Assessing the Accuracy
of High Spatial
Resolution Effort Data
Southwest
Fisheries
Science Center,
Ecology Division
Comparing VMS and Logbook Data in the
California Groundfish Trawl Fishery
Alice Thomas-Smyth, Aaron Mamula, & Cameron Speir
Objective
Quantify error in the self-reported data of the California Groundfish trawl
fishery using fine-scale spatial data for the years 2007-2011 to assess
whether logbooks are an appropriate source of information for spatial
analysis and to what scale the information is accurate.
Data
•  Logbook data provides a historical record of fishing activity in the
West Coast fisheries, however this data is self-reported
•  Vessel monitoring system (VMS) data provides fine-resolution spatial
and temporal data, however is only recently available and contains
no vessel or activity information
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 2
Data - VMS
Data
Points
Vessels
Raw
22,081,317
1,139
Study area
20,522,715
1,134
Removed speeds and
spikes
19,180,243
1,036
Removed ports
4,583,006
983
Fishing activity
1,017,613
973
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 3
Data - Logbook
Year
Vessels
Trips
Tows
2007
69
1,976
7,682
2008
62
1,883
7,711
2009
55
2,078
7,826
2010
58
1,884
6,505
2011
48
1,469
5,609
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 4
Methods – identify fishing activity in VMS
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Methods – identify fishing activity in VMS
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Methods – tow path
construction
•  Straight line
•  Bathymetry contours
•  Least-cost path
•  Change in
bathymetry from
set and up average
depth
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Methods – matching the data
•  No way to identify individual trips or tows in the VMS
data
•  Vessel days are units of comparison between the
data
•  Trips in this fishery tend to be short, 1-3 days
•  Average distance per vessel day
Original
Logbook Data Original
VMS Data Matched
Data Vessel Days 13,951 165,507 7,508 Number of Recordsa 35,334 4,583,006 18,193 87 973 69 9,290 -- 4,571 456 17,498,311 -- Unique Vessels Unique Trips Removed Records a. Each logbook records is trawl tow consisting of set and up points. Each VMS record is a point consisting of a
position, time, speed, and bearing. Each record in the matched data is a trawl tow, either from the logbook
or constructed from consecutive points in the VMS data.
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 8
Results
Straight line distance (km) Year Vessel Days Avg Median Std. Dev Min Max 2007 385 6.7195 1.43 33.2257 0.0096 622.6739 2008 1745 6.3975 2.2826 12.4967 0.0082 124.7562 2009 2464 7.8560 2.9384 12.5955 0.0154 132.9931 2010 1734 7.3914 2.7175 18.1061 0.0079 448.1858 2011 1180 6.5925 2.4612 12.9976 0.0094 114.5433 All years 7508 6.9914 2.3669 17.8843 0.0101 288.6305 Bathymetry line distance (km)
Year
Vessel Days
Avg
6.4994
Median
1.09
Std. Dev
32.4420
Min
0.0217
Max
604.2819
2007
385
2008
1745
6.3958
2.2198
12.5531
0.0046
124.7528
2009
2464
7.6804
2.6915
12.6336
0.0104
132.9627
2010
1734
6.2094
2.2690
17.0049
0.0398
448.1811
2011
1180
6.4348
2.1894
13.0296
0.0498
114.5202
All years
7508
6.7894
2.2673
15.3924
0.0046
604.2819
Set and up logbook points and nearest VMS fishing point distance (km)
Year
Vessel Days
Avg
9.1947
Median
3.4533
Std. Dev
32.7166
Min
Max
0.2396 606.2721
2007
385
2008
1745
6.5738
2.7450
12.2941
0.0702 121.7944
2009
2464
6.8644
2.5452
11.7657
0.0669 142.4202
2010
1734
6.6534
2.3614
16.9603
0.0486 445.8807
2011
1180
6.6399
2.0731
13.5149
0.0787
All years
7508
6.8337
2.5299
15.1865
0.0486 606.2721
114.0566
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 9
Results - straight line vs bathymetry
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Results – set and up points
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Results – examining error (directionality)
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Results – examining error (hang time)
Logbook tow hang time distance (km)
Year
Trawls
Avg
2007
7682 0.9784 Median
0.2225 Std. Dev
2.4102 Min
0 Max
106.1484 2008
7712 1.0880 0.3668 1.4426 0 29.1300 2009
7826 0.9612 0.2396 1.3759 0 28.4577 2010
6298 1.0044 0.2567 2.6647 0 178.0504 2011
5609 0.8355 0.2246 1.1955 0 15.2121 All years
35127 0.9805 0.2586 1.9122 0 178.0504 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 13
Conclusions
•  Lack of systematic directional error in the logbook
data
•  Speed-based criteria for fishing activity classification
in VMS data feasible to allow for fine spatial
resolution analysis of catch data
•  Straight line tow paths are accurate representation
of fishing activity in this fishery
•  However a new method to draw tow paths
bathymetrically is now available
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | NOAA Fisheries | Page 14