Estimate of reproductive value of the big eye Priacanthus macracanthus in the north-eastern waters off Taiwan

Abstract

Abstract The reproductive value and population status of the big eye in the north-eastern Taiwan waters was estimated by demographic analysis using available life-history parameters. Life-history tables were constructed using estimates of natural mortality (M) of 10.4920/year for age 0 and 0.3256/year for ages 1-9, with a maximum age of 9. Age-specific batch fecundity (Fe) was from Fe=1391.34e0.1782FL. The age-specific proportion of maturity was estimated from the relationship between the proportion of female maturity (Pr) and fork length (FL): Pr=1/(1+e15.081-0.796FL). Females mature at age 3 and mature females reproduce every year. The population increase rate (λ) was estimated to be 20.5% per year and the generation time (G) was 6.25 years without exploitation. The net reproductive value (R0), generation time and intrinsic rate of natural increase (r) decreased with increased fishing mortality. For fixed fishing mortality, when F=1.2/year and fishing started at age 3, R0 was estimated to be 1.0 and the population was considered to be in equilibrium. For age-specific fishing mortality, when fishing started at age 3, R0 was estimated to be 0.96/year, G being 6.18 years, and the population decreased 0.7% per year. The big eye population had a strong resilience as long as F<=1.3/year started at an age that was older than the age at maturity (i.e. 3 years old) but would decline when intensive fishing (F>=1.2/year) started at age 2 or younger. Sensitivity analysis indicated that the mortality of age 0 is the most sensitive parameter in demographic analysis.