Non Technical Summary

This work was done as part of a larger collaborative study involving scientists from all four eastern states in Australia.

This study documents that the two species of adult river eels (shortfin and longfin) from the coastal rivers of eastern Australia spawn in the ocean somewhere north of New Caledonia. The eggs hatch into leaf-shaped baby eels which are carried to the east coast of Australia by ocean currents. Along the coast, the leaf-shaped eels change into "glass eels", which are transparent miniatures (50 millimetres long) of the adults. The glass eels swim into our coastal rivers and grow into adults. As they travel up the rivers, small quantities (less than 200 kilograms per year) of glass eels are harvested with special nets for a developing eel aquaculture industry. The main aim of this study was to determine: 1) the seasons that the two species of glass eels move into the rivers and their relative abundance in the four eastern states; 2) what conditions trigger their movement into the rivers; and 3) what other species are caught in glass eel nets and how the quantity of these other species (known as bycatch) can be reduced.

Glass eels where caught using standardised nets at locations in each state from 1997 to 2000. The numbers of each eel species in the samples were measured along with size, age and condition of the eels. The type and amount of bycatch was also recorded. The abundance of both shortfin and longfin glass eels varied widely between and within seasons over the wide geographical range. In NSW, shortfins migrated into the rivers from May through September and longfins migrated from December through May. The largest quantities of eels at all areas were caught on incoming tides at night during new and full moon periods. The largest quantities of glass eels were consistently caught in one river in Queensland and another river in Victoria. The industry may have to try collecting glass eels at many rivers in NSW and Tasmania before finding such productive areas. Juveniles of many fish species were also caught in the glass eel nets, but this bycatch can be minimised by using bycatch reduction devices.

Commercial quantities of glass eels can be harvested in a sustainable manner from rivers in eastern Australia. All states now have annual quotas to prevent over-harvest. A database of glass eel catch and effort should be maintained for all states in eastern Australia.