Calf Mysteries

By Carrie Cramer, Field Assistant

The dolphin photo-identification (photo-ID) process often feels like solving a puzzle, especially when dealing with calves! To identify dolphins, we primarily analyze the nicks and notches gained over time on their dorsal fins. Scars can sometimes also be used, although they often fade or disappear over time. The overall shape of the dorsal fin can be an additional clue, but it can look deceivingly different when viewed from different angles. Because calves usually have not accumulated many nicks, notches, and scars, their dorsal fins can be extremely difficult to identify. Check out the photos below to see how the dorsal fins of some calves have changed over the past year.

Dorsal fin of one-year-old calf Treasure (TESG) in 2023 (left) versus 2024 (right). Treasure’s fin hasn’t changed much over the past year. Can you spot the two tiny, new notches in the photo from this year?

​Dorsal fin of one-year-old calf Artemisia (AAOO) in 2023 (left) versus 2024 (right). Artemisia’s  fin has changed quite a bit over the past year. We have sighted this calf in close association with its mother, Orazio (OOWB), several times this year, which helped us confirm that it is indeed Artemisia. 

Dorsal fin of two-year-old calf Chomp (CPBE) in 2023 (left) and with fresh wounds in 2024 (right).
 
Dolphin calves remain closely associated with their mothers for their first several years of life, so we can usually identify who their mothers are. When a calf is seen repeatedly swimming and surfacing right alongside an adult, this is a good indication that the adult may be the mother. However, we need to wait a few times to see them, because sometimes other adults will swim closely to calves. Especially in sightings with multiple calves and many other dolphins, it can be tricky to identify the mom-calf pairs. Calves are also notoriously difficult to photograph because they surface more quickly than adult dolphins, as they are still experimenting with their buoyancy. For these reasons, we wait to name a calf and add it to the catalog until it has been seen with its mother on at least three separate days.
 
This year, we’ve been able to identify and name twelve young-of-the-year (YOYs), which are calves born this year. Four of the mothers of these YOYs were not known to be females until they were observed with their calves this year. We have been excited to see one known mother, Bow (BWDI), with two calves in tow this year! Her older calf, Quiver (QRBW), was born in 2021, and Feather (FRBW) was born this year. There are six remaining calves sighted this year who will hopefully gain their names next year!

Furthermore,we recently solved a calf mystery that began in 2022! This calf was only seen once in 2022 with its mother, Mavis (MSWB). Mavis was also only seen once in 2023, and we didn’t get any clear pictures of her calf during that sighting. This year, we saw Mavis with her calf on four separate days, so we were able to name it Beacon (BNMS)! We were excited to discover that Beacon is still alive and well, especially since it had a fresh shark bite wound in 2022. Because Beacon’s dorsal fin has changed a lot since 2022, the scars from this wound were actually very helpful for identifying this dolphin (see photos below).

Calf Beacon (BNMS) with a fresh shark bite wound in 2022 (left) and in 2024 (middle and right). Can you spot the shark bite scars in the photos taken this year?
  
In another interesting calf sighting, we observed the three-year-old calf Velocity (VYSD) without its mom, Speed (SDWE), for the first time. Velocity was seen foraging with six-year-old Bumps (BSWE), who is also a calf of Speed! While we know that dolphin calves nurse and remain closely associated with their mothers for several years, we don’t know exactly how long this period lasts in this population. A long-term study of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Shark Bay, Australia, revealed that the average age that calves were weaned was around four years old, with the youngest weaning ages around two years old and the oldest over eight (Karniski et al. 2018). This is an example of the insights that can only be gained from long-term studies, such as those conducted by CKDP!
 
As we are always collecting more data, we are looking forward to solving more calf mysteries while learning more about the communication and behavior of these fascinating animals!
  
References
 
Karniski, C., Krzyszczyk, E., & Mann, J. (2018). Senescence impacts reproduction and maternal investment in bottlenose dolphins. Proceedings. Biological Sciences, 285(1883). https://doi.org/10.1098/rspb.2018.1123