Ensure all permits, safety plans and approvals have been obtained. Any research undertaken within Australian Marine Parks (AMPs) requires a research permit issued from Parks Australia. See Appendix B for a list of potential permits needed. The observation of animals should be undertaken in an ethical manner and in many cases, surveys may require approval from an Animal Ethics Committee.
Define the aim of the project. This is a mandatory step in any marine monitoring project, but with their multiple capabilities (imagery, sampling, sensors), projects using ROVs may be particularly vulnerable to competing research interests or distractions during a dive. A clearly defined aim or hypothesis ensures the ROV pilot stays on task and is not distracted.
Confirm sampling design is statistically sound with adequate spatial coverage and replication, and addresses the aim or hypothesis. This is generally achieved through the use of an explicit randomization procedure to ensure that a sufficient number of independent replicates are obtained (Foster et al. 2017, 2019, Smith et al. 2017). See Chapter 2 for further details on sampling design.
Select appropriate transect design for ROV deployment (Foster et al. 2019). The decision to which transect design is most appropriate is driven by the question being addressed, the applied capabilities of the ROV (i.e. sampling may be applied concurrently with image acquisition), the environment, available time and logistics of ROV deployment and retrieval (e.g. size of system). For example, tether and vessel drag within environments exposed to strong currents makes piloting an ROV along a predetermined transect difficult if not impossible. In such situations ROVs (particularly small ROVs) may not be the best system for temporal monitoring purposes because of the challenges with maintaining physical position to enable sufficient overlap between repeat surveys (i.e., within 20 m) (e.g. Przeslawski et al. 2012 in northern Australia). In addition, some consideration must be given to the unique capability of ROVs to traverse steep slopes, including vertical deployments, when undertaking quantitative image transects of a set distance. For these situations, calculated distance cannot be ‘as the crow flies’ and will rely on high-resolution bathymetry as well as continuous monitoring by the ROV crew during deployment to determine actual distance traversed.
For marine monitoring demersal fishes on the continental shelf a transect of ~150-200 m is sufficient. Monk et al. (Unpublished) contrasted three transect lengths (50, 100, 150 m) finding that at least 150 m was a generally sufficient design for monitoring purposes of demersal fish diversity (< 200 m). For surveys aiming to collect imagery of the epibenthos, or in deeper environments, then longer transects are possibly required to gather sufficient imagery to characterise the focal regions.
For surveys that include fauna of mixed mobility, for example fish and invertebrates, a dual transect approach may be suitable. The transect area can first be surveyed rapidly to ensure individuals of highly mobile taxa are included, and then again at a slower speed to ensure observation of smaller and more cryptic species.
For survey of fauna associated with topographical features, for example seamounts, vertical reef structures or oil and gas facilities, transects conducted in an arc around the feature may be more suitable than linear transects. The ROV can be thrusted laterally, allowing cameras to be consistently oriented toward the feature throughout the transect.
Stereo-cameras specifications and calibration (must be pre- and post-calibrated) in shallow water using the techniques similar to those outlined in Boutros et al. (2015). We recommend cameras with full, high-definition resolution of at least 1920 x 1080 pixels and a capture rate of at least 30 frames per second. Higher camera resolution will improve identification of fish, and the pixel selection required for measurement, but some models of action cameras can overheat at high resolution. Higher frame rates reduce blur on fast-moving species. To maintain stereo-calibrations, cameras must have video stabilisation disabled, and a fixed focal length can facilitate measurements both close to and far from the camera systems when correctly calibrated (Boutros et al. 2015). The field of view should be standardised and chosen to limit distortion in the image (e.g. no more than a medium angle, ~95° H-FOV). When sampling demersal fish assemblages at typical maximum range (6 m) from the cameras, Boutros et al. (2015) suggested a separation < 450 mm will result in a decrease in the accuracy of measurements. Cameras are fixed to a rigid base bar to preserve the stereo-calibration required to calculate accurate length and range measurements (Boutros et al. 2015). As outlined in Chapter 5 for stereo-BRUVs, SeaGIS software and 3D calibration hardware is recommended for calibration of stereo video imagery. For stereo still imagery then a similar approach documented in Chapter 4 for AUVs, with consistent lighting and adequate base separation ~ 300 mm are important to obtain well-lit and calibrated stereo imagery (Boutros et al. 2015).
Decide on appropriate navigational systems (e.g. USBL) and required spatial precision of imagery. In many cases a USBL should be used for both navigation and georeferencing imagery. However, other methods can be employed such as doppler velocity logging or simple timed directional transects for navigation and calibrated stereo imagery or stereo lasers for image scaling. For many ROV studies the choice of navigational and georeferencing of imagery is often limited to what is fitted to the unit available. However, appropriate effort must be given to this during the survey planning phase as it may limit the questions sought to be answered by the imagery. For example, spatial precision is very important for fine scale analysis whereas navigational accuracy is important for temporal replication. Some alternative navigational methods, simple timed directional transects are sometimes used if a USBL is not used, are not well suited to temporal replication as the exact spatial location of the track cannot be determined. This results in resultant data needing to be pooled to transect level. This reduces a key advantage of ROVs that individual observations can be co-location with finescale covariates (such as from multibeam sonar). This makes that data collected in this fashion more akin to stereo BRUVs or underwater visual census which essentially aggregate individuals to a sample. We suggest that both accuracy and spatial precision need to be addressed for distance and swept area determination.
Ensure appropriate software is installed on onboard laptops (e.g. ROV navigation software platform, GIS, etc), and potential users are familiar with it so that the ROV can be tracked and its mission success monitored while underway. It is worth setting all equipment up in the laboratory or at dock to ensure everything is operational and no software updates are required.
Ensure a trained technical team. For the work-class ROVs, a professional technical and piloting team with training specific to the designated ROV will be required. For the smaller ROVs, training on piloting and technical issues is still highly recommended during the pre-survey planning stage.