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

Abstract

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 <1 mg m⁻³ Chl-a, while data collected from whales had a broad distribution with Chl-a reaching >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.

Keywords:

• Bowhead whale
• chlorophyll-a
• fluorometer
• MODIS
• remote sensing

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

This study was supported by the Greenland Institute of Natural Resources, National Environmental Research Institute, the US National Science Foundation (KLL), and the Danish Cooperation for the Environment in the Arctic (DANCEA). All work was conducted under permits from the Greenland Home Rule and according to guidelines for IACUC approved by the University of Washington and Greenland Institute of Natural Resources. The Arctic Station, University of Copenhagen, is gratefully acknowledged for use of their facilities in Qeqertarsuaq. The data used in this study were acquired as part of NASA's Earth Science Enterprise. The level 3 algorithms were developed by the MODIS Science Teams. The data were processed by the MODIS Adaptive Processing System (MODAPS) and Goddard Distributed Active Archive Center (DAAC), and are archived and distributed by the Goddard DAAC. Thanks to WetLabs for customizing their equipment for bowhead whales. Comments from Ole Gorm Norden Andersen and one anonymous reviewer improved the manuscript. Hans Christian Schmidt and Anders Villum Jensen and several hunters from Qeqertarsuaq assisted with tagging whales and are gratefully acknowledged.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark