Observation of silver carp spawning in a Mississippi River tributary

This technical note seeks to better understand spawning cues of invasive carp for management and control purposes.

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

<em>Abstract</em>.—Timing of reproduction differs among fish species in nearly all rivers, and reproductive phenology is predicted to strongly influence freshwater fish community structure in some systems. Despite its potential importance, few long-term studies of reproductive phenology in river fishes have been conducted in a community context. Here, we evaluated timing and sequence of reproduction of fishes in the Rio Grande, New Mexico over 9 years. Dates and rank order of first appearance of larvae varied among species and years, but three consistent spawning guilds were evident: early season, late season, and species that were intermediate in rank order of spawning. We hypothesized that appropriate reproductive timing enhanced recruitment to the extent that spawning cues predicted future availability of critical resources for larvae. Analysis of historical discharge records indicated that present and future discharge exhibited positive autocorrelation for up to 90 d. Likewise, larval fish densities were highest at moderate flows and coincident with high food resource abundance. However, stable isotope data for larval and adult fishes indicated considerable overlap in food resource use among larvae and adult fishes. There may be pressure for spawning time to converge among species to match the appearance of seasonal resources, but to diverge to lessen competition among young-of-year fishes in a classical trade-off scenario. More long-term studies are needed, and we propose that an integrated research program that combines detailed analysis of reproductive phenology, food web dynamics, and comparative genomic analyses could forge connections between environmental variation in spawning cues, recruitment success, and community assembly in river fishes. Such an integrated program could lead to better predictions about fish community responses to global warming, especially in vulnerable arid-land systems like the Rio Grande.

Seasonal movements of lake sturgeon in Lake of the Woods and the Rainy River, Ontario

Lake sturgeon (Acipenser fulvescens) inhabiting the southern portion of Lake of the Woods and the Rainy River, a north-temperate watershed straddling the Canada – United States border, were studied to test hypotheses concerning seasonal movement patterns, including spawning migrations, and habitat use. We implanted radio transmitters into 26 fish and monitored seasonal movements during 3 consecutive years. Data indicated the existence of two discrete populations of sturgeon in this watershed, differentiated by seasonal habitat use, movement patterns and rates, and timing of spawning. The "lake" population, a designation suggested by a consistent preference for lentic winter habitat, appeared to spawn and initiate extensive spring and summer movements later than the "river" population, which consistently inhabited the river during the winter months. Overall, movement rates were significantly greater in the spring and summer months than at other times of the year and decreased with water temperature. General preferences exhibited by lake sturgeon for certain habitat types at different times of the year appeared to be linked to foraging behaviour. The results suggest that population differentiation may be prevalent for this species inhabiting large lake–river systems, given some diversity in habitat structure and spawning cues. In management efforts, this potential should be taken into consideration and reflected.