Fish normally have one pair of gill openings. Sharks have 5, 6, or 7 pair of gill openings. These gill openings
will be located on the sides of the head. (The 18 species of flat, bottom dwelling angel shark's gills are an
exception.They are more like the skates and rays that have their multiple gill openings on the underside.
All sharks in New England will have 5 pair of gill openings.
There are approximately 500 species of sharks around the world.
Most of them have five pairs of gill openings.
Only a total of 7 shark species out of 500, have 6 or 7 pair of gill openings,
and they are not in the New England area.

Six gill sharks :
Bluntnose sixgill -
Hexanchus griseus
Bigeye sixgill - Hexanchus nakamurai
Frilled shark - Chlamydoselachus anguineus
Southern african frilled shark-Chlamydoselachus africana
Sixgill sawshark - Pliotrema warreni (8 other species of sawsharks have 5 pairs of gills)

Seven gill sharks:
Broadnose sevengill - Notorynchus cepedianus
Sharpnose sevengill - Heptranchias perlo

Sharks have their skin covered with dermal denticles,
which are tooth like scales. The pattern and roughness
of these scales will vary depending on the shark species.
These are not the flaky scales we are used to seeing
on other fish. These denticles give the skin an abrasive
feeling - very abrasive on some species and relatively
smooth on others. A basking shark has very abrasive
skin. The silky shark has relatively smooth skin.

There are many shark species that lack a fork
in their tail that would define an upper and lower
tail lobe, as you can see on the zebra shark below.

What is a shark?

On the right are many different size and
shaped fish that qualify to be sharks, because
they have multiple pairs of gills, and meet the
other requirements of shark classifications.
Fully grown, some shark species are less than
a foot long, and several are over 20 feet long.
When scientists break down sharks into
categories they use the following methods.
They start with grouping by whether the shark
has an anal fin or not. (The anal fin is a single
fin closest to the tail on the bottom side.)
The other fin on the bottom side is the pelvic
fin, which is paired, and closer to the pectoral
Then the classification branches off into two
groups using several more criteria to place the
Ultimately, you end up with roughly 500 shark
species in 2015, put into 34 shark families.
Some families having only 1 member and
others having many.

Not all sharks have eye protection called nictitating membranes.
There are many shark species that lack this type of eye protection.
They can roll their eyes back into the eye socket for protection.
Species in New England coastal waters without a nictitating membrane are:
the white, shortfin mako, porbeagle, thresher, sand tiger, dogfish, and basking shark.

The mako below left, which lacks a nictitating membrane, rarely rolls its eyes for protection no matter what
difficulty it is in. The blue shark below right, has brought up it's nictitating membrane for protection.

How to identify male and female sharks
It's easy. A male shark will have two claspers extending from his pelvic fins.
The male's two rod like white claspers are visible in the picture below on the right.
A female will not have claspers as shown in the photo below on the left.
In case you are wondering only one clasper will be used during mating.
Welcome to

An example of a forked tail
Shark eyes.
Any fin on the back is a dorsal fin. Dorsal fin
characteristics on sharks can vary widely from
species to species. Dorsal fin size and location
on sharks also varies. Examples: having only one dorsal fin (six and seven gill sharks); or having two
dorsal fins nearly the same size (sandtiger,
Carcharias taurus - lemon shark, Negaprion brevirostris, plus
many others.) The most common dorsal fin configuration for a shark in New England is having the first
dorsal much larger than the second. The sandtiger and spiny dogfish are two New England examples of
having a fairly large second dorsal
. Rigid pectoral fins are a characteristic most sharks share in common.
The shark's pectorals don't fold back against the body as they do in other fish species.
From JAWS -
"And, you know, the thing about a shark... he's got lifeless eyes. Black eyes. Like a doll's eyes. When he
comes at ya, doesn't seem to be living... until he bites ya, and those black eyes roll over white and then...
ah then you hear that terrible high-pitched screamin'. The ocean turns red, and despite all the poundin'
and the hollerin', they all come in and they... rip you to pieces."
(Not all shark species have black eyes.)

Sandbar - Carcharhinus plumbeus
Carcharias taurus
A shark
with a ridge
on its back is
called a
"ridgeback" shark.
Notice both species
have a yellowish eye but
the sandbar eye has a
vertical pupil, and the
sandtiger has a round

The sandbar has a
"ridge" on its back; as
does the dusky and

The sandtiger is not a
"ridgeback" shark.
A problem with gathering information on sharks is that they are cartilaginous, without rib cages, with very
little if any bone in their bodies. So there aren't any fossilized bony skeletons with rib cages to analyze.
Only shark teeth survive, or a few fossilized impressions. Until recently the so-called shark experts did not
spend much time out on the water. Henry B. Bigelow and William C. Schroeder were noticeable exceptions
to this. Their book
Fishes of the Gulf of Maine was written from hands on experience over 60 years ago.

Recreational anglers participating in shark tagging have helped in some areas of shark study; especially
migratory patterns, and age /growth studies.

I will give you a couple of examples of how gathering shark information has been a slow process.
It's a big ocean, and the number of scientists working on sharks has always been small, increasing somewhat
in recent years, and no doubt being helped by new technology; and also being helped by them getting off
their asses and getting out of the lab and onto, and into the water. Recently, I was at a seminar and a young
female biologist summed it up about the same, when one of her slides said. "What we need are more marine
biologists peeing in the ocean."

These anecdotes will give you an idea of how far behind the times shark researchers were.
Our New England porbeagle,
Lamna nasus, was classified in 1788, but its relative, the West Coast salmon
Lamna ditropis, wasn't classified as a separate species until 1947, a passage of 159 years.

The shortfin mako,
Isurus oxyrinchus was classified in 1810, but the longfin mako, Isurus paucus, wasn't
classified as a separate species until 1966.

In the past, the dangerous salt and freshwater going bull shark,
Carcharhinus leucas, was thought to be
several different shark species. The Lake Nicaragua shark, the Zambezi shark, are in fact bull sharks and
not separate species as was implied in the past.

The plankton eating Megamouth shark,
Megachasma pelagios, was not known to exist until an accidental
capture of one in 1976. In early 2014 the 58th megamouth was documented. Incredible that a shark species
that may reach 18 feet in overall length, was not documented until 1976.

The Australian black tip shark (Carcharhinus tilstoni) and the common black tip shark (C. limbatus) have
overlapping distributions along the northern and eastern Australian coastline. There are biologists who
claimed in 2011 that these two species have interbred.

Caution- older literature on sharks contains inaccuracies, omissions, exaggerations, and has missed
many of the existing species. The so-called shark experts of the past knew very little about sharks.

During the July, 1916 shark attacks off New Jersey, where 4 people were killed and 1 seriously injured, the
statements to the newspapers made by so called credentialed experts about sharks were naive and
ridiculous. Unfortunately some of that mis-information still persists to this day.
Because of the abundance of new information gathered in the last few years on sharks; read the latest
literature, and get it from more than one source. Sometimes the experts are wrong. -tom

A blue shark will
have a white ring
around its eyes.
A mako will not.
Sharks have several eye
configurations; such as a contrasting
Iris, with vertical slit pupils, horizontal
slit pupils, or more rounded pupils,
similar to our eyes. The eyes are also
of different colors. Some
species have black eyes, but many
other sharks do not.
When I say black, that is what it will
look like to you and me at a distance.
Inside of the outer coating on some
shark's eyes there may be a diferent
color in there, that can only be seen
from a very short distance.
Sandtigers have yellow eyes with a
round black pupil. (see below)
This mako was released
because it was thought
to be a blueshark
because of the body
coloring. Take a look
at the eyes of
each species.
Blue shark
Prionace glauca
Mako Isurus oxyrinchus