Title: Testing methods to estimate the age of blackspot picarel (Spicara melanurus) using otoliths, from the waters of Cape Verde Islands.

Author(s): Alciany da Luz
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Supervisors: Anna Heida Ólafsdóttir , Guðrún Finnbogadóttir
age estimation; blackspot picarel; otoliths; Cape Verde;


Blackspot picarel (Spicara melanurus) is a fish species from the Sparidae family and is an important species for the artisanal fishery in Cape Verde. Despite being commercially important, stock assessment is not performed for this species due to limited knowledge of life story traits and a lack of methodology to investigate the age of the species. In this study, methodology to estimate age of blackspot picarel from Cape Verde waters, was investigated by counting otolith increments and by measuring otolith size. Otoliths from 134 specimens ranging in fork length from 4.5 cm to 29 cm were analysed. Increments became visible once the otolith was sectioned, polished, image taken, and the image enhanced. An age-length key was produced. The precision of the ageing method was estimated by replicating increment count for 23% of otoliths. For replicas, the mean coefficient of variation was 8.76% which is acceptable. The maximum age estimated was 17 years and the von Bertalanffy growth parameters were L_∞=36.17 cm, k=0.09 〖year〗^(-1), t_0=0.89 year. This suggests that blackspot picarel is a slow-growing and a long-lived species. Maturity-at-age was 7.1 years. The relationship between specimen length and otolith dimension, and between specimen age and otolith dimensions was strong and explained 89% or more of variance in otolith dimensions. The age-length key, maturity-at-age, and growth rate provide vital information for stock assessment.

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