Krill Biomass Estimate of weight (grams) of krill through water column at a single point Averaged over survey grid for each day = mean daily krill biomass
Krill Aggregations For each aggregation we calculate: Mean depth, dimensions (L, H), nearest neighbor distance Volumetric abundance and biomass (ind. m -3 and g m -3 ) Aggregation-specific integrated biomass (g m -2 ) Biomass encounter rate (kg m -1 )
Central place foraging – Minimize foraging time – Maximize energy intake Krill aggregation structure impacts foraging efficiency Depth, size, densities and distance to next aggregation are important
Diurnal Tide Shallow Large Closer together More dense Highest biomass encounter rate Semi-Diurnal Tide Deep Small Further apart More dense Low biomass encounter rate Shallow Large Further apart Less dense Low biomass encounter rate Palmer Deep
Summary…and more questions Nearshore Antarctic krill distribution patterns are highly variable Tide plays a role - but how? Aggregation structure seems to be affected by tide and has an impact on penguin foraging, but to what degree? What types of aggregations are penguins going after?
Pilot Field Season Palmer 2013-2014 Two acoustic grids within the Palmer Station boating limits: – East Grid (~13 nm, 23 km) – West Grid (~12 nm, 22 km) – Traveling at ~3-4 knots = 6-8 hours Sampling as frequently as possible Predator observations from the water – species identification, behavior