Comparison of age and growth of grass and silver carp above and below Changzhou Dam in the Pearl River, China

Abstract

The life cycles of potamodromous fishes are generally interrupted by the presence of a dam, and populations often display different life history traits between upstream and downstream. This study compared the age and growth rates of grass carp and silver carp above and below Changzhou Dam in the Pearl River. Standard length (SL) composition and back-calculated SL at ages one and two years were greater for grass carp upstream than for downstream individuals; and the length–weight relationship differed between upstream and downstream populations, while the sex ratio, age structure and growth were not significantly different. For silver carp, only SL compositions differed between upstream and downstream populations; sex ratio, age structure, SL-at-age and growth rates were similar. Mean SL-at-age and growth rates of both species were lower at high latitudes than at middle and low latitudes, and populations in the Yangtze River had greater mean SL-at-ages and faster growth relative to silver carp at low latitudes. There were no differences in mean SL or growth among populations at middle and low latitudes. For grass carp, age and growth varied with small-scale ecological processes and regions or latitude, while for silver carp, such variations were proportionate to latitude and the large-scale geographical range. This study provides not only guidelines for fisheries management and conservation of exploited potamodromous fishes, but also insights into the relationship between life history trait variation and adaptive capacity.