Novel Drone Technology Improves Habitat Mapping for a Coastal Octopus Species
Patterson, Samantha Michele
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This Master’s project combines UAV footage and synchronous SCUBA footage with ArcGIS Pro, developing a robust method to map and record underwater environments using diver observations. Our focus organism is the ‘peachy’ octopus, Octopus tetricus, a coastal species commonly encountered in northern Te Ika-a-Māui (North Island, Aotearoa New Zealand), including the Hauraki Gulf. This species is known to occupy high-density den sites around Sydney, Australia, and has been anecdotally observed to do so in several local sites around Tāmaki Makaurau (Auckland). Two of these sites were examined across the summer season 2020–2021, aiming to observe octopus density and small-scale distribution across the breeding season using non-invasive methods and evaluate their ecological impact while trialling and refining our observation, recording, and mapping techniques. This project successfully demonstrated the proof of concept for our subtidal mapping technique using low-cost drones with synchronous diver footage. During the study, high-density O. tetricus sites were discovered and socially tolerant behaviour (two cases of adjacent occupied dens) was observed in the Tāmaki Makaurau region, though not all octopus found were exclusively in high-density areas. Mean observed den density at Kawau Island across all sampling occurrences was calculated as 3.2 dens per 500m2, with boulder and sandpit den types most prevalent; Stanmore Bay’s mean observed den density was calculated as 0.1 dens per 500m2, with only rocky reef dens observed. The composition of shell middens between the two sites did vary, with Kawau Island having Pecten novaezelandiae (present in 92 middens) and Tucetona laticostata (present in 70 middens) constituting the majority of observed middens (94 observed middens across the sampling period), and Stanmore Bay having Austrovenus stutchburyi present in all observed middens (11 observed middens across the sampling period); this could suggest a difference in individuals' diet between sites. The observation methods used during this project were designed to have a low impact on the habitat and animals observed, as well as lower the task load for divers; this goal was met based on fish and octopus reoccurrence, as well as diver reports.