Biševo has rich terrestrial and submarine natural heritage. The island abounds in plant species. So far, a total of 485 plant species have been recorded in the terrestrial flora of Biševo island. The island boasts 43 plant species that belong to various categories of endangered species, 88 protected plant species and seven endemic species. On the sandy substrate of the central part of the island characteristic vegetation of sandy soils developed, comprising the woodruff (Asperula staliana Vis. subsp. arenaria Korica) as a stenoendemic species that can be found only on Biševo island. There are three stenoendemic species at the cape Gatula: the woodruff (Asperula staliana Vis.), the Dubrovnik cornflower (Centaurea ragusina L.) and the common sea lavender (Limonium busianum Bogdanović et Brullo). In 2019, the rock rose (Helianthemum jonium Lacaita et Grosser ex Fiori et Bég.) was discovered in the vicinity of Salbunara and Polje settlements. Tommasini’s Ophrys (Ophrys tommasinii Vis.) is one of the two new orchid species in the Biševo flora, growing in the wider Stražbenica area. Another endemic plant, the Dalmatian chrysanthemum (Tanacetum cinerariifolium Trevir. Sch.Bip.), can be found on the dry grasslands and thickets. The vegetation of rosemary (Rosmarinus officinalis L.) and the Mediterranean Heather (Erica multiflora L.) is especially important for the island, accompanied by the strawberry tree (Arbutus unedo) bushes, interesting as they simultaneously bear flowers and fruits. Its fruits are edible, thus the name strawberry tree. After the 2003 wildfire, the most widespread trees are those of the Aleppo pine, the pioneering species of the forest ecosystem.
The underwater flora comprises 183 species, with the red algae of the species Lithophyllum byssoides being most prominent. They form an endemic Mediterranean habitat, the so-called coralline algal pavements. They are the most beautiful in the east Adriatic, on the shores of Biševo island. The algal pavements are an indicator of the cleanliness of the sea, as well as an excellent indicator of the mean sea level. There are also meadows of a sea flowering plant, the Neptune grass (Posidonia oceanica), producing significant quantities of oxygen and preventing the washing of the sand and gravel from beaches. They also serve as shelter and feeding grounds for a number of marine species. In short, the entire marine and littoral ecosystem depends on the preservation of the Neptune grass.
When it comes to animal species, the marine mammals are especially interesting. The most common mammal in Biševo waters is the common bottlenose dolphin (Tursiops truncatus), but other cetacean species can be found in the wider area: the fin whale (Balaenoptera physalus), the striped dolphin (Stenella coeruleoalba) and the Risso’s dolphin (Grampus griseus). Other interesting sea animals living in greater depths of Biševo waters include corals, such as the gold coral (Savalia savaglia) and the small polyped gorgonian (Paramuricea clavata). The red coral (Corallium rubrum) lives in the greatest depths, hidden in the crevices. Biševo waters abound in fish species, but not to its former extent. Large quantities of blue fish had been caught in the Trešjavac cove, at the location where the Mediterranean monk seal (Monachus monachus) once lived. Its presence usually indicates there is an abundant fish stock it feeds on.
In addition to sea mammals, there are interesting bird species on Biševo island. So far, 16 species of nesting birds have been observed. Eleonora’s falcon (Falco eleonorae) is one of those species, known to locals as sokolić or hmanzá. This small bird of prey migrates all the way from Madagascar in order to raise its young on the pelagic islands of the Vis archipelago. Two more bird species use the pelagic islands of the Vis archipelago as their northernmost nesting area. The first is the Scopoli’s shearwater (Calonectris diomedea), named after the ancient Greek hero Diomedes, who was buried on one of the pelagic islands of the Adriatic Sea. The second is the yelkouan shearwater (Puffinus yelkouan), floating on the sea surface in flocks during the day. Both species are endemic to the Mediterranean. Biševo island is an important station for migratory birds during the migration. The best time of the year for bird watching on Biševo is autumn, because the autumn migrations are slower and the birds stay at way stations for a longer time. Nevertheless, one should bear in mind that different species migrate at different periods of the year, so the “autumn” begins already in the second half of July, lasting until mid-November.
Besides birds, Biševo is also on the route of migratory insects. When it comes to migratory butterflies, the painted lady (Vanessa cardui) is commonly found on Biševo, followed by the red admiral (Vanessa atalanta), the convolvulus hawk-moth (Agrius convolvuli) and the striped hawk-moth (Hyles livornica). Migratory dragonfly species called the red-veined darter (Sympetrum fonscolombii) can also be found on Biševo. A non-migratory insect that lives in caves is a diplopoda class centipede Eroonsoma adriatica. It is endemic to the island, probably a relict of a former land bridge between the island and some of the former Apennine islands, the present-day Italy.