By: Tommy Acton
The
blue whale, or the Balaenoptera musculus,
is a cosmopolitan species of baleen whale (Lockyer,
1984). It is the largest
animal ever known to have lived on Earth; and adults in the Antarctic have
reached a maximum body length of about 33 m and can weigh more than 150,000 kg.
Blue whales are long-bodied and slender
in comparison to other whales such as the right whale. The dorsal fin is set
far back, closer to the tail flukes than to the middle of the body. The blue
whale species inhabits and feeds in both coastal and pelagic environments. When
feeding, the blue whale’s pleated throat and chest expands to accommodate the
enormous intake of seawater and food, before filtering the plankton into their
stomach and releasing the water back into the ocean. There has been slight
variability found in the blue whale species, leading to the creation of three
subspecies (Rice, 1977):
1)
m. Musculus in the Northern Hemisphere
2)
m. Intermediary from the Antarctic
3)
m. Brevicauda is significantly smaller and found in
the sub Antarctic zone of the southern Indian Ocean
Is
it assumed that the blue whale distribution is fueled by food requirements and
that regional populations are based on seasonal migration patterns. Poleward
movements in the spring allow whales to take advantage of high plankton
production in the summer. Movement toward the subtropics in the fall allows
blue whales to reduce their energy expenditure while fasting, avoid ice
entrapment in areas, and engage in reproductive activities in warmer waters of
lower altitudes. Blue whales have been described as “very nomadic”, as they
rarely stay in the same particular area for more than ten days. Individual
whales were documented to travel more than 400 km in a two-week period during
the summer.
Blue
whales were protected in portions of the Southern Hemisphere beginning in 1939.
In 1955, they were given complete protection in the North Atlantic and this was
extended to the Antarctic in 1965 and the North Pacific in 1966 (Gambell,1979;
Best,1993). Blue whales are protected under both the Endangered Species Act (as
an endangered species) and under the Marine Mammal Protection Act. The IUCN Red
List of Threatened Animals (Baillie and
Groombridge 1996)
lists three geographical populations
of blue whales, as follows: Antarctic stocks are “endangered”, North Pacific
stocks are “low risk, conservation dependent”, and the North Atlantic stock is
“vulnerable.”
The human impact on blue whales is
tremendous. Besides the Southern Japan subpopulation, which has nearly been
extirpated by whaling, other human impacts on the blue whale population
includes: collisions and disturbances from vessels, entrapment and entanglement
in fishing gear, habitat degradation, and military operations such as sonar
signals. Commercial whalers in the North Pacific, between 1910 and 1965, killed
a reported total of 9,500 blue whales (Ohsumi
and Wada 1972).
.
The
goal of the Recovery Plan is to promote recovery of blue whale populations to levels
at which it becomes appropriate to down list them from endangered to threatened
status, and to ultimately remove them from the list of Endangered and
Threatened species. The primary purpose of the Plan is to identify a set of
actions that will minimize or eliminate effects from human activities that are
detrimental to the recovery of blue whale populations. However, since blue
whales move freely across international borders, the Plan is going to need to
not only focus on US waters but also involve a multi-national approach to blue
whale protection. A brief outline of the Blue Whale Recovery Plan involves 7 major steps:
1)
Determine
stock structure of Blue Whale populations occurring in U.S. waters and
elsewhere
2)
Estimate
the size and monitor trends in abundance of Blue Whale populations
4)
Reduce
or eliminate human-caused injury and mortality of Blue Whales
5)
Minimize
detrimental effects of directed vessel interactions with Blue Whales
6)
Maximize
efforts to acquire scientific information from dead, stranded, and entangled
Blue Whales
7)
Establish
criteria for deciding whether to delist or down list Blue Whales
Works Cited Page
Baillie, J., and B. Groombridge (eds.).
1996. 1996 IUCN red list of threatened animals. IUCN, Gland, Switzerland. 368 pp.
Best, P.B. 1993. Increase rates in
severely depleted stocks of baleen whales. ICES J. mar. Sci. 50:169-186.
Gambell, R. 1979. The blue whale.
Biologist 26:209-215.
Lockyer, C.L. 1984. Review of baleen
whale (Mysticeti) reproduction and implications for management. Rep. int. Whal. Commn., Special Issue
6:27-48.
Ohsumi, S., and S. Wada. 1972. Stock assessment
of blue whales in the North Pacific
Unpublished working paper for
the 24th meeting of the Scientific Committee of the International Whaling Commission, 20 pp.
Rice, D.W. 1977. A list of the marine
mammals of the world. NOAA Tech. Rep. NMFS SSRF-711.
http://ecos.fws.gov/docs/recovery_plan/whale_blue.pdf
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