Age-based demography of the glacier lanternfish (Benthosema glaciale) in the Flemish Cap

Abstract

It is important to understand the population dynamics of myctophids for a better understanding of the functioning of the ecosystem. In this work, age-based demography parameters of glacier lanternfish (Benthosema glaciale (Reinhardt, 1837)) were calculated. This study was based on 1213 individuals collected in the Flemish Cap during June–July 2008 and 2010. Ages were estimated from counts of annuli in the whole otolith. A strong relationship was found between both diameters of the otolith and fish length, and between otolith weight and increment number. Males predominated in 2008 (37.6% were females) whereas no differences from the expected sex ratio of 1:1 were observed in 2010. The somatic growth of B. glaciale is quite fast for the first three years and decreasing thereafter. The von Bertalanffy growth curves revealed interannual differences and no sexual dimorphism in growth. The instantaneous natural mortality coefficient, M, was 0.65 year–1 for the overall population. The maximum age recorded was 7. Our results were compared with age-based demographic parameters from previous studies in the Flemish Cap and in other regions. Because myctophids are considered opportunistic strategists, changes in their demographic features may reflect shifts in the ecosystem.