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A stage-based estimator of daily egg production

McGarvey, R, Steer, MA, Matthews, JM and Ward, TM ORCID: 0000-0002-9003-2772 2018 , 'A stage-based estimator of daily egg production' , ICES Journal of Marine Science, vol. 75, no. 5 , pp. 1638-1646 , doi: 10.1093/icesjms/fsy021.

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Abstract

Snapper (Chrysophrys auratus) in South Australia spawn over a wide range of daily times and hatch in ∼1.5 d. Traditional estimates of daily egg production (i) divide sampled eggs into daily age cohorts, e.g. days 1 and 2, (ii) compute cohort ages by assuming that all spawning occurs at a fixed daily peak hour, and (iii) link the estimation of spawning egg density with egg mortality rate by regressing cohort egg densities against cohort age. We propose a method for estimating daily egg production, the number of eggs spawned per unit area per day (P0), without these assumptions. We use a range of estimates of snapper egg mortality rate obtained from prior studies to backcorrect for egg mortality to the age 0 spawning egg density for each stage of eggs individually rather than aggregating into daily cohorts. P0 is estimated as a mean of sample tow densities rather than as a regression intercept. This stage-based P0 estimator avoids errors associated with assuming a fixed daily spawning hour and classifying eggs into day 1 or 2. It requires no regressions of sampled daily cohort egg densities against age, which often provide imprecise estimates of mortality rates. Simulation testing showed 1–2% accuracy for this estimator of P0. The uncertainty of assuming egg mortality rates is moderated by the insensitivity of estimates of P0 to the input value of egg mortality rate.

Item Type: Article
Authors/Creators:McGarvey, R and Steer, MA and Matthews, JM and Ward, TM
Keywords: daily egg production method, stage-based estimator, egg mortality rate, hatching age, snapper, spawning egg density
Journal or Publication Title: ICES Journal of Marine Science
Publisher: Academic Press Ltd Elsevier Science Ltd
ISSN: 1054-3139
DOI / ID Number: 10.1093/icesjms/fsy021
Copyright Information:

Copyright 2018 International Council for the Exploration of the Sea

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