Growth, episodic recruitment and age truncation in populations of a catadromous percichthyid, Macquaria colonorum

Abstract

Temperate basses and perches (family Percichthyidae) worldwide have declined in distribution and abundance during the past few decades due to anthropogenic impacts such as fishing, habitat degradation and alteration to river flows. This study examined differences in the age, growth and longevity of Macquaria colonorum among three south-eastern Australian coastal rivers. Estimates of ages were made by counting opaque zones in sectioned otoliths. Ages were validated by using marginal increment analysis, staining fish otoliths with oxytetracycline and sampling young-of-the-year fish. Length-at-age data from 1644 fish indicated that growth of M. colonorum is rapid in the first 3 to 4 years, after which it slows considerably. Females grew faster and reached larger asymptotic lengths than males. The species was found to be long lived, with the oldest fish estimated at 41 years. Population age structures indicated variable year-class strengths in all three rivers and there was an absence of larger, older (>10 years) individuals in the populations from the two rivers with a history of commercial fishing. These results indicate that M. colonorum populations, similar to other global percichthyid and estuarine-dependent fishes, have been subjected to episodic recruitment and age truncation and that these are likely influenced by environmental flows and fishing pressure.