Longitudinal Length Back-Calculations from Otoliths and Scales Differ Systematically in Haddock

Parallel macrostructure analysis of otoliths versus scales was conducted on Georges Bank Haddock Melanogrammus aeglefinus sampled in spring 2011 to test whether annuli widths of both structures yield comparable estimates of back-calculated length at age. While generally similar in number, scale and otolith annuli were found to differ systematically in their relative widths, mainly because initial annuli are deposited closer to the origin in scales than in otoliths. Accounting for the delayed onset of scale versus otolith formation did not remove the systematic bias. To make both structures comparable, we developed an age-independent correction approach that can adjust cumulative relative annuli widths (RAWs) of Haddock scales to otolith RAWs by the quadratic formula log (e) (RAW (oto) ) = 0.7244log (e) (RAW (scale) ) + 0.0751log (e) (RAW (scale) )(2). Our study comprises a necessary step towards extracting and comparing longitudinal growth data over the entire time series of archived Haddock scales (1931-1993) and otoliths (1994-present) to improve understanding of decadal drivers of growth patterns in this fish stock. Historical longitudinal growth data for exploited stocks are currently underutilized despite their high potential value, given that such data do not confound growth and mortality the way population-based age-length relationships do. Mixed archives consisting of multiple growth structures exist not only for Haddock but for many commercial fish species; hence, prior to mining these valuable time series of longitudinal data the comparability not only of age but also of back-calculated growth estimates between structures needs to be ascertained. Received May 16, 2012; accepted August 28, 2012