Underwater towed video: a useful tool to rapidly assess elasmobranch populations in large marine protected areas

Abstract

Elasmobranch stock assessment studies are usually made through fisheries surveys data. However, in large marine protected areas (MPAs) the use of destructive techniques must be dismissed in order to avoid population impacts. In 2005, while conducting a marine habitat survey in two marine Special Areas of Conservation (Sebadales de Playa de Inglés and Franja Marina de Mogán) in south Gran Canary Island (Canary Islands, Spain) with underwater towed video (UTV) and underwater visual census (UVC) transects, we recognized the opportunity rose to assess elasmobranch populations through UTV. Number of observed species and specimens, overall field work effort and total surveyed area were determined and compared between methods. Mean observations per day per unit of time (MOPUT) and mean observations per day per unit of surveyed area (MOPUA) were also compared through Mann-Whitney rank sum statistical test (α=0.05). Data analysis demonstrated that UTV is a very useful tool to rapidly assess elasmobranch populations in large MPAs in good visibility underwater environments. It can assess larger areas than UVC with the same effort (statistically significant difference found for the MOPUT; p=<0.001), leading to more observed species (5 vs 2) and specimens (46 vs 3) per day of work, with no loss in resolution power (MOPUA values were not significantly different between UTV and UVC; p=0.104).

An experimental comparison of three towed underwater video systems using species metrics, benthic impact and performance

“…Cost‐effective MPA video monitoring programmes have been developed to detect management effectiveness on seabed habitats (Sheehan et al . ,b) and on fish abundance and size (Assis, Narváez & Haroun ; Tessier et al . ), helping managers to evaluate and adapt their policies (Stevens et al .…”

“…Analysis of underwater imagery is used to enumerate species abundance, diversity and behaviour (Machan & Fedra 1975;Hughes & Atkinson 1997) and characterize habitats to help managers identify and manage vulnerable communities (Larocque & Thorne 2012;Fabri et al 2013). Cost-effective MPA video monitoring programmes have been developed to detect management effectiveness on seabed habitats (Sheehan et al 2013a,b) and on fish abundance and size (Assis, Narv aez & Haroun 2007;Tessier et al 2013), helping managers to evaluate and adapt their policies (Stevens et al 2013).…”

Complementarity of Rotating Video and Underwater Visual Census for Assessing Species Richness, Frequency and Density of Reef Fish on Coral Reef Slopes

“…Other studies compared strip transects or point counts UVC with (i) remote underwater video system (RUV) (stereo or mono) [27], [28], [47]–[53], (ii) towed video system (TOWV) [43], [54], [55], and (iii) diver-operated video (DOV) [56]–[63].…”

A Systematic Review of Remotely Operated Vehicle Surveys for Visually Assessing Fish Assemblages

“…UTVs and BRUVS are well-established methods of obtaining non-destructive assessments of fish communities (Karpov et al, 2004;Trenkel et al, 2004a). UTVs provide rapid assessments of biodiversity over large distances (Assis et al, 2007), whereas the multidirectional thruster-power capabilities of ROV systems allow for greater maneuverability around complex and high relief environments, such as rocky reefs, resulting in more detailed observations of biodiversity and improving the detection of cryptic and rare species (Consoli et al, 2016). BRUVS, on the other hand, have been demonstrated as an effective monitoring tool for monitoring carnivorous, omnivorous, and herbivorous fishes throughout Australia (Harvey et al, 2007;Watson et al, 2010;Caldwell et al, 2016).…”