The objective for the Multinational Large-Scale Krill Synoptic Survey in CCAMLR area 48 in 2019 is to provide an updated estimate of the biomass of Antarctic krill (Euphausia superba) used in models to estimate sustainable yield. The planned survey follows, as close as possible, the design of the CCAMLR 2000 survey, that was undertaken in the year 2000. The basis for comparisons will depend on the degree of coverage and methodology and equipment available. The survey will involve the collaborative efforts of Norway, Association of Responsible Krill fishing companies (ARK: companies from Norway, Korea, China and Chile), United Kingdom, Ukraine, Korea and China, and hopefully also other nations that still needs to confirm their participation.

The current survey plan organization is presented for consideration by SG-ASAM. Norway has volunteered to co-ordinate the survey with other members dedicating personnel to specific tasks. It is requested that members who has already made commitments on ship time, also allocate contact personnel as proposed.

This paper has been developed after a wider consultation extending beyond the authors list. It discusses some specific organizational and technical challenges to be considered by SG-ASAM. We request advice from ASAM on “minimum requirements” regarding acoustic instrumentation and sampling gear to achieve approximate consistency with the CCAMLR B0 data collection protocol.

To investigate the utility of broadband sound for Antarctic krill acoustic surveys, we will conduct echo sampling with a scientific broadband echosounder EK80 (Simrad-Kongsberg) during a dedicated krill survey for CCAMLR Division 58.4.1 during 2018/19 season by Japanese research vessel, Kaiyo-maru. The echo sampling will be performed during targeted RMT1+8 tows. Spectra of volume backscattering strengths will be obtained from the sampled echoes and their characteristics will be investigated. Further, orientation and length distributions will be inferred from the measured spectra with theoretical acoustic scattering models. The survey and analysis plans are presented in this paper.

The performance of echo sounder system is critical for using acoustic data collected from fishing vessel to estimate Antarctic krill biomass. Acoustic data from three surveys (2015, 2016 and 2018) collected at a relatively fixed location with bottom depth around 200 m were used to evaluate the potential to use seabed backscattering as an alternative way to the standard sphere calibration. The largest inter-annual difference of the mean value of the maximum seabed backscattering (S_v, dB) for single ping were less than 1.0 dB with 0.35 dB and 0.78 dB at 120 kHz and 38 kHz, respectively. However, ANOVA analysis indicated that there was no significant difference among years at both frequencies.

A dedicated krill survey for CCAMLR Division 58.4.1 during 2018/19 season will be conducted by Japanese research vessel, Kaiyo-maru. No krill biomass has been estimated in the Division since Australia carried out BROKE in 1996. There are two main objectives of our survey: (1) estimation of krill biomass to update B(0) in the area and (2) oceanographic observations in the area to detect long term changes if any. The krill survey (echosounder–EK80 and RMT) and subsequent biomass estimation will follow the CCAMLR standard protocol. Utility of 70 kHz in addition to 3 standard frequencies (38, 120 and 200 kHz) for biomass estimation will be considered using obtained data. Broadband echosounder measurements of length and orientation of Antarctic krill will also be conducted. An initial plan of the survey was presented to SG-ASAM-17 and WG-EMM-17 as SG-ASAM-17/01 and WG-EMM-17/05, respectively. This paper provides a revised outline of the survey while detailed acoustic survey methods are presented to this meeting in separate papers (Abe et al., 2018; Amakasu et al. 2018). The finalized plan will be submitted to WG-EMM-18.

Japanese multidisciplinary survey with a focus on biomass estimation of Antarctic krill will be conducted in CCAMLR Division 58.4.1 during 2018/19. The biomass estimation will be conducted according to the up-to-date CCAMLR standard protocol. The first standardized survey was conducted by CCAMLR in 2000 as the CCAMLR-2000 survey. Quantitative echosounders has evolved since then and a current model is EK80. Though EK80 can transmit both conventional narrowband continuous wave (CW) and new broadband frequency modulation wave (FM), CW will be used for biomass estimation to follow the CCAMLR standard-method. Three-frequency (38, 120 and 200 kHz) krill identification method which is the current CCAMLR standard will be employed in the analysis but utility of 70 kHz data will also be investigated. Measurements of acoustic impedances (mass density and sound-speed contrasts) of krill will also be conducted during the survey. Currently, the compatibility of the output data between EK60 and EK80 has been discussed at ICES WGFAST and this aspect will also be investigated in this survey.

Three surveys of acoustic data from around South Georgia, collected using a four frequency echosounder (38, 70, 120 and 200 kHz), were used to characterise Antarctic krill. Identification of krill targets was carried out using different permutations of two and three-frequency windows. Density was estimated, from identified krill targets, using the 120 kHz data and an acoustic scattering model. A Bland-Altman analysis with a pre-set nominal cut-off of ≤5 gm^-2 bias between methods identified that only the 120-70 kHz (S_v120-70) identification window was comparable with the regularly used 120-38 kHz (S_v120-38) window, and only the 200-120 kHz and 120-70 kHz (S_v120-70 & S_v200-120) identification window was comparable with the regularly used 120-38 and 200-120 kHz  (S_v120-38 & S_v200-120) three-frequency window.