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