Sillaginodes punctata, above a seagrass meadow. Image by: Julian Finn / Museum Victoria, Rights/Licence: CC BY (Attribution)
Otoliths or ear bones, found within the head of fish, can provide long-term records of fish growth. Otoliths lay down annual growth bands or increments much like tree rings. Differences in the width of these annual growth increments can reflect the effects of environmental variability on the growth of the body of the fish. By measuring the growth increments within long-lived fish a record of growth through time is obtained. Such measurements can be made on a number of fish and then statistical approaches used to evaluate the climate-growth relationships in these series of otolith archives.
We reconstructed climate-growth relations for King George whiting (Sillaginodes punctatus), a commercially and recreationally important fish species in southern Australia. We were able to use the valuable archived collections of otoliths available at the South Australian Research and Development Institute (SARDI) to do this. These samples had been collected as part of other projects between 1995 and 2010. The growth increments in each otolith were measured on previously prepared transverse sections and assigned a calendar year based on the year and month the fish had been collected. Statistical models were then used to investigate inter-annual growth variation and other variables that may influence growth.
Our growth increment data spanned 25 years (1985-2010). Winter sea surface temperature (SST) was negatively correlated to growth, and as the winter SST increased the average width of the growth increments declined suggesting that growth of the fish declined. However, the temperature effect was relatively weak. Fish growth did not vary between different regions of South Australia and was not influenced by recruitment (data obtained from a stock assessment model) or El Niño–Southern Oscillation events.
Our study provides information about the possible effects of climate change on King George whiting growth over a multi-decadal period. Current climate has not yet significantly affected the growth of King George whiting, but further changes in temperature could start to impact growth. Understanding long-term temperature-growth relationships is crucial for disentangling the effects of climate change and other parameters on fish growth, and thus predicting how populations will change in the future.
King George whiting otolith showing growth increments. Image by: Nastaran Mazloumi.
More information on our study can be found at: Mazloumi N, P Burch, AJ Fowler, ZA Doubleday, BM Gillanders. 2017. Determining climate-growth relationships in a temperate fish: a sclerochronological approach. Fisheries Research 186: 319-327.