[CINC] Blue whales Part I

[whalebear at cs.com]

Hello All,

I attempted to send this earlier, but it was too large for the server; I've therefore divided the posting into two parts.  In response to recent postings requesting more blue whale information, I offer a few comments on the skeleton at the museum, followed by excerpts from the blue whale section of my marine mammal handout...As always, please e-mail me with any questions.

Regarding the blue whale, Balaenoptera musculus:
 
 
Blue whale skeleton
 
With respect to the blue whale skeleton at the Santa Barbara Museum of Natural History, there are critical points to emphasize beyond the number of bones.  
 
It is important to note that the mandibles (jawbones) do not articulate with the skull as they do in humans and most other mammals; the attachments are only ligamentous.  This is what allows blue whales and other Rorquals to open their mouth to the vast extent that they do.  If one delves into the fossil record, there are intermediate forms to be found.
 
It is also important to note that few ribs in Mysticetes articulate with the vertebrae and only one pair of ribs articulates with the sternum (unlike Odontocetes and most other mammals).  This allows compression of the thorax with the pressure associated with depth.  Although Mysticetes are not deep divers, they do have enormous lungs; an adult blue whale has a total lung capacity of approximately 3000 liters.  At depth (even the depths at which blue whales sometimes dive), there is thoracic compression, which allows the lung air to be forced into the non gas-exchanging portion of the tracheobronchial tree where it is not subject to absorption into the bloodstream.  This diminishes the possibility of these animals getting the “bends."
 
What follows below is abstracted from my revised handout on marine mammals.
 
 
Some comments on Blue Whales, Balaenoptera musculus.
 
-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.
 
Blue whales are longer than 2 school buses laid end-to-end, and they are heavier than 1500 people.  Their tongue weighs as much as an adult elephant, and their heart is larger than a VW Beetle.  An adult human would be able to crouch in the left ventricle.  When they spout, their blow is up to 3 stories (9m).  Their flukes are as wide as a soccer goal.
 
-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.

Part II will follow.

Chuck Rennie
Adjunct Curator, Marine Mammals
Santa Barbara Museum of Natural History

Medical Director
Channel Islands National Park
 
 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.rain.org/pipermail/channel_islands_naturalist_corps/attachments/20111029/bc0f3d18/attachment-0001.html>