Assessing the suitability of a remotely operated vehicle (ROV) to study the fish community associated with offshore gas platforms in the Ionian Sea: a comparative analysis with underwater visual censuses (UVCs)

Abstract

The effectiveness of a remotely operated vehicle (ROV) to describe the fish communities of three gas platforms located offshore Crotone (Italy, Ionian Sea) was investigated by comparing its observations with underwater visual censuses (UVCs). The study was carried out at two depth layers (0-6 and 12-18 m). Moreover, the ROV was used to survey three deeper depth layers up to 76 m. Overall, the ROV surveys failed to give a truthful representation of the fish communities underestimating the number of species and their abundances as compared to UVCs. The main discrepancies in data regarded cryptobenthic and nekto-benthic species, whereas the ROV proved to be a suitable method to census low-mobile and abundant planktivorous species. The differences between the fish assemblage described by the ROV, with respect to the one depicted by UVC, should be considered in the light of the technical limits of the recording camera, whose resolution and field of vision is clearly lower than the diver's eye. In addition, video images did not allow for the acquisition of a correct estimate of the distance between the individuals and the platform structures. This led, almost certainly, to an under-or over-estimation of fish abundance as regards to the censused volume. In spite of this, as a result of its capacity to reach depths inaccessible to scuba divers and then to add complementary information, the ROV could be used jointly with UVCs, in studies having as their objective the description of the fish communities associated with offshore platforms.

Fitness consequences of habitat variability, trophic position, and energy allocation across the depth distribution of a coral-reef fish

“…ROV footage generally underestimates fish densities in comparison with visual surveys (Andaloro et al 2013). To correct for this discrepancy, predator densities were calculated using each method in an overlapping region in the Dry Tortugas using visual surveys from 2012 and 2014, and ROV surveys from 2012 and 2013.…”

Fish Distribution and Habitat Complexity on Banks of the Strait of Sicily (Central Mediterranean Sea) from Remotely-Operated Vehicle (ROV) Explorations

“…The recent technological enhancement of remotely-operated vehicles (ROVs), which takes advantage of high definition video and digital cameras, is improving the biodiversity assessment of fish and benthic invertebrates especially in natural and artificial complex habitats, where it is difficult to use traditional sampling gears [6,32,33,34,41,42] and in deep environments, where diving is logistically limited and the use of submersibles is very expensive. Moreover, direct observation methods allow assessment of behaviors and other attributes, albeit brief, that are otherwise unattainable.…”

“…Similar conclusions were drawn by Andaloro et al . [41] and Consoli et al . [52] in artificial habitats (extractive platforms and shipwrecks) located in the Mediterranean Sea.…”

“…[62] and Andaloro et al . [41], the ROV is an appropriate method for censusing planktivorous fish, both from a qualitative and quantitative point of view, mostly in relation to their high abundance and low mobility.…”

A comparison of density and length of Pacific groundfishes observed from 2 survey vehicles: a manned submersible and a remotely operated vehicle

“…In a study in which fish abundance near 3 gas platforms was estimated with an ROV and compared with fish abundance estimated by scuba divers, Andaloro et al (2013) found that 9 taxa of small benthic species were reported in the diver surveys but none of those taxa were observed with the ROV. Small rockfishes <20 cm TL could not be identified to species during nearshore ROV surveys in the waters of southeast Alaska (Johnson et al, 2003), and Love et al (2009) suggested that densities of small fish taxa, such as the bluebanded goby (Lythrypnus dalli), could be underestimated in their HOV surveys.…”