Age and growth of Scotia Sea icefish, Chaenocephalus aceratus, from the South Shetland Islands

Abstract

Samples of Chaenocephalus aceratus (Lönnberg) were collected during a trawl survey carried out around the South Shetland Islands in January–February 2002. Fish were caught by commercial bottom trawl fishing down to 500 m depth, using a stratified randomized sampling design. As observed in other recent surveys within the same area, C. aceratus represented one of the predominant species. Overall, 357 specimens ranging from 13 and 67 cm (TL) were selected for the present study. Ages were estimated by counting annuli present in the sagittal otoliths, exposed by grinding and polishing along their sagittal plane. To estimate the precision of age data, we compared blind readings by readers from different institutions. The age range was 1–17 years for females and 1–15 years for males. Von Bertalanffy growth curves were fitted to the estimated age-length data for each sex. The estimated values of asymptotic length L_∞ (cm) and K (year⁻¹) were respectively 79.8 and 0.07 for females and 60.0 and 0.09 for males. The growth performance index ranged between 2 and 2.5, similar to that reported in other icefish. Sexual maturity was attained by females and males at about 10 and 9 years old respectively, at about 60% of their maximum estimated age. These results are compared with age and growth data available in the literature for C. aceratus, and discussed in the light of recent commercial exploitation.