<b>Post-collapse somatic growth and population recovery failure of sardine (</b><b><i>Sardinops sagax</i></b><b>) in the northern Benguela from otolith biochronologies</b>

The sardine (<i>Sardinops sagax</i>) stock was majorly exploited in the past (1950-1999) in Namibia with catches totalling 14.7 million tons which led to sardine’s collapse and it’s yet to recover. We developed a robust otolith biochronology of annual increment width to infer long-term growth patterns of sardine using 744 otoliths archived in Namibia from 1982 to 2021. All archived otoliths used were sourced from the Ministry of Fisheries and Marine Resources (MFMR) in Namibia. The archived otoliths stems from MFMR annual purse-seine surveys as well as commercial port samples. The annual hydro-acoustic pelagic biomass survey covers the entire shelf area, starting from north of Lüderitz town ending south of Angola. Commercial port otolith samples were taken from port of Walvis Bay sampled from commercial purse-seine vessels. Thus, events are titled according to the biomass survey or the commercial port samples.<br>Biological measurement obtained from archived otolith (if available) were recorded such as total lengths (TL ± 0.01 mm), month, year and station number. The sagittal otoliths were mounted whole in black Perspex plate moulds and embedded in epoxy resin. Calibrated images of the sardine otoliths were taken using Zeiss Stemi 508 stereo microscope that is fitted with a Carl Zeiss Axiocam 208 colour camera. In order to assess the age of sardine at a given length, otolith annual growth increments were counted (core to edge) along the otolith's largest radius using a Zeiss Stemi 508 stereo microscope 320× magnification. We analysed a total of 787 otolith images using ObjectJ which is an ImageJ plugin (http://imagej.nih.gov/ij/). The length of each annual increment on the along the post-rostrum axis of the otolith from the nucleus to posterior edge.<br>Linear mixed effect models were applied to separate intrinsic (within individual) and extrinsic (by year – e.g. population density, environment) factors to estimate mean annual growth for fish older than 1 year (&gt;1 years). The increment widths were recorded together with its year when the increment was formed (calendar year), and age at the time of increment formation (Age) for each fish.<br>Project(s): TRIATLAS (Tropical and South Atlantic Climate-based Marine Ecosystem Prediction for Sustainable Management)<br>Funding: Horizon 2020. Grant award no. AMD-817578-41: TRIATLAS Project<br>