[CINC] Blue whales, Part II

[whalebear at cs.com]

Part II, as promised.  References, all either primary or review articles appearing in refereed journals, appear at the end.

-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 3-4% 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..
 
Chuck Rennie
Adjunct Curator, Marine Mammals
Santa Barbara Museum of Natural History

Medical Director,
Channel Islands National Park
 
 
 
 
 
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 107:1286-1300.
 
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.
 
Charles J Rennie, III
Adjunct Curator, Marine Mammals
Santa Barbara Museum of Natural History
 
Medical Director
Channel Islands National Park

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