Subject: Dolphins: Captive breeding request (fwd)

Michael Williamson (
Mon, 24 Mar 1997 19:40:58 -0500 (EST)

---------- Forwarded message ----------
Date: Mon, 24 Mar 1997 12:40:04 -0800
From: MARMAM Editors <marmamed@UVic.CA>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: Re: Captive breeding request (fwd)

---------- Forwarded message ----------
From: Sam Ridgway <>

In response to the question on sex ratio in cetaceans at birth Ridgway and
Benirschke (1977) contains some information on Tursiops born at several
aquaria in North America through 1974 - I count 36 males and 28 females to
that time.  In 1992, I asked my associate, Michelle Reddy, to do a count
on Tursiops in the U.S. Marine Mammal Inventory which would account for
births through 1991.  The count was 65 males and 64 females.  So, for
Tursiops, it looks like about 101 males and 92 females.  I have read that
in most mammals there is a higher ratio of males at birth but males have a
higher mortality rate so that by early adulthood and beyond there tend to
be slightly more females.  There is a great deal of research on sex ratios
and what factors can change them.  So, jumping to some conclusion about
sex ratios in one group or another should be avoided unless one has
controlled experiments or a huge amount of data on which to base
statistical comparisons.
      (1977) Ridgway, S.H. and K. Benirschke, (Eds) "Breeding dolphins,
present status, suggestions for the future." National Technical
Information Service, U.S. Dept. of commerce, pp. 308.
Sam Ridgway

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