Validating age in southern calamary (Sepioteuthis australis) over seasonal and life history extremes

Abstract

Through rearing known age individuals and maintaining chemically marked adults in captivity, this study explored the rate of increment formation in southern calamary (Sepioteuthis australis) statoliths over seasonal (summer and winter) and ontogenetic (hatchlings and adults) extremes. A ‘one increment–one day’ relationship was verified for captive-reared hatchlings up to 40 days post-hatching which remained stable across the seasonal extremes. This relationship, however, was not evident in the chemically marked adults as inconsistencies of up to 44 days were detected between the number of days elapsed post-stain and the increment count. No seasonal effect was detected in the ratio between increment count and days elapsed, however, the degree of underestimation was consistently greater for winter-caught adults by approximately 2.5 increments relative to summer-caught adults. This less-than-daily increment formation in adults may be due to: (1) the periodicity of increment formation changing throughout the squid's lifespan; (2) deleterious effects associated with rearing squid in captivity; and/or (3) compromised interpretation of the statolith microstructure as a result of the preparation method.