Virtual population analysis of the big eye Priacanthus macracanthus in the waters off northeastern Taiwan Kwang-Ming Liu * , Yeu-Long Cheng Department of Fishery Science, National Taiwan Ocean University, 20224 Keelung, Taiwan Received 22 September 1998; received in revised form 6 January 1999; accepted 2 March 1999 Abstract A length±frequency data set including 9548 specimens of the big eye, Priacanthus macracanthus, from the waters off northeastern Taiwan during the period from 1994 to 1997 was analyzed. Six age classes were identi®ed from a length± frequency analysis and dominant age classes were 3  , and 4  . Instantaneous total mortality (Z) was estimated to be 0.88, 1.36, 1.97 and 1.56/yr for 1994±1997, respectively. Natural mortality (M) estimated from Pauly's equation ranged from 0.326 to 0.373/yr. Age-speci®c abundance estimated from virtual population analysis indicated that the abundance of 2  peaked in 1995, 3  in 1996, 4  in 1997, and 5  and 6  in 1994. The abundance of the 1989±1994 year±class indicated that the big eye stock experienced the highest mortality during the period of ages 4 and 5. Abundance of the big eye stock (for 2  to 6  ) increased from 1994 to 1995 and decreased thereafter. Similar patterns of abundance, catch and catch per unit of effort suggested that the big eye stock might ¯uctuate periodically. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Priacanthus macracanthus; Mortality rate; MULTIFAN; Abundance; Virtual population analysis 1. Introduction The big eye, Priacanthus macracanthus Cuvier, is one of the most common and commercially important species for the Taiwanese trawl ®shery. It is caught abundantly in the waters off northeastern Taiwan (Fig. 1). Annual yield of the big eye was 248 Mt (1977±1997) and ranked the ®rst among all species caught at Tahsi ®shing port (Liu et al., 1999). The tonnage of trawlers at Tahsi ®shing port increased about threefold from 1980 to 1997 but total catch decreased considerably in the late 1980s and recovered gradually from 1994 (Fig. 2). Catch of high-valued species such as the lizard ®sh and black cracker declined signi®cantly. However, annual yield of the big eye ¯uctuated periodically with a somewhat positive trend (Fig. 3). How the big eye population responds to the increase of ®shing pressure is an important issue. Biological information for the big eye has been well documented i.e., taxonomy and distribution (Lee, 1980; Starnes, 1988), age and growth (Lester and Watson, 1985; Liu et al., 1992; Joung and Chen, 1992; Liu et al., 1999). However, stock assessment of this species has never been reported in Taiwanese waters. The purpose of this study is to estimate age and growth, age-speci®c abundance and ®shing mortality of the big eye with length±frequency analysis, catch curve and virtual population analysis (VPA). Fisheries Research 41 (1999) 243±254 *Corresponding author. Tel.: +886-2-2462-2192; fax: +886-2- 2462-0291; e-mail: kmliu@ind.ntou.edu.tw 0165-7836/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII:S0165-7836(99)00025-9