Size and age compositions of yellowtail scad (Trachurus novaezelandiae Richardson 1843) and blue mackerel (Scomber australasicus Cuvier 1832) were studied in the inshore purse-seine fishery off the coast of New South Wales, Australia. Ages were assigned by counting annual marks in otoliths for both species. Sampling from two regions showed no geographical differences in the age compositions of catches for either species. The fishery for yellowtail scad was based on 2- and 3-year-old fish, but with significant numbers of fish up to 11 years. Seventy percent of the fishery for blue mackerel was based on fish aged 1 year, with the majority of the rest being in their first or third years. Maximum ages recorded in this study were 14 years for yellowtail. scad and 7 years for blue mackerel. We found no major differences in the sizes of blue mackerel landed in either region sampled, but yellowtail. scad were larger in the northern region than in the southern. Growth rates of blue mackerel were the same from both regions, but yellowtail scad sampled grew significantly faster in the northern region. The fishery for yellowtail scad off New South Wales is currently based on younger and smaller fish than other trachurid fisheries around the world. This, together with the observed spatial variation in growth and population structure, suggests that the fishery for yellowtail scad in New South Wales should be carefully monitored.
