Age and growth in paralarvae of the mesopelagic squid Abralia trigonura based on daily growth increments in statoliths

Abstract

Growth increments in statoliths were used to estimate the age of 55 Abralia trigonura (Berry, 1913), a small tropical mesopelagic enoploteuthid squid collected from Hawaiian waters in 1988 and 1989. Growth increments were examined with light and scanning electron microscopy. Daily periodicity of increment formation and the statolith size at hatching were confirmed by rearing hatchlings in the laboratory. Mantle length (ML) at age data suggested that paralarvae grew exponentially at a rate of 5.9% ML d-1 for ca 40 d post-hatching, while post-paralarvae exhibited slower growth. No significant difference in growth was noted between paralarvae collected from spatially or temporally separated samples, though estimated length diftered at hatching. Estimated paralarval mortality was 7.0 % d-1. Within statolith microstructures, a transition in increment widths occurred at an average of 41.5 increments, which corresponded to 10.9 mm ML. The transition probably represents the end of the paralarval period, which is marked by a shift from an epipelagic to a mesopelagic habitat.