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 (zinc finger protein gene) and SRY (sex-determining region Y gene)) and evaluate the effectiveness of photographic techniques for identifying sex in northern bottlenose whales, Hyperoodon ampullatus, in the Gully, off Nova Scotia, Canada. Samples from individuals of known sex from historic Norwegian whaling (n = 19) and from recent strandings (n = 3) were used to test the reliability 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 the two molecular-sexing methods were in agreement for biopsy samples taken from bottlenose whales in the Gully (7 males and 13 females). Photographs of the melon profile were used to assign free-swimming animals to the categories female - immature male, subadult male, and mature male. Melon photographs of adult-sized animals taken up to 7 years apart were consistently assigned to the same category. Overall, sex identification from melon photographs 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.