Shark Predation on Hawaiian Monk Seals - Pacific Islands Fisheries ...

ange of 200 Hz to 20 kHz. All cables were taut when placed under water and buried when on
land to minimize the potential for entanglement. The boat noise emitted, consisting of four
unique sounds each 28 to 49 seconds in length that played on a rotating basis for approximately
15–20 minutes each hour for 24 hours per day, was believed to be within the frequency range
known to deter sharks.
An empty 15-ft twin hull boat (Livingston) was moored off the northeast side of Trig Island.
The bow was secured into the prevailing weather and attached to a heavy concrete mooring
anchor placed on a sandy substrate.
Summary of Pup Losses at FFS, 2008
Kathleen Gobush, PhD, Hawaiian Monk Seal Research Program
In 2008, 12 (30%) of 41 preweaned pups in FFS either died or disappeared, with 6 (3 Gin pups
and 3 Trig pups) of the losses attributed to sharks (confirmed or inferred–see definitions in
Section II). An additional pup was bitten at Trig resulting in 25% (4 of 16) of the pups born
there affected by shark predation. <strong>Shark</strong> depredations were catastrophic on the two Gins Islets
in 2008, with 3 losses to sharks out of 6 births and an additional nonlethal but multiple bite
wound attack on a pup. The disappearances of 3 other pups (1 from Gin Islet) were categorized
as unknown because they were born late in the season after routine data collection had ceased,
but shark predation could not be ruled out. In 2007, at least 7 of the 43 preweaned pups born at
FFS were lost because of shark predation, and 1 severely bitten pup died post-season because
of the extent of its wounds. Overall numbers lost in 2008 did not differ greatly from those of
2007 when devices to deter sharks were not deployed. However, unlike 2007, the site that
accounted for the most predation in 2008 was Gin, rather than Trig.
Based on the number of shark incidents in 2008 as compared to 2007, the results of the device
trials were equivocal. However, when the number of confirmed and inferred shark attacks
across the season was examined against the deterrent effort (a simple index of the cumulative
number of deterrent types and individual devices of each that was operational each day), more
incidents were associated with diminished deterrent effort at Trig (Fig. 2). Of the 4 shark
incidents at Trig, 2 occurred during the ramp-up period of device deployment and 2 at a later
time when some of the devices were nonfunctional.
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