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Despite the importance of species–area relationships (SARs) to conservation, SARs in human‐fragmented rivers have received little attention. Our aim was to test for the presence and strength of SARs for littoral fish assemblages of an extensively dammed river in south‐central Ontario, Canada, and to examine long‐running hypotheses for the drivers of SARs. Twenty‐six navigational dams with locks built between 1837 and 1913 occur along the 160 km length of the Trent River examined in this study. We evaluated the relationship between richness and fragment area, and then used linear models to test whether the area per se, habitat diversity, or other hypotheses were best supported by the data. A power–function relationship with area explained 46% of the variation in fish species richness, and the slope (z = 0.4) was high compared with SARs reported from other ecosystems, indicating that species accumulated rapidly with an increase in fragment area. Multi‐predictor models suggested that area was significantly related to richness, but that vegetation cover diversity had a stronger relative effect. The slope of our SAR may indicate that there is a high degree of isolation between populations in different fragments, even though the lock system reportedly allows some passage of organisms. Our findings also suggest that mitigating against local extinction due to small population sizes (i.e., area effects), and enhancing aquatic vegetation cover may be viable strategies for promoting species diversity in the study river. Studies of SARs in fragmented rivers may offer additional benefits to supporting restoration planning where efforts are being made to increase species diversity.

Dams have the potential to affect population size and connectivity, reduce genetic diversity, and increase genetic differences among isolated riverine fish populations. Previous research has reported adverse effects on the distribution and demographics of black redhorse (Moxostoma duquesnei), a threatened fish species in Canada. However, effects on genetic diversity and population structure are unknown. We used microsatellite DNA markers to assess the number of genetic populations in the Grand River (Ontario) and to test whether dams have resulted in a loss of genetic diversity and increased genetic differentiation among populations. Three hundred and seventy-seven individuals from eight Grand River sites were genotyped at eight microsatellite loci. Measures of genetic diversity were moderately high and not significantly different among populations; strong evidence of recent population bottlenecks was not detected. Pairwise FST and exact tests identified weak (global FST = 0.011) but statistically significant population structure, although little population structuring was detected using either genetic distances or an individual-based clustering method. Neither geographic distance nor the number of intervening dams were correlated with pairwise differences among populations. Tests for regional equilibrium indicate that Grand River populations were either in equilibrium between gene flow and genetic drift or that gene flow is more influential than drift. While studies on other species have identified strong dam-related effects on genetic diversity and population structure, this study suggests that barrier permeability, river fragment length and the ecological characteristics of affected species can counterbalance dam-related effects.

Redhorse, Moxostoma spp., are considered to be negatively affected by dams although this assertion is untested for Canadian populations. One hundred and fifty-one sites in the Grand River watershed were sampled to identify factors influencing the distribution of redhorse species. Individual species of redhorse were captured from 3 to 32% of sites. The most widespread species were golden redhorse, M. erythrurum (30%) and greater redhorse, M. valenciennesi (32%), while river redhorse, M. carinatum, was only found along the lower Grand River. Redhorse were absent from the highly fragmented Speed River sub-watershed and upper reaches of the Conestogo River and the Grand River. Redhorse species richness was positively correlated to river fragment size and upstream drainage area. Generalized additive models (GAMs) were applied to evaluate the influence of river fragment length, connectivity and habitat on species distribution. Principal component analysis reduced habitat data to three axes representing: channel structure, substrate, and pool, riffle and run habitats (PC1); gradient and drainage area (PC2); and cover (PC3). GAMs indicate that PC2 was important for predicting black redhorse and greater redhorse site occupancy and PC1 was important for golden redhorse. River fragment length was important for predicting site occupancy for shorthead redhorse, but not other species.

Low-head barriers used in the control of parasitic sea lamprey (Petromyzon marinus) in the basin of the Laurentian Great Lakes can alter the richness and composition of nontarget fishes in tributary streams. Identification of taxa sensitive to these barriers is an important step toward mitigating these effects. Upstream–downstream distributions of fishes in 24 pairs of barrier and reference streams from throughout the basin were estimated using electrofishing surveys. For 48 common species from 34 genera and 12 taxonomic families, 8–19 species, 5–16 genera, and 2–7 families showed evidence of being sensitive to barriers, with the variation in number depending on the statistical measure applied. Barriers did not differentially affect species from certain genera or families, nor did they affect species of certain body form. Therefore, taxonomic affiliation and swimming morphology are not useful for predicting sensitivity to barriers for fishes that co-occurred with sea lampreys but were not sampled adequately by our survey. Our estimates of sensitivity will help fisheries managers make sound, defensible decisions regarding the construction, modification (for fish passage), and removal of small, in-stream barriers.

This study compares simple fish communities of ten oligotrophic lakes in south-central Ontario. Species densities and population size structure vary significantly among these lake communities depending on fish species present beyond the littoral zone. Lake whitefish are fewer and larger in the presence of lake herring than in their absence. Diet analysis indicates that lake whitefish shift from feeding on both plankton and benthic prey when lake herring are absent to a primarily benthic feeding niche in the presence of lake herring. When benthic round whitefish are present, lake whitefish size and density decline and they move lower in the lake compared to round whitefish. Burbot are also fewer and larger in lakes with lake herring than in lakes without herring. Burbot, in turn, appear to influence the population structure of benthic coregonine species. Lower densities of benthic lake whitefish and round whitefish are found in lakes containing large benthic burbot than in lakes with either small burbot or where burbot are absent. Predation on the pelagic larvae of burbot and lake whitefish by planktivorous lake herring alters the size and age structure of these populations. As life history theory predicts, those species with poor larval survival appear to adopt a bet-hedging life history strategy of long-lived individuals as a reproductive reserve.

The channel darter, Percina copelandi, is a small benthic fish with a wide but disjunct distribution across central North America. The development of conservation and recovery strategies for Canadian populations is limited by a lack of knowledge regarding ecology, population size and other factors that affect its distribution and abundance. We sampled five rivers in the Lake Ontario basin to test whether the distribution of P. copelandi reflected riffle habitat characteristics or landscape-scale factors such as surficial geology and natural barriers (waterfalls). At most sites yielding P. copelandi, riffles flowed into deep sand bottomed run or pool habitats. Despite a lack of association with local surficial geology or riffle habitat characteristics, both the upstream limits of P. copelandi occurrence and distribution of suitable habitats reflected the distribution of waterfalls, chutes and bedrock outcroppings. In contrast to P. copelandi, distributions of Etheostoma flabellare, P. caprodes and Rhinichthys cataractae reflected among site differences in riffle habitat.

– Non-native species can have substantial impacts on successful restoration of native species. Here, we examined effects of chinook salmon (Oncorhychus tshawytscha), an exotic species introduced to Lake Ontario to enhance recreational angling, on reintroduced Atlantic salmon (Salmo salar) in a Lake Ontario tributary stream. Field enclosure studies revealed that adult Atlantic salmon activity rate was elevated, nest establishment delayed and mortality rates higher in the presence of chinook salmon. These results suggest that chinook salmon in Lake Ontario streams during fall spawning could impede successful re-establishment of Atlantic salmon in the lake.

Low-head barriers are used to block adult sea lamprey ( Petromyzon marinus ) from upstream spawning habitat. However, these barriers may impact stream fish communities through restriction of fish movement and habitat alteration. During the summer of 1996, the fish community and habitat conditions in twenty-four stream pairs were sampled across the Great Lakes basin. Seven of these stream pairs were re-sampled in 1997. Each pair consisted of a barrier stream with a low-head barrier and a reference stream without a low-head barrier. On average, barrier streams were significantly deeper (df = 179, P = 0.0018) and wider (df = 179, P = 0.0236) than reference streams, but temperature and substrate were similar (df = 183, P = 0.9027; df = 179, P = 0.999). Barrier streams contained approximately four more fish species on average than reference streams. However, streams with lowhead barriers showed a greater upstream decline in species richness compared to reference streams with a net loss of 2.4 species. Barrier streams also showed a peak in richness directly downstream of the barriers, indicating that these barriers block fish movement upstream. Using Sorenson's similarity index (based on presence/absence), a comparison of fish community assemblages above and below low-head barriers was not significantly different than upstream and downstream sites on reference streams (n = 96, P > 0.05), implying they have relatively little effect on overall fish assemblage composition. Differences in the frequency of occurrence and abundance between barrier and reference streams was apparent for some species, suggesting their sensitivity to barriers.

Four sampling designs for quantifying the effect of low-head sea lamprey (Petromyzon marinus) barriers on fish communities were evaluated, and the contribution of process-oriented research to the overall confidence of results obtained was discussed. The designs include: (1) sample barrier streams post-construction; (2) sample barrier and reference streams post-construction; (3) sample barrier streams pre- and post-construction; and (4) sample barrier and reference streams pre- and post-construction. In the statistical literature, the principal basis for comparison of sampling designs is generally the precision achieved by each design. In addition to precision, designs should be compared based on the interpretability of results and on the scale to which the results apply. Using data collected in a broad survey of streams with and without sea lamprey barriers, some of the tradeoffs that occur among precision, scale, and interpretability are illustrated. Although circumstances such as funding and availability of pre-construction data may limit which design can be implemented, a pre/post-construction design including barrier and reference streams provides the most meaningful information for use in barrier management decisions. Where it is not feasible to obtain pre-construction data, a design including reference streams is important to maintain the interpretability of results. Regardless of the design used, processoriented research provides a framework for interpreting results obtained in broad surveys. As such, information from both extensive surveys and intensive process-oriented research provides the best basis for fishery management actions, and gives researchers and managers the most confidence in the conclusions reached regarding the effects of sea lamprey barriers.

opment of databases bringing together scientific information from diverse sources. The enthusiasm has arisen for at least three reasons. First, scientists and resource managers recognize that databases are valuable for making scientifically-defensible decisions regarding fish stocks and their environment. Second, database approaches can increase the integrity and consistency of the data, encourage data sharing among researchers with different areas of expertise, and facilitate the transfer of data among different application programs used for analysis (Harvey and Press 1996). Third, developments in statistics, such as meta-analysis, are improving greatly our ability to summarize what has been done, to examine questions at broader spatial, temporal, and taxonomic scales, and to plan future research (e.g., Osenberg et al. 1999). These developments mean that scientists and resource managers whose primary training may emphasize skills in fisheries management, fish ecology, environmental issues, and policy making, will be asked more frequently to be involved in the construction or management of large databases, or to contribute data or funds to them. On one hand, this is desirable because fisheries scientists are likely to be “closer” to the data and methods of collection, and therefore can improve the quality of the design and analysis of the database (Van Alstyne et al. 1995). On the other hand, this can be problematic if the scientists are unfamiliar with database design and management. Indeed, in some

Toxic substances have been suspected of being one of the causes of Great Lakes lake trout reproductive failure. Because toxic substances are present in the Great Lakes basin, managers should be aware of the role of contaminants in preventing lake trout rehabilitation. This paper summarizes studies which have sought to establish a relation between toxic substances and lake trout mortality or morbidity, and offers recommendations for future research and management. The review suggests that exposure to toxic substances has the possibility of affecting the species’ rehabilitation. A variety of toxic substances, specifically organochlorine compounds, concentrated in lake trout eggs, fry, and the environment, have affected the hatching success of lake trout in the laboratory, but the strength of the relation between toxic substances and lake trout mortality and morbidity in the field remains unclear. In order to clarify this relation, more information is needed on lake trout physiology, biochemistry, behavior, and genetics. An interdisciplinary workshop should be convened to evaluate existing evidence by epidemiological methods, to set priorities for further research, and to develop management strategies.

Changes in a grayling spawning population are described that occurred in relation to both natural and man-induced events. The spawning population was monitored from 1982 to 1987 with a trap on a fishway on the Beaverlodge River, Alberta. Most of the spawning run in each year was tagged with recaptures noted in subsequent years. Male grayling grew slightly faster than females. Growth rates were variable and appeared to be quite low in years of low water flow. Grayling first spawned at 2 to 6 years of age. The majority of tagged grayling would have returned to spawn a second time after a delay of one to two years were it not for the high adult mortality. It is hypothesized that the variable time to first maturity and the delay in the second spawning is a response to highly variable juvenile recruitment. Annual mortality rates increased with age, suggesting an increased vulnerability of larger fish to angling. The population appears highly sensitive to over-exploitation, because of the high mortality rates and the delayed time to spawning of the adults.