An evaluation of long-term monitoring of larval fish in eastern Australia

<p>Regular monitoring of larval fish began in 2014-2015 at five locations in the Integrated Marine Observing System (IMOS) National Reference Station (NRS) network. We evaluated the value of this monitoring for detecting spatial and temporal trends in the distribution and spawning of key taxa, and trends in the larval fish community. We focused on 3 East coast NRS (North Stradbroke Island, Port Hacking, and Maria Island) due to the availability of comparable historical larval fish data for this region. Historical data from 7 surveys (spanning 1983-2015) was used to provide long-term context to help evaluate the value of long-term larval fish monitoring at NRS. We found that the abundance of larval fish is high variable in time and space, which makes trend detection <br>difficult. A power analysis predicts that this monitoring would need to occur for at least 20 years to detect moderate declines in the larval abundance of key taxa, and > 50 years for many taxa. There was a clear latitudinal trend in the larval fish community, but we found evidence that this gradient has shifted recently, in part due to poleward shift in the spawning of some temperate species. We conclude that larval fish monitoring is a valuable fishery-independent data source for identifying changes in the marine environment, and the current NRS monitoring will likely be useful for identifying large range shifts, changes in phenology, <br>and trends in abundance for some taxa, if monitoring is continued over the long term. </p>