[4] Deal Island has been extensively modified by human activity, with the construction of facilities, and the clearing of vegetation and regular firing associated with grazing livestock.

[6] On 26 April 1943, during World War II, an RAAF Airspeed Oxford aircraft crashed on the island, killing all four crewmen.

Seabird and wader species that have been recorded breeding on the island include the little penguin, the Pacific gull and the sooty oystercatcher.

Mammals found on the island include the red-necked wallaby, the common brushtail possum, the southern brown bandicoot, the fur seal, and the introduced European rabbit.

[5] Deal Island has a borderline Mediterranean (Csb)/oceanic climate (Cfb) with mild, short, somewhat dry summers and cool, wet winters, owing to its exposed location.