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Fishways are increasingly constructed to maintain longitudinal connectivity for fish in numerous river systems where migrations are interrupted by anthropogenic barriers, although there is a paucity of information on the biological effectiveness of fishways for most species. We evaluated fishway approach behaviour, and quantified attraction and passage efficiency of three catostomid species (silver redhorse Moxostoma anisurum, river redhorse M. carinatum and shorthead redhorse M. macrolepidotum) that undertake annual obligate spawning migrations through the Vianney-Legendre vertical slot fishway at the St. Ours Dam, in the Richelieu River, Quebec, Canada. Use of PIT tagging alone enabled quantification of attraction and passage efficiency and these were; 51, 17 and 50 % for attraction efficiency and passage efficiencies were 88, 50, and 69 % for silver, river, and shorthead redhorse, respectively. Silver redhorse had significantly shorter entrance delay and passage duration times than shorthead redhorse. Attraction efficiency was different among release locations for silver redhorse, and passage efficiency increased with size for shorthead redhorse. For all species, failure to ascend the fishway was most likely to occur before the second turning basin (before the 32 m mark) in the fishway (84 % of failures). Silver redhorse had significantly lower passage failure rates than river and shorthead redhorse. Activity patterns in the three species during fishway passage were different; crepuscular activity patterns were observed in shorthead and river redhorse, whereas silver redhorse activity peaked between 23:00 and 02:00 then decreased through the remainder of the day. To further evaluate fishway approach behaviour we fitted an additional sample of each species with external radio tags, although nearly all radio tagged individuals (n = 119) rapidly moved downstream upon release immediately post-tagging. Subsequently, our results were confounded by the behavioural impairments associated with external radio tagging and fallback. These results demonstrate the value of multispecies fishway evaluations and highlight the variation among individual species fishway performance within a single genus.

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.