Flora and fauna
You can also pay the local fishermen to take you on day trips to mangrove creeks (Bridget Creek is nice) or places like Mt Harriet National Park (where you can beach your boat and go birdwatching). Don't pay more than Rs 2000/day for the boat, and you can often bargain it down to much less. Be sure to check with the Forest Dept before heading out, as many destinations require certain permissions.
Also there is package tour available for Ross Island, North Bay and Viper Island at Rs 360 per head. The trip starts at 9 am and ends at 5pm. Complimentary lunch and breakfast is provided by the tour operator.