Estimates of entanglement risk
for lobster fishing off the coast of Maine
Chris Brehme, Keene State College
Hauke Kite-Powell, Woods Hole Oceanographic Institution
Scott Kraus, Kerry Lagueux, and Brooke Wikgren, New England Aquarium
Patrice McCarron and Heather Tetreault, Maine Lobstermen’s Association
2013 Northeast Regional Sea Grant Meeting
New Bedford, 19 November 2013
Approach:
Estimate the expected number of whale/fishing gear encounters
per year – this will depend on:
• fishing effort
• vertical line density
• trap string configuration
• whale activity
• density
• behavior (transiting, feeding, etc.)
• topography
• water depth
• bottom characteristics
Consider adjustments to fishing effort (time, location, gear
configuration) to reduce risk.
Vertical Line Risk
Probability of whaleline encounter
= f ( lines/km2
whale track/km2
[whale size]
)
Ground Line Risk
Probability of whale-line
encounter
=f(
h line length/km2
whale track/km2
[whale size]
water depth
whale diving )
Model Polygons and Fishing Zones
Fishing Activity Data
5.9 million VL-months
Exempt state:
Non-ex. state:
3-6 miles:
6-12 miles:
12-40 miles:
70.6%
22.7%
3.2%
1.4%
2.1%
Fishing Gear in the Water
Whale Activity Data
SPUE from “on-effort” survey only
Modeled Whale Activity
Interpolation approach based on: E. Bellier and Monestiez P., 2008. Model based block kriging to
estimate spatial abundance of wildlife populations from count data. In Proceedings of the Eighth
International Geostatistics Congress. Julian Ortiz & Xavier Emery (Eds.). GECAMIN. pp 119-128.
ISBN:978-956-8504-18-2.
Whale Activity
Whale Activity
by Zone
511,500 km whale track
“FTWEs”:
Dec, Jan:
Feb, Mar:
Apr, May:
Jun, Jul:
Aug, Sep:
Oct, Nov:
52.5
3.6
5.7
9.0
16.2
28.6
Whale Activity
Inshore
Whale track distribution:
State exempt:
State non-ex.:
3-6 miles:
6-12 miles:
12-40 miles:
0.3%
0.8%
1.7%
5.7%
91.5%
Model Input Summary
Baseline: Expected Encounters 2011
expected encounters/year:
VL
GL
total
2,163
342
2,505
Baseline: Expected Encounters
Baseline Risk by Zone
Sensitivity Analysis
• Both fishing effort and whale activity data sets
incorporate assumptions
– Fishing effort: total number of active traps, and
allocation of traps to areas designated by
fishermen as rarely/sometimes/always fished
– Whale activity: whale activity level in nearshore
waters where there is little systematic survey work
• Question: do risk hot spots predicted by the
model depend on these assumptions?
Sensitivity Scenarios: Fishing Effort
• Five vertical line models:
– 5/35/60 allocation of traps to
rarely/sometimes/often fished areas (base case)
– 0.5/9.5/90 shifts more traps to “often fished”
– 25/35/40 shifts traps to “rarely/sometimes fished”
– 5/ +1 conf is 5/35/60 with more traps active
– 5/ -1 conf is 5/35/60 with fewer traps active
• Moderate uncertainty; +/- 35% (median)
Sensitivity Scenarios: Whale Activity
• Three whale activity models:
– Predicted WA: assumes some degree of whale
activity (0.5 x standard error) in all polygons with
at least one sighting (base case)
– Low WA: Predicted WA minus 2 x standard error
(truncated at zero); represents lower than
predicted nearshore whale activity
– High WA: Predicted WA plus 2 x standard error;
represents higher than predicted nearshore whale
activity
• High uncertainty, esp. inshore; +/- 90% (median)
Sensitivity Analysis: Base case hot spots
• Base case risk hot spots (63%):
–
–
–
–
–
–
A-3 (Aug, Sep) – 32%
A-40 (Jun – Nov) – 8%
C-40 (Oct – Jan) – 9%
D-3 (Jun – Sep) – 5%
F-40 (Nov – Jan) – 4%
G-40 (Dec, Jan) – 5%
• Share of risk in these hot spots is insensitive to fishing effort
assumptions and Predicted/Low WA
• But decreases to 30% with High WA
Sensitivity Analysis continued
Base case has 50-60% of risk in state
waters (more than half of this in A3
Aug, Sep), and 30% in 12-40 nm.
With half of base case near shore
whale activity, state waters risk drops
to less than 20%, and 12-40 nm risk
rises to 60%. (Plausible.)
With 10% of whale activity in state
waters, state waters risk rises to 90%.
(Conceivable but not likely.)
Model Application Examples
(Note: Area 1 Maine only)
• Effect of Sinking Ground Line (rule in place)
• NMFS NE Proposal (2011)
• Offshore Trawl-up (12-40nm)
Sinking Ground Line (rule in place)
347 avoided
encounters/year; 12%
reduction
in total pre-rule encounter
risk
Risk would rise 14% if all
zones went back to
floating ground line,
mainly from:
A non-exempt (Aug, Sep)
A40 (Aug, Sep)
C non-exempt (Jun, Jul)
C40 (Dec, Jan)
D40 (Dec, Jan)
E40 (Nov – Jan)
F40 (Nov – Jan)
G non-exempt (Oct, Nov)
NMFS NE Proposal (2011)
Results: NMFS NE Proposal (2011)
expected encounters/year:
VL
1,987 (-167)
GL
342
total
2,329
7% reduction from baseline
~80% of this from:
C40 (Dec, Jan)
D non-ex (Jun – Sep)
F40 (Nov – Jan)
G40 (Dec, Jan)
Offshore Trawl-ups
Risk reduction:
from 12% (min 20)
to 25% (min 30)
VL-month reduction:
from 46,000 (min 20)
to 72,000 (min 30)
DMR2012: 70,000
NMFS NE: 456,000 (8%)
Most significant months for 12-40 trawl up risk reduction:
Zone A:
Aug, Sep, Oct, Nov
Zone B:
Oct, Nov
Zone C:
Oct, Nov, Dec, Jan
Zone D:
Dec, Jan
Zone E:
Dec, Jan
Zone F:
Nov, Dec, Jan
Zone G:
Dec, Jan
Summary
• Highest resolution fishing effort & more complete
representation of Right Whale activity to date
• Model is operational (spreadsheet implementation), can
easily reflect alternate management measures and
assumptions about fishing & whale activity
• Spatial distribution of risk is sensitive to assumptions about
inshore whale activity
– Assuming inshore activity = 0 is a sure way to NOT address significant
percentage of total risk
• Risk is concentrated in temporal/spatial hot spots
– Danger: blanket measures that miss hot spots are unlikely to reduce
risk significantly (though they may reduce VLs)
– Opportunity: targeted management measures can reduce risk with
minimal disruption of fishing (but may be harder to enforce)
Acknowledgements
Collaborators:
Chris Brehme, Keene State College
Tara Hetz, WHOI Summer Student Fellow
Scott Kraus, New England Aquarium
Kerry Lagueux, New England Aquarium
Cris Lutazzi, WHOI Summer Student Fellow
Patrice McCarron, Maine Lobstermen’s Association
Heather Tetreault, Maine Lobstermen’s Association
Sophia Weinman, WHOI Guest Student
Brooke Wikgren, New England Aquarium
Funding provided by the WHOI and Maine Sea Grant Programs and: