Gizo Lagoon is an important area for undefined aggregations of one shark species.

Regular and predictable aggregations of Blacktip Reef Sharks in this area are supported by citizen science reports and surveys using Baited Remote Underwater Video Station (BRUVS) surveys.

Much of the area is uninhabited but Blacktip Reef Sharks are commonly recorded in shallow waters, close to the resorts scattered along the coastline. Aggregations of 3–7 Blacktip Reef Sharks visually estimated ranging in size from 30–150 cm total length (TL) are reported weekly throughout the year, especially though social media channels (Imagination Island Resort & Fatboys Resort pers. comm. 2024). Size-at-birth for this species is 30–50 cm TL (Mourier et al. 2013) and maturity is reached between 90–112 cm TL (Ebert et al. 2021), indicating that animals sighted are neonates, young-of-the-year (YOY), and juveniles. Provisioning of fish scraps sometimes occurs at the jetties of Imagination Island (northernmost of the area) and in the southwest of the area (during the night). During provisioning times, aggregations can increase to 15 individuals. However, small aggregations of 3–5 individuals are present every day even when there is no provisioning (Imagination Island Resort & Fatboys Resort pers. comm. 2024). Further, aggregations are observed along the whole island area and were recorded between 2020–2022 when no provisioning occurred in the area (Imagination Island Resort pers. comm. 2024). Blacktip Reef Sharks have also been recorded chasing bait balls at Imagination Island. In addition, there are records of mating behaviour northwest of the area, along with a record of a neonate visually estimated at 35 cm TL in the northeast. Neonates and YOY at Imagination Island visually estimated from 30–60 cm TL have been observed since 2010, but observations have become regular in aggregations of ~5 individuals since 2023 (Imagination Island Resort pers. comm. 2010-2024). Neonates and YOY are not recorded near the jetties where aggregations are formed mostly by juveniles (100–150 cm TL). This is the only area in the Solomon Islands where observations of Blacktip Reef Sharks 30–40 cm TL were found.

BRUVS surveys were conducted in October and November 2015 to quantify reef shark abundance in four regions across the Western Province of the Solomon Islands (Goetze et al. 2018). BRUVS were deployed at 160 sites across the Western Province, of which 23 were within this area (Goetze et al. 2018). Blacktip Reef Sharks ranging in size from 67–91 cm fork length were recorded on four of the nine deployments within Gizo Lagoon (Goetze et al. 2018) confirming the regular occurrence of juveniles in similar habitat types of non-inhibited islands within the area. Further information is required to determine the function and nature of these aggregations.