Howard W. Graham, PhD
National Marine Mammal Laboratory, AFSC National Marine Fisheries
Service, NOAA, Seattle, WA
This paper summarizes a review carried out in 1990 on the status of
endangered large whales to meet the 1978 amendments to the U.S. Endangered Species Act (ESA).
The purpose of the review was to determine if any species or population has recovered to its
"initial" or pre-exploitation population size, and to assess whether the
classification of any of the whales under the ESA should be changed from threatened to
endangered, endangered to threatened, or if they should be removed from the ESA altogether.
Status reviews are also used for establishing conservation measures and research priorities for
implementing endangered species recovery plans required by the ESA.
There are eight species and 21 identified populations of large whales
listed as endangered under the ESA--the blue, bowhead, fin, gray, humpback, right, sei, and
sperm whale. Although they have been protected from commercial whaling for several decades,
about half of the major ocean basin populations of large whales are less than 25% of their
pre-exploitation abundance prior to the start of commercial whaling. Because most populations
of large whales are small compared to historic levels, they now face new threats from other
human activities and unpredictable environmental events.
This review compares current abundance to initial abundance, and examines
trends in abundance to determine the level of depletion and rate of recovery. In most cases the
data are not sufficiently precise to determine whether recovery has taken place. Data on total
population size for present and historical levels, and a compilation of catches, are drawn from
the published literature. With a few exceptions, population estimates are not precise. A
selected list of references and suggested reading is at the end of this paper (see National
Marine Mammal Laboratory 1991 for a complete list of citations used in this study).
Blue whales are severely depleted and scarce in all oceans of the world. In
the Northern Hemisphere, the catch records are incomplete and their status is unknown. In the
eastern Pacific, sightings have increased off central California, Mexico, and Central America,
possibly as a result of increased observer effort. The species has also been studied in the
Gulf of St. Lawrence, Canada, but trends in abundance are unknown for any population in the
North Atlantic except off west Iceland where the population may be increasing. The status and
trends of blue whales in the Southern Hemisphere are unknown. Only seven sightings of calves
were made between 1966 and 1986 south of 60°S. The present world abundance of about 8,500
is 4-5% of the estimated abundance earlier this century; the majority of blue whales reside in
the Southern Hemisphere.
Bowhead whales are severely depleted except in the western North American
Arctic. The status of stocks in the Okhotsk Sea (North Pacific Ocean), Spitsbergen-East
Greenland, Davis Strait-Baffin Bay, and Hudson Bay-Foxe Basin (North Atlantic Ocean) is
unknown. Infrequent sightings in these areas suggest that bowhead numbers are very small,
perhaps in the low hundreds. The western Arctic population in the Bering, Chukchi, and Beaufort
Seas has increased at an unknown rate since commercial whaling ended (in about 1914), but since
1978 the population has increased at about 3.1% per year (95% confidence interval of 0.1-6.2%).
The take of bowhead whales by Alaskan Eskimos (including whales landed and struck but lost) has
been 25-40 animals per year since 1978, or about 0.05% of the estimated present stock size. The
present population estimate of 7,800 animals (95% C.I. of 5,700-10,600) is 40.9% (95% C.I. of
38.8-42.0%) of the initial stock size of 18,000-20,000 (range 14,000 to 27,000) in 1848. The
total world abundance of about 8,000 is 12% of its initial abundance.
The status of stocks of fin whales is uncertain, although the species is
severely depleted relative to historic levels. Its present world abundance of about 120,000 is
26% of its estimated initial abundance. Over 700,000 fin whales were landed in all oceans, with
most taken in the southern oceans this century. There are no known trends in abundance anywhere
in the world.
Two populations of gray whales have survived whaling, and both are in the
North Pacific Ocean. The status of the western North Pacific population is uncertain. A review
of the literature coupled with recent surveys along the far east coast of Asia, plus the
sighting of 34 gray whales in the Okhotsk Sea, suggest that the population is still very small
and has not reoccupied its former range. In addition, its initial stock size may have been very
small. The eastern North Pacific population, on the other hand, has fully recovered from
commercial whaling. The present stock size of 21,113 (95% C.I. of 19,737-22,489) is at or above
its initial stock size of 20,000 (in 1846). Between 1967 and 1988, this stock increased 3.2%
(95% C.I. of 2.2-4.2%) per year, in spite of a catch of 167 (95% C.I. of 160-174) whales per
year by the Soviet Union over the past 30 years.
The status of most humpback whale populations is uncertain. The western
North Atlantic population, which migrates from the Greater and Lesser Antilles to Davis Strait
(West Greenland) and Denmark Strait (East Greenland), is currently estimated at 5,505 (95% C.I.
2,799-8,211). There is uncertainty as to whether the stock has increased in recent years. The
initial population size was probably larger than 4,400-6,300, but how much more is unknown,
based on an analysis of the few available whaling records. The eastern North Pacific
population, which migrates from Hawaii and Mexico to Alaska and California, is presently
estimated at about 2,000 animals (range 1,398-2,040). There are no apparent trends in
abundance. Only two populations of humpbacks show any sign of recovery, west of Iceland and off
Western Australia. The total world abundance of about 10,500 is 8-9% of its estimated initial
The right whale is the most severely depleted and least abundant of all the
large whales. In the eastern North Pacific, the species was so severely reduced during the 19th
century that it may be near extinction; only 5-7 sightings (none with calves) have been made in
the past 25 years. The western North Atlantic population, found along the east coast of the
United States and Canada is the most threatened of all the identified stocks of large whales in
U.S. waters. Present estimates of abundance range from 71-333 (coefficient of variation of
26-32%) to 350 (no variance estimate), with over 200 individual animals having been
photographically identified since 1979. No trends have been detected. The status of right
whales in the eastern North Atlantic Ocean is unknown; only five sightings have been made in
the past 30 years. The small number of sightings suggests that this population also may be near
extinction. Only three populations of right whales show any signs of recovery, one each off
South Africa, Argentina, and Western Australia. The present world abundance of less than 3,000
animals is 2-3% of its estimated initial abundance.
The status of sei whales is unknown. The species was severely depleted by
commercial whaling in the 30 year period following 1950. The estimate of present abundance of
about 9,000 in the North Pacific Ocean is not very precise; and about 75-85% are believed to
reside east of 180°. There are no estimates of abundance for the entire North Atlantic
Ocean, although 4,000 are estimated to be west of Iceland. The present world abundance of about
25,000 animals is 24% of its estimated initial abundance.
Sperm whales are the most abundant large whale. The world population of
nearly 2 million is over eight times larger than the combined total of the other seven species
of the listed endangered large whales. Stock definition and structure are not well understood,
as with many of the large whales, and there is uncertainty about the methods and models used to
estimate historical and present abundance. Nonetheless, the present world abundance is
estimated to be about 65% or more of its estimated initial abundance.
Commercial whaling successively over-exploited one stock of large whales
after another, resulting in their eventual depletion in all the world's oceans. Pre-20th
century whaling focused on the slower moving right, bowhead, gray, humpback, and sperm whales.
Modern whaling focused on the faster swimming blue, fin, and sei whales, primarily in the
southern oceans. Fin, blue, and sperm whales constituted almost 80% of the catches of all
species worldwide, and in total, more than 2 1/2 million large whales were taken between 1530
and 1984, the last year of commercial catches. In spite of this large take, all eight species
have survived and a few populations show signs of recovery. No single species and only one
stock of large whale is known to have become extinct since the start of commercial whaling. The
Atlantic gray whale became extinct apparently in the 17th century.
While there is considerable uncertainty about the status of most
large-whale populations, sufficient data are available to conclude that right, blue, bowhead,
humpback, sei, and possibly fin whales are severely depleted species (at or below 25% of their
presumed initial abundance) of the 21 major ocean basin populations, five are less than 5% of
their initial abundance: the Southern Hemisphere blue whales, Southern Hemisphere humpback
whales, North Atlantic and North Pacific right whales, and North Atlantic bowhead whales. These
are the most depleted populations of large whales anywhere in the world. Gray whales and sperm
whales, however, are within or above a range of population sizes that presumably results in
maximum net production, the lower end of the so-called optimum sustainable population (OSP)
level. According to the Marine Mammal Protection Act, a population within or at the lower end
of this range is regarded as no longer depleted. According to this criteria, eastern Pacific
gray whales and sperm whales are candidates for removal from the ESA.
Our knowledge about the recovery of endangered whales is hampered by
insufficient data on how many whales there are and whether the populations are increasing or
decreasing. We have little understanding of the possible impacts of human activities, specific
habitat requirements, or what governs the natural regulation of their populations. Severely
depleted populations of large whales may be particularly vulnerable to the impacts of human
activities and certain kinds of natural changes in the ecosystem because of their low numbers
and low recovery potential. In addition, they may have a difficult time recovering because of
inherent low reproductive potential, resulting in reduced genetic variability, lowered contact
between reproductively active members, and ultimately increased chance of extinction from
large-scale but environmental perturbations.
For a better understanding of how human activities impact small populations
of whales, and to determine whether management actions might help in the recovery process,
additional information is needed on population biology and habitat utilization. The kinds of
information needed for long-term assessment are abundance and trends, stock identification and
structure, seasonal behavior and habit use, disease and other biological condition indices, and
ecological processes. The highest priority for assessing status and trends is having a good
estimate of absolute abundance with a measurement of the variance. The second priority is to
determine which factors in the environment are likely to prevent recovery, including
understanding ecological interactions. For example, recovery may be impeded because human
activities interfere with the whale's normal life history processes, or because of competition
with other organisms in the ecosystem for food and space. Other issues concerning environmental
contaminants and diseases should also be investigated.
Selected references and additional reading
1. Andersen, S. 1989. Science and politics in the international
management of whales. Marine Policy 13(2): 99-117.
2. Baker, C. C., S. R. Palumbi, R. H. Lambertsen, M. S. Weinrich,
J. Calambokidis, and S. J. O'Brien. 1990. Influence of seasonal migration on the geographic
distribution of mitochondrial DNA haplotypes in humpback whales. Nature 344: 238-240.
3. Graham, H. W. 1989. Long-term research at the National Marine
Mammal Laboratory. Bulletin of the Ecological Society of America 70(1): 21-25.
4. Breiwick, J. M. and H. W. Braham (editors). 1984. The status
of endangered whales. Marine Fisheries Review 64(4): 1-64.
5. Brownell, R. L., Jr., P. B. Best, and J. H. Prescott
(editors). 1986. Right whales: Past and present status. Report of the International Whaling
Commission (Special issue 10), International Whaling Commission, Cambridge, U.K.
6. Donovan, G. P. (editor). 1989. The comprehensive assessment of
whale stocks: the early years. International Whaling Commission (Special issue 11), Cambridge,
7. Eberhardt, L. L. and D. B. Siniff. 1977. Population dynamics
and marine mammal management policies. Journal of Fisheries Research Board of Canada 34:
8. Fowler, C. W. 1984. Density dependence in cetacean
populations. In Perrin, W. F., R. L. Brownell and D. P. DeMaster (editors), Reproduction in
whales, dolphins and porpoises,
9. p. 373-379. Report of the International Whaling Commission,
(Special issue 6). International Whaling Commission, Cambridge, U.K.
10. Fowler, C. W. and J. D. Baker. 1991. A review of animal population
dynamics at extremely reduced population levels. Report of the International Whaling Commission
40: (in press).
11. Gulland, J. 1990. Commercial whaling -- The past, and has it a
future? Mammal Review 20(1): 3-12.
12. Hammond, P. S., S. A. Mizroch, and G. P. Donovan (editors). 1990.
Individual recognition of cetaceans: Use of photo-identification and other techniques to
estimate population Parameters. Report of the International Whaling Commission (Special issue
12), International Whaling Commission, Cambridge, U.K.
13. Mlot, C. 1989. The science of saving endangered species.
Bio-Science 39(2): 68-70. National Marine Mammal Laboratory. 1991. Endangered whales: status
update. A report on the 5-year status of stocks review under the 1978 amendments to the U.S.
Endangered Species Act, 37 p., 10 tables. (Available through the U.S. Department of Commerce,
NOAA, National Marine Fisheries Service, 1335 East-West Highway, Silver Springs, Maryland
14. Oldfield, M. L. 1989. Value of conserving genetic resources. Sinaur
Assoc., Inc., Sunderland, MA.
15. O'Brien, S. J. and J. F. Evermann. 1988. Interactive influence of
infectious disease and genetic diversity in natural populations. Trends in Evolution and
Ecology 3(10): 254-259.
16. Rice, D. W. and A. A. Wolman. 1982. Whale census in the Gulf of
Alaska, June to August 1980. Report of the International Whaling Commission 32: 491-497.
17. Soule, M. E. and K. A. Kohn (editors). 1989. Research priorities
for conservation biology, Critical Issues Services: No.1. Island Press, Washington, D.C.
18. Thomas, C. D. 1990. What do real population dynamics tell us about
minimum viable population size? Conservation Biology 4(3): 324-327.
19. U.S. Department of Commerce. 1989. Endangered and threatened
species; listing and recovery priority guidelines. Federal Register 54(102): 22925-22927.
20. Westman, W. E. 1990. Managing for biodiversity. Bio-Science 40(1):
21. Yaffee, S. L. 1982. Prohibitive policy: Implementing the Federal
Endangered Species Act. M.I.T. Press, Cambridge, MA.