摘要:

During a severe drought period in the winter and spring of 1989, we made three collections of dried marsh soils from freshwater sloughs in Everglades National Park, Florida, at sites characterized by either long or intermediate annual periods of flooding (hydroperiod). After rehydrating the soils in aquaria, we documented the temporal patterns of copepod emergence over two-week periods. The species richness of copepods in the rehydrated soils was lower than in predrought samples from the same slough sites. Only six of the 16 species recorded from the Everglades emerged in the aquarium tests. The long hydroperiod site had a slightly different assemblage and higher numbers of most species than the intermediate-hydroperiod sites. More individuals and species emerged from the early dry-season samples compared with samples taken later in the dry season. The harpacticoid,Cletocamptus deitersi, and the cyclopoid,Microcyclops rubellus, were abundant at most sites. The cyclopoids—Ectocyclops phaleratus, Homocyclops ater, andParacyclops chiltoni—are new records for the Everglades. We infer that 1) only a subset of Everglades copepod species can survive drought by resting in soils; and that 2) survival ability over time differs by species.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663774

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We studied the effects of three flow regimes on the activity patterns and movements of one-, three-, six-, and 36-week old Colorado pikeminnows (Ptychocheilus lucius) and two-week old razorback suckers (Xyrauchen texanus) in an experimental tank under light and dark conditions. The seven-chambered tank simulated a system of backwater habitats, which are used by the young fishes in nature. Water flows through the tank were slow, and velocities were discernable only in the vicinity of surface ports that connected each chamber. Fish movements were related to light or dark condition and activity tended to increase with age. Larvae, relatively active in daylight, moved little at night with no flow, but flow stimulated night activity and downstream movement. Older fish also had a diminished response to flow direction during daylight, but responded at night. The tendency for night movement may be a predator avoidance mechanism, but the tendency to move downstream with flow is likely a response to life in backwater habitat. With inflow and backwater filling “downstream” larval movements would access expanding habitat. With outflow and backwater draining, downstream movement would avoid stranding and potential death in a shrinking habitat.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663775

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A catastrophic flood, which was the largest one in the Changjiang (Yangtze) River basin in 20th century, took place during July—August 1998. The densities and biomasses of three plant species (i.e., Potamogeton malaianus, Vallsineria spiralisandCarex cinerascens)in Poyang Lake, which links directly with the Changjiang River, were investigated after the flood and compared to those at several corresponding times before the flood. The results obtained from the comparative analysis showed that 1) density and biomass of each species changed significantly (p<0.01); 2) effects of the flood on the aboveground parts of each species were more serious than on the underground parts, especially of the submersed species; and 3) the flood influenced seriously the recovery of the submersed plants in the next year.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663776

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

I assessed the relationship between Cedar River flow (a major input to Lake Washington) during egg incubation and fry emergence period and longfin smelt (Spirinchus thaleichthys) recruitment to Lake Washington. There was a significant inverse relationship between an index of abundance of odd-year class smelt and Cedar River mean flow during peak spawning period (February). There was no significant relationship between smelt abundance and peak flow during spawning period (March) of the even-year class smelt. Cedar River discharge greater than 28.33 m3/s occurred more frequently during odd years than even years. This, in addition to other factors, may be responsible for the relatively low recruitment of the odd-year spawning smelt and thus the population cycle observed in the Lake Washington smelt. The positive relationship between smelt recruitment and flow during spring, when smelt fry are migrating into the lake, supports other studies that suggest that an increase in turbidity at high flows reduces juvenile fish susceptibility to predation. There have been significant changes in the planktivorous fish assemblage in Lake Washington since the 1960s. Notably, longfin smelt, which was < 12% of the planktivorous fish abundance, now accounts for 58 to 84 % of the planktivore abundance. Recent increases in abundance of smelt may be related to reduced Cedar River mean flow that has enabled a larger proportion of spawned eggs to hatch and survive.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663777

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We developed standard-weight (Ws) equations for kokanee (lacustrineOncorhynchus nerka), golden trout (O. aguabonita), and bull trout (Salvelinus confluentus) using the regression-line-percentile technique. The Wsequation for kokanee of 120–550 mm TL is log10Ws= −5.062 + 3.033 log10TL, when Wsis in grams and TL is total length in millimeters; the English-unit equivalent is log10Ws= −3.458 + 3.033 log10TL, when Wsis in pounds and TL is total length in inches. The Wsequation for golden trout of 120–530 mm TL is log10Ws= −5.088 + 3.041 log10TL, with the English-unit equivalent being log10Ws= −3.473 + 3.041 log10TL. The Wsequation for bull trout of 120–850 mm TL is log10Ws= −5.327 + 3.115 log10TL, with the English-unit equivalent being log10Ws= −3.608 + 3.115 log10TL.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663778

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In a two-year study of a small Ouachita Highland stream, marked sunfishes(Lepomis megalotis and L. cyanellus) were more likely to move from small pools than larger ones, although most fishes did not move from their home pools. Fish size, sex, and species had no effect on tendency to move.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663779

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663780

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663763

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor