Age-based life-history parameters of the mesopelagic fish Notoscopelus resplendens (Richardson, 1845) in the Central Eastern Atlantic

Abstract

The mesopelagic fish Notoscopelus resplendens is distributed mainly between 500 and 1000 m of depth during the day, with diel migration to surface waters at night (<90 m). Fish move during their diel migrations across different water masses, which show strong changes in temperature with depth that can reach 7 °C in the first 300 m during the warm season. N. resplendens show a type of diel migration pattern of the “entire migrant”, showing a clear day-night habitat separation, with peak abundance above 200 m at night. The difference between sexes in maximum size was 1.97 mm SL (84.36 mm, males; 82.39 mm females). The spawning season can be determined from December to March by back calculating the hatching date from daily growth increments. Age at first maturity was 1.7 year for males and 2.05 years for females. The sex ratio showed a predominance of males (1:0.67). Males were significantly more abundant than females in the 1-year age class. In the rest of the age classes, no significant differences were observed. A sexually dimorphic nature in relation to the position of the accessory luminous glands was observed. Three growth regions were observed in the otolith corresponding to different rates of deposition during fish ontogeny. Daily growth increments were calculated as validation of the annuli pattern. The pattern of the increment formation showed that each annulus has a unimodal distribution. The increment width decreases with age from 1 to 4 years. A strong relationship was found between both diameters of the otolith and length and between otolith weight and age. Different growth models have been analysed to understand the growth of this species. Gomperzt and von Bertalanffy were the best models obtained and revealed differences in growth between sexes. The maximum age recorded was 4 years. The SL-TW relationship showed allometric positive growth. The natural mortality coefficient for the overall population derived from the age-frequency distribution was 0.579 year−1. M obtained from the length converted catch curve was very similar at M = 0.549 year−1.