Large-scale synchrony and inter-annual variability in roach recruitment inthe Rhone River: the relative role of climatic factors and density-dependent processes

1. We report patterns of temporal Variation in the recruitment of roach (Ru tilus rutilus). The data consist of the annual abundance of the first 2 year-classes, 0 + and 1+ fish, at four sites in the Rhone River (France) between 1987 and 1997. Over this 11-year period both Of and It fish fluctua ted strongly. 2. Cross-correlation indicated high spatial synchrony in 0+ dynamics, altho ugh correlations among sites in 1+ dynamics were weaker. No clear pattern w as apparent in the relationship between the level of synchrony and distance between pairs of sites. 3. The spatial synchrony in 0 + fish could be attributable to large-scale v ariations in weather, influencing water temperature. Total body length of 0 + roach was correlated with water temperature (expressed in degree-days ov er 12 degreesC), and water temperature was the main factor explaining inter -annual variation in 0+ cohort size. Monthly variation in abiotic factors ( measured by standard deviation in water temperature and discharge) did not influence 0+ fluctuations. Correlations with June water temperature suggest that year-class strength was mainly determined by abiotic factors during t he first few months of life. 4. The absence of spatial synchrony in 1+ fluctuations suggests little corr elation between survival and abiotic conditions during the first year of li fe, other factors influencing survival. 5. Survival in the first year was density-dependent. Intraspecific competit ion within the 0+ cohort could thus influence the fluctuations in recruitme nt to older age-classes. 6. The implications of age- or stage-dependent synchrony in temporal variat ion for species with complex life histories are discussed. Studying spatial synchrony for the different life history stages could enhance our understa nding of the population dynamics of spatially structured species.