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

Passive acoustic telemetry data show that Grey Reef Sharks regularly aggregate in this area (Espinoza et al. 2015; M Espinoza unpubl. data 2025). A total of 40 Grey Reef Sharks (20 females, 20 males) were tagged with internal acoustic transmitters in the broader region around Lodestone (n = 13), Helix (n = 10), Wheeler (n = 7), Glow (n = 5), and other reefs (n = 5) between January 2012 and August 2013 (Espinoza et al. 2015). Their size ranged from 52–142 cm fork length (FL), and included 10 immature and 10 mature males, and six immature and 14 mature females. A total of seven females and seven males were detected within the area, with records between April 2012 to April 2014. Aggregations were defined as three or more tagged individuals detected at a receiver within five minutes. Aggregations in consecutive five-minute bins were grouped into an event, and its duration was calculated.

There were ~320,000 detections recorded at this reef, but five receivers had few detections (0.2–1.7% of total) and one additional receiver (10.1% of detections) recorded only few and sporadic aggregations. These were excluded and the remaining two receiver locations were used to define the boundary of the area. There were 4,953 five-minute bins with aggregations recorded within the area, grouped into 3,088 aggregation events that lasted between 0.2–94 min (mean = 6.3 min). Aggregations comprised 3–7 individuals at a time (mean = 3.2 individuals). As aggregations lasted up to 1.5 h, these events comprised up to nine unique tagged sharks (64% of total), but a maximum of seven (50% of total) were recorded at the same time. There was a seasonal signal, with aggregations persisting longer and comprising more individuals during July–September. There were also more aggregations during August (25.1% of total) and September (14.6%) compared to other months. This was partly driven by mature females being detected less frequently during October–February, potentially related to mating and parturition outside the receiver array. Aggregations were recorded on 357 of 677 days (53%). Combined, the data show that specific locations in the northwest of this reef (i.e., this area) regularly host aggregations of Grey Reef Sharks that last up to ~1.5 h. Only three of 11 reefs with receivers in this study off Townsville had significant aggregations of Grey Reef Sharks. Additionally, only 14 of 40 Grey Reef Sharks tagged in group of reefs were detected at reefs other than their home reef, generally only spending a few hours to days before returning to their home reef. At Lodestone Reef specifically, only four individuals were detected at other reefs, with one shark initially tagged, and mostly (99%) detected, at Brewer Reef. The limited movement highlights their high residency and site fidelity, and the individual importance of Lodestone Reef (Espinoza et al. 2015; M Espinoza unpubl. data 2025). More information is required to understand the nature and function of these aggregations.