Section 1 Introduction - National Marine Fisheries Service - NOAA

NBK at Bangor EHW-1 Pile Replacement Project Final Marine Mammal Monitoring Report
Extrapolated Level B Takes for the Unmonitored Zone
The measured behavioral harassment zone during vibratory pile installation and removal, defined
as the area within the average distance to the 120 dB isopleth during the EHW-1 PRP (calculated
as a 2.7 miles [4.4 km] radius from the construction location), covered 8.8 mi 2 (22.84 km 2 ).
Only a subset of this area was monitored (1.5 miles [2.4 km] radius from the pile, or 4 mi 2
[10.32 km 2 ]) because of logistical constraints. It is therefore appropriate to estimate the number
of potential Level B marine mammal takes that may have occurred in the ensonfied, but
unmonitored, zone. To extrapolate missed takes, species density in Hood Canal (individuals
observed during EHW-1 per km² per hr) was multiplied by the unmonitored area that fell within
the measured harassment zone. The product of these two numbers represents the estimated
density (individuals/km²/hr) in the unmonitored zone. Species density in the unmonitored zone
was then multiplied by the total number of construction hours during the EHW-1 PRP to arrive at
an estimate of the numbers of takes missed in the unmonitored, ensonified zone (Table 11).
Only sighting rates from outside the WRA were considered in the analysis, since these were
likely more representative of animal densities in the unmonitored zone. It should be noted that
the density estimates were not collected using standard line-transect methodology, since at the
time of writing these data were not available for Hood Canal for all species in question. Using
the methods outlined above, it is estimated that approximately 5 harbor porpoise, 8 harbor seals,
30 California sea lions and 1 Steller sea lion were “taken” in the unmonitored section of the
behavioral harassment zone for marine mammals.
Table 11. Missed Takes in the Unmonitored Area of the Behavioral Harassment Zone
Species
Density
Estimate
Measured
Level B
Harassment
Zone
(Area, km²)
Monitored
Area
(km²)
Unmonitored
Harassment
Zone
(Area, km²)
Estimated
Density in
Unmonitored
Area
Total
Construction
Hours During
EHW-1
Missed
Takes
(Estimated)
Harbor porpoise 0.032
0.40
4.96
Harbor seal
California sea lion
0.048
0.195
22.84 10.32 12.52
0..60
2.44
12.4
7.44
30.26
Steller sea lion 0.004 0.05 0.62
Marine Mammal Mitigation Procedures: Construction Delays and Shutdowns
In most cases, when a marine mammal was observed in the 164 ft (50 m) shutdown zone,
ongoing construction was shut down, and imminent construction was delayed. Shutdowns as a
result of pinnipeds inside the 164 ft (50 m) accounted for ten hours and sixteen minutes of delays
throughout the lifetime of the project. In five cases, where cessation of pile driving posed a
safety hazard, construction was allowed to continue even though a marine mammal was sighted
within the 164 ft (50 m) shutdown zone (see highlighting in Table 12). Nine piles (EHW-8
through EHW-16) were installed in and under the existing EHW-1 structure, and required the
construction crane, hammer and pilings to be positioned within a few feet of the building.
Because the hammer required delicate positioning over the pile to avoid building damage, in
these situations the construction foreman notified the MC that it was not possible to interrupt the
pile driving event without risk to the crew and to the EHW-1 structure from the piling and/or
vibratory hammer hitting the building.
Bangor, Washington 41