This is the first such park in Greece, established for the protection of monk seals and some other species of wildlife, and encompasses both the inhabited island of Alonissos, and some uninhabited islets as well as open sea within its bounds.
The Aegean Sea has most of the remaining monk seals in Europe, with this park the essential core area, with some 30 adults estimated a few years ago. Monk seal populations have been in decline for many years due to their being killed by fishermen (because the seals are competitors for fish and sometimes raid nets), injury by boats, dynamite fishing, pollution, etc.
This park, along with a pan-Aegean network of reserves, is hoped to reverse the decline of this rare sea mammal. The more strictly protected area (Zone A) covers 1578 square km, Zone B (less protected) covers 678 square km, includes the inhabited island of Alonissos, which has Aleppo pine forest, mastic trees, holm and kermes oak, Mediterranean buckthorn, and other trees.
On uninhabited Piperi islet (in Zone A) pine forests cover around 60% of the land, and there are large numbers of breeding Eleonora's falcon (and in the park in general with estimates ranging wildly). Gioura islet has some 500 wild goats, which resemble the indigenous Cretan kri-kri; in the park in general are found many species of fish and cetaceans, the latter include the sperm whale, striped and common dolphin, long-finned pilot whale, and (less common), the killer whale, which is not a whale at all but a large dolphin.
There are many reptiles, and some 80 species of birds have been recorded, with good populations of rare birds, including (besides the Eleonora's falcon), peregries, Bonelli's eagle, lesser kestrels, and buzzards. Audouin's gulls breed here, as do Cory's shearwaters in summer (these birds having a wingspan of over a meter) and there are many other birds that breed here, and others that come at passage periods.
Rare and endemic species are found on all of these islands. There are various restrictions on visiting the islets within Zone A (Piperi being the most restricted).