Methodology:

Krill sampling was carried out during the scientific cruise JR15004 which studied the South Orkney Ecosystem between 15 January - 23 February 2016 on board the RRS James Clark Ross.

Krill were sampled when located using a rectangular midwater trawl net (RMT8; 3 mm mesh).

Krill samples were taken from RMT8 samples where there were sufficient numbers of krill to select 100 decent state specimens for length frequency and maturity.

Measurements of krill body length were obtained from randomly selected sub-samples (100-200 individuals per net), measured as the distance between the front of the eye and the tip of the telson, with measurements rounded down to the nearest millimetre (Morris et al. 1988). Information on sex and maturity status were collected based on the scale of Makarov and Denys (1981) with the nomenclature described by Morris et al. (1988). All measurements and staging was carried out by a single analyst (Ryan Saunders). A total of 11 successful RMT8 hauls were undertaken to ground truth the acoustic observations and inform on population structure, primarily around the northwest shelf-break of the South Orkney Islands.

Data collection:

Krill were captured with a rectangular midwater trawl net (RMT8; 3 mm mesh).

Data quality:

All body length measurements were rounded down to the nearest mm. All were performed by a single analyst (Ryan Saunders) to minimise inter-analyst error and bias.

Net hauls cover a variable distance of between 0.1 and 1 nautical mile.