Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
Hermes Reef, and Midway and Kure Atoll. In the last decade, however, sightings of Hawaiian monk
seals in the main Hawaiian Islands have increased considerably (Baker and Johanos 2004; Carretta
et al. 2004). Most monk seal haulout events in the main Hawaiian Islands have been on the western
islands of Ni’ihau and Kaua’i (Baker and Johanos 2004; Carretta et al. 2004), although sightings or
births have now been reported for all of the main Hawaiian Islands, including Lehua Rock and Kaula
Rock (MMC 2003; Baker and Johanos 2004). These sightings include “surplus” males that were
relocated from the main breeding islands to reduce the problem of mobbing of breeding females
(Zevin 1995; Baker and Johanos 2004). Births of Hawaiian monk seal pups have been recorded in
the main Hawaiian Islands, including Kaua’i and Ni’ihau (Baker and Johanos 2004). Hawaiian monk
seals wander to Mar Reef and Gardner Pinnacles and have occasionally been sighted on nearby
island groups, such as Johnston Atoll, Wake Island, and Palmyra Atoll (Rice 1998).
Hawaiian monk seals show very high site fidelity to natal islands, with only about 10% of individuals
moving to another island in their lifetime (Gilmartin and Forcada 2002). While monk seals do move
between islands, long-distance movements are not common. Seals move distances of up to 250 km
on a regular basis, but distances of more than 1,000 km have not been documented (DeLong et al.
1984; Ragen and Lavigne 1999).
Information Specific to the Marianas MRA Study Area—There are no confirmed records of
Hawaiian monk seals in the Micronesia region; however, Reeves et al. (1999) and Eldredge
(1991; 2003) have noted occurrence records for seals (unidentified species) in the Marshall and
Gilbert islands. The monk seal is not known to make long-distance movements; however, its
numbers are increasing in the main Hawaiian Islands as individuals expand their range from the
Northwestern Hawaiian Islands, so extralimital occurrences are possible. The highly endangered
status of this species necessitates mentioning the possibility of encountering this species in the
Marianas study area (Jefferson personal communication).
Behavior and Life History—Unlike many other pinniped species, Hawaiian monk seals are not very
gregarious on land and are more-or-less solitary when at sea. The monk seal also appears to be
intolerant of human presence; occurrence trends at Kure Atoll, Midway Atoll, and French Frigate
Shoals appear to be determined by the pattern of human disturbance from military or USCG activities
(Kenyon 1973; MMC 2003; Baker and Johanos 2004; Carretta et al. 2004). Likewise in the main
Hawaiian Islands, seals tend to frequent remote areas where human access is limited (MMC 2003).
Although births are documented year-round, pupping occurs during a protracted breeding season
mostly from February to August, with a peak in April to June (Gilmartin and Forcada 2002; Stewart
2004). Sometimes groups of males exhibit an aggressive behavior called “mobbing,” in which they
gang together and attempt to mate with, and by doing so, injure and often kill, adult females and
immature seals of both sexes (Starfield et al. 1995). This behavior seems to occur to a far greater
extent in those subpopulations where there are more males than females.
Molting takes place once a year between April and December. Hawaiian monk seals have a
“catastrophic molt” in which large patches of skin and fur are shed. This type of molt is considered to
be very energetically expensive.
Hawaiian monk seals feed opportunistically on a wide variety of at least 40 species of benthic and
demersal fishes, cephalopods, and spiny lobster (MacDonald 1982; Goodman-Lowe 1998; Parrish et
al. 2000). Juveniles feed on small, cryptic, benthic prey items (Parrish et al. 2005). Monk seals also
interact with various fisheries, such as longlines and the lobster fishery (Nitta and Henderson 1993;
Carretta et al. 2004). Hawaiian monk seals were previously not thought to be deep divers, with most
known dives in the 10 to 40 m depth range (DeLong et al. 1984; Ragen and Lavigne 1999). However,
deeper dives to at least 121 m (DeLong et al. 1984) and to over 500 m (Parrish et al. 2002) have
recently been recorded.
Acoustics and Hearing—There is no information available regarding underwater sounds produced
by Hawaiian monk seals. In-air sounds include: (1) a soft liquid bubble at 100 to 400 Hz; (2) a loud,
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