Occurrence of killer whale Orcinus orca rake mark occurrence on Eastern Canada-West Greenland bowhead whalesBalaenamysticetus
Polar Biology
N.R. Reinhart1
S.H. Ferguson
W.R. Koski
J.W. Higdon
B. LeBlanc
O. Tervo
P.D. Jepson
1 Corresponding author
Royal Veterinary College, Royal College Street, London, NW1 0TU, United Kingdom,
Institute of Zoology, Zoological Society of London, Regent’s Park, London, NW1 4RY, United Kingdom
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Zone / Description
Ventral fluke, left / Referring to the whale’s left; ventral surface of the fluke, extending medially from the leftmost portion of the fluke and terminating at the median notch. Terminates anteriorly where the tailstock begins at the base of the fluke
Ventral fluke, right / Referring to the whale’s right; ventral surface of the fluke, extending medially from the rightmost portion of the fluke and terminating at the median notch. Terminates anteriorly where the tailstock begins at the base of the fluke
Ventral tailstock / Ventral surface of the tailstock/caudal peduncle extending from the base of the fluke anteriorly to the point on the ventral surface directly beneath the dorsal keel. Extends posteriorly to include the ventral median portion of the fluke that separates the fluke into left and right halves
Dorsal tailstock / Dorsal surface of the tailstock/caudal peduncle extending from the base of the fluke anteriorly to the dorsal keel. Extends posteriorly to include the dorsal median portion of the fluke that separates the fluke into left and right halves
Dorsal fluke, left / Referring to the whale’s left; dorsal surface of the fluke, extending medially from the rightmost portion of the fluke and terminating at the median notch. Terminates anteriorly where the tailstock begins at the base of the fluke
Dorsal fluke, right / Referring to the whale’s right; dorsal surface of the fluke, extending medially from the leftmost portion of the fluke and terminating at the median notch. Terminates anteriorly where the tailstock begins at the base of the fluke
Table 2 Rating system for the degree of scarring for images of EC-WG bowhead whales used in the current study. Rankings were applied to each defined zone on whale flukes and tailstocks, unless <10% of the zone was visible. Degree of scarring rankings recognize whales that may be more easily re-identified based on the presence of distinct scars and/or the number of rake mark sets if present (adapted from Rugh et al. 1998 and Steiger et al. 2008)
Rank / Description
5 / Scarring is severe with three or more sets of rake marks. Damage from rake marks is substantial enough to damage the zone and/or fluke’s integrity. The individual is considered easily re-identifiable due to the presence of distinct and high numbers of rake marks and potentially other scars and/or scratches
4 / Scarring is severe with three or more sets of rake marks. Damage should have no effect on the zone and/or fluke’s integrity. The individual is considered easily re-identifiable due to the presence of rake marks and potentially other scars and/or scratches
3 / Scarring is moderate with one or two sets of rake marks. The individual may be easily re-identifiable depending on the distinctiveness of the rake mark(s). Other scars and/or scratches may also be present and if distinct, may make the whale more easily re-identifiable. Scarring size, severity and/or location may contribute to a more distinctive scar, scratch or set of rake marks
2 / Scratches and scars are present, but are not congruent with the rake mark definition in the present analysis. The individual may be fairly re-identifiable depending on the distinctiveness of the scars and/or scratches. Scarring size, severity and/or location may contribute to a more distinctive scar or scratch
1 / No visible rake marks, scratches or scars are present; the zone may be entirely monochromatic if no white or grey is present. The individual is not easily re-identifiable by use of scar or scratch presence and/or distinctiveness
Table 3 Ranking system for photographic quality that incorporates the visibility of each defined zone on bowhead whale flukes and tailstocks, as well as photograph quality criteria. Each zone received a score for image quality in the present study, unless <10% was visible (adapted from Rugh et al. 1998)
Rank / Description
5 / The entire zone (100%) is clearly visible with no factors affecting visibility and/or clarity of the zone, allowing even small or faint scratches, scars and/or rake marks to be identified if present. Nothing compromises or blocks visibility of the designated zone. The whale comprises ≥50% of the photograph. The image is neither under- or over-exposed and image contrast is neither too low or too high
4 / Seventy to 100% of the zone is visible. Some factors may affect the visibility and/or clarity of the zone, but still allows even small or faint scratches, scars and/or rake marks to be identified if present. Factors may compromise or block the visibility of the designated zone, however not >30%. The whale comprises ≥50% of the photograph. The image is neither under- nor over-exposed and image contrast is neither too low nor too high
3 / Some of the zone may be partially blocked from view, such that only 50 to 70% of the zone is visible. Large and/or distinct scratches, scars and/or rake marks are identifiable if present. Other factors may compromise the visibility of the zone such as water, camera blur or motion, such that faint and/or small and medium marks may be missed if present. The whale comprises ≥30% of the photograph. The image may be slightly under- or over-exposed and/or contrast may be slightly too high or too low, however not enough to affect the visibility of any size scratches, scars and/or rake marks if present
2 / Some of the zone may be partially blocked from view, such that only 20 to 50% of the zone is visible. Physical obstructions such as another whale, person or a boat may be present. Other factors such as water, glare, camera blur or motion may compromise the visibility and/or image clarity of the zone, such that faint and/or small and medium marks are unidentifiable and/or not visible if present. The whale may comprise ≥30% of the photograph. The image may be under- or over-exposed and/or contrast may be too high or too low, enough to affect the visibility of small and/or some medium scratches, scars and/or rake marks if present
1 / Only 10 to 20% of the zone is visible. Physical obstructions such as another whale, person or boat may be present. Obstructions to visibility and/or image clarity such as water, sun glare, camera blur or motion prevent any scars, scratches and/or rake marks from being identified if present. The whale may comprise <10% of the photograph. The image may be greatly under- or over-exposed and/or contrast may be too high or too low, enough to affect visibility of small, medium or large scratches, scars and/or rake marks if present
No score / The zone is partially (<10%) or entirely obstructed. If present, scars, scratches and/or rake marks of any size are not likely identifiable due to other factors affecting the visibility of the zone and/or image clarity such as water, camera blur or motion. Physical obstructions such as another whale, person, boat or water may be present. The whale may comprise <10% of the photograph. Contrast may be too high or too low and the image may be greatly under- or over-exposed, enough to affect the visibility of small, medium or large scratches, scars and/or rake marks if present. No accurate scarring estimate can be made as the accurate degree of scarring cannot be observed
Table 4 Cross-tabulation of the number of whales identified per year and region
Region
Year / Cumberland Sound / Disko Bay / Foxe Basin / Isabella Bay / Repulse Bay / Total
1986 / 0 / 0 / 0 / 44* / 0 / 44
2007 / 0 / 0 / 128 / 0 / 0 / 128
2008 / 0 / 0 / 37 / 0 / 26 / 63
2009 / 0 / 0 / 188 / 0 / 0 / 188
2010 / 0 / 35 / 0 / 0 / 0 / 35
2011 / 30 / 43 / 0 / 0 / 0 / 73
2012 / 0 / 0 / 67 / 0 / 0 / 67
Total / 30 / 78 / 420 / 44 / 26 / 598
*Only one year and region is represented in this group of whales.
Table 5Total number of photographs and whales identified and used in the present analysis by region and corresponding year(s) and month(s)
Region / Year(s) / Month(s) / Total number of photographs / Total number of whales identified / Number of whales used in the present analysis (NT) / Flukes from NT available for I3S Contour
Isabella Bay / 1986 / Sep / 94 / 89 / 44 / 0
Repulse Bay / 2008 / Sep / 549 / 43 / 26 / 8
Disko Bay / 2010 / Mar – May / 336 / 38 / 35 / 14
2011 / Mar – May / 369 / 66 / 43 / 11
Cumberland Sound / 2011 / Aug / 544 / 49 / 30 / 10
Foxe Basin / 2007 / Jun – Jul / 456 / 183 / 128 / 24
2008 / Jun - Jul / 413 / 44 / 37 / 14
2009 / Jun – Jul / 2083 / 229 / 188 / 69
2012 / Jul / 431 / 82 / 67 / 29
Total / 5266 / 823 / 598 / 179
Table 6 Descriptive statistics and SPSS outputs for all four predictor variables used in statistical analysis
Variable / Total whales identified / Whales identified with rake marks / Proportion of whales with rake marks (%) / Odds ratio (OR) / 95% Confidence intervals (CI) / Significance in ULR (P value)
Year
1986*1 / 44 / 1 / 2.3 / N/A / N/A / 0.1101
2007/2008*2 / 154 / 14 / 9.1 / 4.31 / (0.6, 33.7)1 / 0.1651
N/A2 / N/A2 / 0.1882
2009/2010 / 260 / 25 / 9.6 / 4.81 / (0.6, 34.7)1 / 0.1411
1.12 / (0.5, 2.1)2 / 0.8602
2011/2012 / 140 / 21 / 15.0 / 2.61 / (1.0, 58.1)1 / 0.0511
1.82 / (0.9, 3.6)2 / 0.1222
Sex
Female / 11 / 4 / 36.4 / N/A / N/A / N/A
Male / 0 / 0 / 0.0
Unknown / 587 / 57 / 9.7
Age
Adult* / 79 / 8 / 10.1 / N/A / N/A / 0.874
Sub-adult / 81 / 6 / 7.4 / 0.7 / (0.2, 2.2) / 0.544
Juvenile / 20 / 1 / 5.0 / 0.5 / (0.1, 4.0) / 0.486
Calf / 12 / 0 / 0.0 / 0.0 / (0.0, 0.0) / 0.999
Region
Foxe Basin* / 420 / 11 / 2.6 / N/A / N/A / < 0.0001**
Repulse Bay / 26 / 11 / 42.3 / 18.5 / (7.4, 46.7) / < 0.0001**
Disko Bay / 78 / 30 / 38.5 / 15.8 / (8.0, 31.0) / < 0.0001**
Isabella Bay / 44 / 1 / 2.3 / 0.6 / (0.1, 4.5) / 0.610
Cumberland Sound / 30 / 3 / 10.0 / 2.8 / (0.8, 10.2) / 0.118
*Variables used as the reference variable in univariate logistic regression. **Variable(s) with an overall significance of <0.05.
1Univariate logistic regression including 1986. 2Univariate logistic regression excluding 1986.
Table 7 Minimum, maximum and mean image quality scores by year for identified whales
Year / Minimum / Maximum / Mean
1986 / 1.3 / 2.0 / 1.7
2007/2008 / 1.3 / 5.0 / 2.2
2009/2010 / 1.2 / 5.0 / 2.5
2011/2012 / 1.2 / 4.8 / 2.5