Julie Nielsen (USGS/UAF)

Jim Taggart (USGS)

Tom Shirley (Texas A&M)

U.S. Department of the InteriorU.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

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

Gulf of Alaska

Bering Sea

Glacier BayKodiak

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

1300 km2

?

??

??

?

D

D

DD

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D

D

D

D

DD

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Distribution during tagging

D DDD D

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DDDD

Hypothesized distribution during larval release

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

New telemetry technique:

SYNAPSTM

Synthetic array from towed hydrophones

Synthetic Aperture Positioning System

Developed by George Niezgoda, Lotek Inc.

Estimated positions within 20 m, or better!!!

Synthetic array andPosition estimation from time delays

Synthetic array andPosition estimation from time delays

Previous hydrophone position

Synthetic array andPosition estimation from time delays

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

Previous hydrophone positions

SYNAPSTM error surface

Synthetic array

Estimated tag position

Estimated - actual:

X - 4 mY + 2 m

Actual tag position

X Coordinate

Y C

oord

inat

e

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

>90 mm carapace width

50 adult female Tanner crabs tagged

USGS Research Vessel Alaskan Gyre

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

Female crabs captured during spring tracking trips to monitor reproductive stage

Adult female Tanner crab distribution (2002):

10 km0

Study area:

100 km2

50150250350450

Depth (m)

October (release)

Adams Inlet (21)

Muir Sill (23)

Central Bay (7)

Muir Sill

0 1 km

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

Greatest degree of aggregation

0 1 km

Muir Sill

April 11, 2006

0 1 km

Muir Sill

April 24, 2006Large movements to shallow waters

Captured crabs:• Hatching• Extrusion of new clutch

0 1 km

Muir Sill

May 11, 2006

More movement to shallow water

Movement to deeper water

0 1 km

Muir Sill

May 21, 2006

Movement to deeper water

• 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

Hypothesized distribution:

D DDD DD DDDDDD DD

D

DDD

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 km2

• Consistent with patch size determined from pot survey

Summary

D

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Multiple aggregations?

DD

DD

DD D

D

D

DDD

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…..Or one larger aggregation?

DD

D

DNeed direct observation!

Submarine or ROV

Thank you!!!

Funding CrewWC&PR NURPUSGSADF&GNOAA Fisheries

Captain Jim de La BruereMayumi ArimitsuJeff DouglasGinny EckertHeidi HerterJennifer MondragonQuinn SmithSherry TamoneBronwen WangJoel Webb

Dean Courtney Bill Eichenlaub Louisa HayesTrevor LeagueKaren OakleyBob StoneDoug Woodby

Special thanks:

Lotek, Inc.George NiezgodaPeter AnsonMitch Sisak