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Effect of Light Intensity on Predation of Sockeye Salmon Fry by Prickly Sculpin and Torrent Sculpin

机译:光照强度对刺槐和红烧鱼捕食红鲑鱼的影响

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Recent dramatic declines in sockeye salmon (Oncorhynchus nerka) in Lake Washington, WA, have caused considerable alarm among concerned managers, scientists and citizens. Many factors may be involved, however, one possibility is that the increasing incidence of residential and commercial nighttime lighting along the lower portions of the Cedar River, the major sockeye producing tributary of Lake Washington, has led to substantially increased predation one migrating fry by nocturnal predators. Freshwater sculpins are a major predator of sockeye salmon fry and are also the most abundant predator in the Cedar River. Previous research has shown that sculpin predation on salmon fry is greater under high levels of natural nighttime light(i.e., under moonlight). We tested the hypothesis that above-natural nighttime light levels further increase sculpin predation of sockeye salmon fry. Light may differentially affect behavior of both sockeye fry and sculpin. Thus, we first tested the ability of sculpin to prey on sockeye fry under six light levels (0.0-1.0 lm/ft2) in laboratory tanks with minimal water circulation to separate the effect of the migratory behavior of the fry from the ability of sculpin to capture them. The two species of sculpin most abundant in the lower portions of the Cedar River, Cottus asper and C. rhotheus, were each tested separately in groups of 20 by exposing them to 100 sockeye fry for 40 min. This experiment showed that both species preyed effectively on sockeye fry but surprisingly, that they preyed most effectively in complete darkness, capturing an average of 82 and 87% for C. asper and C.rhotheus, respectively (N = 6 trials each). As light level was increased, predation rate declined for both species with least predation occurring at the highest light level (42 and 21% for C. asperand C. rhotheus, respectively). Additional trials at 1.0 lumens/ft2 with one of the species, C.rhotheus, given shorter, longer, and the same duration trials as used in the first experiment,showed that similar numbers of fry were captured regardless of trial duration.

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