Use of otolith chemical signatures to estimate carp recruitment sources in the mid-Murray River, Australia

Abstract

Recent research has suggested that the Barmah-Millewa forest (BMF) floodplain provides a particularly important spawning ground for carp in the Murray River and that there is a large export of juvenile carp from the BMF into other parts of the Murray River system. This study examined whether chemical analysis of otoliths (fish ear stones) represents a feasible technique for estimating the relative importance of particular sources of carp recruitment in the Murray River. Otolith chemical signatures were analysed for fish collected from three lakes on the BMF floodplain and from three major tributaries of the mid-Murray River. A single site downstream of these potential sources of carp recruitment (Torrumbarry Weir) was then examined to estimate the relative contribution of the BMF and the tributaries to carp recruitment at this site. The results of the study suggest that at least some of the lakes on the BMF floodplain are important sources of carp in the mid-Murray River. Using a maximum likelihood analysis of otolith chemical signatures, it was estimated that Barmah Lake and Moira Lake were the most likely recruitment sources for 98% of the fish collected from Torrumbarry Weir. The study demonstrates the potential application of otolith chemical analyses for determining the relative importance of potential recruitment sources of fish in rivers.