- Population Estimates from 1978-2004
- Population Estimate from 2011
- Acoustic Data Collection during Census
- Passive Acoustic Monitoring Study
Principal Investigator: J. Craig George, Ph.D.
Collaborators: Judy Zeh (University of Washington), Geof Givens (Colorado State University), Chris Clark (Cornell University), Robert Suydam
Funding: NSB, AEWC, NOAA, BP
Summary: The ice-based bowhead whale census began in 1978 by NOAA after the moratorium imposed by the International Whaling Commission (IWC) in 1977 on subsistence whaling of bowhead whales. NOAA had conducted preliminary ice-based surveys before 1978. The IWC's decision on a moratorium was based on NOAA's report that there were fewer than 1000 bowhead whales in the Bering-Chukchi-Beaufort (BCB) stock and on an increasing number of strikes. The census effort was proposed to obtain a more accurate population count of the bowhead whales. The Bowhead Census project was transferred from NOAA to the AEWC in 1981 and then to the NSB Department of Wildlife Management (at that time, the department was named the Environmental Protection Office or EPO) in 1982.
The visual census occurs from about 15 April to the end of May. The census period captures most of the migration but some whales pass before and after the census period. A theodolite is used to position whales in the lead once they are spotted by eye or with binoculars. Three observers work 2-4 hour watches during daylight hours (which is 24 hours roughly by the first week of May). Whale positions are plotted to help determine if the sightings are new or duplicated. Also offshore distribution, whale speed and other statistics are estimated. A new abundance estimate is required by the IWC at least every 10 years.
The 2001 ice-based census estimate was 10,470 (or between 8,100 and 13,500 with 95% confidence intervals) bowhead whales (see George et al. 2004), and an updated estimate was obtained via aerial surveys and photogrammetry in 2004. The graph below shows the population trend as of 2004 when the calf production reached 10.4% and the growth rate was estimated at 3.4%, indicating a healthy, growing population of about 12,634 (or between 7,900 and 19,700 with 95% confidence intervals) (see Koski et al. 2010) bowhead whales in the Bering-Chukchi-Beaufort (BCB) stock.
A new ice-based census (combined with aerial surveys and photogrammetry) was carried out in the springs of 2009, 2010, and 2011. The 2011 bowhead whale census was the most successful ever conducted with full visual, acoustic and aerial coverage of the bowhead migration. After two years of intensive analysis, the new 2011 abundance estimate for the Bering-Chukchi-Beaufort Seas stock of bowhead whales was presented at IWC 2013 in Korea. The estimate is 16,892 with a “margin of error” between 15,704 to 18,928 whales. This stock continues to grow at about 3.7% annually, which indicates that the health status of this population is very good.
This is a drawing of the bowhead whale census camp in 1984. You can see the two perches placed on pressure ridges on either side of the drawing, two small camps, and one main campsite. (Drawing by Craig and Jean Craighead George)
Tim Obritschkewitsch looks through the theodolite to accurately position the location of a bowhead whale sighted in the lead. The theodolite provides the angle, distance and bearing of the sighting from the perch. (Photo credit: NSB-DWM)
This graph shows the population trend for the Bering-Chukchi-Beaufort stock of bowhead whales obtained from census efforts between 1978 and 2001. The 2001 census estimate was 10,470 whales (or 8,100-13,500 with 95% confidence intervals). The population growth rate was estimated at 3.4% (or 1.7-5.0% with 95% confidence intervals) (Source: George et al. 2004). The graph below also includes an estimate from the 2004 photogrammetry work of 12,600 whales (95% confidence intervals 7,900 – 19,700).
The BCB bowhead whale population trend from 1978-2004. The circles indicate ice-based census estimates. The bars on the census estimates are the 95% confidence intervals. (Source: Craig George)
Census coordinators, Craig George and Robert Suydam, Director Taqulik Hepa and Deputy Director Harry Brower, Jr., and all from the NSB-DWM thank the whaling community, AEWC, NSB, NOAA, BP and other entities who have supported our research over the years. Maintaining the bowhead quota is one of our main goals, and this new estimate will help considerably with future quota renewals.
Bowhead Population Estimate 2011
Scenes from the Perch
Bowhead whale breaching in the lead system (photo: Kate Stafford), and...
...splashing in the open lead near Barrow in the spring. (Photo: Peter Lourie)
Scenes from the census camp
On the way to the perch, crossing an active crack in the landfast ice. Note: this is a "good crack" at the beach head and is caused by tidal activity.
This photo shows a typical tent set up at the census camp. Note freight sled set alongside the tent for hauling camp.
This outhouse was carved out of a piece of multi-year ice at the census camp.
This 'bear alarm' is used to alert the census crew if a polar bear enters the campsite. Note the rat trap mechanism at the heart of the device, which was designed by Dave Ramey.
Journal articles and reports on the bowhead census:
Braham, et al. 1984. Bowhead and white whale migration, distribution, and abundance in the Bering, Chukchi, and Beaufort Seas, 1975-1978. NOAA Technical Report NMFS SSRF-778.
Krogman, B.D., et al.1987. A photographic study of environmental factors affecting the 1985 visual and acoustic population estimates of bowhead whales (Balaena mysticetus), passing Pt. Barrow, Alaska. Final report to the North Slope Borough, Dept. of Wildlife Managment, Barrow, Alaska. 36 pp.
George, J.C., et al. 1988. Preliminary report on bowhead whale, Balaena mysticetus, census-related field activities during spring 1987 off Point Barrow, Alaska. Presented to the 39th International Whaling Commission. SC/39/PS13.
Zeh, J.E., and A.E. Raftery. 1990. Population size and trend estimation for the bowhead whale, Balaena mysticetus, from ice-based visual census and acoustic location data. Final report to the Department of Wildlife Management, North Slope Borough, Barrow, Alaska. 200 pp.
Zeh, J.E., and A.E. Raftery. 1996. Popluation assessment methods for the bowhead whale, Balaena mysticetus, and 1994 bowhead assessment results. Report to the Department of Wildlife Management, North Slope Borough, Barrow, Alaska. 260 pp.
George, J.C., et al. 2002. Population size of the Bering-Chukchi-Beaufort Seas stock of bowhead whales, Balaena mysticetus, based on the 2001 census off Point Barrow, Alaska. Presented to the 54th International Whaling Commission. SC/54/BRG5.
George, J.C., et al. 2004. Abundance and population trend (1978-2001) of western arctic bowhead whales surveyed near Barrow, Alaska. Marine Mammal Science 20(4):755-773.
Taylor, B.L., et al. 2007. Synthesis of lines of evidence for population structure for bowhead whales in the Bering-Chukchi-Beaufort region. Presented to the 59th International Whaling Commission. SC/59/BRG35.
George, J.C., and R. Suydam. 2009. Preliminary report of the spring 2009 ice-based bowhead whale census activities near Barrow, Alaska. Presented to the 61st International Whaling Commission. SC/61/BRG23.
George, J.C., et al. 2010. Preliminary results of the 2010 ice-based whale census at Barrow, Alaska. Presented to the 62nd International Whaling Commission. SC/62/BRGWP__.
Givens, G. H., et al. 2011. Estimation of detection probabilities from the 2010 ice-based independent observer survey of bowhead whales near Barrow, Alaska. Presented to the 63rd International Whaling Commission. SC/63/BRG1.
George, J.C., et al. 2011. Report of the 2010 bowhead whale survey at Barrow with emphasis on methods for matching sightings from paired independent observations. Presented to the 63rd International Whaling Commission. SC/63/BRG3.
Givens, G. H., et al. 2012. Detection probability estimates from the 2011 ice-based independent observer survey of bowhead whales near Barrow, Alaska. Presented to the 64th International Whaling Commission. SC/64/BRG4.
Givens, G. H., et al. 2013. Estimate of 2011 Abundance of the Bering-Chukchi-Beaufort Seas Bowhead Whale Population. Presented to the 65th International Whaling Commission. SC/65a/BRG01.
George, J.C., et al. 2013. Summary of the spring 2011 ice-based visual, acoustic, and aerial photo-identification survey of bowhead whales conducted near Point Barrow, Alaska. Presented to the 65th International Whaling Commission. SC/65a/BRG11.
Givens, G.H., et al. 2015. A population dynamics model and assessment of Bering-Chukchi-Beaufort Seas bowhead whales. Presented to the 66th International Whaling Commission. SC/66a/BRG09.
Givens, G.H., et al. 2016. Horvitz-Thompson whale abundance estimation adjusting for uncertain recapture, temporal availability variation, and intermittent effort. Environmetrics 27:134-146.
Givens, G.H., et al. 2017. Survival rate and 2011 abundance of Bering Chukchi Beaufort Seas bowhead whales from photo-identification data over three decades. Submitted as paper SC/67a/AWMP/09 to the Scientific Committee of the International Whaling Commission, May 2017.
Salomi Akpik, Kate Stafford, Perry Anashugak and Jason Herreman looking for whales from the perch in 2009.
Along with the visual count, the bowhead whale census project added the collection of acoustic data in 1984. Hydrophones were placed in the water along the edge of the lead. Received sounds were transmitted to and recorded in a small shed on runners, the 'sledshed,' that contained the acoustic equipment. The technicians sitting in the shed monitored the hydrophones to make sure the hydrophone array and computer equipment was functioning and to note the number and types of whale calls. Acoustic surveillance continues throughout the ice-based census (24 hours/ 7 days a week) mainly to estimate the proportion of whales greater than 4 kilometers offshore. The acoustic data provides an important correction factor for the visual population estimate. For bowhead sounds and other marine mammal sounds collected, see this page. Go to this page for our current Passive Acoustic Monitoring Study.
The 'sledshed' containing the sound recording equipment for the hydrophone array placed on the edge of the lead during the ice-based census. On runners, it was designed to be easily moved during ice emergencies.
Dr. Chris Clark, from the Laboratory of Ornithology, Cornell University, inside the sledshed in 1984, listening to the hydrophones.
Diagram of the acoustic zone compared to the visual range for ice-based census. The star denotes the location of the perch and the black dots denote the placement of the hydrophones. The location of the whale call was obtained through a technique roughly similar to "triangulation." Time delays of sounds received at several hydrophones are measured to compute positions. (Source: George et al. 2004)
Graphic display of bowhead whale acoustic locations, obtained from the hydrophone array in 2001. The zero point (0,0) is the location of the census 'perch' used for the visual count. The blue line indicates the approximate 4 kilometer limit of visual range. (Source: NSB-DWM)
Mike Wald and Billy Adams placing a Cornell MARU (marine autonomous recording unit) under the ice in a refrozen lead during the 2009 census. This new technology collects and stores acoustic data and can be retrieved at a future date. It eliminates the need for the 'sledshed' and personnel to monitor the array in real time.
Acoustic Data from the Fall Migration of Bowhead Whales
Moore, S.E. et al. 2006. Listening for large whales in offshore waters of Alaska. Bioscience 56(1):49-55.
Abstract: "In 1999, the first phase of a multiyear program was initiated at the National Oceanic and Atmospheric Administration’s National Marine Mammal Laboratory and Pacific Marine Environmental Laboratory to advance the use of passive acoustics for the detection and assessment of large whales in offshore Alaskan waters. To date, autonomous recorders have been successfully deployed in the Gulf of Alaska (1999–2001), the southeastern Bering Sea (2000–present), and the western Beaufort Sea (2003–2004). Seasonal occurrences of six endangered species (blue, fin, humpback, North Pacific right, bowhead, and sperm whales) have been documented on the basis of call receptions in these remote ocean regions. In addition, eastern North Pacific gray whale calls were detected in the western Beaufort Sea from October 2003 through May 2004. Here we provide an overview of this suite of research projects and suggest the next steps for applying acoustic data from long-term recorders to the assessment of large whale populations."
More journal articles and reports on acoustics:
Clark, C. 1983. The use of bowhead vocalizations to augment visual censusing estimates on the number of whales migrating off Barrow, Alaska in the spring of 1980. Report to the North Slope Borough, Dept. of Wildlife Management, Barrow, Alaska. 21 pp.
Clark, C.W., W.T. Ellison, and K. Beeman. 1986. An acoustic study of bowhead whales, Balaena mysticetus, off Point Barrow, Alaska during the 1984 spring migration. Report to the North Slope Borough, Dept. of Wildlife Management, Barrow, Alaska. 145 pp.
Krogman, B.D., D.R. Corbit, and W.T. Ellison.1987. A photographic study of environmental factors affecting the 1985 visual and acoustic population estimates of bowhead whales (Balaena mysticetus), passing Pt. Barrow, Alaska. Final report to the North Slope Borough, Dept. of Wildlife Managment, Barrow, Alaska. 36 pp.
Clark, C.W., W.T. Ellison and K. Beeman. 1988. An acoustic study of bowhead whales, Balaena mysticetus, off Point Barrow, Alaska during the 1985 spring migration. Report to the North Slope Borough, Dept. of Wildlife Management, Barrow, Alaska. 143 pp.
Clark, C.W. and W.T. Ellison.1988. Numbers and Distributions of bowhead whales, Balaena mysticetus, based on the 1985 acoustic study off Pt. Barrow, Alaska. Report to the International Whaling Commission 38:365-370.
Clark, C.W. and W.T. Ellison. 1989. Numbers and distributions of bowhead whales, Balaena mysticetus, based on the 1986 acoustic study off Pt. Barrow, Alaska. Report to the International Whaling Commission 39:297-303.
Zeh, J.E. and A.E. Raftery. 1990. Population size and trend estimation for the bowhead whale, Balaena mysticetus, from ice-based visual census and acoustic location data. Final report to the Department of Wildlife Management, North Slope Borough, Barrow, Alaska. 200 pp.
Clark, C.W., R. Charif, S. Mitchell and J. Colby. 1996. Distribution and behavior of the bowhead whale, Balaena mysticetus, based on analysis of acoustic data collected during the 1993 spring migration off Point Barrow, Alaska. Report to the International Whaling Commission 46:541-552.
Clark, C.W. 1998. Acoustic study of the bowhead whale, Balaena mysticetus, conducted during the 1993 spring migration off Point Barrow, Alaska. Final report to the Department of Wildlife Management, North Slope Borough, Barrow, Alaska. 168 pp.
Clark, C.W. and W.T. Ellison. 2000. Calibration and comparison of the acoustic location methods used during the spring migration of the bowhead whale, Balaena mysticetus, off Pt. Barrow, Alaska, 1984-1993. The Journal of the Acoustical Society of America 107(6):3509-17.
Clark, C.W., R. Suydam, and C. George. 2010. Acoustic monitoring of the bowhead spring migration off Pt. Barrow, Alaska: Results from 2009 and status of 2010 field effort. Presented to the 62nd International Whaling Commission. SC/62/BRG17.
Clark, C.W., et al. 2013. Acoustic data from the spring 2011 bowhead whale census at Point Barrow, Alaska. Presented to the 65th International Whaling Commission. SC/65a/BRG09.
Clark, C.W., et al. 2018. Acoustic data from the spring 2011 bowhead whale census at Point Barrow, Alaska. Journal of Cetacean Research and Management 19:31-42.
Banner photo credit: Lisa Baraff