[1] The islands are largely managed as nature reserves by the Isles of Scilly Wildlife Trust, principally for breeding seabirds and grey seals (Halichoerus grypus).

Gweal is a small rocky island consisting of two hills linked by a boulder beach, just off the west coast of Bryher and is an occasional pupping site for grey seals.

Several species nest on the island including the largest breeding colony of Cormorant (Phalacrocorax carbo) in the Isles of Scilly as well as Puffin, Great Black–backed Gull (Larus marinus), Razorbill (Alca torda) and Common Shag (Gulosus aristotelis).

On Mincarlo he recorded the following spiders; Trochosa terricola, Oedothorax fuscus, Lepthyphantes tenuis, Dismodicus bifrons, Xysticus kochi and Halorates reprobus which is associated with the nests of seabirds, especially cormorant and shag.

[6] (Cornish: Enys Welsek, grassy island) (grid reference SV858139) 0.90 hectares (2.2 acres) Several species have bred on Illiswilgig, including a small colony of only three pairs of European Storm–petrel, recorded during the Seascape 2000 survey.

Plants recorded are tree mallow, thrift, sea beet, rock sea–spurrey, common scurvy grass, orache and English stonecrop (Sedum anglicum).

(Cornish: Kastel Breyer, Bryher's castle)(grid reference SV863140) 0.39 hectares (0.96 acres) and 26 metres (85 ft) The Seabird 2000 survey recorded 17 occupied sites of European Storm–petrel.