Life history of Argyrosomus japonicus, a large sciaenid at the southern part of its global distribution: implications for fisheries management

The life-history of the sciaenid Argyrosomus japonicus in South Australia was investigated to inform a review of fisheries management. Validated, otolith-based growth coefficients for females (L_inf = 1430.52, K = 0.137, t₀ = −0.303, n = 209) and males (L_inf = 1356.23, K = 0.159, t₀ = 0.000, n = 185) suggested high asymptotic size and low growth rates, relative to other populations. A growth performance index (ω) was lower for A. japonicus in South Australia than for other populations. Sizes at 50 and 95% maturity (SAM_50,95) were 850 and 1028 mm TL, respectively for females and 778 and 923 mm TL, respectively for males. Age structures from 2011 appeared truncated compared to those from 2001 and 2002 with no individuals greater than 10 years old. The dominant year class observed in age structures from 2001 and 2002 was not present in 2011. This may reflect the combined effects of historically severe drought from 2002 to 2010 and fishing. This population is vulnerable to fishing as juveniles in estuarine habitat and as adults in spawning aggregations in marine habitat. Loss of protected estuarine habitat for juveniles from flow regulation and drought may make this population particularly vulnerable to overfishing. Whilst maintenance of appropriately timed freshwater inflows to estuarine habitat is important for this population their availability is uncertain. Populations of A. japonicus in South Australia would benefit from management measures that: (i) aim to preserve capacity for egg production; (ii) allow recruits to enter the adult population; and that (iii) rebuild and maintain long-tailed age structures. Amendments to the legal minimum size and the protection of juveniles in estuaries and the adult spawning/feeding aggregations are recommended.