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

Wariness of <strong>Shark</strong>s to Humans
HMSRP also hypothesizes that Galapagos sharks in FFS are wary of humans. A decrease in
CPUE and sightings over time without a coincident drop in incidents support this notion.
Fishing efficiency (removals per effort hours) progressively deteriorated throughout the 2000–
2006 fishing period, when number of hook hours ranged from 10 to 30 hours per season
(Harting et al., in prep.). The sighting rate of Galapagos sharks during the 2001–2004 intensive
tower observation period had declined over time, but the total number of incidents (confirmed
and inferred attacks) did not decline and the number of inferred attacks increased. This suggests
that shark wariness of humans and/or the tower may have contributed to a decrease in day
predation and an increase in crepuscular and night predation (when observation of attacks is not
possible). Also, there is no history of shark incidents on preweaned or newly weaned pups at
Tern, where researchers and USFWS staff reside in a large compound (NMFS, 2003; NMFS,
2004; NMFS, 2005; NMFS, 2008; Harting et al., in prep.). A report on shark densities and their
proximity to human population centers showed a highly significant negative relationship
between grey reef and Galapagos shark densities and proximity to human population centers.
High numbers of sharks were prevalent around islands with no human habitation but within
reach of populated areas at only 15–40% of the population densities around the most isolated
near-pristine reefs (NMFS, 2009b).
The “human wariness” premise warrants more investigation because human presence may be a
useful shark deterrent itself, as suggested at Workshop II. On the other hand, human presence
may also hamper the effectiveness of some fishing methods. For example, fishing techniques
requiring constant attention or maintenance by fishermen may lead to lower catch rates.
Predatory Behavior
A third premise of HMSRP is that any Galapagos sharks sighted in the nearshore areas of
pupping sites (within 50 m of shore given that preweaned pups will range up to 30 m from land
with their mothers) are potential predators of monk seal pups. Galapagos sharks frequent
deeper waters and are rarely found in shallow waters in FFS as demonstrated by the CPUE
across the atoll (see Sections I and II). The majority of Galapagos sharks sighted near Trig and
Gin Islands when pups were present demonstrated predatory behavior (patrolling, lunging,
chasing and attacking pups) and pursued pups in water as shallow as the wave wash (NMFS,
2003; NMFS, 2004; NMFS, 2005; NMFS, unpubl. data). Circling out from deeper water into
the wave wash is a frequent pattern of the movement of Galapagos sharks observed prior to
attack (NMFS, unpubl. data). Video footage demonstrates that some individuals circled
repeatedly for 20 minutes to 2 hours prior to or between attack attempts (NMFS, unpubl. data).
<strong>Shark</strong> Culling
Removing a limited number of Galapagos sharks to mitigate this source of seal mortality likely
facilitates the maintenance of biodiversity at this atoll overall. As an endangered genus,
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