| Autor: |
McGarvey, Richard, Steer, Mike A, Matthews, Janet M, Ward, Tim M, Anderson, Handling editor: Emory |
| Předmět: |
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| Zdroj: |
ICES Journal of Marine Science / Journal du Conseil; Sep/Oct2018, Vol. 75 Issue 5, p1638-1646, 9p |
| Abstrakt: |
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 (P 0), 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. P 0 is estimated as a mean of sample tow densities rather than as a regression intercept. This stage-based P 0 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 P 0. The uncertainty of assuming egg mortality rates is moderated by the insensitivity of estimates of P 0 to the input value of egg mortality rate. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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