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A simple two-dimensional model of ship encounter risk for right whales in Cape Cod Bay: Final results and management implications. Owen C. Nichols 1 , Hauke L. Kite-Powell 2 , Robert D. Kenney 3 , Moira W. Brown 4      1) Center for Coastal Studies, PO Box 1036, Provincetown, MA 02657, USA

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A simple two-dimensional model of ship encounter

risk for right whales in Cape Cod Bay:

Final results and management implications

Owen C. Nichols1, Hauke L. Kite-Powell2, Robert D. Kenney3, Moira W. Brown4

     1) Center for Coastal Studies, PO Box 1036, Provincetown, MA 02657, USA

2) Marine Policy Center, Woods Hole Oceanographic Institution, MS 41, Woods Hole, MA 02543, USA

3) Graduate School of Oceanography, University of Rhode Island, Bay Campus Box 41, Narragansett, RI 02882, USA

4) New England Aquarium, Central Wharf, Boston, MA 02110, USA


Provide a baseline estimate of risk to right whales from

collisions with shipping traffic in Cape Cod Bay

Evaluate potential management measures designed to reduce

collision risk

Sightings Per Unit Effort (SPUE)

  • Study area partitioned into 117 3-minute quadrats (23 km2)

  • 14 quadrats completely over land; thus 103 quadrats sampled

  • Standardized aerial survey effort: visibility  2 nm, sea state ≤ 3,

  • altitude < 325 m (1066 ft), observers on watch

  • Only sightings and effort meeting the above criteria used in analysis

  • The sampling season was defined as December through mid-May

  • and divided into twelve two-week periods (1 December – 17 May)

Sightings Per Unit Effort (SPUE)

  • Total effort and total sightings within each quadrat summed by year

  • and separated into two-week periods

  • Number of whales sighted divided by effort to generate SPUE index

SPUE = right whales sighted/1000 km survey effort


  • Kriging interpolation algorithm* used to estimate SPUE at twice the

  • geographic resolution (1.5 minute quadrats)

  • * GLOBEC Kriging Software Package, Dezhang Chu, WHOI

Density Estimates

SPUE converted to density estimate (whales/km2) for each 1.5 min

quadrat over 2-week periods - assuming 3 km effective survey swath

Vessel Transits

  • Data provided by USACE Cape Cod Canal Field Office

  • 6 routes based on origin/destination in USACE dataset

  • ~ 7 vessel movements/day: 4 - Boston, 2 - Gulf of Maine

  • 75% of the traffic is tug-barge combinations


Traffic to/from…

Course (true) from Cape Cod Canal


Greater Boston area

45○ to longitude 70.38○W,

then 340○

Gulf of Maine

north of Cape Ann



Plymouth/Duxbury and vicinity

355○ to latitude 41.92○N, then 330○ to latitude 42.00○N


Provincetown and anchorages

45○ to latitude 42.03○N


inner “elbow” region of CCBay

85○ to longitude 70.05○W

Cape Cod Bay

unspecified locations in CCBay

45○ to latitude 41.92○N


(based on origin/destination in USACE dataset)


Calculation of Expected Ship/Whale Encounters

For each route and 2-week period, the expected number of ship/

whale encounters was calculated based on the passage of a known

number of vessels through quadrats of estimated right whale density

  • Routes divided into 1 km segments – right whale density is assumed

  • based on the 1.5 min quadrat over which most of the segment lies

# of ship/whale encounters =

area of path “swept” by vessel (beam x 1 km) x density (whales/km2)

  • Effective beam (width of path “swept” by vessels) estimated based

  • on vessel type: tug = 10m; tug-barge, dry cargo, passenger = 15 m;

  • tanker = 20m

  • Assumptions: whales always at surface and neither whales nor vessels

  • attempt to avoid collision

Expected Ship/Whale Encounters

  • Results of model = 1.5 ship/whale encounters/year

  • Boston traffic contributes ~ 46% of expected encounters, while Gulf

  • of Maine traffic contributes ~ 35% - the latter poses high risk

  • despite relatively low volume - transects areas of high whale density

Effects of Rerouting

  • Two proposals incorporated into model

Proposal A: Simple demonstration exercise

Proposal B: Draft routing option presented at ANPR meetings

  • Both proposals involved shifting Boston, Gulf of Maine, and

  • Provincetown traffic to the west


expected ship-whale encounters/year


Proposal A

Proposal B





Gulf of Maine








Cape Cod Bay












Effects of Rerouting

  • Expected ship-whale encounters reduced by about 60% on the

  • Gulf of Maine route and by about 40% on the Provincetown and

  • Boston routes

  • Across all routes, reduction of 37% (Proposal A) to 45%

  • (Proposal B) in the overall ship-whale encounter risk for Canal

  • traffic in Cape Cod Bay (from ~ 1.5 encounters/year to ~ 0.9)


  • Model results allow identification and comparison of areas of risk

  • to right whales – baseline estimate that can be used to inform

  • management decisions

  • Routing existing vessel traffic away from known concentrations

  • of right whales will cause a quantifiable reduction of the potential

  • number of ship/whale encounters

  • Expected encounters calculated based on several assumptions –

  • Model can be refined with additional data as it becomes available:

  • detection probability for density estimates, surface/dive and

  • avoidance behavior, addition of subsequent years of right whale

  • and traffic data


  • Funding provided by the NOAA Fisheries North Atlantic Right

  • Whale Competitive Grant Program

  • Aerial surveys supported by the Massachusetts Division of Marine

  • Fisheries as part of the Commonwealth of Massachusetts Right

  • Whale Conservation Plan – funding sources include National Fish

  • and Wildlife Foundation, NOAA Fisheries, Massachusetts

  • Environmental Trust, and the Northeast Consortium – Special

  • thanks to Dan McKiernan

  • Vessel traffic data provided by the US Army Corps of Engineers

  • Cape Cod Canal Field Office – Scott Barr, Bill Norman and Fran

  • Donovan - Guidance and advice on routes: Pat Gerrior, Bruce Russell