Age and growth of Brauer's lanternfish Gymnoscopelus braueri and rhombic lanternfish Krefftichthys anderssoni (Family Myctophidae) in the Scotia Sea,Southern Ocean

This study examines age and growth of Brauer's lanternfish Gymnoscopelus braueri and rhombic lanternfish Krefftichthys anderssoni from the Scotia Sea in the Southern Ocean, through the analysis of annual growth increments deposited on sagittal otoliths. Otolith pairs from 177 G. braueri and 118 K. anderssoni were collected in different seasons from the region between 2004 and 2009. Otolith-edge analysis suggested a seasonal change in opaque and hyaline depositions, indicative of an annual growth pattern, although variation within the populations of both species was apparent. Age estimates varied from 1 to 6 years for G. braueri (40 to 139 mm standard length; L_S) and from 0 to 2 years for K. anderssoni (26 to 70 mm L_S). Length-at-age data were broadly consistent with population cohort parameters identified in concurrent length-frequency data from the region for both species. The estimated values of von Bertalanffy growth curves for G. braueri were L_∞ = 133.22 mm, k = 0.29 year⁻¹ and t₀ = −0.21 year and the values for K. anderssoni were L_∞ = 68.60 mm, k = 0.71 year⁻¹ and t₀ = −0.49 year. There were no significant (P > 0.05) differences in growth between sexes for either species, suggesting that males and females have similar growth and development trajectories in the Scotia Sea. A positive allometric relationship between L_S and wet mass was found for each species, as well as a significant (P < 0.0001) linear relationship between otolith size and L_S. Growth performance (Ф′) was similar between the two species and congruent with other myctophid species across the Southern Ocean. This study provides important parameters for future Southern Ocean ecosystem studies in a resource management context.