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Gulf of Alaska Bering Sea Glacier Bay Kodiak Importance of aggregation behavior for Tanner crab populations????
Citation preview
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
?
??
??
?
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Distribution during tagging
D DDD D
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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
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DD
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DDD
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Multiple aggregations?
DD
DD
DD D
D
D
DDD
DDD
DD DD
…..Or one larger aggregation?
DD
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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
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