Age and growth of monkfish (Lophius vomerinus) in Namibian waters based on illicia age estimation and length frequency analysis

Abstract

A multiple approach to the growth of Lophius vomerinus is presented for the first time, based on age estimation of 2282 illicia (first dorsal fin ray) sections, length-frequency analyses (SLCA, ELEFAN, Bhattacharya) and corroborated by tracking cohorts. The growth is studied based on the widest time series (2000–2017) and the largest sample analyzed to date. Individuals ranging from 3 to 109 cm, representing the whole range commercially landed, were collected from annual research surveys in Namibian waters. Modification in the age interpretation using illicia is presented, suggesting a new more accurate criterion at early ages. Two main different growth patterns were obtained, being that of the length-frequency analyses faster than from illicia age estimation. Both growth patterns estimated here are faster than those from previous studies. Possible causes of differences among all studies are discussed. The von Bertalanffy growth parameters from illicia age estimation (L∞ = 110, k = 0.08, t0 = −1.16) are proposed to be used in age-structured models for the annual assessment of this population. Growth pattern provides tracking of cohorts in the abundance-at-age matrix, with high correlation values obtained between the age abundance indices of the same year-class for most of the age groups compared. Greater lengths and ages were found in females, showing a slightly higher growth rate than males in older specimens.