Photo-identification of individual humpback whales (Megaptera novaeangliae) using all available natural marks: implications for misidentification and automated algorithm matching technology

As the ventral-tail fluke catalogues used to study humpback whales (Megaptera novaeangliae) increase in size, the time and cost involved with curation and manual photo-identification matching increases accordingly, and this is becoming a significant challenge for field researchers. In addition, misidentification errors in catalogue matching can seriously affect population dynamics parameter estimates and capture-mark recapture estimates of population size. In this study we used long-term photo-identification data, derived from an innovative matching system, which yielded a reconciled catalogue of 2,821 individual ventral-tail flukes and 578 resighting histories in Hervey Bay between 1992 and 2009. To investigate and examine the long-term stability and/or changes in natural marks on ventral-tail flukes, dorsal-fin shapes and lateral body marks, we used a subsample of 79 individual humpback whales, resighted in 2 to 11 years over timespans ranging from 2 to 21 years. A binary logistic mixed effects model was applied to a pair-matched sample of changes of marks in the 79 individual whales. The model found no significant difference between the proportion of changes in primary and secondary ventral tail fluke marks and the proportion of changes in primary dorsal-fin shape characteristics plus secondary lateral body marks (F = 0.939, df = 1/156, p = 0.334). The results of this study substantiate the value and reliability of using ventraltail flukes together with dorsal-fin shapes and lateral body marks, as multiple complementary tags in the photo-identification process. The data were used to discuss minimisation and management of misidentification errors in the photo-identification matching process, and the use of multiple complementary tags in the development of automated algorithm matching technology for white-dominant Southern Hemisphere humpback whale ventral-tail flukes.