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

Aggregations of Grey Reef Sharks are regularly observed in this area, as documented by underwater visual censuses and baited remote underwater video station (BRUVS) surveys (National Geographic 2009; Friedlander et al. 2022).

Two expeditions were undertaken in the Southern Line Islands (National Geographic 2009; Friedlander et al. 2022). Between 27 March–5 May 2009, underwater visual censuses were conducted by a team of paired divers at ~15 m depth at 29 sites in this area (National Geographic 2009). Between 9–20 October 2021, similar surveys were undertaken at 17 sites in this area (Friedlander et al. 2022). Each site was surveyed using three transects separated by ~10 m. During each survey, divers counted and measured (average total length [TL] was visually estimated) all sharks observed along three fixed-length (25 m) corridor transects. Additionally, during the expedition in October 2021, BRUVS were deployed and the maximum number of individuals in a single video frame (MaxN) was recorded for each taxon (Friedlander et al. 2022). Mid-water BRUVS were deployed at 10 survey sites in the area at a depth of 10 m and ranged from 500 m to 5 km from shore (Friedlander et al. 2022). Further, BRUVS were deployed in mesophotic reefs at nine survey sites in this area at depths between 50–65 m and in habitats from plate coral reefs to rubble/sand slopes (Friedlander et al. 2022).

In 2009, total fish biomass estimated in the underwater visual censuses ranged between 2.1–5.8 tonnes per 0.01 km² for the five islands assessed in the southern Line Islands (Flint, Vostok, Starbuck, Malden, and Millennium). Vostok had a biomass of ~4 t per 0.01 km². This area is among the top seven highest fish biomass ever reported globally (National Geographic 2009). Top predators, including sharks and other fishes (e.g., Twinspot Snapper Lutjanus bohar, trevally Caranx ssp.), accounted for most of the biomass (~70%). The most abundant top predators were Grey Reef Sharks (National Geographic 2009). Fish biomass was highest on the windward side of islands or near the island tips, where dominant currents form eddies and enhance water motion.

The underwater visual censuses showed that the Grey Reef Shark was the first-ranked top predator species with an average of 16.7 (SD = ±44.7) individuals per 0.01 km²  (Pristine Seas unpubl. data 2022). Maximum values were recorded from four surveys with 100 sharks per 0.01 km², and in one survey with 200 individuals per 0.01 km² (Pristine Seas unpubl. data 2022).

In five surveys, Grey Reef Sharks had body sizes that ranged between 53–153 cm TL, with an average of 98 cm TL (Pristine Seas unpubl. data 2022). Considering the size-at-maturity (120–142 cm TL for females, 130–145 cm TL for males), and the size-at-birth (45–64 cm TL) for this species (Ebert et al. 2021), individuals were mostly neonates, young-of-the-year, and juveniles. This area could be an important reproductive area for this species, however, further information is needed to confirm the function and nature of these aggregations.

Data from BRUVS surveys conducted in mesophotic reefs indicated that Grey Reef Sharks had a maximum MaxN of 13 and an average of 3.3 individuals per frame (Pristine Seas unpubl. data 2022).