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Julie Nielsen (USGS/UAF) Jim Taggart (USGS) Tom Shirley (Texas A&M) U.S. Department of the Interior U.S. Geological Survey Using a synthetic aperture acoustic telemetry method to determine the location, timing and spatial aggregation of female Tanner crabs during reproductive events
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NMFS Kodiak Occurs annually prior to larval release on spring tides Estimated 100,000 females in a 2 ha area 150 m depth Up to 6 weeks duration Stevens, B.G. 2003. Timing of aggregation and larval release by Tanner crabs, Chionoecetes bairdi, in relation to tidal current patterns. Fisheries Research 65: 201-216 Photo: Kodiak aggregation Adult female Tanner crabs
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Gulf of Alaska Bering Sea Glacier Bay Kodiak Importance of aggregation behavior for Tanner crab populations????
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1300 km 2 ? ? ? ? ? ?
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D D D D D D D D D D D D D D D D D D D D D D Distribution during tagging
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D D DDD D D DD D D D D D D D D D D D Hypothesized distribution during larval release
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Lotek Wireless, Inc. MAP technology All tags on same frequency Digital tags automatically decoded No signal collision
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New telemetry technique: SYNAPS TM Synthetic array from towed hydrophones Synthetic Aperture Positioning System Developed by George Niezgoda, Lotek Inc. Estimated positions within 20 m, or better!!!
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Synthetic array and Position estimation from time delays
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Synthetic array and Position estimation from time delays Previous hydrophone position
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Synthetic array and Position estimation from time delays Previous hydrophone positions
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Synthetic array Subtract tag burst interval for each subsequent signal Creates an array in space from positions in time Triangulation to calculate position Previous hydrophone positions
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SYNAPS TM error surface Synthetic array Estimated tag position Estimated - actual: X - 4 m Y + 2 m Actual tag position X Coordinate Y Coordinate
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October 2005: Survey to determine adult female distribution 1.5 km grid of study area
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>90 mm carapace width 50 adult female Tanner crabs tagged
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USGS Research Vessel Alaskan Gyre
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Hydrophones on V-fins Towed on 50 m cables Tow speed 3-4 kts Operational depth 20 m Tracking trips: Every six weeks during winter Every 2 weeks during April and May
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Female crabs captured during spring tracking trips to monitor reproductive stage
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Adult female Tanner crab distribution (2002): 10 km 0
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Study area: 100 km 2 50 150 250 350 450 Depth (m)
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October (release) Adams Inlet (21) Muir Sill (23) Central Bay (7) Muir Sill
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01 km Muir Sill October (release) to December 2005
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01 km Muir Sill December 2005
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01 km Muir Sill February 2006
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01 km Muir Sill March 1, 2006
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01 km Muir Sill March 27, 2006
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Greatest degree of aggregation 01 km Muir Sill April 11, 2006
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01 km Muir Sill April 24, 2006 Large movements to shallow waters Captured crabs: Hatching Extrusion of new clutch
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01 km Muir Sill May 11, 2006 More movement to shallow water Movement to deeper water
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01 km Muir Sill May 21, 2006 Movement to deeper water
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Aggregation of tagged animals in conjunction with larval hatching Similarities to Kodiak aggregation Greatest degree of aggregation preceded observations of larval hatching by 2 weeks Similar depths
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Hypothesized distribution: D D D D D D D DD D D D D D D D D D D D We did not observe 50 tagged crabs converging on one location Tagged crabs remained in the general area where they were tagged Approximately 5 km 2 Consistent with patch size determined from pot survey Summary
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D D D D D D D D D D D D D D D D D D D D Multiple aggregations?
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D D D D D D D D D D D D D D D D D D D …..Or one larger aggregation? D D D D Need direct observation! Submarine or ROV
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Thank you!!! FundingCrew WC&PR NURP USGS ADF&G NOAA Fisheries Captain Jim de La Bruere Mayumi Arimitsu Jeff Douglas Ginny Eckert Heidi Herter Jennifer Mondragon Quinn Smith Sherry Tamone Bronwen Wang Joel Webb Dean Courtney Bill Eichenlaub Louisa Hayes Trevor League Karen Oakley Bob Stone Doug Woodby Special thanks: Lotek, Inc. George Niezgoda Peter Anson Mitch Sisak
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