Calf mortality
- Groups of dolphins containing calves are more vulnerable sound disturbance than adult only groups.
- 75% of all calves die before reaching adulthood.
- No new calves were born during summer calving season (December-February) in 2019-20.
How do we know calves are not surviving?
Photo Identification – researchers take photos of every dolphin in the group, focusing in on their dorsal fin. The dorsal fin of a dolphin is as unique as a human finger print, allowing scientist to track individual dolphins movements. By creating a catalogue of fin and tracking re-sightings of individuals a population size can be calculated. By tracking calves and their mothers researchers can document calf survival. Calves can only survive independently of their mother once they reach two years old. If a mother is seen without her calf (when the calf is less than 2 years old) on three or more occasions this calf is deemed to have not survived.
Is research on why they are not surviving underway?
Photogrammetry – researchers are using calibrated lasers on an SRL camera to accurately measure the size and development of calves in the Bay of islands with minimal impact. This research began in 2019 and will continue.
Do researchers examine calves that have not survived?
Necropsy – when a calf dies, it is important that researchers allow the natural grief behaviour of marine mammals. This can effect the whole pod/group and last for several days. As such researchers do not interfere with this process and remove the calf. This means information from forensic necropsy is lacking.
“Without babies, marine mammal populations have no future. We need to think about the future generations of both dolphins and humans, if we can’t co-exist we will all feel the effects.” Dr. Cat Peters
