Long-term variation in brown trout, Salmo trutta L., stocking success in a large lake: interplay between availability of suitable prey and size at release

Abstract –  Factors affecting long-term variation in brown trout, Salmo trutta L., stocking success were examined in a large lake, Lake Oulujärvi, in central Finland. Brown trout were stocked in spring (late May to early June) in 1974–1991 and in summer (late June to early July) in 1992–2001. The biomass of the vendace, Coregonus albula (L.), population (prey) at release time had the largest positive effect on stocking success within both periods: biomass of adult vendace in spring and both 0+ and adult vendace in summer. Increasing the size of stocked fish had a positive effect if the vendace available at release were only adults. The increasing trend of predator-catch-per-unit-effort (CPUE) [combined CPUE of northern pike Esox lucius L., burbot Lota lota (L.), and pike-perch Stizostedion lucioperca (L.)] through the study period and its negative effect on trout stocking success suggested an increasing effect of predation within the entire time series.     

Effects of predation and intraspecific interactions on habitat use and foraging by brown trout in artificial streams

Abstract— We studied habitat use, foraging rates and behavior of 10 cm and 12 cm long brown trout, Salmo trutta , at two densities, 1.5 and 3.0 fish. m⁻², in artificial streams that contained either the amphipod, Gammarus pulex , alone or G. pulex together with the piscivore, northern pike, Esox lucius. Gammarus were stocked in and largely restricted to the pools at a density of 128 Gammurus. m⁻² . pool⁻¹ Large trout (12 cm) used pools more and riffles less when small trout (10 cm) were present than when small trout were absent. Small trout consumed fewer Gammarus when together with large trout than when alone, but showed no difference in habitat use in the presence and abscnce of large trout. Habitat use and number of Gammarus consumed per trout were not affected by trout density for either size-class when alone. For both size-classes of trout, use of pools and foraging rates were higher in the absence than in the presence of pike, and pike primarily resided in the pools. The number of aggressive interactions by both size-classes of trout decreased when pike was present. Our results indicate that for habitats that differ in food resources and predation risk, size structure may affect habitat use and foraging by brown trout.     

Competitive exclusion of brown trout Salmo trutta L., by rainbow trout Oncorhynchus mykiss Walbaum, in lake tributaries, New Zealand

Spawning runs of brown trout Salmo trutta L., and rainbow trout, Oncorhynchus mykiss Walbaum, were compared in three tributaries of two lakes for timing, numbers and redd characteristics. Redd characteristics for the two species in four other streams were examined. No significant differences in redd characteristics between the two species were observed, but in all lake tributaries the possibilities of superimposition of spring spawning rainbow trout on redds of brown trout were examined. A common feature was the high ratio of numbers of spawners to the area of preferred spawning gravel, and it was concluded that in the lake tributaries, superimposition resulted in increased mortality of brown trout eggs, and in one case elimination of the brown trout population. Management possibilities for control of the species proportions in comparable situations are discussed.     

链条锅炉的新型松煤装置

本文简单介绍了链条锅炉的一种新型松煤装置,燃烧的优越性及产生的经济效益。     

水稻品种南京14号对褐飞虱定位和繁殖的影响

应用稻苗生物测定法,比较了水稻抗虫品种南京１４号、ＩＲ２８,感虫品种南京１１号、ＴＮ１和汕优６３,非寄主植物稗草对褐飞虱定向和繁殖的影响。     

木薯褐斑病菌的室内药剂筛选

采用孢子萌发法对分离自海南的木薯褐斑病菌进行了10种杀菌剂的室内筛选。结果表明,国光多菌灵(50%多菌灵WP)和咪鲜胺(25%咪鲜胺EC)的EC50值最小,抑菌效果最好;腐霉利(50%WP)的EC50值最大,抑菌效果最差。建议生产上使用多菌灵和咪鲜胺等来防治木薯褐斑病。