Tidal influence on Antarctic krill in Adélie penguin foraging hot spots
Penguin Foraging Patterns
Figures courtesy of Matt Oliver
10 years of data
Sampling
Tidal Phase Variability
What we can see with acoustics
Sea floor
http://detlaphiltdic.blogspot.com
Krill Biomass
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
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)
Mean Daily Krill Biomass
Error bars are 2 standard errors
Nearshore Tidal and Offshore Comparisons
Spatial Krill Distribution PatternsSemi-Diurnal Tide
Spatial Krill Distribution PatternsDiurnal Tide
Optimal Foraging andKrill Aggregation Structure
• 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
Variability in Aggregation StructureDiurnal 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 SeasonPalmer 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
Acoustic Grids
