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41.
Feeding activity of harbor seals ( Phoca vitulina ) was monitored while the California Department of Fish and Game seined and tagged migrating adult salmonids between 1984 and 1988. The number of predations observed each week of observation was significantly correlated with the number of fish seined during that week. There was a significantly higher number of predations observed on days when seining took place than on days when no seining occurred. Our observations suggest that most, if not all, predations we observed on days when seining occurred involved fish that had been recently seined and released. The estimated percentage of seined fish taken by seals was relatively constant over the five years of the study, ranging from 3.1% to 5.5%. Various strategies for reducing the level of predation on seined salmonids in the lower Klamath River are discussed. 相似文献
42.
Charles E. Sasser James G. Gosselink Erick M. Swenson D. Elaine Evers 《Wetlands Ecology and Management》1995,3(3):171-187
Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham 相似文献
43.
拉萨郊区藏族的指纹研究 总被引:2,自引:0,他引:2
本文报道了拉萨郊区517例(男226人,女291人)藏族健康人的指纹参数正常值、调查分析了指纹类型、指纹组合、指纹指数和指嵴纹计数。比较了藏族不同居群、不同民族和人种间的差异。结果表明,藏族有自己的指纹特点,又显著蒙古人种的一般特征。 相似文献
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The degradation of plant material was studied in order to obtain degradation coefficients and nutrient release kinetics of the vegetation that will be submerged during the filling of the future Parana Medio man-made lake. A group of 13 plant species representative of the whole vegetation of the area were chosen.The plant samples (submerged at 2.5–4 m in the Setubal lagoon), were periodically analyzed during 97 days. The experimental data were fitted to an exponential decomposition model. The plants were classified according to their velocities of degradation into three groups: fast (K>0.01), mean (0.01>K>0.005) and slow (K<0.005). The curves of release of P, N, Ca, Mg, Na and K in function of time are presented and discussed. 相似文献
47.
Within the great expanse of the Brazilian Amazon Basin,Sphagnum has been greatly overlooked, in part because of its scarcity and in part because of the paucity of trained bryological collectors in the area. During a Projeto Flora Amazônica expedition in 1979, seven specimens ofSphagnum were collected, representing six species, five of which are newly described:S. amazonicum, S. dimorphophyllum, andS. subsecundoides in sectionSphagnum;S. curicuriariense andS. ripense in sect.Subsecunda. Also discussed areS. negrense Mitt. andS. sanguinale Warnst. 相似文献
48.
Laurence J. Dorr 《Brittonia》1992,44(1):53-13
In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other
natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original
expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists
had preceded him into that poorly explored region. 相似文献
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50.
Synopsis Pearl dace, Semotilus margarita, are common in slow-moving channels and pools of the headwaters of the Brokenhead River. From May to September age groups 0, 1 and 2+ were partially segregated in space based on water depth with age 0 occupying shallow pools and shallow channels. Age 1 were abundant in shallow pools and deep channels while age 2+ occurred in deep channels and deep pools. In November all age groups coexisted in deep pools. Pearl dace are omnivorous consuming invertebrates, plant material, and detritus. From May to September age groups 0 and 1 consumed mainly terrestrial invertebrates (Diptera, Hymenoptera, Thysanoptera) but age 1 consumed more detritus than age 0. Age 2+ consumed mainly aquatic Diptera larvae. Although all ages consumed aquatic insects almost exclusively in November differences in diet between age groups still existed. Younger fish fed higher in the water column than older fish. Intraspecific resource partitioning of food and space occurs between age groups and this combined with the omnivorous diet is highly adaptive to the headwaters of streams. 相似文献