Variation in growth, length and age characteristics of estuarine Acanthopagrus (Sparidae) populations in New South Wales, Australia

Abstract

Knowledge of spatial variation in growth and demographic characteristics of exploited teleost populations is informative for understanding levels of resilience and susceptibility to environmental and anthropogenic perturbations and for resource management. This study investigated variation in length- and age-compositions, length-at-age and growth, longevity and mortality of Acanthopagrus (A. australis, A. butcheri and their hybrids) population complexes across seven estuaries spanning seven degrees of latitude in eastern Australia. Populations were sampled using two gears according to standardised fishery-independent survey protocols. Populations within each estuary displayed considerable variation in length-at-age, with sex-specific growth attributes evident in some estuaries but not others. Nevertheless, females dominated populations, and on average, the mean lengths and ages of females were greater than males within each estuary population. Estuary type and location appeared to influence the estuary-specific growth characteristics of both sexes, with populations in the southern coastal lakes having, on average, greater mean lengths at age and faster growth than those in the northern riverine estuaries. Length and age compositions of populations did not vary accordingly, with observed longevities and estimated natural mortalities varying among estuaries, most likely reflecting estuary-specific environmental conditions and anthropogenic activities. In general, populations across all estuaries primarily comprised fish <25 cm fork length (FL) and 10 years of age. Given their potential to reach FLs up to 50 cm and ages >20 years, populations across most estuaries appeared length and age truncated. Ecological relationships and resource management implications are discussed.