corridors as habitat, and (3) the impact of herbivores on diversity by comparing the fauna at periods of different ungulate densities. Many species occurred in the farthest clearings from the forest edge to arable land. Two third of species occurred in clearings smaller than 10,000 m2. Dry linear corridors of 10–40 m width and wet linear corridors of 100–200 m width had a species richness that corresponded to that of clearings of about 10,000 m2. Four species disappeared from the Białowieża Forest when ungulate density decreased from 20 individuals/km2 (3000 kg/km2 biomass) at the beginning of the 20th century to 10 individuals/km2 (1000 kg/km2) at the end of the 20th century. We conclude that most Orthoptera, Dermaptera, and Blattodea species could survive in Central Europe if human land use was replaced by intensive grazing and browsing by wild herbivores.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号