Listening for Lime Kiln fish
Last Sunday (11/09/2008), Jason Wood and Scott Veirs deployed a receiver that can detect and record the signals emitted by acoustic tags implanted surgically in migratory fish, like the Chinook and chum salmon that southern resident killer whales appear to prefer. The Vemco “VR2″ receiver, provided by Fred Goetz through a collaboration with UW Fisheries, was deployed during a scheduled maintenance dive on the hydrophones at the Lime Kiln lighthouse. The plan is to retrieve the VR2 in early 2009, download any serendipitous detections that may help in the interpretation of the echosounder data (to be presented at the Puget Sound Georgia Basin conference), and then redeploy it for the remainder of the winter (and perhaps the entire year).
The dive went well and lasted from about 11-12am. We enjoyed visibility of about 20m and pleasantly calm seas (it was very rough on Saturday when we initially planned to dive). We cleaned and secured the intertidal hydrophone and echosounder cable protectors, checked the VR2 mooring for buoyancy, and then followed the hydrophone cable to the two hydrophone stands (cement-filled paint-buckets with a broad tripod of embedded rebar). The VR2 was deployed 3m NW of the southern hydrophone and its mooring anchor was tethered to that hydrophone stand’s embedded chain and one of its rebar legs.
The VR2 mooring had a total height above bottom of 2m, with the receiver hydrophone oriented upwards about 1.4m above bottom. Since the mooring was deployed in 9m of water when the tidal height was ~2m, the depth of the receiver is about 6m below the tidal datum (0m). The mooring consists of a ~2m length of 1/2″ 3-strand polypropelene line connecting a ~3kg buoyancy crab float (used in lieu of an incompressible trawl float since minimal compression is expected at this depth), the VR2 (cabled-tied through and around the strands), and a stainless steel threaded shackle (bowlines at both ends). The shackle connects to a loop of 3/16” plastic-coated wire rope that extends through a pier-block (via a 3/4 inch hole drilled through center line). The loop is secured with a clamp and is attached via sheet-bend to the ~4m-long tether (same type of line). All knots’ tails are secured with electrical tape. The float is marked with UW Fisheries research and Scott’s cell phone number.
Detailed photos of the mooring, including closeups of each component are available in the Beam Reach gallery.
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