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Can anchovy age structure be estimated from length distribution data collected during surveys?

Can anchovy age structure be estimated from length distribution data collected during surveys? Historically, a time-series of proportions-at-age 1 from annual November hydro-acoustic surveys has been used to inform the assessment of, and in particular the choice of appropriate values for juvenile and adult natural mortality for, the South African anchovy Engraulis encrasicolus. However, information from direct ageing is limited and almost two decades old. A new method is developed to estimate the annual proportions of anchovy at age 1 directly from the population length distributions estimated from samples taken during the November surveys. This method involves modelling the annual length distributions of age 1 and age 2+ anchovy. The analysis provides a new time-series of proportions-at-age 1, together with associated standard errors, for input into assessments of the resource. The results also caution against the danger of scientists reading more information into data than is really there. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png African Journal of Marine Science Taylor & Francis

Can anchovy age structure be estimated from length distribution data collected during surveys?

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Can anchovy age structure be estimated from length distribution data collected during surveys?

Abstract

Historically, a time-series of proportions-at-age 1 from annual November hydro-acoustic surveys has been used to inform the assessment of, and in particular the choice of appropriate values for juvenile and adult natural mortality for, the South African anchovy Engraulis encrasicolus. However, information from direct ageing is limited and almost two decades old. A new method is developed to estimate the annual proportions of anchovy at age 1 directly from the population length distributions...
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Publisher
Taylor & Francis
Copyright
Copyright © NISC (Pty) Ltd
ISSN
1814-2338
eISSN
1814-232X
DOI
10.2989/1814232X.2013.830991
Publisher site
See Article on Publisher Site

Abstract

Historically, a time-series of proportions-at-age 1 from annual November hydro-acoustic surveys has been used to inform the assessment of, and in particular the choice of appropriate values for juvenile and adult natural mortality for, the South African anchovy Engraulis encrasicolus. However, information from direct ageing is limited and almost two decades old. A new method is developed to estimate the annual proportions of anchovy at age 1 directly from the population length distributions estimated from samples taken during the November surveys. This method involves modelling the annual length distributions of age 1 and age 2+ anchovy. The analysis provides a new time-series of proportions-at-age 1, together with associated standard errors, for input into assessments of the resource. The results also caution against the danger of scientists reading more information into data than is really there.

Journal

African Journal of Marine Science – Taylor & Francis

Published: Sep 1, 2013

Keywords: anchovy; effective sample size; length distribution; proportion-at-age; proportion-at-length

References

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