How many sharks are in the waters of the eight major Hawaiian islands
within a 5 mile boundy?

There are 8 sharks within a 5 mile boundary.  Well, except for during
summertime, when the baby sharks are home from college.  Then, there
are 11 sharks.

My joke is intended to show you that your question is somewhat
ridiculous.  Because sharks swim, it is difficult to emphatically
state how many sharks are within said boundary at any given time. 
Average values are available, no doubt, but the way you have worded
the question, it would be impossible to answer.

I'm responding to the comment made about the question of sharks.
Actually, sharks are territorial and tend to stay in specific regions
so it would be possible through tracking devices and other methods of
data collection to determine the approximate density of sharks in a
given area over a period of time. The question is a valid one if
somewhat vague, the comment was simply rude.

Look at this picture, there are over 2 dozen sharks in this picture alone:
http://www.alohafriends.com/Sharks.html

Your 5 mile boundry is 3 miles past the International Waters zone. 
The number is in the hundreds of thousands, if not over a million.

An excerpt:

Hawaii - Wilderness Safety
http://www.letsgo.com/HAW/03-Essentials-275
..."About 40 species of sharks inhabit Hawaiian waters, ranging in
size from the eight-inch Pigmy Shark to the Whale Shark, which can
measure over 50 ft. in length. There are eight species that are
commonly sighted near shore, most of which pose little threat to
humans. The Tiger Shark, recognizable by its blunt snout and the
vertical stripes on its sides, is the most dangerous species of shark
found in Hawaiian waters, and is known to attack humans. Shark attacks
in Hawaii are actually quite rare---only 2-3 occur each year and few
of these prove fatal. Surfers and spearfishers are at greatest risk of
attack, and swimmers are advised to stay out of the water at dawn and
dusk, when sharks move inshore to feed. Experts also advise against
wearing high-contrast clothing or shiny jewelry and to avoid excessive
splashing, all of which can attract sharks..."

I think you oversimplified the migration of shark species when you said :

"...sharks are territorial and tend to stay in specific regions
so it would be possible through tracking devices and other methods of
data collection to determine the approximate density of sharks in a
given area over a period of time."

Actually sharks are divided into 3 categories according to
migration/terrritory behavior:
Local Sharks- these  sharks do not migrate, and range only about 100
miles from their  habitat.
Coastal Pelagic  Sharks- these sharks can migrate over 1000 miles from
their  habitat.
Highly Pelagic  Sharks- these sharks migrate across the oceans.

You would have to categorise the 40 species of sharks that cynthia-ga
gave in her answer to begin to determine how many species make up the
local population.  Any of the pelagic species are mostly going to have
transient or seasonal occurence in the Hawaiin ocean zone you defined.
 You will also notice that the Local sharks can have a range of 100
miles-this puts all 3 cetgories of sharks outside you boundary
conditions. This means that the population will most likey fluctuate.

One of the things that I do know about sharks- is how little we
actually know about them.  What you may be able to find are shark
census data from around hawaii- but I doubt that many scientists would
say that data gives enough evidence to definitively answer your
question.

I apologize if my comment was construed as rude.