University of Cape Town
FISHERIES_2020_AUG_SWG-PEL_73.pdf (295.77 kB)

Refining the November 2019 sardine west component recruitment estimate

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posted on 2021-02-03, 04:37 authored by Doug ButterworthDoug Butterworth, Andrea Ross-GillespieAndrea Ross-Gillespie
The estimate of the west component of sardine recruitment from the 2020 recruitment survey has relatively high variance, and it is conventional before basing management advice on such a single estimate alone to reduce that extent of uncertainty by combining the result in some way with the information provided by immediately preceding values of recruitment and spawning stock size. Here that further information is taken to be provided by the sardine assessment estimates of November recruitment for the years 2014 to 2018, and three different approaches are used to combine this information with the 2020 survey estimate. These three approaches are crossed with three variants of a regression method to relate the 2020 survey result to the corresponding recruitment strength as at November 2019. In broad terms, the results from these combinations suggest that the 2019 November sardine recruitment estimate of about 9 billion provided by the mean for the previous five years’ recruitment estimates from the assessment to be updated to lie in the range of 11 to 13 when the new information provided by the 2020 survey result is incorporated.



Department of Mathematics and Applied Mathematics, University of Cape Town