Age and growth of small red scorpionfish, Scorpaena notata (Actinopterygii: Scorpaeniformes: Scorpaenidae), a common discard species from the Portuguese fishery

Abstract

Background. The small red scorpionfish, Scorpaena notata Rafinesque, 1810, appears as a bycatch of Portuguese fisheries. Bycatch species are likely to suffer the same declines as commercial species with which they co-occur but information on those species for Portuguese waters does not exist. In order to increase the knowledge for the Portuguese continental-shelf waters several aspects of the species growth were investigated. Materials and methods. Age and growth of Scorpaena notata from Portuguese continental-shelf waters were studied using 379 otoliths. A subsample of 70 otoliths, covering all length classes, was read by three of the authors to establish a reading and interpretation pattern. The von Bertalanffy growth model was fitted to sex-specific age–length data. The likelihood ratio tests were used to evaluate the significance of differences on growth parameters between sexes and with the parameters estimated in different areas. Results. Females dominated in smaller length classes while males prevailed in larger ones, although overall sex ratio did not deviate from 1 : 1. Females ranged from 10.5 to 18.8 cm total length (TL) and from 1 to 6 years; males ranged from 11.4 to 20.7 cm TL and from 1 to 7 years. The von Bertalanffy growth parameters estimated for the Portuguese shelf waters showed significant differences between sexes and were: L∞ = 18.23 cm TL, k = 0.43yr–1, t0 = –0.99 yr for females and L∞ = 21.17 cm TL, k = 0.28yr–1 and t0 = –1.73 yr for males. The age range found in the Portuguese shelf waters was similar to that found in the Balearic Islands but about half of that found for the Adriatic Sea. Significant differences between growth parameters from the Portuguese coast and those from the Balearic Islands and Adriatic Sea were found. Conclusion. Estimates of L∞ in the presently reported study were the highest but rather consistent with the maximum length given for the species.