Preliminary analysis on the stock structure and biological characteristics of the Antarctic Krill in the Antarctic Peninsula region

From 16 to 23 February 2024, a multidisciplinary krill survey was conducted by two Chinese krill fishing vessels in the Antarctic Peninsula region, covering all the five (5) core candidate Management Units of the Revised Krill Fishery Management Approach (KFMA) in Subarea 48.1. Preliminary results on krill biomass distribution and biological information from aboard analysis were presented to WG-ASAM and WG-EMM meetings in 2024. In this paper, further analysis on krill length composition, maturity stage based on laboratory observation and hydrographic condition from CTD data were presented, with a focus on interpreting the potential linkage between krill stock distribution and typical water masses in the survey area. Preliminary results shown that krill spawning stock mainly distributed in the open sea deep water dominated by the TBW and the mCDW (Zone 1), while juvenile krill mainly distributed in the Antarctic Peninsula shelf water within the Bransfield Strait dominated by the TWW and mCDW (Zone 3); the shelf waters surrounding the South Shetland Islands and associated southwest-northeastward upstream and downstream waters (Zone 2) also showed importances to juveniles but exhibited convergence of multiple stocks. Such structures suggested there were distinctive geographic distribution pattern between the spawning and juvenile krill, and oceanographic processes may play a critical role on shaping their distribution. Length at 50% maturity showed a sexual difference (male: 46.5 mm vs female: 39.6 mm) and larger than the previous estimates with samples collected in early spawning season. The above findings provided useful insight for the development of the Krill Stock Hypothesis (KSH)and also highlighted the needs for biological study to improve the KFMA in the future.