Expert report on the sex determination of Timmy/Hope

On 17 April 2026, at around 09:45, drone footage was captured documenting a humpback whale rolling in shallow water. The animal rolls from a prone position over its left side and, during this movement, briefly exposes parts of its ventral side before returning to the prone position. During this process, anatomical features in the genital area become visible, allowing for a subsequent determination of its sex. The previously unpublished footage is shown exclusively on this platform and has been used for the subsequent sex determination of Timmy/Hope. Veterinarian and long-time cetacean specialist author Jan Herrmann was commissioned to carry out the professional assessment of this footage.

Jan Herrmann has been intensively involved with whales and dolphins for more than three decades. The veterinarian is a co-founder and managing editor of the specialist portal Cetacea.de. His work focuses on the biology of cetaceans, North Sea whales, harbour porpoises, stranding events, and scientific marine mammal literature. He has a particular interest in humpback whales, having studied their occurrence, behaviour, and development in the North and Baltic Seas for many years.

In his expert report, Jan Herrmann refers to the scientific work of Deborah Glockner-Ferrari.

Deborah Glockner-Ferrari is one of the pioneering humpback whale researchers who scientifically studied the sex determination of living humpback whales based on externally visible anatomical features. Her study published in 1983, ‘Determining the sex of humpback whales (Megaptera novaeangliae) in their natural environment’, is one of the relevant scientific sources in this field (additional information on the person: historical photo of Glockner-Ferrari from 1992).

Jan Herrmann's expert report is available for download at the end of our report.

Excerpt: After a long stay in the Baltic Sea and repeated strandings, the humpback whale was last located in shallow water in the mud off Poel. Drone footage of the whale was taken there. From minute 0’22 to 0’52 of the provided drone footage, the whale performed a roll over its left side. During this roll, the humpback whale showed its ventral side and the genital slit became visible. As a detail of the genital slit, a hemispherical protrusion was visible here at the caudal (tail-facing) edge. This protrusion corresponds to the ‘hemispheric lobe’ described by GLOCKNER (1983) as an external distinguishing feature of female humpback whales. It is absent in male humpback whales.

This sex determination does not offer the same level of certainty as determination via behaviour (cow with calf) or genetics. However, it allows for the statement that this humpback whale is highly likely to be a female animal.