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
Butterworth et al. (1993), however, estimated the Antarctic population at 710 individuals. More recently, Stern
(2001) estimated the blue whale population in the Southern Ocean at between 400 and 1,400 animals (c.v. 0.4). The
pygmy blue whale population has been estimated at 6,000 individuals (Yochem and Leatherwood 1985)
The information available on the status and trend of blue whales do not allow us to reach any conclusions about the
extinction risks facing blue whales as a species, or particular populations of blue whales. With the limited data
available on blue whales, we do not know whether these whales exist at population sizes large enough to avoid
demographic phenomena that are known to increase the extinction probability of species that exist as “small”
populations (that is, “small” populations 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) or if blue
whales might are threatened more by exogenous threats such as anthropogenic activities (primarily whaling,
entanglement, and ship strikes) or natural phenomena (such as disease, predation, or changes in the distribution and
abundance of their prey in response to changing climate).
Diving and Social Behavior
Generally, blue whales make 5-20 shallow dives at 12-20 second intervals followed by a deep dive of 3-30 minutes
(Mackintosh 1965; Leatherwood et al. 1976; Maser et al. 1981; Yochem and Leatherwood 1985; Strong 1990; Croll
et al. 1999). Croll et al. (1999) found that the dive depths of blue whales foraging off the coast of California during
the day averaged 132 m (433 ft) with a maximum recorded depth of 204 m (672 ft) and a mean dive duration of 7.2
minutes. Nighttime dives are generally less than 50 m (165 ft) in depth (Croll et al. 1999).
Blue whales are usually found swimming alone or in groups of two or three (Ruud 1956, Slijper 1962, Nemoto 1964,
Mackintosh 1965, Pike and MacAskie 1969, Aguayo 1974). However, larger foraging aggregations and aggregations
mixed with other species like fin whales are regularly reported (Schoenherr 1991, Fiedler et al. 1998). Little is
known of the mating behavior of blue whales.
Vocalizations and Hearing
The vocalizations that have been identified for blue whales include a variety of sounds described as low frequency
moans or long pulses (Cummings and Thompson 1971, 1977; Edds 1982, Thompson and Friedl 1982; Edds-Walton
1997). Blue whales produce a variety of low frequency sounds in the 10-100 Hz band (Cummings and Thompson
1971, Edds 1982, Thompson and Friedl 1982, McDonald et al. 1995, Clark and Fristrup 1997, Rivers 1997). The
most typical signals are very long, patterned sequences of tonal infrasonic sounds in the 15-40 Hz range. The sounds
last several tens of seconds. Estimated source levels are as high as 180-190 dB (Cummings and Thompson 1971).
Ketten (1997) reports the frequencies of maximum energy between 12 and 18 Hz. In temperate waters, intense bouts
of long patterned sounds are very common from fall through spring, but these also occur to a lesser extent during the
summer in high latitude feeding areas. Short sequences of rapid calls in the 30-90 Hz band are associated with
animals in social groups. The seasonality and structure of long patterned sounds suggest that these sounds are male
displays for attracting females, competing with other males, or both. The context for the 30-90 Hz calls suggests that
they are communicative but not related to a reproductive function. Vocalizations attributed to blue whales have been
recorded in presumed foraging areas, along migration routes, and during the presumed breeding season (Beamish
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