Monster Seminar Jam - Potential Prey of Killer Whales in Pudget Sound: A Pilot Study
Dr. John Horne, School of Aquatic and Fishery Sciences, University of Washington
In an initial effort to characterize potential interactions between southern resident killer whales and their prey in the San Juan archipelago, fixed and adaptive transects were surveyed using echosounders and a multibeam sonar during September 2004. A midwater trawl was used to confirm species presence and to collect length frequency samples. Relative densities of surf smelt, larger acoustic targets, and a mixed layer were quantified using the 38 kHz backscatter data. Marine mammal observers counted and identified all surfacing animals within a 180o swath in front of the vessel. The echosounder efficiently characterized fish densities throughout the water column. Relative fish densities in the three backscatter categories differed among days, locations, and depths. The largest fish concentrations were observed within Haro Strait. Individual and groups of killer whales were observed in the vicinity of and in the absence of fish backscatter. Quantitative analysis of multibeam data is not currently possible but images of whales and fish schools were observed on the screen during adaptive transect sampling. Representative echograms and catch records will be used to illustrate the approaches used and the challenges involved when correlating large mobile predators with prey densities.
Date and Time:
March 17, 2005,
11:00 am - 12:30 pm