Carp age validation in the northern MDB

Project Leader: Michael Hutchison, Qld DEEDI

Aim: To determine whether northern carp populations form annual check marks on their earstones or otoliths

Project: 4.f.11

Project summary

Being able to accurately age carp is important for modelling carp population dynamics. Age at maturity, and carp growth rates may vary between catchments of the Murray-Darling Basin (MDB). Population dynamics models such as CarpSim assist in predictions of the effects of different carp management methods. Models such as these will be important for selection of control measures most likely to succeed in different parts of the catchment.

To date, aging validation of carp in Australia has been based on southern temperate populations. Slow growth during the winter months followed by increased growth in spring results in formation of annual check marks in the earstones or otoliths of carp in the southern Basin. However, in the northern MDB, which has a more subtropical climate, winter temperatures are not as low, so it is not known if checks form annually in northern carp populations.

This project determined if checks do form annually in northern basin carp populations and estimated the timing of check formation. Results from this study are applicable to the adjacent Logan-Albert River catchment population of carp.

The project involved marking of otoliths of a closed or semi-closed wild population in the northern Murray-Darling Basin. Tank-held specimens were also marked and maintained for over 12 months in Brisbane as a back-up to the wild population study. Examination of marked otoliths from fish at large from 12 to 24 months enabled validation of whether northern populations of carp form annual check marks on otoliths.

Key achievements

  • The field and tank based components of this project have been completed.
  • Monthly sub-sampling of chemically marked carp occurred to validate the presence of the chemical mark on the earstones, or otoliths, of the carp and the timing of first check or increment formation.
  • Results using whole otoliths from juvenile carp to check for the timing of first increment formation suggest that the northern basin carp do appear to lay down their first check slightly earlier than fish in Victoria. This is consistent with the timing determined from adult carp otoliths also.
  • All sectioned otoliths examined suggest that only one increment forms per year.
  • Increments were less clear in some tank-held individuals than in lagoon fish.

Key deliverables

  • Scientific paper on ageing validation of northern Basin carp populations.

Project team

Michael Hutchison, Keith Chilcott, Adam Butcher, John Kirkwood, Mark McLennan, Stephanie Backhouse.

Project partners

IA CRC, Queensland Department of Employment, Economic Development and Innovation, Victorian Department of Primary Industries, Murray-Darling Basin Authority