Download Some comments on Blue Whales, Balaenoptera musculus

Some comments on Blue Whales, Balaenoptera musculus.
Charles J Rennie, III
Adjunct Curator, Marine Mammals
Santa Barbara Museum of Natural History
Medical Director,
Channel Islands National Park
-General: General characteristics of Balaenopteridae include a streamlined shape (Megaptera is the
sole exception), small dorsal fins which vary widely among members of a given species in shape (in
general, the larger the species, the more posterior the dorsal fin), and numerous throat grooves.
-External Morphology: B. musculus is the largest organism known ever to inhabit the earth. As with
all balaenopterids, females are larger than males. The largest individual ever measured (a female)
was 33.6m (110 ft.) in length. The heaviest weighed was 190 tons (if lost blood volume were factored
in, the weight would probably have been 200 tons). At adulthood, the mouth measures 6m in length
and the flukes 4.5m in width. Dorsal fins are small (0.4m) and posterior. >300 baleen plates (<1m in
length) are in each upper jaw. The baleen and fringe bristles are black. 55-88 ventral pleats, of
varying length, are found on the ventral surface. A single midline ridge extends from the blowhole to
the rostrum.
-Subspecies: Three subspecies have been recognized: B musculus intermedia (the largest, inhabiting the Southern Hemisphere), B musculus musculus (intermediate in size, inhabiting the North
Atlantic and North Pacific), and B musculus brevicauda (the shortest, inhabiting the tropical Southern
Hemisphere in the Indian Ocean and Southeast Atlantic). Specimens from elsewhere are often
assigned to intermedia, but their true subspecies is unknown. B. musculus brevicauda has a shorter
tail than other subspecies, a proportionately longer body, and is less than 24.4m (80 ft) in length.
Although controversy accompanied the first description of brevicauda by the Japanese (many felt the
separation into what was originally claimed as a new species was simply a ploy to exceed International Whaling Commission limits on blue whales), the subspecies is now fully accepted. The degree
of hybridization among subspecies is unknown. Theoretically, the temporal displacement of migrations between Northern Hemisphere and Southern Hemisphere animals should prevent intermingling
(and DNA work supports this), but there is some interchange of animals. There is also evidence of
some hybridization between B. musculus and B. physalus.
-Communication: Vocalizations are in the 15-20 HZ range with intensities of 180-190 decibels,
among the loudest in the animal kingdom. Four different vocalizations have been recorder in Eastern
North Pacific blue whales. These include long-duration, low frequency calls referred to as pulsed A
calls and tonal B calls. Repetitive A and B calls together constitute song. The characteristics of this
song have been well-described and occur on Northeastern Pacific feeding grounds ranging from the
Costa Rica Dome to the Gulf of Alaska. Singing (repetitive AB units) has been observed only in
males and appears to occur only while the males are traveling and not feeding. High source levels of
these song units and their repetition and duration (they may last for 30 minutes) have led to hypotheses that they are designed to be heard over long distances. Their presence only in males suggests
a reproductive context; perhaps, as has been hypothesized for humpback singing on feeding
grounds, it “may serve as low-cost advertisement to estrous females who did not conceive the previous winter or may promote pair-bonding for the upcoming breeding season.” This is supported by
high rates of male-female association in the summer.”
Singular A and B calls are also seen only in males but have been recorded during “feeding, milling,
resting, and traveling.” The singular A and B calls occur with other blue whales in proximity; where
sex of the associated animals has been determined, it has been female. The proximity of other
whales suggests communication with those nearby, but no coordinated activities have been observed
in this context.
Within a season, there is little variability of A and B call frequencies for any given blue whale or between individuals. An annual temporal change has been observed, however: the mid-frequency of A
and B calls has decreased each year since the mid-1960s. It has been concluded that populations of
blue whales synchronize their A and B calls annually and shift the call frequency annually at a predictable rate.
A third type of call, the D call, is a downswept call with greater variation in frequency and duration
than A and B calls. They are produced by both males and females during shallow non-feeding dives
in whales otherwise feeding at greater depths. Multiple calls are produced throughout the dive profile
at depths between 15 and 35 m. They often occur in association with another whale, and have been
almost uniformly recorded with other whales within 1 km distance. It has been hypothesized that
these calls are related to social interactions. Again, no coordinated activities have been observed in
this context
Additionally, blue whales produce occasional highly variable frequency modulated (FM) and amplitude modulated (AM) calls. Their function is unknown.
Ultrasonic clicks have also been recorded from blue whales. Crude echolocation has been postulated but not substantiated, and these animals lack the Odontocete anatomy that makes echolocation
possible.
-Respiration/Diving: Older literature, based in large part on whaler observations (under non-chase
conditions) and summarized by Yochem and Leatherwood in 1985, indicates that blue whales make
10-12 shallow dives of 10-20 seconds duration in a row. 8-14 respirations are taken between dives.
This is then followed by a deeper dive of 10-30 minute duration. The species has never been considered a particularly deep diver and has generally been believed to feed in the top 100m of the water
column.
There is now a substantial body of recent literature regarding diving behavior off the Central California coast. Much of this is corroborated by similar work done on balaenopterids in other parts of the
world. The numbers below are not absolute. Different prey species behavior and differing physical
oceanographic conditions modify behavior within and in different environments. Numbers also vary
due to the differing ways in which dives are defined by researchers.
Lagerquist (2000) monitored dive time for four blue whales off the Central California coast. The
whales spent a total of 94% of their time submerged. Number of dives observed during 3 hour periods ranged from 83-128. 72% of dives lasted <1 min. Average duration of true dives (defined as >1
min) for each whale ranged from 4.2 to 7.2 min. Duration of the longest dive for each whale ranged
from 10-18 min. Average surface time between dives was 64.8 seconds, and the average number of
blows during this time was 4.0. Duration of dives from studies during older whaling operations log
dives from 10-50 minutes (which may be measuring maximum dive capacity/fright response rather
than “normal” dives); studies from later whaling operations logged dives from 5-7, 2-5, and 2-7 min.
Another study logged average dive times of B. musculus brevicauda at 9.9 min. Croll (1998) in work
in the Santa Barbara Channel logged average dive duration of 4.3 min. Fiedler (1998) logged dive
times of 3-5 minutes in the same area.
75% of dives recorded by Lagerquist were to <16 m and represented 78% of the animal’s time. The
average depth of dives >16 m was 105 m; the average depth of all dives (including those <16m) was
33m. Croll (1998) reported an average depth of dive at 68.1m, but did not give a definition of dive.
Maximum depth in this study was 152m. Only 1.2% of dive time was spent at depth of 97-152m.
Croll (2001) attached time-depth recorders to 9 B. musculus. He found the average depth of foraging
dives to be 140.0m with an average time of 7.8 min. The average depth of non-foraging dives was
67.6m with an average time of 4.9 min (dive was defined as submergence >20m). Only 4 of 21 dives
were to depths of >100m, with the deepest dive to 172.8m. The longest dive was for 14.7 min. Calculated theoretical aerobic dive limit (TADL) was 31.2 min. He concluded that this limit was not
reached (many marine mammals do exceed this limit) either because of prey dispersal or because of
energy cost of lunge feeding. To this I would add a third hypothesis—that adequate caloric intake did
not necessitate exceeding the TADL.
Calambokidis (2008) studied 13 B. musculus tagged with Crittercams. Four of these animals had
dives to >250m.
In general, these animals dive for 4-7 minutes, with dives under non-stressed conditions not exceeding 18 minutes. Most foraging dives are in the upper 150 meters of the water column.
Flukes are not regularly shown during diving, although the Makah refer to blue whales as kwakwe
axtLi, or “noisy tail.” Blue whales generate peak respiratory flows of 624,000 liters per minute during
exhalation/inhalation; human maximum is 800 liters per minute.
-Feeding: Blue whales feed primarily on euphausids. In the North Pacific, the primary prey species
are Euphausia pacifica, Thysanoessa spinifera, and Nematoscelis difficilis.
E. pacifica is the most common species in the Santa Barbara Channel, but T. spinifera is the preferred prey. The latter is larger and more coastal in distribution. B. musculus is considered the most
selective feeder among the baleen whales. They may also take in small fish, particularly sardines
and capelin, but this ingestion may be accidental. This species is considered a “swallower” or
“gulper” as opposed to Balaenidae (right whales), which are considered “skimmers.” Side feeding (on
the surface) and lunge feeding while submerged are characteristic of this species. Peak feeding is in
the evening and early morning, which correlates with euphausid abundance in the water column.
Dietary intake for a full-sized adult is 3-4 million calories per day, which corresponds to 4-5 tons of
krill. The oral cavity of an adult blue whale can hold 2+ tons of water, while the stomach can hold 1-2
tons of krill. Recent work by Goldhagen (2011) regarding massive intake of water is in substantial
part theoretical. The translation of its findings in the lay press has been oversimplified and grossly
exaggerated.
-Reproduction: Blue whales mate in the fall and winter. Migratory phase differences prevent substantial Northern and Southern Hemisphere interbreeding. Gestation is 10-11 months, and sexually
mature females usually bear a single calf every 2-3 years. Calves are 6-7m and 3 tons at birth.
Calves receive approximately 380 liters of milk per day. The milk is 41-50% milk fat (human milk is 34% milk fat). Calf weight gain is 4kg per hour, and length gain is 4cm per day. Weaning occurs at 7
months, when calves average 16m (53 ft) and 23 tons. The mother may lose 50 tons (one-third her
body weight) while nursing. Northern Hemisphere females are 21-23m at sexual maturity and 25m at
physical maturity. Northern Hemisphere males are 20-21m at sexual maturity and 24m at physical
maturity. Sexual maturity generally occurs at 8-10 years; this has been lowered considerably by the
population pressure exerted by whaling during the twentieth century.
-Life Span/Population Estimates: Blue whales have an estimated life span of 80-90 years, although methodology in aging studies is problematic. Individual life spans of 40 years have been
documented through photo ID. Individuals are usually solitary or found in groups of 2-3. Where
males and females are paired, the males usually follow behind the females. Pre-exploitation population of blue whales is usually estimated at 350,000 individuals. The invention of the modern harpoon
gun in the latter part of the 19th century and fast catcher vessels in the early 20th century made this
species the favorite target of hunters (due to its size and oil yield). Approximately 350,000 blue
whales were taken in the 20th century, with 30,000 taken in 1930-1931 alone. Approximately 9000
remain today. The population off the California/Mexican coast has been estimated at 2000 animals
by capture-recapture (photo-identification), and 3000 individuals by line-transect. The eastern North
Pacific population now extends from the Costa Rica Dome into the Gulf of Alaska. There is some
exchange with the western North Pacific population.
-Swimming Speeds: Various estimates exist. Sears and Perrin (2009) give estimates of 3-6km/hr
while feeding, 5-40km/hr traveling, and 35+km/hr for brief bursts while being chased. The latter
speed is not sustainable for long periods.
-Disease/Mortality: Little is known about diseases in blue whales. Strandings are relatively uncommon and the animals are generally so decomposed that good necropsies are difficult. They appear
to be less parasitized than other species of marine mammals, which may be due to a diet low on the
food chain. This may also account for the relatively low level of pollutants found in their tissues,
although much more work is needed. The ventral surface of blue whales often becomes covered with
diatoms, particularly in the Antarctic; this has given rise to the name “sulphurbottom.” Blue whales
may also act as host to remoras. Shipping accidents and Orcinus attacks are causes of mortality.
Approximately 25% of blue whales in the St. Lawrence Seaway bear marks of encounters with ships.
The same number bear scars from encounters with Orcinus in the Sea of Cortez, although such
predation is probably not a major cause of mortality. Limited necropsy data on Orcinus has demonstrated little balaenopterids material in their GI tracts.
-Research: Blue whales are the focus of intensive photo identification work. The use of satellite
tagging and Crittercams is also giving new insights into their world, as is krill research. Mortality by
ship strikes recently documented in the Santa Barbara Channel has intensified ship-strike work already in progress.
REFERENCES
Calambokidis, John and J Barlow. 2004. Abundance of Blue and Humpback Whales in the Eastern
North Pacific Estimated by Capture-Recapture and Line-Transect Methods. Marine Mammal Science
20: 63-85.
Calambokidis, John, G Schorr, G H Steiger, et al. 2007. Insights into the Underwater Diving, Feeding, and Calling Behavior of Blue Whales from a Suction-Cup-Attached Video-Imaging Tag
(Crittercam). Marine Technology Society Journal 41: 19-29.
Calambokidis, John, J Barlow, J K B Ford, et al. 2009. Insights into the population structure of blue
whales in the Eastern North Pacific from recent sightings and photographic identification. Marine
Mammal Science 25: 816-832.
Croll, Donald A, A Acevedo-Gutierrez, B R Tershy, et al. 2001. The diving behavior of blue and fin
whales: is dive duration shorter than expected based on oxygen stores? Comparative Biochemistry
and Physiology Part A: 797-809.
Dunn, Robert A and O Hernandez. 2009. Tracking blue whales in the eastern tropical Pacific with an
ocean-bottom seismometer and hydrophone array. J. Acoust. Soc. Am. 126: 1084-`094.
Fiedler, Paul C, S B Reilly, R P Hewitt, et al. 1998. Blue whale habitat and prey in the California
Channel Islands. Deep-Sea Research II 45: 1781-1801.
Goldbogen, J A, J Calambokidis, E Oleson, et al. 2011. Mechanics, hydrodynamics and energetics
of blue whale lunge feeding: efficiency dependence on krill density. Journal of Experimental Biology
214: 131-146.
Lagerquist, B A, K M Stafford, and B R Mate. 2000. Dive Characteristics of Satellite-Monitored blue
Whales (Balaenoptera musculus) off the Central California Coast. Marine Mammal Science 163:
375-391.
McDonald, Mark A, J Calambokidis, A Teranishi, et al. 2001. The acoustic calls of blue whales off
California with gender data. J. Acoust. Soc. Am. 109: 1728-1735.
Oleson, Erin M, J Calambokidis, W Burgess, et al. 2007. Behavioral context of call production by
eastern North Pacific blue whales. Mar. Ecol. Prog. Ser. 330: 269-284.
Panigada, Simone, M Zanardelli, S Canese, et al. 1999, How deep can baleen whales dive? Marine
Ecology Progress Series 187: 309-311.
Sears, Richard and W Perrin. 2009. Blue Whales. In Perrin, William F, B Wursig, and JGM
Thewissen, eds. Encyclopedia of Marine Mammals, 2nd ed. New York: Academic Press,
Slijper, E J. 1962. Whales. New York: Basic Books.
Small, George. 1971. The Blue Whale. New York: Columbia University Press.
Stewart, Brent S. 2009. Diving. In Perrin, William F, B Wursig, and JGM Thewissen, eds. Encyclopedia of Marine Mammals, 2nd ed. New York: Academic Press.
Thode, Aaron M, G L D’Spain, and W A Kuperman. 2000. Matched-field processing, geoacoustic
inversion, and source signature recovery of blue whale vocalizations. J. Acoust. Soc. AM 107:12861300.
Yochem, Pamela K and S Leatherwood. 1985. Blue Whale—Balaenoptera musculus, pp 193-240.
In Ridgway, Sam H and R Harrison, eds. Handbook of Marine Mammals Volume 3: The Sirenians
and Baleen Whales. New York: Academic Press.