Subject: Dolphins

Lindsay J Porter (
Wed, 25 Jun 1997 13:54:06 +0800

>What are the names of the different kinds of dolphins, how do you tell
>the Difference between a male and a female fish, what body of water is
>the deepest in the world how and how deep is the Atlantic Ocean?

Dear Evan,
A lot of qustions that cannot be easily answered!!!!

First - dolphins, if you classify 'dolphins' strictly as those species in
the family delphinidae (and include river dolphins) there are approximately
40 species.  There is still some discussion and discovery to be made over
these as some dolphins are rarely seen and poorly understood - or are
physically similar but are infact very different genetically.  In addition
to dolphins - there are beaked whales, mesoplodons, white whales, porpoise,
baleen whales and sperm whales - which are all separated by differences in
morphology and lifestyle and yet science is still investigating these
differences at a biological level.  A good reference that explains all this
in detail is The Sierra Club HAndbook of Whales and Dolphins.  Leatherwood,
S. and Reeves, R.R.  San Fransisco: Sierra Club Books 1983.

Second - fish - a little out my field!!  Of the thousand of fish species in
our oceans there are many different ways to tell the difference in sexes
depending on species.  Biologically - cut the fish up and look for the
reproductive organs - males having gonads and females ovaries.  Some species
do however change sex throughout their life stages - depending on the
surrounding environment (ie skewed sex ratios within the population).
Physically some  species have very different morphology depending on sex -
ie the male fish will be more colourful or flamboyant compared to the
female, like Siamese Fighting Fish (males are rainbow blue with extravegant
fins, females are a dull red/brown).  

Third - the deepest part of the worlds oceans is the Mariannas Trench -
which lies to the west of the Pacific, near the Philippines and is approx.
11000m deep.  The basin of the Atlantic is approx. 5000m deep although
bisecting teh Atlantic there is the atlantic ridge - whch is like an
underwater mountain range the highest part of which is apprx. 1000m below
the surface.

If you have any further questions - or wish me to expand on teh above -
please don't hesitate to email me again

best wishes

Lindsay J Porter
Dolphin Research Group
The Swire Institute of Marine Science
The University of Hong Kong
Cape d'Aguilar
Shek O
Hong Kong