PHOTOGRAPHIC IDENTIFICATION OF NORTHERN BOTTLENOSE WHALES (HYPEROODON AMPULLATUS): SOURCES OF HETEROGENEITY FROM NATURAL MARKS

Abstract

The use of natural marks in capture‐recapture studies can lead to unequal capture probabilities. This paper examined a catalog of northern bottlenose whale (Hyperoodon ampullatus) photographs from the Gully, Nova Scotia, to identify potential sources of heterogeneity. This information can be used to select appropriate individuals and photographs to include in analyses. Individual northern bottlenose whales were sufficiently marked to uniquely identify individuals (x̄= 14.5 marks/individual; range 1‐67), but not all mark types persisted over time. Reliable marks were defined as mark types that were not lost over the nine‐yeat study period (notches, back indentation, and mottled patches). Individuals were considered reliably marked if they possessed at least one back indentation or mottled patch (located within one dorsal fin width, at the base of the dorsal fin) or a notch on the dorsal fin. Sixty‐six percent (SE = 5%) of the population were reliably marked. Longterm analyses (months to years) should use only reliably marked individuals, and the results scaled to account for the rest of the population. Our results also showed that photographic quality affected an observer's ability to identify individuals. For this catalog, quantitative analysis indicated only photographs of Q ≥ 4 (on a 6‐point scale with 6 representing the highest quality) should be included in mark‐recapture analyses sensitive to heterogeneity.

Abundance, survival and temporary emigration of bottlenose dolphins (Tursiops sp.) off Useless Loop in the western gulf of Shark Bay, Western Australia

“…There are several special considerations when using photo-identification data for population demographic capture-recapture analyses (Gowans and Whitehead 2001;Friday et al 2008;Hammond 2010). First and foremost, individuals should be photographed so as to ensure sufficient quality to confirm identification, as well as to ensure the photograph passes the quality-grading process.…”

“…Only excellent-and good-quality (≤11) photographs and distinctly marked (D1 and D2) individuals were included in capture-recapture analyses, so as to ensure that more distinctly marked individuals would not have a higher probability of being captured (Gowans and Whitehead 2001) and to reduce errors in data as a result of misidentification. Capture histories, consisting of 1s and 0s, corresponding to whether or not an individual was captured within a sampling period (a run through all 10 transects), were compiled for each identified individual remaining after the photograding process, except calves.…”

“…All photographs containing a dorsal fin were graded for quality so as to minimise misidentification and heterogeneity in capture probabilities (Friday et al 2000;Gowans and Whitehead 2001). The photographic quality-grading protocol used in this study was modified for the Sarasota Dolphin Research Program (2006) from a protocol developed by Urian et al (1999).…”

Evaluating monitoring methods for cetaceans

“…Only highly distinctive (D1) fins in photographs of excellent and good quality were included in the capture-recapture analyses (Gowans and Whitehead 2001;Urian et al 2015). A capture was defined as a photograph of sufficient quality of an individual dolphin's distinctly marked dorsal fin.…”

Injury and Subsequent Healing of a Propeller Strike Injury to a Heaviside's Dolphin (<I>Cephalorhynchus heavisidii</I>)

“…Additionally, frequency, type, and size of body scars on cetaceans have also been used to infer age, sex, and social status in wild populations (Chu & Nieukirk, 1988;Gowans & Whitehead, 2001;Rowe & Dawson, 2008) as well as rates of interaction with other species, particularly predators (Corkeron et al, 1987b;Cockcroft et al, 1989;Gowans & Whitehead, 2001) and humans (Best & Schell, 1996;Best et al, 2001). It is thus important to have some understanding of the healing rate of these injuries.…”