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Life History of Argyrosomus Japonicus, a Large Sciaenid at the Southern Part

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Life History of Argyrosomus Japonicus, a Large Sciaenid at the Southern Part Author's personal copy Fisheries Research 151 (2014) 148–157 Contents lists available at ScienceDirect Fisheries Research j ournal homepage: www.elsevier.com/locate/fishres Life history of Argyrosomus japonicus, a large sciaenid at the southern part of its global distribution: Implications for fisheries management a,∗ a a b Greg J. Ferguson , Tim M. Ward , Alex Ivey , Thomas Barnes a South Australian Research and Development Institute (Aquatic Sciences), PO Box 120, Henley Beach, South Australia 5024, Australia b School of Earth & Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia a r t a b i s c l e i n f o t r a c t Article history: The life-history of the sciaenid Argyrosomus japonicus in South Australia was investigated to inform a Received 26 July 2013 review of fisheries management. Validated, otolith-based growth coefficients for females (Linf = 1430.52, Received in revised form 5 November 2013 K = 0.137, t0 = −0.303, n = 209) and males (Linf = 1356.23, K = 0.159, t0 = 0.000, n = 185) suggested high Accepted 7 November 2013 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 Keywords: (SAM50,95) were 850 and 1028 mm TL, respectively for females and 778 and 923 mm TL, respectively for Sciaenidae males. Age structures from 2011 appeared truncated compared to those from 2001 and 2002 with no Life-history Age individuals greater than 10 years old. The dominant year class observed in age structures from 2001 Growth and 2002 was not present in 2011. This may reflect the combined effects of historically severe drought Size at maturity from 2002 to 2010 and fishing. This population is vulnerable to fishing as juveniles in estuarine habitat Fishery biology and as adults in spawning aggregations in marine habitat. Loss of protected estuarine habitat for juve- Argyrosomus japonicus niles from flow regulation and drought may make this population particularly vulnerable to overfishing. Japanese meagre Whilst maintenance of appropriately timed freshwater inflows to estuarine habitat is important for this Mulloway Kob 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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Many large sciaenids have “periodic strategist” life histories with characteristic high longevity and late maturity. Additionally, Body size of fishes is one of the most important factors in deter- many sciaenids form spawning aggregations in and near estuaries mining vulnerability to fishing (Jennings and Kaiser, 1998; Jennings and recruitment success of several species has been linked to fresh et al., 1999; Reynolds et al., 2005). Large-bodied fishes are usu- water inflows into estuaries (Cisneros-Mata et al., 1995; Griffiths, ally long-lived and their vulnerability is evident by their loss from 1996; Ferguson et al., 2008; Rowell et al., 2005, 2008). The evolu- multi-species catches (Ferguson et al., 2013; Winemiller and Rose, tion of late maturity in sciaenids may have been facilitated by low 1992). The life-history of such large, long-lived fishes is often based juvenile mortality in protected estuarine and surf zone habitats on delayed maturity and high fecundity and has been termed ‘bet (Griffiths, 1996) and a possible “river-discharge” spawning rela- hedging’ or periodic strategist (Winemiller and Rose, 1992) because tionship (Ferguson et al., 2008). reproductive output is allocated across many years allowing popu- The delayed maturity of some sciaenid species may make them lations to survive periods that are unfavourable for spawning and particularly vulnerable to overfishing (Musick, 1999; Musick et al., larval dispersal (Longhurst, 2002). For periodic strategists, recruit- 2000). Recruitment overfishing resulting from the combined effects ment of newly mature individuals is low relative to the number and of targeting juveniles in estuaries and adults in spawning aggrega- biomass of older adults with the exception of occasional very strong tions, referred to as the “one-two punch” approach (Rowell et al., year classes for those species with highly variable reproductive 2008), has been implicated in the declines of several sciaenid success (Heppell et al., 2005). species worldwide. Sciaenid populations in serious decline include five species in the west Pacific (Liu and Sadovy de Mitcheson, 2008; Sadovy and Cheung, 2003), one species in Europe (Quéméner, 2002) ∗ and seven species in North America (Musick et al., 2000). For exam- Corresponding author. Tel.: +61 8 8207 5467; fax: +61 88207 5481. E-mail address: [email protected] (G.J. Ferguson). ple, estuarine dependence, slow growth rates, and high age at 0165-7836/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fishres.2013.11.002 Author's personal copy G.J. Ferguson et al. / Fisheries Research 151 (2014) 148–157 149 maturity have been identified as factors contributing to the decline Management of this fishery assumes a single stock in South of Sciaenops ocellatus and Totoaba macdonaldi in the Gulf of Mexico Australia however regional differences in the elemental chemistry (Lercari and Chávez, 2007; Murphy and Crabtree, 2001) and Bahaba and morphology of otoliths suggest that separate populations occur taipingensis and Larimichthyes crocea in China (Liu and Sadovy de along eastern and western coasts of South Australia (Ferguson et al., Mitcheson, 2008; Sadovy and Cheung, 2003). 2011). Management of A. japonicus comprises (i) a legal minimum Fishery management depends on understanding the dynam- length (LML) of 460 mm TL in the Murray River estuary and 760 mm ics of the variation in population abundance and determining the TL for all nearshore marine waters for commercial and recreational impact of fishing on the natural population processes (Hilborn fishers, and (ii) bag and boat limits for recreational fishers. and Walters, 1992). This information can be provided by val- This study provides validation of the ageing methodology for idated, otolith-based age estimates (Campana, 2001; Campana A. japonicus in South Australia and seeks to improve understand- and Thorrold, 2001). Consideration of life-history strategies is ing of the life history and demography by providing estimates of also important because such strategies are linked to population growth rates and age/size at maturity to inform a review of fishery dynamics and environmental forcing (King and McFarlane, 2003). management. In addition, the possible impact of drought on this Traditional stock assessment methods based on biomass may population is examined by comparing age structures from before be inappropriate for species with late age at maturity and high and after recent, severe drought (2002–2010). Findings are dis- longevity because of difficulties associated with estimating the cussed in the context of populations in other locations and used instantaneous rate of fishing mortality (Heppell et al., 2005). Conse- to identify options for improving the management of exploited quently, age distribution and status of the adult stock may be critical populations of long-lived sciaenids. for assessing population health of such species (Chale-Matsau et al., 2001). 2. Materials and methods The Japanese meagre, Argyrosomus japonicus (Temminck & Schlegel, 1843), known as mulloway in Australia, is a large, preda- 2.1. Samples tory sciaenid that is widely distributed in estuaries and nearshore coastal waters (<100 m depth) of the Pacific and Indian Oceans Biological samples from sub/adult and adult A. japonicus were including sub-tropical and temperate waters in Australia (Griffiths collected from commercial gill net and recreational line catches and Heemstra, 1995; Silberschneider et al., 2008). Like other sci- taken from spring/summer aggregations in the nearshore marine aenids, A. japonicus has life-history characteristics that make it environment adjacent the Murray River in eastern South Australia ◦ ◦ vulnerable to anthropogenic impacts including estuarine asso- in 2001, 2002, and 2011 (139 22 40.34 E, 35 54 24.88 S). ciation (Ferguson et al., 2008; Griffiths, 1996), high age/size at (Fig. 1, Table 1). Additional, information on size/age and reproduc- maturity, and high maximum age (Farmer, 2008; Griffiths, 1996; tive development of juvenile A. japonicus (460–600 mm) within the Griffiths and Hecht, 1995). Populations of A. japonicus have been Murray River estuary was collected from commercial net catches reported as overfished in South Africa and eastern Australia within the estuary. Information on sub-legal size fish (<460 mm (Griffiths, 1997; Silberschneider et al., 2008). TL) within the estuary were obtained from a research programme For the population of A. japonicus associated with the Mur- which used multi-panel gill (Table 1). ray River estuary in eastern South Australia, temporal trends in For all samples, each fish was measured for total and standard freshwater inflows, commercial catches, and population age struc- lengths (TL, SL, nearest mm) and where possible weighed to the tures suggest estuarine
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