The Agreed Method to Determine the Maximum Sardine Catch West of Cape Agulhas During 2017

This document details the method agreed at the Small Pelagic Scientific Working Group meeting on 27th June 2017 to be used to inform the maximum directed >14cm sardine catch to be recommended to be caught west of Cape Agulhas during 2017. The agreement involves setting the maximum directed >14cm sardine catch west of Cape Agulhas for 2017 to the average of the maximum catch calculated from two different methods. Note that this maximum may also not be more than the total directed >14cm sardine TAC for 2017 as calculated by OMP-14

A proposal for determining the final desirable maximum catch of directed sardine west of Cape Agulhas during 2017

The maximum directed >14cm sardine catch recommended to be caught west of Cape Agulhas during 2017 was initially set at 21 400t (DAFF 2016) based on the method set out in de Moor and Butterworth (2016). The mid-year revision in the South African sardine and anchovy TACs and TABs for 2017 is to be based on OMP-14, as OMP-17 is still under development. The maximum directed >14cm sardine catch recommended to be caught west of Cape Agulhas thus requires some revision to take account of further work on the underlying sardine Operating Model and information resulting from the 2017 recruit survey

The two mixing stock hypothesis for South African sardine without an assumed stock-recruit relationship

The two mixing stock hypotheses for South African sardine presented in de Moor and Butterworth (2016) and de Moor (2016) assumed a Hockey-Stick stock-recruit relationship, with the stock-recruit parameters estimated to differ by “effective spawning stock”. In addition, recruitment to the west stock during the “peak” 2000-2004 years was estimated to vary about a different median level. In this document the two-mixing stock hypothesis is re-run without any assumed stock-recruit relationship

Assessment of the South African sardine resource using data from 1984-2015: Results at the joint posterior mode for the single stock hypothesis

The assessment of the South African sardine resource has been revised and updated using data available up to November 2015. Two primary hypotheses regarding the sardine stock structure have been agreed for investigation. The first considers sardine distributed off the west and south coasts of South Africa to form a single homogeneous “stock” (or “population”). The second considers the sardine to consist of a western stock and southern stock with some mixing between the two. While there is growing evidence supporting the existence of sub-population structure amongst sardine distributed off the west and south coasts of South Africa (e.g. Coetzee et al. 2008, van der Lingen et al. 2009, 2015, van der Lingen 2011, Weston et al. 2015), the single stock hypothesis continues to be modelled as it allows for easy comparison to past assessments and, in particular, to past risk statistics and previous Operational Management Procedures. It also reflects a limiting case of the mixing model as the extent of mixing becomes very large. This document presents results at the joint posterior mode for the single stock hypothesis only

Assessment of the South African sardine resource using data from 1984-2015: Results at the joint posterior mode for the single stock hypothesis

The assessment of the South African sardine resource has been revised and updated using data available up to November 2015. Two primary hypotheses regarding the sardine stock structure have been agreed for investigation. The first considers sardine distributed off the west and south coasts of South Africa to form a single homogeneous “stock” (or “population”). The second considers the sardine to consist of a western stock and southern stock with some mixing between the two. While there is growing evidence supporting the existence of sub-population structure amongst sardine distributed off the west and south coasts of South Africa (e.g. Coetzee et al. 2008, van der Lingen et al. 2009, 2015, van der Lingen 2011, Weston et al. 2015), the single stock hypothesis continues to be modelled as it allows for easy comparison to past assessments and, in particular, to past risk statistics and previous Operational Management Procedures. It also reflects a limiting case of the mixing model as the extent of mixing becomes very large. This document presents results at the joint posterior mode for the single stock hypothesis only

Discussion of OMP-17 simulation projection framework in respect of sardine

The simulation projection framework to be used to test Candidate Management Procedures for OMP-17 is yet to be developed (cf de Moor and Butterworth (2013a) for the framework used when developing OMP-14). However, given experience gained during the testing of OMP-14, some initial assessment results (de Moor and Butterworth 2016a,b) and discussions in the SPSWG, we can begin to consider some alternative key assumptions to be used in the simulation projection framework to be used for developing OMP-17

Initial exploration of available data to estimate sardine recruitment on the south coast

Annual May/June survey estimates of sardine recruitment east of Cape Infanta are low in comparison to those west of Cape Infanta and in comparison to the numbers of recruits needed to result in the recent peak in 1+ biomass on the south coast. The assessment model for two sardine stocks (split east and west of Cape Agulhas) consequently estimates the majority of the “south” stock biomass to originate from “west” stock recruits, at least across the turn of the century (de Moor and Butterworth 2013). Although sardine are known to spawn throughout the year, this winter recruit survey is timed to measure the recruits emanating from the postulated spawning peak between September – March (van der Lingen and Hugget 2003). However, in contrast to observations on the west coast of South Africa, high sardine egg concentrations have also been observed in winter on the south coast (van der Lingen et al. 2005). This could potentially give rise to local south coast recruitment, which would not be detected during the winter recruit surveys. This document explores the extent to which winter spawning on the south coast and subsequent successful local recruitment there may have an impact on the “south” stock biomass with the data currently available, and proposes future work to explore this possibility further

Revised estimates of abundance of South African sardine and anchovy from acoustic surveys adjusting for echosounder saturation in earlier surveys and attenuation effects for sardine

Hydro-acoustic surveys have been used to provide annual estimates of May recruitment and November spawner biomass of the South African sardine Sardinops sagax and anchovy Engraulis encrasicolus resources since 1984. These time-series of abundance estimates form the backbone of the assessment of these resources, and consequently the management of the South African sardine and anchovy is critically dependent on them. Upgrades to survey equipment over time have resulted in recent surveys providing more accurate estimates of abundance, yet in order to maintain comparability across the full time-series, estimates of biomass mimicking the old equipment were used for a number of years. In this paper we develop a method to revise the earlier part of the time-series to correct for receiver saturation in the older generation SIMRAD EK400 and EKS-38 echo sounders and to account for attenuation in dense sardine schools. This is applied to provide a revised time-series of biomass estimates for the South African sardine and anchovy resources with associated variance–covariance matrices. Furthermore, the time-series presented here are based on updated acoustic target strength estimates, making this the most reliable time-series currently available for both resources