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