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    Proposal to continue the time series of research surveys to monitor abundance of Antarctic toothfish (Dissostichus mawsoni) in the southern Ross Sea, 2022/23-2024/25: Research Plan under CM 24-01

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    Número de documento:
    WG-FSA-2022/41 Rev. 1
    Delegation of New Zealand
    Presentado por:
    Mr Nathan Walker (Nueva Zelandia)
    Aprobado por:
    Mr Nathan Walker (Nueva Zelandia)

    This paper proposes a continuation of the Ross Sea shelf survey (RSSS) for three years from 2023–2025. The primary objective (1) of the survey is to monitor Antarctic toothfish recruitment in the southern Ross Sea. This would be a continuation of the annual time series of research surveys carried out since 2012 using a random stratified design. Continuing the time series is essential as the data collected is used to estimate year class strength of Antarctic toothfish and provide essential input into the stock assessment used to inform management decisions. An additional objective (2) is to monitor trends in abundance of the larger (sub-adult and adult) toothfish in McMurdo Sound and Terra Nova Bay. These are areas where toothfish may form an important part of the diet of Type C killer whales and Weddell seals. The regions are sampled individually by rotation on alternate years. In addition, Objective 3 of this programme collects and analyses a wide range of data and samples from these areas including benthic invertebrates, fish stomach and tissue samples, and associated environmental and acoustic data. Objectives 2 and 3 are specified as high priority research topics in the research and monitoring plan for the Ross Sea region Marine Protected Area (RSrMPA).

    The proposed survey design is the same as that implemented throughout the time series of surveys since 2012. A power analysis indicated that 45 stations in the core strata and 10 stations in McMurdo Sound and Terra Nova Bay were sufficient to detect a change of 20% between years with 80% power. A power analysis was conducted using the mean weighted CV for only the year classes of interest, which are fully selected by the survey (ages 5–10, CV5-10). The power analysis indicated that 45 stations in the core strata were sufficient to detect a change of 20% over 5 years, the amount of time to track a cohort from when it was first fully selected through to the maximum size for a pre-recruit fish, with 80% power and a mean weighted CV5-10 of 16%. Ecosystem impacts, or long-term changes, were of concern in the alternate strata, therefore time frames of 25 years (or one generation) and 35 years (time frame of the RSrMPA) were used to determine that 10 stations were adequate to detect a change of 20% with 80% power.

    To ensure the likelihood that the survey is not restrained by a catch limitation other than once every 20 surveys we propose a catch allocation of 60 t for the core strata based on the 95th percentile of survey catch rates from the entire time series (2012–2022).  Based on the same approach used for the core strata, we propose an additional catch allocation of 9 t for McMurdo Sound in even years and 39 t for Terra Nova Bay in odd years, where the allocation is based upon the 90th percentile of the entire time series. 

    The results of each survey and trends in the time series will be reported to WG-FSA for review each year and the results included in future Ross Sea toothfish stock assessments. A full review will be completed and presented to WG-SAM, WG-EMM, and WG-FSA in 2025.