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The light that diving elephant seals may see C Campagna2; J Dignani2; Susanna B Blackwell*1; MR Marin2 (1) 120 Tamarack Drive, Aptos, CA, 95003, USA; (2) Centro Nacional Patagonico, 9120 Puerto Madryn, Argentina      *(apoflav@leland.stanford.edu) Diving elephant seals are apparently visual predators that may cue on bioluminescent organisms to detect prey. We deployed time-depth-irradiance recorders on 5 free-ranging southern elephant seal females (Mirounga leonina) from Peninsula Valdes, Argentina. Photodiodes sensitive to a narrow irradiance range yielded an irradiance profile every 5 sec during 12 days at sea. Samples occuring deeper than the first "no light" sample for each dive were interpreted as bioluminescence and made up 20% of over 500,000 samples. We found that: (a) 50 % of samples around 400 m yielded some level of irradiance, (b) sensors detected irradiance to 1,000 m, near the seals' max dive depth, (c) no abrupt change in irradiance was found at any depth of the water column except during sudden changes in swim speed and (d) the rate of irradiance signals increased in the transition from the continental shelf to deep oceanic waters. We conclude: (1) this technique has the potential to shed light on predatory strategies used by diving seals, and (2) elephant seals are low-cost platforms which could be used to collect large amounts of data over wide areas on oceanographic variables such as the stratification in time and space of bioluminescent organisms. [Talk: blackwel.susann.12531]

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