Reliability of photographic and molecular techniques for sexing northern bottlenose whales (Hyperoodon ampullatus)

Identifying the sex of living cetaceans can be difficult, even when species are sexually dimorphic. We compare two methods of molecular sexing (ZFY (z inc finger protein gene) and SRY (sex-determining region Y gene)) and evalu ate the effectiveness of photographic techniques for identifying sex in nor thern bottlenose whales, Hyperoodon ampullatus, in the Gully, off Nova Scot ia, Canada. Samples from individuals of known sex from historic Norwegian w haling (n = 19) and from recent strandings (n = 3) were used to test the re liability of the molecular techniques. Although both methods gave accurate results, the ZFY method was found to be unsuitable for degraded (historic) samples, owing to the large size of the target DNA fragment. Results from t he two molecular-sexing methods were in agreement for biopsy samples taken from bottlenose whales in the Gully (7 males and 13 females). Photographs o f the melon profile were used to assign free-swimming animals to the catego ries female - immature male, subadult male, and mature male. Melon photogra phs of adult-sized animals taken up to 7 years apart were consistently assi gned to the same category. Overall, sex identification from melon photograp hs was in agreement with results from molecular sexing. However, animals in the category female - immature male were difficult to assign on the basis of morphological features alone.