Subject: Longevity of fetal folds and bent dorsal fins (fwd)

Mike Williamson (
Fri, 30 Apr 1999 12:51:53 -0400 (EDT)

---------- Forwarded message ----------
Date: Tue, 27 Apr 1999 15:50:50 +0000
From: Shannon Gowans <>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Longevity of fetal folds and bent dorsal fins

Summary of responses on the longevity of folded over dorsal fins and
fetal folds in young cetaceans

I posted a message to Marmam about the longevity of folded over dorsal
fins and fetal folds in young cetaceans, as I wanted to use
observations of animals with these features to identify calving
seasonality in northern bottlenose whales.  Here is a summary of the
responses I received.

Folded over dorsal fins:
All of the responses indicated that dorsal fins straightened over very
short time periods and may be useful for identifying very young
animals and indicating calving seasonality.  Most responses about the
persistence of folded over dorsal fins came from studies on captive
animals.  The only published reference came from  Tavolga and Essapian
(1957) who state that the dorsal fin in bottlenose dolphins becomes
upright within hours.  This observation was confirmed by several other
trainers of bottlenose dolphins, who had observed in total over 20
births.  There were also rare cases when the dorsal fin never
straightened but remained bent throughout life and may be a congenital
problem.  The straightening (firming up of the dorsal) occurs as the
collagen in the fin cools after birth.

Killer whales also are born with folded over dorsal fins and
observations in captivity the dorsal fins straightened within hours.
Observations in the wild of a calf approximately 2 hours old also had
its fin stiffened.

In contrast, bent dorsal fins of northern bottlenose whales are curved
over and not as floppy as reported in killer whales and bottlenose
dolphins,.  Bent dorsal fins also may last longer in northern
bottlenose whales.  I have one young animal (birthdate unknown) who
was photographically identified 9 days apart and its dorsal was still
folded on the later date. However most young animals had straight

Fetal folds:

The longevity of fetal folds were much more variable and therefore it
is difficult to use the presence of fetal folds to identify potential
birth dates.

Kastelein et al (1990) state that the fetal folds last 6 weeks in
bottlenose dolphins.  Several trainers from other facilities also
indicated that they had observed a similar time frame.  However fetal
folds on bottlenose dolphins in the Moray Firth of Scotland  are still
visible a year after birth (Wilson, 1995).

Observations on southern right whales from birth till approximately 3
months indicate that most animals have lost the fetal folds within 2
weeks of birth and few if any possess fetal folds 4-5 weeks after

Observations of Sowerby's beaked whales had less prominent fetal folds
later on in the summer and it was estimated that fetal folds lasted
approximately 4 months.  Similarly observations of dense beaked whales
indicated that calves approximately 6 months old did not have fetal

Fetal folds in Hector's dolphins lasted approximately 6 months
(Slooten and Dawson, 1988).

Hope this information is useful.  If anyone has further observations,
or would like more detail on any of this information please contact
me.  Thank you to everyone who responded.


Literature cited
Kastelein RA, Dokter T, Zwart P (1990) The suckling of a bottlenose
dolphin calf (Tursiops truncatus) by a foster mother, and information
of transverse birth bands. Aquat Mamm 16:134-138

Tavolga M.C., Essapian F.S.; 'The behavior of the bottlenosed dolphin
(Tursiops truncatus): Mating, pregnancy, parturition and mother-infant
behabvior', Zoologica, 1957, 42, 11-31.

Slooten E, Dawson SM (1988) Studies on Hector's dolphin,
Cephalorhynchus hectori: a progress report. Rep int Whal Commn
(special issue) 9:325-338;

Wilson B (1995) The ecology of bottlenose dolphins in the Moray Firth,
Scotland: a population at the northern extreme of the species' range.
Ph.D. Dissertation, Aberdeen
Shannon Gowans
PhD candidate
Dalhousie University
Halifax Nova Scotia
B3H 4J1
phone: (902)494-3723
fax: (902)494-3736