Hi -
not from T I ,-but have sailed in , out ,and around that area a number of times .
There is a very shallow mud flat area just North of the Pier and pavilion ,--don't go there - -and tides are pretty severe .I.ve always seen plenty of sea life in the area and particularly hammer head sharks , had about a 10 ftr so close once a could almost reach out and touch it ,---but didn.t
team Tybee website has links to info -tides etc
http://www.teamtybee.com/
they have basic info on the distance race in May also -

Have a great time
always enjoy Tybee Is
Carl