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

Kodiak aggregation Adult female Tanner crabs Estimated 100,000 females in a 2 ha area Photo:

NMFS Kodiak

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

Bering Sea

Importance of aggregation behavior for Tanner crab populations????

Gulf of Alaska

Kodiak Glacier Bay

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1300 km 2 ?

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Distribution during tagging

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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

New telemetry technique:

SYNAPS TM Synthetic Aperture Positioning System Developed by George Niezgoda, Lotek Inc.

Synthetic array from towed hydrophones Estimated positions within 20 m, or better!!!

Synthetic array and Position estimation from time delays

Synthetic array and Position estimation from time delays Previous hydrophone position

Synthetic array and Position estimation from time delays Previous hydrophone positions

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

SYNAPS TM error surface

Synthetic array Estimated tag position Actual tag position

Estimated actual: X - 4 m Y + 2 m

X Coordinate

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

50 adult female Tanner crabs tagged

>90 mm carapace width

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

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Tracking trips: Every six weeks during winter Every 2 weeks during April and May

Female crabs captured during spring tracking trips to monitor reproductive stage

Adult female Tanner crab distribution (2002):

0 10 km

Study area:

100 km 2 Depth (m) 50 150 250 350 450

October (release) Muir Sill

Adams Inlet (21) Muir Sill (23) Central Bay (7)

Muir Sill

October (release) to December 2005 0 1 km

Muir Sill

December 2005 0 1 km

Muir Sill

February 2006 0 1 km

Muir Sill

March 1, 2006 0 1 km

Muir Sill

March 27, 2006 0 1 km

Muir Sill

April 11, 2006 0 1 km

Greatest degree of aggregation

Muir Sill

April 24, 2006 0 1 km

Large movements to shallow waters

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Captured crabs: Hatching Extrusion of new clutch

Muir Sill

May 11, 2006 0 1 km

Movement to deeper water More movement to shallow water

Muir Sill

May 21, 2006 0 1 km

Movement to deeper water

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

Summary

Hypothesized distribution: D D D 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

D D D D D D Multiple aggregations?

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D D D D D D D …..Or one larger aggregation?

D D D D D D D D D D D D D D Need direct observation!

Submarine or ROV

Funding WC&PR NURP USGS ADF&G NOAA Fisheries Lotek, Inc.

George Niezgoda Peter Anson Mitch Sisak

Thank you!!!

Crew Captain Jim de La Bruere Mayumi Arimitsu Jeff Douglas Ginny Eckert Heidi Herter Jennifer Mondragon Quinn Smith Sherry Tamone Bronwen Wang Joel Webb Special thanks: Dean Courtney Bill Eichenlaub Louisa Hayes Trevor League Karen Oakley Bob Stone Doug Woodby