Age Determination - Cetaceans

In cetaceans, length is usually the first and main clue as to the relative age of an individual and this will of course be species specific. At the bottom of this page you can find standard lengths for various age classes for Atlantic harbor porpoises from the published literature.

Sometimes length is not enough though! Luckily, there are a variety of other clues that can help narrow age down even further. In particular neonatal characteristics, as shown below, can help estimate age to within days or weeks of birth.

Once the necropsy has begun there are other clues that you can use. For example, the presence of milk in the stomach indicates the animal was still in the dependent phase. When combined with length and presence or absence of neonatal characteristics, this can help determine neonate from juvenile for example. Finally, once the gonads are examined, it is often possible to determine whether the animal was mature depending on whether the gonads are mature or not (presence of sperm in the epididymis, presence of corpora in ovaries).

 


 

Below you will find some helpful hints on determining age in cetaeans.

Fetal folds Cetaceans are bent dorso-laterally in womb and this creates characteristic FETAL FOLDS that remain on the sides of the animal for several weeks to months after birth, fading as time progresses. Also notice the FLOPPY DORSAL FIN in the photograph. Traveling through the birth canal would be pretty difficult if the dorsal fin and flukes were the rigid structures they are in juvenile and adult animals! Ouch!
floppy fluke In this image you can see that the FLUKES are still FLOPPY though not quite as flexible as they were shortly after birth.
marginal papillae Another fetal characteristic are MARGINAL PAPILLAE along the outside margin of the tongue.  While the papillae will be retained until the animal is potentially 10-15 years old, they are much more prominent in neonatal animals.  These papillae function in helping the neonate suckle milk even without lips!
fetal hairs You may have learned in school that one of the key features of mammals is the presence of hair! Cetaceans are no exception but they only have hair for a very short period. ROSTRAL HAIRS on the rostrum or beak of the neonate are one of the first characteristics to disappear after birth; in bottlenose dolphins they are usually gone within two to three weeks if not sooner. 
fetal hairs porpoise Look closely! Can you see the ROSTRAL HAIRS on this harbor porpoise neonate?
baby bottlenose dolphin In this photo of a bottlenose dolphin calf, you can see the MARGINAL PAPILLAE, ROSTRAL HAIRS, and the UNERUPTED TEETH in this neonate.
umbilicus All mammals also have a belly button, or umbilicus, and a HEALED UMBILICAL SCAR also occurs very quickly after birth.  In bottlenose dolphins, the scar is usually healed within 2-3 weeks.
adult Beyond the neonatal characteristics, look for internal clues as to age including milk in the stomach indicating a dependent animal while  mature gonads and evidence of a prior pregnancy in females all indicate a fully adult animal.
straight lengths porpoise