NMFS Biological Opinion on U.S. Navy training ... - Govsupport.us

FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013
numbers of seals (Bailey 1952). A survey in 1958 suggested that the population had partially recovered from its
initial collapse.
Consistent declines in the monk seal population trends have been recorded since range-wide surveys began in the
late 1950s (survey results that were reported by Kenyon and Rice 1959 and Rice 1960). Rice (1960) conducted
additional counts at Midway Islands in 1956-1958 and Wirtz (1968) conducted counts at Kure Atoll in 1963-1965.
Between the late 1950s and 1980s, counts at the atolls, islands, and reefs in the Northwest Hawai’ian Islands
suggested a 50 percent decline in this population (Kenyon 1973, Johnson et al. 1982). The total population for the
five major breeding locations plus Necker Island for 1987 was estimated to be 1,718 seals including 202 pups of the
year (Gilmartin 1988). This compares with 1,488 animals estimated for 1983 (Gerrodette 1985). In 1992 the
Hawai’ian monk seal population was estimated to be 1580 (standard error = 147) (Ragen 1993). The best estimate of
total abundance for 1993 was 1,406 (standard error = 131, assuming a constant coefficient of variation).
Beach counts of juveniles, sub-adults, and adults declined by about 5 percent per year from 1985 – 1993, and then
became relatively stable until the current decline began in 2001 (<strong>NMFS</strong> 2007). Between 1958 and 1993, mean beach
counts declined by 60 percent and included declines in the number of monk seals at French Frigate Shoals, which
once accounted for more than 50 percent of the total non-pup beach counts among the six primary Northwest
Hawai’ian Island sub-populations. Between the years 1958 and 2006, beach counts of juveniles, sub-adults and
adults declined by 66 percent; the total abundance of monk seals at the six primary subpopulations in the Northwest
Hawai’ian Islands is declining at annual rate of 3.9% (95% CI = -4.8% to - 3.0%; <strong>NMFS</strong> 2007). In 2006, the monk
seal population was estimated to number about 1,200 animals.
Based on the evidence available, Hawai’ian monk seals exist as a population that is subject to the dynamics of
“small” populations. That is, they experience phenomena such as demographic stochasticity, inbreeding depression,
Allee effects, among others, that cause their population size to become a threat in and of itself. For example,
Hawai’ian monk seals have very low survival of juveniles and sub-adults due to starvation (which is believed to be
caused by limitations in the food base), low juvenile survival has lead to low juvenile recruitment into the adult
population, and the adult population increasingly consists of ageing females who reproductive success is expected to
decline (if it has not already declined) in the foreseeable future. A positive feedback loop between reduced
reproductive success of adult females and reduced recruitment into the adult population (which reduces the number
of adult females) is the kind of demographic pattern that is likely to increase the monk seal’s decline toward
extinction. As a result, we assume that Hawai’ian monk seals have elevated extinction probabilities because of
exogenous threats caused by anthropogenic activities (primarily whaling, entanglement, and ship strikes), natural
phenomena (such as disease, predation, or changes in the distribution and abundance of their prey in response to
changing climate), and endogenous threats caused by the small size of their population.
Diving and Social Behavior
Several recent studies of the foraging patterns of Hawai’ian monk seals near rookeries in the northwestern Hawai’ian
Islands provide insight into their diving behavior. Dive depths appear to differ slightly between rookeries as well as
between age classes and genders. At Pearl and Hermes Reef, most dives were from 8-40 m with a second much
smaller node at 100- 120 m (Stewart, 2004). At Kure Atoll, most dives were shallower than 40 m, with males
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