Photographic identification of northern bottlenose whales (Hyperoodon ampullatus): Sources of heterogeneity from natural marks

The use of natural marks in capture-recapture studies can lead to unequal c apture probabilities. This paper examined a catalog of northern bottlenose whale (Hyperoodon ampullatus) photographs from the Gully Nova Scotia, to id entify potential sources of heterogeneity. This information can be used to select appropriate individuals and photographs to include in analyses. Indi vidual northern bottlenose whales were sufficiently marked to uniquely iden tify individuals ((x) over bar = 14.5 marks/individual; range 1-67), but no t all mark types persisted over time. Reliable marks were defined as mark t ypes that were not lost over the nine-year study period (notches, back inde ntation, and mottled patches). Individuals were considered reliably marked if they possessed at least one back indentation or mottled patch (located w ithin one dorsal fin width, at the base of the dorsal fin) or a notch on th e dorsal fin. Sixty-six percent (SE = 5%) of the population were reliably m arked. Longterm analyses (months to years) should use only reliably marked individuals, and the results scaled to account for the rest of the populati on. 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 greater than or equal to 4 (on a 6-point sc ale with 6 representing the highest quality) should be included in mark-rec apture analyses sensitive to heterogeneity.