Estimates of entanglement riskfor lobster fishing off the coast of Maine

Chris Brehme, Keene State CollegeHauke Kite-Powell, Woods Hole Oceanographic Institution

Scott Kraus, Kerry Lagueux, and Brooke Wikgren, New England AquariumPatrice McCarron and Heather Tetreault, Maine Lobstermen’s Association

2013 Northeast Regional Sea Grant MeetingNew 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 whale-line 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 depthwhale diving )

Model Polygons and Fishing Zones

Fishing Activity Data

5.9 million VL-months

Exempt state: 70.6%Non-ex. state: 22.7%3-6 miles: 3.2%6-12 miles: 1.4%12-40 miles: 2.1%

Fishing Gear in the Water

Whale Activity Data

SPUE from “on-effort” survey only

Modeled Whale ActivityInterpolation 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

“FTWEs”:

Dec, Jan: 52.5Feb, Mar: 3.6Apr, May: 5.7Jun, Jul: 9.0Aug, Sep: 16.2Oct, Nov: 28.6

511,500 km whale track

Whale Activity Inshore

Whale track distribution:

State exempt: 0.3%State non-ex.: 0.8%3-6 miles: 1.7%6-12 miles: 5.7%12-40 miles: 91.5%

Model Input Summary

Baseline: Expected Encounters 2011expected encounters/year:

VL 2,163GL 342total 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 continuedBase 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% reductionin 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)G40 (Nov-Jan)

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

Most significant months for 12-40 trawl up risk reduction:Zone A: Aug, Sep, Oct, NovZone B: Oct, NovZone C: Oct, Nov, Dec, JanZone D: Dec, JanZone E: Dec, JanZone F: Nov, Dec, JanZone G: Dec, Jan

Risk reduction: from 12% (min 20) to 25% (min 30)

VL-month reduction:from 46,000 (min 20) to 72,000 (min 30)DMR2012: 70,000NMFS NE: 456,000 (8%)

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 CollegeTara Hetz, WHOI Summer Student Fellow

Scott Kraus, New England AquariumKerry Lagueux, New England Aquarium

Cris Lutazzi, WHOI Summer Student FellowPatrice McCarron, Maine Lobstermen’s AssociationHeather Tetreault, Maine Lobstermen’s Association

Sophia Weinman, WHOI Guest StudentBrooke Wikgren, New England Aquarium

Funding provided by the WHOI and Maine Sea Grant Programs and: