Some parameters for consideration regarding improvement of the CCAMLR protocol for calculating krill biomass

CCAMLRs protocol for calculating krill biomass contains recommendations for procedures to process data collected from acoustic surveys. For instance, only the data collected within the limit of 250 m of the water column are to be included in the calculations. This depth limit was decided assuming that most krill are distributed shallower than this, and that data from deeper layers may more likely be associated with noise that reduces data quality. We illustrate with some examples from 2023 survey off the South Orkney Islands, when the noise level of 120 kHz is low, that significant proportions of krill were observed below 250 m. Including the deeper layers in the biomass estimate, improved calculations of krill biomass are obtained by both manual and LSSS template scrutiny. Besides, we have compared the biomass calculations from 38 kHz and 120 kHz, using survey data from 2019 and 2023, biomass calculation differences are observed, and it indicates under estimation can happen when only 38 kHz is used due to the unavailability of 120 kHz. Manual and template scrutiny are also compared through this paper, and it shows that the template scrutiny can be recommended in the future. CCAMLRs protocol for calculating krill biomass contains recommendations for procedures to process data collected from acoustic surveys. For instance, only the data collected within the limit of 250 m of the water column are to be included in the calculations. This depth limit was decided assuming that most krill are distributed shallower than this, and that data from deeper layers may more likely be associated with noise that reduces data quality. We illustrate with some examples from 2023 survey off the South Orkney Islands, when the noise level of 120 kHz is low, that significant proportions of krill were observed below 250 m. Including the deeper layers in the biomass estimate, improved calculations of krill biomass are obtained by both manual and LSSS template scrutiny. Besides, we have compared the biomass calculations from 38 kHz and 120 kHz, using survey data from 2019 and 2023, biomass calculation differences are observed, and it indicates under estimation can happen when only 38 kHz is used due to the unavailability of 120 kHz. Manual and template scrutiny are also compared through this paper, and it shows that the template scrutiny can be recommended in the future.