Long-term increase in growth of an estuarine predator, mulloway Argyrosomus japonicus, predicted to continue under future warming scenarios

Understanding the effects of climate change on fish biology and ecology is crucial for effective management of fisheries resources. Estuaries are warming at a faster rate than nearby oceans in south-eastern Australia, yet there is little understanding of how this may impact the growth of estuarine fish. We examined long-term changes and drivers of growth in an ecologically and economically important estuarine fish in this region, the mulloway Argyrosomus japonicus, using a growth chronology spanning 39 yr (1980−2018). The chronology was developed using 3112 otoliths collected over 12° of latitude. Mixed effects models identified a long-term increase in the growth rate of A. japonicus spanning nearly 3 decades in south-eastern Australia and a positive growth response to temperature. Temperature during the months of November−February best explained this growth response, likely representing a specific growing season for the species. However, there also remained some variation in growth not explained by increasing temperature over the period. We also found evidence of faster growth in individuals sampled at both younger and older ages, potentially caused by selectivity mechanisms. Regional climate forecasts predict that, based upon the observed response to temperature, the mean annual growth rate of A. japonicus in south-eastern Australia may increase by up to 8.9% by 2099. These results add to the growing body of literature demonstrating positive growth responses by marine species in warming environments and highlight the value of understanding the drivers of long-term growth variation in exploited fish stocks in order to predict future productivity under a range of environmental and fisheries management scenarios.