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Julie Nielsen (USGS/UAF) Jim Taggart (USGS) Tom Shirley (Texas A&M)

Using a synthetic aperture acoustic telemetry method to determine the location, timing and spatial aggregation of female Tanner crabs during reproductive events. Julie Nielsen (USGS/UAF) Jim Taggart (USGS) Tom Shirley (Texas A&M). U.S. Department of the Interior U.S. Geological Survey.

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Julie Nielsen (USGS/UAF) Jim Taggart (USGS) Tom Shirley (Texas A&M)

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  1. Using a synthetic aperture acoustic telemetry method to determine the location, timing and spatial aggregation of female Tanner crabs during reproductive events Julie Nielsen(USGS/UAF) Jim Taggart(USGS) Tom Shirley(Texas A&M) U.S. Department of the Interior U.S. Geological Survey

  2. Photo: Kodiak aggregation NMFS Kodiak Adult female Tanner crabs Estimated 100,000 females in a 2 ha area Occurs annually prior to larval release on spring tides 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

  3. Glacier Bay Importance of aggregation behavior for Tanner crab populations???? Bering Sea Gulf of Alaska Kodiak

  4. ? ? ? ? ? ? 1300 km2

  5. Distribution during tagging D D D D D D D D D D D D D D D D D D D D D D

  6. Hypothesized distribution during larval release D D D D D D D D D D D D D D D D D D D D

  7. Lotek Wireless, Inc. MAP technology • All tags on same frequency • Digital tags automatically decoded • No signal collision

  8. New telemetry technique: SYNAPSTM Synthetic Aperture Positioning System Developed by George Niezgoda, Lotek Inc. Synthetic array from towed hydrophones Estimated positions within 20 m, or better!!!

  9. Synthetic array and Position estimation from time delays

  10. Synthetic array and Position estimation from time delays Previous hydrophone position

  11. Synthetic array and Position estimation from time delays Previous hydrophone positions

  12. Previous hydrophone positions Synthetic array • Subtract tag burst interval for each subsequent signal • Creates an array in space from positions in time • Triangulation to calculate position

  13. SYNAPSTM error surface Synthetic array Estimated tag position Actual tag position Y Coordinate Estimated - actual: X - 4 m Y + 2 m X Coordinate

  14. October 2005: • Survey to determine adult female distribution • 1.5 km grid of study area

  15. 50 adult female Tanner crabs tagged >90 mm carapace width

  16. USGS Research Vessel Alaskan Gyre

  17. 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

  18. Female crabs captured during spring tracking trips to monitor reproductive stage

  19. Adult female Tanner crab distribution (2002): 10 km 0

  20. Depth (m) 50 150 250 350 450 Study area: 100 km2

  21. Adams Inlet (21) Muir Sill Muir Sill (23) Central Bay (7) October (release)

  22. 0 1 km Muir Sill October (release) to December 2005

  23. 0 1 km Muir Sill December 2005

  24. 0 1 km Muir Sill February 2006

  25. 0 1 km Muir Sill March 1, 2006

  26. 0 1 km Muir Sill March 27, 2006

  27. Greatest degree of aggregation 0 1 km Muir Sill April 11, 2006

  28. Large movements to shallow waters 0 1 km Muir Sill April 24, 2006 • Captured crabs: • Hatching • Extrusion of new clutch

  29. Movement to deeper water More movement to shallow water 0 1 km Muir Sill May 11, 2006

  30. Movement to deeper water 0 1 km Muir Sill May 21, 2006

  31. Similarities to Kodiak aggregation • Aggregation of tagged animals in conjunction with larval hatching • Greatest degree of aggregation preceded observations of larval hatching by 2 weeks • Similar depths

  32. D D D D D D D D D D D D D D D D D D D D Summary Hypothesized distribution: • We did not observe 50 tagged crabs converging on one location • Tagged crabs remained in the general area where they were tagged • Approximately 5 km2 • Consistent with patch size determined from pot survey

  33. Multiple aggregations? D D D D D D D D D D D D D D D D D D D D

  34. D D …..Or one larger aggregation? D D D D D D D D D D D D D D D D D D D D D Need direct observation! Submarine or ROV

  35. Lotek, Inc. George Niezgoda Peter Anson Mitch Sisak Funding Crew 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 Thank you!!! Special thanks: Dean Courtney Bill Eichenlaub Louisa Hayes Trevor League Karen Oakley Bob Stone Doug Woodby

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