Identifying Individual Identifying Individual Bowhead Whales Bowhead Whales Through Aerial Through Aerial
PhotographyPhotography
Supporting organizations• National Marine Mammal Laboratory,
Alaska Fisheries Science Center, NOAA Fisheries Service,Seattle, Washington
• LGL, Ltd. Environmental Research Assoc., King City, Ontario, Canada
• North Slope Borough, Dept. of Wildlife Management, Barrow, Alaska
• Minerals Management Service, Environmental Studies Program, Alaska Outer Continental Shelf Region, Anchorage, Alaska
• Cascadia Research Collective, Olympia, Washington
Available images of bowheads
• There are currently over 17,000 images of bowhead whales in collections archived at LGL and NMML.
• Over the past 30 years, aerial surveys have been conducted mostly near Point Barrow during the spring migration and in the Beaufort Sea in summer.
Whale images are measured for length and corrected relative to camera lens, aircraft altitude (calibrated), and any known photogrammetric biases.
15.5 m
Whale lengths
Growth of individual whales
• Calves are 4.75 - 5.0 m long in May,
and 6.25 - 6.5 m long by October.
• Yearlings in May are 6.5 - 8.0 m long.
• Small whales (~9.5 m) grow 22 - 44 cm/yr.
• Medium size (~12 m) grow 12 - 15 cm/yr.
• Large whales (~15 m) grow 0 - 5 cm/yr.
Components of categorizing bowhead images
ZONESZONES IDENTIFIABILITYIDENTIFIABILITY QUALITYQUALITY
Rostrum H+ 1+
Mid-back H- 1-
Lower back M+ 2+
Fluke M- 2-
U+ 3
U-
X
Four zones used to categorize areas on a bowhead image
Rostrum zone(1)
Mid-back zone(2)
Lower-backzone(3)
Fluke zone(4)
Sizes of marks used in categorizing identifiability
Identifiability by zonesRostrum zone
unmarked(U-)
Mid-back zone(U+)
Lower-back zone (H+) Fluke zone(H+)
Large, fairly
distinctive mark
Large, non- distinctive
markOne medium not unique
mark
Image qualityRostrum zone is quality 1+
(= clearly visible)Mid-back zone is
quality 2+
Lower-back zone is quality 2+ (= adequately visible)
Fluke zone is quality 1+
(=clearly visible)
Some of this zone is obscured
by splash
Computer-assisted matching program
• Because the number of photos in the catalog has been growing, it is becoming necessary to increase matching efficiency through a computer program that prioritizes most likely matches.
Applications of results from bowhead photo-identification
• Abundance estimates
• Growth rates of individual whales
• Calving intervals
• Population dynamics
• Stock structure
Abundance Estimates
n
Photo ID abundance
Ice-based abundance
Spring 1985 641
6,700(3,195-12,561)
6,039(3,300-11,100)Summer 1985 1,069
Spring 1986 401 7,734
(5,400-11,100)Summer 1986 441
Resightings of adult whales with calves indicates calving intervals of 3-4 years
Survival probability is remarkably high for bowheads (0.95 to almost 1.00);
some bowheads live for over a century
Seasonal distribution of bowhead sightings through the spring migration near Barrow
Date bins Census Photos Difference<24 Apr 5.6% 7.8% 2.0%
24-30 Apr 16.5% 6.5% -10.0%1-7 May 24.9% 16.8% -8.0%
8-14 May 30.1% 26.7% -3.0%15-21 May 12.3% 18.8% 7.0%22-28 May 6.6% 13.1% 6.0%
>28 May 4.0% 10.4% 6.0%
Spring migration of bowheads at Barrow(gray = aerial photo data;
burgundy = ice-based census data)
0%5%
10%15%20%25%30%
4/5 to4/21
4/22 to4/28
4/29 to5/5
5/6 to5/12
5/13 to5/19
5/20 to5/26
5/7 to6/10
Stock-structure issues
Resighting dates for bowheads seen on more than one year
during the spring migration
Differences in dates (delta T) between initial sightings and
resightings of individual bowheads migrating past Barrow
0
1
2
3
4
5
6
1 6 11 16 21 26 31
Delta T
Freq
uen
cy
Differences in sighting dates of individual bowhead whales as a
function of whale size
5
10
15
20
0 10 20 30 40
Delta T (days)
Wha
le le
ngth
(m
)
Cumulative frequency of dates of all photographed bowheads
0%
20%
40%
60%
80%
100%
1976-94(not 1985)
1985