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 abundance.

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, UK.

7.  Eberhardt, L. L. and D. B. Siniff. 1977. Population dynamics and marine mammal management policies. Journal of Fisheries Research Board of Canada 34: 183-190.

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 20910.)

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): 26-33.

21. Yaffee, S. L. 1982. Prohibitive policy: Implementing the Federal Endangered Species Act. M.I.T. Press, Cambridge, MA.