February 15-18, 2009 Washington State Convention Center Seattle ...

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ULTRAVIOLET AND VISIBLE WAVELENGTH REFLECTANCE VALUES OF
AQUACULTURE PONDS AND THE ASSOCIATED USE BY DOUBLE-CRESTED
CORMORANTS
Andrew A. Radomski* and Paul Zimba
Harry K. Dupree-Stuttgart National Aquaculture Research Center
U.S. Department of Agriculture
Agriculture Research Service
P.O. Box 1050
Stuttgart, AR 72160 USA
Andy.Radomski@ars.usda.gov
Double-crested cormorants (Phalacrocorax auritus) are a frequent and major migratory avian predator on channel catfish
(Ictalurus punctatus) and other aquaculture species during the winter months throughout southeastern USA. Cormorant
numbers and foraging activity indicate a nonrandom distribution within the aquaculture industry. To address the hypothesis
that cormorants are selecting ponds based on reflectance values, we quantified bird use at each 3 spatially isolated commercial
aquaculture facilities. Although cormorant movements, numbers, and occurrence within the aquaculture production region
have been addressed, no studies have focused on the potential mechanisms utilized by these avian predators in selecting
foraging sites within the aquaculture high density prey-based systems.
The focus of this study was to determine if cormorants are associated with specific reflectance spectrum within channel catfish
ponds. Four ponds classified as ‘preferred’ and another four ponds were classified as ‘avoided’ based on observing cormorant
numbers for three months prior to measuring pond reflectance; >100 hrs observed per farm on three commercial catfish farms.
Reflectance and pond turbidity samples were measured every 10 days from January to March 2007; corresponding with peak
number of over-wintering cormorants within the region. Pond samples were measured at the subsurface (1 cm) and secchi
depths to determine spectral reflectance and turbidity. The overall pond surface reflectance model explained 54 per cent of the
variation within high and low bird use pond. The surface reflectance values between 380-410 nm (ultraviolet) and 540-680
nm, 750-760 nm and 800 nm (visible) were significantly different between the high bird use and low bird use. The secchi depth
reflectance showed similar patterns to the subsurface findings. The reflectance wavelengths may serve as a partial cue that
cormorants utilize in selecting particular commercial catfish ponds. The association of particular reflectance and cormorant use
will serve as the building block for creating predictive models and though cormorant numbers and movement patterns may not
change, this improved understanding of avian depredation at commercial aquaculture facilities will greatly impact the overall
effectiveness and cost to implement management strategies.