A whale of an opportunity: Examining the vertical structure of chlorophyll-a in high Arctic waters using instrumented marine predators

Sixty hours of direct measurements of fluorescence were collected from six bowhead whales (Balaena mysticetus) instrumented with fluorometers in Greenland in April 2005 and 2006. The data were used to (1) characterize the three-dimensional spatial pattern of chlorophyll-a (Chl-a) in the water column, (2) to examine the relationships between whale foraging areas and productive zones, and (3) to examine the correlation between whale-derived in situ values of Chl-a and those from concurrent satellite images using the NASA MODIS (Moderate Resolution Imaging Spectroradiometer) EOS-AQUA satellite (MOD21, SeaWifs analogue OC3M and SST MOD37).

Bowhead whales traversed 1600 km2, providing information on diving, Chl-a structure and temperature profiles to depths below 200 m. Feeding dives frequently passed through surface waters (>50 m) and targeted depths close to the bottom, and whales did not always target patches of high concentrations of Chl-a in the upper 50 m.

Five satellite images were available within the periods whales carried fluorometers. Whales traversed 91 pixels collecting on average 761 s (SD 826) of Chl-a samples per pixel (0-136 m). The depth of the Chl-a maximum ranged widely, from 1 to 66 m. Estimates of Chl-a made from the water-leaving radiance measurements using the OC3M algorithm were highly skewed with most samples estimated as 9 mg m-3.

The correlation between the satellite-derived and whale-derived Chl-a maxima was poor, a linear fit explained only 10% of the variance.