An invasive dreissenid mussel given the working name of "quagga" has a present (spring 1993) distribution in the Laurentian Great Lakes from the western basin of Lake Erie to Quebec City. In Lake Erie, quaggas were collected as early as 1989 and now are most common in the eastern basin. In Lakes Erie and Ontario, proportions of quaggas increased with depth and decreasing water temperature. In the eastern basin of Lake Erie, quaggas outnumbered zebra mussel (Dreissena polymorpha) by 14 to 1 in deeper waters (>20 m). In Lake Ontario, quaggas were observed at depths as great as 130 m, and both quagga and zebra mussel were found to survive at depths (>50 m) where temperatures rarely exceed 5 °C. Quaggas were sparse or absent along inland waterways and lakes of New York State. Mean shell size of quagga mussel was larger than that of zebra mussel at sites in the Niagara River, Lake Ontario, and the St. Lawrence River. The largest quaggas (38 mm) were observed in the St. Lawrence River at Cape Vincent.
The impacts associated with streamside clear-cut logging (e.g., increased temperatures and sedimentation, loss of habitat complexity) are potentially stressful to stream-dwelling fish. We examined stream habitat and rainbow trout physiological stress responses to clear-cut logging in north-central British Columbia using 15 streams divided into three categories: old growth (reference), recently logged (clear-cut to both banks 19 years prior to the study), and second growth (clear-cut 2528 years prior to the study). We used plasma cortisol and chloride concentrations as indicators of acute stress, and interrenal nuclear diameters, impairment of the plasma cortisol response, and trout condition and length-at-age estimates as indicators of chronic stress. No statistically significant acute or chronic stress responses to streamside logging were found, despite increases in summertime stream temperatures (daily maxima and diurnal fluctuations) and a reduction in the average overall availability of pool habitat. Our observed stress responses were approximately an order of magnitude lower than what has previously been reported in the literature for a variety of different stressors, and trout interrenal nuclear diameters responses to the onset of winter were approximately five times greater than those to logging. The overall consistency of our results suggests that the impacts of streamside clear-cut logging are not acutely or chronically stressful to rainbow trout in our study area.
We conducted a meta-analysis using data from 37 studies to assess whether the effects of streamside clear-cut logging on large wood (LW), pool size and number, and summertime salmonid density and standing crop biomass were influenced by stream size and gradient, time since logging was last conducted (1–100 years), and removal of in-stream LW. Age-specific (age 0 (fry) and age 1+ (juveniles)) and species-specific (coho salmon ( Oncorhynchus kisutch ), cutthroat trout ( Oncorhynchus clarki ), and steelhead and rainbow trout ( Oncorhynchus mykiss )) comparisons were also made. The majority of studies reported negative postlogging responses for LW and pool habitat but positive responses for salmonid density and biomass, with the greatest reductions in all variables generally associated with a thorough removal of in-stream LW. The magnitude of postlogging responses was largely independent of stream size, gradient, and time since logging last occurred. In terms of density and biomass, juveniles were more negatively affected by logging than fry. Of the surveyed species, steelhead trout appeared to be most resilient to riparian logging. Within the time frame covered by the analyses, streams whose riparian zones have been logged may be able to sustain salmonid populations (and even exceed preharvest levels) as long as rigorous removal of LW is not undertaken.
We determined the effects of zebra mussel (Dreissena polymorpha) on water column phosphorus (P) and chlorophyll a levels and algal community size structure as well as rates of P excretion in laboratory experiments. Zebra mussel at a threshold density of 0.25/L were able to decouple the nutrient–chlorophyll relationship, to induce erratic patterns in P and chlorophyll a trends, and to decrease mean algal cell sizes. Using shell length we explained 75 and 71% of the variability in P excretion rates in trials held at 17 and 22 °C. Using mass balance modeling, we examined the effects of zebra mussel growth and mortality on mean annual steady-state P levels as functions of hydraulic flushing and P loadings for the western basin of Lake Erie, for Lake St. Clair, and for Oneida Lake. Zebra mussel affected water column P levels only when the annual P accumulated into mussel biomass represented >20% of the lake's annual P loading. The mussel populations in all three lakes did not substantially affect water column P levels but decoupling of the nutrient–chlorophyll relationship was observed in lakes Erie and St. Clair. No evidence was found for increased decoupling of this relationship with increasing zebra mussel density in European lakes.
Abstract Movement forms an important part of salmonid life histories, and although previous studies have largely concluded that the majority of stream‐dwelling salmonids are sedentary, the paradigm of restricted movement has been questioned by recent findings. We conducted a 3‐year study to examine the seasonal movement patterns of rainbow trout Oncorhynchus mykiss in three small, lake‐headed streams situated in north‐central British Columbia and to determine whether movement was related to environmental conditions. Two of the three streams were subjected to streamside clear‐cut logging during the second year. The trout in our study streams generally remained sedentary during the summer, autumn, and winter seasons for a period of approximately 1–2 years before undertaking long‐range (>372–607‐m) movements during springtime. These springtime long‐range movements were most closely linked to stream discharge, as they generally ceased with the onset of summer low flows (<10–20 L/s), but they did not resume in the autumn despite increasing flows. Links between movement patterns and stream temperature were less clear, as long‐range movements occurred over a wide range (0–30°C) of temperatures. The predominant direction of long‐range movements was lakeward. All three streams supported relatively large populations of resident trout during the summer and autumn months; densities of 0.4–1.0 trout/m 2 were primarily associated with age‐0 to age‐2 fish. Our data provide insights into how the movement patterns and life history strategies of stream‐dwelling rainbow trout are intertwined, as well as how the timing of sampling efforts may be an important factor when assessing whether stream‐dwelling fish are sedentary or mobile.
Much of the future timber supply in the Northern Hemisphere will come from boreal and sub-boreal forests, yet there has been little investigation of how aquatic communities in these regions would be affected by logging. We conducted an empirical, comparative study to investigate the effects of streamside clear-cut logging on benthic macroinvertebrates, algal standing stock, and in-stream physical and chemical habitats in the sub-boreal central interior region of British Columbia. We found that streams that flowed through old-growth forests (sites termed "not logged") did not differ from streams flowing through older logged forests (where the riparian zones were harvested 2025 years before our sampling; sites termed "older logged") with respect to macroinvertebrate total density or biomass, feeding guild density or biomass, and chlorophyll a biomass. However, streams flowing through newly logged forests (where the riparian zones were harvested within 5 years of our sampling; sites termed "recently logged") had nearly twice the macroinvertebrate biomass as those in not logged or older logged sites and higher chlorophyll a biomass. There were no differences among the three stream categories in regard to structural aspects of the physical habitat (e.g., substrate composition, large organic debris density, dimensions of pools and riffles). Streamside logging in sub-boreal forests appears to enhance primary and secondary production, but this phenomenon may only be evident for the first two decades following logging.
Using SCUBA and an in situ method of quantifying substrate characteristics, we describe patterns of zebra mussel (Dreissena polymorpha) distribution along the St. Lawrence and Hudson rivers and in Oneida Lake, New York, and develop empirical models for their abundance. Calcium-poor waters originating from rivers draining the Canadian Shield resulted in a complete lack of zebra mussel colonization along the north shore of the St. Lawrence River east of Montreal despite an abundance of suitable substrate. Calcium concentrations of 15 mg/L or less limited the distribution of zebra mussel. The entire south shore from Cornwall, Ontario, to île d'Orléans, Quebec, was colonized by zebra mussel wherever suitable substrate was found. Among the three systems, substrate size explained between 38 and 91% of the variability in density. Other factors such as Secchi depth, calcium concentration in the water, the presence of crayfish, native unionid abundance, and the maximum width of the river at the site increased the amount of explained variance across the different systems. A model based on substrate size also successfully explained patterns of zebra mussel abundance from published sources.
