Fall AGU Meeting (Dec. 2002) COAST abstracts:

• Allen
  
• Bane et al.
  
• Barth et al.
  
• Carney et al.
  
• Couch et al.
  
• Cowles et al.
  
• Dale et al.
  
• Durski et al.
  
• Egbert et al.
  
• Gan et al.
  
• Hales et al.
  
• Kosro et al.
  
• Kuebel et al.
  
• Kurapov et al.
  
• Perlin et al.
  
• Pierce et al.
  
• Ruttenberg et al.
  
• Samelson
  
• Spitz et al.
  
• Wheeler
  

Abstracts should be cited as:

EOS Trans. AGU, 83 (47),
Fall Meet. Suppl.,
Abstract XXXXX-XX, 2002

OS62A-0232

Mesoscale Bio-acoustic Surveys in the Northern California Current System

S D Pierce, J A Barth, W T Peterson, T J Cowles, and M Zhou

During spring and summer 2000, two mesoscale mapping cruises surveyed
the northern California Current system from 41.9-44.6N and about
150 km offshore.  Concurrent with the physical and bio-optical
measurements made from a towed undulating vehicle (SeaSoar), a
multi-frequency (38, 120, 200, and 420 kHz) towed bio-acoustics
instrument collected backscatter data. The bio-acoustics were
collected in 12 s ensembles (about 50 m horizontal resolution)
and 1 m vertical bins, comparable to the resolution of the SeaSoar
measurements, allowing for close evaluation of the physical control
of biological distributions on these scales.  The acoustics were
sea-truthed using nearby MOCNESS samples. Predicted scattering
was computed for each net sample using body lengths in a
randomly-oriented bent cylinder scattering model, a reasonable
approximation for both copepods and euphausiids. Predicted volume
backscattering for the MOCNESS samples explained 44% of the variance
of the nearby acoustics backscatter, a typical result in this
context. A non-negative least squares inverse method is applied
in conjunction with the scattering model, yielding estimates of
biomass in four size classes over the entire survey region. For
the spring 2000 case, we also compare our bio-acoustic results with
zooplankton measurements made with an Optical Plankton Counter (OPC)
mounted on the SeaSoar vehicle. The overall mean OPC and acoustic
zooplankton estimates agree moderately well for the 5-9 mm and
9-17 mm size classes, with biovolumes within factors of two. For
the 1-5 mm size class, the mean OPC value is an order of magnitude
larger than the acoustic estimate. On the other hand, the 1-5 mm
bio-acoustic map reveals some mesoscale spatial structure over a
submarine bank which the OPC does not show. The different methods of
observing zooplankton will be discussed in more detail. Preliminary
bio-acoustic results from other years (2001 and 2002) off the Oregon
coast will also be shown.