ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Using current age-structure of commercial catches to help us understand the importance of freshwater flows for barramundi recruitment

Jonathan Staunton-Smith, I Halliday, M Sellin and J Robbins

Southern Fisheries Centre, DECEPTION BAY, AUSTRALIA

THEME: ASFB

Understanding the role of freshwater flows in maintaining populations of estuarine fish species is an important requirement for managing Australia's limited and precious water resources. Many of these species are important components of estuarine communities as well as being popular targets for commercial and recreational fisheries. However, investigating links between recruitment variability of fish species and environmental conditions (eg freshwater flows), would normally take a long term study and be spread throughout a large number of potential nursery areas. Alternatively, the age-structures of populations, which often show strong and weak year-classes, have potential to provide several years worth of data about past rates of recruitment. These data can then be compared with historical environmental data. In our study, we collected barramundi otoliths from the Fitzroy River's commercial net fishery in October 2000, February and October 2001 and February 2002. Not only did we find that strong cohorts were consistent from one period to the next, but that these corresponded to birth years of 1991 and 1996, years in which large summer flows resulted in flooding in the region. These results support what is known and suspected about barramundi in the region. In particular, while the species is not an obligate catadromous one, juveniles have better survival when they spend time in brackish or freshwater nursery areas. In the Fitzroy River, barramundi can only gain access to many of these areas, which are spread throughout low-lying flood plains, during times of heavy local rain or large flows that result in flooding.