Can length frequency analysis be used to determine squid growth? – An assessment of ELEFAN

Abstract

Jackson, G. D., Alford, R. A., and Choat, J. H. 2000. Can length frequency analysis be used to determine squid growth? – An assessment of ELEFAN. – ICES Journal of Marine Science, 57: 948–954. Current scientific literature presents two viewpoints regarding squid growth. One view suggests that squid have long life spans and asymptotic growth. This viewpoint exists primarily as a direct consequence of researchers fitting asymptotic growth curves to squid length-frequency data. The second view arises from statolith ageing and culture studies, which have produced a divergent description of squid growth, specifically, a rapid non-asymptotic growth pattern that is linear or exponential in form, with short life spans. We revisit this controversy by producing and analysing a computer simulated squid length-frequency distribution. Our computer program produced a series of 30 d length frequencies based on biological parameters of an exponentially growing tropical near-shore loliginid with a sub-annual life span. We then analysed our computer generated data with the ELEFAN software program which produced asymptotic von Bertalanffy growth curves and life spans of up to 35 months for our simulated squid which had a life span of <200 d. This demonstrates at least 2 points; (1) that length frequency analysis is an inadequate means of describing growth for a rapid growing organism with multiple cohorts and (2) ELEFAN is not suitable for application to exponential growing organisms as it assumes a wrong model of asymptotic von Bertalanffy growth. 2000 International Council for the Exploration of the Sea